Backreaction

How does the world of science differ from the world of art?

2012-05-25T11:59:00.000-04:00

"How does the world of science differ from the world of art?" was a question posed to Scott Snibbe in an interview published in the recent Nature issue. Scott Snibbe is a media designer who, among other things, was executive producer of Björk's "Biophilia" project. If you're nuts you can pay 32 bucks for the interview, which fills roughly one page, here. I'll quote Snibbe's answer for you:

"There is an irreproducible uniqueness to an artist's work that makes the field less stressful than science. In science, if you don't make a certain discovery, someone else will, so even people in the same lab are competing with one another. In art, innovation and risk-taking are lauded, but in science there is an aversion to risk because people need to get grant money from conservative review boards. I know scientists who could speak a single sentence that would completely ruin their careers. [...]"

And if you've collected enough sentences that could ruin other people's careers, you get tenure.

Testing variations of Planck's constant with the GPS

2012-05-23T06:36:00.000-04:00

Sketch of GPS satellite orbits.
Not to scale. Image source.

In a recent PRL, James Kentosh and Makan Mohageg of California State University at Northridge, report on a neat little analysis of GPS time correction data that they used to put bounds on a position dependence of Planck's constant:

Phys. Rev. Lett. 108, 110801 (2012)

The GPS satellites orbit the Earth in about 12 hours in orbits at about 26,600 km altitude with very small eccentricity (ie the orbits are almost circular). Each satellite carries an atomic clock which is needed for the position measurements that are made, essentially, by triangulation with several satellites.

The clocks in the satellites move relative to ground-based clocks at roughly 4 km/s in a weaker gravitational field, so their proper times differ. Just how much they differ can be computed from their position data, using general relativity. Since the exact synchronization between the different clocks is crucial for the precision of position measurements, the GPS clock data that the satellites transmit is followed by a correction that synchronizes the clocks with each other and with the ground base. The correction data is updated every 15 minutes and is publicly available. It is this clock correction data that was used for the study.

Kentosh and Mohageg looked if the correction data has an altitude-dependent excess that is not explained by general relativistic corrections. For this, they selected seven of the satellites that had slightly more eccentric orbits and small standard deviations in the changes of the clock corrections. They used the clock corrections for a period somewhat longer than a year. They first extracted the relics of the corrections that are off the general relativistic predictions. The unfiltered result has several long-term oscillations, for example on annual and monthly periods, that are probably due to atmospheric effects whose exact origin is unknown. These oscillations however are not what they are looking for. In the end, they are left with average off-sets for each of the satellites. According to general relativity, one expects them to be statistically distributed around zero. The offsets they found are consistent with zero (ie consistent with general relativity) though the maximum is a little off.

So far so good. What it a little murky is the relation to a position-dependence of Planck's constant, ℏ. If Planck's constant was position-dependent and would change with altitude, then this would affect the proper time of the satellite clocks as follows. Assuming that the atomic transition energies remain constant, the number of oscillations per unit of time depends on ℏ. If ℏ was position-dependent, this would then add to the clock-correction. The problem with this argument is that ℏ itself is dimensionful and such a statement thus rests on the assumption that the units (for example for energy and time) themselves are not changing. (A point also made in this Physics Today article.)

Besides this, I can't make much sense of a position-dependent ℏ. I mean, depending on your choice of coordinate system, positions can change all the time or never. With some imagination, one could consider a dependence on a physical quantity, maybe the strength of the gravitational field. But then I'd expect there to be much stronger constraints from other astrophysical observations.

In any case, leaving aside that it's not so clear this study actually tests the constancy of ℏ, it's a great documentation for what can be done with publicly available data of technological gadgets we use every day.

Are your search results Google’s opinion?

2012-05-20T03:36:00.000-04:00

New information technology is a challenge for all of us, but particularly for lawyers who have to sort out the integration into existing law. A question that has been on my mind for a while, and one that I think we will hear more about in the future, is what is the legal status of search engines, or their search results respectively?

There has now been an interesting development in which Google asked a prominent law professor, Eugene Volokh, for an assessment of the legal classification of their service.

In a long report titled “First Amendment Protection for Search Engine Results,” which was summarized on Wired, Volokh argues that Google’s search engine is a media enterprise, and its search results are their opinion. They are thus covered by the US American First Amendment, which protects their “opinion” on what it might have been you were looking for, as a matter of “free speech.” (It should be noted that this report was funded by Google.)

It is hard for me to tell whether that is a good development or not. Let me explain why I am torn about this.

Search engine results, and Google in particular, have become an important, if not the most important, source of information for our societies. This information is the input to our decision making. If it is systematically skewed, democratic decision making can be altered, leading to results that are not beneficial to our well-being in the long run.

Of course this has been the case with media before the internet, and this tension always existed. However, non-commercial public broadcasting, often governmentally supported, does exist in pretty much all developed nations (though more prominently so in some countries than in others). Such non-commercial alternatives are offered in cases when it is doubtful that the free market alone will lead to an optimal result. When it comes to information in particular, the free market tends to optimize popularity because it correlates with profit, a goal which can differ from accuracy and usefulness.

There is also what I called the “key in the trunk” effect, the unfortunate situation in which the solution to a problem can only be assessed if the problem is solved: You need information to understand you lack information. Information plays a very crucial role to democracy.

Research in sociology and psychology has shown over and over again that people, when left to their own devices, will not seek for and think about the information they would need to make good decisions. We are, simply put, not always good in knowing what is good for us. Many problems that can be caused by making wrong decisions are irreversible – by the time the problem becomes obvious, it might be too late to change anything about it. This is often the case when it comes to information, and also in many other areas whose regulation is therefore not left to the free market alone. That’s why we have restrictions on the use of chemicals in food, and that’s why no developed nation leaves education entirely to the free market.

(Sometimes when I read articles in the US American press, I have the impression that especially the liberals like to think of the government as “they” who are regulating “us.” However, in any democratic nation, we do impose rules and regulations on ourselves. The government is not a distinct entity regulating us. It’s an organizational body we have put into power to help improve our living together.)

That it is sometimes difficult for the individual to accurately foresee consequences is also why we have laws protecting us from misinformation: Extreme misinformation makes democratic decision making prone to error. Laws preventing misinformation sometimes conflict with free speech.

Where the balance lies differs somewhat from one country to the next. In the USA, the First Amendment plays a very prominent role. In Germany, the first “Basic Right” is not the protection of free speech, but the protection of human dignity. Insults can bring you up to a year prison sentence. Either way, freedom of the press is a sacred right in all developed nations, and a very powerful argument in legal matters. (It is notoriously difficult to sue somebody for insult in any of its various manifestations. Aphrodite's middle-finger, see image to the right, which was on the cover of a German print magazine in February 2010, was covered by press freedom.)

So how should we smartly deal with an information source as important as Google has become?

On the one hand, I think that governmental intervention should be kept to a minimum, because it is most often economically inefficient and bears the risk of skewing the optimization a free market can bring. If you don’t like Google’s search result, just use a different search engine and trust in the dance of supply and demand. George Orwell's dystopian vision told us aptly what can happen if a government abuses power and skews information access to its favor, putting the keys into the trunk and slamming it shut.

On the other hand, Google is a tremendously influential player in the market of search engines already, and many other search engines are very similar anyway. Add to this that it’s not clear our preferences which Google is catering to are actually the ones that are beneficial in the long run.

This point has for example been made by Eli Pariser in his TED talk on “Filter Bubbles” that we discussed here. Confirmation bias is one of the best documented cognitive biases, and our ability to filter information to create a comfort zone can lead to a polarization of opinions. Sunstein elaborated on the problem of polarization and its detrimental effect to intelligent decision making to quite some length in his book “Infotopia.”

It is sometimes said that the internet is “democratic” in that everybody can put their content online for everybody else to see. However, this sunny idea is clearly wrong. It totally doesn't matter what information you put online if nobody ever looks at it, because it has no links going to it and is badly indexed by search engines. It might be that, in principle, your greatly informative website appears on rank 313 on Google. In practice that means nobody will ever look at it. Information doesn't only need to exist, it also has to be cheap in the sense that it doesn't necessitate great cost of time or energy to access it, otherwise it will remain unused.

Then you can go and say, but Google is a nice company and they do no evil and you can't buy a good Google ranking (though spending money on optimizing and advertising your site definitely helps). But that really isn't the point. The point is that it could be done. And if the possibility exists that some company's “opinion” can virtually make relevant information disappear from sight, we should think about a suitable mode of procedure to avoid that.

Or you could go and say, if some search engine starts censoring information, the dynamics of the free market will ensure some other takes the place, or people will go on the street and throw stones. Maybe. But actually it's far from clear that will happen. Because you need to know information is missing to begin with. And, seeing that Google's “opinion” is entirely automated, censorship might occur simply by mistake instead by evil thought.

So, are your search results Google's opinion? I'd say they are a selection of other people's opinions, arranged according to some software engineers' opinion on what you might find useful.

That having been said, I don't think it is very helpful to extrapolate from old-fashioned print magazines to search engines and argue that they play a similar role, based on a 1980 case in which an author, unsuccessfully, tried to sue the NYT over the accuracy of their best-seller list, a case which Volokh refers to. The diversity in search engines is dramatically lower than opinions that could be found in print in the 80s. At the same time the impact of online search on our information availability is much larger. Would you even know how to find a best-seller list without Google?

Now, I'm not a lawyer, and my opinion on this matter is as uninformed as irrelevant. However, I think that any such consideration should take into account the following questions:

First, what is the impact that search engine rankings can have on democratic decision making?

Second, what market share should make us get worried? Can we find some measure to decide if we are moving towards a worrisome dominance?

Third, is there any way to prevent this, should it be the case? For example by offering non-commercial alternatives or monitoring by independent groups (like it is the case eg with press freedom)?

Books in E major

2012-05-18T06:45:00.001-04:00

Look! Listen! I've made a music video for your smooth start into the weekend:

I finally realized I won't be able to do any painting till the girls are old enough to not try to lick on the brushes. So, I was looking for a new hobby and that is my first try. I made a series of mistakes that I'll try to learn from.

Stefan and I needed three attempts to throw the books down. First, a book hit the camera stand. At second try, I lost my glasses and had to laugh. Third, I realized belatedly that I had moved the camera and cut off my own head. I then decided it will do, after all I don't want to win an Oscar. I also had a small disagreement with the video editing software and accidentally didn't save the file, so no more editing on that one. Stefan kindly said that the brightness correction of the camera which overreacted to passing clouds "adds drama."

In case you wondered, we had cushions on the floor and the books fell softly. For all I can tell they were not seriously injured.

Anyway, the biggest shortcoming is that I can't actually sing. Worse, I noticed somewhat belatedly that I particularly can't sing anything below the middle C. Somewhat surprisingly so, because I always thought my voice is rather deep for a woman. After two weeks or so of practice, I finally managed to hit the C#5 (at 2:04 min). Luckily our downstairs neighbor is on vacation and the upstairs neighbor doesn't hear well.

3 hours after uploading the video to YouTube I got a message saying they suspect a copyright violation, if I could please provide documentation that I have permission to use the song. A quite dramatic shift in procedure there.

Below the lyrics. I promise the next one won't be quite as serious ;o)

[Intro]
What do you know?

[Verse 1]
You know it all
So many things I do not understand
You know it all
The wrong and the right
You like to talk
So many items I had marked all read
Right or wrong
Hard to decide

[Verse 2]
I see the world
Neatly filtered for my Daily Me
I have it all
Too much and too fast
No need to see
So many things I do not want to see
We have it all
No time to ask

[Chorus 1]
What do you know?
I would appreciate some input here
What do you know?
Your conclusions are not clear to me
What do you know?
I could recommend some books to you
What do you know
We got a long way to go

[Verse 3]
Is it too much for you to watch
Is it finally enough
Do you follow, do you share
Do you listen, do you care
We know it all
So many things that we simply take for such
Who do you trust
And do you dare

[Repeat Chorus 1]

[Interlude]
What do you know? I don't know.
What do you know? I don't know.

[Chorus 2]
What do you know?
The facts are not consistent with your claim
What do you know?
The assumptions that were used are not the same
What do you know?
I could recommend some books to you
What do you know
We got a long way to go

Tales from the Future

2012-05-16T05:04:00.001-04:00

Europe has a plan. It's called Europe 2020 and it's "the EU's growth strategy for the coming decade." Part of that plan is an initiative called "Innovation Union" which "aims to improve conditions and access to finance for research and innovation in Europe". So many nice words.

In what I found to be a great idea for communicating science, part of this initiative is a collection of short science fiction stories based on actual research projects. The short stories, called "Tales from the Future," are written by Robert Billing, and while they seemed to me a little constructed towards their aim, they are not bad at all. You can read them online here. Enjoy!

A note on the black hole entropy in LQG

2012-05-14T04:46:00.000-04:00

If you know anything about Loop Quantum Gravity, you know that people working on it suffer from an inferiority complex because, when counting black hole microstates, they only get the Bekenstein-Hawking entropy of black holes up to a factor. This factor, known as the Barbero-Immirzi parameter, enters the theory through the quantization condition and then has to be fixed to match the correct semi-classical result.

Now there has been a recent paper on the arXiv by Eugenio Bianchi

arXiv:1204.5122 [gr-qc]

which addresses the issue, or at least that's what I thought when I first read the abstract. Bianchi derives the black hole entropy in a spin-foam formalism and finds the usual Bekenstein-Hawking entropy - without any additional factors.

I've been scratching my head over this paper for a while now. The purpose of this blogpost is twofold: First to draw your attention to what is potentially an important contribution in the field, check. And second, I want to offer you my interpretation of that finding, and hope some reader who knows more about LQG than I will correct me when I'm wrong.

The Bekenstein-Hawking entropy is not a quantum gravitational result. One finds that black holes have a temperature by considering a quantum field (usually a massless scalar field but that doesn't matter) in the classical background geometry of a black hole. If one has the mass of the black hole, one can identify it with the total energy and integrate dE = TdS to get the entropy. The validity of this argument breaks down at the Planck scale, but that's not the regime of interest here. One can also abuse the Unruh effect to argue that black holes have a temperature, same result.

If one has some candidate theory for quantum gravity, one can ideally go and compute the microstates of a black hole. In LQG, areas and volumes are quantized in multiples of the Barbero-Immirzi parameter. Even without knowing the details, this leads one to expect that the number of possible microstates depends on that parameter. Thus, the number of microstates will generically not reproduce the Bekenstein-Hawking entropy, unless the parameter is chosen suitably. Now what I would conclude at this point is that the Bekenstein-Hawking entropy is not a measure for the microstates of the black holes. Alas, most of my colleagues seem to believe it is, especially the string theorists, and there's then the origin of the loop quantized inferiority complex.

So, with that avant-propos, why does Bianchi get a result different from the previous LQG results, a result that reproduces the Bekenstein-Hawking entropy?

Well, it looks to me like that's because he doesn't count the black hole microstates to begin with. He considers an observer in the black hole background with a two-level detector and finds the temperature, then S=E/T, and no Barbero-Immirzi parameter ever appears because it's a kinetic effect that has nothing to do with the quantization of areas and volumes. I am greatly simplifying and omitting many details, but that is what it looks like to me.

It is good to see this can be done by constructing the worldline of the observer in the spin-network and express the acceleration and so on in the proper kinetic formalism; that is an interesting calculation in its own right. But does that solve the problem with the black hole entropy in LQG?

In my opinion, it doesn't. In fact, it only manifests the problem further. Now not only is the microstate counting inconsistent with the Bekenstein-Hawking entropy unless a free parameter of the model is fixed appropriately, but the kinetic result is inconsistent with the microstate counting within the same theory.

Truth be said, this paper has created more questions for me than it has answered. I am wondering now for example, what really is the observer fundamentally? It ought to be described by quantum fields. But these quantum fields have a quantization prescription. And that quantization prescription, not having anything to do with gravity, doesn't have an additional parameter in it. That after all is why the Bekenstein-Hawking result is reproduced, because it doesn't have anything to do with the quantization of gravity. But the fields interact with the geometry, so how can they have a different quantization prescription?

If somebody can point me into the direction of a helpful reference or a bottle of ibuprofen, please dump in the comments.

Top Ten

2012-05-10T09:29:00.000-04:00

This is a repost and update of a six year old post in which I listed what I think are the most interesting and pressing open problems in theoretical physics, or at least the area that I work in, quantum gravity. I thought it might be worthwhile to revisit. This list doesn't even pretend to be objective - it omits entire areas of theoretical physics - it is mainly a reflection of my personal interests; a summary of puzzles I find promising to spend brain time on.

How can the apparent disagreement between general relativity and quantum gravity be resolved? Does it require to quantize gravity?
(Still 1. Haven't changed my mind about that.)
Can we understand quantization?
(Up from 9. The more I think about it, the more I believe our problem with quantizing gravity is in the quantum part, not in the gravity part.)
~~Do black holes destroy information?~~ What happens to the matter that collapses to a black hole?
(I think we spent enough time on the black hole information loss problem. It would be fruitful to instead think about what happens to matter at Planckian densities. Down from 2.)
Are the electroweak and strong interaction unified at high energies? If so, are they also unified with gravity?
(That is, is there a theory of everything? Up from 8. I'm undecided whether or not unification is helpful to the problem of quantizing gravity.)
Are the currently known particles of the standard model (SM) elementary? Are there more so far unobserved particles? Why are the parameters of the SM what they are and are they in yet unknown ways related to each other? Why are the gauge groups of the SM what they are? Is it even possible to uniquely answer this question?
(Formerly 8, minus the question for unification plus the question whether there's a unique answer.)
Did the universe start with a big bang, a big bounce or something else entirely?
(This is a reformulation of the earlier question number 4 which focused on singularities specifically. Down from 3.)
Why do we experience 3+1 dimensions? Are there extra dimensions? Does the effective dimension of space-time decrease at short distances?
(This is an extension of the earlier question 7, taking into account that dimensional reduction to 2 dimensions has received some attention recently.)
Why is gravity so much weaker than the other interactions?
(Up from 10.)
Does dark energy exist? If so, what is it? Is the coincidence problem more than a coincidence?
(Down from 4. I think that the dark energy puzzle is possibly a relevant hint for quantum gravity. But then, maybe not.)
How do we correctly assign an entropy to gravitational degrees of freedom? Is this testable at all?
(Newcomer.)

Dark matter has dropped off the list. I think we're well on the way to finding some direct evidence for dark matter. It will be difficult to pin down, but at this point it seems unlikely to me that it will be relevant for quantum gravity.

Imitation Nation

2012-05-08T11:04:00.000-04:00

The Edge features a half hour talk by Mark Pagel that I found very thought stimulating. Pagel is an evolutionary biologist, and his talk is provocatively titled “Infinite Stupidity.” The title primarily describes itself though and doesn’t have much to do with Pagel’s argument, which is a speculation about the origin and evolution of ideas.

Pagel starts with the analogy that ideas evolve similarly to genes, in that they reproduce and are selected for performance. Only good ideas continue to reproduce, which is however a tautology if you define a good idea by its ability to spread, and questionable otherwise. I am not particularly fond of the comparison to natural selection that he uses. The evolution of organisms and ideas are both examples for adaptive systems, and the reference to natural selection imo sets an unnecessary anchor.

In any case, this idea reproduction works well among humans because we are very good at social learning, that is learning by imitating each other. The ability of humans to copy behavior sets us apart from all other species on the planet. Sure, some other mammals are able to learn new tricks when offered rewards, but these abilities and the animals’ understanding of purpose are very limited. Humans have very little hardwired knowledge, which has the advantage that we adapt very well to new circumstances, but has the disadvantage that it takes a long time for human infants to have learned enough to be able to survive independently.

Hang on, Lara is trying to eat my post-its.

During the evolution of mankind, our ability to communicate ideas has steadily improved. Beginning with the evolution of language, over the written word, print, telegraph, phone and to the internet, we have improved on our connectivity. Since we are so good at copying others, this means, so argues Pagel, that we need fewer and fewer people to produce ideas. Innovation takes time and energy, and if we can shortcut this investment by relying on somebody else’s knowledge, we can avoid this cost.

Pagel is speaking here not primarily about innovation in the sense of technological development. He refers to things like, say, building a house. If you want to build a house, you don’t invent architecture from scratch. You ask somebody who knows, or you read a book, or, most likely, you hire somebody to do it for you. Either way, you’re copying other people’s innovations rather than innovating yourself, and in terms of time- and energy-investment that’s arguably the smart thing to do.

A consequence of our high skills in social learning combined with increasing connectivity is thus that we have become good copiers and less good inventors, which is unfortunate since we need innovators to come up with smart solutions to our problems. Or so are Pagels concerns. He says

“And so, we might see that there has been this tendency for our psychology and our humanity to be less and less innovative, at a time when, in fact, we may need to be more and more innovative, if we're going to be able to survive the vast numbers of people on this earth.”

I don’t know what he means with “tendency for our psychology.” It could mean two things. Either the (conjectured) decline in innovation is hardwired, ie it’s a genetic change. Or, it’s a reversible adaption to changing circumstances. Given the short time that has passed since the invention of print, it is most likely a social or cultural change he is referring to. But if that is so, then I have to conclude that Pagel’s perception of “a need to be more and more innovative” is apparently not reflected in our environment, at which point we’re left with opinions about societal investments in research and development, rather than facts. This is not to say that I disagree with Pagel, just that I don’t really know what insight to gain here.

So let me get to the next point he’s making, which I actually found more interesting, that is the question where ideas originate. Pagel says that ideas are probably randomly produced in our brains, like genetic mutations are randomly produced. This hypothesis doesn’t seem to be based on any actual study for all I can tell, it’s mostly an argument from plausibility.

That ideas might be random produced in our brains doesn’t mean though that we try them all. No, luckily our brains are large enough to virtually explore consequences of an idea before actually acting on it. And in that process, we discard most of the nonsensical random ideas, possibly already unconsciously. I am not sure how well this idea of Pagel fits with current research, but it makes a certain sense to me.

However, I think Pagel omitted to point out that a random generation of ideas cannot mean random from scratch, but random over a pool of already existing material. That is to say, you can only generate ideas on the information that your brain contains. Which brings me back to the need of education, and investment into research and development.

Pagel's argument is interesting, but it lacks substance. Maybe it is worth checking out his book, Wired for Culture, which might offer more support for his idea.

Book review: "Infotopia" by Cass Sunstein

2012-05-05T06:20:00.001-04:00

Infotopia: How Many Minds Produce Knowledge
By Cass R. Sunstein
Oxford University Press, USA (2006)

It's taken me a while to get through Sunstein's book though I am very interested in the topic. "Infotopia" addresses the question under which circumstances, and with which aggregation mechanisms, groups can make good decisions - and under which circumstances groups fail. With that, Sunstein's book offers the details that I found missing in Surowiecky's "Wisdom of Crowds."

Sunstein summarizes a lot of research that has been done on how groups deal with information, and how they aggregate it, and how good or bad they make decisions. He has classified modern aggregation tools into markets and prediction markets, wikis, open source, and blogs. This order seems to be a declining one for Sunstein's judgement of usefulness; he is clearly enthusiastic about prediction markets and critical about the blogosphere.

The book has grown out of his review article for the New York University Law Review, and that is, unfortunately, very noticeable. "Infotopia" contains a lot of information and many references, but it is not very engagingly written. It is essentially a long list of who did what study when and where. It is in several places repetitive, as if the author himself had forgotten what he had already covered. It is repetitive also in the choice of words, eg the word "blunder" seems to appears like every other page.

I learned a lot from this book, most notably what difficulties befall groups that want to come to good decisions.

The major problems are that group members might not disclose information that they have, and that information which is held by few or single group members has less influence on the decision than the information shared by many, irrespective of actual relevance. Sunstein discusses many studies that have shown that deliberation in groups, under very general circumstances, makes decisions worse and polarizes opinions. The reason is that people tend to focus on what they have in common and reinforce their views rather than to diversify. So, after talking it out, people often edge towards more extreme views, and are more certain about them too because they then know others share their opinion. An additional problem is that people might have a conflict of motivation, ie their personal motivation to not look stupid might not agree with the goal of coming to a good decision in the group.

Most of the examples that Sunstein draws upon are 6 years later already outdated, but the general lessons for good decision making are pretty much timeless. In the final chapter Sunstein makes suggestions for how to alleviate these problems in different situations: online communities, group meetings and so on. I'll try to learn from that book, and hope to realize some of the suggestions in the future.

In summary, this book is very useful, but it's not very inspiring and not very well written. I'd give three out of five stars.

Surprise me - But not too much

2012-05-03T07:26:00.000-04:00

Flute recording. Source.

A decades old paper made me philosophical.

In 1975, Voss and Clarke, two physicist from Berkeley, studied noise in electronic devices. For the fun of it, they also analyzed the spectra of different types of music. They found that the fluctuations in loudness and pitch decrease with the inverse of the frequency; they have a 1/f spectrum. This finding was basically independent of the type of music; Western, Oriental, Blues, Jazz, Classic all showed the same pattern. Voss and Clarke’s musical power spectrum made it into Nature.

A Fourier-transformation of a 1/f power spectrum leads to a power-law decay in the autocorrelation time of the fluctuations, meaning there are correlations over all times, rather than over a characteristic decay time as is most often the case. Physicists like power-law autocorrelated fluctuations because systems show them on a critical point, ie if something cool is going on, you get a power law. The opposite is not necessarily true though; there are more mundane ways to get a power law, but that hasn’t deterred enthusiasts. The 1/f spectrum is scale-invariant, so it has – theoretically – no preferred time scale or frequency to it, as one might have expected to be present in music.

In the 70s and 80s everything power-law was chique, and not all of that power-law-finding was very meaningful. To some approximation, in some parameter range, everything is a power-law. If you put your data on a log-log plot, you can make a linear fit, at least over some range. Yet, strictly speaking nothing really is a power law. And of course music doesn’t really have a 1/f spectrum either. To begin with, because it doesn’t use the full frequency spectrum, most of which we couldn’t hear. Also, Mozart hasn’t been composing since the Big Bang.

Scale-invariance is a property also shared by fractals. When I first heard about Voss and Clarke’s study, I jokingly asked when we’ll be listening to fractal music. Needless to say, I learned that had been said and done when I was still wearing diapers. Google “fractal music” to see where this thought leads you.

I’m not sure what the power-law finding means for the origin of music, but intuitively what it means for what you hear is that music (at least the type we find appealing) lives on the edge between predictability and unpredictability. White noise has a constant spectral density and no autocorrelation. A random walk moving a melody along adjacent pitches has a strong correlation and a 1/f² spectrum. Somewhere in between are Bach and Adele.

When you turn on the radio, you want to be surprised – but not too much. Popular music today follows quite simple recipes. In most cases, you’ll be able to sing along when the chorus repeats. If you’ve heard a song a dozen times it gets dull though – it’s become too predictable. Symphonies are more complex, but they all have recurring motives and variations around that.

However, the musical edge must have a finite width. For some purposes, music can be more predictable than for others. What amount of predictability we find appealing doesn’t only depend on the occasion, it is also individually different. If you spend a lot of time analyzing pop songs, I suspect what’s in the charts today will sound very repetitive to you, though for the casual listener it arguably has an appeal.

It is tempting to extrapolate this to areas where autocorrelations are less easily measureable than pitch, for example to ideas in the written and spoken form. A scientific paper or a talk needs to strike a balance between the known and the unknown. Repeat too much common knowledge, and you’re obvious. Jump too far, and you’re crazy. The scientific pop stars are the ones on the edge. That also means the pop stars are the ones not too far ahead of their time.

It seems to me today the width of the scientific edge is very thin, maybe too thin. Sometimes, the obvious must be stated just so it remains in awareness. And sometimes the crazy starts making sense if you’ve listened to it often enough.

There’s another lesson. While fashions seem to come back, the cycle never is perfectly periodic, but always comes with a new twist. Thus, when the colors of the 70s will return to haunt us, maybe they’ll come with a metallic shine. And so, my impression that we’re having the same discussions over and over again must be wrong. They can’t be periodic, I am missing a change on longer time scales. History may be self-similar, but it’s not repeating. Though that's one of my all-time favorite songs.

Interna

2012-04-30T02:04:00.000-04:00

Spring came late to Germany, but it seems it finally has arrived. The 2012 Riesling has the first leaves and the wheat is a foot high.

Lara and Gloria are now 16 months old, almost old enough so we should start counting their age in fraction of years. This month's news is Lara's first molar, and Gloria's first word:

I have been busy writing a proposal for the Swedish Research Council, which is luckily submitted now, and I also had a paper accepted for publication. Ironically, from all the papers that I wrote in the last years, it's the one that is the least original and cost me the least amount of time, yet it's the only one that smoothly went through peer review.

Besides this, I'm spending my time with the organization of a workshop, a conference, and a four-week long program. I'm also battling a recurring ant infection of our apartment, which is complicated by my hesitation to distribute toxins where the children play.

The Nerdly Painter's Blog

2012-04-27T07:41:00.001-04:00

In expecto weekendum, I want to share with you the link of Regina Valluzzi'a blog Nerdly Painter. Regina has a BS in Materials Science from MIT and PhD in Polymer Science from University of Massachusetts Amherst, and she does the most wonderful science-themed paintings I've seen. A teaser below. Go check out her blog and have a good start into the weekend!

The Cosmic Ray Composition Problem

2012-04-25T09:49:00.000-04:00

A recent arXiv paper provides an update on the cosmic ray composition problem:

arXiv:1204.1488 [astro-ph.HE]

First the basics: We're talking about the ultra-high energetic end of the cosmic ray spectrum, with total energies of about 10⁶ TeV. That's the energy of the incident particles in the Earth rest frame, not the center-of-mass energy of their collision with air molecules (ie mostly nucleons), which is "only" of the order 10 TeV, and thus somewhat larger than what the LHC delivers.

After the primary collision, the incoming particles produce a cascade of secondary particles, known as a "cosmic ray shower" which can be detected on the ground. These showers are then reconstructed from the data with suitable software so that, ideally, the physics of the initial high energy collison can be extracted. For some more details on cosmic ray showers, please read this earlier post.

Cosmic ray shower, artist's impression. Source: ASPERA

The Pierre Auger Cosmic Ray Observatory is a currently running experiment that measures cosmic ray showers on the ground. One relevant quantity about the cosmic rays is the "penetration depth," that is the distance the primary particle travels through the atmosphere till it makes the first collision. The penetration depth can be reconstructed if the shower on the ground can be measured sufficiently precise, and is relatively new data.

The penetration depth depends on the probability of the primary particle to interact, and with that on the nature of the particle. While we have never actually tested the collisions at the center-of-mass energies of the highest energetic cosmic rays, we think we have a pretty good understanding of what's going on by virtue of the standard model of particle physics. All the knowledge that we have, based on measurements at lower energies, is incorporated into the numerical models. Since the collisions involve nucleons rather than elementary particles, this goes together with an extrapolation of the parton distribution function by the DGLAP equation. This sounds complicated, but since QCD is asymptotically free, it should actually get easier to understand at high energies.

Shaham and Piran in their paper argue that this extrapolation isn't working as expected, which might be a signal for new physics.

The reason is that the penetration depth data shows that at high energies the probability of the incident particles to interact peaks at a shorter depth and is also more strongly peaked than one expects for protons. Now it might be that at higher energies the cosmic rays are dominated by other primary particles, heavier ones, that are more probable to interact, thus moving the peak of the distribution to a shorter depth. However, if one adds a contribution from other constituents (heavier ions: He, Fe...) this also smears out the distribution over the depth, and thus doesn't fit the width of the observed penetration depth distribution.

This can be seen very well from the figure below (Fig 2 from Shaham and Piran's paper) which shows the data from the Pierre Auger Collaboration, and the expectation for a composition of protons and Fe nuclei. You can see that adding a second component does have the desired effect of moving the average value to a shorter depth. But it also increases the width. (And, if the individual peaks can be resolved, produces a double-peak structure.)

Fig 2 from arXiv:1204.1488. Shown is the number of events in the energy bin 1 to 1.25 x 10⁶ TeV as a function of the penetration depth. The red dots are the data from the Pierre Auger Collaboration (arXiv:1107.4804), the solid blue line is the expectation for a combination of protons and Fe nuclei.

The authors thus argue there is no compositions for the ultra high energetic primary cosmic ray particles that fits the data well. Shaham and Piram think that this mismatch should be taken seriously. While different simulations yield slightly different results, the results are comparable and neither code fits the data. If it's not the simulation, the mismatch comes about either from the data or the physics.

"There are three possible solutions to this puzzling situation. First, the observational data might be incorrect, or it is somehow dominated by poor statistics: these results are based on about 1500 events at the lowest energy bin and about 50 at the highest one. A mistake in the shower simulations is unlikely, as different simulations give comparable results. However, the simulations depend on the extrapolations of the proton cross sections from the measured energies to the TeV range of the UHECR collisions. It is possible that this extrapolation breaks down. In particular a larger cross section than the one extrapolated from low energies can explain the shorter penetration depth. This may indicates new physics that set in at energies of several dozen TeV."

The authors are very careful not to jump to conclusions, and I won't either. To be convinced there is new physics to find here, I would first like to see a quantification of how bad the best fit from the models actually is. Unfortunately, there's no chi-square/dof in the paper that would allow such a quantification, and as illustrative as the figure above is, it's only one energy bin and might be a misleading visualization. I am also not at all sure that the different simulations are actually independent from each other. Since scientific communities exchange information rapidly and efficiently, there exists a risk for systematic bias even if several models are considered. Possibly there's just some cross-section missing or wrong. Finally, there's nothing in the paper about how the penetration depth data is obtained to begin with. Since that's not a primary observable, there must be some modeling involved too, though I agree that this isn't a likely source of error.

With these words of caution ahead, it is possible that we are looking here at the first evidence for physics beyond the standard model.

Can we probe planck-scale physics with quantum optics?

2012-04-23T11:26:00.000-04:00

You might have read about this some weeks ago on Chad Orzel's blog or at Ars Technica: Nature published a paper by Pikovski et al on the possibility to test Planck scale physics with quantum optics. The paper is on the arXiv under arXiv:1111.1979 [quant-ph]. I left a comment at Chad's blog explaining that it is implausible the proposed experiment will test any Planck scale effects. Since I am generally supportive of everybody who cares about quantum gravity phenomenology, I'd have left it at this, and be happy that Planck scale physics made it into Nature. But then I saw that Physics Today picked it up, and before this spreads further, here's an extended explanation of my skepticism.

Igor Pikovski et al have proposed a test for Planck scale physics using recent advances in quantum optics. The framework they use is a modification of quantum mechanics, expressed by a deformation of the canonical commutation relation, that takes into account that the Planck length plays the role of a minimal length. This is one of the most promising routes to quantum gravity phenomenology, and I was excited to read the article.

In their article, the authors claim that their proposed experiment is feasible to "probe the possible effects of quantum gravity in table-top quantum optics experiment" and that it reaches a "hitherto unprecedented sensitivity in measuring Planck-scale deformations." The reason for this increased sensitivity for Planck-scale effects is, according to the authors own words, that "the deformations are enhanced in massive quantum systems."

Unfortunately, this claim is not backed up by the literature the authors refer to.

The underlying reason is that the article fails to address the question of Lorentz-invariance. The deformation used is not invariant under normal Lorentz-transformations. There are two ways to deal with that, either breaking Lorentz-invariance or deforming it. If it is broken, there exists a multitude of very strong constraints that would have to be taken into account and are not mentioned in the article. Presumably then the authors implicitly assume that Lorentz-symmetry is suitably deformed in order to keep the commutation relations invariant - and in order to test something actually new. This can in fact be done, but comes at a price. Now the momenta transform non-linearly. Consequently, a linear sum of momenta is no longer Lorentz-invariant. In the appendix however, the authors have used the normal sum of momenta to define the center-of-mass momentum. This is inconsistent. To maintain Lorentz-invariance, the modified sum must be used.

This issue cannot be ignored for the following reason. If a suitably Lorentz-invariant sum is used, it contains higher-order terms. The relevance of these terms does indeed increase with the mass. This also means that the modification of the Lorentz-transformations become more relevant with the mass. Since this is a consequence of just summing up momenta, and has nothing in particular to do with the nature of the object that is being studied, the increasing relevance of corrections prevents one from reproducing a macroscopic limit that is in agreement with our knowledge of Special Relativity. This behavior of the sum, whose use, we recall, is necessary for Lorentz-invariance, is thus highly troublesome. This is known in the literature as the "soccer ball problem." It is not mentioned in the article.

If the soccer-ball problem persists, the theory is in conflict with observation already. While several suggestions have been made how this problem can be addressed in the theory, no agreement has been reached to date. A plausible and useful ad-hoc suggestion that has been made by Magueijo and Smolin is that the relevant mass scale, the Planck mass, for N particles is rescaled to N times the Planck mass. Ie, the scale where effects become large moves away when the number of particles increases.

Now, that this ad-hoc solution is correct is not clear. What is clear however is that, if the theory makes sense at all, the effect must become less relevant for systems with many constituents. A suppression with the number of constituents is a natural expectation.

If one takes into account that for sums of momenta the relevant scale is not the Planck mass, but N times the Planck mass, the effect the authors consider is suppressed by roughly a factor 10¹⁰. This means the existing bounds (for single particles) cannot be significantly improved in this way. This is the expectation that one can have from our best current understanding of the theory.

This is not to say that the experiment should not be done. It is always good to test new parameter regions. And, who knows, all I just said could turn out to be wrong. But it does mean that based on our current knowledge, it is extremely unlikely that anything new is to be found there. And vice versa, if nothing new is found, this cannot be used to rule out a minimal length modification of quantum mechanics.

(This is not the first time btw, that somebody tried to exploit the fact that the deviations get larger with mass by using composite systems, thereby promoting a bug to a feature. In my recent review, I have a subsection dedicated to this.)

Experimental Search for Quantum Gravity 2012

2012-04-22T10:58:00.000-04:00

It is my great pleasure to let you know that there will be a third conference on Experimental Search for Quantum Gravity, October 22 to 25, this year, at Perimeter Institute. (A summary of the ESQG 2007 is here, and a summary from 2010 is here.) Even better is that this time it wasn't my initiative but Astrid Eichhorn's, who is also to be credited for the theme "The hard facts." The third of the organizers is Lee Smolin, who has been of great help also with the last meeting. But most important, the website of the ESQG 2012 is here.

We have an open registration with a moderate fee of CAN$ 115, which is mostly to cover catering expenses. There is a limit to the number of people we can accommodate, so if you are interested in attending, I recommend you register early. If time comes, I'll tell you some more details about the meeting.

Schrödinger meets Newton

2012-04-19T00:49:00.000-04:00

In January, we discussed semi-classical gravity: Classical general relativity coupled to the expectation value of quantum fields. This theory is widely considered to be only an approximation to the still looked-for fundamental theory of quantum gravity, most importantly because the measurement process messes with energy conservation if one were to take it seriously, see earlier post for details.

However, one can take the point of view that whatever the theorists think is plausible or not should still be experimentally tested. Maybe the semi-classical theory does in fact correctly describe the way a quantum wave-function creates a gravitational field; maybe gravity really is classical and the semi-classical limit exact, we just don't understand the measurement process. So what effects would such a funny coupling between the classical and the quantum theory have?

Luckily, to find out it isn't really necessary to work with full general relativity, one can instead work with Newtonian gravity. That simplifies the issue dramatically. In this limit, the equation of interest is known as the Schrödinger-Newton equation. It is the Schrödinger-equation with a potential term, and the potential term is the gravitational field of a mass distributed according to the probability density of the wave-function. This looks like this

Inserting a potential that depends on the expectation value of the wave-function makes the Schrödinger-equation non-linear and changes its properties. The gravitational interaction is always attractive and thus tends to contract pressureless matter distributions. One expects this effect to show up here by contracting the wave-packet. Now the usual non-relativistic Schrödinger equation results in a dispersion for massive particles, so that an initially focused wave-function spreads with time. The gravitational self-coupling in the Schrödinger-Newton equation acts against this spread. Which one wins, the spread from the dispersion or the gravitational attraction, depends on the initial values.

However, the gravitational interaction is very weak, and so is the effect. For typical systems in which we study quantum effects, either the mass is not large enough for a collapse, or the typical time for it to take place is too long. Or so you are lead to think if you make some analytical estimates.

The details are left to a numerical study though because the non-linearity of the Schrödinger-Newton equation spoils the attempt to find analytical solutions. And so, in 2006 Carlip and Salzmann surprised the world by claiming that according to their numerical results, the contraction caused by the Schrödinger-Newton equation might be possible to observe in molecule interferometry, many orders of magnitude off the analytical estimate.

It took five years until a check of their numerical results came out, and then two papers were published almost simultaneously:

Schrödinger-Newton "collapse" of the wave function
J. R. van Meter
arXiv:1105.1579 [quant-ph]
Gravitationally induced inhibitions of dispersion according to the Schrödinger-Newton Equation
Domenico Giulini and André Großardt
arXiv:1105.1921 [gr-qc]

They showed independently that Carlip and Salzmann's earlier numerical study was flawed and the accurate numerical result fits with the analytical estimate very well. Thus, the good news is one understands what's going on. The bad news is, it's about 5 orders of magnitude off today's experimental possibilities. But that's in an area of physics were progress is presently rapid, so it's not hopeless!

It is interesting what this equation does, so let me summarize the findings from the new numerical investigation. These studies, I should add, have been done by looking at the spread of a spherical symmetric Gaussian wave-packet. The most interesting features are:

For masses smaller than some critical value, m less than ~ (ℏ²/(G σ))^1/3, where σ is the width of the initial wave-packet, the entire wave-packet expands indefinitely.
For masses larger than that critical value, the wave-packet fragments and a fraction of the probability propagates outwards to infinity, while the rest remains localized in a finite region.
From the cases that eventually collapse, the lighter ones expand initially and then contract, the heavier ones contract immediately.
The remnant wave function approaches a stationary state, about which it performs dampened oscillations.

That the Schrödinger-Newton equation leads to a continuous collapse might lead one to think it could play a role for the collapse of the wave-function, an idea that has been suggested already in 1984 by Lajos Diosi. However, this interpretation is questionable because it became clear later that the gravitational collapse that one finds here isn't suitable to be interpreted as a wave-function collapse to an eigenstate. For example, in this 2002 paper, it was found that two bumps of probability density, separated by some distance, will fall towards each other and meet in the middle, rather than focus on one of the two initial positions as one would expect for a wave-function collapse.

The hunt for the first exoplanet

2012-04-16T04:30:00.000-04:00

The little prince

Today, extrasolar planets, or exoplanets for short, are all over the news. Hundreds are known, and they are cataloged in The Extrasolar Planets Encyclopaedia, accessible for everyone who is interested. Some of these extrasolar planets orbit a star in what is believed to be a habitable zone, fertile ground for the evolution of life. Planetary systems, much like ours, have turned out to be much more common results of stellar formation than had been expected.

But the scientific road to this discovery has been bumpy.

Once one knows that stars on the night sky are suns like our own, it doesn't take a big leap of imagination to think that they might be accompanied by planets. Observational evidence for exoplanets was looked for already in the 19th century, but the field had a bad start.

Beginning in the 1950s, several candidates for exoplanets made it into the popular press, yet they turned out to be data flukes. At that time, the experimental method used relied on detecting minuscule changes in the motion of the star caused by a heavy planet of Jupiter type.

If you recall the two-body problem from 1st semester: It's not that one body orbits the other, but they both orbit around their common center-of-mass, just that, if one body is much heavier than the other, it might almost look like the lighter one is orbiting the heavier one. But if a sufficiently heavy planet orbits a star, one might in principle find out by watching the star very closely because it wobbles around the center-of-mass. In the 50s, watching the star closely meant watching its distance to other stellar objects. The precision which could be achieved this way simply wasn't sufficient to reliably tell the presence of a planet.

In the early 80s, Gordon Walker and his postdoc Bruce Campbell from British Columbia, Canada, pioneered a new technique that improved the possible precision by which the motion of the star could be tracked by two orders of magnitude. Their new technique relied on measuring the star's absorption lines, whose frequency depends on the motion of the star relative to us because of the Doppler effect.

To make that method work, Walker and Campbell had to find a way to precisely compare spectral images taken at different times so they'd know how much the spectrum had shifted. They found an ingenious solution to that: They would used the, very regular and well-known, molecular absorption lines of hydrogen fluoride gas. The comb-like absorption lines of hydrogen fluoride served as a ruler relative to which they could measure the star's spectrum, allowing them to detect even smallest changes. Then, together with astronomer Stephenson Yang, they started looking at candidate stars which might be accompanied by Jupiter-like planets.

To detect the motion of the star due to the planet, they would have to record the system for several completed orbits. Our planet Jupiter needs about 12 years to orbit the sun, so they were in for a long-term project. Unfortunately, they had a hard time finding support for their research.

In his recollection “The First High-Precision Radial Velocity Search for Extra-Solar Planets” (arXiv:0812.3169), Gordon Walker recounts that it was difficult to get time for their project at observatories: “Since extra-solar planets were expected to resemble Jupiter in both mass and orbit, we were awarded only three or four two-night observing runs each year.” And though it is difficult to understand today, back then many of Walker's astronomer colleagues thought the search for exoplanets a waste of time. Walker writes:

“It is quite hard nowadays to realise the atmosphere of skepticism and indifference in the 1980s to proposed searches for extra-solar planets. Some people felt that such an undertaking was not even a legitimate part of astronomy. It was against such a background that we began our precise radial velocity survey of certain bright solar-type stars in 1980 at the Canada France Hawaii 3.6-m Telescope.”

After years of data taking, they had identified several promising candidates, but were too cautious to claim a discovery. At the 1987 meeting of the American Astronomical Society in Vancouver, Campbell announced their preliminary results. The press reported happily yet another discovery of an exoplanet, but the astronomers regarded even Walker and Campbell's cautious interpretation of the data with large skepticism. In his article “Lost world: How Canada missed its moment of glory,” Jacob Berkowitz describes the reaction of Walker and Campbell's colleagues:

“[Campbell]'s professional colleagues weren't as impressed [as the press]. One astronomer told The New York Times he wouldn't call anything a planet until he could walk on it. No one even attempted to confirm the results.”

Walker's gifted postdoc Bruce Campbell suffered most from the slow-going project that lacked appreciation and had difficulties getting continuing funding. In 1991, after more than a decade of data taking, they still had no discovery to show up with. Campbell meanwhile had reached age 42, and was still sitting on a position that was untenured, was not even tenure-track. Campbell's frustration built up to the point where he quit his job. When he left, he erased all the analyzed data in his university account. Luckily, his (both tenured) collaborators Walker and Yang could recover the data. Campbell made a radical career change and became a personal tax consultant.

But in late 1991, Walker and Yang were finally almost certain to have found sufficient evidence of an exoplanet around the star gamma Cephei, whose spectrum showed a consistent 2.5 year wobble. In a fateful coincidence, when Walker just thought they had pinned it down, one of his colleagues, Jaymie Matthews, came by his office, looked at the data and pointed out that the wobble in the data coincided with what appeared to be periods of heightened activity on the star's surface. Walker looked at the data with new eyes and, mistakenly, believed that they had been watching all the time an oscillating star rather than a periodic motion of the star's position.

Briefly after that, in early 1992, Nature reported the first confirmed discovery of an exoplanet by Wolszczan and Frail, based in the USA. Yet, the planet they found orbits a millisecond pulsar (probably a neutron star), so for many the discovery doesn't score highly because the star's collapse would have wiped out all life in that planetary system long ago.

In 1995 then, astronomers Mayor and Queloz of the University of Geneva announced the first definitive observational evidence for an exoplanet orbiting a normal star. The planet has an orbital period of a few days only, no decade long recording was necessary.

It wasn't until 2003 that the planet that Walker, Campbell and Yang had been after was finally confirmed.

There are three messages to take away from this story.

First, Berkowitz in his article points out that Canada failed to have faith in Walker and Campbell's research at the time when just a little more support would have made them first to discover an exoplanet. Funding for long-term projects is difficult to obtain and it's even more difficult if the project doesn't produce results before it's really done. That can be an unfortunate hurdle for discoveries.

Second, it is in hindsight difficult to understand why Walker and Campbell's colleagues were so unsupportive. Nobody ever really doubted that exoplanets exist, and with the precision of measurements in astronomy steadily increasing, sooner or later somebody would be able to find statistically significant evidence. It seems that a few initial false claims had a very unfortunate backlash that did exceed the reasonable.

Third, in the forest of complaints about lacking funding for basic research, especially for long-term projects, every tree is a personal tragedy.

Book review: “How to Teach Relativity to Your Dog” by Chad Orzel

2012-04-14T05:50:00.000-04:00

How to Teach Relativity to Your Dog
By Chad Orzel
Basic Books (February 28, 2012)

Let me start with three disclaimers: First, I didn’t buy the book, I got a free copy from the editor. Second, this is the second of Chad Orzel’s dog physics books and I didn’t read the first. Third, I’m not a dog person.

Chad Orzel from Uncertain Principles is a professor for physics at Union College and the best known fact about him is that he talks to his dog, Emmy. Emmy is the type of dog large enough to sniff your genitals without clawing into your thighs, which I think counts in her favor.

That Chad talks to his dog is of course not the interesting part. I mean, I talk to my plants, but who cares? (How to teach hydrodynamics to your ficus.) But Chad imagines his dog talks back, and so the book contains conversations between Emmy and Chad about physics.

In this book, Chad covers the most important aspects of special and general relativity: time dilatation and length contraction, space-time diagrams, relativistic four-momentum, the equivalence principle, space-time curvature, the expansion of the universe and big bang theory. Emmy and Chad however go beyond that by introducing the reader also to the essentials of black holes, high energy particle collisions, the standard model of particle physics and Feynman diagrams. They even add a few words on grand unification and quantum gravity.

The physics explanations are very well done, and there are many references to recent observations and experiments, so the reader is not left with the impression that all this is last century’s stuff. The book contains many helpful figures and even a few equations. It also comes with a glossary and a guide to further reading.

Emmy’s role in the book is to engage Chad in a conversation. These dialogues are very well suited to introduce unfamiliar subjects because they offer a natural way to ask and answer questions, and Chad uses them masterfully. Besides Emmy the dog, the reader also meets Nero the cat and there are a lot of squirrels involved too. The book is written very well, in unique do..., oops, Orzel-style, with a light sense of humor.

It is difficult for me to judge this book. I must have read dozens of popular science introductions to special and general relativity, but most of them 20 years ago. Chad explains very well, but then all the dog stuff takes up a lot of space (the book has 300 pages) and if you are, like me, not really into dogs, the novelty wears off pretty fast and what’s left are lots of squirrels.

I did however learn something from this book, for example that dogs eat cheese, which was news to me. I also I learned that Emmy is partly German shepherd and thus knows the word “Gedankenexperiment,” though Stefan complains that she doesn’t know the difference between genitive and dative.

In summary, Chad Orzel’s book “How to Teach Relativity to Your Dog” is a flawless popular science book that gets across a lot of physics in an entertaining way. If you always wanted to know what special and general relativity is all about and why it matters, this is a good starting point. I’d give this book 5 out of 5 tail wags.

Some physics-themed ngram trends

2012-04-12T05:44:00.004-04:00

I've been playing again with Google ngram, which shows the frequency by which words appear in books that are in the Google database, normalized to the number of books. Here are some keywords from physics that I tried which I found quite interesting.

In the first graph below you see "black hole" in blue which peaks around 2002, "big bang" in red which peaks around 2000, "quantization" in green which peaks to my puzzlement around 1995, and "dark matter" in yellow which might peak or plateau around 2000. Data is shown from 1920 to 2008. Click to enlarge.

In the second graph below you see the keywords "multiverse" in blue, which increases since about 1995 but interestingly seems to have been around much before that, "grand unification" in yellow which peaks in the mid 80s and is in decline since, "theory of everything" in green which plateaus around 2000, and "dark energy" in red which appears in the late 90s and is still sharply increasing. Data is shown from 1960 to 2008. Click to enlarge.

This third figure shows "supersymmetry" in blue which peaks around 1985 and 2001, "quantum gravity" in red which might or might not have plateaued, and "string theory" in green which seems to have decoupled from supersymmetry in early 2002 and avoided to drop. Data is shown from 1970 to 2008.

A graph that got so many more hits it wasn't useful to plot it with the others: "emergence" which peaked in the late 90s. Data is shown from 1900 to 2008.

More topics of the past: "cosmic rays" in blue which was hot in the 1960s, "quarks" in green which peaks in the mid 90s, and "neutrinos" in red peak around 1990. Data is shown from 1920 to 2008.

Even quantum computing seems to have maxed (data is shown from 1985 to 2008).

So, well, then what's hot these days? See below "cold atoms" in blue, "quantum criticality" in red and "qbit" in green. Data is shown from 1970 to 2008.

So, condensed matter and cosmology seem to be the wave of the future, while particle physics is in the decline and quantum gravity doesn't really know where to go. Feel free to leave your interpretation in the comments!

Be careful what you wish for

2012-04-10T12:44:00.002-04:00

Michael Nielsen in his book “Reinventing Discovery” relates the following anecdote from the history of science.

In the year 1610, Galileo discovered that the planet Saturn, the most distant then known planet, had a peculiar shape. Galileo’s telescope was not good enough to resolve Saturn’s rings, but he saw two bumps on either side of the main disk. To make sure this discovery would be credited to him, while still leaving him time to do more observations, Galileo followed a procedure common at the time: He sent the announcement of the discovery to his colleagues in form of an anagram

smaismrmilmepoetaleumibunenugttauiras
This way, Galileo could avoid revealing his discovery, but would still be able to later claim credit by solving the anagram, which meant “Altissimum planetam tergeminum observavi,” Latin for “I observed the highest of the planets to be three-formed.”

Among Galileo’s colleagues who received the anagram was Johannes Kepler. Kepler had at this time developed a “theory” according to which the number of moons per planet must follow a certain pattern. Since Earth has one moon and from Jupiter’s moons four were known, Kepler concluded that Mars, the planet between Earth and Jupiter, must have two moons. He worked hard to decipher Galileo’s anagram and came up with “Salve umbistineum geminatum Martia proles” Latin for “Be greeted, double knob, children of Mars,” though one letter remained unused. Kepler interpreted this as meaning Galileo had seen the two moons of Mars, and thereby confirmed Kepler’s theory.

Psychologists call this effort which the human mind makes to brighten the facts “motivated cognition,” more commonly known as “wishful thinking.” Strictly speaking the literature distinguishes both in that wishful thinking is about the outcome of a future event, while motivated cognition is concerned with partly unknown facts. Wishful thinking is an overestimate of the probability that a future event has a desirable outcome, for example that the dice will all show six. Motivated cognition is an overly optimistic judgment of a situation with unknowns, for example that you’ll find a free spot in a garage whose automatic counter says “occupied,” or that you’ll find the keys under the streetlight.

There have been many small-scale psychology experiments showing that most people are prone to overestimate a lucky outcome (see eg here for a summary), even if they know the odds, which is why motivated cognition is known as a “cognitive bias.” It’s an evolutionary developed way to look at the world that however doesn’t lead one to an accurate picture of reality.

Another well-established cognitive bias is the overconfidence bias, which comes in various expressions, the most striking one being “illusory superiority”. To see just how common it is for people to overestimate their own performance, consider the 1981 study by Svenson which found that 93% of US American drivers rate themselves to be better than the average.

The best known bias is maybe confirmation bias, which leads one to unconsciously pay more attention to information confirming already held believes than to information contradicting it. And a bias that got a lot attention after the 2008 financial crisis is “loss aversion,” characterized by the perception of a loss being more relevant than a comparable gain, which is why people are willing to tolerate high risks just to avoid a loss.

It is important to keep in mind that these cognitive biases serve a psychologically beneficial purpose. They allow us to maintain hope in difficult situations and a positive self-image. That we have these cognitive biases doesn’t mean there’s something wrong with our brain. In contrast, they’re helpful to its normal operation.

However, scientific research seeks to unravel the truth, which isn’t the brain’s normal mode of operation. Therefore scientists learn elaborate techniques to triple-check each and every conclusion. This is why we have measures for statistical significance, control experiments and double-blind trials.

Despite that, I suspect that cognitive biases still influence scientific research and hinder our truth-seeking efforts because we can’t peer review scientists motivations, and we’re all alone inside our heads.

And so the researcher who tries to save his model by continuously adding new features might misjudge the odds of being successful due to loss aversion. The researcher who meticulously keeps track of advances of the theory he works on himself, but only focuses on the problems of rival approaches, might be subject to confirmation bias, skewing his own and other people’s evaluation of progress and promise. The researcher who believes that his prediction is always just on the edge of being observed is a candidate for motivated cognition.

And above all that, there’s the cognitive meta-bias, the bias blind spot: I can’t possibly be biased.

Scott Lilienfeld in his SciAm article “Fudge Factor” argued that scientists are particularly prone to conformation bias because

“[D]ata show that eminent scientists tend to be more arrogant and confident than other scientists. As a consequence, they may be especially vulnerable to confirmation bias and to wrong-headed conclusions, unless they are perpetually vigilant”

As I scientist, I regard my brain the toolbox for my daily work, and so I am trying to learn what can be done about its shortcomings. It is to some extent possible to work on a known bias by rationalizing it: By consciously seeking out the information that might challenge ones beliefs, asking a colleague for a second opinion on whether a model is worth investing more time, daring to admit to being wrong.

And despite that, not to forget the hopes and dreams.

Mars btw has to our best current knowledge indeed two moons.

Happy Easter!

2012-04-08T03:01:00.005-04:00

Stefan honors the Easter tradition by coloring eggs every year. The equipment for this procedure is stored in a cardboard shoe-box labeled "Ostern" (Easter). The shoe-box dates back to the 1950s and once contained a pair of shoes produced according to the newest orthopedic research.

I had never paid much attention to the shoe-box but as Stefan pointed out to me this year, back then the perfect fit was sought after by x-raying the foot inside the shoe. The lid of the box contains an advertisement for this procedure which was apparently quite common for a while.

Click to enlarge. Well, they don't xray your feet in the shoe stores anymore, but Easter still requires coloring the eggs. And here they are:

Happy Easter everybody!

Book Review: "The Quest for the Cure" by B.R. Stockwell

2012-04-06T06:40:00.005-04:00

The Quest for the Cure: The Science and Stories Behind the Next Generation of Medicines
By Brent R. Stockwell
Columbia University Press (June 1, 2011)

As a particle physicist, I am always amazed when I read about recent advances in biochemistry. For what I am concerned, the human body is made of ups and downs and electrons, kept together by photons and gluons - and that's pretty much it. But in biochemistry, they have all these educated sounding words. They have enzymes and aminoacids, they have proteases, peptides and kineases. They have a lot of proteins, and molecules with fancy names used to drug them. And these things do stuff. Like break up and fold and bind together. All these fancy sounding things and their interactions is what makes your body work; they decide over your health and your demise.

With all that foreign terminology however, I've found it difficult to impossible to read any paper on the topic. In most cases, I don't even understand the title. If I make an effort, I have to look up every second word. I do just fine with the popular science accounts, but these always leave me wondering just how do they know this molecule does this and how do they know this protein breaks there, fits there, and that causes cancer and that blocks some cell-function? What are the techniques they use and how do they work?

When I came across Stockwell's book "The Quest for the Cure" I thought it would help me solve some of these mysteries. Stockwell himself is a professor for biology and chemistry at Columbia university. He's a guy with many well-cited papers. He knows words like oligonucleotides and is happy to tell you how to pronounce them: oh-lig-oh-NOOK-lee-oh-tide. Phosphodiesterase: FOS-foh-dai-ESS-ter-ays. Nicotinonitrile: NIH-koh-tin-oh-NIH-trayl. Erythropoitin: eh-REETH-roh-POIY-oh-ten. As a non-native speaker I want to complain that this pronunciation help isn't of much use for a non-phonetic language; I can think of at least three ways to pronounce the syllable "lig." But then that's not what I bought the book for anyway.

The starting point of "The Quest for the Cure" is a graph showing the drop in drug approvals since 1995. Stockwell sets out to first explain what is the origin of this trend and then what can be done about it. In a nutshell, the issue is that many diseases are caused by proteins which are today considered "undruggable" which means they are folded in a way that small molecules, that are suitable for creating drugs, can't bind to the proteins' surfaces. Unfortunately, it's only a small number of proteins that can be targeted by presently known drugs:

"Here is the surprising fact: All of the 20,000 or so drug products that ever have been approved by the U.S. Food and Drug Administration interact with just 2% of the proteins found in human cells."

And fewer than 15% are considered druggable at all.

Stockwell covers a lot of ground in his book, from the early days of genetics and chemistry to today's frontier of research. The first part of the book, in which he lays out the problem of the undruggable proteins, is very accessible and well-written. Evidently, a lot of thought went into it. It comes with stories of researchers and patients who were treated with new drugs, and how our understanding of diseases has improved. In the first chapters, every word is meticulously explained or technical terms are avoided to the level that "taken orally" has been replaced by "taken by mouth."

Unfortunately, the style deteriorates somewhat thereafter. To give you an impression, it starts more reading like this

"Although sorafenib was discovered and developed as an inhibitor of RAF, because of the similarity of many kinases, it also inhibits several other kinases, including the patelet-derived growth factor, the vascular endothelia growth factor (VEGF) receptors 2 and 3, and the c-KIT receptor."

Now the book contains a glossary, but it's incomplete (eg it neither contains VEGF nor c-KIT). With the large number of technical vocabulary, at some point it doesn't matter anymore if a word was introduced, because if it's not something you deal with every day it's difficult to keep in mind the names of all sorts of drugs and molecules. It gets worse if you put down the book for a day or two. This doesn't contribute to the readability of the book and is somewhat annoying if you realize that much of the terminology is never used again and one doesn't really know why it was necessary to use to begin with.

The second part of the book deals with the possibilities to overcome the problem of the undruggable molecules. In that part of the book, the stories of researchers curing patients are replaced with stories of the pharmaceutical industry, the start-up of companies and the ups and downs of their stock price.

Stockwell's explanations left me wanting in exactly the points that I would have been interested in. He writes for example a few pages about nuclear magnetic resonance and that it's routinely used to obtain high resolution 3-d pictures of small proteins. One does not however learn how this is actually done, other than that it requires "complicated magnetic manipulations" and "extremely sophisticated NMR methods." He spends a paragraph and an image on light-directed synthesis of peptides that is vague at best, and one learns that peptides can be "stapled" together, which improves their stability, yet one has no clue how this is done.

Now the book is extremely well referenced, and I could probably go and read the respective papers in Science. But then I would have hoped that Stockwell's book saves me exactly this effort.

On the upside, Stockwell does an amazingly good job communicating the relevance of basic research and the scientific method, and in my opinion this makes up for the above shortcomings. He tells stories of unexpected breakthroughs that came about by little more than coincidence, he writes about the relevance of negative results and control experiments, and how scientific research works:

"There is a popular notion about new ideas in science springing forth from a great mind fully formed in a dazzling eureka moment. In my experience this is not accurate. There are certainly sudden insights and ideas that apear to you from time to time. Many times, of course, a little further thought makes you realize it is really an absolutely terrible idea... But even when you have an exciting new idea, it begins as a raw, unprocessed idea. Some digging around in the literature will allow you to see what has been done before, and whether this idea is novel and likely to work. If the idea survives this stage, it is still full of problems and flaws, in both the content and the style of presenting it. However, the real processing comes from discussing the idea, informally at first... Then, as it is presented in seminars, each audience gives a series of comments, suggestions, and questions that help mold the idea into a better, sharper, and more robust proposal. Finally, there is the ultimate process of submission for publication, review and revision, and finally acceptance... The scientific process is a social process, where you refine your ideas through repeated discussions and presentations."

He also writes in a moderate dose about his own research and experience with the pharmaceutical industry.

The proposals that Stockwell has how to deal with the undruggable proteins have a solid basis in today's research. He isn't offering dreams or miracle cures, but points out hopeful recent developments, for example how it might be possible to use larger molecules. The problem with large molecules is that they tend to be less stable and don't enter cells readily, but he quotes research that shows possibilities to overcome this problem. He also explains the concept of a "privileged structure," structures that have been found with slight alterations to bind to several proteins. Using such privileged structures might allow one to sort through a vast parameter space of possible molecules with a higher success rate. He also talks about using naturally occurring structures and the difficulties with that. He ends his book by emphasizing the need for more research on this important problem of the undruggable proteins.

In summary: "The Quest for the Cure" is a well-written book, but it contains too many technical expressions, and in many places scientific explanations are vague or lacking. It comes with some figures which are very helpful, but there could have been more. You don't need to read the blurb to figure out that the author isn't a science writer but a researcher. I guess he's done his best, but I also think his editor should have dramatically sorted out the vocabulary or at least have insisted on a more complete glossary. Stockwell makes up for this overdose of biochemistry lingo with communicating very well the relevance of basic research and the power of the scientific method.

I'd give this book four out of five stars because I appreciate Stockwell has taken the time to write it to begin with.

On the importance of being wrong

2012-04-04T11:54:00.000-04:00

Some years ago, I attended a seminar by a young postdoc who spoke about an extension of the standard model of particle physics. Known as “physics beyond the standard model,” this is a research area where theory is presently way ahead of experiment. In the hope to hit something by shooting in the dark, theorists add stuff that we haven’t seen to the stuff we know, and then explain why we haven’t seen the additional stuff – but might see it with some experiment which is about to deliver result. Ie, the theorists tell experimentalists where to look.

Due to the lack of observational evidence, the main guide in this research area is mathematical consistency combined with intuition. This type of research is absolutely necessary to make progress in the present situation, but it’s also very risky. Most of the models considered today will turn out to be wrong.

The content of the seminar wasn’t very memorable. The reason I still recall it is that, after the last slide had flashed by, somebody asked what the motivation is to consider this extension of the standard model, to which the speaker replied “There is none, except that it can be done.”

This is a remarkably honest answer, especially since it came from a young researcher who had still ahead of him the torturous road to tenure.

You don’t have to look far in the blogosphere or on Amazon to find unsolicited advice for researchers for how to sell themselves. There now exist coaching services for scientists, and some people make money writing books about “Marketing for Scientists.” None of them recommends that when you’ve come to the conclusion that a theory you looked at wasn’t as interesting as you might have thought, you go and actually say that. Heaven forbid: You’re supposed to be excited about the interesting results. You were right all along that the result would be important. And there are lots of motivations why this is the one and only right thing to do. You have won great insights in your research that are relevant for the future of mankind, at least, if not for all mankinds in all multiverses.

It’s advice well meant. It’s advice for how to reach your presumed personal goal of landing a permanent position in academia, taking into account the present mindset of your older peers. It is not advice for how to best benefit scientific research in the long run. In fact, unfortunately, the both goals can be in conflict.

Of course any researcher should in the first line work on something interesting, well motivated, and something that will deliver exciting results! But most often it doesn’t work as you wish it should. To help move science forward, the conclusion that the road you’ve been on doesn’t seem too promising should be published to prevent others from following you into a dead end, or at least telling them where the walls are. Say it, and start something new. It’s also important for your personal development. If you advertise your unexciting research as the greatest thing ever, you might eventually come to believe it and waste your whole life on it.

The reason nobody advises you to say your research project (which might not even have been your own choice) is unexciting is that it’s difficult if not impossible to publish a theoretical paper that examines an approach just to come to the conclusion that it’s not a particularly convincing description of nature. The problem with publishing negative results might be familiar to you from medicine, but it exists in theoretical physics as well. Even if you get it published, and even if it’s useful in saving others the time and work that you have invested, it will not create a research area and it’s unlikely to become well-cited. If that’s all you think matters, for what your career is concerned it would be a waste of your time indeed.

So, they are arguably right with their career advice. But as a scientist your task is to advance our understanding of nature, even if that means concluding you’ve wasted your time – and telling others about it. If you make everybody believe in the excitement of an implausible model, you risk getting stuck on a topic you don’t believe in. And, if you’re really successful, you get others stuck on it too. Congratulations.

This unexciting seminar speaker some years ago, and my own yawn, made me realize that we don’t value enough those who say: “I tried this and it was a mistake. I thought it was exciting, but I was wrong.” Basic research is a gamble. Failure is normal and being wrong is important.

Interna

2012-04-02T05:00:00.001-04:00

In the past month, Lara and Gloria have learned to learn. They try to copy and repeat everything we do. Lara surprised me by grabbing a brush and pulling it through her hair and Gloria, still short on hair, tries to put on her shoes. They haven't yet learned to eat with a spoon, but they've tried to feed us.

They both understand simple sentences. If I ask where the second shoe is, they'll go and get it. If I tell them lunch is ready, they'll both come running and try to push the high chairs towards the table. If we tell them we'll go for a walk, they run to the door. If we do as much as mention cookies, they'll point at the bag and insist on having one.

Lara is still the more reserved one of the two. Faced with something new, she'll first watch from a distance. Gloria has no such hesitations. Last week, I childproofed the balcony. Lara, who was up first, saw the open door and froze. She stood motionless, staring at the balcony for a full 10 minutes. Then Gloria woke up, came running while yelling "Da,da" - and stumbled over the door sill, landing on her belly. Lara then followed her, very carefully.

Now that spring is coming and the girls are walking well, we've been to the playground several times. Initially Lara and Gloria just sat there, staring at the other children. But meanwhile they have both made some contacts with other children, though not without looking at me every other minute to see if I approve. Gloria, as you can guess, is the more social one. She'll walk around with her big red bucket and offer it to others, smiling brightly. She's 15 months and has at least 3 admirers already, all older boys who give her toys, help her to walk, or even carry her around. (The boys too look at me every other minute to see if I approve.) Lara and I, we watch our little social butterfly, and build sand castles.

From my perspective, the playground is a new arena too. Weekdays, the adult population is exclusively female and comes in two layers of generations, either the mothers or the grandmothers. They talk about their children and pretty much nothing but their children, unless you want to count pregnancies separately. After some initial mistakes, I now bring a book, paper, or a magazine with me to hide behind.

Another piece of news from the past month is that I finally finished the review on the minimal length in quantum gravity that I've been working on since last year. It's now on the arXiv. The first 10 pages should be understandable for pretty much everybody, and the first half should be accessible also for undergraduates. So if you were wondering what I'm doing these days besides running after my daughters, have a look at my review.

Computer Scientists develop Software for Virtual Member of Congress

2012-04-01T02:00:00.001-04:00

A group of computer scientists from Rutgers university have published a software intended for crowd-sourcing the ideal candidate. "We were asking ourselves: Why do we waste so much time with candidates who disagree with themselves, aren't able to recall their party's program, and whose intellectual output is inferior even to Shit Siri Says?" recalls Arthur McTrevor, who lead the project, "Today, we have software that can perform better."

McTrevor and his colleagues then started coding what they refer to as the "unopinionated artifical intelligence" of the virtual representative, the main information processing unit. The unopinionated intelligence is a virtual skeleton which comes alive by crowd-sourcing opinions from a selected group of people, for example party members. Members feed the software with opinions, which are then aggregated and reformulated to minimize objectionable statements. The result: The perfect candidate.

The virtual candidate also has a sophisticated speech assembly program, a pleasant looking face, and a fabricated private life. Visual and audial appearance can be customized. The virtual candidate has a complete and infallible command of the constitution, all published statistical data, and can reproduce quotations from memorable speeches and influential books in the blink of an eye. "80 microseconds, actually," said McTrevor. The software moreover automatically creates and feeds its own Facebook account and twitter feed.

The group from Rutgers tested the virtual representative in a trial run whose success is reported in a recent issue of Nature. In their publication, the authors point out that the virtual representative is not a referendum that aggregates the opinions of the general electorate. Rather, it serves a selected group to find and focus their identity, which can then be presented for election.

In an email conversation, McTrevor was quick to point out that the virtual candidate is made in USA, and its patent dated 2012. The candidate will be thus be eligible to run for congress at the "age" of 25, in 2037.