Rethinking nuclear

As someone who has spent decades studying the evolution of nuclear energy, I’ve seen its emergence as a promising transformative technology, its stagnation as a consequence of dramatic accidents and its current re-emergence as a potential solution to the challenges of global warming.

While the issues of global warming and sustainable energy strategies are among the most consequential in today’s society, it is difficult to find objective sources that elucidate these topics. Discourse on this subject is often positioned at one or another polemical extreme. Further complicating the flow of objective information is the involvement of advocates of vested interests as seen in the lobbying efforts of the coal, gas and oil industries. My goal has been to present nuclear energy’s potential role in a sustainable energy future—alongside renewables like wind and solar—without ideological baggage.

An additional hurdle that must be overcome in dealing with the pros and cons of nuclear energy is the psychological context in which fear of nuclear weapons and of radiation impedes rational analysis. The deep antipathy to nuclear phenomena is illustrated by what might be called the “Godzilla Complex” that developed after the crew of the Japanese fishing boat, the Lucky Dragon 5, was exposed to heavy radiation from a nuclear weapons test in 1954. Godzilla was conceived as a monster that emerged from the depths of the ocean due to radiation exposure. It has become an enduring concept that has been portrayed in nearly forty films in the United States and Japan and in numerous video games, novels, comic books and television shows.

It is not surprising that fear of nuclear reactor radiation has been widespread. In spite of the fact that there are no documented deaths due to nuclear reactor waste (in contrast to deaths from accidents), it is widely assumed that nuclear reactor waste is quite dangerous. In contrast, the fact that premature deaths attributable to the fossil-fuel component of air pollution worldwide exceeds more than 5 million annually generates little concern. Similarly, the total waste produced from nuclear energy can be stored on one acre in a building 50 feet high, whereas for every tonne of coal that is mined, 880 pounds of waste material remain. Furthermore, this waste contains toxic components. Yet public concern for nuclear waste clearly overshadows that for coal, despite these contrasting impacts.

After an in-depth review of the most significant nuclear accidents and recognition of the deep psychological antipathy to nuclear energy, I’ve become increasingly interested in the emergence of an international effort to develop safe, cost-effective nuclear energy known as the Generation IV Nuclear Initiative. This began in 2000 with nine participating countries and has since grown substantially.

In the early years, the Generation IV Nuclear Initiative took a systematic approach to identify reactor designs that could meet demanding criteria—including the key characteristic of being “fail safe”. Rather than depending upon add-on safety apparatus, “fail safe” designs rely on the laws of nature—such as gravity and fluid flow—to provide cooling in the event that the reactor overheats. Another high priority design feature is modular construction, allowing multiple units to be constructed in a timely and economical fashion.

After reviewing dozens of options, the Generation IV Nuclear Initiative settled on six designs that it found to be the most attainable and desirable. Since its initial efforts, countries that have embraced the goals of the Generation IV Nuclear Initiative have been pursuing additional designs including reactors that range in size from quite small to about one third the size of the typical one megawatt reactor.

In my book, I’ve focused my attention on four promising designs. These four designs eschew the vulnerabilities of using water as a coolant that proved so devastating at Chernobyl and Fukushima. The explosion at Chernobyl was due to steam and the three explosions at Fukushima were due to hydrogen gas that resulted from oxidation of fuel rods by overheated water. These were not nuclear explosions. Instead, the four designs I’ve highlighted use liquid sodium, liquid lead, molten salts and helium gas as coolants. Liquid sodium and liquid lead cooled reactors are operating successfully in Russia, while China incorporated a gas cooled reactor into its grid in 2023. In the United States, Kairos Power is constructing a molten salt cooled reactor, while the TerraPower company (founded by Bill Gates) has broken ground on construction of a sodium cooled reactor in Kemmerer, Wyoming. These are intended to be models for replacing coal fired power plants with Generation IV nuclear plants. Multiple implementations of this approach are planned through the early 2030s.

Given the world-wide interest in Generation IV reactor development and the many initiatives that are being pursued, it is likely that at least some of these projects will come to fruition in the near future. While success is not guaranteed, there is clearly a need for the general public and students to be kept informed of progress leading up to 2030 and beyond.

To help bridge the knowledge gap in this rapidly evolving domain, I’ve launched a newsletter on Substack called “Nuclear Tomorrow.” It’s written for anyone concerned with the intersection of public policy, energy generation, and its impact on global warming. I hope it serves as a resource for those seeking clarity in a complex and consequential field.

^{Feature image: nuclear power plant via Pixabay.}

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Quantum information theorists use Einstein’s Principle to solve “Einstein’s quantum riddle”

Albert Einstein, Boris Podolsky, and Nathan Rosen introduced the mystery of quantum entanglement (entanglement) in 1935 and it has been called “Einstein’s quantum riddle.” Many physicists and philosophers in foundations of quantum mechanics (foundations) have proposed solutions to Einstein’s quantum riddle, but no solution has received consensus support, which has led some to call entanglement “the greatest mystery in physics.” There is good reason for this 90-year morass, but there is also good reason to believe that a recent solution using quantum information theory will end it in ironic fashion.

Simply put, entanglement is one way that quantum particles produce correlated measurement outcomes. For example, when you measure an electron’s spin in any direction of space you get one of two outcomes, i.e. spin “up” or spin “down” relative to that direction. When two electrons are entangled with respect to spin and you measure those spins in the same direction, you get correlated outcomes, e.g. if one electron has spin “up” in that direction, then the other electron will have spin “down” in that direction. Einstein believed this was simply the result of the electrons having opposite spins when they were emitted from the same source, so this was not mysterious. For example, if I put two gloves from the same pair into two boxes and have two different people open the boxes to “measure” their handedness, one person will find a left-hand glove and the other person will find a right-hand glove. No mystery there. The alternative (which some in foundations believe) is that the electron spin is not determined until it is measured. That would be like saying each glove isn’t a right-hand or left-hand glove until its box is opened. No one believes that about gloves! So, Einstein argued, if you believe that about electron spin, then explain how each electron of the entangled pair produces a spin outcome at measurement such that the electrons always give opposite results in the same direction. What if those electrons were millions of miles apart? How would they signal each other instantly over such a great distance to coordinate their outcomes? Einstein derided that as “spooky actions at a distance” and instead believed the spin of an electron is an objective fact like the handedness of a glove. No one knew how to test Einstein’s belief until nine years after his death, when John Bell showed how it could be done.

In 1964, Bell published a paper that tells us if you measure the entangled electron spins in the same direction, you can’t discern if Einstein was right or “spooky actions” was right. But if you measure the spins in certain different directions, then quantum mechanics predicts correlation rates that differ from Einstein’s prediction. In 1972, John Clauser (with Stuart Freedman) carried out Bell’s proposed experiment and discovered that quantum mechanics was right. Apparently, “spooky actions at a distance” is a fact about reality. Later, Alain Aspect and Anton Zeilinger produced improved versions of the experiment and, in 2022, the three shared the Nobel Prize in Physics for their work.

Given these facts, you might think that the issue is settled—quantum mechanics is simply telling us that reality is “nonlocal” (contains “spooky actions at a distance”), so what’s the problem? The problem is that if instantaneous signaling (nonlocality) exists, then you can show that reality harbors a preferred reference frame. This is at odds with the relativity principle, i.e. the laws of physics are the same in all inertial reference frames (no preferred reference frame), which lies at the heart of Einstein’s theory of special relativity. In 1600, Galileo used the relativity principle to argue against the reigning belief that Earth is the center of the universe, thereby occupying a preferred reference frame, and, in 1687, Newton used Galileo’s argument to produce his laws of motion.

Physicists loathe the idea of abandoning the relativity principle and returning to a view of reality like that of geocentricism. So in order to save locality, some in foundations have proposed violations of statistical independence instead, e.g. causes from the future with effects in the present (retrocausality) or causal mechanisms that control how experimentalists choose measurement settings (superdeterminism). But most physicists believe that giving up statistical independence means giving up empirical science as we know it; consequently, there is no consensus solution to Einstein’s quantum riddle. Do we simply have to accept that reality is nonlocal or retrocausal or superdeterministic? Contrary to what appears to be the case, the answer is “no” and the alternative is quite ironic.

The solutions that violate locality or statistical independence assume that reality must be understood via causal mechanisms (“constructive efforts,” per Einstein). This is the exact same bias that led physicists to propose the preferred reference frame of the luminiferous ether in the late nineteenth century to explain the shocking fact that everyone measures the same value for the speed of light c, regardless of their different motions relative to the source. Trying to explain that experimental fact constructively led to a morass, much like today, in foundations and here is where the irony begins—Einstein abandoned his “constructive efforts” to solve that mystery in “principle” fashion. That is, instead of abandoning the relativity principle to explain the observer-independence of c constructively with the ether, he doubled down on the relativity principle. He said the observer-independence of c must be true because of the relativity principle! The argument is simple: Maxwell’s equations predict the value of c, so the relativity principle says c must have the same value in all inertial reference frames to include those in uniform relative motion. He then used the observer-independence of c to derive his theory of special relativity. Today, we still have no constructive alternative to this principle solution to the mystery of the observer-independence of c.

The next step in the ironic solution occurred when quantum information theorists abandoned “constructive efforts” in the exact same way to produce a principle account of quantum mechanics. In the quantum reconstruction program, quantum information theorists showed how quantum mechanics can be derived from an empirical fact called Information Invariance and Continuity, just like Einstein showed that special relativity can be derived from the empirical fact of the observer-independence of c. The ironic solution was completed when we showed how Information Invariance and Continuity entails the observer-independence of h (another constant of nature called Planck’s constant), regardless of the measurement direction relative to the source. Since h is a constant of nature per Planck’s radiation law, the relativity principle says it must be the same in all inertial reference frames to include those related by rotations in space. So, quantum information theorists have solved Einstein’s quantum riddle without invoking nonlocality, retrocausality, or superdeterminism by using Einstein’s beloved relativity principle to justify the observer-independence of h, just as Einstein did for the observer-independence of c.

^{Feature image credit: Jian Fan on iStock.}

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Brighter than a trillion suns: an intense X-rated drama

You may be unaware of the celestial wonder known as OJ 287 but, as you will see, it is one of the most outlandish objects in the cosmos. Astronomers have known of periodic eruptions from OJ 287 since 1888 and in recent decades a mind-boggling explanation has emerged. It seems that the outbursts arise deep in the heart of a distant galaxy where two supermassive black holes are locked in a deadly embrace.

What is a black hole?

A black hole forms when a huge quantity of matter collapses under its own gravity to form an object whose gravitational attraction is so intense that nothing can escape, not even light. This fate awaits the most massive stars at the end of their lives.

Such stellar mass black holes may be a whopping five, ten, or even a hundred times the mass of the Sun. The first stellar mass black hole to be identified is known as Cygnus X-1. A black hole’s size is characterized by its event horizon. This is the sphere of no return: once inside all roads lead inexorably inwards. The radius of the event horizon of a 10 solar mass black hole is just 30 kilometres.

Astronomers believe that at the centre of every galaxy there lurks a black hole on another scale entirely. These are the supermassive black holes whose mass may be millions or even billions of times that of the Sun. We do not, as yet, fully understand how they grow to be so enormous in the time available since the Big Bang.

Brighter than a trillion stars

Over time galaxies collide and merge, and this may bring their central supermassive black holes into close proximity. Indeed, OJ 287 is the most well-studied example of such a system where two colossal black holes dance around each other performing a celestial tango de la muerte. Astronomers estimate that the primary black hole is a staggering 18 billion solar masses, while its much smaller companion is a mere 150 million solar masses. This gives the primary’s event horizon a radius of over 50 billion kilometres. To put this into context, the distance between the Sun and the outermost planet Neptune is 4.5 billion kilometres. So, the primary black hole is a vast bottomless pit that would dwarf the entire solar system.

Surrounding this chasm is the black hole’s accretion disc—an incredibly hot swirling disc of plasma with a temperature of billions of degrees—so hot that it emits X-rays and gamma rays. As the secondary dances around its gigantic partner, it periodically crashes through this seething whirlpool of fire releasing a blast of radiation that is picked up by telescopes here on Earth, and this is how we know of this amazing system.

These two-week-long flares are brighter than the combined light of an entire giant galaxy of a trillion stars. The radiation blast is produced mainly by hot plasma from the accretion disc spiralling into the secondary black hole. The OJ 287 system is 5 billion light years distant, so the light in these flares has been travelling our way since before the Earth formed. It is only because the flares are so bright that we can see them from such an incredible distance.

The clash of the cosmic titans

There are two flares every 12 years, the most recent in February 2022, as the secondary black hole plunges and re-emerges through the primary’s accretion disc. Like a cosmic duel in Lucifer’s inner sanctum, the two writhing supermassive black holes twist, twirl, and cavort around each other. Researchers led by Finnish astrophysicist Mauri Valtonen of Turku University and his colleague Achamveedu Gopakumar from the Tata Institute of Fundamental Research in Mumbai, India have used the precise timing of the flares to build a detailed picture of the orbit of the black holes based on our best theory of gravity—Einstein’s theory of general relativity. This enables them to predict when future flares will occur. The extreme nature of OJ 287 challenges our understanding of the fundamental laws of nature, offering tests for general relativity that have not been possible before. A wide range of astronomical instruments will be ready and waiting when the next blast is due to arrive. In the years ahead, we are sure to learn much more about this amazing system that illustrates just how weird the universe can be.

References: Mauri J Valtonen et al, ‘Refining the OJ 287 2022 impact flare arrival epoch’, Monthly Notices of the Royal Astronomical Society, Volume 521, Issue 4, June 2023, Pages 6143–6155, https://doi.org/10.1093/mnras/stad922

_{Feature image: Black Hole and a Disk of Glowing Plasma by Daniel Megias via iStock.}

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Tuning in to the cosmic symphony: restarting LIGO

In 2015 history was made when LIGO (Laser Interferometer Gravitational-Wave Observatory) detected the first ever gravitational wave signal. This was an incredible technological achievement and the beginning of a completely new way of investigating the cosmos.

The collision of two massive objects shakes the fabric of space, making it ring like a bell and producing ripples that travel unhindered through space. For several decades astronomers and physicists worked on the construction of LIGO with the goal of detecting these ripples. LIGO is the most sensitive instrument ever devised. It consists of two laboratories, one located in Hanford, Washington, and the other in Livingston, Louisiana. Each houses an L-shaped interferometer whose arms extend for 4 kilometres (2.5 miles). Within these arms, a powerful laser beam travels back and forth, bouncing between mirrors before recombining to form an interference pattern. As a gravitational wave passes by, the fabric of space is pulled and pushed and this alters the distance between the mirrors and these tiny disturbances change the interference pattern. LIGO’s sensitivity is truly astonishing. It can detect changes in distance of around one billionth of the size of an atom. Having two observatories is important; like listening in stereo, it helps to determine the direction from which the waves arrive. It also ensures that a signal came from deep space and not a local disturbance.

By comparing the data captured by LIGO to computer models, physicists can determine how each gravitational wave signal was created. It is possible to deduce the masses of the colliding bodies, the rate at which they were spinning, the energy released in the collision and how far away they are. LIGO’s first signal arrived from the collision and merger of two black holes located around 1.3 billion light years away. In the subsequent five years, LIGO received close to one hundred signals. Almost all of them came from collisions between pairs of black holes. The most epic was the collision and merger of black holes with 85 and 66 times the mass of the Sun that produced a black hole of 142 solar masses. During this collision, a mind-boggling nine solar masses were converted into pure energy in the form of gravitational waves.

In 2017, the Italian gravitational wave observatory Virgo also achieved the exquisite sensitivity necessary for the detection of gravitational waves and joined the LIGO observatories in their quest for distant cosmic dramas. Later that year on 17 August one of the most spectacular duly arrived. This event, named GW170817, was the first detected signal to come from the merger of two neutron stars rather than two black holes. Neutron stars are bizarre objects formed from the collapsed cores of stars that have run out of nuclear fuel. They are just 20 kilometres in diameter but contain at least one and a half times the mass of the Sun. In many ways they are like gigantic atomic nuclei. This was the first time and, so far, the only time that the source of a gravitational wave signal has been located with optical instruments, heralding the dawn of multi-messenger astronomy. The combination of optical and gravitational data has greatly advanced our understanding of what happens when two neutron stars collide. It is like being able to both see the lightning and hear the thunderclap. These observations lent support to the idea that many of the heavier chemical elements such as gold are created and dispersed in neutron star collisions.

In 2020, LIGO’s operations were suspended to allow for a major upgrade of the system. Now, after a three-year hiatus, LIGO is back up and running. On 24 May LIGO started a new observing run with refined instruments. With its enhanced sensitivity, it is expected to detect a gravitational wave signal every two to three days. LIGO is the lynchpin of the LIGO-Virgo-KAGRA collaboration—a partnership with the world’s other two gravitational wave observatories: Virgo in Italy and KAGRA in Japan. The construction of a third LIGO detector in India has also recently been approved. This expansion of the global network of gravitational wave observatories will help to pinpoint the location of gravitational wave sources so that they can also be studied optically.

LIGO has provided the most direct evidence that we have for black holes and their properties, and offers wonderful new tests of our best theory of gravity, Einstein’s theory of general relativity. By observing and studying the mergers of black holes and neutron stars, scientists are gaining new insights into fundamental physics, the nature of gravity, and the evolution of the universe itself. The restart of LIGO and the global gravitational wave research network launches a new phase of deep space exploration. We can look forward to more incredible discoveries in the near future.

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Supporting researchers at every career stage

Academia is a complex ecosystem with researchers at various stages of their careers striving to make meaningful contributions to their fields. In support of furthering knowledge, academic journals work with researchers to disseminate findings, engage with the scholarly community, and share academic advances.

Oxford University Press (OUP) publishes more than 500 high-quality trusted journals, two-thirds of which are published in partnership with societies, organizations, or institutions. The remaining third is a list of journals owned and operated by the Press. Fundamental to this list of owned journals is our mission to create world-class academic and educational resources and make them available as widely as possible, including expanding our fully open access options for authors. As a not-for-profit university press, our financial surplus is reinvested for the purpose of educational and scholarly objectives of the University and the Press, thereby fostering the continued growth of open access initiatives and supporting the scholarly community.

How do we support researchers in different career stages through our journals?

Early Career Researchers: nurturing talent

For early career researchers (ECRs), having their work published in a reputable journal is a crucial step in establishing their academic reputation. OUP journals provide several avenues of support including:

• Mentoring and guidance: Some journals provide mentorship programs or editorial support to help young researchers navigate the publishing process.

Featuring Oxford Open Immunology and Oxford Open Energy:

Two of our Oxford Open series journals, Oxford Open Immunology and Oxford Open Energy run dedicated ECR boards, which provide a key channel for direct engagement between ECR participants and our high profile academic senior editorial teams. Activities are planned throughout the year and may include assisting with facilitating journal webinars, joining ECR board meetings to discuss journal strategy and direction, suggesting and coordinating special collections or commissioned pieces on highly topical areas of research.

• Open access initiatives: 120 of the journals we publish are fully open access and the vast majority of the remaining journals offer authors open access options, making research freely available for a global audience to read, share, cite, and reuse. This helps early career researchers, and researchers of all stages in their career, gain visibility of their work and reach a wider readership.

Featuring our Oxford Open series:

The Oxford Open series is underpinned by a set of guiding principles, which include an emphasis on open research, with each journal having been developed in a bespoke way to best serve the needs of its own research community.

Hear more about OUP’s approach to OA published and the Oxford Open series in The Oxford Comment podcast.

Many of our Oxford Open journals offer article types that are specifically developed for ECRs to start their publication journey, these may take the form of a Rapid Report, Short Communication, or Perspective article, for example. We regularly invite ECRs to submit their work to the journal, often in collaboration with their mentors or supervisors as appropriate.

Mid-career researchers: advancing expertise

As researchers progress in their careers, they require journals that can help them deepen their expertise and broaden their impact. OUP journals provide several avenues of support including:

• Cutting-edge research: OUP journals prioritise publishing high-impact, innovative research, allowing mid-career researchers to stay updated with the latest advancements in their fields.

Featuring Exposome:

Exposome is the home of cutting-edge research from the emerging field of exposomics. The journal sits at the systematic intersections of environmental science, toxicology, chemistry, and public health and policy, and it calls on daring science from a broad community of investigators to provide a forum for engagement, redefine our understanding of the human exposome, and critically advance the field.

Editor-in-Chief Gary W Miller outlines the need for this new field in the inaugural editorial.

• Editorial and reviewer roles: Many researchers at this stage are invited to serve as peer reviewers or editorial board members to further contribute their knowledge to the academic community and enhance their own expertise.

Featuring STEM CELLS Translational Medicine:

For over 10 years, STEM CELLS Translational Medicine has served as a home for timely and important research to advance the utilization of cells for clinical therapy. The journal’s peer reviewers play a critical role in ensuring that the research published in the journal serves the needs of this research community by helping move applications of these critical investigations closer to accepted best patient practices and ultimately improve outcomes.

STEM CELLS Translational Medicine is proud to work with mid-career researchers, and reviewers of all career stages and encourages researchers to join the journal’s network of expert peer reviewers where researchers can get a first-hand look at the quality of research that is required and preview cutting-edge scientific work that helps them stay atop their field.

Established researchers: global recognition

For established researchers, maintaining a high level of visibility and recognition in the academic world is paramount. OUP journals provide several avenues of support including:

• Prestige and impact in the field: OUP journals are known for their prestige and rankings in their relevant fields. Publishing in our journals can bolster an established researcher’s reputation.

Featuring Nucleic Acids Research:

For almost 50 years, Nucleic Acids Research (NAR) has provided the scientific community with detailed and constructive editorial feedback resulting in publications of the very highest standard. The quality of content has been demonstrated in this year’s Nobel Prize in Physiology or Medicine, which cited this article from NAR as one of three publications fundamental to the research recognized by the award.

Edited by a fully independent team of leading academic researchers, the journal serves as a beacon of trusted and high-quality research in a rapidly advancing field. Having flipped to fully OA in 2005, NAR has opened the doors to rigorous, impactful research, sharing knowledge globally and it remains at the cutting edge of molecular biology science.

• Leadership opportunities: As a partner to academic research, all of OUP’s journals are edited by members of the academic community, longstanding experts in their own fields. Our journals therefore offer established researchers the opportunity to take on leadership roles within journal editorial boards as associate editors or editors-in-chief, helping to shape the direction of the journal and their fields.

Featuring Oxford Open Neuroscience:

Oxford Open Neuroscience is run by a representative group of five active scientists who are subject specialists, rather than a single editor-in-chief. Representing the needs of that community and making science-based decisions, the journal’s senior editors act as ambassadors for their individual fields.

As a researcher-led publication with a focus on diversity, transparency and innovation, Oxford Open Neuroscience is a fully open access alternative to more traditional neuroscience journals and enables researchers themselves to propel the field into a new publishing era.

OUP’s owned journals are more than just platforms for publishing research, they are invaluable partners in the academic journey of researchers at every career stage. From nurturing early career talent to supporting mid-career researchers in advancing their expertise and providing global recognition for established scholars, our journals contribute to the growth and success of the academic community. As the world of research continues to evolve, our journals will remain dedicated to supporting researchers around the world, ensuring knowledge is disseminated, shared, and celebrated.

_{Featured image by Pexels on Pixabay (public domain)}

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Elon Musk, Mars, and bioethics: is sending astronauts into space ethical?

The recent crash of the largest-ever space rocket, Starship, developed by Elon Musk’s SpaceX company, has certainly somewhat disrupted optimism about the human mission to Mars that is being prepared for the next few years. It is worth raising the issue of the safety of future participants in long-term space missions, especially missions to Mars, on the background of this disaster. And it is not just about safety from disasters like the one that happened to Musk. Protection from the negative effects of prolonged flight in zero gravity, protection from cosmic radiation, as well as guaranteeing sufficiently high crew productivity over the course of a multi-year mission also play an important role.

Fortunately, no one was killed in the aforementioned crash, as it was a test rocket alone without a crew. However, past disasters in which astronauts died, such as the Space Shuttle Challenger and Space Shuttle Columbia disasters, remind us that it is the seemingly very small details that determine life and death. So far, 15 astronauts and 4 cosmonauts have died in space flights. 11 more have died during testing and training on Earth. It is worth mentioning that space flights are peacekeeping missions, not military operations. They are carried out relatively infrequently and by a relatively small number of people. 

It is also worth noting the upcoming longer and more complex human missions in the near future, such as the mission to Mars. The flight itself, which is expected to last several months, is quite a challenge, and disaster can happen both during takeoff on Earth, landing on Mars, and then on the way back to Earth. And then there are further risks that await astronauts in space. 

The first is exposure to galactic cosmic radiation and solar energetic particles events, especially during interplanetary flight, when the crew is no longer protected by both Earth’s magnetic field and a possible shelter on Mars. Protection from cosmic radiation for travel to Mars is a major challenge, and 100% effective protective measures are still lacking. Another challenge remains being in long-term zero-gravity conditions during the flight, followed by altered gravity on Mars. Bone loss and muscle atrophy are the main, but not only, negative effects of being in these states. Finally, it is impossible to ignore the importance of psychological factors related to stress, isolation, being in an enclosed small space, distance from Earth.

A human mission to Mars, which could take about three years, brings with it a new type of danger not known from the previous history of human space exploration. In addition to the aforementioned amplified impact of factors already known—namely microgravity, cosmic radiation, and isolation—entirely new risk factors are emerging. One of them is the impossibility of evacuating astronauts in need back to Earth, which is possible in missions carried out at the International Space Station. It seems that even the best-equipped and trained crew may not be able to guarantee adequate assistance to an injured or ill astronaut, which could lead to her death—assuming that care on Earth would guarantee her survival and recovery. Another problem is the delay in communication, which will reach tens of minutes between Earth and Mars. This situation will affect the degree of autonomy of the crew, but also their responsibility. Wrong decisions, made under conditions of uncertainty, can have not only negative consequences for health and life, but also for the entire mission.

Thus, we can see that a future human mission to Mars will be very dangerous, both as a result of factors already known but intensified, as well as new risk factors. It is worth raising the question of the ethicality of the decision to send humans into such a dangerous environment. The ethical assessment will depend both on the effectiveness of available countermeasures against harmful factors in space and also on the desirability and justification for the space missions themselves. 

Military ethics and bioethics may provide some analogy here. In civilian ethics and bioethics, we do not accept a way of thinking and acting that would mandate the subordination of the welfare, rights, and health of the individual to the interests of the group. In military ethics, however, this way of thinking is accepted, formally in the name of the higher good. Thus, if the mission to Mars is a civilian mission, carried out on the basis of values inherent in civilian ethics and bioethics rather than military ethics, it may be difficult to justify exposing astronauts to serious risks of death, accident, and disease.

One alternative may be to significantly postpone the mission until breakthrough advances in space technology and medicine can eliminate or significantly reduce the aforementioned risk factors. Another alternative may be to try to improve astronauts through biomedical human enhancements. Just as in the army there are known methods of improving the performance of soldiers through pharmacological means, analogous methods could be applied to future participants in a mission to Mars. Perhaps more radical, and thus controversial, methods such as gene editing would be effective, assuming that gene editing of selected genes can enhance resistance to selected risk factors in space. 

But the idea of genetically modifying astronauts, otherwise quite commonsensical, given also the cost of such a mission, as well as the fact that future astronauts sent to Mars would likely be considered representative of the great effort of all humanity, raises questions about the justification for such a mission. What do the organizers of a mission to Mars expect to achieve? Among the goals traditionally mentioned are the scientific merits of such a mission, followed by possible commercial applications for the future. Philosophers, as well as researchers of global and existential catastrophes, often discuss the concept of space refuge, in which the salvation of the human species in the event of a global catastrophe on Earth would be possible only by settling somewhere beyond Earth. However, it seems that the real goals in our non-ideal society will be political and military.

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Five books to celebrate British Science Week 2023

British Science Week is a ten-day celebration of science, technology, engineering and math’s, taking place between 10-19 March 2023. To celebrate, join in the conversation, and keep abreast of the latest in science, delve into our reading list. It contains five of our latest books on plant forensics, the magic of mathematics, women in science, and more.

1. Planting Clues: How Plants Solve Crimes

Discover the extraordinary role of plants in modern forensics, from their use as evidence in the trials of high-profile murderers such as Ted Bundy to high value botanical trafficking and poaching.

In Planting Clues, David Gibson explores how plants can help to solve crimes, as well as how plant crimes are themselves solved. He discusses the botanical evidence that proved important in bringing a number of high-profile murderers such as Ian Huntley (the 2002 Soham Murders), and Bruno Hauptman (the 1932 Baby Lindbergh kidnapping) to trial, from leaf fragments and wood anatomy to pollen and spores. Throughout he traces the evolution of forensic botany, and shares the fascinating stories that advanced its progress.

Buy Planting Clues, How Plants Solve Crimes

Take a look at Gibson’s blog on Environmental DNA, as well as John Parrington’s (author of ‘Mind Shift’) blog on what neuroscience can tell us about the mind of a serial killer.

2. The Spirit of Mathematics: Algebra and all that

 What makes mathematics so special? Whether you have anxious memories of the subject from school, or solve quadratic equations for fun, David Acheson’s book will make you look at mathematics afresh.

Following on from his previous bestsellers, The Calculus Story and The Wonder Book of Geometry, here Acheson highlights the power of algebra, combining it with arithmetic and geometry to capture the spirit of mathematics. This short book encompasses an astonishing array of ideas and concepts, from number tricks and magic squares to infinite series and imaginary numbers. Acheson’s enthusiasm is infectious, and, as ever, a sense of quirkiness and fun pervades the book.

Buy The Spirit of Mathematics, Algebra and all that

To learn more, discover our Very Short Introductions series, including editions about Geometry, Algebra, Symmetry, and Numbers.

3. Not Just for the Boys: Why We Need More Women in Science

Why are girls discouraged from doing science? Why do so many promising women leave science in early and mid-career? Why do women not prosper in the scientific workforce?

Not Just For the Boys looks back at how society has historically excluded women from the scientific sphere and discourse, what progress has been made, and how more is still needed. Athene Donald, herself a distinguished physicist, explores societal expectations during both childhood and working life using evidence of the systemic disadvantages women operate under, from the developing science of how our brains are—and more importantly aren’t—gendered, to social science evidence around attitudes towards girls and women doing science.

Buy Not Just for the Boys, Why We Need More Women in Science

Make sure not to miss Athene Donald’s limited 4-part podcast series featuring Donald in conversation with fellow female scientists and allies about the issues women face in the scientific world. 

4. Distrust: Big Data, Data-Torturing, and the Assault on Science

Using a wide range of entertaining examples, this fascinating book examines the impacts of society’s growing distrust of science, and ultimately provides constructive suggestions for restoring the credibility of the scientific community.

This thought-provoking book argues that, ironically, science’s credibility is being undermined by tools created by scientists themselves. Scientific disinformation and damaging conspiracy theories are rife because of the internet that science created, the scientific demand for empirical evidence and statistical significance leads to data torturing and confirmation bias, and data mining is fueled by the technological advances in Big Data and the development of ever-increasingly powerful computers.

Buy Distrust, Big Data, Data-Torturing, and the Assault on Science

Check out Gary Smith’s previous titles, including: The Phantom Pattern Problem, The 9 Pitfalls of Data Science, and The AI Delusion.

5. Sentience: The Invention of Consciousness

What is consciousness and why has it evolved? Conscious sensations are essential to our idea of ourselves but is it only humans who feel this way? Do animals? Will future machines?

To answer these questions we need a scientific understanding of consciousness: what it is and why it has evolved. Nicholas Humphrey has been researching these issues for fifty years. In this extraordinary book, weaving together intellectual adventure, cutting-edge science, and his own breakthrough experiences, he tells the story of his quest to uncover the evolutionary history of consciousness: from his discovery of blindsight after brain damage in monkeys, to hanging out with mountain gorillas in Rwanda, to becoming a leading philosopher of mind. Out of this, he has come up with an explanation of conscious feeling—”phenomenal consciousness”—that he presents here in full for the first time.  

Buy Sentience, The Invention of Consciousness (UK Only)

As an added bonus, you can also read more on the topics of evolutionary biology, the magic of mathematics, and artificial intelligence with the Oxford Landmark Science series. Including “must-read” modern science and big ideas that have shaped the way we think, here are a selection of titles from the series to get your started.

You can also explore more titles via our extended reading list via Bookshop UK.

OUPblog - Academic insights for the thinking world.

Looking into space: how astronomy and astrophysics are teaching us more than ever before [podcast]

It’s been 500 years since the first circumnavigation of the globe, and few could have predicted then that we would see detailed images of stars, galaxies, and exoplanets like the ones produced by the James Webb Space Telescope this year.

On today’s episode of The Oxford Comment, we’re looking at what these recent discoveries mean to our understanding of the universe. Why should we all know about distant galaxies? How will this learning impact us? And what role will artificial intelligence and machine-learning play in the wider astronomy field in the coming years?

The questions are big, the area is even bigger, and we are delighted to be joined by two eminent fellows from the Royal Astronomical Society to review this expansive subject.

First, we welcome Claudia Maraston, Professor of Astrophysics at the University of Portsmouth, and an expert in theoretical astrophysics, in particular the calculation of theoretical spectra for stellar populations. She also sits on the editorial board of Monthly Notices of the Royal Astronomical Society.

Our second guest is Jonathan Tennyson, Massey Professor of Physics at University College London, whose research specialises in the accurate quantum mechanical treatments of both the spectroscopy and collision properties of small molecules, with an emphasis on the provision of data for other research areas. Jonathan is also Editor-in-Chief of the Open Access Royal Astronomical Society Techniques & Instruments.

Check out Episode 78 of The Oxford Comment and subscribe to The Oxford Comment podcast through your favourite podcast app to listen to the latest insights from our expert authors.

Recommended reading

To learn more about the themes raised in this podcast, we’re pleased to share a selection chapters and articles.

If you would like to find out more about recent discoveries in observational astronomy, why not start with a title in our Very Short Introductions series, Observational Astronomy: A Very Short Introduction by Geoff Cottrell?

You may also be interested in Astronomy: The Human Quest for Understanding by Dale A. Ostlie which looks at how science operates practically in relation to astronomy, leading the reader down a path to our present-day understanding of our Solar System, stars, galaxies, and more.  

If you’re interested in the role ordinary people taking part in cutting-edge science and what humans can bring to interpreting big data which smart machines can’t, The Crowd and the Cosmos: Adventures in the Zooniverse by Chris Lintott highlights that, “You, too, can help explore the Universe in your lunch hour.”

Numerous articles written and co-written by our guests Claudia Maraston and Jonathan Tennyson can be found in Monthly Notices of the Royal Astronomical Society. Tennyson also co-wrote this introductory article to RAS Techniques and Instruments earlier this year.

Discover more about the James Webb Telescope on Oxford Academic through our range of journal articles, many of which are Open Access. This range includes Royal Astronomical Society articles such as the following:  

• “Hiding in plain sight: observing planet-starspot crossings with the James Webb Space Telescope” by Giovanni Bruno et al
• “Conditions for detecting lensed Population III galaxies in blind surveys with the James Webb Space Telescope, the Roman Space Telescope, and Euclid” [Open Access] by Anton Vikaeus et al.  

_{Featured image: “NASA’s Webb Reveals Cosmic Cliffs, Glittering Landscape of Star Birth,” July 2022. NASA/ESA/CSA, Public Domain via Wikimedia Commons.}

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The CERN Large Hadron Collider is back

The CERN Large Hadron Collider, the LHC, is the world’s highest-energy particle accelerator. It smashes together protons with energies almost 7,000 times their intrinsic energy at rest to explore nature at distances as small as 1 part in 100,000 of the size of an atomic nucleus. These large energies and small distances hold clues to fundamental mysteries about the origin and nature of the elementary particles that make up matter.

The LHC is a high-performance machine, a Formula 1 race car, not a Toyota. As such, it needs to spend time in the shop. The previous run of the LHC ended in December 2018. Since then, scientists and technicians have installed numerous fixes and improvements to both the accelerator and the particle detectors. In mid-April, the LHC began a series of final tests and tunings, raising the collision energy from 13 TeV to 13.6 TeV, moving closer to the design energy of 14 TeV. On 5 July the new run of data-taking began. The new Run 3, planned to end in late 2025, is expected to double the current LHC data set.

Run 3 is an intermediate stage in the LHC program. Run 1 began in 2010. Its major highlight was the discovery of the long-anticipated Higgs boson in July 2012. In 2013, the accelerator shut down for an earlier period of repair and upgrade. Run 2 began two years later, in the spring of 2015. Its primary achievements were the discoveries of the major decay modes of the Higgs boson, verifying that this particle is indeed the origin of mass, at least for all of the relatively heavy known elementary particles. CERN plans that Run 3 will be followed by a longer preparation period extending through 2029. Then the fully-grown LHC, now called HL-LHC, will burst into action again with a rate of collisions 10 times larger than the current one. Running until 2042, it will gather its ultimate data set, 10 times larger than that expected at the end of Run 3.

The data challenge

The key to LHC physics is accumulation of a huge number of records of proton-proton collisions for analysis. The proton is the easiest particle to manipulate and thus the particle of choice for acceleration to the highest energies. But it is not an elementary particle. It is a bound state of quarks, held together by particles called gluons that are the quanta of the strong nuclear force. 

To describe collisions at the LHC, it is useful to think of the proton as a bag of jelly beans, holding quarks and gluons and also, by quantum processes, anti-quarks, quarks of exotic flavor—such as the bottom quark—and even heavier particles such as the W and Z bosons that are the quanta of the weak interactions responsible for radioactive decay. When two protons collide, the most likely thing to happen is that the two “bags” are ripped apart, spilling out particles that re-form into protons, pions, kaons, and other more familiar nuclear particles. But, occasionally, two quarks or gluons will collide head-on, compressing all of their energy to a tiny spot and then releasing it back to quarks and gluons or perhaps to heavier elementary particles, known and unknown. 

By studying these rare reactions with tremendous energy release, physicists can glimpse the laws of nature at very short distances. As the LHC accumulates data, the experiments will build up larger and larger samples of these rare reactions, eventually accumulating enough events for strong evidence of a discovery.

Finding these occasional hard collisions is a tremendous data challenge. Bunches of protons at the LHC collide 40 million times per second. Each bunch collision leads to 50 or more individual proton-proton collisions. The photographic records of these collisions taken by the major LHC detectors ATLAS and CMS must be written into permanent storage. The size of each picture is already 20 times larger than a typical smart-phone photo, and so keeping everything for one second of operation would already produce a million-GigaByte database. But, in each second of data-taking, the 40 million events are mostly simple and familiar ones, with only a few thousand W bosons events and only one Higgs boson event buried in the stream. Thus, a crucial part of each LHC experiment is the “trigger,” a bank of computer processors that selects a few hundred per second of these collisions for the permanent record that physicists will analyze. Even with such a severe selection, the LHC experiments already create one of the world’s largest computer databases.

The LHC events rush out at tremendous speed, and this creates a problem that events must be selected at a rate too fast for human intervention. The trigger has two stages. Level 1 must select 1 in 100 events in 100 microseconds and throw away the rest. Then the high-level trigger can take the luxury of a whole second to make a more sophisticated decision—but it must still throw away all but 1 in 10,000 of the events it receives. If an event does not make it into the final event record, it is as if it never happened.

By LHC standards, it is not so difficult to find the events with very large energy transfer from the initial quarks and gluons. What is more difficult is to find less prominent events that are special in another way, perhaps containing hints of new weakly-coupled interactions or particles of the cosmic dark matter. The most important upgrades to the major detectors for Run 3 are improvements to the trigger, including new detector elements and re-wiring of the existing elements to bring more information to Level 1. The CMS experiment will add special-purpose processors running machine-learning algorithms at blinding speed to make the Level 1 decisions.

The new particle targets

The primary goal of the LHC now is to discover new elementary particles that might give evidence for new, still-undiscovered, fundamental interactions. Some of the new particles proposed would be heavy and would decay to clusters of quarks and leptons displaying very high energy. My personal favorite for eventual discovery at the LHC is a new heavy quark, a partner to the top quark. Unfortunately, it is quite unlikely that such a particle can be discovered in Run 3. The current searches already exclude these particles up to a mass about 10 times that of the Higgs boson. A top quark partner at a slightly higher mass—which could well be there—would not appear in enough events for an unambiguous discovery. At best, the experiments would give interesting statistical hints, and even some suggestive event pictures with novel features. That will get theorists talking. The HL-LHC, in Run 4 and beyond, would be needed to confirm these suggestions.

However, there is a real opportunity in searches for weakly-coupled new particles, such as those predicted in models of the dark matter. Reactions that produce such particles have low rates, since they are not produced by the strong interactions but rather by the electromagnetic and weak interactions. Thus any increase in the data set would be helpful. The dark matter particle interacts too weakly to leave a signal in the LHC detectors. This is not a problem in itself because one can look for visible particles recoiling against the invisible emissions, in accord with Newton’s third law. But, in many models, the partners of the dark matter particle release very little visible energy, leading to very small recoil signals that cannot be recognized by the experiments’ triggers. The trigger improvements in Run 3 will improve the coverage for such subtle signals, and the increased rate will produce a sample of rarer events in which the recoiling particles are pushed out into easier view. With these improvements, the ability of the ATLAS and CMS to recognize these signals will measurably increase.

Machine learning

Though most searches for new particles target particles predicted by theorists, there is an increasing trend to search for new particles that theorists have not yet imagined. It is hopeless to ask humans to search through the whole library of LHC event pictures in hopes of discovering anomalous ones. But this could be possible with advanced “deep learning” computer algorithms that use artificial intelligence to scan through mounds of data. 

Particle physicists have very challenging problems of signal classification, and so they entered early into the creation of machine-learning tools. Already in 1980, the SLAC Mark II experiment was using trainable decision trees to separate signals of gamma rays and pi mesons. Today, machine-learning is used in almost every decision made by the LHC detectors, for example, the identification of bottom quarks in a sample of quark signals. These tools, though, are trained on simulation data. Simulation programs for LHC events, such as the commonly used program PYTHIA, are remarkably accurate, but still they cannot model all relevant physics. If an anomaly is detected by a machine-learning algorithm, we must ask, is this truly new physics or just a defect in PYTHIA? 

In Run 2, a number of algorithms were proposed for “minimally supervised classification.” For example, one might compare two data samples that would be expected to have different proportions of a reaction containing a new particle. With even this minimal hint, these algorithms can identify events in one sample that are anomalous with respect to the other. It will be very interesting to run these algorithms blindly on the new data set that becomes available in Run 3. It is quite possible that they will turn up completely unanticipated signals.

Electrons versus muons

So far, I have discussed only the general-purpose LHC detectors ATLAS and CMS. But the LHC also hosts a specialized detector LHCb, dedicated to studying the large samples of particles containing the bottom and charm quarks that are produced in LHC reactions.  The LHCb detector has different goals from ATLAS and CMS and so it is not built to accept the very high data rate of those detectors. But, during the shutdown, the LHCb data-taking system was completely rebuilt to take 10 times more data in Run 3 than in the previous runs.

In contrast to ATLAS and CMS, the specialized study of B mesons by LHCb has turned up some tantalizing anomalies. The most prominent of these is the observation of different rates for the decays of the B meson to a K meson plus a muon-antimuon pair versus decays to a K meson plus an electron-positron pair. In our current understanding of particle physics, the muon is a heavy version of the electron. Its mass is 200 times larger than that of the electron, but its interactions are precisely identical. This muon-electron universality has been tested in many settings. In contrast to this body of evidence, the LHCb experiment reports 20% fewer events of these B meson decays to muons as opposed to electrons. Because muons and electrons are observed rather differently in the LHCb detector, the result is not statistically definitive, but still it is striking. Could new interactions, involving heavy quarks, differentiate the muon and the electron and play a role in explaining their very different masses? The observation moves muon-electron universality tests even at ATLAS and CMS from routine projects to the center of attention. Can the highest-energy reactions show corroborating evidence, or will they support the standard universality? We will certainly learn more in Run 3.

Like all Big Science projects, the LHC advances slowly but gives access to deeply buried knowledge that cannot be obtained in any other way. Run 3 is the next stage in this progress. Please watch for the surprises it will bring.

_{Featured image: “View of the LHC tunnel sector 3-4” by CERN, via Wikimedia Commons (CC BY-SA 3.0)}

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Celebrating women in STEM [timeline]

March is Women’s History Month, an annual occurrence dedicated to commemorating and highlighting the contributions that women have made throughout history. Many of these contributions have gone unsung or undervalued, particularly in the fields of science, technology, engineering, and medicine, where women have historically been underrepresented. Celebrating and recognizing the work of women in these field remains a priority for Oxford University Press, and this month and every month we are proud to support diverse voices across our publishing. We seek to create an inclusive space to highlight the work of women in STEM, and celebrate the contributions of trans and cis women, and women of all races, ethnicities, and sexual orientations.

The timeline—first published in 2018, now updated in 2022—provides a curated selection of achievements, discoveries, and innovations made by women in STEM, from the foundation of modern nursing to critical contributions in the effort to fight the COVID-19 pandemic. This is just a small picture of the countless women making an impact in STEM. For more on this subject we also offer two collections featuring the work of women in STEM: women in medicine and women in science.

_{Featured image by Dmytro Zinkevych via Shutterstock.} 

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Five books to celebrate British Science Week

British Science Week is a ten-day celebration of science, technology, engineering and maths, taking place between 11-20 March 2022. To celebrate, join in the conversation, and keep abreast of the latest in science, delve into our reading list. It contains five of our latest books on evolutionary biology, the magic of mathematics, artificial intelligence, and more.

1. The Parrot in the Mirror: How evolving to be like birds made us human

How similar are your choices, behaviours, and lifestyle to those of a parrot?

Discover how many of our defining human traits are far more similar to birds than to our fellow mammals in The Parrot in the Mirror, by Antone Martinho-Truswell. From our lifespans to our intelligence, our relationships and our language, we can learn a great deal about ourselves by thinking of the human species as “the bird without feathers.” In this insightful read, learn more about how parrots, specifically, are our biological mirror image; an evolutionary parallel to ourselves. And how they are the only species to share one particular human trait: spite.

Read The Parrot in the Mirror: How evolving to be like birds made us human.

To learn more about how, much like humans, the senses of animals are key to their survival, discover Secret Worlds: The extraordinary senses of animals, by Martin Stevens.

2. Mind Shift: How culture transformed the human brain

The mental capacities of the human mind far outstrip those of other animals. Our imaginations and creativity have produced art, music, and literature; built bridges and cathedrals; enabled us to probe distant galaxies, and to ponder the meaning of our existence. What makes the human brain unique, and able to generate such a rich mental life? In this book, John Parrington draws on the latest research on the human brain to show how it differs strikingly from those of other animals in its structure and function at a molecular and cellular level. And he argues that this “shift,” was driven by tool use, but especially by the development of one remarkable tool—language.

Read Mind Shift: How culture transformed the human brain.

You can also read Parrington blog on what neuroscience can tell us about the mind of a serial killer, as well as listening to his podcast on culture and the human brain.

3. Colliding Worlds: How cosmic encounters shaped planets and life

In Colliding Worlds, Simone Marchi explores the key role that collisions in space have played in the formation and evolution of our solar system, the development of planets, and possibly even the origin of life on Earth. Analysing our latest understanding of the surfaces of Mars and Venus, gleaned from recent space missions, Marchi presents the dramatic story of cosmic collisions and their legacies. You can also read his blog’s on the Earth’s wild years and the creative destruction of cosmic encounters, as well as his response to Netflix’s “Don’t Look Up!” satire, Do Look Up! Could a comet really kill us all?

Read Colliding Worlds: How cosmic encounters shaped planets and life.

To learn more, discover our Very Short Introductions series, including Planetary Systems, Climate Change, Evolution, Human Evolution, and The Animal Kingdom.

4. The Wonderful Book of Geometry: A mathematical story

How can we be sure that Pythagoras’s theorem is really true? Why is the “angle in a semicircle” always 90 degrees? And how can tangents help determine the speed of a bullet?

David Acheson takes the reader on a highly illustrated tour through the history of geometry, from ancient Greece to the present day. He emphasizes throughout elegant deduction and practical applications, and argues that geometry can offer the quickest route to the whole spirit of mathematics at its best. Along the way, we encounter the quirky and the unexpected, meet the great personalities involved, and uncover some of the loveliest surprises in mathematics.

Read The Wonderful Book of Geometry: A mathematical story.

Take a sneak peek inside, and listen to Acheson explain the magic of geometry.

5. Human-centered AI

Focusing not on the risks of AI, but on the opportunities it presents and how to capitalize on them, Ben Shneiderman puts forward 15 recommendations about how programmers, business leaders, educators, professionals, and policy makers can implement human-centered AI. Bridging the gap between ethical considerations and practical realities to make successful, reliable systems, Schneiderman provides a range of human-centered AI design metaphors to show ways to get beyond current limitations and see new design possibilities that empower people, giving humans control.

Read Human-centered AI.

To learn more, discover our What Everyone Needs to Know® series, including titles on Artificial Intelligence (and a blog post on What is Artificial Intelligence?), and Evolution.

As an added bonus, you can also read more on the topics of evolutionary biology, the magic of mathematics, and artificial intelligence with the Oxford Landmark Science series. Including “must-read” modern science and big ideas that have shaped the way we think, browse the series here:

You can also explore more titles via our extended reading list via Bookshop UK.

OUPblog - Academic insights for the thinking world.

Do Look Up! Could a comet really kill us all?

It’s no mystery why the movie industry likes dramatic stories. Certainly, the occasional contemplative movie may achieve critical praise and general acclamation, but a well-written story about death and destruction often carries the day. When it comes to catastrophic events for humans, a big nasty asteroid or comet colliding with Earth tops the chart, and several movies have exploited this scenario. The recent Netflix movie Don’t Look Up did that again, but as a satire and a warning. It is widely considered an allegory for climate change, but let’s consider the astronomical scenario as presented. In the movie, a couple of astronomers serendipitously discover a comet on course to collide with the Earth in about six months, give or take. Is such a scenario scientifically sound?

First, we need to know the orbit of a celestial body, whether asteroid or comet, very precisely in order to establish that it’s highly likely to be on a collision course (99.78% probability, the astronomers claim). The Earth is less than a grain of sand, a mere 12,742 km in diameter, compared to the vast expanse of the Solar System, extending tens of billions of kilometres from the Sun. In the movie, the comet is first seen to pass by Jupiter (say, 1 billion km away). That means the angular precision on the position of the comet needs to be about 10^-5 arcseconds – equivalent to seeing a fly from 500 m away. Such precision can’t be achieved with a single observation, even by the most powerful telescopes. That is why astronomers usually need to observe asteroids and comets multiple times over a long interval, typically years. So, the premises of the movie are a bit flimsy. 

The other aspect is the size of the object. How likely is it for a 5-10 km asteroid or comet to be hurtling towards Earth? As I discuss in my book Colliding Worlds, collisions have occurred throughout the history of the Solar System. In its heady early days, the Earth and other planets were formed and shaped by massive collisions. Although things are quieter today, we know that asteroids—the rocky leftovers of planet formation found within Jupiter’s orbit—can occasionally skim the Earth. We also know from years of observation that there are very few asteroids close to Earth larger than five km (just 12 to be precise), and none of them has a serious probability of collision with the Earth for hundreds of thousands of years. By then, we would probably have gone extinct through other causes, or left the planet, so we don’t need to worry about these large asteroids. There are plenty of smaller asteroids, but they pose a more limited threat. 

Comets, however, as correctly presented in the movie, are a different beast. They are much harder to observe when far away, beyond Jupiter’s orbit. And many of them are parked so far from Earth, in a wide spherical shell called the Oort Cloud more than 150 billion kilometers away, that they are simply not visible to us until they get dislodged and hurtle towards the inner Solar System. The likelihood of such objects colliding with the Earth are very low, but not zero; one in every 500 million Oort Cloud comets is a potential destroyer of life on Earth. 

How can we mitigate this cosmic threat from the cold outer reaches of the Solar System? Or the more likely scenario of collision by a smaller asteroid that may not destroy life on Earth but would still be able to cause significant local damage?

Do look up! There is really no other way. Knowledge of how many hazardous objects are out there is the first course of action. The movie highlights and satirizes the tension between scientists trying to present the evidence and politicians more concerned with election prospects and lucrative interests (mining the comet, really?!), and a media too busy feeding celebrity trivia to a public suspicious about science. We know how it’s all going to end. The personal, obtuse interests of the few in power, swayed by the hare-brained schemes of technocrats, will prevail, with little hope for the human race. These are important messages for the failure to tackle climate change. But focusing on the celestial collision scenario, even if all of humanity could come together, would it even be possible to knock an astronomical foe from its course?

There is no way a 5-10 km comet could be deflected. Nor even a much smaller body. We simply do not know how to do this. Several ideas have been proposed, ranging from nuclear bombs to focused solar energy, but without an actual experiment we really don’t know what would work. And consider that building a space mission from scratch to intercept an object would likely require a few years. So, at the very least, we would need to identify a deflection method that works, and then have a spacecraft stand by, just in case. Not to sound pessimistic, but that is where we stand today. Still, it’s not all doom and gloom, and international efforts are under consideration. In October 2022, NASA’s DART mission will send a spacecraft to collide with a small asteroid (not a risk to Earth) and measure the resulting change in its trajectory. If successful, this could be an avenue for future, more capable missions.

The movie ends with a motley crew of rich and powerful humans, including the US president and the creepy tech billionaire who wanted to mine the comet, escaping Earth in a spaceship until, after hibernating in space for 27,000 years, they land on an Earth-like planet where, ironically, dinosaur-like creatures roam free. If the dinosaurs on Earth hadn’t been wiped out 66 million years ago by a large asteroid, giving a chance to early mammals, we wouldn’t be here. So, let’s consider the positive. In Colliding Worlds, I stress that collisions can be constructive too. We owe our existence to a random impact 66 million years ago, and maybe it was the multitude of early impacts that seeded the Earth with the ingredients for life. But all the same, now we’re here, and just in case, do look up!

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The tree of life and the table of the elements

Darwin’s tree of life and Mendeleev’s periodic table of the elements share a number of interesting parallels, the most meaningful of which lie in the central role that each plays in its respective domain. 

Darwin’s tree of life, incidentally the only diagram of which appears in his book The Origin of Species, is a sketch of the central idea that all animal species have a common descent, much like members of an extended family can be displayed on a genealogical tree. Mendeleev’s periodic table is likewise the central icon for chemistry and serves to summarize and classify all the elements, the ways in which they show similarities among themselves, and how they react and bond with other elements.

Even more importantly, perhaps, is the fact that almost all subsequent developments in biology and chemistry can be seen as attempts to flesh out the ideas of Darwin and Mendeleev, respectively, and to provide an explanatory mechanism for their discoveries in each case. The parallel developments of the fields of evolutionary biology and modern chemistry illustrate the way that scientific discoveries begin as observations and systematizations and eventually lead to detailed explanatory theories that feature newly discovered scientific entities—such as the DNA molecule in 1953, in the case of biological evolution, and the electron in 1897, explaining the grouping of the chemical elements. The overall nature of the process appears to be largely the same, irrespective of the details of the particular branch of science in question. 

Establishing the theories

The tree of life

Evolution was in the air long before Darwin. His grandfather, Erasmus, mused about evolution in his book Zoonomia 1794 and 1796, while Lamarck presented a formal theory of evolution in 1801. The anonymously authored and widely read “Vestiges of the Natural History of Creation”, first published in 1844, speculated on the transmutation of species. None of these precedents truly anticipated Darwin, but all showed that evolution was on peoples’ minds.

Alfred Russell Wallace was the only substantive rival to Darwin’s priority and who clearly defined natural selection as the mechanism that causes evolution in his 1858 essay. Like Darwin, he invokes Malthus’ essay on population growth, Spencer on the “struggle for existence” as the ultimate brake on population growth, and the selective survival of individuals better suited to the struggle as the ultimate cause of evolution. He invokes the “tree of life” as a conceptual model for how life diversifies over time and abstracts Darwin’s argument that the fossil record and the distribution of living organisms preserve the history of how life changed over time and space. However, it seems Wallace’s essay was too brief to make a strong impression.

More to the point, the impact of the publication of On the Origin of Species in 1859 was like a tidal wave that swept away all that came before it. Darwin’s book was more than 20 times longer than the combined length of Wallace’s earlier essays. With that length came an argument that was far more wide-ranging, comprehensive, and convincing. Wallace’s essays were suggestive, but Darwin’s book was a complete argument for evolution as the unifying concept for all of the life sciences.   

The periodic table of elements

Mendeleev’s great discovery of the periodic table was presented to the world in 1869 at a meeting of the recently formed Russian Chemical Society. Like Darwin, Mendeleev also wrote a very influential book, The Principles of Chemistry, which helped to propagate his ideas further afield. As in the case of most scientific discoveries, many other scientists—such as De Chancourtois, Newlands, and Lothar Meyer—had arrived at earlier precursors to the periodic table of the elements but none of them achieved the kind of lasting success that Mendeleev did.

This fact is generally believed to be due to a number of successful predictions that Mendeleev made about the existence of new elements that were eventually discovered and that had almost exactly the properties that Mendeleev had foreseen. Even in his first published table of 1869, Mendeleev clearly predicted the existence of three new elements, which he stated would have atomic weights of 44, 68, and 72, respectively. Within a period of 15 years all three of these elements—subsequently named gallium, germanium, and scandium—were indeed discovered and found to have atomic weights of 44, 69.2, and 72.3. Mendeleev’s theory provided genuine predictions in the temporal sense and numerous retrodictions or rationalizations of already known chemical facts.

Challenges to the theories

It is also interesting to examine how the tree of life and the table of the elements faced a number of challenges during their 150 year-plus development.

The tree of life

Darwin convinced a critical mass of people that evolution was real, but not that natural selection caused evolution. Natural selection requires laws of inheritance and Darwin’s conceptual model of inheritance was wrong. Darwin invoked artificial selection as an explanation for how inheritance and evolution work. In his review of the Origin, Fleeming Jenkin, an engineer from the University of Edinburgh, proved with a mathematical model that artificial selection and “blending inheritance” could not produce evolution.

Mendel’s laws of inheritance appeared in 1865, between the publication of the first and last editions of the Origin, but Darwin never learned of his work. These laws would ultimately redeem Darwin but when they were re-discovered in 1900, they were used against him. It was not until the 1930s that Mendelian inheritance, in which copies of genes can skip a generation and reappear unchanged, was reconciled with natural selection and Darwin’s concept of inheritance. 

Given these objections, why was Darwin ultimately successful? The success of any theory is determined by how well it accommodates and integrates available knowledge and its ability to make predictions. Darwin’s near-term success was dominated by accommodation, or his unification of the life sciences under a single explanatory framework.  

The periodic table of elements

Just like Darwin’s theory of common descent, Mendeleev’s table faced a number of challenges but none of them seem to have been as serious as those faced by Darwin.

One of the first hurdles that Mendeleev’s system had to overcome was the fact that ordering the elements according to their increasing atomic weight, as he did, resulted in two pair reversals. For example, the element iodine has a lower atomic weight than that of tellurium, which would lead one to think that iodine should be placed before tellurium along one of the rows of the table. But doing so would be chemically inconsistent; the elements must be “reversed” if the table is to make chemical sense. The discoverers of the periodic table, Mendeleev included, made the required reversal because they were primarily interested in chemical similarities rather than upholding the notion of strictly increasing atomic weights. Mendeleev was even bolder in that he believed that the then-known atomic weights of one or both of these elements were mistaken. In the case of this prediction, Mendeleev was later shown to be incorrect by the English physicist Henry Moseley who discovered that the elements are ordered more effectively on the basis of their nuclear charges (or atomic number) rather than their weights.

A second challenge erupted in the year 1894 when a new and highly unreactive gas named argon was isolated by William Ramsay and colleagues at University College in London. Placing this new element into the periodic table was made especially difficult because its atomic weight was 40 and another element, namely calcium, already existed with precisely the same atomic weight. Mendeleev tried to meet the challenge by claiming that the new gas consisted of a triatomic nitrogen molecule. Here, too, Mendeleev was shown to be mistaken. After five years of much controversy regarding the status of argon, Ramsey himself realized that a new column could be added to the right-hand edge of the periodic table to house neon, as well as a number of other noble gases that were discovered in his laboratory in rapid succession. 

The periodic table escaped being refuted and indeed was strengthened by the realization that it was capable of accommodating these new elements successfully. Mendeleev, never one to shy away from proclaiming his achievements, was among the first to embrace Ramsay’s newly created group of elements.  

Differences

There are clearly similarities but also substantial differences between the case of Darwin’s tree and Mendeleev’s table. One is surely that Darwin’s theory concerns diachronic changes, meaning those that occur across time while the periodic table is of the synchronic type, in that the elements do not evolve over the time period over which they are being compared in modern chemistry. Even more obviously, perhaps, biological systems are orders of magnitude more complex than atoms are and subsequently their behavior is, not surprisingly, less predictable. In the same way, theories concerning biological systems are expected to be more controversial and more subject to internal challenges than is the case of chemical systems.   

Rather interestingly, the elements themselves are believed to all have evolved from the first or primordial element of hydrogen which has just one proton, somewhat analogously to a single-celled organism in the biological realm. However, the evolution of the elements of this kind has taken place over many millions of years and requires gargantuan energies that in most cases can only occur at the center of massive stars or in the course of a supernova explosion.    

Finally, whereas we have classified Darwin’s discovery as a theory, this is not the case for the periodic table. Instead the periodic table is more akin to an uninterpreted classification scheme for the elements that is in need of a theoretical explanation, and one that was duly provided by the development of quantum mechanics in the 20^th century. 

Darwin’s tree and Mendeleev’s table represent momentous discoveries which continue to drive the development of modern biology and chemistry respectively. Surprisingly, perhaps, the more fundamental science of physics seems to lack any such iconic and all-encompassing unifying motif. 

_{Featured image: Photo of Mendeleev from Wikimedia Commons; Photo of Charles Darwin also from Wikimedia Commons.}

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The top 10 science blog posts of 2021

From the evolution of consciousness to cosmic encounters, the Brain Health Gap to palliative medicine, 2021 has been a year filled with discovery across scientific disciplines. On the OUPblog, we have published blogs posts showcasing the very latest research and insights from our expert authors at the Press. Make sure you’re caught up with the best of science in 2021 with our top 10 blog posts of the year:

1. Why did evolution create conscious states of mind?

“When we open our eyes in the morning, we take for granted that we will consciously see the world in all of its dazzling variety. The immediacy of our conscious experiences does not, however, explain how we consciously see.”

Read the blog post from Stephen Grossberg, author of Conscious Mind, Resonant Brain: How Each Brain Makes a Mind, to learn how—and why—we have evolved to consciously see.

Read the blog post ->

2. The neuroscience of human consciousness

How can the study of the human brain help us unravel the mysteries of life? Going a step further, how can having a better understanding of the brain help us to combat debilitating diseases or treat mental illnesses?

On this episode of The Oxford Comment, we focused on human consciousness and how studying the neurological basis for human cognition can lead not only to better health but a better understanding of human culture, language, and society as well.

Listen to episode 63 on The Oxford Comment ->

3. 10 books on palliative medicine and end-of-life care

Each year an estimated 40 million people are in need of palliative care, 78% of whom live in low- and middle-income countries. This reading list of recent titles can help you to reflect on palliative medicine as a public health need.

Explore the reading list ->

4. Can what we eat have an effect on the brain?

Food plays an important role in brain performance and health. In general, the old saying, “a healthy mind in a healthy body,” is still very valid, and the overall positive results on cognitive ability of entire diets can be summarised with: “what is good for your heart, is also good for your brain.”

This blog post from review co-author Bo Ekstrand discusses the role of diet in key areas of brain development and health from the findings published in the journal Nutrition Reviews.

Read the blog post ->

5. What can neuroscience tell us about the mind of a serial killer?

Serial killers—people who repeatedly murder others—provoke revulsion but also a certain amount of fascination in the general public. But what can modern psychology and neuroscience tell us about what might be going on inside the head of such individuals?

Read the blog post from the John Parrington, author of Mind Shift: How Culture Transformed the Human Brain, to learn more about recent neuroscience studies investigating serial killers’ minds.

Read the blog post ->

6. Does “overeating” cause obesity? The evidence is less filling

The usual way of thinking considers obesity a problem of energy balance. Take in more calories than you expend—in other words, “overeat”—and weight gain will inevitably result. The simple solution, according to the prevailing Energy Balance Model (EBM), is to eat less and move more. New research shows that viewing body weight control as an energy balance problem is fundamentally wrong, or at least not helpful, for three reasons.

Discover the three reasons in this blog post from David S. Ludwig, co-author of new research published in The American Journal of Clinical Nutrition.

Read the blog post ->

7. Earth’s wild years: the creative destruction of cosmic encounters

Contrary to common sense, cosmic collisions are not all about destruction and death. It appears entirely possible that collisions could have been beneficial to the development of conditions suitable for the formation of first organisms—our distant relatives—on Earth. What do we know about these early cosmic catastrophes?

Learn about the innumerable challenges facing the research of early cosmic events by reading the blog post from Simone Marchi, author of Colliding Worlds: How Cosmic Encounters Shaped Planets and Life.

Read the blog post ->

8. What if COVID-19 emerged in 1719?

We’re often told that the situation created by the attack of the new coronavirus is “unique” and “unprecedented.” And yet, at the same time, scientists assure us that the emergence of new viruses is “natural”—that viruses are always mutating or picking up and losing bits of DNA. But if lethal new viruses have emerged again and again during human history, why has dealing with this one been such a struggle?

In this blog post, Lesley Newson and Peter Richerson, authors of A Story of Us: A New Look at Human Evolution, consider what makes our “cultural DNA” unique and how the story of COVID-19 would have been very different had it emerged 300 years ago.

Read the blog post ->

9. Closing the brain health gap: addressing women’s inequalities

There is a clear sex and gender gap in outcomes for brain health disorders across the lifespan, with strikingly negative outcomes for women. The “Brain Health Gap” highlights and frames inequalities in all areas across the translational spectrum from bench-to-bedside and from boardroom-to-policy and economics.

Read the blog post to learn how closing the Brain Health Gap will help economies create recovery and prepare our systems for future global shocks.

Read the blog post ->

10. The case for readdressing the three paradigms of basic astrophysics

A long-held misunderstanding of stellar brightness is being corrected, thanks to a new study published in the Monthly Notices of the Royal Astronomical Society based on International Astronomical Union (IAU) General Assembly Resolution B2.

Learn about the key findings in this blog post from Zeki Eker, lead author on the study published in Monthly Notices of the Royal Astronomical Society.

Read the blog post ->

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How research abstracts succeed and fail

The abstract of a research article has a simple remit: to faithfully summarize the reported research. After the title, it’s the most read section of the article. It’s freely available on the publisher’s website and in online databases. Crucially, it makes the case to the reader for reading the article in full. 

Alas, not all abstracts succeed. 

Some take the notion of abstraction to extremes. This example is from a physics article:

Unitarity and geometrical effects are discussed for photon-photon scattering.

It has just ten words. Fortunately, most abstracts say rather more, though it’s possible to say too much. The next example, from a geology article, has over 370 words. It starts:

Diagenesis of the Holocene-Pleistocene volcanogenic sediments of the Mexican Basin produced, in strata of gravel and sand, 1H₂O- and 2H₂O-smectite, kaolinite, R3-2H₂O-smectite (0.75)-kaolinite, R1-2H₂O-smectite (0.75)-kaolinite, R3-kaolinite (0.75)-2H₂O-smectite and R1-1H₂O-smectite (0.75)-kaolinite. Smectite platelets…

It continues in a similar vein for a further 350 words, accumulating more and more detail. The reason for the work is hinted at, but only becomes clear in the full article, at which point it’s too late.

Some abstracts introduce citations to previous research to provide background, contrary to the expectation that abstractions stand alone. In practice, citations can block the reader’s progress, as in this example from a remote-sensing article: 

The purpose of this paper is to extend the stationary stochastic model defined in [1] to a time evolving sea state and platform motion.

The reference pointed to by “[1]” isn’t attached to the abstract, and the source article is obviously elsewhere. Yet without it, the rest of the text is difficult to appreciate. Similar problems can occur with abbreviations explained only in the article.

Some abstracts confuse their remit by summarizing the paper rather than its content. The shift to meta-reporting can lead to uninformative boiler-plate text. This example is from a medical education article:

Implications of these results are discussed.

It’s uninformative because readers already know that most research articles contain a discussion section where, by definition, results and their implications are discussed.

Some abstracts expand their remit to include personal research plans. This example is from a clinical article:

We plan to investigate why general practitioners are not complying with the pathway.

It’s common to find research aspirations in internal reports and in research grant applications, where they have a specific function. But published in an abstract, they can present a reader working in the same area with a difficult choice.

Some abstracts expand their remit even further with a self-evaluation of the research. This example is from a finance article:

We believe this study will benefit academics, regulators, policymakers and investors.

The problem is that the reader may not see these pronouncements as truly impartial, with the result that the authority of the article is weakened, not strengthened.

Abstracts can of course fail in many other ways, for example, omitting caveats, adding new information, exaggerating certainty, or providing no more than an advertisement, a piece of puffery.

How to write a successful abstract

In the light of all this, what should go into a successful abstract? Some clinical journals settle the matter by imposing a structured format. But most journal and conference proceedings don’t and may offer little or no detailed guidance to the author, who may be left confused about what’s needed.

One starting point is to think of the abstract not as a condensed version of the paper that preserves the original structure and proportions, but as a mini- or micro-paper in its own right, with certain basic elements:

• the context or scope of the work
• the research question or other reason for the work, if relevant
• the approach or methods
• a key result or two
• a conclusion, if appropriate, or other implications of the work.

Naturally the weight given to each element depends on the research—whether it’s experimental, observational, or theoretical, and whether the expected audience is general or specialized. How much to write about each element is then a balance between including detail and retaining the reader’s interest. 

Within those constraints, it’s important to identify any critical assumptions, non-standard methods, and limitations on the findings so that the scope and potential application of the research is clear. The reader shouldn’t discover on reading the article that the abstract was misleading.

Here’s an example of a well-written abstract from a neuroscience article: 

An unresolved question in neuroscience and psychology is how the brain monitors performance to regulate behavior. It has been proposed that the anterior cingulate cortex (ACC), on the medial surface of the frontal lobe, contributes to performance monitoring by detecting errors. In this study, event-related functional magnetic resonance imaging was used to examine ACC function. Results confirm that this region shows activity during erroneous responses. However, activity was also observed in the same region during correct responses under conditions of increased response competition. This suggests that the ACC detects conditions under which errors are likely to occur rather than errors themselves.

From C. S. Carter et al., Science 1998, 280, 747-749. Reprinted with permission from AAAS.

Successive sentences describe the context, the reason for the work, the methods, some results, and an implication. According to Elsevier’s Scopus database, the article has been cited over 2,500 times.

Encapsulating a body of research so effectively usually takes repeated rewriting. The timing, though, can be a challenge, since the abstract is often prepared last, when the main sections of the paper have found a settled form. It then risks being rushed while material is assembled for submission for publication. 

Despite these pressures, the abstract needs as much attention as any other section of the paper. After all, if it doesn’t do its job, the reader may turn to other abstracts that do. And the published article may languish unretrieved and unseen, waiting in vain for the recognition it deserves.

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A cosmic census

A new census of the Universe will allow scientists to understand more about how galaxies are born, age, and die. The millions of galaxies that have been painstakingly catalogued come in many shapes and sizes and this new work shines a light on every variety that we can see.  

The new measurements, which were published in Monthly Notices of the Royal Astronomical Society, will allow many other people to look for unusual and new types of galaxy hidden within the data. It will also help them to look at whole “populations” to better understand how they evolve. It has already been used to find interesting rare galaxies and to understand how and why they stand out from the crowd. 

The international group of scientists, led by astronomers working with Professor Seb Oliver at the University of Sussex, decided to create the Herschel Extragalactic Legacy Project. This project was set up to understand images from the Herschel Space Observatory; a huge telescope in space which measured the far infrared light that is emitted from the cool dust in galaxies. 

They brought together observations from across the electromagnetic spectrum; from the bluest light emitted by hot young stars to the reddest which comes from cool dust. The team then used all this information to weigh galaxies, measure how far away they are, and count how many stars are being born within them. 

Usually scientists use a small area of the night sky, but this new work brings together all of the best-studied regions allowing them to search through an unprecedented volume of the Universe. The more sky that we observe, the more rare objects we can find in order to understand all types of galaxies. One unusual object already found in the data was a giant black hole discovered only 1.4 billion years after the Big Bang.

By bringing together public data from many different telescopes and making sure everything is freely available, the team believe it will also open up data to more groups and maximise how many people can get involved. First author Raphael Shirley said: “it will be like a digital library of galaxies where anyone can take out a book on any galaxy that can be seen.” He is keen that this “open science” practice will be more widely adopted as it also means the public can use it. “Maybe there is an intrepid school student who might find an exciting new discovery hidden amongst the millions of galaxies that has been missed by the professionals.”

Featured image: © 2021, Ève Barlier

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The case for readdressing the three paradigms of basic astrophysics

A long held misunderstanding of stellar brightness is being corrected, thanks to a new study published in the Monthly Notices of the Royal Astronomical Society based on International Astronomical Union (IAU) General Assembly Resolution B2.

“Stars have been observed for millennia and were crucial in navigating across deserts, seas, and oceans,” noted Zeki Eker, the study’s lead author. Stars are even more crucial today for guiding us to the secrets of universe. This is, however, assured only if their radiating power is measured correctly.

Brightness differences as small as hundredths—even thousandths—of magnitude is measurable today since the advent of Charge Coupled Devices, or CCDs, in space-born observations. There were only visual magnitudes until photography met telescopes at the end of the nineteenth century. Soon sensitivity difference in photographs was discovered; as soon as photo-plates like human eyes were invented, the two kinds of magnitudes, blue (photographic) and visual, started to be used. Today, there are many filters to see how a star shines at various colours, including those the eye cannot see. Filtered magnitudes are calibrated by a star called “Vega,” the zero point for all magnitudes. Measuring the magnitude of a star at various filters is needed for obtaining its surface temperature. Its absolute size or distance and angular size are also needed to obtain its absolute power: luminosity, energy radiated per second (Watt) from a star. But, these are only accessible in certain types of binary stars. Astronomers had to find a way to assign luminosity to each star, in the same way as light bulbs sold in markets would be useless if the power (Watt) is not written on them.

By the end of 1930s, a new kind of magnitude with an arbitrary zero point flourished. Unlike blue and visual, this new magnitude, named bolometric, represents the luminosity of a star, including all its colours—visible and not visible. This new magnitude is for calculating the luminosity of a star in one step, but it is not observable; no telescope could observe total radiation of a star including gamma-rays, X-rays, UV, visible, infrared, and radio at once. Bolometric magnitudes, therefore, were computed first from known luminosities of a very limited number of binary stars. Because luminosity is more than one of its parts, called visual luminosity, the idea that “bolometric magnitudes should be brighter than visual magnitudes” entered astrophysical textbooks and literature as the first paradigm and went unchallenged for 80 years.

The difference between bolometric and visual magnitudes is called bolometric correction (BC). BC is a useful concept: if it is added to a visual, the bolometric magnitudes can be obtained, and so there is no need to observe a star of various colours at once. Using the limited number of existing BC as a calibrating sample, many tables are published to give BC as a function of stellar effective temperature, a parameter available from multicolour photometry, simply from blue and visual magnitudes.

BC is like a missing part; when added to visual magnitude, the bolometric magnitude is obtained. The magnitude scale is in reverse order, like first class is more valuable (brighter) than the second, and second is brighter than the third, so on. That is, the smaller the number the brighter it is. Therefore, the BC values were recognized as negative numbers. Consequently, “the BC of a star must be negative” became the second paradigm.

Inconsistencies between paradigms become obvious if one pays attention to the third paradigm; the arbitrariness attributed to the zero point of BC scale. Studying BC tables published, one realizes that there are two groups: a group of BC tables with all negative numbers, and a group of BC tables with mostly negative but also containing a limited number of positive. Obviously, the first group of producers took the arbitrariness granted and felt free to change computed BC in such a way that no single positive BC was left in the table in order to avoid dilemmas; while the other group trusted their calculations by keeping them as calculated and did not care about the paradigms. It is obvious that both cannot be right: either one of them is wrong. Another inconstancy is that there are occurrences that the same star is found to have different bolometric magnitude and luminosity, which is not true, among the scientists who use different BC tables with different zero point.

A solution was suggested by the IAU General Assembly in 2015, where the zero point of bolometric magnitude scale is fixed by a convention of worldwide astronomers and astrophysicists, called 2015 IAU General Assembly Resolution B2. Apparently, the established paradigms must be very strong, however, as even after the resolution published, an article appeared in one of the major journals still defending arbitrariness of the zero point of BC scale. IAU’s solution, therefore, stayed hidden for six years. Finally, proving that fixing the zero point of bolometric magnitudes has a firm consequence, the zero point of BC scales must also be fixed by a zero-point constant equal to the difference of the zero-point constants of bolometric and visual magnitudes. This firm positive zero-point constant of BC scale, on the other hand, requires a limited number of positive BC. So, “bolometric magnitudes should be brighter than, visual magnitudes” is not necessarily true.

Now, it is time to remove those paradigms from the textbooks, teaching minds, and researchers. This is needed urgently for consistent astrophysics as well as achieving accurate standard BC and stellar luminosities. Accurate standard stellar luminosities are needed not only by stellar structure and evolution theories, but also by galactic and extragalactic astrophysics to search amount of luminous matter in galaxies, to determine galactic and extragalactic distances, and thus even it could be useful for recalibrating Hubble law and restudying cosmological models of universe with better galactic and extragalactic luminosities, because galaxies are made of stars. This is how stars would lead us to the secrets of the universe.

Featured image by Faruk Soydugan

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The mermaid in the fishbowl: the rise of optical illusions and magical effects

The nineteenth century saw the publication of several books explaining how magical effects and spectral appearances could be performed using the science of optics. It started in 1831, when Sir David Brewster (famed for his discovery of Brewster polarization and inventing the kaleidoscope) published Letters on Natural Magic. In this book, Brewster showed how to produce images of ghosts using partially silvered mirrors and by using a magic lantern to project images onto screens or onto clouds of vapor.

Brewster’s work inspired generations of stage magicians including Henry Dircks and John Henry Pepper, who eventually patented what came to be called the “Pepper’s Ghost” illusion. Pepper’s Ghost, impressive as it was, barely scratched the surface of what was possible using optical engineering. It’s a little surprising that more sophisticated optical tricks did not appear until the twentieth century, considering that the rules of imaging had been derived well over two hundred years earlier. But in 1909 something new and impressive burst forth in its fully formed glory. Antoine Francois Sallé, an engineer living in Paris, was granted a United States patent on a “Means for Producing Theatrical Effects” (US 922,722).

Sallé’s holographic invention

Sallé’s invention used the Newtonian rules of imaging, which hold both for lenses and for curved mirrors. Under the correct circumstances, one can create a “real” image (through which light rays pass, as opposed to a “virtual” image, which light rays do not pass through; if you place a screen where a real image is located, it will show up on the screen—a virtual image will not) that is the same size as the object, or magnified, or reduced, depending upon the relative positions of the lens or mirror, the object, and the focal length of the optic. The image will, however, be upside-down, but this can be corrected with an image inverter.

Using mirrors has advantages over using lenses to work this trick. There is no separation of colors as with a simple lens. In addition, a curved mirror can be used to cover a larger angular region, letting the image be viewed farther off-axis than can be seen with a lens, unless a very large and expensive lens is used. The result is that an image produced using a curved mirror can look much more convincingly real, and over a larger range of angles, than an image produced by a lens. With a subject that is brightly illuminated, the result was that a viewer on the other side of the apparatus saw a perfect reduced image of the subject. If the subject was a person, it could walk around and interact with things. Moreover, the image appeared to be three-dimensional, since each eye of the observer saw the image from a slightly different angle that provided a stereoscopic effect. The word wasn’t yet being used in this context, but a later generation would describe such images as holographic—perfect miniature 3D images of a moving person.

Sallé licensed his invention throughout Europe, and it was displayed in a number of places, including the Crystal Palace in London, the Werkbund Exhibition in Cologne, Germany, and the 1914 Jubilee Exposition in Norway. It was also exhibited in a limited way in the United States at the Steel Pier in Atlantic City and at the St. Francis Hotel in San Francisco, but the image’s bigger splash in the United States was yet to come.

Tanagra Theater reaches the United States

In 1922, the German Edward B. Schreyer bought the North American rights to Sallé’s patent, moved to the United States, and set up the Tanagra Theater Company at 229 West 42^nd Street, in the heart of New York’s Theater District.

Schreyer arranged for a Miniature Fashion Show at the 71^st regiment Armory, featuring miniaturized models wearing the latest clothes from the Bijou Dress company of Fifth Avenue. Meanwhile, the illusion was also on display at Coney Island, New York. A behind-the-scenes description (which wasn’t quite accurate) of how it worked was published in Huge Gernsbach’s popular technology magazine Science and Invention.

At about the same time, a production of Karel Čapek’s science fiction play R.U.R. (Rossum’s Universal Robots) was staged in Berlin and Vienna with sets designed by Frederick Keisler, who had seen the effect at the Werkbund Exhibition eight years earlier and incorporated it into the design for the show. Sallé’s effect, now called Tanagra Theater (because the miniature images resembled the tiny figurines that had been unearthed in Tanagra in Greece), had finally made the big time.

The wide use of the Tanagra Theater illusion for advertising and for displays in front of small groups of people is due to the technical limitations of the illusion. Although it provides a perfect miniature illusion, this can only be viewed over a small range of angles, which are limited by the size of the mirror. If you can’t see the mirror, then you can’t see the image.

Tanagra Theater is inherently made for small, close-packed audiences. You can have a situation where you limit the viewing time of your audience and keep moving them through so that everyone gets a view, paying for a necessarily time-limited seat. Or you can use it for advertising, luring viewers in with the promise of seeing something interesting, but which repeats the same things after a short period so that you get high turnover. Tanagra Theater was limited to short ads or to peep show experiences. Kiesler’s use of it in a stage show has to be seen as a stunt, since most of the audience would have been unable to see the miniature image at all.

Peep shows and nude exhibitions

Patents at the time only had a twenty-year lifespan. By 1928, Sallé’s original patent had expired and anyone was free to use the invention without having to pay royalties. Not surprisingly, the field opened up, with many people exploiting the liberated technology. Anthony “Tony” Sarg was already famous as a puppeteer, children’s book artist, and producer of unusual artworks. He is credited with reviving interest in puppets and marionettes. His huge inflatable sculptures were a hit at his Cape Cod studio, and he eventually filled them with helium, effectively creating the Macy’s Thanksgiving Parade. Possibly because of his love of puppetry, he experimented with the Tanagra Theater. He installed a Tanagra Theater in the display window at Filene’s Department store in downtown Boston. Like Schreyer’s Tanagra Theater, it was used for miniature fashion shows.

Later he created The Car in the Clouds, an advertisement for the Ford Motor company that featured a miniature woman in a miniature latest-model Ford car that appeared to be flying over a landscape. There was a microphone hidden in the steering wheel that connected to speakers outside, so the woman could hear questions from viewers and reply. The Car in the Clouds showed up at the Ford pavilion at the 1933 Century of Progress Exposition in Chicago, the 1937 Great Lakes Expo in Cleveland, and at the Steel Pier in Atlantic City (where there was a long-running automobile display).

Others discovered the extremely powerful draw of sex and started exhibiting miniature nude women using the Tanagra apparatus. In 1931, the 365 Club in San Francisco (later Bimbo’s 365 Club) began showing Dolphina, the mermaid at their bar. Dolphina didn’t have a fish tail, but she was naked. Being reduced to fantasy size and clearly untouchable probably helped keep the show from being shut down, but this was the golden age of burlesque and the Depression, and public mores had loosened somewhat—Sally Rand’s Bubble Dance and Fan Dance were the hit of the 1933 Exposition. Dolphina still appears at Bimbo’s today.

Naturally, there were imitators. Billy Rose’s Casino de Paree in New York featured its own nude mermaid. When that nightclub shut down after a very short life, other nightclubs in New York started featuring them. There appears to have been a Fishbowl Mermaid at the 1933 Exposition, as well. The 1937 Great Lakes Exposition featured a “Little French Nudist Colony” that lived up to its name, literally.

A traveling show called the “French Follies” or the “Parisian Spices” toured the United States. As an enticement, they featured a Mermaid in a Bowl in the theater lobby. This might not always have been a nude mermaid, but the one displayed in Washington, D.C. in 1935 apparently was. The Daughters of the American Revolution took offence and protested to the theater owners. They responded by putting a “strawberry colored” bathing suit on the mermaid.

The Fishbowl Mermaid

A Miniature Mermaid display, compact and transportable enough to be displayed in a theater lobby, sounds like something that wouldn’t work with the full Tanagra Theater. It might work with Bostock’s negative lens, but it’s likely that it was around this time a third major method of producing the illusion debuted. This is likely the same one that later ended up being used by traveling carnivals. It’s very simple and uses very inexpensive and easy-to-obtain components, rather than expensive and hard-to-fabricate curved mirrors or large lenses.

The fishbowl in which the mermaid appears is also the optical element responsible for the illusion (see diagram below). The bowl is filled with water. Better still, it is filled with clear mineral oil, which won’t let algae grow in it and won’t evaporate. This fluid-filled spherical bowl acts like a lens. It’s not a perfect lens, because it doesn’t have constant power across its face and has lots of chromatic aberration. But that’s okay, because it does make the mermaid appear to be truly underwater. The bowl sits atop a large rectangular box. There’s a large mirror behind the bowl, angled downward at 45 degrees, directing up light rays from inside the box.

Inside the box is a woman dressed as a mermaid, and maybe some undersea props. Her image is upside-down, but that’s not a big deal—she’s lying down and can lie with her feet in either direction, but appears to be upright. Her image is actually projected forward beyond the fishbowl, but most customers won’t notice—her image is a line with the fishbowl, so she appears to be in it. If you want to make the illusion perfect, put a second fishbowl in front of the first one, into which her image is projected (amazingly, this innovation isn’t documented until it showed up in a 1978 patent).

The proliferation of nude illusions bothered one entrepreneur who had worked at Billy Rose’ nightclub and had seen the nudes in 1933. Mike Todd felt that this use limited the potential audience. Children were the ideal targets for this technology, and he proposed using Santa Claus as the miniaturized subject (wasn’t he, according to Clement Clark Moore, “a right tiny old elf” with “eight tiny reindeer”? How else could he slip down chimneys?). This individual re-invented Bostock’s device, using war-surplus lenses bought for pennies on the dollar. Like the woman in The Car in the Clouds advert, he could speak to the audience using a telephone on a stand at his side. It was granted a patent and licensed to major department stores at Christmas in the big cities and made a small fortune for its creator. He was later to become a film producer and the driving force behind the Todd-AO widescreen process.

Interest in the illusion fell off after the second World War. The novelty was gone. The Girl in the Fishbowl still showed up at Bimbo’s and a few other nightclubs as an eccentricity. The Fishbowl Mermaid became a fixture of traveling carnivals and freak shows. Carnival operators could learn how to build one from the plans in “Brill’s Bible”, the mail-order guide for carnies.

Ultimately, the Tanagra Theater illusion suffered from its inability to play to a large enough audience to justify its expense. In many ways, Tanagra Theater resembles a much later optical effect—3D holographic movies. Such movies exist and are restricted to small sizes (being limited by the size of the holographic film) and small audience size, and limited range. Holographic movies, like Tanagra Theater, produce amazing 3D images, but they are expensive to make, have limited interest, and can only play to a small “house”. Both technologies, unable to pay their own way, have been reduced to the status of curiosities.

Featured image via Wikimedia Commons

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Earth’s wild years: the creative destruction of cosmic encounters

We earthlings enjoy the spectacle of shooting stars: small fragments of asteroids and comets that burn in sudden flashes upon entry in the Earth’s atmosphere. The largest of these fragments pose a limited threat to us as their mid-air blasts can produce local damage to buildings and infrastructures. Larger events are increasingly rarer, but their consequences can be devastating on a global scale. Fortunately, we do not have first-hand experience of such events, but the extinction of the dinosaurs by a collision with a 10-km asteroid about 66 million years ago is etched in our imagination. Planetary scientists are finding immense cosmic collisions were common during Earth’s first billion years. Compared to the most energetic of these early events, the dinosaur-killing collision was a modest firecracker.

At the dawn of the Solar System, about 4.6 billion years ago, collisions were responsible for the growth of the Earth and the formation of the Moon; later, they modulated Earth’s evolution by enriching the chemistry of its atmosphere and oceans. New worlds emerged from the upheaval of cosmic catastrophes, and our planet as we know it today may be the result of random events that occurred billions of years ago. The planet could have followed innumerable other paths, in unpredictable directions; a multitude of possible Earths could have emerged from the clamour of early collisions. And all the while Earth was reshaped by these events, life was taking a toehold on our planet, some 4 to 3.5 billion years ago. Contrary to common sense, cosmic collisions are not all about destruction and death. It appears entirely possible that collisions could have been beneficial to the development of conditions suitable for the formation of first organisms—our distant relatives—on Earth. What do we know about these early cosmic catastrophes?

The research of these distant events faces innumerable challenges. We estimate the Earth was fully formed by 4.5 billion years ago, and yet its surface rocks are much younger. There are only a few scattered localities exposing rocks older than 3 billion years, and the oldest known terrestrial rocks date back about 4 billion years. Scientists—it may seem—are subject to an unfair punishment suitable for Dante’s Inferno: the most accessible planet to study in the Universe, our Earth, has erased its early history. But not all is lost. Clues of ancient collisions can be found elsewhere in the Solar System, pretty much everywhere we look. Scars of collisions are visible in impact craters found on nearly any solid surface in the Solar System, from our Moon to asteroids and other planets. Mars’ barren surface, for instance, is sculpted by countless impact craters, some of which may have hosted ancient lakes. Small pieces of extraterrestrial rocks that serendipitously land on Earth—called meteorites—also record catastrophic collisions that have shuttered their progenitor asteroids at the dawn of the Solar System.

Should we surmise the Earth experienced similar cosmic catastrophes in its wild years? Certainly. Scientists are able to trace the flow of key atoms in a restless Earth to reveal traces of ancient collisions. Among the various elements, there are a few such as gold and platinum that exhibit a strong affinity with iron, and they are aptly known as highly iron-loving elements. So, we can expect that the Earth’s mantle and crust should be strongly depleted in these highly iron-loving elements, as they would have followed the fate of most of the Earth’s iron, which sank to the core during the early stages of the planet’s formation. Yet we find these elements in the Earth’s crust. Why? While several theories have been put forth, the most likely explanation is that they were delivered by ancient cosmic collisions. It is a rather intriguing thought that the gold ring I wear while typing these words may not have existed without ancient cosmic collisions!

We still do not know the number and magnitude of these ancient collisions, nor their consequences for the nascent Earth, but it is estimated that some of the largest bodies may have been up to 3000 km in diameter. One such collision would have been large enough to wipe out the whole Earth’s surface within hours, either by direct disruption of the impact or by fall back of molten rocks spread in orbit by the energy of the event. It does appear inevitable that during the Earth’s wild years, the first billion years or so, collisions were capable of forever transforming surface environments, and with them, the earliest forms of life. How much do we humans owe to these distant events? What form of life, if any, would have spurred on our planet without these random events? These questions underline the fascinating story behind the creative disruption of ancient cosmic collisions.

Featured image via Pixabay

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Extreme collision of stellar winds at the heart of Apep, the cosmic serpent

The stellar system known as Apep was recently discovered due to its spectacular and elegant spiral dust structure. This pinwheel pattern originates from two Wolf-Rayet stars located at its heart. Wolf-Rayet stars represent the very last stages in the life of the most massive stars, representing the phase of stellar life immediately before they collapse to produce a supernova explosion. In this case, Apep is strange as it is the by far brightest of such colliding-wind systems, especially at radio wavelengths.

To understand the origin of this surprising brightness, and unveil what was happening at the core of the spiral of dust, astronomers conducted radio observations of Apep with the Australian Long Baseline Array (LBA). This array combines data from ten radio telescopes spread around Australia and New Zealand, reaching a resolution that is sharp enough to identify a truck on the surface of the Moon when looking from the Earth.

By pointing all these telescopes to Apep, astronomers discovered the origin of all this radio emission: the light arises from an extreme shock produced by the collision of the two stellar winds. “The two Wolf-Rayet stars in Apep total 20 times the mass of the Sun, and exhibit winds of up to millions of kilometers per hour. When these two winds collide they produce a very strong and extreme shock, never observed in our Galaxy before. This shock is observed as a banana-shaped structure that emits brightly at radio waves,” says Dr Benito Marcote from the Joint Institute for VLBI ERIC, The Netherlands, who led the study.

The imaging of this region where the two winds collide allowed the astronomers to test the behavior of the stellar winds of these dying Wolf-Rayet stars. Given that the stars only spend a limited time in the Wolf-Rayet phase before their death in a supernova explosion, astronomers have confirmed that these systems must be very rare in our Galaxy. “Apep is the first system of its kind and we are now starting to understand how these stars may behave, the dynamics of their strong stellar winds, and how the enormous amounts of dust are produced in the wake of the wind collision,” says Dr Joe Callingham, of Leiden University and ASTRON, The Netherlands, who is the original discoverer of Apep and a co-author of the study. This dust, which is expelled out the system following the orbital motion of the two stars, is the responsible for the beautiful pinwheel spiral structure.

The two Wolf-Rayet stars in Apep are slowly dying. If the environment around the system is already significantly more extreme than any other known system involving two massive stars, astronomers expect this system to end its life in an extreme explosion. Extreme enough to make Apep the most likely system to produce a gamma-ray burst at its end—a very energetic flash of gamma-rays that to date has only been observed at cosmological distances, never in our Galaxy.

Featured image: Real images of the dust spiral seen in Apep in infrared and, right at its center, the region where the two stellar winds collide and emitting in radio (seen as the blue structure in the inset, where the two stars represent their real positions). Credit: B. Marcote & ESO/Callingham.

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Giant hidden black hole discovered only 1.4 billion years after the Big Bang

Black holes are some of the most bizarre objects in the Universe but their existence is a robust prediction of the general theory of relativity of Albert Einstein. The discovery by Roger Penrose in the 1960s was honored with the Nobel Prize in Physics in 2020, along with the more recent discovery of Andrea Ghez and Reinhard Genzel of a giant black hole at the center of our Galaxy with a mass millions of times that of the sun.

Scientists have known for some time that much larger black holes with mass billions of times that of the sun existed as early as a few hundred million years after the Big Bang. The processes that led to the formation of such giant black holes that power the well-known population of quasars so early in the history of the Universe remain a mystery to theorists.

Scientists have also suspected for some time that a much larger population of these ancient giant black holes may be hidden by clouds of gas and dust that circle the black hole in a toroidal structure. These black holes can only be identified by the glow of infrared radiation from the toroidal structure that hides them. An international team of astrophysicists have discovered such a hidden giant black hole in a galaxy that existed only 1.4 billion years after the Big Bang. Over the past few year, the team of scientists has pursued a project called Herschel Extragalactic Legacy Project or HELP that put together the data from a number of telescopes, including ESA’s Hershel Space Observatory and NASA’s Spitzer Space Telescope, which observed the cosmos at infrared wavelengths. Infrared astronomy is especially difficult as the observations need to be carried out from space using telescopes that need to be cooled to a temperature close to -270 degrees Celsius.

One of the first areas of the sky analyzed by the HELP team was the Cosmological Evolution Survey (COSMOS) field, which is one of the best studied regions of the sky with an area about ten times that of the full moon. The galaxy that hosts the black hole is barely visible even in the deepest image of the COSMOS field taken by the Hubble Space Telescope, which can only observe the optical and ultraviolet emission of galaxies. What made the discovery of this black hole possible is that fact that it is much brighter at infrared wavelengths.

What is exciting about this discovery is that the COSMOS field where the galaxy that hosts the black hole was discovered is only a very small part of HELP. The HELP survey covers an area of the sky which is about 600 times larger. The team estimate that when the analysis of all the HELP data is complete a lot more of these hidden black holes will be found. The team, which was led by Professor Andreas Efstathiou of European University Cyprus, estimate that there may be at least as many hidden black holes as the ones we can see directly as luminous quasars.

Featured image by John Paul Summers

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Isaac Newton’s London life: a quiz

Isaac Newton is known as the scientist who discovered gravity, but less well-known are the many years he spent in metropolitan London, and what precisely he got up to in that time…

How well do you know the latter part of Newton’s life? Test yourself with this quiz from Patricia Fara, author of Life after Gravity: Isaac Newton’s London Career:

Featured image by Luke Stackpoole

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Understanding black holes: young star clusters filling up gaps

Since their groundbreaking discovery of gravitational waves from a pair of in-spiralling black holes back in 2015, the LIGO-Virgo-KAGRA collaboration has detected nearly 70 candidates of such events, 50 being confirmed and published until now. A tight binary comprising black holes or neutron stars would always spiral in and become tighter with time by losing energy in the form of gravitational waves until they plunge onto each other and merge. The final phase (typically, some ten seconds long) of this merger process would generate the strongest “chirp” of gravitational waves which the mammoth laser interferometers of LIGOVirgo can register as an “event.” Each of such event, apart from being fascinating by its own right, also provides us with valuable information such as how heavy the black holes are, how fast they are spinning, and whether the spins are tilted. Such information is the key to understanding how black holes are formed out of stars and how they end up in binaries.

Most, if not all, of the stars in the Universe form in densely-packed spherical groups. Such a fresh hatch of stars, called a young cluster, is held together by the stars’ mutual gravitational pull. Black holes are formed when the most massive and shortest living of the stars, some tens to hundreds of times heavier than the Sun, run out of their nuclear fuel and collapse under their own gravity. Once formed, these black holes become by far the heaviest members of the cluster. Therefore, they sink up to the stomach of the cluster where they are free to interact and exchange energy with each other via gravitational attraction. That way, they often end up pairing.

The interaction chain doesn’t stop there, though. The binary black holes continue to interact with neighbouring black holes, forming triples of black holes (rarely, even up to quadruples and quintuplets). Such a triple, by itself, is a highly active system undergoing extreme internal oscillations (known as the Kozai-Lidov oscillation), a process which causes its constituent black holes to periodically zip by, approaching each other’s event horizon: this is when things become relativistic. This is how, mediated purely by gravitational interactions, binary black holes form and go all the way up to in-spiral and merge inside star clusters.

I recently conducted a computer simulation of this whole picture that has explicitly reproduced all the key properties of the merging binary black holes that LIGOVirgo have derived from their observations. These are extensive and ab initio simulations of star clusters, comprising tens of thousands of stars, with practically no inherent simplifying assumptions. No compromise is made in these simulations: the latest knowledge of black hole formation from stars and Einstein’s general relativity are knit together with a rigorous mechanism for tracking all sorts of encounters that the stars and the black holes would go through. In terms of physical ingredients, these are the most advanced and realistic computer simulations of star clusters to date which successfully tackle a long-awaited problem in computational and multi-disciplinary astrophysics.

The binary black hole mergers from these calculations reproduce not only the overall trends in masses and spins of the observed LIGO-Virgo merger events but also the oddest ones among them—. Events, for example, like the recently revealed GW190521, involving a black hole of 80 solar mass that is “forbidden” by stellar evolution theory, occur naturally in these simulations. Current understanding of stars and binaries tells us that black holes cannot have masses in between 60 and 120 solar masses which is why GW190521 is, so far, the oddest among the odds. Of course, in my own simulations, black holes are never born within this forbidden range. However, as time passes, some of the black holes jump up in mass to enter the forbidden zone. The mass jump happens either by merging with another black hole (which is itself a “normal” event) or by eating up a star. Inside a cluster, such a massive object becomes a mighty attractor enabling it to participate in a merger again and thus create an apparently impossible gravitational-wave event. In these simulations, black holes of up to 100 solar mass undergo mergers, forming intermediate-mass black holes as in GW190521.

The computed star cluster models also make mergers resembling other remarkable LIGO-Virgo events such as GW170729 (formation of an 80 solar mass, unusually spinning black hole) and GW190412 (merger of two black holes that are unexpectedly dissimilar in mass). By virtue of their high internal activity and ambience, young, moderate-sized star clusters have the potential to explain both the trend and the oddities of the observed gravitational-wave merger events. The importance of these apparently humble clusters in generating the most energetic events in the Universe is just beginning to be realised.

Featured image by Brett Ritchie

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Modifying gravity to save cosmology

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Supermassive black holes: monsters in the early Universe

When matter is squashed into a tiny volume the gravitational attraction can become so huge that not even light can escape, and thus a black hole is born. A star such as the Sun will never leave a black hole because the quantum forces between matter stop this from squeezing into a sufficiently small volume. Once the Sun dies it will merely leave a white dwarf star, which slowly cools and dims over billions of years. But when the nuclear furnace of a star weighing more than approximately 20 times the Sun exhausts itself, the quantum forces cannot halt its immense gravitational collapse, sparking its explosion as a supernova and often leaving a stellar mass black hole in memory of its previous glory. Such a black hole weighs from a few Suns to perhaps a few dozen. But black holes weighing millions of Suns have been found. And these monstrous things are aptly called super-massive black holes.

As a result of very arduous observations, astronomers have discovered that more-massive elliptical galaxies have bigger super-massive black holes and that these super-massive black holes appear extremely rapidly after the birth of the Universe. This raises three hitherto baffling questions:

1. How can super-massive holes even form?
2. Why do heavier elliptical galaxies contain heavier super-massive black holes? The most-massive galaxies, weighing more than a hundred times the Milky Way in stars, have super-massive black holes that nearly reach the mass of the Milky Way.
3. How can such incredibly heavy super-massive black holes form within a few hundred million years after the Big Bang when this is basically in the first blink of the cosmic baby’s eye?

The biggest problem is that there is no known physics that can be used squash the fantastic amount of normal matter into a sufficiently small volume to make a super-massive black hole within a hundred million years. The matter resists: if squashed too much it becomes relativistic and radiates much of its mass in the form of photons. So, to try and tackle this issue, some wild theories have been developed in the hope of finding an explanation.

Some of these theories have tried to utilise exotic primordial black holes or with dark matter, while others have attempted to construct hyper-massive stars that collapse to black holes weighing more than a hundred solar masses. Some have even tried to use combinations that also invoke special ways of accreting normal matter onto such a seed-massive-black hole. All of these theories are problematical as they are based on hypotheses that have not been confirmed by observation. For example, the evolution of the first putative hyper-massive stars is extremely uncertain because such objects should blow off most of their mass within the first million years.

In spite of the seemingly unsolvable nature of this issue, a team of astrophysicists from Charles University in Prague, Bonn University, the European Space Agency, and the University of Tokyo may have solved all three problems simultaneously.

The team noted that when two black holes merge then approximately 95% of the mass combines to the new more massive black hole with only a tiny amount of the rest being radiated as gravitational waves. This is very nicely shown by the ongoing detection of merging black holes using gravitational wave detectors. They also noted that stellar populations that form in the very early Universe, when there is only hydrogen and helium, are dominated by massive stars weighing more than 20 and up to 150 or so Suns. Additionally, they also indicated that more-massive elliptical galaxies formed more quickly thereby transforming their gas more vigorously into stars. The final ingredient of this theory is that the more vigorously the galaxy forms its stars, the heavier the star clusters are that form in the galaxy at its centre.

The astrophysicists computer-coded the above and calculated what happens when an elliptical galaxy begins to form when, roughly two hundred million years after the Big Bang, the gas in the cosmos had sufficiently cooled through its expansion to gravitationally collapse. The first-formed extremely massive star clusters were full of heavy stars, leaving many millions of normal black holes in regions spanning not much more than 10 light years across. This was over after about 10 to 20 million years when the last massive star died. But around these first clusters of black holes, the elliptical galaxies were just starting to form. The formation of a whole galaxy continued for about a billion years and, during this extremely violent time, very large amounts of gas fell onto the cluster of black holes near its centre. The gas squeezed the cluster together until the black hole velocities within the cluster became relativistic. At this point, the cluster of black holes started radiating a critical amount of its energy as gravitational waves. It consequently collapsed within a dozen million years to a combined black hole mass of a hundred thousand to millions of Suns. As the elliptical galaxy continued to form around this massive black hole, gas kept falling onto it so that it grew more in mass as a quasar, with additional massive elliptical galaxies hosting more massive central black holes that grew faster.

Using conventional physics and the most updated observational data, this theory thus answers all three questions noted above and makes two predictions:

1. The very first quasars may not be actually accreting super-massive black holes, but the extremely early hyper-massive star clusters containing many millions of brilliant massive stars could be the precursors of real accreting super-massive black holes.
2. When the cluster of black holes reaches its relativistic state, its hundreds of thousands and millions of black holes will be radiating gravitational waves in bursts as the black holes pass each other ever more frequently. This type of signal still needs to be calculated in detail and should allow this theory to be tested the future gravitational wave observatories.

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