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

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

~~~
bermanoid
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...](http://www.amazon.com/Road-Reality-Complete-Guide-
Universe/dp/0679454438)) 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...

~~~
enko
Unless you and bugsbunnyak are in cahoots somehow - unlikely - that's two
completely independent recommendations for _The Road To Reality_ within 5
minutes, on HN. That's enough for me. Grabbing it. Thanks.

~~~
bermanoid
Not in cahoots at all, it really is a very interesting book. One of the
most...different, I guess is the word, math/physics books I've read in quite a
while.

Be warned, it might not be the best book for beginners, and in all honesty
it's more a math book than a physics one, but if you feel at least somewhat
math-competent, it's worth a read. At least I enjoyed it a lot.

~~~
enko
As a professional programmer, I often feel as if I should be more on top of
maths than I feel I am. Maybe this book is above my level. Only one way to
find out!

<http://xkcd.com/435/>

------
drbaskin
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.

~~~
bermanoid
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._

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Symmetry
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
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.

------
inuhj
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.

~~~
hugh3
Your profile says you're a medical student. Are you a physicist too?

~~~
inuhj
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 ;).

