Beyond space-time: Welcome to phase space

http://www.newscientist.com/article/mg21128241.700-beyond-spacetime-welcome-to-phase-space.html?full=true

by ColinWright • 15 years ago

75 18 15 years ago

Symmetry• 15 years ago

Interesting, but because of the words "phase space" I kept expecting them to relate general relativity to thermodynamics somehow, since that's the physics context I'm used to seeing them in. But it ends up just being a "measly" 8 dimensions. http://en.wikipedia.org/wiki/Canonical_ensemble

Natsu• 15 years ago

And here I thought we'd end up with discussions of Star Trek, which I'm reasonably sure used phase space as the technobabble for something or another. I don't remember what, exactly, it was supposed to be there, but I suspect there were dangerous aliens living in it or something like that.

drbaskin• 15 years ago

I haven't read Smolin's paper, so I'm not sure exactly what this article is getting at. Is he suggesting that there should be a different connection (i.e., not the Levi-Civita one) on the cotangent bundle of spacetime or is it something more pedestrian? Is he just doing microlocal analysis on spacetime? If the latter is the case, this article doesn't describe what is (mathematically) new about it.

On a second read of this article, it seems clear that my interpretation above is incorrect. It might still be that they are coming up with physical interpretations of microlocal analysis on curved spacetimes. (Though how you fix a quantization, I'm not sure.)

I'm not a physicist and have not read the original source, so please take anything I say with a large dose of salt.

bermanoid3• 15 years ago

As confused as this article seems, it does at least reference one Actual Paper: http://arxiv.org/PS_cache/arxiv/pdf/1101/1101.0931v2.pdf

I haven't had a chance to look through it yet, but here's the abstract:

We propose a deepening of the relativity principle according to which the invariant arena for non-quantum physics is a phase space rather than spacetime. Descriptions of particles propagating and interacting in spacetimes are constructed by observers, but different observers, separated from each other by translations, construct different spacetime projections from the invariant phase space. Nonetheless, all observers agree that interactions are local in the spacetime coordinates constructed by observers local to them.

This framework, in which absolute locality is replaced by relative locality, results from deforming momentum space, just as the passage from absolute to relative simultaneity results from deforming the linear addition of velocities. Different aspects of momentum space geometry, such as its curvature, torsion and non-metricity, are reﬂected in different kinds of deformations of the energy-momentum conservation laws. These are in principle all measurable by appropriate experiments. We also discuss a natural set of physical hypotheses which singles out the cases of momentum space with a metric compatible connection and constant curvature.

inuhj2• 15 years ago

I stopped reading at 'Lee Smolin'. If you are a trained physicist read ahead and pick apart his misconceptions. If you're not a trained physicist then you are likely to be misled and I encourage you to not bother. Time is too valuable to be wasted here.

hugh33• 15 years ago

Your profile says you're a medical student. Are you a physicist too?

inuhj2• 15 years ago

Yes, but not that kind of physicist. I have a masters in medical physics, worked three years as a radiation physicist, and am now pursuing a career as a radiation oncologist. Perhaps I should update my profile ;).

logjam• 15 years ago

That's a bit harsh. I won't guess your own objections to what Smolin says, but for everyone else -- Smolin wrote "The Trouble with Physics" and has expressed some controversial views regarding string theory, and the anthropic principle, eg:

http://www.edge.org/3rd_culture/smolin_susskind04/smolin_sus...

goodside• 15 years ago

I've gotten in the habit of trying to explain poorly written NewScientist and Popular Science articles as they appear on HN, just because they're so consistently peppered with nonsense that even non-physicist enthusiasts like me can do substantially better. But, in this case, I just want to say this:

If you can't close your eyes right now and give me a formal definition of a tensor, you really don't want to waste your time on this. Go buy a good undergrad textbook for $2 used on Amazon. Do the practice problems. It will contain information that will genuinely enlighten you. You will learn things that geniuses of a hundred years ago would have chewed off their own legs just to have hints about. Until you do that, worrying about Lee Smolin will do nothing. At best.

hugh33• 15 years ago

Reading things like this is like playing Chinese whispers ("Telephone" in US-ish).

As opposed to the usual situation where the writer knows what the article is about and is struggling to explain it to the audience, in the average New Scientist article we have a situation where the writer doesn't really grasp what the article is supposed to be about either, but has a deadline and a certain amount of space to fill. So you'll see detailed explanations of the bits that the writer did manage to understand combined with quick handwaving and quote-insertion for the bits the writer didn't manage to understand.

The net result is something that contains all the right words and sounds sufficiently clever for laymen, but doesn't make much actual sense. Still, it fills in pages and sells magazines, so it's good enough!

lobo_tuerto• 15 years ago

I'm a total physics newbie, what book(s) would you recommend picking up?

hugh33• 15 years ago

The admissions guide to your nearest major university.

bermanoid3• 15 years ago

If you're up for a real wild ride and have some time to kill (no, seriously - the thing is over 1000 pages), Roger Penrose's The Road To Reality (http://www.amazon.com/Road-Reality-Complete-Guide-Universe/d...) actually covers this stuff in a reasonably accessible way.

I can't say how it would read to a newbie, but ostensibly he wrote that book to be aimed more at the smart but uninitiated pop-sci audience than the practicing physicists. I'm not sure he hit his mark, quite, but when I was a second year physics undergrad I found it pretty easy to get through at least the first half (though I had worked through MTW's Gravitation first, so I wasn't totally new to the material - also an excellent book, if you've got months to spend on it and some more lightweight general relativity books to look at as supplements).

It probably depends, though - when you say "newbie", do you mean "F=MA means nothing to me and I barely passed single variable calculus", or "I got straight A's in vector calculus and excelled at freshman physics through basic quantum mechanics but never took more"? If it's the former, you'll want to grab Feynman's freshman lectures first, they'll get you thinking right about this stuff if you make it through them, and later you can start to worry about stuff like tensor calculus...

bugsbunnyak• 15 years ago

Complete physics curriculum up to research-level, available here from a Nobelist: http://www.staff.science.uu.nl/~hooft101/theorist.html

Roger Penrose's "Road to Reality" is great for an overview in one not-so-compact book. It's a bit hand-wavy, admittedly. The neophyte problem, and reason we have universities, is that "you don't know what you don't know." Penrose's book and t'Hooft's curriculum get you some part of the way to knowing what you need to know.

One more option is Lev Landau's series. They're dense but fairly readable for graduate-level tracts.

Beyond space-time: Welcome to phase space

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