Peter Woit's Blog: Good Stuff, Not Too Hard on String Theory

[pelastration]

there are some remarkable dramatic characters who have appeared
in the comments of Woit's blog
named petitot
moyentot
and grantot

some appear to be French anti-scientific or "post-modern" parodists.

Probably it has to do with his June 5 comment "(quote)A couple years ago two French brothers, Igor and Grichka Bogdanov, managed to get Ph.Ds in France and publish several nonsensical papers about quantum gravity in refereed physics journals, several of them rather well-known and prestigious ones. John Baez has a useful web-page about this story.(end of quote).
Internet revenge.

 

[marcus]

Woit blogged again today 12 June
this time about "cosmic strings"

I've taken a look at Sean Carroll's "preposterous universe" blog
which seems highly entertaining especially about GW Bush
has some good cartoons, as well as science news
It looks like one can easily get into the habit of checking
into these mini-amusement-parks and private fun-houses
that people set up, another addictive feature of the internet

 

[selfAdjoint]

The Top Quark Mass

Check out his latest post , about the reanalysis by the Tevatron group of the top quark mass, and the implications this has for the mass of the Higgs particle. Also many of us will want to follow his links, which between them constitute a nice little tutorial on the subject.

 

[marcus]

still more recently a 17 June post about
some expository mathematics by Barry Mazur
and a weekly "Basic Notions" seminar at Harvard which
is partly available online.

Woit also had some words today about a talk by Leonard Susskind
concerning, among other things, "the stupendous Landscape of string theory vacuua"
and a new string theory "rising from the ashes" of the already established string theory

 

[selfAdjoint]

Woit seems to be skeptical about Susskind's papers. Odd.

 

[arivero]

Check out his latest post , about the reanalysis by the Tevatron group of the top quark mass, and the implications this has for the mass of the Higgs particle. Also many of us will want to follow his links, which between them constitute a nice little tutorial on the subject.

The top quark issue is also blogged in
http://golem.ph.utexas.edu/~distler/blog/archives/000380.html#comments
http://blogs.salon.com/0001092/2004/06/09.html#a690
http://preposterousuniverse.blogspot.com/

 

[John]

It's hard to follow all of the new technical terms, like blog, for non-string theory. But there seems to be an attack on string theory, and on funding for powerful accelerators, and on the acquisition of knowledge of the universe in general.

Not being a physics student, I am very good at physics. I started thinking about another model for the universe in about 1985. The strange thing was that all of my ideas seemed to connect with current physics. My ideas got more and more developed; so when the Internet came along, I started to post my ideas, hoping someone would have been lead in the same direction and I could start a discussion: that is, if my ideas were in the direction of right. I hoped my ides would receive some positive response, and we could develop the ideas further, not my ideas, but the right ideas. I kept meeting with a lot of agreement between my ideas and current physics.

Instead, my ideas met with negative attacks.

Here is one of my ideas. I believe protons are hollow spheres made of strings, just the way you would make a hollow sphere out of chicken wire. The “chicken wire” vibrates, and the mass of the vibrating "wire" inflates the proton. When we look at a proton, we only see the one string that is vibrating. We don’t see all the wires that make up the proton. It’s like studying a radio and only seeing the electrical impulses traveling along the wires, without seeing the wires. We would say is a radio is made of tiny electrical impulses, separated by vast distances of nothing. That is absurd, but we would swear that is exactly what the math is telling us, and it would be true.

I am seeing or imagining the wires that make up the proton, and not just the energy that is in the wires.

My latest discovery happened when I learned what a quark is, something every physicist knows, but I didn’t: there are three quarks in a proton. If a proton is a hollow sphere as I say, then each quark is one third of the sphere, so I can know the exact shape of a quark: it's shape is one-third the surface of a sphere. I cut a round orange in three parts and peeled the skin, which gave me one-third the surface of a sphere, so I have my theorized shape of a quark sitting on a table, sticky with orange juice.

What is a string? I say, it is the distance between two separate points. So I take ten quarters that represent points, and arrange them on a table. Start with three quarters to make a triangle, then add a fourth to make a diamond. Then add three more to make a solid hexagon. Add three more, and then you can precisely cover the quarters with the one-third orange peel. The ten quarters and the shape of the orange peel are the same.

Attach three of these quarks made of points together, and you have a hollow sphere. Electrons travel by vibrating one point, then another, then another. They soon vibrate the whole array of points, and you can’t really define where the electron is, except to say it is in the shape that “surrounds” the proton. But that shape is really the proton. The proton is not in the middle, but it IS the shape we call the electron cloud.

The fact ten separate points make the exact shape of one-third the surface of a sphere is an amazing indication my ideas may actually be correct. I say the entire universe is made of individual points of matter, the way a dust cloud is made of individual specks of dust. Light and electrons travel from point to point, which means at the most basic level light can only travel in six directions, and it means there are two forms of dimension. There are spatial dimensions which contain 9 dimensions (plus time) for ten. And there are M-dimensions, which are the energized membranes that make up all the solid objects. It is easy to imagine a picture of that. The dots that make up the picture are arranged sparsely to form space, and they are arranged more densely to form objects.

 

[jeff]

and a new string theory "rising from the ashes" of the already established string theory

The actual quotation due to susskind is:

During the last couple of years an entirely new paradigm has emerged from the ashes of a more traditional view of string theory

I find the difference between this and your quote telling.

 

[marcus]

Peter Woit posted yesterday 1 July
pointing out that Susskind has now withdrawn
his paper about the "stupendous landscape"
and about the new Stringery which he sees "emerging from the ashes"
of yesterday's Stringery

this paper of Susskind, which happly I saved on my desktop
because it was so splendid
provided a window on
the current state of stringy affairs

 

[marcus]

Woit's 1 July blog also talks about the fact
that Mike Douglas paper of 30 May has gone through
several revisions already and is in its 4th version.

We should really try to follow some of this----it seems there is
a lot of vacillation about whether to "predict" (guess?)
the new collider will find evidence of supersymmetry or not,
at the energy level it will be able to acheive

At one time, string theory was supposed to "predict" supersymmetry would be found at that level (and earlier at even lower levels but it wasnt)
but the "predictions" now seem to have evaporated

Is it possible to make the theory predict whatever outcome one guesses is most likely? that would then be a limp and pliable theory. And we would see, as the deadline for prediction approaches, that people's guesswork waffles, and the "predictions" become drained of confidence and start to wobble.

Mike Douglas paper indicates not to expect LHC to see SUSY
and IIRC a recent talk by Witten in Davis carried the same message
and yet only a little while ago there was triumphant confidence---"just wait till LHC comes on line! that will show you skeptics!" It is strange and not a little funny.

 

[Ontoplankton]

Naive question from someone with no technical knowledge of string theory and therefore no opinion on its validity:

Here and elsewhere, I see a lot of people ridiculing the anthropic principle. Can anyone point me to an explanation of the objections to it on the level of rigor of e.g. http://anthropic-principle.com/book?

It just seems like basic common sense to me: if a theory says there are a lot of different worlds, and only some of them contain observers, then we should expect to be in one of those worlds that do contain observers. If we're in a sort of world that is atypical for the set of worlds claimed to exist, but typical for the set of worlds claimed to exist that also happen to contain observers, then this is not evidence against the theory.

I don't understand the people saying "the anthropic principle isn't falsifiable", either. If it's just a decision-theoretical (or confirmation-theoretical, whatever) principle, then why should it be falsifiable?

 

[Ontoplankton]

Mike Douglas paper indicates not to expect LHC to see SUSY
and IIRC a recent talk by Witten in Davis carried the same message
and yet only a little while ago there was triumphant confidence---"just wait till LHC comes on line! that will show you skeptics!" It is strange and not a little funny.

Are you saying this disconfirms string theory in some way? I don't see how. If different people claim the theory predicts different things, then that just means we don't know what the theory predicts yet, and we can maybe find out by thinking harder; it does not mean the theory can say anything we want.

Again, I don't know enough to have any opinion about string theory itself. But if anyone wants a meaningless data point: some of what I do understand of the objections by string theory's detractors looks unfair to me.

 

[selfAdjoint]

Are you saying this disconfirms string theory in some way? I don't see how.

Well if SUSY were to fall, so would superstrings and everything derived from them. You would still have bosonic strings and string field theory.

But it would seem to me that LHC could only falsify low energy SUSY extensions of the standard model. Corrections, anybody?

 

[marcus]

Hi Ontopl. (I guess it means "wandering being" in greek)

I was not sure about your reference to Anthropic principle so i looked back and the nearest post that mentioned it was my post #62.
as you see I was NOT criticizing Anthropic Principle!
quarreling about that principle is a symptom of troubles in string
(I watch but am not part of the quarrel)

the people to look at to see why they reject the Anthropic principle are the string theory insiders like Lubos Motl, David Gross, Edward Witten.

Rejecting the A.P. is part of their resistance to where Susskind has been going and leading a portion of the stringfolk with him.

The A.P. is not an issue for me since i don't find string/M theorizing interesting or relevant to the goal of a background indep. quantum theory of gravity.

I am more interested in theories that preserve the essential features of Gen Rel like background independence, and quantize it in as transparent and straightforward a way as possible.

but when people important in String say something about A.P. I try to keep track.

So my post #62 a ways back in this thread was keeping track of what Witten said about it.

Peter Woit's 3 June blog comments on the latest Witten paper
(in Nature vol 429, n. 6991, about electroweak symmetry breaking)
Woit supplies a link to Witten's paper and quotes Witten's opinion
concerning the "Anthropic Principle".

unfortunately the link only works for Nature subscribers
so this may mean a trip to the library

(not the paper in question but a related talk by witten at fermilab
in 2003:
http://conferences.fnal.gov/lp2003/program/papers/witten.pdf)

...

to get the latest Witten word on A.P. I guess you have to go back to that 3 June post of Peter Woit!

String seems to be in a muddle with some saying "Dont give up! We aren't forced to Anthropologize! Keep working to solve the basic problems!"

but on the other hand some like Susskind saying that the huge number of possible basic states (string vacua)----the "stupendous landscape" he has called it, of an estimated 10-to-the-100 power of distinct possible models of nature all with a potential for predicting distinct things about nature----can only be resolved by appealing to the A.P.

As you can imagine, I rather avoid arguing about the A.P.
My personal suspicion is that it is wishful thinking for String theorists to imagine that it could help them out of the
String theory crisis. Susskind looks to me like he is clutching at straws.

In the end a successful physical theory that pretends to improve on the Standard Model plus incorporate gravity has to explain certain numbers (numbers that the Standard Model explains, the cosmological constant, etc.)

Historical example: when Feynman and Schwinger made QED the theory explained certain numbers, like the magnetic moment of the electron. (it did not thow up its hands in a vague appeal to the fact that we have a life-friendly universe)
this is what physical theories are supposed to do: explain why the magnetic moment of the electron is such-and-such.
That was the 1950s.
So? It is different now?

so I am sympathetic to what I think is an honorable courageous stand by string theorists who want their theory to have explanatory power.
they aren't ready to lower their expectations.
I can understand how a self-respecting string theorist might deplore the anthropic tendencies of his colleagues

but intellectually I do not take a position on it.

I do not anticipate much from string theory whichever way they go, whether they accept A.P. and try to get some benefit or whether they reject it. so I do not have an opinion about A.P.----it is just not an issue.

 

[Haelfix]

Well if SUSY were to fall, so would superstrings and everything derived from them. You would still have bosonic strings and string field theory.

But it would seem to me that LHC could only falsify low energy SUSY extensions of the standard model. Corrections, anybody?

Thats right, but much of the theoretical prejudice to like SUSY in the first place starts vanishing really fast as you push it to higher and higher energy. In fact, things get downright ugly (at the level of minimal SUSY), as you start having to do really nasty finetuning to make things work... Which defeats the original purpose. We might additionally have to rethink GUT theory...

Not to mention, there are atmospheric tests that will need an explanation.

Several other things will happen. Wimp based models based on the hope that SUSY will save them, will run into a dead end. At which point, we'll be stuck with some very unnappealing alternatives.

Imo it would be one of the bigger crisis's physics has undergone in recent history.. Larger even then the measurement of the Lamb shift.

 

[marcus]

... some of what I do understand of the objections by string theory's detractors looks unfair to me.

You may be mistaking being skeptical of string hype as being a "detractor".
I don't favor this school of quantum gravity or that. If string theory ever managed to predict a number, and they could put the theory on the line for real testing, I would be happy either way it came out.
It would be great to get some progress in quantum gravity.
But all I hear on that score is excuses and wishful thinking.

String theory has been way over-hyped and IMO has made limited progress since say 2001, while some of the alternative approaches have gotten little attention but have made considerable advances. (that would be an interesting thread topic! new QG results, progress since 2001)

I am not partisan to one alternative or the other, if Loop gravity fails and Simplex gravity succeeds, or viceversa, that is fine with me either way. Or if spin foam succeeds and the others fail.
If String would make a surprise comeback and turn out to be genuine theoretical physics (intead of an Elegant Mathematical Contruct) that would be wonderful too!

I try to report what is happening: the battle royal inside String, the decline in String papers, the decline in String citations, the progress in other lines of Quantum Gravity research, like Simplex, Foam, and Loops. (and Hawking seems to think also in Path Integral--his own non-string approach to quantum gravity).

Dont confuse reporting with detracting. If the muddle changes, and the string people get their act together, I will be delighted to report that. I find the main effort required is to cut through the hype Stringsters constantly put out: the lengthy litany of reasons why the newer alternatives have to fail, the "theoretical" reasoning is offered to prove that only string can succeed. They treat as sacred cow what is looking suspiciously like another failed attempt.

 

[marcus]

Some recemt Not Even Wrong blogs and comments

Peter Woit has been busy and some interesting comments have been
coming in from Thomas Larsson, Urs Schreiber, Arivero and others

Smolin on the Anthropic Principle
http://www.math.columbia.edu/~woit/blog/archives/000059.html

Polyakov: String Theory Is Crazy
http://www.math.columbia.edu/~woit/blog/archives/000058.html

Hawking in Dublin
http://www.math.columbia.edu/~woit/blog/archives/000057.html


some other memorable N.E.W. blogs

http://www.math.columbia.edu/~woit/blog/archives/000039.html

http://www.math.columbia.edu/~woit/blog/archives/000032.html

http://www.math.columbia.edu/~woit/blog/archives/000031.html

http://www.math.columbia.edu/~woit/blog/archives/000028.html

http://www.math.columbia.edu/~woit/blog/archives/000027.html


anyone who doesn't check Woit's blog regularly is missing a treat

 

[jeff]

You may be mistaking being skeptical of string hype as being a "detractor".
I don't favor this school of quantum gravity or that. If string theory ever managed to predict a number, and they could put the theory on the line for real testing, I would be happy either way it came out.
It would be great to get some progress in quantum gravity.
But all I hear on that score is excuses and wishful thinking.

String theory has been way over-hyped and IMO has made limited progress since say 2001, while some of the alternative approaches have gotten little attention but have made considerable advances. (that would be an interesting thread topic! new QG results, progress since 2001)

I am not partisan to one alternative or the other, if Loop gravity fails and Simplex gravity succeeds, or viceversa, that is fine with me either way. Or if spin foam succeeds and the others fail.
If String would make a surprise comeback and turn out to be genuine theoretical physics (intead of an Elegant Mathematical Contruct) that would be wonderful too!

I try to report what is happening: the battle royal inside String, the decline in String papers, the decline in String citations, the progress in other lines of Quantum Gravity research, like Simplex, Foam, and Loops. (and Hawking seems to think also in Path Integral--his own non-string approach to quantum gravity).

Dont confuse reporting with detracting. If the muddle changes, and the string people get their act together, I will be delighted to report that. I find the main effort required is to cut through the hype Stringsters constantly put out: the lengthy litany of reasons why the newer alternatives have to fail, the "theoretical" reasoning is offered to prove that only string can succeed. They treat as sacred cow what is looking suspiciously like another failed attempt.

I don't favor this school of quantum gravity or that. If lqg ever managed to predict a number, and they could put the theory on the line for real testing, I would be happy either way it came out.
It would be great to get some progress in quantum gravity.
But all I hear on that score is excuses and wishful thinking.

lqg has been way over-hyped and IMO has made limited progress since say 2001, while some of the alternative approaches have gotten little attention but have made considerable advances. (that would be an interesting thread topic! new QG results, progress since 2001)

I am not partisan to one alternative or the other, if strings fail and some other theory succeeds, or viceversa, that is fine with me either way. Or if strings succeeds and the others fail.
If lqg would make a surprise comeback and turn out to be genuine theoretical physics (intead of an Elegant Mathematical Contruct) that would be wonderful too!

I try to report what is happening: the dissolution of lqg, the decline in lqg papers, the decline in lqg citations, the progress in other lines of Quantum Gravity research, like strings.

Dont confuse reporting with detracting. If the muddle changes, and the lqg people get their act together, I will be delighted to report that. I find the main effort required is to cut through the hype lqger’s constantly put out: the lengthy litany of reasons why the newer alternatives have to fail, the "theoretical" reasoning is offered to prove that only LQG or some theory other than strings. They treat as sacred cow what is looking suspiciously like another failed attempt.

All joking aside though, the difference between strings and the other approaches is that the difficulties in the latter are actually fatal.

 

[arivero]

All joking aside though, the difference between strings and the other approaches is that the difficulties in the latter are actually fatal.

Is there a non-go theorem, thus?

 

[selfAdjoint]

A good discussion starting over at ]Not Even Wrong[/URL] on whether the quantisation prescription in LQG is really pukka. Smolin started off with an email to Woit making the same claims for LQG that he does in the paper we've been reading. Then Urs Schreiber weighs in making the same claim that LQG quantisation is deficient, or at least not standard, that he made in the aftermath to Thiemann's string quantisation paper.

Basically his point is that "canonical quantisation" means you transform the p and q variables which span the phase space, into operators, and in the Ashtekar new variables approach to LQG one of the corresponding variables, the "magnetic" form, cannot be elevated to an operator because it becomes ill-defined. So the LQG people simply replace it with an operator that seems to them what the magnetic form could have become if it woulda transformed meaningfully. Or so Urs says, reading their papers. I have not confirmed this for myself and I am eager to see what Smolin replies.

Then Urs says this procedure is itself ill-defined because there are many possible choices for the "reasonable" operator. Or at least you have to prove that there aren't, which the LQG folks haven't done. Urs' point then is that this vitiates Smolin's repreated assertion that the the quantisation and uniquesness theorems are rigorous.

It would be really nice if somebody with real chops from the Ashtekar school, like Thiemann or Sahlmann, could get into this discussion. But we take what we can get. Urs is also pursuing some related topics at the String Coffee Table.

 

[sol2]

It is interesting to see Peter softening.

 

[marcus]

Hi selfAdjoint, sol.
Urs comment puzzled me because it did not engage what Smolin was talking about in his letter.

In the email Smolin says:
A key result is the LOST uniqueness theorem which shows that for d >=2 the hilbert space LQG is based on is the UNIQUE quantization of a gauge field that carries a unitary rep of the diffeo group, in which both the wilson loop and non-abelian electric flux operator are well defined operators. (see the paper and references for the precise statement).

this is a clear reference to some papers by Lewandowski Okolow Sahlmann and Thiemann.

but Urs acts as if he does not know what he is talking about and does not mention these papers or give links to any of them.

Instead he talks about something different: a paper that has been discussed
some months back by Ashtekar, Josh Willis. At one point Josh Willis came to SPR and had what looked to me like an inconclusive exchange with Urs concerning this paper. One could go back and look at it. But what puzzles me is the the disconnect with the L-O and S-T papers.

these are somewhat abstract and I do not recall Urs ever discussing them

Smolin's assertion of uniqueness refers to the uniqueness theorem for A-L measure and a certain representation I would guess, there has been a recent paper about this by yet a fifth person IIRC.

Urs should check the papers out and direct his comments at what Smolin was talking----not make distractive noises off in some other direction with links to papers Smolin was not talking.

selfAdj, thanks for the clarification!

maybe YOU can connect logically what Urs and the KaffeeKreis are saying to the LO-ST papers, earlier ones of which we were reading last year at PF
(or making our best efforts to)

A good discussion starting over at ]Not Even Wrong[/URL] on whether the quantisation prescription in LQG is really pukka. Smolin started off with an email to Woit making the same claims for LQG that he does in the paper we've been reading. Then Urs Schreiber weighs in making the same claim that LQG quantisation is deficient, or at least not standard, that he made in the aftermath to Thiemann's string quantisation paper.

Basically his point is that "canonical quantisation" means you transform the p and q variables which span the phase space, into operators, and in the Ashtekar new variables approach to LQG one of the corresponding variables, the "magnetic" form, cannot be elevated to an operator because it becomes ill-defined. So the LQG people simply replace it with an operator that seems to them what the magnetic form could have become if it woulda transformed meaningfully. Or so Urs says, reading their papers. I have not confirmed this for myself and I am eager to see what Smolin replies.

Then Urs says this procedure is itself ill-defined because there are many possible choices for the "reasonable" operator. Or at least you have to prove that there aren't, which the LQG folks haven't done. Urs' point then is that this vitiates Smolin's repreated assertion that the the quantisation and uniquesness theorems are rigorous.

It would be really nice if somebody with real chops from the Ashtekar school, like Thiemann or Sahlmann, could get into this discussion. But we take what we can get. Urs is also pursuing some related topics at the String Coffee Table.

 

[sol2]

Just a link correction in Self Adjoint's post, and of quote in Marcus's post.

By Lee's own statement and question(about it's qualification as a measure of quantum geometry, one has to ask how he might figure topological relevances to LQG interpretations could have any value as the discrete measures are limited to a range in Glast determinations?

Does this make sense?

 

[marcus]

It is interesting to see Peter softening.

Hi sol, the big change that I see is not a "softening" toward LQG but simply registering it at all. Peter has hardly acknowledged the existence of Loop till now.

He has simply been a critic of String, from a straight mathematical physics perspective. If he had noticed Loop he probably would have criticized it too!

There has been a huge change brought about by Smolin recent paper
"Scientific Alternatives..."

this paper has got Peter's attention because of its postion in the debate over Anthropy

suddenly Peter has acknowledged that Loop exists and is part of the picture and has even quoted Smolin email

this is how I see it.

-----------------------
I have a criticism of your viewpoint sol:

It seems to me that you constantly look at things as if there are two Camps (loop and string) between which peace must be made so that a higher synthesis or something can emerge.

I don't think that is quite the right historical model.

I can't tell you what historical paradigm to use.

But the strongest and most telling critiques of string have always come from people like Woit and Sheldon Glashow who are by no stretch of the
imagination in the "Loop Camp". (thinking of Glashow as in the LQG camp is ludicrous)

-----------
the discussion between looper and stringer concerns whether or not
String is the Only Game in Town or whether Loop can be recognized as a possible alternative approach. People like Lubos Motl repeatedly suggest that string is Destined to be the solution and all the other approaches to quantum gravity have Fatal Flaws. this is a mystical perception and a kind of faith. If that mystical vision prevailed at the NSF-NAS level then you could not do Loop in the USA---you'd have to go to Canada or Mexico or Germany or France or India etc. (this is almost the case now!)

so String is "beset" on two sides: on the one side is a little guy who keeps tugging at your sleeve wanting simply to be recognized as a potentially valid approach to quantum gravity and whom Lubos keeps beating up.

On the other side is a portion of the High Energy Physics establishment which is worried by certain self-indulgences and unempirical fantasy-land tendencies they see in String. This could eventually have an unfortunate effect of bringing discredit on the HEP establishment. So they don't even recognize that Loop exists---he is just this little guy who appears now and then and gets run off by Lubos. They are concerned with house-cleaning.
Susskind is a kind of dust-devil that bothers the hell out of them.

So the solution is not to make peace between Loop and String---that is a side issue. Ultimately (besides waiting till Susskind gets tired and can somehow be somewhat muted) the resolution must be
to bring String as fast as possible to a point of making some testable predictions. Read Peters blog-----basically he is always saying "LHC is almost ready to go! When are you guys going to make an unequivocal prediction about the $64,000 SUSY? When are you guys going to predict anything definite that LHC could test?"

When a new machine nears completion it a timehonored custom for the theory crowd to prepare a prediction (by which some theory lives or dies) to test in the machine. If they dont, then all right-thinking people are scandalized. Look! We pay 1000 string theorists to make theory. Look!
we build these expensive toys just so their theory can be tested! what is
happening! (the predictions have to come BEFORE the experiment otherwise science is not done.)

So I seriously challenge your suggestion that Peter is softening.
I don't think you will see him softening towards String (until and if it predicts something, which it certainly might do)

and I don't think his attitude towards Loop is softening so much as simply
acknowledging it as an alternative that possibly makes testable predictions.

Read smolin's "invitation" and you will see that almost the whole point is the fact that Loop is entering the stage where it makes testable predictions. read the "nearterm experimental situation"

Read smolin's "scientific alternative" and you will see that the whole point is the testability. you can have a Multiverse model which makes testable predictions and is thus a legitimate part of empirical science.

the testability is what is threatening to Susskind and is what those who feel threatened may wish to deny

Smolin and his friend are also under a rigorous time pressure. If GLAST flies by 2007 they must have made predictions before then because after the experiment it doesn't count. In "Invitation" Smolin explicitly says this---I can find the page if you want. he says to other physicists "we have this deadline, come on over and help us derive what to expect from GLAST".

the agenda is not making peace or what theory to believe---it's for amateurs to believe or disbelieve in theories---the issue is to get the sh*t in order so you can test a model. Anyway that's my perspective on the discussion at Peter's blog.

 

[sol2]

It seems to me that you constantly look at things as if there are two Camps (loop and string) between which peace must be made so that a higher synthesis or something can emerge.

Before you run off Marcus read post above yours again.

It seems to me that you constantly look at things as if there are two Camps (loop and string) between which peace must be made so that a higher synthesis or something can emerge.

No Marcus. I am trying to determine the limitations that each has figured theoretically might have been there respective downfalls, and I suspect I have found both these places

Read smolin's "invitation" and you will see that almost the whole point is the fact that Loop is entering the stage where it makes testable predictions. read the "nearterm experimental situation"

Thank you Marcus. I have come to enjoy Smolin's summations, becuase he is flexible to entertain all possibilties even though he is coming at it from a loop approach. Smolin included Penrose as one of the three.


Lubos contributing to wikpedia for Loop is another good example that fellows can do for us people who are trying see what roads to quantum gravity materialize.

And there are published predictions for observable Planck
scale deviations from energy momentum relations[22, 23] that imply predictions for experiments in progress such as AUGER and GLAST. For those whose interest is more towards formal speculations concerning supersymmetry and higher dimensions than experiment, there are also results that show how the methods of loop quantum gravity may be extended to give background independent descriptions of quantum gravity in the higher and super realms[31]-[35]. It thus seems like a good time for an introduction to the whole approach that may help tomake the basic ideas, results and methods accessible to a wider range of physicists.

http://arxiv.org/PS_cache/hep-th/pdf/0408/0408048.pdf

Of course it's still theorizing in bold by association? But trully, accepting the bulk as gravitons is not so far fetch?

So you can see where LQG is relying on SRian apporaches to help in this determination, but the graviton intersection, asks us to take it one step further. Of course we are limited here, and by this recogniton even LQG will suffer, falling short of describing the geometry of the quantum gravity? I have shown the interactive links in this way as respnse to Haelfix's continuing quest



Thanks

 

[marcus]

Just a link correction in Self Adjoint's post, and of quote in Marcus's post.

Ho! thanks for correcting that link to Not Even Wrong!

 

[marcus]

Ah hah! Good quote from Smolin you just provided, sol!

"... there are published predictions for observable Planck
scale deviations from energy momentum relations[22, 23] that imply predictions for experiments in progress such as AUGER and GLAST..."

but there have to be more predictions and they have to be more vitally connected to the basic structure of the theory. experiments that can potentially test quantum gravity are few and far between

one wants to place as much of the theory at risk as possible so there is the maximum possibility for refutation.

then when GLAST flies one can say that in a certain sense "theory has been a guide to experiment"

when this happens it is the bar mitzvah day of theory, and it is doing what it is supposed to do


now I am feeling that maybe you and I see eye to eye on this, because of the Smolin paragraph you just quoted.

 

[sol2]

Ah hah! Good quote from Smolin you just provided, sol!

"... there are published predictions for observable Planck
scale deviations from energy momentum relations[22, 23] that imply predictions for experiments in progress such as AUGER and GLAST..."

but there have to be more predictions and they have to be more vitally connected to the basic structure of the theory. experiments that can potentially test quantum gravity are few and far between

if we falsify strings then it is good, and if we follow the logic of theory development, then predictions supported of LQG, is good

I believe Smolin holds this attribute in mind, and why his summation might have forced him to consider the reasons why he goes the way he does. Peter Woit would pick up on this as well I am sure, but the softness comes from the question in regards to the Planck epoch to grand unification. Supergavity still has to be dealt with even if the understanding might issue from stringtheory. Supersymmetry has to be dealt with, and sure we can voice our opinions on the safe side, but until it is falsifiable, we are in a interesting position. Shall we all stop theorizing

one wants to place as much of the theory at risk as possible so there is the maximum possibility for refutation.

Yes but how would you do this? By recognizing the limitations as I have said in one, but by the recogniton of the other. Holding these two views together, and in light of each othe,r helps one to discern the relevance of one from the other.

then when GLAST flies one can say that in a certain sense "theory has been a guide to experiment"

Absolutely. But, and this is the point that must be considered. It has its limitations too here.

So, LQG can go no further to describing the geometry of, and by answering this, you realize why string surpasses. The validation here in terms of Glast would move forward LQG in regards to a solid foundation experimentally, to the point of leading to supergravity. Lqg cannot go here.

Glast support of LQG would force strings to reconsider some of its work with regards to Lorentz invariance. We have spoken on this before.

now I am feeling that maybe you and I see eye to eye on this, because of the Smolin paragraph you just quoted.

In the sense, that support and validation, helps theoretical development

Yes Marcus there are Peacemakers, with well intentioned views, to fuel the debate. To help us see the essence of things. Everyone wins

 

[marcus]

OK sol, now let's give selfAdjoint a chance to respond to my post #122
Urs seems to have made some misdirected criticisms of Smolin's email that did not actually connect with what Smolin was saying. Let's move the peacemaking discussion to another thread and get back to what just happened on Woit's blog. Peter posted an email from Lee and Urs challenged an assertion in the email whose basis he didnt seem to recognize (referring as he did to some completely different papers).

Urs comment puzzled me because it did not engage what Smolin was talking about in his letter.

In the email Smolin says:
A key result is the LOST uniqueness theorem which shows that for d >=2 the hilbert space LQG is based on is the UNIQUE quantization of a gauge field that carries a unitary rep of the diffeo group, in which both the wilson loop and non-abelian electric flux operator are well defined operators. (see the paper and references for the precise statement).

this is a clear reference to some papers by Lewandowski Okolow Sahlmann and Thiemann.

but Urs acts as if he does not know what he is talking about and does not mention these papers or give links to any of them.

Instead he talks about something different: a paper that has been discussed
some months back by Ashtekar, Josh Willis. At one point Josh Willis came to SPR and had what looked to me like an inconclusive exchange with Urs concerning this paper. One could go back and look at it. But what puzzles me is the the disconnect with the L-O and S-T papers.

these are somewhat abstract and I do not recall Urs ever discussing them

Smolin's assertion of uniqueness refers to the uniqueness theorem for A-L measure and a certain representation I would guess, there has been a recent paper about this by yet a fifth person IIRC.

Urs should check the papers out and direct his comments at what Smolin was talking----not make distractive noises off in some other direction with links to papers Smolin was not talking.

selfAdj, thanks for the clarification!

maybe YOU can connect logically what Urs and the KaffeeKreis are saying to the LO-ST papers, earlier ones of which we were reading last year at PF
(or making our best efforts to)

https://www.physicsforums.com/showthread.php?p=292877&posted=1#post292877

 

[marcus]

Here is the previous selfAdjoint post I was responding to.

A good discussion starting over at Not Even Wrong on whether the quantisation prescription in LQG is really pukka. Smolin started off with an email to Woit making the same claims for LQG that he does in the paper we've been reading. Then Urs Schreiber weighs in making the same claim that LQG quantisation is deficient, or at least not standard, that he made in the aftermath to Thiemann's string quantisation paper.

Basically his point is that "canonical quantisation" means you transform the p and q variables which span the phase space, into operators, and in the Ashtekar new variables approach to LQG one of the corresponding variables, the "magnetic" form, cannot be elevated to an operator because it becomes ill-defined. So the LQG people simply replace it with an operator that seems to them what the magnetic form could have become if it woulda transformed meaningfully. Or so Urs says, reading their papers. I have not confirmed this for myself and I am eager to see what Smolin replies.

Then Urs says this procedure is itself ill-defined because there are many possible choices for the "reasonable" operator. Or at least you have to prove that there aren't, which the LQG folks haven't done. Urs' point then is that this vitiates Smolin's repeated assertion that the the quantisation and uniquesness theorems are rigorous.

It would be really nice if somebody with real chops from the Ashtekar school, like Thiemann or Sahlmann, could get into this discussion. But we take what we can get. Urs is also pursuing some related topics at the String Coffee Table.

If Lee is saying something about the LO and ST papers, and those results, and if Urs wants to vitiate it, as you say, then doesn't Urs need to examine and find something wrong with the LO and ST papers?
Just wondering

the was a new one in that line fairly recently. they strengthened the theorem. it was a May 2004 posting by Okolow and Lewandowski
http://arxiv.org/gr-qc/0405119

this summarizes the situation and extends the results. it would be the paper for Urs to try vitiating if he is anxious to vitiate something

 

[sol2]

I did not deviate from Peter Woit's thread.

as I too, wave off your comment...

and as to Self Adjoint's response...of course.

 

[selfAdjoint]

Hi selfAdjoint, sol.
Urs comment puzzled me because it did not engage what Smolin was talking about in his letter.

In the email Smolin says:
A key result is the LOST uniqueness theorem which shows that for d >=2 the hilbert space LQG is based on is the UNIQUE quantization of a gauge field that carries a unitary rep of the diffeo group, in which both the wilson loop and non-abelian electric flux operator are well defined operators. (see the paper and references for the precise statement).

this is a clear reference to some papers by Lewandowski Okolow Sahlmann and Thiemann.

but Urs acts as if he does not know what he is talking about and does not mention these papers or give links to any of them.

Instead he talks about something different: a paper that has been discussed
some months back by Ashtekar, Josh Willis. At one point Josh Willis came to SPR and had what looked to me like an inconclusive exchange with Urs concerning this paper. One could go back and look at it. But what puzzles me is the the disconnect with the L-O and S-T papers.

these are somewhat abstract and I do not recall Urs ever discussing them

Smolin's assertion of uniqueness refers to the uniqueness theorem for A-L measure and a certain representation I would guess, there has been a recent paper about this by yet a fifth person IIRC.

Urs should check the papers out and direct his comments at what Smolin was talking----not make distractive noises off in some other direction with links to papers Smolin was not talking.

selfAdj, thanks for the clarification!

maybe YOU can connect logically what Urs and the KaffeeKreis are saying to the LO-ST papers, earlier ones of which we were reading last year at PF
(or making our best efforts to)

Marcus, I think you are missing the point. All of the papers by Thiemann, Lewandowski, Ashtecar, and their coworkers quantize the Ashtekar variables in the same way, or so I recall, and so Urs says. And Urs says this quantization is defective, in the manner I explained. The fact that the the LOST paper proves uniqueness is fine and important. But it is worthless if the whole program is doomed, and it could be that unless this quantization problem is fixed, that there IS no LQG with the Ashtekar variables. That's why I want to hear from somebody on the LQG side, not about Smolin's claims, but about THIS problem.

 

[marcus]

Marcus, I think you are missing the point. All of the papers by Thiemann, Lewandowski, Ashtecar, and their coworkers quantize the Ashtekar variables in the same way, or so I recall, and so Urs says. And Urs says this quantization is defective, in the manner I explained. The fact that the the LOST paper proves uniqueness is fine and important. But it is worthless if the whole program is doomed, and it could be that unless this quantization problem is fixed, that there IS no LQG with the Ashtekar variables. That's why I want to hear from somebody on the LQG side, not about Smolin's claims, but about THIS problem.

thanks for replying. so for example we have this new paper in the LO bunch Lee referring to

sounds stupid to ask, but where is the step?

http://arxiv.org/gr-qc/0405119

this is by Lewandowski and Okolow and it came out in May

there is kind of mystique that Urs et al know what they are talking
but when I ask, for any particular paper that I am interested in, "where is the step you think isn't right?"

then I get an arrogant put-down or they start talking about some other paper by Thomas Thiemann or by Willis and Ashtekar.
if they really understand. if they really have a clear idea of what seems
different about the approach to quantizing
then they should easily point to the step in the sample I hold up
for inspection. that's all

maybe they can do it, but simply disdain to.

 

[marcus]

Another place where Urs could point out the step in quantization he has in mind is in


http://arxiv.org/gr-qc/0404018
Ashtekar Lewandowski
"Background Independent Quantum Gravity: A Status Report"

this is a 2004 patient rigorous development, combined with a review,
and it is about 125 pages

somewhere in the standard development on pages 24-40
there is a step which Urs can quickly point to if he knows
what he is talking about, I would suppose

instead we got something very disappointing from him, a reference
to a 2002 paper by Ashtekar, Fairhurst, Willis

Urs just is not showing enough consideration in his response. Look:

Smolin makes an assertion based on LO and ST papers.
the most recent is the 2004 one I linked.
http://arxiv.org/gr-qc/0405119
"Automorphism covariant representations of the holonomy-flux *-algebra"
by Mr. L and Mr. O.

If Urs has actually identified something novel in the approach to quantizing used in this paper I would love to know what it is, he can have a heyday pointing it out. this is a recent paper and part of a substantial advance in Loop. It would be valuable to know!

But sadly he does not, he goes and drags out a 2002 paper which was not what Smolin was basing his claim on.
He acts like he is responding to Smolin's claim without reading it and figuring out what work Smolin was referencing.

This kind of carelessness and arrogance is all too characteristic (and Urs is by far one of the nicer ones of that fraternity)

 

[marcus]

In case anyone is joining us here is the link to the discussion at
Not Even Wrong blog
http://www.math.columbia.edu/~woit/blog/archives/000072.html

it is pretty much at the top of the blog at the moment so if you just go to the usual

http://www.math.columbia.edu/~woit/blog/

you should see it.

there's a fairly interesting brief summary of where Loop is at the moment consisting of an email which Peter elicited from Lee and asked to put on the blog, and then there are comments from various and sundry Readers of the Blog.

as selfAdjoint said when he first called our attention to this bit of Woit action:
"A good discussion starting over at Not Even Wrong on whether the quantisation prescription in LQG is really pukka..."

I believe that pukka is a Kipling-Hindoo word for kosher as in
pukka sahib for respectable gentleman.

Here is selfAdjoint's initial post which states the Bone of Contention in succinct fashion

https://www.physicsforums.com/showthread.php?p=292773&posted=1#post292773

 

[marcus]

in desperation I am trying to guess what step Urs would say was novel
if he would look at one of the papers Lee referred to

so how about this:
Definition 3.4 of the flux operator on page 8,
of Lewandowski Okolow May 2004
http://arxiv.org/gr-qc/0405119

kind of nice paper, clear style
"Automorphism covariant representations of the holonomy flux *-algebra"

if anybody really knows what Urs means about something innovative in the approach to quantizing---and offensive to righteous tradition---maybe they can say if this Definition 3.4 is really it or not.
it would be interesting to know----maybe it really is novel and might even be good---mathematically seems kind of nice. but is it that which Urs would anathematise or something else?

 

[selfAdjoint]

thanks for replying. so for example we have this new paper in the LO bunch Lee referring to

sounds stupid to ask, but where is the step?

http://arxiv.org/gr-qc/0405119

this is by Lewandowski and Okolow and it came out in May

there is kind of mystique that Urs et al know what they are talking
but when I ask, for any particular paper that I am interested in, "where is the step you think isn't right?"

then I get an arrogant put-down or they start talking about some other paper by Thomas Thiemann or by Willis and Ashtekar.
if they really understand. if they really have a clear idea of what seems
different about the approach to quantizing
then they should easily point to the step in the sample I hold up
for inspection. that's all

maybe they can do it, but simply disdain to.

I have never seen anything arrogant from Urs. Maybe you are thinking of a couple of other guys. You keep talking about this paper which is rigorous, or that paper which shows how great LQG is, but you fail to come to grips with the objection, which is mathematical. Here is what Urs says in his first post at NEW:

When quoting results about uniqueness of the Hilbert space in LQG it must be emphasized that the quantization presciption used there is not what is usually called canonical quantization, and by this I mean differences over and above the ambiguities of canonical quantization itself. LQG uses 'relaxed' canonical quantization where not both of canonical coordinates and momenta are represented as operators on a Hilbert space.

He goes on to say that Thiemann and Ashtekar have both confirmed this "relaxed" quantization.

Now you want to be pointed to the exact statement in some linkable paper where that relaxed approach is stated. But the quantization argument in those papers is broken into a large number of segments, and the problem has to be fileted out. I have been reading the A&L paper you linked to and have some preliminary thoughts, but it will be a while before I can track the whole matter down, and frankly, I have other things going on in my life right now.

 

[marcus]

I have never seen anything arrogant from Urs. Maybe you are thinking of a couple of other guys. You keep talking about this paper which is rigorous, or that paper which shows how great LQG is, but you fail to come to grips with the objection, which is mathematical. Here is what Urs says in his first post at NEW:



He goes on to say that Thiemann and Ashtekar have both confirmed this "relaxed" quantization.

Now you want to be pointed to the exact statement in some linkable paper where that relaxed approach is stated. But the quantization argument in those papers is broken into a large number of segments, and the problem has to be fileted out. I have been reading the A&L paper you linked to and have some preliminary thoughts, but it will be a while before I can track the whole matter down, and frankly, I have other things going on in my life right now.

enjoy the other things, hope they go well

it seems unlikely then that anyone can simply look at definition 3.4 on
page 8 of this short paper by L and O and say "yes that is the definition I have doubts on, or seems novel" or "no, that is not it"

http://arxiv.org/gr-qc/0405119

that would be the best because it is what Smolin was referencing (the LO and ST papers) and it is a short clear paper.

I will look at A&L too, since you are----and try to guess what they are talking about. It might turn out to be a beneficial mutation, if it is real.

 

[marcus]

I have been reading the A&L paper you linked to and have some preliminary thoughts, but it will be a while before I can track the whole matter down, and frankly, I have other things going on in my life right now.

Since you are looking at A&L timepermitting, I had a look and have
identified the definition which apparently offends the Hidebound in THAT paper as well

I would guess it is (4.48) on page 39.

but again I cannot know Urs mind
the definition has the reassuring feature of being
adapted to poisson brackets of classical config. and momentum observables
which was calculated a few pages earlier on page 33
"As a prelude to quantization, let us calculate the Poisson brackets between these observables. Since the phase space is a cotangent bundle, the configuration observables have vanishing Poisson brackets among themselves..."
So then, 6 pages later, they are doing the quantum operators corresponding and I think it may be this (4.48) in which a germ of novelty is perceived.

Again it would be great to know----Loop has been shaping up well lately and if there is some innovation it might, as I say, be a benign mutation.
the trouble is I don't see a operational repeatable handle on what they are talking. Just Urs spin on what Urs says Thiemann told him or Ashtekar told him at a time when they were all in great uproar anyway.

 

[selfAdjoint]

I looked also at the 0405119 paper you suggested, but I don't think that paper is relevant to this discussion, because it is about extending Sahlmann's uniqueness theorem from the trivial bundle he worked with to a general principle bundle. As such it assumes the properties of the Sahlmann algebra and does not discuss the process of quantization as such.

A rereading of parts of the A&L paper suggests some attention to page 34. In Hamiltonian analysis the Poisson brackets of the P's with each other are supposed to vanish. But with the "electric fluxes" playing the role of the P, or momentum, variables, their Poisson bracket does not vanish. Instead A&L construct an algebra that supports this noncommutativity. Right here they have parted from "canonical quantization" and struck out into new territory. I won't have time tonight to see what they do with this further down in the paper, but I feel it must have some effect. I believe Urs would say this failure to commute signals an anomaly.