Thursday, May 05, 2011

Hello from Perimeter Institute

Sorry for the silence. I seem to have caught a stomach bug on the trip to Canada and spent the better half of the week commuting between bed and bathroom. I'll call it the Air Canada diet. Nothing quite like it to get rid of that excess pregnancy weight.

The construction at Perimeter Institute has been progressing well. The new part of the building is supposed to be finished sometime early fall or so, and I hear they're still on schedule. (See here for the photos from last year.)




The main entrance to the building is well hidden between fences, walls, and various dangerous looking machinery. Its location seems to be changing by the day like some secret code. The reception has been replaced by a study area, the bistro is now in the lobby, and staff features some new, unfamiliar faces. Still, after the last year's many changes in my life, it is comforting to come back and find things are still like they've always been. People are still talking about spin foams and black holes and their favorite interpretation of quantum mechanics. They still drink too much coffee and on your way to Starbucks on a Sunday morning you might run into the director. Waterloo is really a small town and the physicists' universe is expanding while they're orbiting around the center of their own gravity.

34 comments:

Uncle Al said...

1) Calabi-Yau manifolds are mirror-symmetric (arxiv:hep-th/0002222).
2) The universe isn't.
3) A chiral de Rham complex won't save you.
4) Pookie pookie. "8^>)

Welcome back to the New World! Enjoy it while there is some chrome remaining on its fenders. (The recent Ottawa election replaced fools who should know better with crooks who really mean it.)

Neil Bates said...

"People are still talking about spin foams and black holes and their favorite interpretation of quantum mechanics." OK, as someone very interested and even irritated about some IOQMs, I'll bite (maybe literally, but politely here): just what sort of interpretations are getting favor or not, are people aware there might be a way to test some of them that wasn't thought of before (ask me about that, I kid you not), etc? (Answers from all around appreciated.) Thanks. BTW I think PI is a good idea and a place of serious work, not a grandstanding joint.

PS: Al, I didn't know you appreciated the angle on Canada so well. I can't wait to see what Phil has to say bye and bye.

Robert L. Oldershaw said...

I would be curious to know what people make of Joy Christian's refutation of the mathematical foundations and logic of Bell's theorem.

It seems like such a major challenge to the standard interpretations of QM, especially non-locality.

And yet I have not seen any formal attempts at criticism of Christian's challenge.

What's the scuttlebut from the deep thinkers and heavy hitters on this issue?

RLO

Bee said...

Hi Neil,
Well, you pick a name and you get your interpretation on the arxiv. For a recent novelty, try this. Best,

B.

Phil Warnell said...

Hi Bee,

Travel just doesn’t seem to be going your way as of late. That is with fainting spells, being ferried off to hospital and now the dreaded Air Canada flu. However it’s good to hear you’re back to the hive that Lazaridis built (and continues to). It also nice to see all the photos showing the Hawking addition now nearing completion; although with your run of luck lately please avoid the construction area:-)

As it turns out you arrived about a month too early for their sponsored upcoming event, “Equinox Summit: Energy 2030”, which is focused around what being the possible solutions for the impending energy crisis. This news might also make our favourite Uncle happy learning that tinsel town is doing more than counting how many angels can dance on a multiversal pin head:-)

Just as further comment regarding Al’s remarks, I would draw to his attention that us Canadians, when it comes to choosing our leaders don’t just limit our dicision making to accessing unqualifiable rhetoric, yet do have actual metrics at our disposal. Now as you know I never self promote as (rather not have the attention ;-)) and thus I would beg your indulgence Bee in permitting Al to look at this recent post of my own which demonstrates just how this is accomplished :-)

Best,

Phil

Neil Bates said...
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Bee said...

Hi Phil,

I thought the next equinox is in September? It would certainly help matters in terms of saving energy if people wouldn't be flying to all these conferences and workshops and summits. Let's all just meet virtually ;-) Best,

B.

Neil Bates said...

Robert, I hadn't even heard about this supposed refutation (or maybe partial, contextual etc.) of Bell's Theorem. I check around some, not comprehensively, but if it had been "going around" I think I would have seen about it. So, AFAICT neither formal refutation or informal discussion is much in the news, but since BT is such a philosophical BFD as Biden would put it, and refutation would be "one of those WTF moments" as Sarah would say, you'd think sci-media (e.g., New Scientist of course - are they?) would be all over this.

That doesn't mean he doesn't have a point, and it should be fairly considered. However, from reading descriptions e.g. from Penrose I thought the BT was rather logically fundamental, a deep proof that strong correlations just could not be ever explained in principle by local/realism. So, "how could it be wrong"? BTW a relevant paper can be found here: arxiv.org/abs/0707.1333.
I don't have time now for any but a glance, but it seems to me already that Christian may be saying the BT "fails" in this sense: the type of variables he studies, *can't* do what Bell says variables can't do, which means Bell was right in the usual sense. IOW, could it be one of those ironic, confusing ways of saying "fail"?

I think that we can get a better understanding of the "quantum measurement paradox" in two main ways: looking at repeated sub-critical measurements, and by attempts to extract information from supposedly decohered systems. I have more to say via the obvious route.

Steven Colyer said...

Joy Christians original article:
Disproofs of Bell, GHZ, and Hardy Type Theorems and the Illusion of Entanglement.

He was heavily criticized (well, it's Physics .... so what the hell? Why should we be happy and today be different than any other day?>.

He responded to his critics here: Disproof of Bell's Theorem: Reply to Critics.

New Scientist had an article about it, here: Quantum Untanglement: Is spookiness under threat?.

"Un"tanglement. On a scale of 1-10, how adorable are the New Scientist editors at writing copy?

Robert L. Oldershaw said...

Hi Steve,

Many thanks for the reference to Christian's "Reply" article.

That was what I was looking for. It is a bit dated but useful none-the-less.

Wouldn't you love to see Joy Christian and David Deutsch (quantum computers and "many worlds" fantasies) go head-to-head in a no-holds-barred debate?

RLO

Uncle Al said...

Given only Euclid, explain deep sea navigation. Perturbation treatments are elegant, convenient, and wrong. Imagination is intelligence having fun. Less work, more silliness. Dei ex taedio.

Uncle Al did research time in BC and Manitoba. The Commons servery was puke on compost, and expensive. Fantastic forest. The U/Manitoba servery was heaven itself. Manitoba mosquitoes are best killed with hammers.

Hysterias of inserted symmetry breakings in fundamentally derived physical theory are diagnostic. Theory must not be mirror-symmetric at the onset. PI has the brains for less Tommy Aquinas and more Baruch Spinoza. Put a Bee in their bonnet.

Robert L. Oldershaw said...
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Neil Bates said...

Thanks for the many links, Steve. I would have put in more first but I didn't know we could get away with that many links. So I see, Christian indeed says the BT/BI is "wrong" in the usual sense. However, with correlated photon measurements you realize IMHO that a theoretical "some kind of HV theory, of any type" isn't the main point in practice. If one of a pair of entangled photons (AKA "biphoton") passes a given lin-pol filter etc. then e.g. the other one will definitely pass a filter at the same orientation. Assume that the photons could be any state when coming out - if their states are considered "real," and we do have a known basis composition for that. Then, the first one has "by itself" a certain probability P of passing filter #1 (from cos^2 of phi the angle difference), and the other one - even if "same polarization" - the same chance P of passing #2. The probability of mutual passage, in that sense, is P^2. Well, that doesn't average out to "one" no matter what "variables" you imagine. Mutual passage or absorption would be an occasional event.

Instead, the Bell Theorem made the point that even *if* you imagine some weird tricking up (that isn't the usual concept of probability of passage through a filter), you still can't get the full scope of correlations at all angles. BT says "There is no way to." It does not say "realist photon polarization projection statistics don't allow it" - because we already knew that! If BT was wrong about whether "some way" could allow the correlations, those hidden variables still aren't part of the basic structure of measurement statistics as we know them, so I think it's hokey to make such a big deal that there might be "some way" to get correlations. (Have you seen some of the outlandish ways to imagine photon behavior, to explore whether correlations could "somehow" happen?) Also, the BT focussed on delicate reasoning about mis-matched filter orientations and not as much the sheer miracle of perfectly dependable correlations using matched detector states.

OK, the Captcha genii is being catty with me again. Really, it is "copen" - just add the "hagen" and we're on track.

Eric said...

I really don't understand why people continue to deny the possibility of hidden variables. I just read the introduction of Joy Christian's paper and am not sure if the papers logic rests on that or not. Nevertheless, if hidden variables do exist entanglement could easily dissolve to a local phenomenon, whether that is his argument or not.

An example going even further back than rigid entanglement would illustrate the point. In the double slit experiment the wave/particle nature of quantum mechanics is illustrated. If particles are observed throughout their path from the origin to the target then the particles act like single discrete particles. That is, there is no interference between the paths from either slit to the target. However if ithe particles are not observed in their trajectory then an interference pattern builds up between the two paths between the slits and the target and show up as a wave distribution on the target.

But a classical example in everyday experience shows that hidden variables would exhibit the same reaction. If an object is moving through water, air, or any transparent medium to our eyes it creates a pathway through that medium that exists for a short time. This is observed as wake turbulence. If there is wake turbulence in an invisible medium between the two slits it seems to me it would cause exactly the interference between the two paths that is observed. That wake pathway will exist for a shorter or longer time depending on thermal properties surrounding the pathway. So if a particle is moving through a slit that did not previously have a particle move through it it will still be affected by the pathway created by an earlier particle moving through the other slit. The same thing happens to large airplanes following to close to one another.

In the other example where particles are observed in their trajectory - in this case the simple observation implies photons interfering with these wake turbulence pathways. Remember, that in general quantum properties depend not only on the characteristic of being submicroscopic but also on thermal properties. Superconductivity depends on pathways that do not deteriorate over time. When you attack a pathway by shooting them with photons you essentially randomize the pathway. Then there is no longer a pathway for a later particle to interfere with and the particles then act like individual particles.

Eric said...

"If there is wake turbulence in an invisible medium between the two slits it seems to me it would cause exactly the interference between the two paths that is observed."

I misspoke here. What I meant to say is if there is wake turbulence in an invisible medium between each slit and the target then each particle can be considered to create a temporary pathway that will be seen as wake turbulence by a later particle coming from the opposite slit. I hope it is clear that this property of interference isn't being created by the diffraction effects of passing through the slits. That is a completely separate issue.

Steven Colyer said...
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Steven Colyer said...

Rob and Neil, you're more than welcome. I got that from Andrew Thomas' Best-Site-That-Explains-Quantum-Mechanics website "What is Raelity?", in the replies section under his Quantum Entanglement chapter/page.

Eric, keep thinking, good stuff. Not sure how to answer your first question. I'd attempt: because HV's are not necessary to explain current experimental data. Is that correct?

Bohm's work is nevertheless amazing, and HV is currently used as a teaching tool in Quantum Hydrodynamics as an example of what does NOT work, I believe. Wish I knew more of each subject.

Bee, how is Joy doing? Still at Perimeter? He gave a talk at the wonderful Quantum Gravity Phenomenology conference you ran this past summer. Has he dropped discussion of the subject, because if I recall correctly, Bell's wasn't his topic of discussion there.

Also, say hello to John Moffat for us, and how is he doing. The last living person who befriend Bohr AND Einstein. Awesome.

Neil Bates said...

Eric, a left-over "wake" could hardly last long enough for experiments with sporadic photons of long waits. Things like that tend to not work out. Consider for example, you don't even need two actual slits for interference: You can have one, and a slightly-tilted mirror makes a virtual extra source from the one slit. (See en.wikipedia.org/wiki/Lloyd's_mirror .)

Steven, Andrew Thomas buys into the post-modernist decoherence doubletalk, but aside from that his site is informative.

Eric said...

Neil, actually the double slit is the classic example and for that reason I think it's best to stick to that, at least for the time being. It is always performed in the dark. Any light surrounding the purported pathway destroys the experiment. So even the circumstances of the experiment points to photons upsetting things. I think your just stuck in the old way of thinking.

Uncle Al said...

Wow! That is as good as the "transparent Coke can,"

http://en.wikipedia.org/wiki/Arago_spot

Focus a slide on a projection screen, remove the slide, put an unopened Coke can between the light and the screen, long axis parallel to the light path. At the center of the dark circle is a bright spot.

We found no suitable Pyrex solid cylinders, but a leaded glass, Plexiglas, or styrene polyester cylinder is obtainable. One would need anneal the strain out of the transparent medium for a proper control. Refractive index is the phase discontinuity.

Neil Bates said...
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Neil Bates said...

Eric, I actually do think beyond "old ways of thinking" - as and when it is actually warranted by some careful thinking, not just stuff off the top of my head that I would expect everyone should just "see" the terrific advance being made. Sorry, your line is too often a defensive and lazy cliché. You may have something, but you'll need more solid case and rebuttals when someone complains, at least if you're going to complain back about their attitudes.

Good luck, though - I sure haven't had enough since I started picking at "old ways of thinking" myself, many years ago.

Heh, my Captcha is "supper" - I want to know, where's the beef!

Eric said...

Neil, I looked at your link. That seems to be an even an even more dramatic example of the persistence of pathways in the vacuum. But in the sentence before that you said that persistence isn't likely to happen....? Not sure what your point is or if you are just in mid process of changing your philosophical position. Sometimes people don't make a lot of sense in their arguments when they are in the midst of weighing two mutually exclusive positions. I hope it resolves itself in my favor.

Phil Warnell said...
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Phil Warnell said...

Hi Bee,

Well I finished reading Lee Smolin’s new interpretation of quantum mechanics, only to discover I need an interpreter to interpret the interpretation:-) That is all I’ve managed so far is to having been told for each individual microscopic system we have two beables, one being the value of some observables and the second a phase e^ ıφI. This has all microscopic (copiable) systems governed by nonlocal and indeterminate laws, hence only being able to be expressed statistically, while all macroscopic systems being unique (non-copiable) and thus separately distinct following determinable local rules.

So first I need to understand what a phase e^ ıφI is as to represent as being a beable. That is as John S. Bell said “observables are made out of beables” and what stands as being “observables” here and therefore measurable and what does not. I guess what I’m actually suffering from is in having difficulty for this physics becoming physical for me; which means I’ll probably have to wait for the book to come out:-)

Best,

Phil

Bee said...

Hi Phil,

I can't say I actually understood it, but the main point seems to be that when you're trying to observe some quantum state, you're actually measuring something that's part of an ensemble of similar states that might be distributed somewhere in the universe. The point I keep getting stuck at is what means 'similar' (besides that it seems to necessitate some equal-time slicing). I haven't thought much about the phase since I have no problem with non-realist interpretations. In any case, you might find this useful. Best,

B.

Phil Warnell said...
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Phil Warnell said...
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Phil Warnell said...

Hi Bee,

Thanks so much for Smolin’s presentation and it has helped somewhat in two ways. The first being now I’m more certain about what it is that I don’t understand and second I’m now certain there is much that Smolin still struggles to understand. Never the less it is interesting and in some respects I think he should have more discussions about this with Bohmians extending beyond just Antony Valentini. Those would be to include people such as Sheldon Goldtstein, Detlef Dürr, Stefan Teufel and others.

Smolin talks a lot about how Bohmian Mechanics gives no explanation for the wave function not having a backaction imposed upon it. He then goes on to say his highly nonlocal ensemble then has there no need for one. This demonstrates some misunderstanding regarding Bohmian Mechanics, that is at least from those holding as first order perspective of the theory, where they don’t consider the universal wavefunction as something physically real and also dismiss the need for maintaining the quantum potential; this as opposed to how de Broglie and Bohm considered things differently in having it as a second order theory.

Now this is not to have it believed that I understand Smolin’s proposal in any great depth, yet I have the feeling that in such regards he’s essentially just reframed what many Bohmians have already insisted how the theory should be envisioned.

“We propose that the reason, on the universal level, that there is no action of configurations upon wave functions, as there seems to be between all other elements of physical reality, is that the wave function of the universe is not an element of physical reality. We propose that the wave function belongs to an altogether different category of existence than that of substantive physical entities, and that its existence is nomological rather than material. We propose, in other words, that the wave function is a component of physical law rather than of the reality described by the law.”

-“ Bohmian Mechanics and the Meaning of the Wave Function”, Detlef Dürr, Sheldon Goldstein, Nino Zanghì (1995)

Best,

Phil

Luke said...
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Luke said...

Bee,

Imagine my surprise at noticing that your photo was on the board today at PI. I'll have to stop by and say hello. I didn't see you there this afternoon but I'll try and stop by tomorrow.

Steven Colyer said...
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Steven Colyer said...

I don't know why people struggle with all this. Strings have a background called loops, because loops are made out of strings. Loops don't have a background. Everyone wins.

Or everyone loses. Maybe they're all wrong.

Phil Warnell said...
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