Blogs / Cosmic Variance

A little treat for loyal CV readers: Tom Levenson is a professor of science writing at MIT, and the proprietor of the Inverse Square Blog, one of the most erudite scientifically-minded outposts in this blogosphere of ours. I’ve been enjoying how Tom writes engagingly about science while mixing in cultural and artistic references, so I asked if he would like to guest-blog a bit here at CV. This is the first of three posts he’ll be contributing; look for the other two later this week. [Here is two, and here is three.]

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Monday Isaac Newton blogging: A little light reading, Principia edition.

Update: See correction below.**

To introduce myself to the Cosmic Variance community (at Sean’s very kind invitation), let me just admit up front that I am a glutton for punishment.

Exhibit A: last year I read the Principia for pleasure.*

That’s not exactly right– it is more accurate to say that in the context of writing a book on Isaac Newton’s role as currency cop and death penalty prosecutor, I found myself reading the Principia as literature rather than the series of proofs it appears to be. Just like John Locke, who had to ask Christiaan Huygens if he could take the mathematical demonstrations on faith (Huygens said he could), I read to see what larger argument Newton was making about the ways human beings could now make sense of material experience. (This is, by the way, the only connection I can imagine that Locke and I share.)

What I got out of the exercise, more than anything else, was a reminder of how something we now mostly take for granted is in fact truly extraordinary: taken all in all, it seems genuinely remarkable that cosmology exists at all as a quantitative, empirical science.

That is: it is not obvious – or at least it wasn’t, all that long ago, that it would ever be possible to treat the universe as a whole as an object of study – especially given our very constrained vantage point from within that which we want to examine.

Most accounts of the story of modern cosmology more or less unconsciously downplay the strangeness of the claim that we can in fact make sense of the universe as a whole. They begin – mine did — with Einstein and the 1917 paper “Cosmological Considerations in the General Theory of Relativity, (to be found in English translation here.) Cosmology in this telling becomes more or less an inevitable extension of a recent advance in theoretical physics; the change in worldview precedes this extension of the apparatus of general relativity into a new calculation.

I recant: though I certainly wrote my version of this basic tale, reading Newton has reminded me of the much more radical change in the understanding of what it is possible to think about that had to precede all that cosmology (among much else) has achieved.

It certainly was not clear that the universe as a whole was subject to natural philosophical scrutiny in 1684, the year of Edmond Halley’s fortunate visit to Trinity College, Cambridge, and his more-or-less innocent question about the curve traced by a planet, assuming “the force of attraction towards the sun to be reciprocal to the square of their distance from it? that would produce an elliptical planetary orbit with the sun at one focus.

An ellipse inverse square relationship, Newton told Halley.

How did he know?

Why – he had calculated it.

By 1686, Newton had extended and revised his off-the-cuff answer into the first two books of Principia, both titled “The Motion of Bodies.” These pursued the implications of his three laws of motion through every circumstance Newton could imagine, culminating in his final demolition of Cartesian vortex physics.

But even though he had worked through a significant amount of mathematical reasoning developing the consequences of his inverse square law of gravitation, he left the ultimate demonstration of the power of these ideas for book three.

Books one and two had been “strictly mathematical,” Newton wrote. If there were any meat and meaning to his ideas, though, he must “exhibit the system of the world from these same principles.”

To make his ambitions absolutely clear Newton used the same phrase for the title of book three. There his readers would discover “The System of the World.”

This is where the literary structure of the work really comes into play, in my view. Through book three, Newton takes his audience through a carefully constructed tour of all the places within the grasp of his new physics. It begins with an analysis of the moons of Jupiter, demonstrating that inverse square relationships govern those motions. He went on, to show how the interaction between Jupiter and Saturn would pull each out of a perfect elliptical orbit; the real world, he says here, is messier than a geometer’s dream.

He worked on problems of the moon’s motion, of the issues raised by the fact that the earth is not a perfect sphere, and then, in what could have been a reasonable resting point for the book as a whole, he brought his laws of motion and gravity literally down to earth, with his famous analysis of the way the moon and the sun influence the tides.

Why not stop there? The story thus far had taken gravity from the limits of the observed solar system to the ground beneath each reader’s feet. More pragmatically – it told a story whose significance Newton’s audience would have grasped immediately: the importance of understanding the rules governing tides was obvious enough to the naval powers of the day.

No matter. Newton kept on going. The last section of his world-system turned to the celestial and seemingly impractical: the motion of comets, in an analysis of the track of the great comet of 1680.

Newton presented his findings through two different approaches: one produced by collecting all the data points he could of traveler’s observations and plotting the comet’s track against those points; and the other in which he selected just three points and calculated the path implied.

The two analyses matched almost exactly, and both showed that this comet did not complete a neat, elliptical orbit. Rather, it traced a parabola.

Newton knew what he had done. He was no accidental writer. A parabola, of course, is a curve that keeps on going – and that meant that at the end of a very long and very dense book, he lifted off again from the hard ground of daily reality and said, in effect, look: All this math and all these physical ideas govern everything we can see, out to and past the point where we can’t see anymore.

Most important, he did so with implacable rigor, a demonstration that, he argued, should leave no room for dissent. He wrote “The theory that corresponds exactly to so nonuniform a motion through the greatest part of the heavens, and that observes the same laws as the theory of the planets and that agrees exactly with exact astronomical observations cannot fail to be true.” (Italics added).

And now, finally, to get back to the point: this, I would argue, was the essential first and in some ways the most difficult step in the foundations of cosmology. With it Newton transformed the scale of the universe we inhabit, making it huge, perhaps infinite. Even more important, he demonstrated that a theory that could not fail to be true made it possible to examine one phenomenon — matter in motion under the influence of gravity — throughout all space.

That thought thrilled Newton’s contemporaries – Halley caught the mood in his dedicatory poem to the Principia, writing that “Error and doubt no longer encumber us with mist;/….We are now admitted to the banquets of the Gods;/We may deal with laws of heaven above; and we now have/The secret keys to unlock the obscure earth….” To catch a distant echo of that euphoria, just imagine what it would have been like to contemplate that ever receding comet, fifteen years into its journey towards who knew where at the time of Newton’s writing, and know that its behavior was knowable through an extraordinary act of human invention.

It’s a whole ‘nother story to ask what it would take to create a similar sense of pride and pleasure in a general audience today. But just to get the discussion going, I’d suggest that one of the oddities of contemporary cosmology as presented to the public is the degree to which the universe at large has become more homey; the very success in making the argument that there is a continuous scientific narrative to be told from the Big Bang to the present makes it harder to see just how grand a claim that is.

So, to end with an open invitation to this community: what would make current physical ideas as powerful and as intelligibly strange as Newton was able to make his story of a comet traveling from and to distances with out limit?

Last housekeeping notes: in one of the more premature bits of self-promotion in publishing history, the Newton material discussed above derives from my book, tentatively titled Newton and the Counterfeiter, coming early next year from Houghton Mifflin Harcourt (and Faber, for those of you across the pond).

Also – my thanks again to Sean Carroll for welcoming me here. If you want to see what I do when I’m at home, check out The Inverse Square Blog.

*If you are minded to pick up a copy of Principia, get this edition. Not only is it a well made book, easy to look at, well printed, with clear diagrams, it comes with the invaluable guide to reading the Principia written by I. Bernard Cohen. Accept no substitutes.

**Thanks to reader and award-winning physics teacher David Derbes for catching my inversion of the problem Halley put to Newton. Let this be a lesson to me: blog in haste; check one’s notes at leisure; repent in public.

Image: Woodcut by Jiri Daschitzsky, “The Great Comet of 1577.” Source: Wikimedia Commons.

You may have heard some of the buzz about a new result concerning the direct detection of dark matter particles in an underground laboratory. The buzz originates from a new paper by the DAMA/LIBRA collaboration; David Harris links to powerpoint slides from Rita Bernabei, leader of the experiment, from her talk at a meeting in Venice.

The new experiment is an upgrade from a previous version of DAMA, which had already been on record as having recorded a statistically significant signal of the form you would expect from the collision of weakly interacting massive particles (WIMP’s) with the detector. The experiment uses a challenging technique, in which their focus is not on eliminating all possible backgrounds so as to isolate the dark-matter signal, but to look at the annual modulation in that signal that would presumably be caused by the Earth’s orbital motion through the cloud of dark matter in the Solar System: you expect more events when we are moving with a high velocity into the dark-matter wind. Other workers in the field have not been shy about expressing skepticism, but the DAMA team has stood their ground; as Jennifer notes in her report from the recent APS Meeting, the DAMA collaboration home page currently features a quote from Kipling: “If you can bear to hear the truth you’ve spoken/ twisted by knaves to make a trap for fools,/ ……………you’ll be a Man my son!”

To help provide some insight and context, we’ve solicited the help of a true expert in the field — Juan Collar of the University of Chicago. I got to know Juan back in my days as a Midwesterner, and a trip to his bustling underground experimental empire was always a highlight of anyone’s visit to the UofC physics department. You can hear him talk about his own work in this colloquium at Fermilab; he’s agreed to post for us about his views on the new DAMA result, and more general thoughts on what it takes to search for 25% of the universe. I promise you won’t be bored.

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My dear friend Sean has me blogging: hey, I’ll try anything once. On the subject of the recent DAMA results no less, as per his request. I am normally a bit of a curmudgeon but… Sean, you really want the worst of me out there permanently on the internets, don’t you?

I’ll try to keep this to the point. A bard I am not, nor the subject invites any poetry. I have therefore chosen brief eruptions of flatulence as the metric and style for this piece. The result of indigestion, you see. I’ll start with the most negative, so as to end up on a brighter note:

• The modulation is undeniable by now. I don’t know of any colleagues who doubted these data were blatantly modulated already back in 2003, when “the lady” (DAMA) decided to keep mum for a while. However, to conclude from something this mundane that the experiment “confirms evidence of Dark Matter particles in the galactic halo with high confidence level” or that there is “an evidence for the presence of dark matter particles in the galactic halo at 8.2 sigma confidence level” is simply delusional. There is evidence for a modulation in the data at 8.2 sigma, stop. Compatible with what would be expected from some dark matter particles in some galactic halo models, full stop. Anything beyond this is wanting to believe, and it smears on the rest of us in the field. Of course, of course… there is no other observed process in nature that peaks in the summer and goes through a low in winter, so this must be dark matter, right? (Occam is turning in his grave, rusty razor still in hand. He is thinking a remake of that opening scene in “Un chien andalou“, with help from this little lady. I am channeling him loud and clear).
• Someone should take the DAMA folks aside for a beer, make them see the following. If one day soon we are all convinced that this effect was DM-induced (see below for what that will really take), they will be recognized for one of the greatest discoveries in the history of science, without them having to look desperate or foolish today. Or making the rest of us in the field do, by association: thanks DAMA, for cheapening the level of our discourse to truly imbecilic levels. (Sean, if you edit this I will scratch the paint off your car. I may not write blogs, but I do read them: I know how to hurt you).
• Deep breath. Having cleared the air some (or just made it toxic, whatever), it is not DAMA’s fault that there is a penury of signatures in this field of ours, laboratory searches for particle dark matter. The one possible exception to this is a detector with good recoil directionality and sufficient target mass to be truly competitive, but we don’t know of a good enough way to do this as of today (”good enough” folds in the price tag). People are still trying. The diurnal modulation in the DM signal that would be sensed by such a device is wickedly rich in features, extremely hard for nature to imitate with anything else. The annual modulation resides on the other side of this spectrum of complexity. It is the poor man’s smoking-gun to DM “evidence”. Inspected carefully, it is disappointingly feeble: different models of the halo can shift the phase of this modulation completely, turning expected maxima into minima and vice-versa, changing the expected amplitude as well. Add to this the fact that essentially every possible systematic effect able to pass for a “signal” can be yearly-modulated, for one reason or another. That’s the ones we can presently think of, and the ones yet to be proposed. To grow convinced that we have observed dark matter in the lab we’ll require a number of entirely different techniques, using a variety of targets, all pointing at the same WIMP (mass, cross sections), with additional back-up information from accelerator experiments and from gamma-ray satellite observations (so-called indirect searches). All of those lines crossing at one point, so to speak. This I (for one) will call “evidence”. I know of no single existing or planned DM experiment, including those I participate in, that would be able to make anything close to a bulletproof claim on its own. My advice to any overambitious individuals looking for a quick kill is to look elsewhere in physics. WIMP hunting is not it, no matter how important the discovery of these particles might be.

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Michelangelo is a grad student at Berkeley who had the fun opportunity to write a diary for the Economist that will continue through this week about his adventures doing particle physics in Antarctica. I would say more, but he does a pretty good job himself!

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First off, I’d like to thank Sean for giving me the chance to write this guest post. It’s not every day (in fact, this would be the first time) that I get to write something for a blog that I both read and enormously respect. This is an especially great opportunity since the scions of CV are graciously allowing me to do a bit of shameless self-promotion for a five-part journal, being published this week, that I got to write for the website of the Economist magazine.

Maybe I should back up and introduce myself. I’m currently a fifth year physics PhD student at UC Berkeley. My research is on the IceCube project, a neutrino physics experiment located at the South Pole. Basically, we’re building the world’s largest particle detector out of the polar icecap itself. Using hot water, we melt holes 2,500 m down into the ice and install very sensitive light detectors. This allows us to study the particle debris that results from collisions of high-energy neutrinos in the ice. Ultimately, we’re hoping to learn about the basic physics of neutrinos as well about the properties of some of the violent astrophysical objects that might produce them and send them hurtling through the universe towards our detector.

This means that I do what many physicists do. I sit in front of a computer, writing code and analyzing data. I do calculations and simulations. I drink coffee and talk and argue with colleagues. But it also means that I get to do something only a smaller subset of astrophysicists and physicists get to do. I get to travel to a really exotic location to do fieldwork.

I think this is an aspect of being a physicist that sometimes gets overlooked. It’s true that astronomers have always gone to mountaintops to build the best telescopes, and particle physicists have always traveled to underground accelerator facilities. However, fanning out to other locations to take advantage of particular natural features is something that has become increasingly important as we build bigger, deeper detectors to try to understand weak signals and/or rare and exotic phenomena. In recent years, physicists have been traveling to the vast Argentinean plains to understand the origins of the highest energy cosmic rays, particles that are constantly bombarding Earth. Folks who study the CMB and other long-wavelength radiation have been heading up to the high-altitude Atacama Desert (here, here, and here) and to the South Pole to take advantage of their thin, dry atmospheres. Selection and planning has been moving forward for a deep underground facility for doing basic neutrino and dark matter physics.

All this means that graduate students for years to come will have the exciting opportunity to go out into the field to do their work. While the research itself is exciting, traveling to these exotic locations brings us in contact with scientists from other fields doing all sorts of other great science. For those of us who get to go to Antarctica, we meet people on the cutting edge of climate and atmospheric research. For those working underground, they may encounter earth scientists or researchers study life in extreme environments. All of which make for rich and stimulating conversations and experiences.

This brings me back to the shameless self-promotion. When the Economist opportunity came up to share some of my experiences traveling, living, and doing research at the South Pole, I jumped at it. I’ve tried to squeeze in as much basic climate science and physics as I could, so if you’re interested, check it out here…

Science or Sociology?
Joseph Polchinski, 5/20/07

This is a continuation of the on-line discussion between Lee Smolin and myself, which began with my review of his book and has now continued with his response. A copy of this exchange (without the associated comment threads) is here.

Dear Lee,

Thank you for your recent response to my review. It will certainly be helpful in clarifying the issues. Let me start with your wish that I do more to address the broader issues in your book. When I accepted the offer to review these two books, I made two resolutions. The first was to stick to the physics, because this is our ultimate goal, and because it is an area where I can contribute expertise. Also, keeping my first resolution would help me to keep the second, which was to stay positive. I am happy that my review has been well-received. Your response raises some issues of physics, and these are the most interesting things to discuss, but I will also address some of the broader issues you raise, including the process of physics, ethics, and the question in the title. Let me emphasize that I have no desire to criticize you personally, but in order to present my point of view I must take serious issue both with your facts and with the way that they are presented.

Regarding your points:

The fictitious prediction of a non-positive cosmological constant. This is a key point in your book, and the explanation that you now give makes no logical sense. In your book you say (A) “… it [a non-positive cosmological constant] was widely understood to be a consequence of string theory.” You now justify this by the argument that a non-positive cosmological constant is a consequence of unbroken supersymmetry (true), so A would follow from (B) Unbroken supersymmetry was widely understood to be a consequence of string theory. But even if this were true, it would not support your story about the observation of the dark energy leading to a “genuine crisis, … a clear disagreement between observation and a prediction of string theory.” There would already have been a crisis, since supersymmetry must obviously be broken in nature; seeing the dark energy would not add to this. But in fact the true situation, as you can find in my book or in many review articles, was closer to the opposite of B than to B: (B’) Supersymmetry is broken in almost all Calabi-Yau vacua of heterotic string theory. We have no controlled examples because at least one modulus rolls off, usually to a regime where we cannot calculate. The solution to this problem may have to wait until we have a non-perturbative formulation of gravity, or even a solution to the cosmological constant problem.

In your response you largely raise issues surrounding B’, including the Witten quote, but I want to return to what you have actually written in your book. It is a compelling story, which leads into your discussion of “a group of experts doing what they can to save a cherished theory in the face of data that seem to contradict it.” It surely made a big impression on every reader; it was mentioned in several blogs, and in Peter Shor’s Amazon review. And it never happened. It is an example of something that that happens all too often in your book: you have a story that you believe, or want to believe, and you ignore the facts.

You go on to challenge the ethics of string theorists in regard to how they presented the issue of moduli stabilization in their talks and papers. I am quite sure that in every colloquium that I gave I said something that could be summarized as “We do not understand the vacuum in string theory. The cosmological constant problem is telling us that there is something that we do not understand about our own vacuum. And, we do not know the underlying principle of string theory. These various problems may be related.” The cosmological constant and the nature of string theory seemed much more critical than the moduli stabilization problem, and these are certainly what I and most other string theorists emphasized.

This scientific judgment has largely been borne out in time. In 1995-98 these incredible new nonperturbative tools were developed, and over the next few years many string theorists worked on the problem of applying them to less and less supersymmetric situations, culminating in the construction of stabilized vacua. Obviously many questions remain, and these are widely and openly debated. It seems like a successful scientific process: people knew what the important problems were, worked in various directions (a fair number did work on moduli stabilization over the years), and when the right tools became available the problem was solved. As you point out, the stabilization problem is nearly one hundred years old, and now string theorists (primarily the younger generation, I might add) have solved it. You are portraying a crisis where there is actually a major success, and you are creating an ethical issue where there is none.

AdS/CFT duality. You raise the issue of the existence of the gauge theory. There are two points here. First, Wilson’s construction of quantum field theory has been used successfully for 40 years. It is used in a controlled way by condensed matter physicists, lattice gauge theorists, constructive quantum field theorists, and many others. To argue that a technique that is so well understood does not apply to the case at hand, the scientific ethic requires that you do more than just say Not proven! Sociology! as you have done. You need to give an argument, ideally pointing to a calculation that one could do, or at least discuss, in which one would get the wrong answer.

I have given a specific argument why we are well within the domain of applicability of Wilson: there are 1+1 and 2+1 dimensional versions of AdS/CFT, which are also constructions of quantum gravity, and for which the gauge theory is super-renormalizable (and there are no chiral fermions): the counterterms needed to reach the supersymmetric continuum limit can be calculated in closed form – thus there is an algorithmic definition of the gauge theory side of the duality. You could perhaps argue that there will be a breaking of supersymmetry that will survive in the continuum limit, and we could sit down and do the calculation. But I know what this answer is, because I have done this kind of calculation many times (it is basically just dimensional analysis). Similar calculations, for rotational invariance and chiral symmetry, are routine in lattice gauge theory.

As a further ethical point, in your book you state that it is astounding that Gary Horowitz and I ignore the question of the existence of the gauge theory, and you then use this to make a point about groupthink (this is in your chapter on sociology). While you were writing your book, you and I discussed the above points in detail, so you knew that we had not ignored the issue but had thought about it deeply. You do not even acknowledge the existence of a scientific counterargument to your statement, and in saying that Gary and I ignore the issue you are omitting facts that are known to you in order to turn an issue of science into one of sociology. Again you impose your own beliefs on the facts; thus I am reluctant to accept as accurate the various statements that you attribute elsewhere to anonymous string theorists and others.

You raise again the issue of a weak form of Maldacena duality. As you know, it is very difficult to find a sensible weak form that is consistent with all the evidence and yet not the strong form. In my review I have gone through your book and papers and identified three proposals, and explained why each is wrong. Again, you have not acknowledged the existence of scientific counterarguments, but have just reasserted your original point. If your arguments had been made in a serious way, I would expect that you would have given some deep thought to them and be ready to defend them.

There are some interesting points, one of which I will turn to next.

The role of rigor and calculation. Here we disagree. Let me give some arguments in support of my point of view. A nice example is provided by your paper `The Maldacena conjecture and Rehren duality’ with Arnsdorf, hep-th/0106073.

You argue that strong forms of the Maldacena duality are ruled out because Rehren duality implies that the bulk causal structure is always the fixed causal structure of AdS_5, and so there cannot be gravitational bending of light. But this would in turn imply that there cannot be refraction in the CFT, because the causal structure in the bulk projects to the boundary: null geodesics that travel from boundary to boundary, through the AdS_5 bulk, connect points that lie on null boundary geodesics. Now, the gauge theory certainly does have refraction: there are interactions, so in any state of finite density the speed of propagation will be less than 1. (Since Rehren duality does not refer to the value of the coupling, this argument would hold even at weak coupling, where the refraction can be calculated explicitly.)

You have emphasized that Rehren duality is rigorous, so apparently the problem is that you have assumed that it implies more than it does. Generally, rigorous results have very specific assumptions and very precise consequences. In physics, which is a process of discovery, this can make them worse than useless, since one tends to assume that their assumptions, and their implications, are broader than they actually are. Further, as this example shows, a chain of reasoning is only as strong as its weakest step. Rigor generally makes the strongest steps stronger still – to prove something it is necessary to understand the physics very well first – and so it is often not the critical point where the most effort should be applied. Your paper illustrates another problem with rigor: it is hard to get it right. If one makes one error the whole thing breaks, whereas a good physical argument is more robust. Thus, your paper gives the appearance of rigor, yet reaches a conclusion that is physically nonsensical.

This question of calculation deserves further discussion, and your paper with Arnsdorf makes for an interesting case study, in comparison with mine with Susskind and Toumbas, hep-th/9903228. (I apologize for picking so much on this one paper, but it really does address many of the points at issue, and it is central to the discussion of AdS/CFT in your various reviews.) You argue that there are two difficulties with AdS/CFT: that strong forms of it are inconsistent with the bending of light by gravitational fields, and that the evidence supports a weaker relation that you call conformal induction. We also present two apparent paradoxes: that the duality seems to require acausal behavior, and negative energy densities, in the CFT. The papers differ in that yours contains a handful of very short equations, while ours contains several detailed calculations. What we do is to translate our argument from the imprecise language of words to the precise language of equations.

We then find that the amount of negative energy that must be `borrowed’ is exactly consistent with earlier bounds of Ford and Roman, gr-qc/9901074, and that a simple quantum mechanical model shows that an apparent acausality in the classical variables is in fact fully causal when one looks at the full quantum state. Along the way we learn something interesting about how AdS/CFT works.

This process of translation of an idea from words to calculation will be familiar to any theoretical physicist. It is often the hardest part of a problem, and the point where the greatest creativity enters. Many word-ideas die quickly at this point, or are transmuted or sharpened. Had you applied it to your word-ideas, you would probably have quickly recognized their falsehood. Further, over-reliance on the imprecise language of words is surely correlated with the tendency to confuse scientific arguments with sociological ones.

Finally, I have recently attended a number of talks by leading workers in LQG, at a KITP workshop and the April APS meeting. I am quite certain that the standard of rigor was not higher than in string theory or other areas of physics. In fact, there were quite a number of uncontrolled approximations. This is not necessarily bad – I will also use such approximations when this is all that is available – but it is not rigor. So your insistence on rigor does not actually describe how science is done even in your own field.

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Today at Fermilab, the MiniBooNE experiment announced to a packed auditorium their long-awaited results looking for neutrino oscillations. Below is a guest post from Dr. Heather Ray, a scientist at Los Alamos National Lab, who has been working on the experiment for several years. I have known Heather since she was a graduate student on the CDF experiment at Fermilab, when she was at the University of Michigan. To the right is a photo of her with her significant other, Ivan Furic.

MiniBooNE Neutrino Experiment Results

by Dr. Heather Ray, Los Alamos National Lab

Neutrinos, a fundamental particle of nature, are believed to oscillate, or change from one type to another. In the long list of experiments which have claimed an observation of neutrino oscillations, one stands apart : LSND. The LSND result doesn’t fit in with our picture of oscillations from other experiments, and as such is highly controversial. The MiniBooNE experiment was designed to explore the LSND result, to conclusively prove or disprove the claimed oscillations. MiniBooNE announced it’s first results today (April 11th, 2007). The illustrious rulers of the Cosmic Variance blog have asked me to write a bit about this result. So, let the amazing neutrino story begin!

In the Standard Model of physics there are three main categories of fundamental particles: quarks, leptons, and gauge bosons, or force carriers. The leptons are the electron, muon, and tau, as well as their partner neutrinos : &#957_e, &#957_&#956, and &#957_&#964. Neutrinos in the Standard Model have no charge and are massless. Imagine for a minute that neutrinos do have mass. If they have mass then they are able to oscillate, or change type. Neutrinos have definitively been observed changing from one type into another, yet the Standard Model of physics says that neutrinos do not have mass. The simplest solution to this conundrum is to allow the neutrinos to have mass.

In more technical terms we say that the weak eigenstates ( &#957_e, &#957_&#956, and &#957_&#964) are made up of a combination of mass eigenstates. For example, in a two-neutrino scenario, at the time of creation the muon neutrino is a combination of the two mass eigenstates :

|&#957_&#956(0)> = -sin &#952 |&#957₁> + cos &#952 |&#957₂>

where the probability for two-neutrino oscillations is given by :

P_osc = sin²(2&#952) * sin²[ (1.27 * &#916m² * L) / E ]

The probability has two terms which are constrained by the design of the experiment (L, the distance from the neutrino source to the detector, and E, the energy of the neutrino beam), and two terms which are fit for when performing a two-neutrino oscillation analysis (&#916m² and sin²(2&#952), where &#952 is the mixing angle between the two neutrino states and &#916m²_ab = m²_a – m²_b).

Neutrino physicists illustrate the current status of neutrino oscillations using a two dimensional plot that is the function of the two fit parameters. Oscillation results from the solar and atmospheric sectors (the tiny red and blue dots) have been observed and confirmed by several experiments. The set of several independent measurements allows us to constrain the range of fit parameters for those oscillations. The LSND result, which spans the upper third of this plot, has a large allowed region in parameter space.

In the Standard Model there are only three neutrinos, all of which interact with matter. The &#916m² is the mass squared difference between the two neutrino states. These three results represent three differences, or splittings, between the mass states. If the Standard Model of physics is correct and there are 3 and only 3 neutrinos, a summation law should exist : &#916m²₁₃ = &#916m²₁₂ + &#916m²₂₃. You can see that even at LSND’s lowest allowed &#916m² point the summation law does not hold.

If LSND’s observation is found to be a true fact of nature, the Standard Model of physics cannot fully accommodate/explain neutrino interactions! This “breaking” of the Standard Model is very exciting to physicists, and indicates there is new physics that we haven’t previously thought possible. Many things could be true – there could be new allowed interactions for neutrinos (Lorentz Violation, CP/CPT violation, the list goes on!), or there could be additional particles – sterile neutrinos, which don’t interact with other matter but only can been seen through mixing with other neutrinos.

To properly explore the LSND signal we need an experiment that has the same experimental constraints (L/E, from the oscillation probability formula), so that the entire allowed region of LSND can be explored. The follow-up experiment also should have more events (smaller statistical errors), and a different signal signature, backgrounds, and sources of systematic errors. This experiment is MiniBooNE.

MiniBooNE is located at Fermi National Accelerator Laboratory, in Batavia, IL. To produce our neutrino beam we start with an 8 GeV beam of protons from the Booster. The proton beam enters a magnetic focusing horn where it strikes a beryllium target. The interactions of the protons+Be produce positively and negatively charged mesons (pions and kaons). The positively charged mesons will decay to produce a neutrino beam, while the negatively charged mesons will decay to produce an anti-neutrino beam.

There are still a lot of mysteries surrounding the interactions of neutrinos. We don’t yet know if neutrinos mix with the same probability as anti-neutrinos. Therefore, the LSND result, which claims observation of anti-&#957_&#956 &#8594 anti-&#957_e oscillations, needs to be explored using both neutrinos and anti-neutrinos. For the first check of LSND we chose to focus the positively charged mesons, which means we’re looking for &#957_&#956 &#8594 &#957_e oscillations. This choice was solely dictated by physics : the proton + Be interactions produce far more positively charged mesons. This means the rate of collection for our neutrino sample is much higher than our rate of collection for an anti-neutrino sample. We chose to collect the quick data set first, and then proceed with analyzing that data while collecting the anti-neutrino data set.

The mesons decay in flight into the neutrino beam seen by the detector : K⁺ / &#960⁺ &#8594&#956⁺ + &#957_&#956, where the &#957_&#956 comprise the neutrino beam seen at MiniBooNE. These mesons decay in flight in our vacuum decay region. Following the decay region is an absorber, put in place to stop any muons and undecayed mesons. The neutrino beam then travels through approximately 450 meters of earth before entering the MiniBooNE detector.

MiniBooNE is a 12.2 meter diameter sphere. The detector is filled with pure mineral oil and lined with photomultiplier tubes (PMTs). PMTs work like a reverse light bulb – instead of putting in electricity to produce light the PMTs collect light from neutrino interactions in our detector and output an electrical pulse. There are two regions of the MiniBooNE detector : an inner light-tight region and an optically isolated outer region known as the veto region, which aids in vetoing cosmic backgrounds.

Neutrinos interact with material in the detector. It’s the outcome of these interactions that we look for. These neutrino interactions in the MiniBooNE detector leave a distinct mark in the form of Cerenkov and scintillation light. Cerenkov light is produced when a charged particle moves through the detection medium with a velocity greater than the speed of light in the medium (v > c/n). This produces an electro-magnetic shock wave, similar to a sonic boom. The shock wave is conical and produces a ring of light which is detected by the PMTs. We can use Cerenkov light to measure the particle’s direction and to reconstruct the interaction vertex. This effect occurs immediately with the particle’s creation and is known as a prompt light signature.

Charged particles moving through the detector also may deposit energy in the medium, exciting the surrounding molecules. The de-excitation of these molecules produces scintillation light. This is an isotropic, delayed light source, and provides no information about the track direction. We can however use the PMT timing information to locate the point, or vertex, where the neutrino interaction occurred.

We can use the patterns of light seen in our PMTs to determine what type of neutrino interacted in our detector. In the charged-current quasi-elastic events, a neutrino interaction in the detector will produce the lepton partner of the neutrino. For example, an electron neutrino interaction will produce an electron, and a muon neutrino interaction will produce a muon. Electrons travel for only a very short time before their velocity falls below the Cerenkov threshold. They multiple scatter along the way, as well. This leaves a fuzzy Cerenkov ring in the detector. Muons tend to travel for a much longer distance. As they travel through the detector they lose energy, and the angle at which the Cerenkov light is being emitted shrinks. Muons also emit scintillation light. The signature of a muon in the detector isn’t one of a ring, as in the case of an electron. It is instead a filled in circle of light. Neutral pions decay into two photons, which then pair produce. The electrons from this pair production each create a ring in the detector.

MiniBooNE is performing a blind analysis. This means that we can either :

• see some of the information in all of the data : we can check the charge per PMT as a function of time, to verify our detector isn’t failing,
• see all of the information in some of the data : we are able to select data sets which will have no oscillation events present, if we assume maximal allowed oscillations from LSND. We can use these data sets to then tune and verify our Monte Carlo simulation.

but we can’t see all of the information in all of the data. Having access to all of the information in all of the data is unblinding. Prior to unblinding we had to have all components of the analysis completely fixed. We aren’t allowed to go back and change event selection cuts or error estimates once we unblind.

Our oscillation analysis can be boiled down to this simple algorithm : determine a set of event selection cuts which will isolate the electron neutrino events but remove the majority of all other events. There are a certain amount of electron neutrino events inherent in the beam, which come from kaon decays. There are also a small amount of other types of events (delta decays, pi0 events) which will pass the electron neutrino cuts, but which are not from true electron neutrino events. The sum of the estimated intrinsic electron neutrino events plus the fake events is the total number of events we expect to see, if no oscillations are present. We compare the number of events observed in data to the number expected, as a function of the reconstructed neutrino energy in these events. If we observe oscillations we should see an excess of data events over the expectation, whose shape will change as a function of the oscillation parameters.

This plot shows the MiniBooNE final sensitivity, compared to the prediction from our 2003 Run Plan. Curves are shown overlaid on the allowed LSND region.

This plot shows the final result from the likelihood analysis. Data points are the black dots. The expected event spectrum is shown in red, and is broken down into the intrinsic electron neutrino and fake event shapes in the green and blue.

We have two separate analyses that are used in the oscillation search : one which depends on likelihood variables, and one which depends on a boosted decision tree. These two analyses have a small overlap in event composition, and provide a good check of each other. We have complete confidence in our analysis if these two analyses find the same result. Before we unblinded our data we had to decide which of the two analyses we would call our primary analysis, for the purpose of quoting numbers in publications. We made this decision based on the expected sensitivity found using Monte Carlo. The sensitivity is the amount of parameter space allowed by the LSND result that we expect to be able to probe. Our sensitivity studies showed that with the likelihood analysis we were able to achieve a sensitivity which agrees quite well with the sensitivity MiniBooNE was designed for. This is something to be quite proud of! We also agreed that the final result quoted for the two neutrino oscillation search would be from 475 MeV to 3 GeV, based on the LSND best fit region.

MiniBooNE unblinded on Monday, March 26th, 2007. When we opened the box we found no evidence for an excess of events over the background prediction. The MiniBooNE neutrino data set agrees with the no neutrino oscillation hypothesis, in the range of reconstructed neutrino energy from 475 MeV to 3 GeV. The probability that MiniBooNE and LSND both are due to two-neutrino oscillations is only 2%. The likelihood and the boosting analyses also agree quite well in measured excess events.

I’m sure by now you’ve noticed that MiniBooNE observes an excess of events in the low energy region. We first saw this excess two weeks ago, when we unblinded. At that point we began working like madmen to determine what those events could possibly be. We’re rechecking our detailed understanding of various low energy background events: interactions in the dirt surrounding the detector, radiative delta decays, low energy neutral current events, you name it, we’re exploring it. Obviously, we don’t want to make any additional comments about this excess until we’re certain that we’ve performed all possible checks on our event predictions in that region. We’re hoping to have this excess mystery resolved in the next few months.

MiniBooNE’s neutrino oscillation analysis was the first of two analyses needed to conclusively explore the LSND result. An anti-neutrino oscillation analysis will also need to be performed. At MiniBooNE it would take many more years to accumulate the data set needed to perform this anti-neutrino analysis. Instead, I’m hoping that we can continue this exploration at the Spallation Neutron Source, at Oak Ridge Laboratory in TN. The SNS is designed to be a world-class neutron facility. One of the side-effects of the process which produces the neutrons is that you get an amazing neutrino beam for free! Funding permitting I’m hoping we can begin taking data at the SNS within 3 to 4 years. At the SNS we could perform neutrino and anti-neutrino measurements simultaneously (no need to switch the horn polarity!), look for oscillations, sterile neutrinos, and look for CP/CPT violation in the neutrino sector.

References

• S. Ahmed et al. [SNO Collaboration], Phys. Rev. Lett. 92, 181301 (2004), arXiv.org/nucl-ex/0309004
• G. Fogli et al., Phys. Rev. D 67, 093006 (2003), arXiv.org/hep-ph/0303064
• A. Aguilar et al. [LSND Collaboration], Phys. Rev. D 64, 112007 (2001), arXiv.org/hep-ex/0104049
• http://www-boone.fnal.gov
• D. Smith, “Calculating the Probability for Neutrino Oscillations”, http://physicsx.pr.erau.edu/Office/oscillations.pdf
• http://en.wikipedia.org/wiki/Cherenkov\_radiation
• http://nevis1.nevis.columbia.edu/heavyion/e910
• The HARP Collaboration, CERN-SPSC/2003-027, SPSC-P-325
• S. Kopp, “The NuMI Neutrino Beam at Fermilab”, arXiv.org/physics/0508001
• http://www.phy.ornl.gov/workshops/nusns/

You may have read here and there about the genteel discussions concerning the status of string theory within contemporary theoretical physics. We’ve discussed it on CV here, here, and even way back here, and Clifford has hosted a multipart discussion at Asymptotia (I, II, III, IV, V, VI).

We are now very happy to host a guest post by the man who wrote the book, as it were, on string theory — Joe Polchinski of the Kavli Institute for Theoretical Physics at UC Santa Barbara. Joe was asked by American Scientist to review Peter Woit’s Not Even Wrong and Lee Smolin’s The Trouble With Physics. Here is a slightly-modified version of the review, enhanced by footnotes that expand on some more technical points.

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This is a review/response, written some time ago, that has just appeared in American Scientist. A few notes: 1) I did not choose the title, but at least insisted on the question mark so as to invoke Hinchliffe’s rule (if the title is a question, the answer is `no’). 2) Am. Sci. edited my review for style, I have reverted figures of speech that I did not care for. 3) I have added footnotes on some key points. I look forward to comments, unfortunately I will be incommunicado on Dec. 8 and 9.

All Strung Out?

Joe Polchinski

The Trouble with Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next. Lee Smolin. xxiv + 392 pp. Houghton Mifflin, 2006. $26.

Not Even Wrong: The Failure of String Theory and the Search for Unity in Physical Law. xxi + 291 pp. Basic Books, 2006. $26.95.

The 1970’s were an exhilarating time in particle physics. After decades of effort, theoretical physicists had come to understand the weak and strong nuclear forces and had combined them with the electromagnetic force in the so-called Standard Model. Fresh from this success, they turned to the problem of finding a unified theory, a single principle that would account for all three of these forces and the properties of the various subatomic particles. Some investigators even sought to unify gravity with the other three forces and to resolve the problems that arise when gravity is combined with quantum theory.

The Standard Model is a quantum field theory, in which particles behave as mathematical points, but a small group of theorists explored the possibility that under enough magnification, particles would prove to be oscillating loops or strands of “string.” Although this seemingly odd idea attracted little attention at first, by 1984 it had become apparent that this approach was able to solve some key problems that otherwise seemed insurmountable. Rather suddenly, the attention of many of those working on unification shifted to string theory, and there it has stayed since.

Today, after more than 20 years of concentrated effort, what has been accomplished? What has string theory predicted? Lee Smolin, in The Trouble With Physics, and Peter Woit, in Not Even Wrong, argue that string theory has largely failed. What is worse, they contend, too many theorists continue to focus their efforts on this idea, monopolizing valuable scientific resources that should be shifted in more promising directions.

Smolin presents the rise and fall of string theory as a morality play. He accurately captures the excitement that theorists felt at the discovery of this unexpected and powerful new idea. But this story, however grippingly told, is more a work of drama than of history. Even the turning point, the first crack in the facade, is based on a myth: Smolin claims that string theorists had predicted that the energy of the vacuum — something often called dark energy — could not be positive and that the surprising 1998 discovery of the accelerating expansion of the universe (which implies the existence of positive dark energy) caused a hasty retreat. There was, in fact, no such prediction [1]. Although his book is for the most part thoroughly referenced, Smolin cites no source on this point. He quotes Edward Witten, but Witten made his comments in a very different context — and three years after the discovery of accelerating expansion. Indeed, the quotation is doubly taken out of context, because at the same meeting at which Witten spoke, his former student Eva Silverstein gave a solution to the problem about which he was so pessimistic. (Contrary to another myth, young string theorists are not so intimidated by their elders.)

As Smolin charts the fall of string theory, he presents further misconceptions. For example, he asserts that a certain key idea of string theory — something called Maldacena duality, the conjectured equivalence between a string theory defined on one space and a quantum field theory defined on the boundary of that space — makes no precise mathematical statements. It certainly does. These statements have been verified by a variety of methods, including computer simulations [2]. He also asserts that the evidence supports only a weak form of this conjecture, without quantum mechanics. In fact, Juan Maldacena’s theory is fully quantum mechanical [3].

A crucial principle, according to Smolin, is background independence — roughly speaking, consistency with Einstein’s insight that the shape of spacetime is dynamical — and Smolin repeatedly criticizes string theory for not having this property. Here he is mistaking an aspect of the mathematical language being used for one of the physics being described. New physical theories are often discovered using a mathematical language that is not the most suitable for them. This mismatch is not surprising, because one is trying to describe something that is different from anything in previous experience. For example, Einstein originally formulated special relativity in language that now seems clumsy, and it was mathematician Hermann Minkowski’s introduction of four-vectors and spacetime that made further progress possible.

(more…)

I first met Chanda (briefly) when she was visiting the University of Chicago as a summer undergraduate research student. Since then we’ve corresponded occasionally about life as a physicist and which general relativity textbook is the best. She emailed me a thoughtful response to a couple of posts about string theory and the state of physics (here and here), and I thought it would be good to have those thoughts presented as a full-blown guest post rather than just a comment; happily, Chanda agreed.

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A few months ago, Sean posted an entry on this blog addressing his concerns about Dr. Lee Smolin’s (then forthcoming) book, The Trouble With Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next. Dramatically titled and well-hyped, Lee’s book was sure to arouse strong emotions and plenty of debate on publication. However, it managed to do that even before it was out, and the commentary on Sean’s entry included correspondence from Lee as well as several other great contemporary thinkers in theoretical physics. The dialogue was inspired, passionate, argumentative, sometimes rude, and always exploratory.

But something was missing. I wondered how there could be a discourse about the marketplace of ideas and about who gets to participate in science without a component that addresses the obvious (at least for those of us with some relationship to the US academic system): the community of scientists in the United States is overwhelmingly homogeneous, white (of European descent) and male. That sounds like a pretty narrow marketplace to me, given that over half of the US population is either female or a member of an underrepresented minority group or both. Surely this must mean that we are under-utilizing our potential talent pool in our drive to better understand the physical world.

As a member of the National Society of Black Physicists’ (NSBP) Executive Committee and Editor of their newsletter, I like to stay on top of the statistics related to these issues, so let me mention a few to satisfy those who like to see data. (All stats are borrowed from the NSF unless otherwise noted.) At the moment, only about 12% of doctoral degrees in physics go to women. The number going to people identified as Black/African-American hovers around an average of 14 per year out of an average 738 total degrees. That’s 1.8% despite making up about 12% of the population. Further investigation uncovers the (to me) monumental tragedy that almost no other field in science and technology is doing worse at diversifying than ours, physics. (See Dr. Shirley Malcolm’s symposium paper from AIP’s 75th Anniversary celebration.)

Knowing all this, I want to share with you how shocking it is to me when I have regular conversations with my peers who express to me that they don’t see a problem. And if they do express concerns to me, a lot of the time it’s guys who want more women in the field because they want to find dates. Sorry guys, we’re here because we’re interested in physics, not you, and on top of that, some of us like women better! And yes, sometimes it’s just a joke, but sometimes it’s hard to tell, and believe me, we’ve heard that one many, many times before. On the topic of seeing more people of color (Blacks, Latina/os, etc.) most often I am met with disinterested silence or an insistence (the knowledge base this derives from is always hazy, in my opinion) that there’s nothing the physics community can do to resolve the issue because the problem is in the high schools and has nothing to do with post-secondary academe.

This attitude is disappointing, to say the least. First of all, the numbers contradict these sentiments. While it is true that there are deeply troubling issues facing the K-12 education system in the US, especially in low-income neighborhoods which are disproportionately populated by people of color, women and other underrepresented groups fall out of the pipeline at all stages, from the post-baccalaureate to the post-doctorate level, and they do so at a much higher rate than white men. Clearly something is happening. What is happening is far too full a topic to tackle here, but perhaps I will be invited to say more about it in the comments section. I invite readers to participate in a knowledge-based discourse about this issue.

On the other hand, if you’re having a hard time figuring out why you should care about diversity, the President of Princeton can offer you a helping hand. In the 2003 Killam Lecture at the University of British Columbia, Princeton University President Shirley M. Tilghman identified four reasons for why we should care about diversity in science. I paraphrase them here:

1. If we aren’t looking at the entire talent pool available, scientific progress will be slower by default.
2. It’s possible that women and other underrepresented minorities will identify unique scientific problems that their majority peers might not.
3. Science will find it increasingly difficult to recruit the brightest minorities as other fields diversify and therefore look attractive to members of underrepresented groups. An attractive work environment is essential to competing on the job market for the best thinkers.
4. The scientific establishment ought to pursue diversification as a matter of fairness and justice.
   In a small (statistically insignificant) survey of various scientists and leaders in scientific organizations, I found that the question of “why is diversity in science important?” is addressed in these four points. While point four is possibly closest to my heart, I think that points one and two are two of the strongest arguments out there. (An aside: As I am tidying up this essay, one professor writes me and says that he finds four to be most compelling! I hope that others will agree.)

I would like to reflect on point one in the context of work in theoretical physics, specifically in quantum gravity and cosmology. If we are to take seriously the concept that what we seek in physics is truth and a better understanding, don’t we want to have the broadest pool of talent available to participate in the process? I think this applies to people and ideas alike. Until we have a theory that pulls out ahead of the others, what are we doing arguing about whose theory is doing better? Right now, neither loops, nor strings, nor triangles, nor anything else has ANY data to back it up, so perhaps the best thing we can all do on that front is get back to work.

An aside to that last remark: It’s hard to get to work when no one will hire you. It remains true that even if I do good work in my field, if my field is not strings, I will have a difficult time finding a job in theoretical physics. Some might argue that this is fair because I have made the foolish error of working on a silly (let’s say loopy) theory. But honestly, to those who like to toe that line, I’d like to say that since you don’t have the LHC data in hand or anything else that proves/disproves strings/loops/anything else, at this stage we’re all in the same boat. And what if strings is wrong? Has the physics community gained anything by suppressing and/or ignoring the alternatives?

To speak in more general terms, I could ask the broader question: what has the scientific community gained by choosing not to pro-actively welcome a broad and diverse set of people and ideas into the fold? Well, again there isn’t enough space for the details, but there is increasing evidence from research in science education that supports the point that diversity of perspectives accelerates problem solving.

Moreover, a fellow grad student and active member of NSBP’s sister organization, the National Society of Hispanic Physicists (NSHP), pointed out to me that we can definitely be aware of what the scientific community potentially loses when people from different backgrounds aren’t allowed to participate in science. Laura noted that our society has thrived on the contributions of women like Marie Curie (discovered radioactivity) and Emmy Noether (Noether’s theorem) and African-Americans like Benjamin Banneker (early civil and mechanical engineer, self-taught astronomer and mathematician). At this point, I think it is easy to ask and answer, “what would our world be like without the Marie Curies and Benjamin Bannekers?” Most likely lacking.

But another, equally important question isn’t raised often enough: What are we missing by living in a world where only the Marie Curie’s make it through? A few women and underrepresented minorities have always found a way to challenge the status quo. Let’s face it: physics is hard for anyone. It’s not hard to imagine that it takes a certain type of determined personality to overcome barriers and make new discoveries. What of the rest? The people who didn’t find the right friends and family to help them? The ones who never had a chance to learn physics? The ones who thought that people who look like them don’t succeed at physics? (And yes, they are out there; I’ve met some of them.) Might we be further along in our understanding of dark matter? Perhaps, perhaps not, but until we push harder to integrate, we’ll never know.

At this stage, it occurs to me that many of you will look at my definition of diversity and think it is too narrow. I’ve left out all of the international collaboration that goes on in physics, and surely, isn’t that a wonderful kind of diversity which is plentiful in our world? Yes! One thing that endeared the Perimeter Institute to me almost immediately was the fact that my peer group hails from all over Europe and Asia, and at the lunch table, as many as five or more cultures may be represented. But to me this highlights the problem — if the North American physics community has been able to welcome an international populace with open arms, why can’t they do the same with the diversity that already exists at home?

In the end, perhaps this is not a fair way to raise the question. International members of the physics community also have to confront issues of racism and discrimination. Racism is not a uniquely American problem, nor do people of color suffer alone from it in the US. But I still have a question, then: if the academy is ready to bring those of us who earn Phds into the fold, why isn’t it doing more to encourage more of us to reach that far? Those of us who do make it that far are left wondering why it doesn’t bother anyone else that we are more likely to see a German in our graduate classes than another Black person.

The challenges we face in confronting these issues are not easy. First we must accept there is an issue, a problem. Then there must be open discussion about how we understand the problem. I realize that it is difficult to step into someone else’s shoes and understand where they are coming from. But to an extent, like Albert Einstein before us, we must rise to the challenge of the barriers placed before our understanding and transcend them.

For my part, as a Black woman, I would ask my white (and male) peers to remember that many of us (though not all) experience our differences as a negative in this environment. Where I see it as a Black cultural tradition to lend a helping hand even as I continue to achieve my own dreams, others see my commitment to NSBP as a signal that I am wasting my time not doing science. Do my friends who play music in their spare time get this same signal? Moreover, many of us who are women or people of color or both are often involved in efforts to change the face of science. When we are challenged about that by our peers, not only are they standing in our way, but they are also failing to recognize that for many of us, this investment in the community is necessary to our survival, much like someone else might say playing music is for theirs.

Furthermore, where I wish to understand other people’s choices of identification, there are those amongst my peers who have felt they had the right to make my choices for me. I find myself now terrified of mentioning my Blackness in any way, lest I become dehumanized, my personal identity reduced to an object of debate. These are examples of the way my background has been turned into a negative for me. I know others have similar and worse experiences, and surely, this is one major leak in the aforementioned pipeline. My hope is that physics will evolve not only in concept, but also in its sensibilities about who a physicist is and what she looks like. What if we came to value our heterogeneity, to see it as an advantage?

It is important to note that there are white men out there thinking about these issues. I know Sean Carroll is one of them. For me, Professor Henry Frisch at the University of Chicago has been an amazing mentor. His father, the late Professor David Frisch of MIT, was influential in the graduate career path of Dr. Jim Gates, now an accomplished African-American theorist at the University of Maryland. People who take the time to be concerned, therefore, do have an impact. A common complaint that I hear from interested people is that there aren’t enough people with diverse backgrounds in the talent pool when they are choosing grad students, postdocs, and faculty. I believe that this points to a fundamental problem that physicists can help with: somewhere a pool of talent is getting lost, and we need to push harder to find it again by taking a pro-active role in education policy, mentoring (studies show this makes a big difference in minority performance), and anti-discrimination activism.

I hope that many of you will take this to heart and realize that for the sake of science, if nothing else, diversity matters. There’s a lot to be done to change things, and I encourage you to support work that is being done in your community, whether it’s by contributing hours designing a website or giving a tour of your department to local students who wouldn’t normally be exposed to science. Moreover, I strongly urge you, especially those of you who are not from an underrepresented background, to take seriously the idea that not everyone experiences the physics community like you, not everyone has the same ideas, that some people face real barriers to academic progress, and that we’re all better off when we make a genuine effort to listen to and understand the other side.

Before I finish, I’ll make a last comment on the science. One of the ways I’ve seen these divisions hurt us is the way in which we seem completely stuck on some pretty major problems. As it stands, we have a standard model of cosmology where we don’t know what form 96% of the energy of the universe takes, and we only know the barest of details about the properties of dark energy and dark matter. The model is also still hazy on many of the details of the first 400,000 years or so. This is where the quantum gravity community should rise to the challenge of seeking new and unique ways of approaching the problem since the old ones clearly aren’t working. This means we have to encourage new ideas. Even if they turn out to be wrong, we’ll probably still learn something. So to partake in some near trademark infringement, it’s time to “Think Differently.”

Chanda Prescod-Weinstein earned her BA in Physics and Astronomy and Astrophysics (yes, it is gramatically incorrect on her diploma) from Harvard College in 2003. She went on to earn an MS in Astronomy and Astrophysics at University of California, Santa Cruz (2005), where she studied black holes in higher dimensions. She is now beginning a Phd under Dr. Lee Smolin in Waterloo, Ontario, recently dubbed the Geek Capital of Canada. A product of the integrated public magnet schools of Los Angeles, she is proud to be both a Black woman and a physicist.

The Foundational Questions Institute (FQXi) was mentioned in the comments of Mark’s post about John Barrow’s Templeton Prize. This is a new organization that is devoted to supporting innovative ideas at the frontiers of physics and cosmology. It is led by Max Tegmark of MIT and Anthony Aguirre of UCSC, two leading young cosmologists, backed up by an extremely prestigious Scientific Advisory Panel.

Sounds like a great idea, but some of us have questions, primarily concerning the source of funding for FQXi — currently the John Templeton Foundation. The Templeton Foundation is devoted to bringing together science and religion, which may or may not be your cup of tea. I’m already on the record as turning down money from them (see also this Business Week article) — and believe me, turning down money is not part of my usual repertoire. But Max and Anthony and the rest are good scientists, so we here at Cosmic Variance thought it would be good to hear the story behind FQXi in their own words. We invited Anthony to contribute a guest post about the goals and procedures of the new institute, and he was kind enough to agree. Feel free to ask questions and be politely skeptical (or for that matter enthusiastically supportive), and we can all learn more about what’s going on.

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I (Anthony Aguirre) have been invited by Sean to write a guest blog entry discussing an exciting new project that Max Tegmark and I have been leading: Foundational Questions in Physics and Cosmology (”FQX”). This program was publicly announced in October, and the Foundational Questions Institute (FQXi) was formally launched as a legal entity in February, as was its first call for proposals. There is a plethora of information on FQXi at www.fqxi.org, but the kind invitation by Cosmic Variance provides a good opportunity to outline informally what FQXi is, why we think it is important, to address some reservations voiced in this forum, and to generate some discussion in the physics and cosmology community.

What is FQXi all about? Its stated mission is “To catalyze, support, and disseminate research on questions at the foundations of physics and cosmology, particularly new frontiers and innovative ideas integral to a deep understanding of reality, but unlikely to be supported by conventional funding sources.” Less formally, the aim of FQXi is to allow researchers in physics, cosmology, and related fields who like to think about and do real research about really big, deep, foundational or even “ultimate” questions, to actually do so — when otherwise they could not. We boiled this type of research down into two defining terms: the research should be foundational (with potentially significant and broad implications for our understanding of the deep or “ultimate” nature of reality) and it should be unconventional (consisting of rigorous research which, because of its speculative, non-mainstream, or high-risk nature, would otherwise go unperformed due to lack of funding.) The particular types of research FQXi will support are detailed in the FQXi Charter and in the first call for proposals, which also features a handy (but by no means whatsoever comprehensive) list of example projects, and their likelihood of being suitable for FQXi funding. In addition to straightforward grants, FQXi will run various other programs — “mini”-grants, conferences, essay contests, a web forum, etc. — focused on the same sort of science.

Why is FQXi important? There are a number of foundational questions that are of deep interest to humanity at large — and are the (often hidden) passion of and inspiration for researchers — but which various financial and “social” pressures make it very difficult for researchers to actually pursue. National funding sources, for example, tend to shy aware from research that is high-risk/high- reward, or speculative, or very fundamental, or unconventional, or “too philosophical”, and instead support research using fairly proven methods with a high probability of advancing science along known routes. There is nothing wrong with this, and it creates a large amount of excellent science. But it leaves some really interesting questions on the sidelines. We go on at length about this in the FQXi Charter — but the researchers FQXi aims to support will know all too well what the problems are. Our goal is to fund the research into foundational questions in physics and cosmology that would otherwise go unfunded.

More money to support really exciting, interesting, and, yes, fun research seems like an unreservedly good thing. Nonetheless, a couple of significant reservations have been voiced to us, both by writers on this blog and others. These are:

1) Some feel research that is very speculative or “borderline philosophical” is just a waste of time and resources — if the research was worth doing, conventional agencies would fund it. We won’t accept this criticism from anyone who has worked on either time machines or the arrow of time (so Sean is out) , but from others we acknowledge that they feel this way, we respectfully disagree, and we think that many of the giants of 20th century physics (Einstein, Bohr, Schroedinger, Pauli, etc.) would also disagree. Ultimately, those who feel this way are free not to participate in FQXi. We also note that we think it would by great if some private donors were also to support more conventional research in a way that complemented or supplemented federal funding (as they do in, e.g., the Sloan and Packard fellowships); that, however, is not the case here: the donation supporting FQXi is expressely for the purpose of supporting foundational research. Which brings us to…

2) The second major reservation concerns FQXi’s current sole source of funding: the John Templeton Foundation (JTF), an organization that espouses and supports the “constructive dialogue between science and religion.” It is understandable that some people may be suspicious of JTF’s involvement with FQXi, and in today’s political climate in which Intelligent Design and other movements seek to undermine science in order to promote a religious and political agenda, such suspicion is especially understandable. But it is as important as ever to also be open-minded and objective. The salient points, we think, regarding JTF and FQXi are:

• FQXi is a non-profit scientific grant-awarding organization fully independent from its donors (we are actively seeking other donors beyond JTF, see below) and operated in accordance with its Charter. Proposal funding is determined via a standard and rigorous peer-review process, and an expert panel appointed by FQXi. The structure of FQXi is such that donors — including JTF — have no control or influence over individual proposal selection or renewal. Specifically, scientific decisions are made (as enshrined in the FQXi corporate Bylaws) by the Scientific Directorate (Max & I), on the basis of advice from review panels and the Scientific Advisory Panel. The only condition of the JTF grant to FQXi is that FQXi’s grantmaking be consistent with the FQXi Charter, which, as stated previously, can be viewed in its entirity at fqxi.org.
• JTF’s stated interest in FQXi is captured in the FQXi Charter: the questions being tackled by researchers funded by FQXi intimately connect with and inform not just scientific fields, but also philosophy, theology and religious belief systems. Answers to these questions will have profound intellectual, practical, and spiritual implications for anyone with deep curiosity about the world’s true nature.
• While FQXi’s funding is currently all from JTF, we have been strongly encouraged by JTF to seek (and are actively working on finding) additional donors; furthermore, there is no guarantee of JTF funding beyond the first four years — though we certainly hope FQXi will go on long past the initial four-year phase.
• As for JTF benefiting “by association” with FQXi and the great research we hope that it will support, well, we feel that JTF has been extremely generous not just in giving a large sum of money to science, without strings attached, and with a great deal of support through the complex process of setting up FQXi as an independent institute of just the sort that Max & I wanted. If all this reflects well on JTF, I would submit that they deserve it.

We’ve tried hard to make FQXi’s operation and goals as transparent as possible, so those in the community can make informed decisions on whether they would like to participate in what we are hoping to do. We are very excited by the proposals that are coming in so far, and invite interested scientists to take a look at the call for proposals before it is too late (April 2). For those who are not actively researching foundational questions, we hope to have a very active public discussion and outreach program for both scientists and the interested public; we invite you to periodically check the FQXi website.

Thank you for this opportunity to discuss FQXi at Cosmic Variance.

The quantum puppies post below was written in response to some excitement generated by recent work from Paul Kwiat’s group at UIUC; specifically, this paper in Nature (which is sadly only available to subscribers). Paul was nice enough to write a little clarification about what they actually did, which we’re reproducing here as a guest post.

Hi,

I’m not normally a Blogger (I also don’t have a cell phone, if you can believe that).
However, given the plethora of commentary on our article (and on articles *about* our article), I thought a few words might be useful. I’ll try to keep it short [and fail ]

1. There has been quite a bit of confusion over what we’ve actually done (due in large part to reporters that won’t let us read their copy before it goes to print), not to mention *how* we did it. For the record—
   1. we experimentally implemented a proposal made several years ago, showing how one could sometimes get information about the answer to a quantum computation without the computer running. Specifically, we set up an optical implementation of Grover’s search algorithm, and showed how, ~25% of the time, we could *exclude* one of the answers.

      Some further remarks:

      - our implementation of the article is not “scalable”, which means that although we could pretty easily search a database with 5 or 6 elements, one with 100 elements would be unmanageable.

      - however, the techniques we discuss could equally well be applied to approaches that *are* scalable.

   2. By using the Q. Zeno effect, you can push the success probability to 100%, i.e., you can exclude one of the elements as the answer. However, if the element you are trying to exclude actually *is* the answer, then the computer *does* run.

      -The Q. Zeno effect itself is quite interesting. If you want to know more about it, you can check out this tutorial.

   3. Unless you get really lucky, and the actual answer is the last one (i.e., you’ve excluded all the others without the computer running, and so you know the right answer is the last element, without the computer running), the technique in 2. doesn’t really help too much, since if you happen to check if the answer wasn’t a particular database element, and it really was, then the computer does run.
   4. By putting the Zeno effect inside of another Zeno effect, you can work it so that even if you are looking to exclude a particular database element, and the answer *is* that element, then the computer doesn’t run (but you still get the answer). Therefore, you can now check each of the elements one by one, to find the answer without the computer running. This was the first main theoretical point of the paper. Contrary to some popular press descriptions, we did not implement this experimentally (nor do we intend to, as it’s likely to be inconveniently difficult).
   5. If you had to use the method of 4. to check each database element one-by-one, then you’d lose the entire speedup advantage of a quantum computer. Therefore, we also proposed a scheme whereby the right answer can be determined “bit-by-bit” (i.e., what’s the value of the first bit, what’s the value of the second bit, etc.). This is obviously much faster, and recovers the quantum speedup advantage.
   6. Finally, we proposed a slightly modified scheme that also seems to have some resilience to errors.

      Taken in its present form, the methods are too cumbersome to be much good for quantum error correction. However, it is our hope this article will stimulate some very bright theorists to see if some of the underlying concepts can be used to improve current ideas about quantum error correction.

2. There have been a number of questions criticisms, either about the article, or the articles about the article. Here are my thoughts on that:
   1. I guess I should disagree that our article is poorly written (no big surprise there ), though I agree 10000% that it is not at all easy to read. There are (at least) two reasons for this:

      – there is a tight length constraint for Nature, and so many more detailed explanations had to be severely shortened, put in the supplementary information, or left out entirely. Even so, the paper took over a year just to write, so that at least it was accurate, and contained all the essential information. For example, we were not allowed to include any kind of detailed explanation of how Grover’s algorithm works. [If you want more info on this, feel free to check out: P. G. Kwiat, J. R. Mitchell, P. D. D. Schwindt, and A. G. White, "Grover's search algorithm: An optical approach", J. Mod. Opt. 47, 257 (2000)., which is available here.

      - the concepts themselves are, in my opinion, not easy to explain. The basic scheme that we experimentally implemented is easy enough. And even the Zeno effect is not so bad (see that above tutorial). But once it becomes "chained", the description just gets hard. (I am pointing this out, because I would reserve the criticism "poorly written" for something which *could* be easily [and correctly!] explained, but wasn’t.)

   2. I agree that some of the popular press descriptions left something to be desired, and often used very misleading wording (e.g., quantum computer answers question before it’s asked – nonsense!). Having said this, I do have rather great empathy for the writers – the phenomenon is not trivial for people in the field to understand; how should the writers (who *aren’t* in the field) explain it to readers who also aren’t in the field. Overall, the coverage was not too far off the mark.

      -To my mind, the most accurate description was in an article in Friday’s Chicago Tribune (the author kindly let us review his text for accuracy before going to print).

Okay, thanks for your attention if you made it this far.

I hope that these words (and the above web link) will clarify some of the issues in the paper.

Best wishes,
Paul Kwiat

PS Please feel free to post this response (in it’s entirely though) on any other relevant Blogs. Thanks.

After the incredible response to two of our recent posts (Krauss on Intelligent Design, Religion (and String Theory); and From the Sublime to the Ridiculous), Sean, JoAnne, Clifford, Risa and I asked Lawrence Krauss if he would be interested in submitting a post summarizing his views on the issues raised regarding string theory, religion, and the popularization of science.

Lawrence is an extremely well regarded member of the physics community, whose research, popular writings and remarkable efforts to defend science against pseudoscience and political distortion have earned the respect of all of us. We were therefore delighted when Lawrence agreed to make time to do this and we welcome him as Cosmic Variance’s first guest blogger.

We look forward to a high level of discussion regarding this post and, since it might need saying explicitly – keep it polite please folks! Here is Lawrence’s post.

__________________________

The contributors asked me to write and clarify some of my thoughts, especially since in one way or another I, and my writing, have been the subject of a few blog threads. I have already tried to respond; eventually hopefully clearly, within the threads to the concerns, but perhaps a single reasonably cogent monologue bringing some of these ideas together may be worthwhile. We will see:

On popularizing: the most important thing to attempt to get at is the difference between what we know, and what we don’t know; and how we can tell the difference.

On String Theory: A mammoth and very deep and original enterprise which, to date, has not been particularly successful, in my opinion. While string theory has been a fruitful stimulation of new mathematical ideas, as a search for physical theory it hasn’t been productive. This is not to say that it one day will not be so. It simply hasn’t achieved the goals it originally had, and thus far has not been able to make contact in any useful way with either experiment or observation, nor has it yet explained any of the fundamental theoretical puzzles that drive particle physics. Is it interesting? Yes! Should theorists continue to investigate it? Yes! Might it be of vital importance if it leads anywhere? Yes.

Is it worth talking about to the general public? I am not sure. As a study in the kinds of things that physicists sometimes like to think about, and why they think about them, yes; and that is what I have tried to talk about in my most recent book, and no doubt others have as well. As a demonstration of what is likely to be the underlying reality beneath what we observe in the world today, no; namely I personally do not think there is any compelling evidence that these ideas are going to be correct. Nor do I think it fair to place the large set of ideas that are currently being explored under the single banner of a “theory”. What seems clear is that as these ideas are explored in greater depth, the mathematical complexities increase and the possible connections to the world we measure seem to have decreased. I don’t know where things are headed, but frankly I see no reason for great optimism. And, as I try to emphasize to popular audiences, it is important to realize that most theoretical ideas, even great ones, are wrong. So in some sense it is important to keep that fact in the back of one’s mind whenever any new ideas are being discussed.

The good news is that ultimately science has been able to determine which ideas are wrong, and one hopes in the case of string theory this might be possible too, although, as Ed Witten himself has pointed out, it may turn out to be impossible for string theory to make any contact with the measurable world. It is also vitally important that those who are going to devote most of their productive years trying to work on an idea have faith that it is going to pan out. There is nothing wrong with that – it is required to keep up one’s motivations – but it might not pan out. That is the way it goes in science. It was in this context that I think the example of the dual-string model and QCD, which so irked Clifford, is relevant. It is not to make fun of infinities; rather it (a) demonstrates some of the subtleties of mathematics, which lord knows is a difficult subject to try and popularize, and (b) it illustrates what I said in one of the blog comments, namely “My point was not to use infinities to argue against anything.. but to point out that canceling infinities, as the dual-string did, was not by itself a guarantee that it was right, but that a completely different theory ended up coming along and replaced it.. as could easily happen again… I didn’t use it to argue that anything was flawed.. but merely that it is a mathematical problem that needs to be solved, but not every solution of it needs to correspond to reality.”

On String sensitivity: I understand that young people who currently work on string theory probably feel that they work under an undue burden, placed upon them by the original hype associated with the remarkable results in the mid 1980’s, which has continued and sometimes escalated since. I also understand that they may be entranced with various aspects of the ideas that have been developed. That is fine. But it simply is not yet on a par–in almost any sense–with any of the other significant, successful, and well-defined theoretical and experimental developments in physics in the past century. That is neither a bad nor a good thing; it is a fact. And relating one’s own excitement is fine, and good, but it should be tempered with a dose of realism, especially when discussing things to a popular audience, which cannot discern science from pseudoscience in general, much less the finer details of particle physics.

It is bad for science to give the impression that we know more than we do. Moreover, I hope this explains some of the sensitivity of others who do not work on string theory – namely, there are truly great and wonderful developments in theoretical and experimental physics that have simply been far more important and successful at describing nature and which have, in addition, led to technological advances. There have also been concrete discoveries, like dark energy, that are astounding and about which we currently have no clear understanding, so that other areas where we may have little understanding, such as the inconsistencies between GR and quantum mechanics, while important, are perhaps not the most overpowering immediate concerns.

On Extra Dimensions: I continue to remain neutral, if skeptical, here. While the notion of large undetectable extra dimensions is fascinating, and the fact that they can exist and have remained undetected is really fascinating, my own impressions, based on my understanding of particle physics data, is that they don’t smell right as a solution of the hierarchy problem. The apparent unification of couplings, large top quark mass, etc, provide at least suggestive evidence to me that there really is a large scale involved in unification, and also that supersymmetry seems to be suggested at some level. The research I did for my new book also made me frankly more skeptical from a theoretical perspective as well; namely, if I think about what the ground state of M-theory might be, the likelihood of some single, relatively isolated, relatively flat brane on which we live existing embedded in a higher dimensional and large space, seems unlikely to me. But we shall see.

On ID and Science: As many of you know who have followed any of my writing in this regard, the reason I took up this cause a bunch of years ago, and have spent many unfortunate hours defending science against attacks rather than doing what I prefer to do, which is getting people excited about science, is that I viewed the attack on evolution as an attack on science as a whole. The more I learned, the more I saw this as a campaign that was based on fear of the fact that God is not an explicit part of the scientific method. For some, this implies that science itself is immoral, and if you read much of the literature, in particular from the Discovery Institute, you will see this expressed explicitly. I also saw this campaign as not merely one by well-meaning but misinformed individuals, but rather by people who were very well schooled in public relations, who had a mission, and wanted to achieve it however possible. And since scientists, by nature, tend to be miserable at public relations, it seemed important to try and counter this in whatever ways possible.

My own awareness for the necessity of being respectful of religious beliefs has increased tremendously during this process. It has also become more clear to me that scientists tend to, whether they want to or not, appear patronizing about this, and also tend to make the philosophical leap from the fact that science deals with natural causes and effects to the statement that there can be no purpose in the universe. Whatever one’s personal perspective on this, and I see no evidence for purpose myself, this is a personal philosophical or religious notion, not a scientific one. In my piece in the NYT in May – the one that provoked the wrath of the Cardinal, Archbishop of Vienna – I used the example of Lemaitre and the Big Bang to point out that science functions independently of questions of purpose.

Now, how does all of this relate to string theory and the source of all the concern in one of the blog posts and the resulting comments? Well; it is the point I mentioned at the end of one of them, when responding to Clifford. I paraphrase: “the context in which I referred to ID was actually to make a point that I am beginning to think is actually relevant… namely that when physicists refer to ’string theory’ it is in the context of ‘field theory’… namely as a technical replacement of one physical and mathematical framework for dealing with relativistic quantum mechanics with another.. but unfortunately in the context in which we complain about IDers saying Evolution is ‘just a theory’, the popular use of the term string theory is unfortunate.. because ’string theory’ is not a theory in the context in which we claim evolution or general relativity is… i.e. something that has been tested time and again against experiment and observation.. calling it the string hypothesis would not be inappropriate in this sense..”

Unfortunately, string theory and extra dimensions are often held up as examples of science being indistinguishable from religion. I have tried, even in my last NYT piece, to explain some of the differences, but in a statement I made elsewhere that got someone very upset, I do believe that saying, other than tongue-in-cheek, that the current ideas are so beautiful that they must be correct–without any recourse to empirical data, is almost indistinguishable from religion.