Knowledge Hub

How to study Dark matter and Dark energy theoretically?

noreply@blogger.com (Saddam Leonardo Kap) — Mon, 18 Dec 2023 19:34:00 +0000

Since 1990, based on the Type Ia Supernova observations, it was established that our universe is dominant with some unknown quantities which generally referred to as Dark Matter and Dark Energy. The term dark has been used to represent the form of quantity which does not interact with light or mainly any known particles. Since, the unknown substance is electromagneticaly neutral, hence the unknown sector has been dubbed as a dark sector. The dark matter is referred to as a form of substance which is essential for structure formation and found to be pressureless. This form of matter can be considered as a gravitating system, which behaves as a dust matter. While the form of dark energy can exhibit a repulsive effect (opposite to the gravitational force), that can generate negative pressure, making universe to grow bigger and bigger with an acceleration. It has been found that the major constituents of our universe is dark energy which is 70%, then dark matter 26% and then rest of the matter from which all the galaxies and visible structures are made of.

Why Dark Matter is Dark??

noreply@blogger.com (Saddam Leonardo Kap) — Fri, 10 Jul 2020 15:41:00 +0000

What Is Dark Matter?

Roughly 80% of the mass of the universe is made up of material that scientists cannot directly observe. Known as dark matter, this bizarre ingredient does not emit light or energy. So why do scientists think it dominates?

Since at least the 1920s, astronomers have hypothesized that the universe contains more matter than seen by the naked eye. Support for dark matter has grown since then, and although no solid direct evidence of dark matter has been detected, there have been strong possibilities in recent years.

"Motions of the stars tell you how much matter there is," Pieter van Dokkum, a researcher at Yale University, said in a statement. "They don't care what form the matter is, they just tell you that it's there." Van Dokkum led a team that identified the galaxy Dragonfly 44, which is composed almost entirely of dark matter.

The familiar material of the universe, known as baryonic matter, is composed of protons, neutrons and electrons. Dark matter may be made of baryonic or non-baryonic matter. To hold the elements of the universe together, dark matter must make up approximately 80% percent of the universe. The missing matter could simply be more challenging to detect, made up of regular, baryonic matter.

Potential candidates include dim brown dwarfs, white dwarfs and neutron stars. Supermassive black holes could also be part of the difference. But these hard-to-spot objects would have to play a more dominant role than scientists have observed to make up the missing mass, while other elements suggest that dark matter is more exotic.

Most scientists think that dark matter is composed of non-baryonic matter. The lead candidate, WIMPS (weakly interacting massive particles), have ten to a hundred times the mass of a proton, but their weak interactions with "normal" matter make them difficult to detect. Neutralinos, massive hypothetical particles heavier and slower than neutrinos, are the foremost candidate, though they have yet to be spotted.

Sterile neutrinos are another candidate. Neutrinos are particles that don't make up regular matter. A river of neutrinos streams from the sun, but because they rarely interact with normal matter, they pass through the Earth and its inhabitants. There are three known types of neutrinos; a fourth, the sterile neutrino, is proposed as a dark matter candidate. The sterile neutrino would only interact with regular matter through gravity.

"One of the outstanding questions is whether there is a pattern to the fractions that go into each neutrino species," Tyce DeYoung, an associate professor of physics and astronomy at Michigan State University and a collaborator on the IceCube experiment, told Space.com.

The smaller neutral axion and the uncharged photinos — both theoretical particles — are also potential placeholders for dark matter.

According to a statement by the Gran Sasso National Laboratory in Italy (LNGS), "Several astronomical measurements have corroborated the existence of dark matter, leading to a world-wide effort to observe directly dark matter particle interactions with ordinary matter in extremely sensitive detectors, which would confirm its existence and shed light on its properties. However, these interactions are so feeble that they have escaped direct detection up to this point, forcing scientists to build detectors that are more and more sensitive."

Or, perhaps the laws of gravity that have thus far successfully described the motion of objects within the solar system require revision.

How do we know dark matter exists?

If scientists can't see dark matter, how do they know it exists?

Scientists calculate the mass of large objects in space by studying their motion. Astronomers examining spiral galaxies in the 1970s expected to see material in the center moving faster than on the outer edges. Instead, they found the stars in both locations traveled at the same velocity, indicating the galaxies contained more mass than could be seen. Studies of the gas within elliptical galaxies also indicated a need for more mass than found in visible objects. Clusters of galaxies would fly apart if the only mass they contained were visible to conventional astronomical measurements.

Albert Einstein showed that massive objects in the universe bend and distort light, allowing them to be used as lenses. By studying how light is distorted by galaxy clusters, astronomers have been able to create a map of dark matter in the universe.

All of these methods provide a strong indication that most of the matter in the universe is something yet unseen.

Dark matter research

Although dark matter is different from ordinary matter, there are a number of experiments working to detect the unusual material.

The Alpha Magnetic Spectrometer (AMS), a sensitive particle detector on the International Space Station, has been operating since its installation in 2011.

So far, AMS has tracked more than 100 billion cosmic ray hits in its detectors, AMS lead scientist Samuel Ting, a Nobel laureate with the Massachusetts Institute of Technology, told Space.com.

"We have measured an excess of positrons [the antimatter counterpart to an electron], and this excess can come from dark matter. But at this moment, we still need more data to make sure it is from dark matter and not from some strange astrophysics sources," Ting said. "That will require us to run a few more years."

Back on Earth, beneath a mountain in Italy, the LNGS's XENON1T is hunting for signs of interactions after WIMPs collide with xenon atoms. The lab recently released the first results of the experiment.

"A new phase in the race to detect dark matter with ultra-low background massive detectors on Earth has just began with XENON1T," project spokesperson Elena Aprile, a professor at Columbia University, said in a statement. "We are proud to be at the forefront of the race with this amazing detector, the first of its kind."

The Large Underground Xenon dark-matter experiment (LUX), seated in a gold mine in South Dakota, has also been hunting for signs of WIMP and xenon interactions. But so far, the instrument hasn't revealed the mysterious matter.

"Though a positive signal would have been welcome, nature was not so kind!" Cham Ghag, a physicist at University College London and collaborator on LUX, said in a statement. "Nonetheless, a null result is significant as it changes the landscape of the field by constraining models for what dark matter could be beyond anything that existed previously."

IceCube Neutrino Observatory, an experiment buried under Antarctica's ice, is hunting for sterile neutrinos. Sterile neutrinos only interact with regular matter through gravity, making it a strong candidate for dark matter.

Other instruments are hunting for the effects of dark matter. The European Space Agency's Planck spacecraft has been building a map of the universe since it was launched in 2009. By observing how the mass of the universe interacts, the spacecraft can investigate both dark matter and its partner, dark energy.

In 2014, NASA's Fermi Gamma-ray Space Telescope made maps of the heart of the Milky Way in gamma-ray light, revealing an excess of gamma-ray emissions extending from its core.

"The signal we find cannot be explained by currently proposed alternatives and is in close agreement with the predictions of very simple dark matter models," lead author Dan Hooper, an astrophysicist at Fermilab in Illinois, told Space.com.

The excess can be explained by annihilations of dark matter particles with a mass between 31 and 40 billion electron volts, researchers said. The result by itself isn't enough to be considered a smoking gun for dark matter. Additional data from other observing projects or direct-detection experiments would be required to validate the interpretation.

Dark matter versus dark energy

Although dark matter makes up most of the matter of the universe, it only makes up about a quarter of the universe's total composition. The energy of the universe is dominated by dark energy.

After the Big Bang, the universe began expanding outward. Scientists once thought that it would eventually run out of energy, slowing down as gravity pulled the objects inside it together. But studies of distant supernovae revealed that the universe today is expanding faster than it was in the past, not slower, indicating that the expansion is accelerating. This would only be possible if the universe contained enough energy to overcome gravity — dark energy.

Quantum Field Theory in Curved Spacetime - Complete Information

noreply@blogger.com (Saddam Leonardo Kap) — Fri, 03 Jul 2020 07:54:00 +0000

Introduction to Quantum Field Theory in Curved Spacetime

Prerequisites, Timetable, Outline, Literature, and more ...

Summary and Overview

The main aim of this course is to explain what are (some of) the obstacles that one faces when trying to generalise the standard formalism and procedures of Minkowski space Poincare-covariant QFT to curved spacetimes, and to illustrate the new phenomena that one encounters by some typical and important examples: particle creation by time-dependent gravitational fields, the Unruh effect, and (some elementary aspects of) Hawking black hole radiation and black hole thermodynamics.

Many of the key-issues can already be understood in a purely quantum-mechanical context by studying the Heisenberg picture quantisation of a time-dependent harmonic oscillator, so I will spend some time to discuss the issue of quantisation ambiguities, Bogoliubov transformations, mode creation etc., in this setting. When moving on to field theory, we will consider the simplest possible case of a free Klein-Gordon scalar field (in 1+1 or 3+1 dimensions). The general lesson is that in general in a curved spacetime the notion of vacuum and particles (and the corresponding particle interpretation of QFT) are ambiguous and observer-dependent.

We will then apply these insights to briefly look at the creation of particles in a time-dependent gravitational field, Minkowski space QFT and accelerated observers (the Unruh effect), and scalar fields in the Schwarzschild black hole metric (Hawking radiation).

Time permitting, and if there is sufficient interest, I will add a few remarks either on black hole thermodynamics, the black hole information loss paradox and the recent debate in the literature on ``firewalls'', or on more general (physically and mathematically more satisfactory) approaches to defining and making sense of quantum field theory in curved spacetime backgrounds.

Prerequisites

Basics of Quantum Field Theory: Canonical Quantisation of Free Scalar Fields (mode expansions, creation and annihilation operators, vacuum, Fock space, ...).
Basics of General Relativity (general formalism, proper distance and proper time, Rindler, Schwarzschild, Kruskal, simple cosmological metrics).

Schedule

Time and Place: Wednesday 10.15 -- 13.00 Room 119
Starting Date: Wednesday, September 21st

Outline (tentative)

Introduction: Motivation and Overview
Heisenberg Picture Quantum Theory of a (Time-dependent) Harmonic Oscillator
QFT in FRW Cosmological Backgrounds and Particle Production
Developing the Formalism
Rindler Space and the Unruh Effect
Aspects of the Classical Theory of Black Holes
Hawking Radiation
Black Hole Entropy and related Issues (if there is time)

Literature

Monographs

N. Birrell, P. Davies: Quantum Fields in Curved Space
V. Mukhanov, S. Winitzki: Quantum Effects in Gravity (the first half of the course will be loosely modelled on the first half of this book)
L. Parker, D. Toms: Quantum Field Theory in Curved Spacetime
R. Wald: Quantum Field Theory in Curved Spacetime and Black Hole Thermodynamics
see also
- chapter 14 of R.M. Wald: General Relativity
- chapter 09 of S. Carroll: Spacetime and Geometry, an Introduction to General Relativity

Online Lecture Notes

R. Brout et al.: A Primer for Black Hole Quantum Physics
L. Ford: Quantum Field Theory in Curved Spacetime
T. Jacobson: Introduction to Quantum Fields in Curved Spacetime and the Hawking Effect
T. Jacobson: Black holes and Hawking radiation in spacetime and its analogues
J. Traschen: An Introduction to Black Hole Evaporation (beware of typos)
A. Wipf: Quantum Fields near Black Holes
G. 't Hooft: Introduction to the Theory of Black Holes
C. Krishnan: Quantum Field Theory, Black Holes and Holography
J. Haro: Topics in Quantum Field Theory in Curved Space
P.-H. Lambert, Introduction to Black Hole Evaporation
J. Preskill: Quantum Field Theory in Curved Spacetime (1990)

Further Information on selected topics

Towards a mathematically more rigorous and satisfactory formulation

B. Kay: Quantum field theory in curved spacetime
R. Wald: The History and Present Status of Quantum Field Theory in Curved Spacetime
R. Wald: [0907.0416] The Formulation of Quantum Field Theory in Curved Spacetime
S. Hollands, R. Wald: [0803.2003] Axiomatic quantum field theory in curved spacetime
M. Benini, C. Dappiaggi, T. Hack, [1306.0527] Quantum Field Theory on Curved Backgrounds -- A Primer
S. Holland, R. Wald, [1401.2026] Quantum fields in curved spacetime
T. Hack, Cosmological Applications of Algebraic Quantum Field Theory in Curved Spacetimes

The Unruh Effect

For a detailed review, with many references, see
L. Crispino et al: The Unruh effect and its applications

Hawking Radiation and Classical and Quantum Black Hole Thermodynamics

L. Susskind, J. Lindesay: Black Holes, Information and the String Theory Revolution

J. Bardeen, B. Carter, S. Hawking: The Four Laws of Black Hole Mechanics
S. Hawking: Particle Creation by Black Holes

S. Hawking: The Nature of Space and Time
G. Gibbons: An Introduction to Black Hole Thermodynamics (pdf-file and ps-file of hand-written notes available at the bottom of the page, highly recommended)
P. Townsend: Black Holes (highly recommended)
R. Wald: The Thermodynamics of Black Holes (highly recommended)
R. Wald: Black Holes andThermodynamics
D. Page: Hawking Radiation and Black Hole Thermodynamics (see section 1 for a detailed account of the history of Hawking's discovery)
T. Jaocbson: Introductory Lectures on Black Hole Thermodynamics (ps-file, highly recommended)
S. Ross: Black hole thermodynamics
S. Carlip: Black Hole Thermodynamics and Statistical Mechanics
S. Carlip: Black Hole Thermodynamics
K. Umetsu: Recent Attempts in the Analysis of Black Hole Radiation
T. Jacobson, D. Marolf, C. Rovelli: Black hole entropy: inside or out? (a trialogue)
A skeptical and critical analysis (mainly on account of the so-called trans-Planckian problem) is given by
A. Helfer: Do black holes radiate? and Black holes reconsidered
(not sure what to make of this, best to form your own opinion)

arXiv

General Analysis and Universality of Hawking-like Radiation

M. Visser: Essential and inessential features of Hawking radiation
C. Barcelo, S. Liberati, S. Sonego, M. Visser, Minimal conditions for the existence of a Hawking-like flux
C. Barcelo, S. Liberati, S. Sonego, M. Visser, Hawking-like radiation from evolving black holes and compact horizonless objects

Black holes and information loss paradox

J. Polchinski: The Black Hole Information Problem
A. Strominger: Les Houches Lectures on Black Holes
S. Mathur: What Exactly is the Information Paradox? (highly recommended)
S. Mathur: The information paradox: A pedagogical introduction
S. Mathur: What the information paradox is not
S. Mathur: The information paradox: conflicts and results

Firewalls

firewall

Ahmed Almheiri, Donald Marolf, Joseph Polchinski, James Sully, Black Holes: Complementarity or Firewalls?
Ahmed Almheiri, Donald Marolf, Joseph Polchinski, Douglas Stanford, James Sully, An Apologia for Firewalls

J. Polchinski: The Black Hole Information Problem

Contact

Matthias Blau, Office 220a

Artificial intelligence yields new antibiotic

noreply@blogger.com (Saddam Leonardo Kap) — Thu, 02 Jul 2020 15:13:00 +0000

Using a machine-learning algorithm, MIT researchers have identified a powerful new antibiotic compound. In laboratory tests, the drug killed many of the world’s most problematic disease-causing bacteria, including some strains that are resistant to all known antibiotics. It also cleared infections in two different mouse models.

The computer model, which can screen more than a hundred million chemical compounds in a matter of days, is designed to pick out potential antibiotics that kill bacteria using different mechanisms than those of existing drugs.

“We wanted to develop a platform that would allow us to harness the power of artificial intelligence to usher in a new age of antibiotic drug discovery,” says James Collins, the Termeer Professor of Medical Engineering and Science in MIT’s Institute for Medical Engineering and Science (IMES) and Department of Biological Engineering. “Our approach revealed this amazing molecule which is arguably one of the more powerful antibiotics that has been discovered.”

In their new study, the researchers also identified several other promising antibiotic candidates, which they plan to test further. They believe the model could also be used to design new drugs, based on what it has learned about chemical structures that enable drugs to kill bacteria.

“The machine learning model can explore, in silico, large chemical spaces that can be prohibitively expensive for traditional experimental approaches,” says Regina Barzilay, the Delta Electronics Professor of Electrical Engineering and Computer Science in MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL).

Barzilay and Collins, who are faculty co-leads for MIT’s Abdul Latif Jameel Clinic for Machine Learning in Health (J-Clinic), are the senior authors of the study, which appears today in Cell. The first author of the paper is Jonathan Stokes, a postdoc at MIT and the Broad Institute of MIT and Harvard.

A new pipeline

Over the past few decades, very few new antibiotics have been developed, and most of those newly approved antibiotics are slightly different variants of existing drugs. Current methods for screening new antibiotics are often prohibitively costly, require a significant time investment, and are usually limited to a narrow spectrum of chemical diversity.

“We’re facing a growing crisis around antibiotic resistance, and this situation is being generated by both an increasing number of pathogens becoming resistant to existing antibiotics, and an anemic pipeline in the biotech and pharmaceutical industries for new antibiotics,” Collins says.

To try to find completely novel compounds, he teamed up with Barzilay, Professor Tommi Jaakkola, and their students Kevin Yang, Kyle Swanson, and Wengong Jin, who have previously developed machine-learning computer models that can be trained to analyze the molecular structures of compounds and correlate them with particular traits, such as the ability to kill bacteria.

The idea of using predictive computer models for “in silico” screening is not new, but until now, these models were not sufficiently accurate to transform drug discovery. Previously, molecules were represented as vectors reflecting the presence or absence of certain chemical groups. However, the new neural networks can learn these representations automatically, mapping molecules into continuous vectors which are subsequently used to predict their properties.

In this case, the researchers designed their model to look for chemical features that make molecules effective at killing E. coli. To do so, they trained the model on about 2,500 molecules, including about 1,700 FDA-approved drugs and a set of 800 natural products with diverse structures and a wide range of bioactivities.

Once the model was trained, the researchers tested it on the Broad Institute’s Drug Repurposing Hub, a library of about 6,000 compounds. The model picked out one molecule that was predicted to have strong antibacterial activity and had a chemical structure different from any existing antibiotics. Using a different machine-learning model, the researchers also showed that this molecule would likely have low toxicity to human cells.

This molecule, which the researchers decided to call halicin, after the fictional artificial intelligence system from “2001: A Space Odyssey,” has been previously investigated as possible diabetes drug. The researchers tested it against dozens of bacterial strains isolated from patients and grown in lab dishes, and found that it was able to kill many that are resistant to treatment, including Clostridium difficile, Acinetobacter baumannii, and Mycobacterium tuberculosis. The drug worked against every species that they tested, with the exception of Pseudomonas aeruginosa, a difficult-to-treat lung pathogen.

To test halicin’s effectiveness in living animals, the researchers used it to treat mice infected with A. baumannii, a bacterium that has infected many U.S. soldiers stationed in Iraq and Afghanistan. The strain of A. baumannii that they used is resistant to all known antibiotics, but application of a halicin-containing ointment completely cleared the infections within 24 hours.

Preliminary studies suggest that halicin kills bacteria by disrupting their ability to maintain an electrochemical gradient across their cell membranes. This gradient is necessary, among other functions, to produce ATP (molecules that cells use to store energy), so if the gradient breaks down, the cells die. This type of killing mechanism could be difficult for bacteria to develop resistance to, the researchers say.

“When you’re dealing with a molecule that likely associates with membrane components, a cell can’t necessarily acquire a single mutation or a couple of mutations to change the chemistry of the outer membrane. Mutations like that tend to be far more complex to acquire evolutionarily,” Stokes says.

In this study, the researchers found that E. coli did not develop any resistance to halicin during a 30-day treatment period. In contrast, the bacteria started to develop resistance to the antibiotic ciprofloxacin within one to three days, and after 30 days, the bacteria were about 200 times more resistant to ciprofloxacin than they were at the beginning of the experiment.

The researchers plan to pursue further studies of halicin, working with a pharmaceutical company or nonprofit organization, in hopes of developing it for use in humans.

Optimized molecules

After identifying halicin, the researchers also used their model to screen more than 100 million molecules selected from the ZINC15 database, an online collection of about 1.5 billion chemical compounds. This screen, which took only three days, identified 23 candidates that were structurally dissimilar from existing antibiotics and predicted to be nontoxic to human cells.

In laboratory tests against five species of bacteria, the researchers found that eight of the molecules showed antibacterial activity, and two were particularly powerful. The researchers now plan to test these molecules further, and also to screen more of the ZINC15 database.

The researchers also plan to use their model to design new antibiotics and to optimize existing molecules. For example, they could train the model to add features that would make a particular antibiotic target only certain bacteria, preventing it from killing beneficial bacteria in a patient’s digestive tract.

“This groundbreaking work signifies a paradigm shift in antibiotic discovery and indeed in drug discovery more generally,” says Roy Kishony, a professor of biology and computer science at Technion (the Israel Institute of Technology), who was not involved in the study. “Beyond in silica screens, this approach will allow using deep learning at all stages of antibiotic development, from discovery to improved efficacy and toxicity through drug modifications and medicinal chemistry.”

The research was funded by the Abdul Latif Jameel Clinic for Machine Learning in Health, the Defense Threat Reduction Agency, the Broad Institute, the DARPA Make-It Program, the Canadian Institutes of Health Research, the Canadian Foundation for Innovation, the Canada Research Chairs Program, the Banting Fellowships Program, the Human Frontier Science Program, the Pershing Square Foundation, the Swiss National Science Foundation, a National Institutes of Health Early Investigator Award, the National Science Foundation Graduate Research Fellowship Program, and a gift from Anita and Josh Bekenstein.

Passionate Teacher

noreply@blogger.com (Saddam Leonardo Kap) — Tue, 30 Jun 2020 10:53:00 +0000

The mediocre teacher tells. The good teacher explains. The superior teacher demonstrates. The great teacher inspires.’

A teacher has the power to transform souls and touch someone’s life in a positive way. It is one of the noblest of professions that deal with life-changing and destiny-altering powers. The teacher has the present as raw material on which she will finally carve and design the future … the children. It’s an ever evolving yet challenging and lifelong learning environment of which we are an integral part.

Teaching is a chance to touch someone’s life in a positive way. Teachers are the pillars of society for they educate and mould the future citizens of a country. Teaching, like any other activity, emerges from ones inwardness. Motivating and exciting students is the key.

Passion for teaching is innate. At the core of caring relationships are positive and high expectations that not only structure and guide behaviours, but also challenge students to perform what they believe they can do. The influence of a teacher does not stay for a limited period of time but it extends over a lifetime.

The dynamics of teaching have changed from the times of the gurukul to the time of today.
The guru, today, is a smart, well educated, knowledgeable person understanding the I-phone generation and keeping a tab on the learners’ lives, learning and most importantly their learning needs. In a vibrant and multidimensional environment like today where we live in a globalized world, the role of a teacher is now a multi-faceted role in an interesting classroom. She/he has to manage the classroom, teach, interact and above all be the active facilitator for a vibrant group of learners waiting to learn from you and trap you if you falter along the way.

A good teacher inspires. She teaches from the heart, not from the book. A teacher is capable of dispelling the clouds of ignorance from the minds of students and lighting the spark of knowledge in them.

The art of teaching is the art of awakening the natural curiosity of young minds for the purpose of satisfying it afterwards. Teaching has the power to redefine lives. Teachers still use the most simple tools, articles and examples to teach the most complicated of lessons. Teaching requires creativity, innovation, passion, intellect, heart and head, love of subject and love of children.

Good teachers learn by reflecting on their experience of the teachers who inspired them, and by watching inspiring teachers in the schools to which they are attached. The best teachers I have known are constantly learning. The very best teachers I have known are as eager to learn on the day they retire as on their first day in the classroom. Good teaching is as much about passion as it is about reason ….

It’s about caring for your craft, having a passion for it, and conveying that passion to everyone, most importantly to your students – Professor Richard Leblanc Let your students know — and show them — how much you care.

‘If you can reach ‘em, you can teach ‘em.’ Making a significant contribution to someone’s life is something money can never buy. Teaching allows teachers to make a positive difference in the lives of the children in their care.

Latex tutorial 2 : Tex studio| How to make your own professional Documen...

noreply@blogger.com (Saddam Leonardo Kap) — Sat, 27 Jun 2020 06:50:00 +0000

You must go through it

Ch 01 Physical world Part 1: Tutorial on Physics for XI IIT Advance, NEET, CBS...

noreply@blogger.com (Saddam Leonardo Kap) — Sat, 27 Jun 2020 06:26:00 +0000

Watch this lecture. This is an amazing Lecture. Hope you will enjoy every bit of it. Don't forget to share and write a beautiful comment.

The road taken: Career Paths for PhD physicists

noreply@blogger.com (Saddam Leonardo Kap) — Thu, 25 Jun 2020 14:49:00 +0000

Two roads diverged in a wood, and I—
I took the one less traveled by,
And that has made all the difference.
—Robert Frost, 1916

In his poem “The Road Not Taken,” Robert Frost famously wrote about choices. For graduate students in physics, the most familiar road is the academic path, but many other career paths are available to PhD physicists—far more than Frost’s two roads. According to NSF’s Survey of Doctorate Recipients, almost half of the 130 000 PhD physical scientists living and working in the US in 2017 were employed in the private sector, about 40% were employed in academia, and 9% worked in government settings

In this article we examine the different career paths of PhD physicists working in private industry, academia, and government, and we describe what physicists in different sectors find rewarding about their chosen careers.

In the first-ever 10-year follow-up survey of physics PhD recipients, the Statistical Research Center at the American Institute of Physics (AIP), which also publishes Physics Today, contacted physics PhD recipients from the classes of 1996, 1997, 2000, and 2001 who were in the US during 2011. Data used in this article were collected from more than 1800 respondents who participated in that PhD Plus 10 Study. We asked a variety of questions about respondents’ postdoctoral positions, their first jobs after receiving their doctorates, and their jobs at the time of the survey. Respondents reported whether they worked in academia (universities or other two- or four-year institutions), for the government (military; national labs; or a local, state, or federal agency), or in the industrial sector (government contractor, private company, or self-employed).

WHO PURSUES A POSTDOC?

The first step in a new PhD’s career is typically the decision of whether to pursue a postdoc. According to AIP’s most recent follow-up survey of physics degree recipients in 2015–16, 47% of PhD graduates accept postdoc positions. Not all physicists pursue postdocs, and our PhD Plus 10 data show that postdoc decisions were different across sectors. We found that far fewer physicists working in industry accepted postdoc positions. When we asked if they would do so again, nearly a third of industrial physicists who took a postdoc said they would not (see figure 2). Furthermore, those in industry who did accept a postdoctoral position spent the least amount of time in it

Of the physicists in our survey, 8% declined postdoc offers and reported their reasons for doing so. They made that choice because they found permanent positions elsewhere, they were no longer interested in an academic career, the postdoc salary was too low, they could not relocate, or they wanted to start a family. Those responses suggest that financial and family considerations are important factors in a PhD physicist’s decision to pursue the postdoctoral path.

DO CAREERS CHANGE OVER TIME?

Since we knew PhD physicists’ first and current jobs, we were able to look at different types of movement across careers. Our survey analysis focused on three questions about career movement:

• Did respondents move across sectors during their careers?

• Did respondents stay with the same employer?

• Did respondents change fields during their careers?

We found little movement across career sectors. Almost all PhD physicists were still working in the same broad sector—industry, academia, or government—in which they had accepted their first job after a postdoc

We saw wide variation in physicists’ tendency to switch employers depending on their job sector (see figure 5). About two-thirds of the physicists working in the academic sector were with the same employer who gave them their first non-postdoctoral job, and almost three-fourths of government employees were still with the same employer. Those working in industry, however, were more likely to have moved; less than 40% were still with the same employer.

Lastly, we examined movement between job fields (figure 6). How common was it for physicists to, for example, move from a physics-focused job to an engineering-focused job or to a nonscience position? Most academic and government physicists began their careers in the field of physics or astronomy, and the majority stayed in their job field. Most industry physicists worked in engineering fields, and those who began in physics or astronomy were more likely to move to a nonscience field. It’s possible that trend reflects a tendency for industry physicists to move to management or nonscience business positions as their careers progress.

We also asked physicists, “What are the most rewarding aspects of your current job?” In examining more than 1300 quotes from our respondents, we found far more similarities than differences across the three sectors (see figure 7). For example, PhD physicists in all three sectors felt rewarded when they collaborated with others, mentored younger employees or students, helped society with their work, and had the autonomy to decide their research and work schedules. Regardless of which job path physicists choose, it appears that working in academia, government, and industry can be fulfilling in similar ways.

Each sector is also unique, and physicists in the three sectors identified specific aspects of their jobs as rewarding. For example, academic physicists felt rewarded when teaching students, performing public outreach to improve science literacy, and helping their departments or the larger scientific field. Industry physicists felt rewarded when helping their clients, supporting their company, and receiving financial benefits like higher salaries and stock options. Government physicists appreciated that they had more job security and conducted research at a faster pace than academics; they also felt rewarded when addressing larger societal issues such as climate change and national security.

When we asked PhD physicists whether they found their jobs intellectually challenging, those in government and academic positions were more likely to respond in the affirmative than those in industry (see figure 8). However, there is no evidence that industrial physicists are less satisfied with their jobs than their counterparts in academia and government. Although industry physicists may feel less intellectually challenged, they may encounter different types of problems that they enjoy tackling and solving.

DIVERGING OR CONVERGING ROADS?

The career options available to PhD physicists are varied. Our data provide insight into the satisfaction that midcareer PhD physicists have found (see online resources on page 34). We should, however, note that the past does not necessarily predict the future. The pace of technological change suggests that career options that do not currently exist may be viable options in 2040. In the same vein, current occupations may become obsolete. Therefore, we cannot give a comprehensive overview of the career paths that today’s PhD students may travel.

The roads in Frost’s poem diverge, and the narrator chooses one. Later, the narrator notes, “Yet knowing how way leads on to way, I doubted if I should ever come back.” We do not know whether the narrator ever went back. Can a PhD physicist? We have seen that most remain in the same sector as their first full-time job. However, some do change their career path over time. The options are many and varied. Which road will you take?

Online resources

If you are interested in reading more about the careers of PhD physicists or gaining inspiration for job searches outside academia, the following reports are available on the American Institute of Physics website.

► Who’s Hiring Physics PhDs (www.aip.org/statistics/whos-hiring-physics-phds) lists employers who have recently hired a physics PhD in various sectors, along with common job titles, salaries, and skills needed.

► Common Careers of Physicists in the Private Sector (www.aip.org/sites/default/files/statistics/phd-plus-10/PhysPrivSect.pdf) contains data on salaries and skills used in eight types of industrial jobs.

► Physics PhDs Ten Years Later: Duties and Rewards in Government Positions (www.aip.org/sites/default/files/phd%2B10-gov-dutiesnrewards.pdf) indicates the job titles of physicists in government positions and what those jobs entail.

► Physics PhDs Ten Years Later: Duties and Rewards in Academic Positions (www.aip.org/sites/default/files/phd%2B10-acad-dutiesnrewards.pdf) indicates the job titles of physicists in academic positions and what those jobs entail.

Top 10 Experiments in physics that revolutionized human Understanding.

noreply@blogger.com (Saddam Leonardo Kap) — Mon, 22 Jun 2020 05:06:00 +0000

Physics is an exploratory science. New experiments in physics change or expand our existing knowledge in one way or another. Let us find out how this has happened in history.

10. Galileo's Tower of Pisa experiment

Before Galileo, a majority of people used to follow the teachings of ancient Greek philosopher, Aristotle, who had proclaimed that different weights when dropped from same height experienced different amounts of attraction from the Earth thus falling at different speeds.

It is said that in 1589 Galileo climbed atop Tower of Pisa and dropped two objects of different masses in order to debunk Aristotelian belief. In 1971, astronaut David Scott re-created Galileo's famous experiment on the moon by dropping a hammer and a feather simultaneously.

9. Faraday's law of induction

A sudden movement of a magnet through a coil produces a reading on the galvanometer meaning that a changing magnetic field can induce an electric current in the coil. This observation was first made by Michael Faraday in the year 1831. Today, electric generators use the same principle to convert mechanical energy into electrical energy that powers our household electric appliances.

8. Michelson Morley experiment

Does light, like other waves, require a medium to travel? Scientists of the 19th century thought so. They proposed the existence of an invisible stationary substance permeating through all of space that they named aether. In the 1880s, American physicist Albert Michelson thought of discovering the aether.

If aether really exists, Earth moving through it would cause a wind in the same way that there seems to be a wind outside a moving car. To a person in the car, the air outside the car would seem like a moving substance. In the same way, aether should seem like a moving substance to things on Earth.

Michelson designed an interferometer to measure the speed of the "aether wind" in 1887 along with one of his colleagues, Edward Morley.

However, no aether wind was detected by the experimental setup making it the most famous failed experiment in history. But, it had been shown that light required no substance medium whatsoever to travel in space.

7. Double slit experiment

Newton believed that light was a stream of energy-carrying particles. But he was proven wrong by Thomas Young, in 1801, who demonstrated with experiment that light was a wave.

In this experiment, when light emitted from two sources is forced to interfere, an unexpected pattern is formed on a distant screen. This interference pattern can be explained by wave theory of light only.

6. Discovery of electron

The atom was greatly regarded as the smallest possible structure in the universe. In 1897, however, Joseph Thomson performed a groundbreaking experiment suggesting that atom was divisible.

Thomson used a cathode ray tube, which is a vacuum-sealed glass tube with a cathode and anode fixed inside it. A beam of electrons was observed to move from one end to another upon the application of high voltage.

Thomson also identified that electron was not electrically neutral because he observed a deflection in the beam when an external electric field was applied.

5. Photoelectric effect

In 1887, German experimental physicist Heinrich Hertz stumbled upon an amazing phenomenon, the photoelectric effect. He discovered that certain metal electrodes when illuminated by the UV light produced electric sparks.

Two decades later, Einstein proposed an explanation of the photoelectric effect using a concept first put forward by Max Planck that light waves consist of tiny bundles or packets of energy known as photons or quanta.

4. Davisson Germer experiment

It was proposed by physicist Louis de Broglie that matter had particle as well as wave nature simultaneously. Davisson and Germer set about to test de Broglie's hypothesis in laboratory.

If electron could behave like a wave, it could interfere with another electron wave much like the light waves do. In 1925, the duo succeeded in obtaining interference pattern.

3. Gravity probe b

This was a satellite-based experiment which was launched on 20 April, 2004 by NASA. Its mission was to measure the space-time curvature around the earth as proposed by Einstein. Total cost of this project was about $750 million.

This was accomplished by measuring the tiny changes in the direction of spin of four gyroscopes contained in the satellite. Initial results confirmed the expected geodetic effect to an accuracy of about 1%.

2. Higgs boson discovery

The Higgs field is a field of energy that is thought to exist in every region of the universe. The field is accompanied by a fundamental particle known as the Higgs boson, which is used by the field to continuously interact with other particles, such as the electron.

In 2012, the particle was finally discovered. Peter Higgs became a worldwide sensation and a Nobel Prize winner.

1. LIGO experiment

The Laser Interferometer Gravitational-Wave Observatory is a large-scale physics observatory which was designed to detect cosmic gravitational waves as predicted by Einstein's general theory of relativity.

By 2017, LIGO had made five detections of gravitational waves, the first four of which were because of colliding black hole pairs. The fifth event, on August 17, 2017, was the first detection of a collision of two neutron stars.

Freeman Dyson - Why is he an important physicist?

noreply@blogger.com (Saddam Leonardo Kap) — Sun, 21 Jun 2020 17:58:00 +0000

The mathematical physicist Freeman Dyson was famed for his visionary ideas that stretched far beyond pure science. Hamish Johnston looks at the life of a scientist who was never afraid to speak his mind

The British-born mathematical physicist and public intellectual Freeman Dyson, who died on 28 February 2020 at the age of 96, was one of the most celebrated figures in 20th-century physics. He had spent most of his professional life at the Institute for Advanced Study (IAS) in Princeton, New Jersey, where he was a professor emeritus and remained active until his final few days. Dyson died at a hospital near Princeton, due to complications from a fall, according to his son, the science historian George Dyson.

Dyson began his career in the 1940s, making important contributions to the development of quantum electrodynamics (QED). Early on, however, he broadened his interests to include nuclear reactors, space travel, climate and biology – both on Earth and elsewhere in the cosmos. Dyson also wrote numerous popular books that focused on the intersection of science and technology, religion and philosophy. Ever the iconoclast, his contrarian views on global warming drew the ire of some leading climate scientists who accused him of acting irresponsibly.

Dyson was born in Crowthorne, Berkshire, on 15 December 1923 to the lawyer and social worker Mildred Atkey, and the musician and composer Sir George Dyson. Hugely interested in numbers as a child, he went on to read mathematics at the University of Cambridge aged just 17. Breaking his studies, Dyson spent part of the Second World War working as a civilian researcher for the Royal Air Force’s Bomber Command. He later returned to Cambridge, graduating with a BA in mathematics, studying under the likes of Paul Dirac, Arthur Eddington and the mathematician Godfrey (GH) Hardy.

Dyson stayed at Cambridge as a fellow of Trinity College until 1947 when he moved to the US, where he worked towards a doctorate with Hans Bethe at Cornell University. However, he did not complete his PhD and Dyson went on to be one of the world’s most famous physicists never to have a doctorate. In 1948–1949 he was based at the IAS before spending the next two years at the University of Birmingham, UK, working alongside Rudolph Peierls, who had played a role in developing the atomic bomb.

Dyson briefly returned to Cornell in 1951 before accepting a lifetime appointment to the IAS that was arranged by its then director Robert Oppenheimer. There, Dyson rubbed shoulders with such luminaries as Albert Einstein and John von Neumann. Commenting on his early years, he once told Physics World (June 2000) that he had contemplated going to the Soviet Union to work with the theoretical physicist Lev Landau but chose the US instead. “All the young people of my generation had been stuck in England all through the war and you couldn’t travel anywhere. There was a violent desire to get out and see the world.”

Scientific thinking

Much of Dyson’s early work focused on QED, taking disparate ideas developed by Richard Feynman, Julian Schwinger and Sin-Itiro Tomanaga and unifying them. This caused some colleagues to dub him “the midwife to the birth of quantum electrodynamics”. Feynman, Schwinger and Tomanaga shared the 1965 Nobel Prize for Physics for their work on QED and some physicists believed that Dyson should have bagged a Nobel prize – a sentiment that Dyson always played down.

The 1950s saw Dyson diversify his research interests, working on Project Orion, which investigated the use of nuclear power for space propulsion. His described his 15 months on Orion as “the most exciting and in many ways the happiest of my scientific life”. Dyson also joined a project headed by the physicist Edward Teller – who pioneered the hydrogen bomb – that focused on the design of small nuclear reactors for research and the production of medical isotopes. More than 60 of these “TRIGA” reactors have been installed worldwide and are still being produced.

Dyson continued to do some fundamental research and in 1967 he made a major contribution to the understanding of the inherent stability of fermionic matter. In the 1970s Dyson reduced his research activities and began to write popular-science books. He credited this shift to his Cambridge mentor Hardy, who once told Dyson: “Young men should prove theorems, old men should write books.” But Dyson still kept up his research interests, and as late as 2012 published a paper on the mathematics of the prisoner’s dilemma (PNAS 26 10409).

He had several fanciful (yet scientifically plausible) concepts named after him including the “Dyson tree”, which is a hypothetical genetically modified plant that lives inside a comet

Dyson’s books are known for their imaginative ideas that verge on science fiction. He had several fanciful (yet scientifically plausible) concepts named after him including the “Dyson tree”, which is a hypothetical genetically modified plant that lives inside a comet. He also popularized the idea of a huge artificial structure that could be built around a star by an advanced civilization – now known as a “Dyson sphere”. Searching for Dyson spheres is an active area of research, with some astronomers looking for changes in the spectral properties of stars that would be the result of such a feature.

In 2006 Dyson published The Scientist as Rebel, in which he questioned the role of human activity in global warming, putting him in conflict with the scientific consensus. Later, in another interview with Physics World (January 2008), he said that the money being spent on addressing climate change should instead be targeted at “other problems that are more urgent and more important such a poverty, infectious diseases, public education and health”. He also said that thinking about potential benefits of climate change “will not do us any harm”.

Dyson believed that the science underpinning global warming is faulty and had challenged the motivations of climate scientists and activists. Referring to the climate campaigner and former US vice-president Al Gore, Dyson once said that “his claims regarding the climate are not based on science. The scientists just go along with it. It’s nice to be important and the way to be important if you are a climate scientist is to say we’re running into a tremendous disaster. It’s a form of corruption in a way”.

Dyson also publicly criticized climate scientist and activist James Hansen, who responded that Dyson was ill-informed about the science. Dyson said that his contrarian views on climate change arose from his philosophical outlook. He described himself as a humanist, rather than a “naturalist”. He said that naturalists believe “nature knows best”, while humanists believe that “humans have the right and the duty to reconstruct nature so that humans and the biosphere can both survive and prosper”.

As a result, Dyson was a proponent of genetic engineering. He believed that it could be used to create new technologies based on living organisms – such as a tree that is engineered to have silicon in its leaves to generate electricity and is also modified to produce liquid fuel.

Religious feelings

Dyson also wrote widely on science and religion, which led him to him winning the Templeton Prize for Progress in Religion in 2000. The award, which included a $600,000 cash prize, is given by the US-based Templeton Foundation to a person who “has made an exceptional contribution to affirming life’s spiritual dimension, whether through insight, discovery or practical works”. Dyson became one of a dozen physicists to have won the prize, which was first awarded in 1972 to Mother Theresa. Dyson’s Templeton citation referred to his “futurist views [that] have consistently challenged humankind to reconcile technology and social justice”.

As for his own person religious convictions, Dyson described himself as a “practising Christian up to a point but not a believing Christian”. In 2000 he told Physics World that his view of Christianity did not include the resurrection of Christ, in which he did not believe, and that he would not use the word “God” to describe a higher entity. Instead, he referred to a “world soul”, adding that “I have a simple feeling that there is something there.”

Dyson appeared to see no conflict between religious faith and science and pointed out in 2000 that Isaac Newton himself “had a very strong Christian faith but was also a tremendously rational person”. He told Physics World that his Christianity “is about taking care of your neighbour and doing good in the world”. Accepting his Templeton prize at a ceremony in Washington DC that same year, Dyson said “neither technology nor religion alone is powerful enough to bring social justice, but technology and religion working together might just do the job”. Despite this call to action, however, Dyson shied away from campaigning roles.

While some of Dyson’s ideas were embraced by scientists and the wider public, others –including the benefits of genetic engineering and climate change – were met with scepticism. This did not deter Dyson. “The rules of the world-historical game change from decade to decade,” he once said,

“and the dogmas that we have now will probably become obsolete. In the years to come, my heresies will probably also be obsolete. It is up to the next generation to find new heresies to guide the way to a more hopeful future.”

Why should physicists study history?

noreply@blogger.com (Saddam Leonardo Kap) — Sun, 21 Jun 2020 17:10:00 +0000

Just as physics is not a list of facts about the world, history is not a list of names and dates. It is a way of thinking that can be powerful and illuminating
Some things about physics aren’t well covered in a physics education. Those are the messy, rough edges that make everything difficult: dealing with people, singly or in groups; misunderstandings; rivals and even allies who won’t fall in line. Physicists often do not see such issues as contributing to science itself. But social interactions really do influence what scientists produce. Often physicists learn that lesson the hard way. Instead, they could equip themselves for the actual collaborative world, not the idealized solitary one that has never existed.

History can help. An entire academic discipline—history of science—studies the rough edges. We historians of science see ourselves as illustrating the power of stories. How a community tells its history changes the way it thinks about itself. A historical perspective on science can help physicists understand what is going on when they practice their craft, and it provides numerous tools that are useful for physicists themselves.

PHYSICS IS A SOCIAL ENDEAVOR

Research is done by people. And people have likes and dislikes, egos and prejudices. Physicists, like everyone else, get attached to their favorite ideas and hang on to them perhaps long after they should let them go. A classic case is the electromagnetic ether, an immensely fruitful concept that dominated physics for most of the 19th century. Even as it became clear that ether theory was causing more problems than it solved, physicists continued to use it as a central explanatory tool—even for many years after Einstein’s 1905 theory of special relativity declared it superfluous. The history of physics is littered with beautiful theories that commanded great loyalty.

People come from places too, and physicists want to protect their homes as much as anyone else. It is easy to forget that 100 years ago during World War I, British scientists refused to talk to their German colleagues on the other side of the trenches. Even after the end of the fighting, Germans and their wartime allies were officially forbidden from joining international scientific organizations. During World War II, the specter of an atomic bomb in the hands of Adolf Hitler terrified Allied physicists into opening the Pandora’s box of nuclear weapons. Many of the scientists involved bemoaned their actions afterward, but war and nationalism make for a potent impetus.

Those incidents are not exceptions. Physicists are not disinterested figures without political views, philosophical preferences, and personal feelings. The history of science can help dismantle the myth of the purely rational genius living outside the everyday world. It makes physics more human.

And a more human physics is a good thing. For starters, it makes physics more accessible, particularly for students. Many promising students drop out of the sciences because the material seems disembodied and disconnected from their lives. Science education researchers have found that those lost students “hungered—all of them—for information about how the various methods they were learning had come to be, why physicists and chemists understand nature the way they do, and what were the connections between what they were learning and the larger world.”1 Students can potentially lose the wonder and curiosity that drew them to science in the first place. Historical narratives naturally raise conceptual, philosophical, political, ethical, or social questions that show the importance of physics for the students’ own lives. A field in which people are acknowledged as people is much more appealing than one in which they are just calculating machines.

Understanding the human side of physics will also better prepare students for what physicists actually do. Physicists work in groups. They need to talk. Physics is a social endeavor. Ideas and experimental equipment are exchanged constantly. In the early days of general relativity, it was extremely difficult to become proficient in the theory without direct contact with Albert Einstein or his inner circle.2 And since the Great War was raging, few physicists could obtain that contact. General relativity became widely known only after Willem de Sitter, in the neutral Netherlands and in personal contact with Einstein, passed his relativistic skills on to Arthur Eddington in the UK. Fortunately, Eddington was a Quaker pacifist and one of the few British scientists willing to look at a German theory.3 Physics works only when people talk to each other, and communication is not always easy.

PHYSICS ISN’T OBVIOUS

Everything seems obvious in retrospect. Textbooks present experimental results as being self-evident and theories as needing at most a few pages of math to be proven true. But crystal-clear expositions conceal the enormous amount of work and confusion that goes into reaching scientific conclusions. The history of physics can remind us how difficult it is to justify ideas—from heliocentrism to atomic theory—that now seem so obvious.

Complexity, not simplicity, has ruled the practice of science. Every discovery has come out of a messy mix of people, ideas, accidents, and arguments. Generally it takes a great deal of effort to understand what an observation or theory means. The Millikan oil drop experiment, for example, appears in textbooks as a model of clear experimental design and immediately persuasive theoretical interpretation. However, even a quick look at Robert Millikan’s lab notebooks shows how immensely difficult it was for him to make his experiment work. (Figure 1 shows a sample notebook page.)

Robert Millikan’s lab notebooks are filled with pages like this, jam-packed with data, calculations, corrections, and occasional comments. Despite the impression textbook presentations may give, perfecting the famous oil-drop experiment and obtaining the charge of the electron was a long, arduous task. This notebook entry is from 27 February 1912. (Courtesy of the Archives, California Institute of Technology.)

Nature rarely gives a straight answer. So researchers in science sometimes follow blind paths and usually need trial and error and second guessing. Once a robust result has been achieved, scientists tend to downplay all the hard work that went into it; simplicity seems more persuasive than complexity. But the complexity is actually quite reassuring. Students and young researchers are often heartened to learn that physics is hard work and that it is okay for their own efforts not to look like a textbook presentation. Messiness is the standard. Mistakes are normal. The great advances in sciences are much more remarkable when coupled with an appreciation that they came out of struggles and screw ups instead of flashes of insight. The results of physics are not self-evident.

Every time physicists disagree on how to interpret a set of data, they provide fresh proof that physics isn’t obvious. Some data only have significance from a certain point of view. Arno Penzias and Robert Wilson saw excess low-frequency noise in their antenna, not the cosmic microwave background. It was only when they looked at the noise in light of Big Bang cosmology that it seemed important.

The history of physics suggests that there are usually several ways to approach a problem. Quantum electrodynamics emerged from its predecessors not because it was clearly superior but because Freeman Dyson showed that the renormalization approaches of Richard Feynman, Julian Schwinger, and Sin-itiro Tomonaga were all equivalent. None of those independent approaches were wrong, they just needed to be reframed. Even the now-indispensable Feynman diagrams were not obviously useful when they first appeared. They were confusing, and it was not clear how to use them. Dyson, again, was instrumental to the acceptance of a new idea: He had to teach everyone what Feynman diagrams were good for and to evangelize about their importance. Things that now seem essential and obvious never started out that way.

Who is Dyson? I will give all the details about his work in my upcoming blog.

PHYSICS NEEDS MANY KINDS OF PEOPLE

Turning complexity into good physics requires creativity. You can never tell what weird idea will help clarify a confusing observation or provide the key to interpreting an equation. History uncovers the strange stew of concepts that were necessary for the development of physics. Consider the second law of thermodynamics. Its formulation and interpretation were largely due to Lord Kelvin (figure 3). But Kelvin did not come to thermodynamics as a blank slate. He came to it as a Victorian obsessed with waste and engineering efficiency. He came to it as a religious figure who studied the heat death of the universe because it made sense in light of Psalm 102, which acknowledges that the heavens and Earth will all wear out like a garment.6 His personal background gave him the tools he needed to grapple with the puzzling phenomena now attributed to the second law. You can see the importance of Kelvin’s particular point of view when you compare his work with that of, say, German physicists working on thermodynamics. They brought very different ideas to the table and came up with different conceptions. The interplay of various approaches is what brought us our modern view, which we wouldn’t have if not for Kelvin’s now-strange ideas.

Strange but ultimately useful perspectives often come from fields and disciplines apparently distant from the problem at hand. James Clerk Maxwell learned about statistical variation from historians. Particle physicist Luis Alvarez brought expertise in isotopes to his son Walter’s geological work and helped solve the mystery of the dinosaurs’ extinction. The history of science shows how important it is for scientists across different fields to talk to each other. Conversation among separate groups is healthy. Apparently isolated problems are often closely tied together, and you never know where you will find the weird idea that solves your difficulties.

The best strategy for encouraging diverse ideas is to cultivate a diverse community. Underrepresented groups that offer different ways of thinking are often the sources of fresh insights and novel methods. Numerous striking examples exist, and they have led to representatives of marginalized communities becoming visible in the mainstream. For instance, how Marietta Blau developed the nuclear emulsion technique—critical to the emergence of the field we now call particle physics—was distinctive of someone on the periphery. As a Jewish woman in interwar Austria, Blau, shown in figure 4, was doubly excluded. Women were often refused entrance to laboratories, sometimes on the grounds that their hair was too flammable. Jews were rarely allowed to hold high-ranking positions even before the rise of the Nazis. Such restrictions meant that if Blau wanted to study particles, she had to develop cheap, portable detectors that could be made with commonly available materials. With her techniques from the margins, she created an essential observational tool that was utterly surprising to those in the largely homogenous physics community of the time.

Underrepresented groups are usually marginalized because of cultural inertia or deliberate decisions made long ago. For that reason, many working to increase diversity in physics see themselves as helping to right a social wrong. Feynman was denied admission to Columbia University because someone there decided it had too many Jewish students—a decision that now seems absurdly wrongheaded. Surely his alma mater, MIT, benefited from its decision to accept someone on the margins.

In 2015 John Roberts, chief justice of the US Supreme Court, was puzzled by the idea that diversity could be helpful in physics. (See Physics Today, March 2016, page 10.) Roberts’s remarks were disappointing even if the idea behind them is not uncommon: The ideal of science as a monolithic enterprise of pure rationality effectively hides the importance of different perspectives and outlooks. However, that importance is clearly documented in the history of science, which can help clarify both why physics is mostly done by white men and why that can often be a limiting factor for future progress. The history of physics is a fantastic example of the importance of intellectual and institutional diversity. Many different ways of thinking can be brought to bear on a problem, and they should be encouraged.

PHYSICS ISN’T FINISHED

The diversity of ideas and interpretation serves as a reminder that physics is a work in progress. Knowledge is provisional. There are always new ways to tackle a problem, and there is always more to be learned. The history of physics should make one hesitant to claim that current theories will hold forever.

Some worry that such admissions of uncertainty make science less attractive. Actually, the opposite is true. If physics is nearly done, why pursue it? Placing the last few bricks in an almost-complete wall is not always exciting, but expanding an unconstrained structure is a thrilling challenge.8 It is heartening to know that not everything has been discovered.

Accepting uncertainty would require changes in how physics and, more generally, science is taught. Physics is typically presented as a list of things that physicists think are true. We call those lists “textbooks.” They do a terrible job of showing what physicists and other scientists actually do—try to solve puzzles. Instead of talking about the things physicists already know, textbooks could emphasize what is still unknown about a subject. They could talk about how much work still remains: What are the mysteries yet to be uncovered? What is the problem that can’t seem to be cracked? Curiosity should be rewarded, and everyone should be encouraged to ask, “What else?”

One effect of such a pedagogical shift would be less of a focus on proof. Few things can be strictly proven true. In practice, scientists accumulate evidence for a particular claim. That evidence provides some level of confidence. Insisting that every scientific concept meets or even should meet the standard of proof is dangerous; it makes knowledge easily attacked, since virtually every claim has some possible doubt.

If scientists are not explicit and honest about their doubts, a crisis of confidence arises when that uncertainty is revealed. That psychological reality is used to great advantage by, for example, those opposed to teaching evolution in schools. Talking about varying levels of evidence and doubt, instead of about proof or its absence, will actually make science more powerful in the public sphere.

PHYSICS WASN’T ALWAYS AS IT IS

The flip side of accepting that physics will be different in the future is accepting that it was different in the past. Everyone has a tendency to assume that the way things are now is the norm. But history makes it clear that things were not always this way. An understanding of why people used to think differently is a powerful tool for understanding people today. By drawing attention to older, unspoken assumptions, history shows us how to start paying attention to our own.

No less a personage than Einstein advocated for that historical method. As a young man, he read Ernst Mach’s writings on the history of science, and he credited Mach with teaching him how to think critically about scientific principles: “A knowledge of the historic and philosophical background,” Einstein once wrote, “gives that kind of independence from prejudices of his generation from which most scientists are suffering.” (See the article by Don Howard, Physics Today, December 2005, page 34.) He complained that physicists tended to regard currently accepted ideas as unalterable givens. Instead, he suggested, they should study the history of those ideas and understand the circumstances in which they were justified and found useful. In that way, a young physicist on the margins—say, one serving as a patent clerk in 1905—will feel emboldened to strike out into new areas and offer creative new suggestions.

History trains you to think critically about received ideas. History provides evidence of roads not taken. There are many ways to think about the mysteries of quantum physics. The ubiquity of the Copenhagen interpretation does not make it the best one, and it is certainly not the only useful one. Einstein himself would want physicists to take a critical approach to the foundations of quantum mechanics.

Historian and philosopher Hasok Chang argues that science’s plurality of interpretations can make the history of science a resource for modern scientific research. He calls his approach complementary science—recovering forgotten and unsolved puzzles from the past. Some earlier ideas and observations, such as the reflection of cold, were simply abandoned rather than being investigated thoroughly and dropped for good reasons. Putting complementary science into practice demands difficult self-examination. Thinking deeply and critically about assumptions and accepted knowledge can be hard to do in professional scientific contexts, but history is a mode in which it is encouraged.

David Kaiser’s How the Hippies Saved Physics is a fascinating example of how that kind of critical thinking can happen. Some physicists in the 1960s and 1970s were dissatisfied with the “shut up and calculate” culture of the field (four of them are shown in figure 5). They were interested in the deeper philosophical meaning behind their equations. To find that meaning, they engaged with both the mystical counterculture of the era and the history of quantum physics. Along the way, they helped to instigate broader interest in Bell’s theorem and quantum entanglement. The simple realization that people used to think differently can be quite powerful.

PHYSICS DOESN’T HAVE RIGID RULES

People encountering the history of science for the first time are often shocked that the actual practice of science bears so little resemblance to the step-by-step scientific method they learned in school. Scientists simply do not follow a rigid, linear problem-solving system. Sometimes they start with a hypothesis, sometimes with a strange observation, sometimes with a weird anomaly in an otherwise straightforward experiment. Einstein himself reflected late in life that a scientist must be an “unscrupulous opportunist,” adopting and adapting various approaches as new challenges arise.11

Instead of applying a rigid method, scientists work with whatever evidence they have and make the best explanation possible. Consider the claim that theories are disproved by contrary observations. In the early 19th century, Uranus’s orbit seemed incompatible with Newtonian gravity. One reaction would have been to declare that Newtonian gravity had been disproved. Of course, very few people did that. The Newtonian theory of gravity had proven so fruitful that much more than one anomalous observation would be needed to discard it. An easier resolution to the problem was that a new planet, Neptune, was hidden in the darkness. So it seemed obvious that a later discrepancy in Mercury’s orbit should be explained the same way. To again redeem Newtonian gravity, astronomers searched for a planet Vulcan hidden in the Sun’s light. Eventually, however, Einstein proposed that Mercury’s orbital anomaly was a good reason to scrap Newton in favor of his own theory.12

Sometimes a discrepancy is a good reason to discard a theory, and sometimes it is worth inventing a whole new entity to save a theory. Different situations call for different approaches. Physicists usually have good reasons for making their choices, but they need to acknowledge the difficulty and complexity of those choices.

The stories told about scientific discoveries matter. One can easily find completely different versions of the origin of special relativity. Was it a straightforward deduction from the results of the Michelson–Morley experiment? Or did it come from Einstein’s philosophical ponderings of the nature of space and time? Or, historical origins notwithstanding, should it just be derived abstractly from Maxwell’s equations? You conceptualize physics in different ways depending on which story you hear. Those who do the telling should make sure their stories are the ones best supported by the historical evidence.

One should not get too anxious about work that seems to endanger the scientific method. There are many ways to go about doing physics, and it was probably not fair to attack string theory for violating methodological guidelines, though string theorists might want to heed the earlier warnings about being overly attached to beautiful theories. Physicists nowadays are typically not trained in the philosophy of science—although both Einstein and Niels Bohr were—and the philosophical principles they invoke are usually far out of date. Karl Popper’s notion that the mark of science is falsifiability doesn’t do much work anymore—for example, astrology is perfectly falsifiable, but it’s not considered science. Even the currently popular Bayesianism can only take one so far. The history of science shows how definitions and standards of science have shifted over time and, hopefully, provides some impetus to engage with the important work being done today by philosophers of science.

IDEAS ON THEIR OWN TERMS

History teaches that knowledge is not fixed. Historical thinking involves asking incisive questions: Why did people in the past think that was true? Why do I think the opposite is true?

Engaging with history will teach you to understand ideas on their own terms. Aristotle wasn’t a man who was bad at Newtonian physics, he just had a completely different perspective. People in the past worried about different things and tried to solve their problems in different ways. The bugbear of historians is the so-called Whig history that judges everything in the past by how much it looks like the present. Eschewing that kind of judgment is an amazing tool for making sense of the world and its people. If you can understand why people believed heat was a form of matter, you can understand why your colleague is being intractable in a meeting.

Historical thinking makes its subject dynamic. It helps you think about science as a series of questions rather than a series of statements. Those questions will continue into the future, and it is helpful to know what has been asked so far.

I would be remiss not to mention that history of science is, frankly, fun. It is full of fascinating stories that will captivate you. Who doesn’t want to know more after learning that in his experiments James Joule (figure 6) relied on his expertise in beer, or that Newton stuck a dagger into his eye to learn more about colors?

I’ve heard concerns, though, that such stories are a distraction that take time away from science instruction or quantitative research. A good strategy is to integrate history into teaching and thinking. Doing so will make physics majors and physicists better citizens of the world and help attract sharp students to science careers. Even for non science majors, history of science is an excellent way to increase science literacy and engagement with scientific ideas.

In the end, history of science exposes scientists to new ways of thinking and forces them to reexamine what is already known. Such intellectual flexibility is essential for any discipline, but it is particularly important for fields as influential and authoritative as physics and other sciences. How do we know what we know, and how might it be otherwise?

REFERENCES

1. S. Tobias, They’re Not Dumb, They’re Different: Stalking the Second Tier, Research Corp (1990), p. 81. Google Scholar

2. A. Warwick, Masters of Theory: Cambridge and the Rise of Mathematical Physics, U. Chicago Press (2003). Google ScholarCrossref

3. M. Stanley, Isis 94, 57 (2003). https://doi.org/10.1086/376099, Google ScholarCrossref

4. X. Lin-Siegler et al., J. Educ. Psychol. 108, 314 (2016). https://doi.org/10.1037/edu0000092, Google ScholarCrossref

5. D. Kaiser, Am. Sci. 93, 156 (2005). https://doi.org/10.1511/2005.52.957, Google ScholarCrossref

6. C. Smith, M. N. Wise, Energy and Empire: A Biographical Study of Lord Kelvin, Cambridge U. Press (1989). Google Scholar

7. P. Galison, Image and Logic: A Material Culture of Microphysics, U. Chicago Press (1997). Google Scholar

8. M. Gleiser, The Island of Knowledge: The Limits of Science and the Search for Meaning, Basic Books (2014). Google Scholar

9. H. Chang, Inventing Temperature: Measurement and Scientific Progress, Oxford U. Press (2004). Google ScholarCrossref

10. D. Kaiser, How the Hippies Saved Physics: Science, Counterculture, and the Quantum Revival, W. W. Norton (2011). Google Scholar

11. A. Einstein, in Albert Einstein: Philosopher–Scientist, P. A. Schilpp, ed., Library of Living Philosophers, (1949), p. 684. Google Scholar

12. See, for example, T. Levenson, The Hunt for Vulcan … and How Albert Einstein Destroyed a Planet, Discovered Relativity, and Deciphered the Universe, Random House (2015). Google Scholar

Can Atoms Touch Each Other?

noreply@blogger.com (Saddam Leonardo Kap) — Sun, 21 Jun 2020 16:28:00 +0000

A couple of weeks back I posted an answer to a question from a Twitter follower’s child, who asked “How Strong Is Space?” That was fun, so here’s another kid-question answered, this one from my own eight-year-old who goes by “The Pip” for Internet purposes. The other night, he asked “Why can’t atoms touch each other?”

I’m not sure the exact reason why he asked this, but the phrasing suggests it’s related to the observation that there’s almost always some microscopic empty space between things that appear to be touching on a macroscopic scale. Possibly it’s even connected to the “Atoms are mostly empty space” idea that Ethan talked about recently.

The short and simple version of the answer is that it’s not really correct to think of atoms as solid objects like little balls that can be forced into physical contact with one another. Most of the “size” of an atom is just the electron cloud that surrounds the nucleus, and that’s not a solid thing— it will shift around in response to electric and magnetic fields applied from the outside. These can’t be made to “touch” in the everyday sense because they’re not solid in the way that we think of everyday objects being solid.

Of course, when you start to dig into this a little more, it becomes trickier than it initially seems, because of course an everyday solid object is made up of atoms. So what’s happening to those atoms when solid objects “touch” that isn’t what we’d call “touching” in an everyday sense?

Our idea of two objects “touching” is basically that the outer boundary of one is at the same place as the outer boundary of the other, so you would pass between them without going through any intervening space. At the scale we experience the macroscopic world, this is a reasonably good approximation: there is no perceptible gap between two objects that are touching. The microscopic analogue of this would be to have a situation where you can move from the nucleus at the center of one atom to the nucleus at the center of the other atom without passing through any space that isn’t part of the electron cloud of one of the two.

This tends not to happen, because atoms are composed of charged particles that interact at a distance. When you try to bring two objects close together, the atoms in one begin to “see” the atoms in the other not as a perfectly neutral single object, but as a composite of a positive nucleus and negative electrons. Since the electrons are around the outside of the atom, those are the things that first interact, and as they have the same charge, they repel one another.

If you want to look at what happens in extreme detail, this gets very complicated, since the electron clouds in the individual atoms can re-arrange themselves in complicated ways. The end result, though, is that as the separation between the atoms at the contact point decreases, the energy of each pair of atoms increases, until it matches the energy of whatever’s pushing them together. That generally happens in a way that keeps the two distorted electron clouds from overlapping, so technically there’s some tiny amount of space between the atoms in neighboring objects. They’re held apart by electromagnetic interactions, so it wouldn’t be too horribly wrong to imagine that gap as being crisscrossed by innumerable photons carrying the force back and forth between the two.

(It should be noted that even though there’s technically empty space between the atoms, you can still do all the things we associate with “touching” an object. A scanning tunneling microscope (STM) can be used to move atoms around and arrange them into tiny patterns even though there’s technically always a bit of space between the tip and the atom in question.)

So, in most cases atoms aren’t technically “touching” since there’s some space between them that isn’t occupied by the electron cloud of either. If this is just a question of energy, though, it’s not unreasonable to ask how strong a prohibition that is. Is it truly forbidden, or is it possible under the right circumstances for the electron cloud of one atom and the electron cloud of another to come into contact?

The answer here is “sort of.” You can, in fact, have a situation where you don’t cross any space that isn’t part of an electron cloud as you move from the nucleus of one atom to the nucleus of a neighboring atom. It happens all the time— it’s just not clear it makes sense to call it “touching.”

The situation I’m talking about is the formation of an interatomic bond, which in most cases involves having electrons “shared” between atoms within the same molecule or crystal. In a sense, these electrons aren’t orbiting one atom or the other, but both at the same time. There’s no empty space between the atoms, but that’s because they’ve ceased to be entirely independent objects, but are instead components of a large molecule. You can talk about this or that atom within the molecule, in that there are specific regions of space where the interactions are dominated by one particular nucleus, but it’s no longer quite as sensible to talk about them as discrete objects with their own electron clouds.

So, as with basically all kid-questions, the answer to “Can atoms touch each other?” turns out to be more complicated that you might think. In the end, I’d probably go with “Yes, but when they do, they stop being independent atoms.”

Book Review: Quantum Legacies

noreply@blogger.com (Saddam Leonardo Kap) — Sun, 21 Jun 2020 16:23:00 +0000

I greatly enjoyed David Kaiser’s How the Hippies Saved Physics (here’s my review from 2011), so when I ran across a mention of this new book with “Quantum” in the title, I immediately sought out a copy. This sort of thing is highly relevant to my interests.

Kaiser is a professor at MIT with a joint appointment in both physics and history of science, and as you would expect this collection of essays splits time between those two fields. The book contains a handful of pieces relating to Kaiser’s work in physics, chiefly about a “cosmological” test of quantum physics, using light from distant quasars as a random number generator for a Bell’s Inequality test (I talked briefly about this idea in the context of football in 2015). There are also a larger number of pieces primarily about the historical and social context of physics, mostly in the mid-to-late 20th century. Almost all of these were previously published (I think there’s only one that doesn’t have a “A version of this previously...” note), mostly in non-technical outlets (The London Review of Books features prominently, as he had a regular gig with them for a while).

The strongest material here charts the changes in the landscape of physics after World War II: the rise and fall of physics enrollments and employment, and the rise and fall of Big Science projects like the (cancelled) Superconducting Supercollider. Some of this is familiar from Hippies, but some is new, and all together it paints a very compelling picture of how strategic decisions at the public policy level shaped the way physicists have gone about studying the universe. I would disagree a bit about some of the details— Kaiser’s physics background is in particle theory, so he’s more pro-accelerator than I am, and there’s a thread in the history of quantum that I’ll take issue with in a different post— but it’s a good story well told. This thread also includes my single favorite piece from the book, using a chance collision between topics to unpack the history of particle cosmology.

The second interesting theme in these pieces, as noted by Ash Jogalekar in his review, has to do with physics publishing. Again, part of this is recycled, but the story of Frijtof Capra’s Tao of Physics is fascinating enough that I was happy to read it again. The chapter on the writing of the (in)famous Gravitation by Misner, Thorne, and Wheeler was new to me, though, and really interesting.

All in all, this is a very solid work both in terms of the history and the physics discussed in it, and Kaiser is a very engaging writer. As you would expect from an actual (albeit part-time) historian, the pieces are also extensively documented with citations of the original sources (something I appreciate greatly after a lot of time spent trying to chase down the sources of colorful anecdotes that seem like good material for my own book-in-progress...). If you’re interested in (non-technical) writing about physics, and particularly about the historical context of the field, you should check it out.

Importance of creativity in Physics

noreply@blogger.com (Saddam Leonardo Kap) — Sun, 21 Jun 2020 15:49:00 +0000

As someone who derives significant income from writing for money, I end up spending a fair bit of time reading writing advice. Not because I'm in need of tips, myself-- after many years of this, I've got a routine that mostly works for me. Rather, I'm looking for good advice to pass on to other people, because I get asked for advice on a regular basis, and I don't really have much of my own to offer.

That's how I came to read this advice post from Alyx Dellamonica, making an analogy between figuring out how fiction works and trying to learn about cars from a junkyard. I like the junkyard analogy quite a bit, but along the way she makes a couple of passing mentions to physics that I absolutely hate. Here's the first:

With the arts, you not a physics professor laying out a formula, some cut-and-dried procedure for which there is one satisfactory answer. You’re not showing someone how to paint the perfect yellow line down the middle of a strip of road, or fly an airplane without making it go kersplat, or performing open heart surgery. The arts are more fungible.

As a physics professor, this drives me nuts, because it's a terrible misconception about what physics is, one that sadly is shared not only by artists and writers but also by all too many of our students. (It's not even a good representation of modern physics education, but that's a side issue, here.)

Far too many of our students, particularly in the "service" courses that are required for engineering and pre-med majors, think that physics is as Dellamonica describes it: You just find the right magic formula, plug in numbers, and get the one correct answer that you check off against the key in the back of the book. Formula-hunting students are the bane of an intro physics professor's existence-- I see students on exams grabbing totally irrelevant formulae from the equation sheets we provide, just because some of the symbols used happen to be the same (the classic example is using an expression for the period of an oscillator as if it's a tension force, because in many books they both get the symbol T). This after I specifically warn them against looking for random magic formulae.

Even at the intro level, physics is not about finding magic formulae and plugging numbers into them. You can, alas, be somewhat successful in introductory classes by formula hunting and memorizing rote algorithms, but then you can be somewhat successful in introductory English classes by writing competent but formulaic essays.

The number of formulae you really need to know in physics, even at the intro level, is actually very small-- for about the first half of introductory Newtonian mechanics, it's pretty much just "F=ma". The hard part is conceptual, not mathematical-- looking at a complex physical situation and figuring out how to capture the essential physics of the situation, and apply a handful of simple rules. For all but the most basic and artificial examples, there are usually multiple paths to getting the same correct answer-- you can choose a different coordinate system, or work with energy instead of forces, and end up with the same answer for anything you might reasonably expect to measure. You can use symmetry arguments to eliminate big chunks of the calculation, or you can plunge right in and do a bunch of math to get to the same place in the end.

In fact, one of the things I try to drive home in intro classes is that it's often useful to use multiple approaches to a single problem as a way to check the answer. If a brute-force calculation shows that something is zero, you should look for a symmetry argument that shows it should be zero, to make sure you haven't made a mistake. If analyzing a circuit in terms of equivalent resistance gives you a particular current value, plug that into Kirchoff's Laws and make sure it checks out.

And, of course, once you're clear of the intro level, the situation is vastly more complicated. As a few seconds' thought would show it must be-- if physics were nothing but plugging numbers into well-known formulae, "physics research" wouldn't be a thing. In fact, the known formulae are only a tiny, not very interesting slice of physics.

We teach those well-worn formulae not because they're useful as is, but because they can be useful approximations to more complicated scenarios. The real business of physics at higher levels is figuring out creative ways to break complicated situations down and use those simple tools to describe pieces of the problem that you then recombine to get something complicated.

At the highest levels, physics is an intensely creative endeavor, involving finding unique approaches to problems that are impractical by other means. Einstein is admired not because he was great at chugging through rote algorithms, but because he had the startlingly original insight that gravity might be a property of spacetime, which led directly to general relativity. Feynman is revered not because he was a great mathematical calculator-- though he was exceptionally good-- but because he found a new way to look at the problems of QED, that made the calculations accessible to people who weren't brilliant. Julian Schwinger solved the same problems using a more standard mathematical approach, which was a gigantic accomplishment in its own right, but he's not held in the same esteem as Feynman because his techniques don't have the same creative flair.

Creativity is essential for physics in experiment as well as theory. In some ways, creativity is even more important in experiments, where you often don't know about the problems that will crop up until they actually happen. And sometimes what seems like a problem at one stage of an experiment turns into a useful tool down the road. To use a few examples from my home subfield of laser cooling, a set of internal sublevels of atoms that initially seemed pointless turned out to be useful for catching atoms in a Magneto-Optical Trap. A MOT coincidentally uses a set of laser polarizations that were essential to achieving ultra-low temperatures via the Sisyphus Cooling technique. Then a different set of internal levels that was a technical annoyance requiring an additional "repumping" laser turned out to be a key tool allowing the amassing of larger numbers of atoms by selectively removing that light from part of the sample. Putting all those elements together made laser cooling a tool that's still creating new opportunities in AMO physics, and allowed the creation of Bose-Einstein Condensation.

And that's just one small group of many examples of the value of creativity and ingenuity in experimental physics. I've read a ton of physics history over the last several years, and every time I dig into a great experiment of the past, I'm blown away by the creative ways they found to solve problems on the way to their final result.

This probably seems a bit harsh for a passing reference in Dellamonica's writing-advice post (which, again, is otherwise very good), but it pokes at a raw nerve for me and a lot of other physicists. We hear this kind of thing all the time and grapple with it in every class we teach. Real physics is very far from the undergrad misconception of a field full of plug-and-chug formula-hunting: it's a vital and creative field, which values original thinking just as much as the arts.

Scattering In Quantum Mechanics

noreply@blogger.com (Saddam Leonardo Kap) — Sun, 21 Jun 2020 08:13:00 +0000

Scattering Amplitude

Spinless Particle

we are dealing with quantum description of scattering.

Elastic Scattering $ \rightarrow $ between two spinless, non-relativistic particles of masses m1 and m2. During the scattering process, the particles interact with one another. If the interaction is time independent, we can describe the two-particle system with stationary states.

\begin{equation}\Psi\left(\vec{r}_{1}, \vec{r}_{2}, t\right)=\psi\left(\vec{r}_{1}, \vec{r}_{2}\right) e^{-i E_{T} t / n}\end{equation}

$ E_T $ is total energy.

\begin{equation}\left[-\frac{\hbar^{2}}{2 m_{1}} \vec{\nabla}_{1}^{2}-\frac{\hbar^{2}}{2 m_{2}} \vec{\nabla}_{2}^{2}+\hat{V}\left(\vec{r}_{1}, \vec{r}_{2}\right)\right] \psi\left(\vec{r}_{1}, \vec{r}_{2}\right)=E_{T} \psi\left(\vec{r}_{1}, \vec{r}_{2}\right) \end{equation}

defining $ r= \mid \vec{r_1}- \vec{r_2}\mid \implies V(r_1, r_2) = V(r)$

and hence this makes the two body problem as to two decoupled eigenvalue problems: one for the center of mass (CM), which moves like a free particle of mass $M=m_{1}+m_{2}$ and which is of no concern to us here, and another for a fictitious particle with a reduced mass $\mu=m_{1} m_{2} /\left(m_{1}+m_{2}\right)$ which mores in the potential $\hat{V}(r)$

\begin{equation}\label{wave} -\frac{\hbar^{2}}{2 \mu} \vec{\nabla}^{2} \psi(\vec{r})+\hat{V}(r) \psi(\vec{r})=E \psi(\vec{r})\end{equation}

The problem thus reduced to solve this equation. we need to connect differential cross section in the CM frame can be obtained from an asymptotic form of the solution of Differential equation. Its solutions can then be used to calculate the probability per unit solid angle per unit time that the particle $\mu$ is scattered into a solid angle $d \Omega$ in the direction $(\theta, \varphi) ;$ this probability is given by the differential cross section $d \sigma / d \Omega$. In quantum mechanics the incident particle is described by means of a wave packet that interacts with the target. The incident wave packet must be spatially large so that spreading during the experiment is not appreciable. It must be large compared to the target's size and yet small compared to the size of the Lab so that it does not overlap simultaneously with the target and detector. After scattering, the wave function consists of an unscattered part propagating in the forward direction and a scattered part that propagates along some direction $(\theta, \varphi)$ We can view as representing the scattering of a particle of mass $\mu$ from a fixed scattering center that is described by $V(r),$ where $r$ is the distance from the particle $\mu$ to the center of $V(r) .$ We assume that $V(r)$ has a finite range $a$. Thus the interaction between the particle and the potential occurs only in a limited region of space $r \leq a$, which is called the range of $V(r),$ or the scattering region. Outside the range, $r>a$, the potential vanishes, $V(r)=0 ;$ the eigenvalue problem then becomes \[ \left(\nabla^{2}+k_{0}^{2}\right) \phi_{i n c}(\vec{r})=0 \] where $k_{0}^{2}=2 \mu E / \hbar^{2} .$ In this case $\mu$ behaves as a free particle before collision and hence can be described by a plane wave \[ \phi_{i n c}(\vec{r})=A e^{i \vec{k}_{0} \cdot \vec{r}} \] where $\vec{k}_{0}$ is the wave vector associated with the incident particle and $A$ is a normalization factor. Thus, prior to the interaction with the target, the particles of the incident beam are independent of each other; they move like free particles, each with a momentum $\vec{p}=\hbar \vec{k}_{0}$

(a) Angle between the incident and scattered wave vectors $\vec{k}_{0}$ and $\vec{k}$.

(b) Incident and scattered waves: the incident wave is a plane wave, $\phi_{i n c}(\vec{r})=A e^{i \vec{k}_0 \cdot \vec{r}},$ and the scattered wave, $\phi_{s c}(\vec{r})=A f(\theta, \varphi) \frac{e^{i \vec{k} \cdot \vec{r}}}{r},$ is an outgoing wave.

When the incident wave collides or interacts with the target, an outgoing wave $\phi_{s c}(\vec{r})$ is scattered out. In the case of an isotropic scattering, the scattered wave is spherically symmetric, having the form $e^{i \vec{k} \cdot \vec{r}} / r .$ In general, however, the scattered wave is not spherically symmetric; its amplitude depends on the direction $(\theta, \varphi)$ along which it is detected and hence \begin{equation}\phi_{s c}(\vec{r})=A f(\theta, \varphi) \frac{e^{i \vec{k} \cdot \vec{r}}}{r}\end{equation} where $f(\theta, \varphi)$ is called the scattering amplitude, $\vec{k}$ is the wave vector associated with the scattered particle, and $\theta$ is the angle between $\vec{k}_{0}$ and $\vec{k}$ as displayed in Figure 1. a. After the scattering has taken place (Figure $1 \mathrm{b}$ ), the total wave consists of a superposition of the incident plane wave and the scattered wave: \begin{equation}\psi(\vec{r})=\phi_{i n c}(\vec{r})+\phi_{s c}(\vec{r}) \simeq A\left[e^{i \vec{k}_{0} \cdot \vec{r}}+f(\theta, \varphi) \frac{e^{i \vec{k} \cdot \vec{r}}}{r}\right]\end{equation} We now need to determine $f(\theta, \varphi)$ and $d \sigma / d \Omega .$

Scattering Amplitude and Differential Cross Section

In order to find the $ f(\theta , \varphi), $ we need to take into account flux densities. \begin{equation}\begin{aligned} \vec{J}_{\text {inc}} &=\frac{i \hbar}{2 \mu}\left(\phi_{\text {inc}} \vec{\nabla} \phi_{\text {inc}}^{*}-\phi_{\text {inc}}^{*} \vec{\nabla} \phi_{\text {inc}}\right) \\ \overrightarrow{J_{s c}} &=\frac{i \hbar}{2 \mu}\left(\phi_{s c} \vec{\nabla} \phi_{s c}^{*}-\phi_{s c}^{*} \vec{\nabla} \phi_{s c}\right) \end{aligned}\end{equation}

Putting $ \phi_{i n c} \; \& \; \phi_{sc} $ and we will get ,

\begin{equation}J_{i n c}=|A|^{2} \frac{\hbar k_{0}}{\mu}, \quad J_{s c}=|A|^{2} \frac{\hbar k}{\mu r^{2}}|f(\theta, \varphi)|^{2}\end{equation}

Now, we may recall that the number $d N(\theta, \varphi)$ of particles scattered into an element of solid angle $d \Omega$ in the direction $(\theta, \varphi)$ and passing through a surface element $d A=r^{2} d \Omega$ per unit time

\begin{equation}d N(\theta, \varphi)=J_{S C} r^{2} d \Omega\end{equation}

\begin{equation}\frac{d N}{d \Omega}=J_{s c} r^{2}=|A|^{2} \frac{\hbar k}{\mu}|f(\theta, \varphi)|^{2}\end{equation}

Note: The number of particles scattered into an element of solid angle $d \Omega(d \Omega=\sin \theta d \theta d \varphi)$ : the differential cross section which is $d \sigma(\theta, \varphi) / d \Omega,$ is defined as the number of particles scattered into an element of solid angle $d \Omega$ in the direction $(\theta, \varphi)$ per unit time and incident flux: \[ \frac{d \sigma(\theta, \varphi)}{d \Omega}=\frac{1}{J_{i n c}} \frac{d N(\theta, \varphi)}{d \Omega} \] where $J_{i n c}$ is equal to the number of incident particles per area per unit time.

Now, Therefore we have \begin{equation}\frac{d \sigma}{d \Omega}=\frac{1}{J_{i n c}} \frac{d N}{d \Omega}=\frac{k}{k_{0}}|f(\theta, \varphi)|^{2}\end{equation} For elastic scattering $k_{0} = k $ hence reduces to \begin{equation} \boxed{\frac{d \sigma}{d \Omega}=|f(\theta, \varphi)|^{2}} \end{equation} Our job is to find the $ f(\theta, \varphi) $ and this will solve our problem. To do that we need to use the Green's Function.

How do I approach to solve any problem in Physics?

noreply@blogger.com (Saddam Leonardo Kap) — Sat, 10 Aug 2019 17:56:00 +0000

Problem Solving Skill

In one sentence, How do you solve sudoku? You will obviously say that if I am new, I start with easy-on, then move to medium and difficult one and become an expert on this game.Now if I ask, what did learn from easy level? You will say, well, First I learned the rules of filling it, then learned the way to remember the numbers from 1 to 9, and then, I figured out the little connection between them to fill up fast and then I practice enough and feel confident and therefore moved to the next level. More challenging more fun.

While you move to the Medium level, you discover, you need to think hard in order to find the connection and this difficulty even arises more and more while you jump to hard level. To make connections you have to think so much hard, you have to guess, and with enough practice, you become good at guessing the number quite close to the actual number. And the most important thing is, in this process, you never get bored, or afraid of the problem or you say I can’t do this. You start to enjoy the process, still, every puzzle is a pain in the arse.
You can easily see the shifting of attitude.Now, do the process in reverse, If you start with hard level, you would have never understood the process, neither you discovered how to think in order to make the proper connection, nor you could make any close guesses. And you would have frustrated and never would play this game again and you give the feedback, this game is the hardest game and don’t play it, or if someone plays well, you would have asked perpetually, How do you play this game, what are the strategy, how to think like a genius, and so on… And you would have never enjoyed it.Now you see the shift in attitude.

Now compare both shiftings in attitude, and tell me who is wrong or which process is wrong.You see, This is the attitude of every problem solver. Here there are only nine pieces and in physics let’s say there are 900 pieces.You have to think hard and start with easy steps.

Hey, do you know when I face any hard problem what do I do?I take it as a good challenge, think hard, for a long time. What do I think? I first think, How can I make this problem disintegrate in little easy problems. Since I know how to solve easy one, then gradually I add little parts and solve it, and then I see how to make it full realistic version.I use also the internet for the references, and look for a similar problem which has been solved by someone else, and read concepts carefully, follow the derivations, and my basics. If I do so, with little extra effort, I solve most of the problem by my self. If I still don’t get, I go to my friends, professor and so on.

The main thing is, I don’t afraid of problems neither frustration. I see the problem as an opportunity to learn something new.You can learn a new thing only if you are ready to fail, ready to grow, and ready cut loses your ego.

You are the biggest enemy between you and Physics. Your brain doesn’t want to solve problems, rather than keep you engage in this stupid question like, How to do this, How to become genius, How to solve problems, why something happens, why school is bad so on an so forth.These are good questions, but the fact is these are useless. I have faced these questions and searched the answer on the internet or some sources for years and years, it was just garbage.the real answer is, you want to solve the problem, everyday You get your head into the problem, shut your brain off from distraction, no more inside chattering. Just do the fucking job for a month.

And then tell, Can you solve the problem or not?????????????

I bet you will laugh if someone asks this kind of problem again. These are the question if you chase, you can never become a physicist. It’s more like a process, you have to first understand its rules, and then, solve research problems, and then you start thinking of ways how to solve the problems.If you are lucky, you will get the idea, which makes your dream come true.Don’t try to be someone else. Read about others, and be your own hero. You must possess your originality in thinking.

A great scientist becomes the character he posses. So, build your character. Rest you will become.

Thank you

_________________________________________________________________________________________

How can I achieve so many things in life along with my main work.

noreply@blogger.com (Saddam Leonardo Kap) — Sun, 05 May 2019 20:27:00 +0000

My Achievements from 10 February to 5th May. Read books other than Physics which I have never done in my entire life, I have read three books completely, 

1. The compound effect (280 pages)

2. Rich Dad Poor Dad (403 Pages)

3. The millionaire mindset (250 pages)

you may wonder, But I have just done this just investing of 30 minutes more often. It was the challenge to actually change the old habits, old perception about ideas. Now after just marginal changes in life I got some ultimate insight, which opens a whole new world in front of me. This little habit and the outcome makes me really confident, I can do anything, I can learn any skills in no time. Nothing is hard if we just do some marginal changes. By doing the right thing, one can achieve so many things, others can never dream of. COmpounding Always works. I couldn't focus for a minute, Now I can focus for a whole hour. It's the change in life you get after making some adjustment in your life. 

I hope my little story may inspire you to read a little every day, and You will see the power of compounding in your life. 

Spin Theory of Helium Atom-Addition of Spin Angular momentum.

noreply@blogger.com (Saddam Leonardo Kap) — Thu, 08 Nov 2018 12:07:00 +0000

Spin Theory of Helium Atom-Addition of Spin Angular momentum. by saddam leonardo kap on Scribd

Helium Atom problem- Find it's wave Function

noreply@blogger.com (Saddam Leonardo Kap) — Tue, 06 Nov 2018 12:05:00 +0000

Helium Atom problem
Evaluation of wave function and Energy
Approximation Method
Using Variational principle
Many-Body problem

Link to see the paper

https://www.scribd.com/document/392492158/Helium-Atom-Graduate-Text-How-to-find-the-wave-function-and-Energy

If you want to understand how to evaluate the He- atom wavefunction, You need to click on this. I have derived in a rigorous manner. To get more problems to be solved you can suggest me some problem to evaluate. I will write one book on Quantum Mechanics to handle its concept and how to use in a mathematical way to solve problems.

You are here not because of your future but past.

noreply@blogger.com (Saddam Leonardo Kap) — Fri, 08 Jun 2018 21:50:00 +0000

PHILOSOPHY OF LIFE

______________________________________________________________

Saddam Leonardo Kap

________________________________________________________________________

You are here not because of your future but past. _____________________________________________________

The thing that I want to share is, let’s understand it by an example. Suppose you are A, and in past, u had a relationship with B. Now in present u have an amazing and lifelong relationship with C. Now what do u think at this point is, the relationship with B was lousy, it was meant to have vanished, and it was terrible. It happens well that that relationship never worked out. I am now too happy and I will not repeat that mistake. I want to throw that relationship as if I was sick of it like it was a dark era or something like the worst thing ever happened. Now let me stop this here and give you some deep insight into that relationship at that time.

In present moment whatever you are, in the past when you were starting, everything was new to you. In the past relationship, you too valued that relationship, also fantasized that one, had a dream to make that relationship best in the world. That person B was everything for you at that time, you share your every emotion with that person, And now in the present when that relationship didn’t work out, and you got C now you devalued your past. What if your present relationship won’t work out in the future and you again going to say the same thing for this beautiful person C. This mindset is really insane. This makes no sense even at any scale.

It’s really so bad that you broke at once, you found you’re best and you had to leave that relationship. Nobody leaves the relationship just because they want something better than that. Its goddamn time and situation that people enforced to break some relationship. This never entitled that the previous one was bad.

In short, the best thing you can do is never devalue your relationship at any time. In other words, never say that “The time of that moment was bad and now it’s awesome because remember that this awesome time came because of that time only not because of some stupid future time”. So, the thing is that “Always respect the relationship what was made in the past, if it didn’t work out learn from that “Why it didn’t work out?” Try to find the answer, apply it on your present moment, and make your best effort to build this relationship best. Try to fight the odds. Don’t be rude on your down moment of the past, neither cheered up too much for the ups moment you had. It's really privileged that you are good or whatever at the present moment, is only because of your past, not your future.

So, learning is important, respect your past is important, and never devalue the relationship at any moment (of time). They are the reasonable reason what you are now. Be calm, empathic, creative and love what you have because people around you, they believe on you.

In physics, you can’t know about future with certainty, because you are driving out by the past. In Quantum Mechanics you don’t predict future, you have to first measure it, and then the past tells you what the present is. There is no tomorrow if there is no yesterday. So, to understand the nature you first have to understand the time at which the things had happened, because the arrow of future is going to make by the past. Past is not irrelevant, one can easily say, future is irrelevant. It’s impossible to avoid past.

The best way to make your life good is to respect the past and learn from it.

----------------------------------------------------------------------------

How Mass distorts Space-Time

noreply@blogger.com (Saddam Leonardo Kap) — Fri, 02 Feb 2018 06:40:00 +0000

It’s not gravity which distorts Space-Time. The bending or distortion of space-time is due to the mass. If there is more mass, more will be the distortion.

Einstein’s Theory says Gravity is not a force. But a manifestation of Spacetime curve.

If Space-time is flat, means so-called Euclidean and that geometry is called Minkowski. There is no Gravity, no mass at all. or if there is a mass the mass is so small, like an atomic scale. In atomic scale the Space-Time is flat. There is no effect of gravity on that scale. What we best do is neglect the potential due to gravity, because it’s magnitude is so small than any other interactive force like Electromagnetic, Nuclear interaction.

By using the Space-time idea, people have construed Relativistic QM. But due to so much mathematical inconsistency, this theory is no longer valid. People have evaluated more advance theory like QFT (Quantum field theory), Which is consistent with Einstein’s special theory of relativity.

Scientist used to explain the Space-time structure some sort of Rubber Sheet, in which u put some mass and there is a bending due to that mass, which u experience as a gravity. These Space-time concepts are totally mathematical. U can’t see such kind of thing if u see out there using telescopes. But u can always experimentally verify it, This idea works. So, space_time geometry is valid. But still, its a big question that What is Space-Time.

Under certain limit, General Relativity becomes Newtonian gravity. U see Newtonian gravity is also valid for low speed than light and mass not equal to zero.

U can’t predict what kind of shape space-time will take, But when U you make your own guess and that guess explain the experiment you can say that this kind of geometry is there due to any heavy object, like stars, Black holes. Like Schwarzschild Metric, To explain the Blackhole Space-Time.

So if You want to know there are tons of book out there.

Gravitation by Kip Throne

Spacetime and Geometry: An Introduction to General Relativity

by Sean Carroll (Author)

You can follow the Lectures of Prof. Leonard Susskind. It’s one of the best lectures for Beginners.

I hope U got the answer. Give me comment if u have any problem related this explanation

TIME MYTH

noreply@blogger.com (Saddam Leonardo Kap) — Fri, 29 Dec 2017 06:14:00 +0000

TIME MYTH

Before coming to home I was thinking about home being only consumed by my studies. I stimulated so many simulations about this. That was all theoretical. In imagination things are awesome but in reality, things are hell different.

Expectation before coming home.

Ø Study Round O clock because in home I have separate room and nobody is there to disturb me.

Ø I will learn to program for Mathematica and Matlab.

Ø I won’t see the movie and use lapy as it actually for, not for just time pass.

Ø In IIT I don’t get too much free time study different books, so I will spend my most of the time studying books.

Ø I will finish Quantum Field Theory and General Relativity. And I will do some projects of MIT.

Ø I will see lectures.

Ø I will spend my time writing answers on Quora.

Ø Speak less and don’t act like a kid.

Ø Avoid every controversial scenario and statements. Involve yourself only in Physics completely.

Ø Be less social and focus more on studies.

Ø Late night study.

Reality after Coming Home

Ø First three days was as usual as I spend in my hostel and I was driven by IIT’s momentum and did less talk and avoid controversial arguments. And spend my time doing a study and one drawback I faced is that my Matlab and Mathematica didn’t work here. I studied but little. Couldn’t concentrate because “HOME IS NOT A PLACE FOR RESEARCH AND STUDY. HERE IT IS FULL OF DISTRACTION”.

Ø After that went to Aunt’s home. A little study I did. Not anything happened I was quite expected. “Total Failure”. Never think that in the home you can spend your time alone and you don’t have to go to visit your relatives. Hell, it’s damn true that you can’t be left alone in the home and you can’t study in the relative house no matter how much you try.

Ø After a week I came home, and for a week I didn’t even turn on the page of any book. I used to open the lapy and watched a movie and had a fun with kids and family members. “No study at all”. Whatever I had expected didn’t meet with one. Did talk more, watched a movie more, Silly talks more, No Quora, No Reading, Only fun.

Ø After a week went to grandmother’s home, spend four days and during those four days only gossiping. “No study”. I left QFT and everything related to study in such a way that study isn’t part of my life. Never thought of anything. No new !deas no Physics. Just enjoying the village and contemplate their situation.

Ø After coming, came up with an !dea to organize a party in the home to celebrate NEW YEAR 2K18 . Just involve there and fun with kids and again “NO Study” at all.

Ø Here I am in the fifth week of my holiday writing about the myth of Homecoming and Tell myself that there is nothing at Home for doing study and Research. I just enjoy time and free myself with every kind of possible stress. I just forget what Physics is. My head is empty and I dreamed of studying. Now I am becoming real hunger. I did all possible enjoyment. Well, I think that it is also important to have a nice time and good memories with family. But it’s really an awkward moment to stimulate before coming home about the study. Because in my experience whenever I came home I never did a study and didn’t complete my expectation.

Ø Wait, why I am sharing all these fu****g stuff here. What’s the point even mean? Am I falling in love with the words that I am using to describe the past? I simply don’t have any idea. And I think it’s the terrible story you have ever read in your life. But indeed I am really enjoying whatever fu****g thing I am writing.

Ø Lesson to be learned. The expectation must be less. Come home not for study, just for fun. Don’t waste your precious time to stimulate which you know is never possible in your home. Work should be done in the workplace, not in the home. Home is just for enjoyment and being happy and make happy others.

Ø Lesser time is really a myth. In this planet, everybody has the same time. Use it wisely and don’t think that in your IIT you are getting less time to study. That’s the time and everything you have. And everything will happen to be quiet smooth and “!deas is generated only in just isolation or in the free mood.” It’s totally a myth. You will never know when it will come. So don’t trap in this dogma. You don’t need soooooooooo much time. You just need time to work on your stuff and ideas will generate automatically.

Ø “Never think that the ideas you encounter first are one of the best idea you ever have or will give to the world. It just the idea and well nice beginning and surely not the best way to deal with the problem. After sometimes you will encounter so much refinement on your ideas and it often happens that you or someone else would be modified the !dea.”

Ø In life nothing is important. It’s all about priority and you will live a happy life.

Ø Oops! I failed my expectation. I think it’s damn good to fail the expectation. Life is more than the stupid routine life. Who knows how surprising life can be and what kind of story will prepare if we just unbound with the self and others expectations and for some time live a life aimlessly.

Ø One must not think about future so much got worried, and forget to live the precious time. Until the time not come, everything is uncertain. Only time has the ability to overcome the fact of uncertainty. This also applies to Quantum World and Cosmic scales.

Ø Now your job is to find out the mathematics and know how time will be in future. I know this statement is itself weird but before say it wrong, hang on, and think again. First ideas are not always the best ideas. Our job is to modify it.

HOW TO DO RESEARCH LIKE EINSTEIN

noreply@blogger.com (Saddam Leonardo Kap) — Thu, 30 Nov 2017 16:52:00 +0000

To Do Research like Einstein one needs to upgrade his Brain.

Ø Why it’s needed to upgrade the brain?

It’s a nice question and let me answer this in this way… once I was playing some games. I was trying so hard to win that game. I tried each possibilities but still I was not enough to compete my opponent. Its demands only upgradation. I finally upgrade my ingredient and compete the opponent. I then realized that, that’s the approximate same thing also happens in my real life. I try so hard to understand physics, solving problems, but still I am nowhere. That really sucks. What to do?

I thought that upgradation may be the key to handle this problem. Since I study hard, but still there are lots of problem which is out of reach from my level of understanding. Neither, I can think how to solve the mysterious problem of world. If I want to solve these problems I need more mathematical and physical knowledge and different ideas, which I am completely lack of. I can’t even solve mathematical problems fluently, neither understand the higher mathematics, and how to interpret them physically. That’s the big issue. And the greatest issue is that these route learning can never take me anywhere near to these realities. And whenever I try to learn some mathematics, my first question to instructor is why I need this thing? This is a good thing but really a bad habit. The point is, I need to search the why thing by myself only in order to develop any kind of new work, otherwise your brain won’t even work. I study the concept but can’t able to use those concepts without solving examples. Well, this is a big issue, because in reality you need to sometimes develop new concepts to solve problems and while you can’t just solve the problems without the help of examples or some solution manual, it’s a flaw in your brain, that’s you can’t use your brain to explore the things, you can’t by yourself generate ideas to solve problems, where concept is already given, how can you than figure out new theories. Some say that you need more practice, but I think when you are in graduate, and as you have quiet good knowledge about too many things, so now you don’t need to solve thousands of problem in order to solve new ones, or understand how to apply concepts in problem. If you do this it only says that, your brain is copying the info and never understand the deeper logic behind the concept, and you neither have good understanding about your old stuffs, that’s why you can’t even apply your knowledge to explore the problems in different way.

Therefore these are the greatest problem needed to be fixed.

Ø How to do upgradation?

So, here is the main thing that what are the things you need to remove. I have a list of these things.

I. Listen first with patience.

II. Always ask questions.

III. Try to relate the concepts with other concepts.

IV. Don’t speak too much. Balanced speech is somewhat good thing.

V. Always understand the value of time.

VI. Don’t engage yourself always in debates which is irrelevant and what you don’t understand well enough.

VII. Think too much, whatever you think, write that down.

VIII. Understand the topic and then try to solve the problems by yourself. Never see solution, it will make you dull, since seeing solution always helps in route learning, but never in extraordinary things. When you can’t solve the problem discuss with your friend, break the problem into small problems, make it too much easier, and then solve part wise. If you don’t understand any part go to your friends and discuss with them. Sometimes break the rules of thinking and do something wild, and try to understand what you are doing. In this way you will discover that, in your brain there has generated lot of new ideas which was never before there and you have invented new ways to solve problems and extended the ideas to solve other problems and understand different other things. It’s really a panic process and I can guarantee that this is the most amazing moments you will experience in your life.

IX. Study in such a way that you can generate ideas from that, try not to just swell the idea, but see the hidden pattern and think very different way, explore each possibilities such as, what can you do with that idea, is there something in previous where your ideas are helping. Can you make the stuff simple, or can you construct different way to prove the result.

X. Solve the problems, not by looking at the examples, but without seeing anything, think how to apply the ideas which you have learnt so far.

XI. Never relay on your intuition and memories, throw these thing away, and use the logic and scientific reasoning in order to figure out which is which.

XII. During the problem solving time, always ask problems, like why you are doing something, what is the motive behind it? Dictate the problem to yourself.

XIII. Not always new ideas generates, it takes time, and be patient. Not every time you have to just generate new ideas, but sometimes you have to mix old ideas and prepare new stuffs which usually people do, and test your ideas so often in other problems too.

XIV. World needs ideas, people care about ideas, to understand the world you have to be the investigator of the truth. Use your logical brain and do scientific reasoning more and more.

XV. Always think. Route learning can never take you from the deeper insight of world. To go lot deeper you need to break the old patterns, and try to figure out the flaws into the existing ideas. We can’t say anything about the existing ideas, until we don’t understand what the flaws into it. When you will figure out the flaws in today’s understanding, well tomorrow will be your day. Don’t just think that we have to create something new theory in first place before analyzing the current one, so investigate the flaws. This will save you a lot of time and then it will really take you to the ultimate truth.

XVI. The thing flaws means I need to clear it more abstractly. Today, we can’t unify gravity and quantum theory. So it’s doesn’t mean that we have figure out the flaw into the theory, and we need to make some other thing. Now since both theories are quiet good in their all realm, so they are correct. But they are not all correct, something we hadn’t yet considered it. Something is missing, something we have used on them which gives the result, but actually that thing isn’t always true. Which has made a great problem and we have no way observe it. But deep into the nature, there is some different thing is there. There are certain principles, which may be needed to define differently, and not all the time the ideas of more than four dimension will really going to give us true picture of the world. It may give, but doesn’t mean this is the only good idea.

XVII. Some times our interpretation to the experiment isn’t correct. Such as, dark matter and energy. May be there is no dark matter and dark energy, something strange is doing such thing, and we are thinking that this is gravitational lensing, and these are the candidates which stand nice way to explain these phenomena. But you must take care one thing that, Einstein’s general relativity theory isn’t the ultimate truth of gravity, Einstein may be wrong in some point in his own theory, and we have never considered it. Because to search flaws in something isn’t really an easy task. As he had figure out the flaws into the newton’s theory at that time where people thought that there is nothing in gravity that hasn’t been understood. For him it was not an easiest task. The whole world was satisfied with newton, but he questioned very deep on his theory and turns out that there are really great flaws in Newtonian view of world, although his theory is damn correct in lower scales. So we have more theory to see one thing (gravity) in two different versions and two different scales. Still we use Newtonian mechanics to launch rocket into space. And one can safely say that, Einstein can’t be whole correct, there are something which is yet to taken care differently like ‘Time’ theory. I can bet that his idea of time is inadequate. And in quantum mechanics also, they had to extend the ideas in order to merge with relativity. Now we just can’t merge quantum mechanics with relativity just by writing Hamiltonian H= sqrt ((mc^2) ^2+ (pc) ^2). That’s why there is no quantum relativity, instead of it people came up with another idea ‘fields’. And hence quantum field theory came into the picture, but QFT is also not in a good shape. Not absolutely not a best candidate to solve the problem of unification with gravity.

XVIII. Never say that someone is all correct neither say someone is wrong, instead search which is which, with your divergent thinking, and mathematics and so on.

XIX. Always appreciate the tough things, welcome them, and say to your brain that I am really good enough to understand any tough thing. Make less excuses, and work more, and study logically. Don’t just shut the logical door and swell everything which has fed to you.

XX. To do all the things is pretty hard, but these are the most essential steps one has to take in order to make the thing happen and become the good physicist in your life. Oh I think to research like a genius ones.

--------Saddam Leonardo Kap

TACHYON, THAT BEAT THE SPEED OF LIGHT

noreply@blogger.com (Saddam Leonardo Kap) — Mon, 20 Nov 2017 18:49:00 +0000

AN INTERVIEW WITH TACHYON DISCOVERER

Eminent scientist E.C. George Sudarshan on growing up in Kerala, his tryst with physics and on the state of research in India

The physicist Hans Bethe once said, “There are two types of genius. Ordinary geniuses do great things, but they leave you room to believe that you could do the same if only you worked hard enough. Then there are magicians, and you can have no idea how they do it.”

In the world of science, every so often we come across visionaries, ‘magicians’ in the words of Bethe, who dare to perceive the world in ways no one else has before. E.C. George Sudarshan is one of them. From formulating fundamental ideas in particle physics to understanding the quantum nature of light, Dr. Sudarshan’s contributions to physics read like a fascinating chapter from the book of breakthroughs in the science of the past century.

Born in Kottayam in 1931, E C G Dr. Sudarshan studied at the CMS College and later at the Madras Christian College, the University of Madras and the Tata Institute of Fundamental Research. He teaches and does research in physics at the University of Texas, where he has been now for more than 40 years. E C G Dr. Sudarshan was in the city earlier this week to receive the Kerala Sastrapuraskaram, the state lifetime achievement award for science. The following are excerpts from a conversation with Dr. Sudarshan.

It has been an incredible half a century of physics for you. From where you are today, what does physics mean to you?

Everything. I mean, I don’t know anything else. All I know is how to do physics. I am good at it. I took to physics like a duckling to water. I don't even think of what I do as research or work anymore. I like the excitement of looking at the world through the prism of science. That’s all there is to it and I know that I can continue doing it forever.

Did growing up in Kerala in anyway help shape your interest in science?

To be born into a culture that values learning is always an advantage. Kerala was ahead of the rest in terms of the respect we had for the pursuit of knowledge. But outside of that the school curriculum and the textbooks we were asked to read in physics were rather dull, as they probably are even now. Mostly facts with hardly any room for thinking.

We were taught language and mathematics very well. When I moved to college, I could focus on the subjects that really interested me. CMS and Madras Christian College had some really good science teachers. Physics gradually became my way to make sense of the world around.

How do you rate the present standards of scientific research in India? Are you pleased with the work that is happening at our universities and institutes?

At the risk of generalizing, let me say that with all the hype that some of these institutes carry, I hardly see any big ideas coming out of them. Most scientists are locked up in their comfort zones, happy pursuing run-of-the-mill problems. There is no desire to excel. One should, at least occasionally, show the courage to take up big questions and explore intriguing new possibilities. Such attempts are hardly seen.

Progress is not made by repeating what has already been done.

In your writings and talks, you often allude to the parallels between Vedanta and modern science. Can you explain this a bit?

There are certain fundamental questions in physics for which there are no clear-cut answers. For example, what is time? I breathe. I can count the number of times I do that. Can we call those intervals as time? Suppose I stop breathing, does time seize to exist? Einstein’s special theory of relativity interprets time as a subjective experience. The notion of time could be different for different people. Once you bring subjective experience into the picture, science finds close parallels with Indian philosophy. The Upanishads go to great depths on topics of space, time the nature of causality and such. Unlike science, the analysis found in the Upanishads is entirely from an inside point of view. I find that approach reasonable and a lot refreshing.

Now that you are into your golden years, have you considered moving back to Kerala for good?

I think of it often. But I don't think I have the skill to do it. People around here now treat me as a guest. They smile at me. But if I move back permanently, I fear they might perceive me as a pest. I will be asking a lot of questions. I will be behind everyone grilling them with questions on their research. Not a pleasing proposition for everyone. I am happy being a guest.

HOW PARTICLE PHYSICIST THINKS??

noreply@blogger.com (Saddam Leonardo Kap) — Mon, 20 Nov 2017 18:33:00 +0000

MIT Theoretical particle physicist

Jesse Thaler was a high school student in 1995 when a pivotal discovery in science turned his life’s path toward particle physics.
That year, physicists at the Fermi National Accelerator Laboratory confirmed that its Tevatron particle accelerator had detected, for the first time, a subatomic particle known as the top quark. This article had been a missing piece in the Standard Model of particle physics — a theory that describes all the known elementary particles and several majors, fundamental forces governing the universe.
“I remember my physics teacher had a big poster of the Standard Model on the wall, with a question mark next to the top quark,” says Thaler, who recently was granted tenure as an associate professor in MIT’s Department of Physics. “When it was discovered, I remember him writing down the mass of that top quark where there used to be a question mark. I thought discoveries must happen all the time. Little did I know that particle physics is a decades-long, even centuries-long, endeavor to try to understand the fundamental nature of matter and that I would eventually become a part of that.”
Thaler, a member of MIT’s Center for Theoretical Physics and the Laboratory for Nuclear Science, is a self-described “pencil and paper, chalk and chalkboard” theorist, and works to derive theoretical insights to characterize the behavior of subatomic particles, and the fundamental forces that give structure to the universe.
He’s applying his theories to describe in greater detail the particles that are already known to the Standard Model, as well as predict the behavior of those beyond the Standard Model, which scientific theory cannot quite yet describe — namely, dark matter, which is thought to make up more than a quarter of the total mass-energy of the universe but has yet to be directly detected.
Thaler is collaborating with experimental physicists on projects ranging from small tabletop detectors to massive collaborations such as the Large Hadron Collider and applying his theoretical insights to interpret data from current experiments and guide the design of future experiments.
“My research is always a balance between exploring what could, but might not, be there, and what must be there,” Thaler says. “Some would say everything should be beautiful and elegant and mathematical, and others would say the world is messy; you just have to study it. But at this boundary, it’s true some things are messy, and others are elegant, and living at that boundary is where I feel most comfortable.”
“Subtleties at play”
Thaler grew up in York, Maine, where his mother worked as a high school guidance counselor, and his father practiced family medicine. In high school, he attended Phillips Exeter Academy, where he quickly learned to think his way through tricky mathematical problems on his own.
“There wasn’t a textbook,” Thaler recalls. “You showed up the first day, they gave you a relatively thin stack of problems, and you went to class and had discussions but basically had to teach yourself. It was a very humanities-minded way of thinking of mathematics, which could also apply to physics.”
Thaler went on to Brown University, where he pursued a degree in math and physics, doing research into the formation of black holes, while also taking courses in the humanities, from Japanese theatre to the role of women in Islamic society, to race relations in Brazilian history.
“Those classes helped me see that there is nuance, even in cases where you think things might be clear-cut,” Thaler says. “In physics, there are similar types of subtleties at play, where you can take different views on the same problem, and the answer comes from the full synthesis of those views. I try to take that approach in the physics research I do.”
To blow off some academic steam, Thaler picked up the electric bass as part of an eight-piece ’70s funk band, and put in late-night hours at the college radio station, playing jazz records under the pseudonym Lester, after legendary jazz saxophonist Lester Young.
“I would spin vinyl from 2 to 5:30 a.m. and then would have my 9 a.m. quantum mechanics class,” Thaler fondly recalls. “It was rough.”
Flexible physics
From Brown, he went on to graduate school at Harvard University, with the intention of studying string theory, which at the time was thought to uniquely explain the synthesis of gravity and quantum mechanics, in one unifying theory.
“Now I know that to be not quite the right story,” Thaler says. “The modern view of string theory is not that there’s one theory of everything, but many different theories that come out of string theory, and it’s a challenge to figure out which one of those corresponds to our universe if any. So there’s no inevitability built in.”
During his second-semester quantum field theory course, Thaler’s professor, who would become his thesis advisor, helped him redirect his focus toward another theory, not of everything, but of almost everything: the Standard Model of particle physics. It was in this class that Thaler began to see this model as something that could predict, with 100 percent certainty, that many things in the universe, such as the universal strength of gravity, would always be true. He also started to appreciate that there were limits to the Standard Model and that there are some things about the universe, such as dark matter, that the theory so far has failed to describe in any organized, mathematical way.
“This represented a totally new, flexible way of thinking of quantum field theory where you really poked and prodded it from all angles and figured out where it really breaks down,” Thaler says. “So you have these twin realizations: that certain aspects of the Standard Model are fixed and inevitable, and certain aspects are not fixed and are therefore a source of confusion and a target for future research. Those twin aspects really inspired me.”
Knowns and unknowns
Thaler spent three and a half years in Berkeley, California, after graduating from Harvard, working as a postdoc at the Miller Institute for Basic Research in Science at the University of California at Berkeley, and at the Lawrence Berkeley National Laboratory, which was just up the hill from the university. At the time, he was wrestling with whether to concentrate on the dynamics of behaviors that are known in the Standard Model or explore phenomena beyond the Standard Model.
He was able to get a taste of both sides at Berkeley. On campus, he found that researchers tended to theorize about the more speculative, uncertain parts of the Standard Model, while researchers at the laboratory were looking in detail at more fixed phenomena.
“I would spend half my time on campus and half at the lab, and got the synthesis of the two, taking the shuttle bus up and down the hill,” Thaler says. “And sometimes the most exciting things are at the intersection of those two perspectives.”
In 2009, he applied for a faculty position at MIT and while interviewing got to talking with physics professor Richard Milner about ways to test for the existence of dark matter. From that conversation, Thaler proposed an experimental design, which has since evolved to become Dark Light, and MIT-led experiment that aims to look for “dark forces,” or interactions that are thought influence dark matter.
Finding structure within chaos
In January 2010, Thaler moved, “in the dead of winter,” as he recalls, from Berkeley to Cambridge, as an assistant professor in MIT’s Department of Physics. He expected a steep curve in learning how to juggle the various teaching and research responsibilities that come with being a professor. What he didn’t anticipate was how difficult it would be for him to hand over some of those responsibilities, particularly in research, to his students.
“Learning to let go and trust my students was eye-opening,” Thaler says. “The students at MIT are fantastically brilliant, and oftentimes I would have the wrong idea of how something should work. But my students have wonderfully stuck to their guns, even if I was skeptical of their results, and convinced me that they were right.”
At MIT, Thaler’s research has made a major impact on several areas of physics, most notably on understanding the structure and behavior of jets produced from the collision of protons at high energies. Protons are made from accumulations of subatomic particles called quarks and gluons, which are held together by a glue-like interaction called the strong force. When protons collide at significant speeds, they release sprays or jets of quarks and gluons, which can rebind into collections of subatomic particles such as pions and kaons.

Thaler has developed theoretical techniques to study the strong force and the structure of these jets in detail. His techniques are now being applied at the Large Hadron Collider — the largest, most powerful particle accelerator in the world, based in Geneva, Switzerland — to look for interesting physics, and even signs of dark matter.
“Studying these jets is a messy business,” Thaler says. “They look like they’re just chaos. But if you work your way up to the boundary of theoretical insights, you realize within that messiness, there’s structure, and you can exploit that structure to figure out what’s going on. We haven’t yet discovered dark matter in this way, but we have been able to search for it in more exquisite detail than in the past.”
Looking to the future, Thaler is eager to explore more uncharted territories beyond the Standard Model and is working on theoretical designs for other experiments to detect dark matter.
“I have a responsibility to push on whatever I think I can make an impact on, and push it forward,” Thaler says. “For that, I can’t think of a better place to be than MIT, for the next however many decades.”