Sunday, July 01, 2012

Workshop on Nonlocality, Summary

Sorry for the silence. I've been stuck in the workshop on nonlocality that I organized here at Nordita, and it seemed somewhat rude to blog through talks of people I invited to speak.

It all went well, except that my co-organizer cancelled two days before the start of the workshop, so I had to  be the sole entertainer of a group of 27 people. A group that, to my own shame, was almost entirely male except for one student, which however I only realized when I was standing in front of them. I have a public speaking anxiety, one of the most common anxieties there is, but really somewhat unfortunate for a scientist. People tell me my talks are okay, but the more ancient parts of my brain still think the smart thing to do when a group of guys stares at me is to run really fast, and the Scandinavians are a particularly scary audience. Anyway, I think I managed to pull it off, minus the usual projector glitches.

My interest in non-locality comes about because it shows up in different approaches to understand the quantum structure of space time, and it plays a role in many attempts to resolve the black hole information loss problem too. It is, in that, comparable to the minimal length that I've been working on for, ah, a hundred years or so, at least in somebody's reference frame. Nonlocality and the minimal length both seem to be properties of nature deeply connected to quantum gravity, even though we don't yet really understand the details, and they're also related to each other.

Nonlocality comes in many different variants and the purpose of the workshop was to shed some light on the differences and features. The most common forms of nonlocality are

  • Quantum mechanical entanglement. The type of nonlocality that we find in standard quantum mechanics, no information exchange over space-like distances though.
  • Quantum field theory, non-commuting operators on space-like separated points. This can ruin the causal structure of your theory and should be approached with great caution.
  • Quantum field theory, higher-order Lagrangians which show up in many models and approaches but bring a lot of problems with them too. Gariy Efimov and Leonardo Modesto spoke about realizations of this, and how these problems might be remedied. A certain book by Gariy Efimov that was published the year I was born, in Russian, and was never translated into English, plays a central role here. It's so much a clichee I couldn't not mention it - I'll probably end up having to dig out the damned book and learn Russian or at least pipe it into Google (as Leonardo apparently did).
  • Quantum mechanics and quantum field theory, non-commuting operators for space and time themselves, ie non-commutative space time in its many variants. This might or might not be related to the previous two points. The problem is that many approaches towards such a quantum space time are not yet at a point where they can deal with quantum fields, so the relation is not clear. Klaus Fredenhagen gave a very interesting talk about the spectrum of area and volume operators in a non-commutative space-time. Michael Wohlgenannt, Michele Arzano, Jerzy Kowalski-Glikman and his student Tomasz Trzesniewski spoke about other versions of this idea.
  • The whole AdS/CFT bulk-brane stuff, black hole complementarity and so on. Larus Thorlacius spoke about that. Unfortunately, Samir Mathur who had intended to come to the workshop couldn't make it, so the topic was very underrepresented. 
  • It might have passed you by, but Giovanni Amelino-Camelia, Lee Smolin and Kowalski-Glikmann, together with a steadily increasing number of co-workers have cooked up something they call "the principle of relative locality," essentially to cure the problems with nonlocality in DSR (see this earlier post for details). The idea is, roughly, that the notion of what constitutes a point depends on the location of the observer. I've tried and failed to make sense of this - it seems to me just DSR in disguise - but who knows, I might be wrong, and maybe they're onto something big. They too can't do quantum field theory on that space (yet), so it's not well understood how this notion of nonlocality relates to the above ones. Lee went so far to claim relative locality solves the black hole information loss problem, but I think at this point they don't even have a proper definition of what constitutes a black hole in this scenario to begin with, so it seems a little premature to claim victory.
  • A failure to reproduce a local space-time that occurs in lattice or network approaches, that runs under the name of "disordered locality." You can imagine it like tiny wormholes distributed over a nicely smooth space-time, except that the wormholes have no geometry themselves because, fundamentaly, space-time isn't a manifold. Fotini has been on to this for a while, but since she couldn't come the topic only came up once or twice in the discussion.
  • As Ingemar Bengtsson reminded us, trapped surfaces in General Relativity have some non-local features already.
We had a couple of more talks that touched on several of these topics, emergent gravity by Lorenzo Sindoni and Olaf Dreyer, black hole information loss by Jonathan Oppenheim, and Luis Garay who spoke about a stochastic model for nonlocality in quantum mechanics that I found very interesting.

Lastly, I should mention we had two discussion sessions that picked up the topics from the talks, one moderated by George Musser, one by Olaf Dreyer.

It was an interesting group of people that mixed better than I had expected. I had been a little afraid they would just talk past each other, but it seems they found some overlap on many different points. I certainly learned a lot from this meeting, and it has given me food for more thought. 

There are some slides of talks on the website; we hope to receive some more during the next week.

26 comments:

Zephir said...

/*.. "the principle of relative locality," is the notion of what constitutes a point depends on the location of the observer. I've tried and failed to make sense of this..*/

It's consequence of the dispersive reality inside of multiparticle systems. Dense aether model explains it with surface wave scattering model of the Hubble red shift: the ripples are changing wavelength with distance from every observer or source of waves, but their perspectives are mutually exclusive because of higher dimensions involved. We are seeing distant galaxies red-shifted in the same way, like the distant observers would see our Milky Way - although nothing actually moves here. The local nonlocality is essentially another name for multiverse concept, in which observed reality represents a low-dimensional slice of hyperdimensional perspective and the ancient Everett's many world concept.

Zephir said...

In mainstream physics the relative locality manifests with description of the same phenomena from different perspectives, although the physicists don't often realize it. The observable reality is hyperdimensional so that many people often describe the same thing from different subjective perspectives. The above Susskind's example is just one example of many: for example the CMBR noise is phenomenologically equivalent to the gravitational waves, holographic noise, gravitons, extradimensions, inflatons, fat strings and who knows what else. The over employment in physics and the redundancy of abstract poorly understood theories just makes this multiplicity more pronounced.

Zephir said...

/*..it's important to notice that the status of spacetime in contemporary physics resembles the status of the ether at the beginning of last century...*/
Because the low-dimensional models tends to converge into scalar fields at sufficiently distant perspective. But in contrary to Poincare, I don't believe, the aether concept is useless, as the physicists even didn't started to use is as a physically realistic model of otherwise abstract and untouchable hyperdimensional emergent geometry and anthropic landscape (compare the unparticle geometry of H. Georgi).

Eric said...

Hi Zephir,
I'm sure that you're saying something useful, even though I can't discern it. Perhaps the problem is that you don't take time to study and analyze new information, such as inquiring about what was in the talks, before talking about DAT. It comes across as egocentric and completely self-involved. So... Since I know you aren't egocentric and self-involved perhaps you should adopt some new social tactics that don't portray you in the wrong light. This would be in your own self-interest if you want people to take you seriously.

Btw, there is another person who regularly comments here who would also benefit from improving their listening skills.

Phillip Helbig said...

"A group that, to my own shame, was almost entirely male"

Surely you invited the best people. If there was only one woman, that is not your fault. Or are you saying that, in order to address gender imbalance due to other reasons, you should have invited some women who were not as good as some of the men you invited? Please explain.

I just returned from a conference in Prague ("100 Years After Einstein in Prague") which had very few women. Whatever the reason, it is not due to prejudice within that scientific community.

Bee said...

We invited the best people who came to our mind. Clearly we couldn't possibly invite everybody who ever worked on the topic since it was a small workshop. In hindsight I'm thinking we could have paid more attention to the gender balance. The one woman who was there wasn't invited (we had an open registration). Next time I think maybe I should make a more systematic effort. Best,

B.

Zephir said...

/**you don't take time to study and analyze new information, such as inquiring about what was in the talks, before talking about DAT**/
How did you come into it? And why I should ask for it, when all slides were linked?

Giotis said...

Mathur is working on fuzzballs. Why he was invited in a workshop about non-locality? You should have invited Giddings; he is the one working on the resolution of the information loss paradox via non-local effects and he is the authority on the subject.

Phillip Helbig said...

As long as you didn't forget any woman, it looks like you did the right thing. If there were too few women there, then it wasn't your fault. Note that inviting women who aren't as qualified and (due to space limitations) not inviting men who are will probably hurt, not help, the cause of addressing gender imbalance. The last thing most women want in science is to be invited because they are women. Yes, if there are real problems (such as Max Planck telling Lise Meitner it would be a problem to work at his institute since there were no toilets for women (which shouldn't be a problem in Sweden where public toilets are often mixed but public saunas almost never are)), then of course they should be addressed but in most cases the reasons there are too few women in some branches of science (note that some other branches have the "problem" of too few men) are to be found outside the scientific community in question, so addressing them within the scientific community probably does more harm than good in many cases.

Bee said...

Phillip, I understand your point perfectly well, believe me. What I'm saying is, essentially, how do I know I didn't forget anybody. If you send me to a conference and I speak to people chances are I'll pay much more attention to the men, but not necessarily because they're working on more interesting topics if you see what I mean. How do I know, really, how balanced the list of names I produce is? This is why I'm thinking, it would be good to pay somewhat more attention to the bias I bring in myself. So much for now about my self-criticality ;o) Best,

B.

Bee said...

Giotis,

We did invite Giddings, he couldn't make it. The whole black hole information loss issue in string theory, fuzzballs or whatever, requires non-locality. I met Mathur some years ago and we had an interesting exchange about this, that's why I thought he would fit in well. Best,

B.

Phillip Helbig said...

"What I'm saying is, essentially, how do I know I didn't forget anybody."

By definition, if you invite those who pop into your head, then they are probably the most important to you. Perhaps a committee should come up with a list based on suggestions from several people.

"If you send me to a conference and I speak to people chances are I'll pay much more attention to the men, but not necessarily because they're working on more interesting topics if you see what I mean."

I don't. (If a man said the equivalent of what you seem to be implying, he would be the target of almost unlimited criticism.)

"How do I know, really, how balanced the list of names I produce is?"

Unless you think that you might preferentially ignore women (or tall people, or black people, or whatever), then it seems to me the issues of balance and of forgetting someone are independent.

Bee said...

Hi Phillip,

"If a man said the equivalent of what you seem to be implying, he would be the target of almost unlimited criticism."

I know. I've seen it happening, feel free to criticize me if you must, but keep in mind that as a matter of fact most people are straight and we're evolutionary primed to pay attention to the opposite sex. What's the point denying it, or blaming people for something they don't consciously do anyway? The best you can hope for, I think, is that they're aware of their bias and try not to be affected by it on scientific decisions. Best,

B.

Phillip Helbig said...

As my history teacher used to say: just an observation, not a judgement.

I recently commented in a thread on the blog of Peter Coles (who happens to be gay) that some of the most beautiful women in the world are radio astronomers. :-)

Giotis said...

Yes, what I meant is that Mathur most probably would have talked about fuzzballs and not about non-locality. Giddings on the other hand would have given a much more general talk on non-locality and the information loss paradox.

Anyway have you watched this related panel discussion in KITP?

http://online.kitp.ucsb.edu/online/bitbranes-c12/bhinfo/

Don Foster said...

Bee,
At least I can offer a word about public speaking, an experience that can shrink the world a vanishingly small point of discomfort.
You remember those old electric heaters, radiant coil, dish reflector? Imagine one mounted just in front of your chest, turning as you turn and projecting a warm radiant glow. That’s it. Practice a bit.
What it does is change the mental frame from receiving – all those faces and errant inputs -- to output, your own channel, Sesame Street for physicists.

There is the story of the world famous violinist walking with a friend on a street in Paris. They pass a fish market with a display case full of fish on ice, all the dead staring eyes.
“My God,” he say’s, “That reminds me. I’ve got a concert in half an hour.”

Phillip Helbig said...

"I have a public speaking anxiety"

Apparently a common trick people learn at public-speaking courses is to imagine that the audience is nude (and the speaker is not). I once heard a speaker say that she had indeed learned this at a course, but that it wasn't working for the speech she was giving (where she was obviously nervous, despite much experience in public relations). She was a representative of the local tourist bureau and the site was a nudist resort. :-)

Bee said...

Hi Philip,

Yes, I have heard that advice too... I'm not sure though in which way having a group of nude guys staring at me would be any better than when they're dressed. More seriously, I get along somehow, practice certainly has made it better, it's astonishing though, to some extend, the flight or fight response is still instantaneous. I don't think actually there any way to really get rid of it, for what I've read, it's a rather primitive reaction that one can't change much about. The only thing one can do is work on it after the fact, which can be exercised to the point that it's a habit and doesn't require much conscious attention. Susan Cain, in her book Quiet (who writes she also has a public speaking anxiety, apparently it's more common among introverts, that being the topic of her book) summarized essentially that's what neurobiology at this point has to say about this. Best,

B.

Bee said...

Hi Don,

Ha, thanks for the story, it gave me a good laugh. Also thanks for the advice! Best,

B.

Phillip Helbig said...

"I'm not sure though in which way having a group of nude guys staring at me would be any better than when they're dressed."

Well, you're the one who said "If you send me to a conference and I speak to people chances are I'll pay much more attention to the men, but not necessarily because they're working on more interesting topics if you see what I mean." :-)

However, the idea behind the public-speaking trick is not that the nude guys are staring at you, but that you are staring at the nude guys. (Of course, they're not really nude; you're supposed to just imagine it.)

Bee said...

Well, the men I talk to at conferences are usually dressed. Except for one traumatic event were we're all supposed to go swimming together and to this date I still have visual relics of physicists undressing. Anyway, I guess I just can't really see how imagining a group of nude guys is supposed to help me recall what I meant to say. Neither do I know anybody who had any success with this advice. Another piece of advice that helps me much more is to talk to people in the audience right before the talk, so it's less like jumping into cold water head first. Best,

B.

Zephir said...

/*..for one traumatic event were we're all supposed to go swimming together and to this date I still have visual relics of physicists undressing...*/

..eye opening event.. ..The perverts like me could feel enjoyed right now..

tytung said...

Hi, regarding the second form of non-locality, to my knowledge, isn't QFT formulated by positing all operators on space-like separated points commutes (Weinberg's formulation)?

Bee said...

Hi Tytung,

Yes, what I meant to say is if that's not the case, then it's an indication for non-locality, which one normally doesn't have and doesn't want. Best,

B.

Anonymous Snowboarder said...

Bee - having worked for quite some years for the Finns and having a good bit of exposure to the Norwegians Danes and Swedes it is clear to me you failed to supply sufficient chilled vodka. Scandinavians, Finns and Norwegians in particular are only scary when deprived suitable refreshment.

Bee said...

Hi Snowboarder,

I'll keep that in mind ;o) Best,

B.