Perche i nostri discorsi-Galileo quoted by Rovelli

[marcus]

Perche i nostri discorsi---Galileo quoted by Rovelli

"Dialogo sopra i massimi sistemi del mondo", one of Galileo's dialogs about science, contains this quote:

"Perche i nostri discorsi hanno a essere sopra un mondo sensibile, e non sopra un mondo di carta."

http://www.swif.uniba.it/lei/scuola/filosofi/filosofi3h1.htm

Because our discourses have to be about the real world and not about a world of paper.

Hey there, old Galileo! You made it into arxiv, on page 5 of:

http://arxiv.org/hep-th/0310077

thanks to ranyart for the link. Great modern dialog in the tradition of controversial dialogs on science issues going back to Galileo (if not earlier )

 

[Mentat]

You know, that quote (from Galileo) was one of the logical errors that I found in Sal's argument (in the link that ranyart provided on this thread.

 

[marcus]

Please continue

what other logical errors besides the quote from Galileo?

 

[meteor]

I've found this paper to be fun, and is interesting that the author, founder of LQG, has assigned the paper of Simplicius to the stringer
A pair of questions about the paper:
a)What are those infinite fields that cause problems in string theory?
b)What heck can this mean?: LQG has difficulties in recovering the low energy limit

 

[marcus]

Originally posted by meteor
..., has assigned the paper of Simplicius to the stringer

?
has assigned the part of Simplicius to...
has assigned the role of Simplicius to...

greatest debunker of all time (of the Aristotelian system to make way for modern empirical science, and of the Ptolemaic system to make way for the heliocentric model, and his preferred explosive seems to have been serious comic dialogs. Latin flavor in what is going on in quantum gravity, can't quite decide what it is

 

[meteor]

I'm sorry, my english is quite elementary
I meant role, of course

 

[marcus]

Originally posted by meteor
I'm sorry, my english is quite elementary
I meant role, of course

and I was pedantic of course
besides which, to be just, it is certainly not elementary!
BTW have you noticed most people currently at the
front in loop quantum gravity research speak
as their first language something other than English.
Today I was reading two papers by some people at
University of Cordoba in Argentina. the people contributing
most tend to have first-languages like French, Spanish, German,
Hindi, Polish, Italian (ah! Italian). I wonder if the skew is
just an illusion and if it means anything

 

[selfAdjoint]

Mentat still hasn't told us why he thinks the quote from Galilleo was illogical...

Rovelli's vision of how to move forward beyond present day physics boils down to this. Couple the standard model to the set of quantized QG loops so there will be interactions with eigenvalues of length and eigenvalues of momentum, etc. Combined states. Work on the theory non-perturbatively in that way. No infinity problems because no "classical points" - same advantage stringy physics gives, but with perhaps a more basic underpinning. The point for me is, if you could do this you could calculate numbers for the accelerators. The advantage over normal analysis would be non-perturbative calculations without infinities. The advantage over lattice would be, well it's proposed as real physics, no continuum limit required.

I was thinking of posting this up in the mkaku quantum revolution forum, but I felt it would be kind of an insult to kaku, who is so big with string theory.

 

[Mentat]

Originally posted by marcus
Please continue

Very sorry. I ran out of time yesterday, and couldn't respond here (partially due to the Chat that I had to leave early ).

The quote from Galileo is illogical because, if the world were all like we experience, then we would have no need of science (all of our original assumptions would be correct). Also, it was most inappropriate that this be brought up when deciding about the next step after QM and GR (both of which challenge "common experience" at every turn).

what other logical errors besides the quote from Galileo?

I'm saving my actual notes on the discussion (which I typed as I was reading) for the thread that I'm hoping ranyart will start soon.

 

[Mentat]

Originally posted by selfAdjoint
Mentat still hasn't told us why he thinks the quote from Galilleo was illogical...

I apologize again for that. If it were up to me, I would be on much more than my currently alotted hour per day, but it's not up to me.

 

[marcus]

Originally posted by selfAdjoint
...

Rovelli's vision of how to move forward beyond present day physics boils down to this. Couple the standard model to the set of quantized QG loops so there will be interactions with eigenvalues of length and eigenvalues of momentum, etc. Combined states. Work on the theory non-perturbatively in that way. No infinity problems because no "classical points" - same advantage stringy physics gives, but with perhaps a more basic underpinning. The point for me is, if you could do this you could calculate numbers for the accelerators. The advantage over normal analysis would be non-perturbative calculations without infinities. The advantage over lattice would be, well it's proposed as real physics, no continuum limit required.
...

this is a welcome condensed view that gets at the essence IMO. There are two short papers that bear on this:

Relation between polymer and Fock excitations
Ashtekar/Lewandowski
http://arxiv.org/gr-qc/0107043

Polymer and Fock representations for a Scalar field
Ashtekar/Lewandowski/Sahlmann
http://arxiv.org/gr-qc/0211012

"To bridge the gap between background independent, non-perturbative quantum gravity and low-energy physics...Minkowskian Fock states are located, analyzed and used in the background independent framework..."

The papers impress me as well written and as confronting basic questions:

"Can the background independent, non-perturbative theory reproduce the familiar low-energy physics on, say, suitable coarse-graining? and, Can one pin-point where and why perturbation theory fails?"

The coupling you mention seems to depend in a crucial way on connecting polymer and Fock representations as is done in these two papers. As well as "numbers for the accelerators" one can expect numbers for observational astronomy---hardly needs mention since it goes without saying

 

[sol1]

Liminocentric Structures

Liminocentric structures

If U(1)=5d, how is it we could have turned things around?

The limits of energy and matter distinctions, had to be recognized, and how they could flow from one into another?

Here photon interactions, from the source, and back to gravitational influence(thinking of the spacetime fabric and how mass effects)?

Supersymmetry, and the gravity field recognized as a repesentative of interactive forms in matter considerations?

How I came to arrive at U(1)=5d(Kaluza and Klein were instrumental in leading the discussion from spacetime considerationsto [Boson Productions off the Brane]):


http://www.superstringtheory.com/forum/metaboard/messages18/119.html

http://www.superstringtheory.com/forum/metaboard/messages18/347.html

http://www.superstringtheory.com/forum/metaboard/messages18/128.html



I am open here to corrections. I apologize if I am breaking the continuity of the thread.:)

Sol

 

[selfAdjoint]

Marcus, Thanks for the two links. I scanned the first one, and noticed many old friends, like CYL and its dual. The polymerized Fock states lie in CYL*, which lies in full Fock space, but the Fock space product does not leave CYL* invariant. Bummer! Maybe an indication of why they went after the algebraic approach?

I really need to get behind the terminology to se how they do Maxwell theory (first paper) and Klein-Gordan (second one) on the "polymer" realization of their quantum simplexes.

 

[marcus]

selfAdjoint, I would be interested to know if you found
the comparison in the dialog between modernday Simplicio and Salviati to be untrue or unfair at any point---particularly, if it is possible to point to a specific line on some page.

 

[marcus]

the intuitive gist of Loop Gravity

Probably what we need most now is an intuitive sketch of what makes Loop Gravity different from your typical field theory----how is the backgroundlessness implemented?

Things are coming to a head. Rovelli's new book "Quantum Gravity" is major and has IMO material for a bunch of PhD dissertations just expanding on details. It also contains the "Dialog" as a final chapter. You can connect the points made about loop gravity in the Dialog to chapters and sections in the main part of the book. Also Smolin's April 2003 paper lays out what has been accomplished and what remains to do and what the prospects are for getting loop gravity tested---it is a thorough review and comparison: "How far are we from a quantum theory of gravity?"

Plus we have good accounts of loop cosmology by Bojowald
like the recent paper "Quantum Gravity and the Big Bang", and in some of Ashtekar's papers. It appears progress in cosmology has been dramatic of late. New researchers have been getting into LQG at the level of cosmology.

Plus there is this month's Berlin symposium "Strings meets Loops" which will probably generate a series of overview talks
aimed at wider audience----e.g. another cosmology overview by Bojowald, another full theory overview by Ashtekar, a spin foam overview by Rovelli, and so on.

So there is more and more accessible information than there was a year ago, about loop gravity. It looks to me as if new research possibilities are coming into focus. For example, these days I keep seeing papers about the "low energy limit" or "semi-classical limit", another place where newcomers are getting in (like those Argentine people this month---Kozameh, Gleiser, Parisi)

It seems to me to be a good time to try to say what loop gravity is about, in the simplest possible way. I am apt to make several false starts on this. If someone else has been thinking about it and wants to try, go ahead

 

[selfAdjoint]

Originally posted by marcus
this is a welcome condensed view that gets at the essence IMO. There are two short papers that bear on this:

Relation between polymer and Fock excitations
Ashtekar/Lewandowski
http://arxiv.org/gr-qc/0107043

Polymer and Fock representations for a Scalar field
Ashtekar/Lewandowski/Sahlmann
http://arxiv.org/gr-qc/0211012

"To bridge the gap between background independent, non-perturbative quantum gravity and low-energy physics...Minkowskian Fock states are located, analyzed and used in the background independent framework..."

The papers impress me as well written and as confronting basic questions:

"Can the background independent, non-perturbative theory reproduce the familiar low-energy physics on, say, suitable coarse-graining? and, Can one pin-point where and why perturbation theory fails?"

The coupling you mention seems to depend in a crucial way on connecting polymer and Fock representations as is done in these two papers. As well as "numbers for the accelerators" one can expect numbers for observational astronomy---hardly needs mention since it goes without saying

I dug further back into the references from the papers you cited and am reading hep-ph/0005233, by Thiemann, which is the first of a series of papers he wrote with various coauthors on the implementation of a "coherent states" form of QFT on the spin-edged simplex lattice of LQG. He asserts that the coherent state approach is equivalent to the usual approach and more suitable to the purpose. I will try to read up and bring some news on this demarche.

 

[marcus]

Originally posted by selfAdjoint
I dug further back into the references from the papers you cited and am reading hep-ph/0005233, by Thiemann, ...
...I will try to read up and bring some news on this demarche.

Great! I very much look forward to hearing what you find.

 

[selfAdjoint]

First, the Coherent State Transform.

In 1994 Brian C. Hall (at UCSD) generalized an old (1962) result of Segal and Bargmann by defining a transform from the Hilbert Space of square integrable functions under the Haar measure for a compact group to the space of holomorphic functions on the complexified version of the group, supplied with a measure he defined to make the functions "act nice". This was all pure functional analysis, but it caused breakthroughs in a wide range of fields. So now if you google on Coherent State Transform you will find results on its applications to geodesy, to wavelets, to algebraic varieties, and also to this paper by Ashtekar,Lewandowski, Marolf, Mourao, and Thiemann, http://arxiv.org/PS_cache/gr-qc/pdf/9412/9412014.pdf which generalizes the Hall transform and applies it to defining gauge theory on a GR spacetime.

It is this generalized Coherent State Transform which is at the heart of Thiemann's attempt to define quantum theory on the network of LQG.

 

[marcus]

Originally posted by selfAdjoint
First, the Coherent State Transform.

It is this generalized Coherent State Transform which is at the heart of Thiemann's attempt to define quantum theory on the network of LQG.

You've got my complete attention. I will look up the reference and check back to see what follows

 

[selfAdjoint]

The Hall Coherent State Transform.

This is the straight Hall transform, as described in the ALMMT paper gr-qc/9412014.
You have a compact group H and the set of square integrable functions from G to the reals, R, I will denote this set by L and a typical element in it by f. A typical element of G will be denoted g.

The group can be complexified resulting in the group G^C with typical element g^C. Hall has defined a measure on G^C using heat kernel methods. I won't go into details on that unless requested to; the meanure is denoted ν. Now the complexified group has irreps into complex vector spaces, and these irreps fall into isomorphism equivalence classes, so in talking about irreps it will be sufficient to consider one representative in each class. The generic irrep in this sense is denoted π. It maps into the complex vector space V_π. Then define a normalizing constant σ, depending on ν and π by 1/dim V_π times the integral over G^Cdν(g^C DET(π(g^C-1))².

Now define a prototype holomorphic function ρ from G^C to the complex numbers by
&pho;(g^C) = Sum over π (dime V_π/SQRT(σ)) Trace(π(g^{C -1})).

So at each element of the complexification you project with the current irrep for the inverse of that element, resulting in a matrix, and you take the trace of that matrix, which is of course a complex number. The factor in &sigma guarantees that the sum doesn't blow up, so the function ρ is holomorphic. We're almost there.

Now we define Hall's transform from the square integrable functions on G to the holomorphic functions on G^C. For each f the value of the transformed function will be obtained by integrating over G with the Harr measure. At each element of g we will have the value f(g), a real number, and we will also have the complex partner of g, g^C, and the complexification allows the element g^-1g^C to be well determined. The integrand is then f(g)ρ(g^-1g^C). Notice the interplay of group inverses.

This is the transform as Hall did it. The authors , with an assist from John Baez, now generalize this transform for their purposes, which I will get to in the next post on this thread.

 

[marcus]

I am looking forward to the next post. I will erase my response here in a day or two for compactness---I don't want stuff to break the continuity of your series of posts about this. However in the meantime I will try fixing typos in what you wrote and writing the greek nu using (font=symbol)n(/font) and cosmetic stuff like that.

Originally posted by selfAdjoint
The Hall Coherent State Transform.

This is the straight Hall transform, as described in the ALMMT paper gr-qc/9412014.
You have a compact group G and the set of square integrable functions from G to the reals, R, I will denote this set by L and a typical element in it by f. A typical element of G will be denoted g.

The group can be complexified resulting in the group G^C with typical element g^C. Hall has defined a measure on G^C using heat kernel methods. I won't go into details on that unless requested to; the measure is denoted n. Now the complexified group has irreps into complex vector spaces, and these irreps fall into isomorphism equivalence classes, so in talking about irreps it will be sufficient to consider one representative in each class. The generic irrep in this sense is denoted p. It maps into the complex vector space V_p. Then define a normalizing constant s, depending on n and p by 1/dim V_p times the integral over G^Cdn(g^C DET( p(g^C-1))².

Now define a prototype holomorphic function r from G^C to the complex numbers by
r(g^C) = Sum over p (dim V_p/SQRT( s)) Trace( p(g^{C -1})).

So at each element of the complexification you project with the current irrep for the inverse of that element, resulting in a matrix, and you take the trace of that matrix, which is of course a complex number. The factor in s guarantees that the sum doesn't blow up, so the function r is holomorphic. We're almost there.

Now we define Hall's transform from the square integrable functions on G to the holomorphic functions on G^C. For each f the value of the transformed function will be obtained by integrating over G with the Haar measure. At each element of g we will have the value f(g), a real number, and we will also have the complex partner of g, g^C, and the complexification allows the element g^-1g^C to be well determined. The integrand is then f(g) r(g^-1g^C). Notice the interplay of group inverses.

This is the transform as Hall did it. The authors , with an assist from John Baez, now generalize this transform for their purposes, which I will get to in the next post on this thread.

I'm just trying the symbol font to see how it looks, not urging its use----the lower case sigma is wimpy, but the pi looks more like pi. Maybe useful maybe not.

 

[eigenguy]

This thread seems about searching for the way to connect LQG with the low energy world by a correspondence between quantum states as they are expressed in LQG and QFT. The most recent paper I could find which bears on this directly (The specific passage which makes me think this is in bold) and which gives a view that may be more current than previously mentioned papers by Ashtekar et al and Thiemann is another one by Thiemann dated May 1st 2003:

---------------------
"Seven years ago, for the first time a mathematically well-defined Hamiltonian con-straint operator has been proposed for LQG which is a candidate for the definition of the quantum dynamics of the gravitational field and all known (standard model) matter.

Despite this success, three papers were published which criticized the proposal by doubting the correctness of the classical limit of the Hamiltonian constraint operator. In broad terms, what these papers point out is that while the algebra of commutators among smeared Hamiltonian constraint operators does not not lead to inconsistencies, it does not manifestly reproduce the classical Poisson algebra among the smeared Hamiltonian constraint
functions.

While the arguments put forward are inconclusive (e.g. the direct translation of the techniques used in the full theory work extremely well in Loop Quantum Cosmology)

these three papers raised a serious issue and presumably discouraged almost all researchers in the field to work on an improvement of these questions. In fact, except for two papers there has been no publication on possible modifications of the Hamiltonian constraint proposed. Rather, the combination of with path integral techniques and ideas from topological quantum field theory gave rise to the so-called spin foam reformulation of LQG. Most of the activity in LQG over the past five years has focussed on spin foam models, partly because the hope was that spin foam models, which are defined rather independently of the Hamiltonian framework, circumvent the potential problems pointed out. However, the problem reappears as was shown in recent contributions which seem to indicate that the whole virtue of the spin foam formulation, its manifestly covariant
character, does not survive quantization.

One way out could be to look at constraint quantization from an entirely new point of view which proves useful also in discrete formulations of classical GR, that is, numerical GR. While being a fascinating possibility, such a procedure would be a rather drastic step in the sense that it would render most results of LQG obtained so far obsolete.

In this paper we propose a new, more modest, method to cut the Gordic Knot which we will describe in detail in what follows. Namely we introduce the Phoenix Project which aims at reviving interest in the quantization of the Hamiltonian Constraint. However, before the reader proceeds we would like to express a word of warning. So far this is really only a proposal. While there are many promising features as we will see, many mathematical issues, mostly functional analytic in nature, are not yet worked out com-pletely. Moreover, the proposal is, to the best of our knowledge, completely new and thus has been barely tested in solvable models. Hence, there might be possible pitfalls which we are simply unaware of at present and which turn the whole programme obsolete."
----------------------------------

Whatever the "recent trends" are in terms of applications like to cosmology etc., to me this indicates that LQG really is at a crisis point. Maybe this is the real reason for the upcoming LQG - m theory conference. What do you guys think?

 

[selfAdjoint]

I want to thank you for bringing this paper to our attention. The paper is gr-qc/0305080. Two points. First, I posted on another thread today that LQG needs a breakthrough. This may be it (or not). Second, I believe Jeff in one of his posts mentioned the problem with the Hamiltonian constraint as one of the shortcomings of the quantum gravity project. This now clarifies that remark.

I intend to go on explicating these old papers for a while because they have in them the origins of many of the tools that will continue to be used, whatever the status of the breakthrough. But I am going to at least scan the work in gr-qc/0503080 and I hope others will too.

 

[marcus]

Months ago Jeff quoted the same article by Thiemann (Phoenix project, master constraint program, or something like that). I looked at the article around that time myself---came across it at the PI website, or a link to it. My impression is that the others (Rovelli, Smolin, Ashtekar) take on it differs from Thiemann's and he may overstate the import of matters which are naturally very close to his heart.

As far as I can see several different versions or approaches to hamiltonian constraint are worked on or used by several groups or individual researchers. Things are unresolved in that area but its not as if all eyes are on Thomas Thiemann and his "Phoenix" proposal.

Eigenguy's post very much along the same lines as Jeff's earlier. My reaction now is along similar lines to my reaction then

 

[eigenguy]

Originally posted by selfAdjoint
I want to thank you for bringing this paper to our attention. The paper is gr-qc/0305080. Two points. First, I posted on another thread today that LQG needs a breakthrough. This may be it (or not). Second, I believe Jeff in one of his posts mentioned the problem with the Hamiltonian constraint as one of the shortcomings of the quantum gravity project. This now clarifies that remark.

I intend to go on explicating these old papers for a while because they have in them the origins of many of the tools that will continue to be used, whatever the status of the breakthrough. But I am going to at least scan the work in gr-qc/0503080 and I hope others will too.

I guess what I need to understand then is what the hamiltonian constraint is/means and why it is such a problem. I know that the hamiltonian is basically the energy so does this mean that they need to find sstates with the right energies? Also I know that the hamiltonian in schrodingers equation gives the evolution of the wavefunction but it doesn't equal zero. Why must it equal zero here so that the constraint is satisfied? Also, the Ashtekar papers talk about matter and a scalar field. Is the scalar field matter? What is the problem with matter? What do they mean by polymer?

 

[eigenguy]

Originally posted by marcus
Months ago Jeff quoted the same article by Thiemann
(Phoenix project, master constraint program, or something
like that). I looked at the article around that time myself---came across it at the PI website, or a link to it.
My impression is that the others (Rovelli, Smolin, Ashtekar) take on it differs from
Thiemann's and he may overstate the import of matters
which are naturally very close to his heart. As far as I can see
several different versions or approaches to hamiltonian constraint are worked on or used by several groups or individual researchers. Things are unresolved in that area but its not as if
all eyes are on Thomas Thiemann and his "Phoenix" proposal.

Eigenguy's post very much along the same lines as Jeff's earlier
efforts to focus attention on this particular Thiemann article. My reaction now is along similar lines to my reaction then

What was your reaction then?

 

[selfAdjoint]

Originally posted by marcus
Months ago Jeff quoted the same article by Thiemann (Phoenix project, master constraint program, or something like that). I looked at the article around that time myself---came across it at the PI website, or a link to it. My impression is that the others (Rovelli, Smolin, Ashtekar) take on it differs from Thiemann's and he may overstate the import of matters which are naturally very close to his heart.

As far as I can see several different versions or approaches to hamiltonian constraint are worked on or used by several groups or individual researchers. Things are unresolved in that area but its not as if all eyes are on Thomas Thiemann and his "Phoenix" proposal.

Eigenguy's post very much along the same lines as Jeff's earlier. My reaction now is along similar lines to my reaction then

Well Marcus, here's how it looks to me. What those others are doing (Ashtekar, Sahlmann, etc.) is like high or "soft" functional analysis. Theorems about algebras of cylinder functions. It's exciting mathematics, but it's a long way from the double slit.

Thiemann is the only one who stubbornly refuses to give up the idea of getting genuine quantum mechanics out of quantum geometry, just because there's a little glitch in the math. Aside from smarts and creativity, persistence is one of the virtues of a scientist.

Eigenguy, the point of the Hamiltonian constraint is this. Decades ago it was proved (I think by deWitt) that if you tried to get the "wave function of the universe" in GR, you could set up a Schroedinger equation and get a Hamiltonian, but it would come out identically zero. Just one of those glitches like I mentioned above.

Then it was reasoned that the zero Hamiltonian is your friend. It serves as a test of quantum gravity theories. Since any valid theory will eventually give you the "wave function of the universe" it must have H = 0. So if you can prove that, it's good news for your theory. But if you can't prove it, it's bad news. In Thiemann's case he thought he had proven it, but it turned out his development of H was not mathematically well defined.

 

[marcus]

Originally posted by selfAdjoint

Thiemann is the only one who stubbornly refuses to give up the idea of getting genuine quantum mechanics out of quantum geometry, just because there's a little glitch in the math. Aside from smarts and creativity, persistence is one of the virtues of a scientist.

the Hamiltonian story is particularly exciting just now because as you may have noticed in the program for the symposium Thiemann is not giving a talk and it is Lewandowski (morning after opening day) who gives the loop gravity talk on "The Hamiltonian Constraint"

It was Lewandowski who pointed out the "little glitch" in Theimann's math (as you call it) back around 1997-1998 and called into question the "Thiemanntonian". So both Jerzy L and Thomas T have a certain fame or notoreity around this.

Well I hope Lewandowski's 30 October talk on the Hamiltonian Constraint is available online soon because it will put things in clearer perspective (for me at least, I expect) than what has been said about it so far.

 

[eigenguy]

Originally posted by marcus
It was Lewandowski who pointed out the "little glitch" in Theimann's math

Where could I find this?

Originally posted by selfAdjoint
Thiemann is the only one who stubbornly refuses to give up the idea of getting genuine quantum mechanics out of quantum geometry, just because there's a little glitch in the math.

By "getting genuine quantum mechanics out of quantum geometry" do you mean getting a hamiltonian?

Originally posted by selfAdjoint
to get the "wave function of the universe" in GR, you could set up a Schroedinger equation and get a Hamiltonian, but it would come out identically zero. Just one of those glitches like I mentioned above.

I read somewhere that the total energy of the universe must be zero. Could this be why H = 0?

 

[meteor]

Where could I find this?

"Loop Constraints: A Habitat and their algebra"
http://arxiv.org/abs/gr-qc/9710016

"On the consistency of the constraint algebra in spin network gravity"
http://arxiv.org/abs/gr-qc/9710018

 

[marcus]

Originally posted by meteor
"Loop Constraints: A Habitat and their algebra"
http://arxiv.org/abs/gr-qc/9710016

"On the consistency of the constraint algebra in spin network gravity"
http://arxiv.org/abs/gr-qc/9710018

thank you Meteor! I was just getting ready to hunt up those links to Lewandowski et al (shooting down Thiemann) articles when I saw you had kindly provided them for Eigenguy and the rest of us. i think I have one of them on my desk under a pile of other papers

 

[selfAdjoint]

So, what does everyone think. In the light of this breaking news, should I continue explicating the tools Thiemann developed? Or wait for the other shoe to drop?

Marcus, do you know of anyone who could give us a quick hint of Lewandowski's talk? I'll be online on the 30th, but will be out of town with only an occasional connection of the 31st and the weekend.

 

[marcus]

Originally posted by selfAdjoint
So, what does everyone think. In the light of this breaking news, should I continue explicating the tools Thiemann developed? Or wait for the other shoe to drop?

Marcus, do you know of anyone who could give us a quick hint of Lewandowski's talk? I'll be online on the 30th, but will be out of town with only an occasional connection of the 31st and the weekend.

I am completely out of the loop
I've exchanged emails with a couple of those guys but would
never ask for a favor

enjoy the weekend! fall colors? where is it Wisconsin Illinois Michigan?

selfAdjoint we have no graduate students and no responsibilities and no time pressure. we can understand all this stuff for its own sake alone as it comes along and as we feel like it!

you already do 10X more than you need to for the greater glory of the Board, so feeling pressure and obligation should be out of the question (should I say this in a PM or can I just say it out in the open in response to your post?)

I feel sure some of those symposium talks will be on line but have no idea when---will keep an eye out tho

 

[marcus]

BTW as life teaches us it is never safe to assume that there is another shoe or that it is ever going to drop
when all is said and done we may still have to sweat some
over that transform of Brian Hall
perhaps nothing new will come out at that symposium at all
and it will just be a kind of focused clarification of how things
are going and where the problems are that are of most
concern at present----as for me personally I rather do not
expect anything new but that I will just understand how things
stand a little better, but it would be wonderful to be surprised
of course

 

[eigenguy]

I have been studying this stuff all day and now regret bringing Thiemann's phoenix paper up. It's message was that Lewandowski et al's criticism of Thiemann's original construction of the hamiltonian constraint algebra discouraged efforts to find a suitable alternative. It was hoped that the spin foam construction since it is covariant and thus avoid these problems might succeed. Unfortunately as pointed out by Thiemann this covariance does not survive quantization so he tries to get the ball rolling again on the canonical formulation. I hope we hear more about this in that LQG and string theory conference or any conference.

However, originally you guys were interested in Ashtekar's papers about finding correspondence between spin networks and ordinary fock space states necessary to make contact with the classical world. I think we should stick to that because in these papers it seems the LQG states are not required to satisfy the hamiltonian constraints.

Please check this for errors since I am not confident with this stuff.