Should SONY help foundational physics?
By ZEEYA MERALI • Aug. 31, 2010 @ 15:43 GMT

Just a quick post to point you to the BBC’s coverage of FQXi large-grant-winner Gaurav Khanna’s work, using a Playstation supercomputer to test loop quantum cosmology, find out what happened before the big bang, and predict signs of black holes. (More details in Graeme Stemp-Morlock’s article: “The Quantum PlayStation”.)

You can listen to the piece, broadcast on the BBC Worldservice’s Digital Planet, here (Khanna comes in at about the 9 minute mark).

I’m highlighting it here because the host, Gareth Mitchell, picked up on an interesting point: Khanna was able to string together 16 PS3 consoles to create a supercomputer because, until recently, the PS3 was an open platform, running LINUX, which could programmed for scientific tasks. Now, however, SONY have shut down this functionality––possibly because hackers managed to exploit it to run pirate games.

So, sadly, it won’t be so easy for others to follow Khanna’s example and create their own PS3 supercomputers in the future. The programme has a bit of a discussion about whether SONY should feel more obliged to help the progress of foundational physics research. The answer seemed to be, realistically, probably not. But I thought I would throw it out there for you.


GRW vs Free Will
By FLORIN MOLDOVEANU • Aug. 20, 2010 @ 17:21 GMT

This is my last post on key results that were presented during the New Directions in the Foundations of Physics conference in Washington DC. (You can see my other posts about building a black hole in the lab, how quantum mechanics isn’t as strange as it could be, and quantum effects and time travel.) Now I want to talk about advances by FQXi’s Roderich Tumulka in creating a relativistic GRW quantum collapse theory and the Free Will Theorem controversy.

To recap, the Free Will theorem, proposed by John Conway and Simon Kochen, claims that no deterministic interpretation of quantum mechanics is compatible with the notion that humans have free will. So why does that hit up against Tumulka’s model?

Tumulka presented what looked like a consistent relativistic version of the GRW approach to quantum mechanics––that is, an approach in which quantum collapse happens spontaneously, rather than as a result of a measurement. (However, this result contained no interaction, and this is where the hard part lies in light of Haag’s theorem of the impossibility to have a strictly Lorenz invariant vacuum or a Hilbert space in the interaction picture in field theory.) GRW-type theories are stochastic; for an individual particle wavefunction, there is a probability of collapse, but no certainty. The clash with the Conway-Kochen Free Will Theorem arises because Conway and Kochen assert that any GRW-type theory is also proved wrong by their theorem. Randomness, they argue, is no better than determinism.

In light of the talk I re-read the original papers on the archive, and I watched a six part presentation by Conway recorded last year. It is really hard to say who is right and who is wrong––the arguments are very subtle on both sides. But I think I understand clearly enough Conway’s position on randomness to be able to attempt to present it here.

Here is what Conway has in mind: He starts with the “second running” argument for causality. You go to the movies and watch a very exciting story. You do not know the outcome and to you it looks like the characters have free will. Then the next day you take a friend with you to see the same movie. To him, the characters have free will, just as it did for you yesterday, but by now for you they no longer look like that because you know the outcome. This argument shows that it is logically impossible to argue against determinism with a believer in determinism; you would get no logical contradiction. But logical consistency does not guarantee agreement with reality.

A second Conway argument is based on how backgammon tournaments––with multiple pairs of players all conducting games at the same time––are conducted. The random rolling of the dice is done ahead of time and everyone plays the same rolls in parallel to ensure fairness among all players. It does not make any difference to the outcome of the backgammon games if the players roll the dice as they go, or if the random sequence is pre-generated.

To this, Tumulka had two counter-claims: (1) The Free Will Theorem is nothing new, and it was in fact proven by Bell in an equivalent form; and (2) This theory does not apply to stochastic theories.

In his talk, Tumulka specifically focused on the critical statement of the Free Will paper in which Conway and Kochen assert that randomness does not help. In Tumulka’s theory, collapse involves “random flashes.” Conway insists that just as the outcome of the backgammon games is not changed, whether the dice are rolled during the matches or ahead of time, it makes no difference to GRW predictions if the random flashes are given before the Big Bang versus being “computed” when needed, “on the fly,” by nature. This is just as bad as being determined.

Now back to Tumulka’s position. Why is “rolling of the dice” before the Big Bang so bad? Because of the meaning of non-locality. Conway and Kochen assume that the random quantum mechanical behavior can only depend on the past causal cone because one cannot signal faster than the speed of light. Is this bad? Yes, because Tumulka argues that quantum mechanics (and his relativistic GRW theory) accesses non-local information beyond the past causal cone while obeying the no-signaling condition. Moreover, the right way to understand Bell’s result is not in the popular understanding of choosing between locality and hidden variables, but as an outright rejection of locality. Without the incorrect confusion between no-signaling and non-locality, one of the three original assumptions of the Free Will Theory (the FIN, or its later modification to MIN) is wrong, and this opens a loophole allowing the existence of no-signaling, non-local stochastic quantum mechanical theories.

So who is ultimately right hinges on rejecting locality outright from Bell’s inequalities. I feel that the question is not settled one way or another. Take the Aharonov-Bohm effect. It surely looks non-local, until you notice that the vector potential in electromagnetism is the connection in its corresponding gauge theory and it does obey the micro-causality condition in field theory. Or take Bell’s inequality. Joy Christian managed to produce a local explanation at the expense of using geometric algebra instead of real numbers. While his interpretation of measurement is in minority among physicists, his result can be understood as a local theory in the sense of Conway and Kochen.

So here is the challenge: Does anyone have any conclusive proof that Bell’s inequality rejects locality? I would surely like to hear about it and debate it.

Corrected Post Script

After reading all relevant archive papers on this subject, the core papers are as follows: arXiv:0905.4641v1 for another presentation of Tumulka’s arguments, arXiv:1002.1392 for a nice solution of the puzzle of the dispute by Nicolas Gisis and arXiv:1006.2485 (and references inside) by Antoine Suarez for some relevant comparison with his “before-before” model.

The moral of the story is that the origin of the dispute stems from a different expectation about the degree to which a relativistic theory should be covariant. (Tumulka’s “flash ontology” requires a less stringent covariant condition.) Therefore Conway’s claim that FWT rules out stochastic models is false.

Suarez’s „before-before” model shows something more: SPIN, TWIN, and MIN does not prove the free will theorem because he managed to produce a counter-example (albeit logically inconsistent and ruled out by experiments). Instead, the FWT should be derived from full quantum formalism and the MIN axiom for deterministic models. Suarez’s toy model obeys SPIN and TWIN under the standard EPR experiment, but it is incompatible with the C* algebra (and in particular with Hardy’s 5 axioms) because it predicts violations of entanglement under certain conditions.


Parallel Universe on your iPhone
By ZEEYA MERALI • Aug. 16, 2010 @ 21:45 GMT

Got a tough decision to make and just don't know which option to choose? Well, why not choose both options––but perform each in a different parallel universes?

www.cheapuniverses.com

Yes, in what must be one of the boldest marketing ploys yet, the website link:cheapuniverses.com/]www.cheapuniverses.com is offering two fates for the price of one. It even comes recommended by FQXi's Garrett Lisi, so I thought I’d highlight www.cheapuniverses.com it here. There’s also a universe-splitting iPhone app

If you can’t decide between two options--taking a bath or going for stroll are the examples offered on the site––log on to www.cheapuniverses.com, pay $3.95, and the organizers promise to “initiate an actual quantum event – just for you – which has two equally possible outcomes. Both outcomes will happen, but in _separate_ _universes_.”

The physics behind the website is, of course, the Many World’s Interpretation of quantum mechanics, proposed––as the site tells us––by the father of Mark Oliver Everett’s of Eels (or Hugh Everett III). Everett wasn’t happy with the standard interpretation of quantum mechanics that says that before observation, quantum objects don’t exist in a single state, but are described by a wavefunction containing a superposition of multiple states. This is exemplified by Schrödinger’s cat locked in a box with a radioactive atom that on decaying will trigger a mechanism that will release poison that will kill the cat. Until the box is opened, standard wisdom goes, the atom has both decayed and not decayed, and hence the cat is both alive and dead at the same time. When the box is opened, the wavefunction "collapses" and the cat snaps into one set state, life or death.

Everett’s view was, instead, that the observer becomes entangled with the superpositioned object. Due to the correlation between the observer and the object, the observer splits into multiple copies. Each quantum option is satisfied—the cat both lives and dies—just in two parallel worlds.(For more, read “The Many Lives of Hugh Everett III.”

Well, the physics is there. But in practice, why go to this website? Why not just a flip a coin to decide whether to take a bath or go for a walk? (I can’t help thinking though, if you think you need a bath, you probably should take one.) The answer is that a classical coin flip won’t give you a split universe. For that you need a quantum event, which is apparently supplied by the company idQuantique in Geneva.

The company idQuantique specializes in quantum cryptography--and their technology was used at the soccer World Cup in South Africa. I recently wrote a news article for Nature about claims that its supposedly invincible cryptographic system had been hacked, so it’s nice to blog something more cheery about them.

But does it work? Well, I should say that I haven’t (yet) tried it out. And even if I do, as cheapuniverse says itself, in small print: “Due to the separateness of the two universes, you won't be able to check in on your other self. But that other self will exist nonetheless, and will be exploring its universe just as you are yours.”

Plus, there’s a money-back guarantee: “Our universes are 100% guaranteed. If, after using our service, you find that you're not in a universe, contact us immediately. You're entitled to a complete refund, no questions asked. Of course, if you simply don't like the universe you've created, there will be no refund... but you can take some comfort in knowing that the other version of you is probably quite happy with our service.”

Worth a try? (As long as it doesn’t give Max Tegmark any more ideas about quantum suicide.)

And who says foundational physics doesn't pay?


Philosophy vs. Physics
By WILLIAM OREM • Aug. 3, 2010 @ 13:50 GMT

image: xJasonRogersx

It’s not quite timeless, but Steven Weinberg’s *Dreams of a Final Theory* is a classic of the popular science genre. In it, he notes that he was an enthusiastic student of philosophy as an undergraduate . . . that is, until “the insights of the philosophers I studied seemed murky and inconsequential compared to the dazzling successes of physics and mathematics.”

At that point Weinberg turned away from the venerable path of Augustine and Aquinas, Hegel and Husserl, and began a lifetime pursuit in the physical sciences that would prove a glittering triumph. What with his Nobel-winning contribution to field theory that allowed for unification of the weak and electromagnetic forces – not to mention his winning of everything from the Oppenheimer Prize to the James Joyce Award -- it is difficult to conjure up any profound sense of disappointment at the career he chose to forego.

Actually, Weinberg did far more than leave philosophy behind; in *Dreams* he actively campaigns against it. An entire chapter is dedicated to exposing, with a wink to Wigner, the “unreasonable ineffectiveness of philosophy.”

From *Against Philosophy*:

“From time to time since then I have tried to read current work on the philosophy of science. Some of it I found to be written in a jargon so impenetrable that I can only think that it aimed at impressing those who confound obscurity with profundity.

But I do not aim here to play the role of a philosopher, but rather that of a specimen, an unrenegate working scientist who finds no help in professional philosophy. I am not alone in this; I know of no one who has participated actively in the advance of physics in the postwar period whose research has been significantly helped by the work of philosophers. . . .

Physicists do of course carry around with them a working philosophy. For most of us, it is a rough-and-ready realism, a belief in the objective reality of the ingredients of our scientific theories. But this has been learned through the experience of scientific research and rarely from the teachings of philosophers.”

Strong words, and conceivably a bitter pill for those among us—at FQXi, hardly a minority—who feel physics and philosophy may share areas of significant overlap (physics and religion, I should note, is a different claim). Or, at least, those who feel that physics is now in a position to begin to answer certain deep questions long relegated to the philosopher’s café table.

Yet Weinberg is hardly the only great mind to take a dim view of the toga. Here’s Richard Feynman:

“Philosophers, incidentally, say a great deal about what is absolutely necessary for science, and it is always, so far as one can see, rather naive and probably wrong. . . .

You can take every one of Spinoza's propositions and take the contrary propositions, and look at the world - and you can't tell which is right. Sure, people were awed because he had the courage to take on these great questions, but it doesn't do any good to have the courage if you can't get anywhere with the question.”

image: hetemeel

Full disclosure: I am passionate about philosophy, teach courses on Existentialism and Literature, and routinely advocate to undergraduates that they be willing to take the question of the meaning of their lives seriously (against the tide of much modern philosophy, in fact, which emphasizes ironic distance; but leave that aside). Yet in the corner of the Agora where we speculate on the nature of physical reality, and how best to attain knowledge of same, dismissals such as Weinberg and Feynman’s do hit a nerve. I remember in my own undergraduate days suffering mightily under the misapprehension that statements made in philosophy seminar were somehow “true” in the same way as those made in physics survey. Both referred to the world, thought I, so both must be describing aspects of the same thing. Thus I tried for a long time to understand how Kant’s “insights” into space and time, laid out in all their impenetrable obliquity in *The Critique of Pure Reason*, could be put together with Einstein’s.

It was only after a lot of fruitless effort that I came to recognize Transcendental Idealism and Special Relativity don’t go together. (Disagreements with that statement are welcome.) That realization in itself was a frustration; but recognition of the reason behind my error was absolutely fruitful. Kant--I say this with due deliberation--didn’t make any discoveries into the nature of space and time; he made assertions about them. (Hegel made quite other ones; Heidegger still others.) To be sure, the quality philosopher’s positions are hardly guesswork; by rejecting Humean empiricism, Kant was building on a long line of philosophical tradition he and all his admirers regarded as credibly established beforehand, the whole train of Enlightenment epistemology. But the simple question remains: was he right?

Or, with Feynman, perhaps the more important question: Can we even tell?

I recognize that this is a bit of a straw-man argument I am building up here, but a productive one nonetheless. So far, every indication is that Einstein was absolutely right. Not “influential,” not “challenging us to see things in a new way,” – just right. We don’t have to construct those odd sentences around him that we do around pure philosophers, such as “For Einstein, length measurements are relative to the observer’s reference frame,” or “In Einstein’s view, gravity is the result of four-dimensional spacetime curvature.” These aren’t positions in Einstein’s systematic philosophy of Being: they are something far more profound. They are true.

Limited in their scope, yes; still to be unified with QM, yes; all the standard caveats about scientific theory apply. But SR and GR make numerous specific predictions that have been, and are being, tested all the time. Two hundred years later, Kant remains influential, insightful, challenging—but was he right?

And if we can’t answer that question—let’s put the issue boldly--shall we cease burdening our thoughts with the verbal complexities of a tradition that may not actually be progressing at all, but only undergoing an outmoded, self-referential dance?

Are we really at the dawn of a new age of “Physics and Philosophy,” as so many popular books and magazine articles suggest--or at the twilight of Philosophy altogether?

image: Johan J.Ingles-Le Nobel

The Planck Scale: Gravity’s Ultimate Limit?
By MARK WYMAN • Aug. 1, 2010 @ 21:07 GMT

http://toonstoonstoons.net/category/cartoon/

Scientific researchers, especially younger ones dreaming of glory and fame, are generally averse to setting boundaries and claiming absolute limits. This stems both from a hopefulness that Nature will be kind enough to give us plenty of new secrets to unravel in the future as well as an anxiety about ending up later as the villain in a just-so story about how the “establishment” naively criticized a new theory when it first appeared. In light of this, it’s always notable when researchers find a new way of stating just how limiting the laws we know are. A very fine example of this kind of work appeared recently on the arXiv, in a paper by Gia Dvali and Cesar Gomez, Self-Completeness of Einstein Gravity.

This paper rains on the parade of those who hope against hope that there will be a fundamental theory of gravity with a regime of validity that pierces the Planck length. The Planck length is the smallest length scale presently contemplated in all of Physics: it is the length scale where gravity becomes as strong as the other fundamental forces. General relativity (GR) predicts that any experiment with enough energy to probe the Planck length must necessarily form a black hole in the process, thwarting the ability of the experiment to send out any results describing what happened on shorter length scales. What we’re not sure of is whether GR is right about this.

Dvali and Gomez’s paper is a subtle and powerful argument that GR is correct on this point: they pull together a variety of lines of reasoning to this effect, but the central claim and most powerful claim is that there is, in effect, _no_ _difference_ between the super-high energy physics inside the Planck length and well-known black hole physics. The idea is this: the way gravity works is that it wraps a black hole horizon around any region of space that reaches Planckian energy-densities. This black hole is a kind of buffer that absorbs the huge energy density, converting it into the relatively slower moving physics of black holes, where the energy will leak out later in the form of Hawking radiation. In other words: the Planck length also sets a minimum time scale in nature, a Planck time, faster than which nothing can occur. If an event is set to occur more quickly than this time, it get bounced or reflected by gravity into a black hole that flips that fast moving event into a slower-moving black hole horizon. The bigger the energy, the bigger the resulting black hole, and hence the _longer_ it takes for the energy to escape as Hawking radiation.

If true, this means that the real locus of our hope for novel physics is the Planck length itself. A black hole that just barely has enough energy to form evaporates most quickly. If we could see such a thing happen, we could get a window into the ultimate energy scale of physics. However, such a black hole is far beyond the scope of our most powerful Earth-based accelerators: it is fifteen _orders_ _of_ _magnitude_ smaller than the length scales that the Large Hadron Collider’s record-breaking collisions will probe, for instance. (Ie, to get to the Planck length, you’d need an accelerator 1,000,000,000,000,000 times more powerful than the LHC!). So it remains a big open question as to whether Dvali and Gomez’s ideas will ever be tested. In the meantime, we will have plenty of opportunity to explore whether there are any sneaky ways to get around their arguments; and you can count on it that many researchers are already looking to do just that, if they can!

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