Why the Okolow-Lewandowski 2003 paper is interesting

[marcus]

I find the paper that Andrej Okolow and Jerzy Lewandowski posted at the arxiv in February this year to be fascinating. In case anyone wonders why, here's a recent thread that may help you understand why

https://www.physicsforums.com/showthread.php?s=&threadid=4426

 

[jeff]

Originally posted by marcus
I find the paper that Andrej Okolow and Jerzy Lewandowski posted at the arxiv in February this year to be fascinating. In case anyone wonders why, here's a recent thread that may help you understand why

https://www.physicsforums.com/showthread.php?s=&threadid=4426

I respectfully disagree, it's really not fascinating, and to see why requires that one be able to see the forest through the trees. The central problem in LQG is to solve the hamiltonian constraint to find the physical sector of the hilbert space. What little progress has been made isn't enough to tell us whether LQG even has a sensible classical limit never mind whether it reproduces GR as it must to be a true quantum theory of gravity as it's often misleadingly portrayed to be. So instead, the kinematical space of solutions that satisfy the gaussian and diffeomorphism constraints are studied.

The hope underlying a series of papers, of which the aforementioned one is (I think) the most recent, is that the representation theory of an algebra whose structure the basic operators of LQG is argued to possesses can be used to study the kinematical sector of the hilbert space in a more systematic way, shedding light on the solution space of the hamiltonian constraint in the process. Thus there's no new physics involved in these papers and as yet no progress on the physical problems they're meant to address. It's just a bunch of math that may or may not help. (In fact, moving to an algebraic formulation of a quantum theory is often an indication that everyone is pretty much out of good ideas.)

If you do browse the related threads, you'll find no indication that the contributors are aware of this. Instead you'll find only paraphrasing of mathematical methodology with - as is typical in LQG threads - no indication that the physics this mathematics is describing is being understood.

So I encourage people here to challenge the contributors to those threads to explain the physical significance of the mathematics they're discussing, which is something I'm sure they'd welcome. In any event, they're certainly not being done any favors by being given free passes.

 

[selfAdjoint]

LQG research, at least the Ashtekar/Baez sector of it, is being done in the tradition of mathematical physics. That is you build your tools, with attention to rigor, before you build your theory. In that light these papers are interesting and progress is being made.

Since Marcus posted here on the mathematics board it seems captious to complain that the papers don't immediately issue in physics.

 

[jeff]

Originally posted by selfAdjoint
LQG research...is being done in the tradition of mathematical physics. That is you build your tools, with attention to rigor, before you build your theory.

Mathematical physics studies existing physical theory from a mathematically rigorous point of view: The physical ideas precede the mathematics, not the other way round. These papers are of course nothing more than an exercise in mathematical physics.

Originally posted by selfAdjoint
Since Marcus posted here on the mathematics board it seems captious to complain that the papers don't immediately issue in physics.

That's complete bullsh*t and you know it. There are any number of threads in the mathematics section - including marcus's "Gravitivity" thread - that could have equally well been posted in the physics section raising nary an eyebrow. The last time I checked, LQG was a physics theory, and the papers you've been studying are posted in the general relativity and quantum cosmology and not the mathematical physics section of the los alamos archives.

Originally posted by selfAdjoint
In that light these papers are interesting and progress is being made.

I asked marcus why he finds this work so "fascinating". His response was to finesse my question by beginning a new thread.

A few days ago I sent you, selfAdjoint, a private message asking the same question. So now I'm asking you here. What precisely do you find so exciting about this work, because frankly, I'd be surprised if anyone was all that excited about it, including the guys who are actually doing the work. So please, enlighten me.

 

[Brad_Ad23]

I must agree, I do not see much exciting in the paper.

 

[marcus]

Originally posted by Brad_Ad23
I must agree, I do not see much exciting in the paper.

Brad, you are whole-heartedly welcome to your opinion! I'm certainly not going to attack you or try to argue with that you should be excited!

I made a personal statement in a LQG thread that I continue to find this O-L paper fascinating. I got challenged for my personal attitude! Am I expected to defend the fact that an area of scientific investigation excites me?

I hope not.

Anyone who is not interested in LQG can simply not read the thread. If you are NOT interested that is fine, why should I attack you because of that or argue with your UN-interest?

 

[Brad_Ad23]

Calm down there. I'm into LQG and all, however from a technical standpoint, I find little cause to be excited over. Maybe on a personal standpoint, one may be excited (such as it solves a wormhole problem), but in technical terms, it is plain vanilla.

 

[marcus]

I don't go around trashing and trolling other people's threads
that happen to be about something that doesn't interest me.
I don't accuse them of being somehow in the wrong for being
interested in whatever it is.

This is not a criticism of you or your post Brad. I welcome your attitude re the O-L paper

 

[Brad_Ad23]

Where did I accuse you of being wrong? I merely asserted I agreed with Jeff's assessment that technically it was of little interest in the mainstay of LQG. And when you look at it, there are far larger issues to solve that grant bigger meritt. On a personal level, one is free to claim it is of interest. I believe that is what you are doing...saying you personally find it interesting. I am intrigued personally as well, but I know technically it has little bearing towards developing LQG...merely a handy tool found along the way.

 

[jeff]

Originally posted by marcus
I got challenged for my personal attitude!

Nothing wrong with that, as long as the challenge is about physics and not personality, which it was until you turned it into some kind of personal thing, as you always do.

Originally posted by marcus
Am I expected to defend the fact that an area of scientific investigation excites me?

Not defend, enlighten. It's not my fault that you view perfectly valid questions as personal attacks. It's just physics so get real.

 

[marcus]

Originally posted by Brad_Ad23
Calm down there. I'm into LQG and all, however from a technical standpoint, I find little cause to be excited over. Maybe on a personal standpoint, one may be excited (such as it solves a wormhole problem), but in technical terms, it is plain vanilla.

Your interest in LQG may be more in the preliminary practical results: there have been some suggestive results in areas such as

area and volume quantization
black hole entropy
bigbang singularlity resolution
explanation of the cosmological constant
role of time in quantizations of general relativity

This stuff interests me too!
However the C* algebra representation stuff (O-L typical) is
mathematically interesting as well, to those with a taste for it.

 

[jeff]

Originally posted by Brad_Ad23
...I agreed with Jeff's assessment that technically it was of little interest in the mainstay of LQG.

Those forum members that are keen on LQG but unable to make heads or tails of some of these LQG threads deserve to know what the real significance of the material being discussed is. Clearly they weren't going to learn that from marcus.

At this point, based on the nearly complete absence of physical explanation in LQG threads - including the ones posted in the physics section - it's difficult not to attribute the non-responses I get when I try to initiate discussions of the actual physics to a basic lack of understanding of these issues on their part. This isn't surprising since these guys seem to understand only the most elementary aspects of GR and virtually nothing of QFT. I see no need to take attempts by others to fill the vacuum so personally.

 

[selfAdjoint]

Jeff mmaybe try a little introspection. Your affect here is way over the top. How does it threaten you that some people like LQG, which you don't. and find Sahlmann's results fascinating, which you don't?

Far be it from me to engage in theory wars. Which theory will play what role in the physics of the future is something we will just have to wait and see. But in the meantime, let a hundred flowers bloom.

 

[jeff]

Originally posted by selfAdjoint
How does it threaten you that some people like LQG, which you don't.

Where's that coming from? I've never even once discouraged anyone from studying LQG. In fact precisely the opposite is true: I've said many times that because LQG is both simple and interesting, it provides good opportunities for people here to learn some neat physics. I study strings, but I've never thought or advocated that everyone here or in the physics community should just drop LQG and study only strings.

If you want to see a true example of someone who is unreasonably polarized in their views, just check out marcus's comments about strings, which are both completely ignorant and unjustifiably malicious, it's laughable really.

So let's just cut to the chase. You and marcus continue to avoid explaining to me or anyone else apparently - including to each other, at least in your posts - precisely what underlies your remarks about how intrigued you guys are with this latest bit of research. I think the reason must be that you don't know why yourselves. If not, I'd like to hear about what the rest of us are missing.

 

[ahrkron]

Hi Guys,

Try to tone it down. The thread is getting closer to being locked, and I think it can become an interesting one instead.

 

[selfAdjoint]

Jeff, here's the tale from my point of view.

Marcus pointed out the connection of Sahlmann's theorem to the Stone-Weierstrass theorem. That caught my attention because in addition to LQG, I have an interest in functional analysis. So I was glad to dig into Sahlmann's paper with Marcus, hoping to see how the proof went and also pick up some ins and outs of the Ashtekar variables.

We quickly found that young Sahlmann's expository style is not the clearest, and Marcus found the Okolow-Lewandowski paper, which includes and enlarges on Sahlmann's theorem and is much better written. Marcus started this thread for studying it and hoped others would join us.

All of a sudden you jump in with what seemed to me to be scorn for us, the papers we were studying, and the whole Ashtekar school of LQG. Marcus took it personally, but I tend to consider the source, which led to my question. Just what is bugging you, that you vent so much anger on such an unthreatening target?

 

[marcus]

Theory Wars, Hell No!

Originally posted by selfAdjoint
Jeff mmaybe try a little introspection. Your affect here is way over the top. How does it threaten you that some people like LQG, which you don't. and find Sahlmann's results fascinating, which you don't?

Far be it from me to engage in theory wars. Which theory will play what role in the physics of the future is something we will just have to wait and see. But in the meantime, let a hundred flowers bloom.

S.A. this is a great thought! We should have a "theory wars hell no!" thread.

How childish.
No one interested in LQG needs to justify their interest, at least at a science oriented board like PF.

I feel more like being a "watcher" than a "soldier in the cause" (soldiering can often be a compensatory thing anyway)

It looks to me that LQG is attracting first rate postdocs and the number of worldclass centers is growing----they don't need me to do PR for them!

I recently picked up a new bright postdoc on my radar---this time at Marseilles! He is Robert Oeckl, who did his degree with Majid at Oxbridge and is shifting over from Majid's line (quantum groups, noncommutative geometry?) to LQG. This year he did two LQG papers, one with a proposed approach to the trajectory problem called
"Schroedinger's Cat and the Clock"

I thought it was amusing so I will mention the link
http://arxiv.org/gr-qc/0306007
I won't say it is a big paper, quite the opposite, just a
tentative idea offered by a postdoc in a modest speculative way
11 pages
deals with the problem that classical GR give you a trajectory
(thats what space time is---a classical solution to the classical g. field eqn.) and in a quantum theory YOU DONT HAVE TRAJECTORIES.

Clocks are material things in space and the clock the observer is using is a particular case of a clock---he discusses cases where the cat has a clock too, in the box with him. where do you draw the boundary? and so on. looking at the clock is an observable and for the observer its part of the experiment. there are transition amplitudes and correlations etc. but God does not have a clock. (that was Newton's idea but it is wrong) ...Well, things like that.

Well, another smart postdoc. This time at Marseilles. Okolow is at Warsaw. Sahlmann came from Berlin. Bojowald is at Penn----they all seem to spend some time at Penn. I'm doubtless leaving out one or two places.

Anyway last thing I can imagine being incumbent on me is to defend being interested in quantizing general relativity!

Gotta go, be back later

 

[marcus]

afterthought

Maybe you or quart would be willing to correct my grammar,

NON NECESSE METEOROLOGICUS UT SCIAMUS DIRECTIONEM VENTI

 

[jeff]

Originally posted by selfAdjoint
Marcus pointed out the connection of Sahlmann's theorem to the Stone-Weierstrass theorem. That caught my attention because in addition to LQG, I have an interest in functional analysis. So I was glad to dig into Sahlmann's paper with Marcus, hoping to see how the proof went and also pick up some ins and outs of the Ashtekar variables.

So it was the interesting opportunity LQG provided for you to deepen you're understanding of functional analysis that intrigued you. Sounds good to me.

Originally posted by selfAdjoint
All of a sudden you jump in with what seemed to me to be scorn for us, the papers we were studying, and the whole Ashtekar school of LQG. Marcus took it personally, but I tend to consider the source, which led to my question. Just what is bugging you, that you vent so much anger on such an unthreatening target?

Again where are you getting this? My posts about LQG have as a rule been unbiased. Here's what started this:

Marcus posted the following

Originally posted by marcus
The Okolow-Landowski paper continues to fascinate me.

To which I responded,

Originally posted by marcus
Why?

That's pretty much it. (Here's the link:

https://www.physicsforums.com/showthread.php?s=&threadid=4482)

Then, instead of just responding intelligently and respectfully, he pulled the provocative stunt of starting a new thread - this thread - with the following non-response:

Originally posted by marcus
I find the paper that Andrej Okolow and Jerzy Lewandowski posted at the arxiv in February this year to be fascinating. In case anyone wonders why, here's a recent thread that may help you understand why

These are the kind of tactics that should bother you and everyone, and not anything I've done. My guess is that I've probably contributed at least as much to people's knowledge of LQG as you have. In fact, by and large, I've avoided interjecting my own personal opinion of the prospects for the LQG program.

Btw, you should know that I've complained to greg many times about marcus's behaviour, but although he's indicated his agreement with me, he's so far been unwilling to do anything about it. His suggestion was to avoid threads in which marcus participates. This is of course precisely what marcus wants, but I'll be damned if I'm going to reward him for his outrageous behaviour by granting this wish. This is not marcus's forum and he doesn't own the threads he begins. His comments should be subject to the same scrutiny - including mine - that everyone else's are. This is marcus's problem, so as I've told greg, don't make it mine.

 

[marcus]

I just looked at Oeckl's homepage at U. Marseilles to see who he is, degree 2002 from Cambridge where he was in the High Energy Physics Group---advisor was Shahn Majid, with whom he has co-authored. Here's his perspective on quantum gravity:

<<Quantum Gravity aims at unifying general relativity with quantum mechanics and ultimately with the standard model of elementary particle physics. I am working on an approach to this known as loop quantum gravity. One starts with classical general relativity and performs a quantization, either in a Hamiltonian or a path integral framework. The quantization is both background independent and completely nonperturbative. A discrete structure of space-time emerges, encoded in spin foams. Current problems include the definition of appropriate observables and understanding the summation over space-times or histories. The further goal would then be to find classical general relativity and fixed-background quantum field theory as limits.>>

I emphasized two sentences I thought significant. Seems like a clear concise statement of this effort from someone who recently joined it.

 

[jeff]

Originally posted by marcus
S.A. this is a great thought! We should have a "theory wars hell no!" thread.
How childish.

Yes, I agree. But then why did you start a thread "innocently" entitled "String irrelevant to quantizing General Relativity..."?

You began it with the following baloney,

Originally posted by marcus
Gravity IS geometry. As early as the 1940s physicists have seen dynmamic spacetime geometry as something to quantize.

String has no relevance to this effort---it is not even on the radar---not a quantum theory of spacetime geometry. It starts instead with the usual flat, static, unexpanding Minkowski space that conventional particle theorists use. It tries to treat gravity as a force like electrostatic attraction. This is Newton's approach and it is inherently inaccurate. A useful approximation in some situations but not the fundamentally correct way to go about things.

And I ended it with,

Originally posted by jeff
Marcus,

Did you know that LQG people are constantly on the lookout for connections with string theory? Given this, how do you suppose they'd view your maniacal rejection of everything string theoretic? After all, LQG is not a religion, it's a mathematical theory whose ultimate significance, like string theory's, is currently unknown.

 

[selfAdjoint]

Jeff, you may see your "Why" response as a reasonable question, but I took it as scornful, in the sense of why bother? After all Marcus and I had been trading technical problems and insights for some time, and it must have been obvious to any unbiased and learned reader why we were fascinated.

Let's get off this sad bicycle built for two. It frazzles me to think how much math we could have been doing instead of this.

 

[jeff]

Originally posted by selfAdjoint
Jeff, you may see your "Why" response as a reasonable question, but I took it as scornful.

And that should be my problem why?