Quantum Graffiti: MEDIA COVERAGE, JOB OPENINGS & Gossip Around Loll at Utrecht

[marcus]

an effective introduction to Causal Sets is this 2004 set of lecture slides by Dowker

www.dpf2003.org/xx/qg/dowker.pdf[/URL]

the title of the talk is
"Causal Sets as the Deep Structure of Spacetime"

the slides are written-out enough to understand on their own, without the talk. there is an essential reference to a paper by Sorkin et al
Ahmed, Dodelson, Green, Sorkin
[url]http://www.arxiv.org/abs/astro-ph/0209274[/url]
and indirectly to a 1993 Sorkin talk published in 1997
[url]http://www.arxiv.org/abs/gr-qc/9706002[/url]

from Dowker slides one gets the impression that Causets is not a quantum theory yet, it has some probabilities you can calculate but no hilbertspace and no complex amplitudes. seems conceptually nice (if you like discrete finite sets and relations defined on them) but so far not so good for calculating or for imitating General Relativity spacetime dynamics.
however it has a strong appeal for philosophers

Dowker intimates that Sorkin got an amazingly close estimate of the size of the cosmological constant (which if true might be an accident or might mean something) back in 1992 or 1993 just using Causal Sets reasoning.
Causets is still somewhat nebulous as a theory IMO, so this thing about predicting the size of the cosmological constant, even if just an order of magnitude guess, is iffy. Also it is based on a strange picture where Lambda oscillates and we just happen to be in a era when it is E-120.

but even discounting the claim of predicting Lambda, causets is a lively contender for the Nonperturbative Limelight.

 

[marcus]

In case you are interested in that 1997 Sorkin paper mentioned in the previous post

http://www.arxiv.org/abs/gr-qc/9706002
Forks in the Road, on the Way to Quantum Gravity
Rafael D. Sorkin (ICN-UNAM and Syracuse University)
29 pages
Int.J.Theor.Phys. 36 (1997) 2759-2781

'In seeking to arrive at a theory of "quantum gravity'', one faces several choices among alternative approaches. I list some of these "forks in the road'' and offer reasons for taking one alternative over the other. In particular, I advocate the following: the sum-over-histories framework for quantum dynamics over the "observable and state-vector'' framework; relative probabilities over absolute ones; spacetime over space as the gravitational "substance'' (4 over 3+1); a Lorentzian metric over a Riemannian ("Euclidean'') one; a dynamical topology over an absolute one; degenerate metrics over closed timelike curves to mediate topology-change; "unimodular gravity'' over the unrestricted functional integral; and taking a discrete underlying structure (the causal set) rather than the differentiable manifold as the basis of the theory.

In connection with these choices, I also mention some results from unimodular quantum cosmology, sketch an account of the origin of black hole entropy, summarize an argument that the quantum mechanical measurement scheme breaks down for quantum field theory, and offer a reason why the cosmological constant of the present epoch might have a magnitude of around 10^{-120} in natural units.'

Sorkin is one of the invited plenary speakers at the Loop 05 conference at Potsdam in October

it could be an accident but 10^{-120} is about right.

 

[Spin_Network]

an effective introduction to Causal Sets is this 2004 set of lecture slides by Dowker

www.dpf2003.org/xx/qg/dowker.pdf[/URL]

the title of the talk is
"Causal Sets as the Deep Structure of Spacetime"

the slides are written-out enough to understand on their own, without the talk. there is an essential reference to a paper by Sorkin et al
Ahmed, Dodelson, Green, Sorkin
[url]http://www.arxiv.org/abs/astro-ph/0209274[/url]
and indirectly to a 1993 Sorkin talk published in 1997
[url]http://www.arxiv.org/abs/gr-qc/9706002[/url]

from Dowker slides one gets the impression that Causets is not a quantum theory yet, it has some probabilities you can calculate but no hilbertspace and no complex amplituded. seems conceptually nice (if you like discrete finite sets and relations defined on them) but so far not so good for calculating or for imitating General Relativity spacetime dynamics.
however it has a strong appeal for philosophers

Dowker intimates that Sorkin got an amazingly close estimate of the size of the cosmological constant (which if true might be an accident or might mean something) back in 1992 or 1993 just using Causal Sets reasoning.
But causets is not really a numerical theory yet, so this thing about predicting the size of the cosmological constant, even if just an order of magnitude guess, is iffy. Also it is based on a strange picture where Lambda oscillates and we just happen to be in a era when it is E-120.

but even discounting the claim of predicting Lambda, causets is a lively contender for the Nonperturbative Limelight.[/QUOTE]

What I like about the images, you can see Fay embedded into the background of the photographic paper, taking photo's! :!) that..is she taking photo's of slide's, or is she really taking photo's of herself? :rolleyes:

I think its a deliberate action!..a precise action..a double take!

 

[marcus]

Definitely deliberate. hip lady. your term "double take" is nice. I assume you saw that snapshot of Fay posing at the blackboard---had a link to it around post #54 back a ways in this thread.

https://www.physicsforums.com/showthread.php?p=665506#post665506

Let's take a closer look at the program at this month's Paris conference,
http://einstein2005.obspm.fr/indexr.php
http://einstein2005.obspm.fr/programmer.php
The abstracts of some Plenary Session talks are posted. Here is a sample:

Monday July 18
...
11h45 - 12h25: Abhay Ashtekar « Gravity, Geometry and the Quantum »
...
14h00 - 14h40: Brian Greene « The State of String Theory»
...
14h45 - 15h30: Alain Connes « Noncommutative geometry and physics»
...
...
15h45 - 16h25: Fay Dowker « Causal sets and discrete spacetime. »

Tuesday July 19
...
10h15 - 10h55: Carlo Rovelli «Loop Quantum Gravity »
...

Friday 22 July
...
15h45 - 16h45: Gerard t'Hooft « Conclusion Talk »
----------------------------------------------

BTW here is a picture of Fay Dowker. Interesting that both her mother and father were physicists, born c. 1966 undergrad major math, married to physicist Jerome Gauntlett---physics seems to run in the family---has two children.
http://www.stp.dias.ie/events/2004/causal_sets_photos/WorkshopOnCausalSets-FayDowker-1.jpg

Fay Dowker is one of the featured ... speakers not only at Einstein2005 this month in Paris but also at Loops05 this October in Potsdam.

 

[marcus]

Last update was 20 july, time to update again

20 July Paris conference Zohren presented a Loll-Westra-Zohren paper about "sum over topologies"---including topology change in the nonP quantum gravity path integral

if things go as planned, the schedule for the Loops 05 conference should be posted within the next week or so, at this site:
http://loops05.aei.mpg.de/
possibly at this page
http://loops05.aei.mpg.de/index_files/Programme.html
there has already been some understandable delay.


These are CDT papers that have come out in the past 12 months.
http://arxiv.org/find/grp_physics/1...gravity+AND+Lorentzian+quantum/0/1/0/past/0/1

There is a paper in the works by Loll with Dario Benedetti and Francesco Zamponi. I would like to see another from Loll/Dittrich on Black Holes but I don't know of one in the works, and it would be exciting to get a new paper from Loll/Westra about sum-over-topologies.

Here at PF we had a thread to post predictions about whether the QG path integral including sum over topologies would be extendable from the 2D case up to 3D and 4D. the thread is here:
https://www.physicsforums.com/showthread.php?t=81626

This thread, Quantum Grafitti, is mainly about the people doing Loll-type quantum gravity, with random news and gossip. To get an idea of the CDT (Causal Dynamical Triangulations) scene check out Loll's website at the Uni Utrecht in Holland. Here is a list of Loll graduate students/postdocs:

http://www.phys.uu.nl/~loll/Web/students/students.html

Here are some snapshots mostly from the Utrecht Inst. of Theor. Physics:

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Renate.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Willem1.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Dario.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Johan.jpg

http://www.phys.uu.nl/~helios/commissies.php#kas (Jaap)

Here is Loll homepage:
http://www.phys.uu.nl/~loll/Web/title/title.html

A clear brief non-technical description of CDT approach, written by Loll for general audience is here
http://www.phys.uu.nl/~loll/Web/research/research.html

CDT coverage in press here:
http://www.phys.uu.nl/~loll/Web/press/press.html

A commissioned general audience article on CDT, in English, is expected to appear in the forthcoming issue of Contemporary Physics
and should be listed here when it comes out
http://www.ingentaconnect.com/content/tandf/tcph
(unless the publisher is forgetting to update the website)

 

[marcus]

we still have a scarcity of popular English-language media coverage of triangulations gravity, compared with what's available in Dutch and German. So I translate general audience science journalism stuff sometimes.

Here is this popular Austrian magazine article from November 2004
http://science.orf.at/science/news/130119

As for the brow-level (hi-brow, middle, low-brow) get a load of this
http://orf.at/
it definitely looks Cross-section Austrian to me---sports, politics, celebrities, photomodels, online lottery, advertisments

And yet in their science section
http://science.orf.at/science/
which looks mass-audience enough
they had this thing about CDT last november.

what did Americans know about CDT last november?
Well maybe we will catch up. Something in newsweek? or the NYT? I didnt see it yet.

Anyway, I better translate at least a sample from this Austrian magazine article---anybody who wants to help, please do. Just post a chunk and I will merge it in with mine.

 

[marcus]

Here is a short exerpt from the article by Robert Czepel, 11 November 2004, for ORF.at "World of Science" section, as a sample of CDT coverage in Austrian popular press. I will just translate the beginning paragraphs:
http://science.orf.at/science/news/130119

HOW TO BUILD A FOUR-DIMENSIONAL UNIVERSE

With the help of so-called Quantum Gravity, physics researchers are trying to bring the large and small alike under one roof. ["under one hat", as the hat-loving Austrians like to say]. Until now this effort has been flawed, in that the theory could not explain why the universe's spacetime exhibits exactly four dimensions. Three physicists have now, with the help of Quantum Gravity, been able for the first time to establish why that is so.

A team led by Renate Loll at the University of Utrecht has succeeded in this by integrating a simple principle of cause and effect into the equations of the model. In the medium-scale world of everyday life, it is hardly a surprise that events have causes. But applied to the model of Quantum Gravity, this principle frankly works wonders.

CAUSALITY - A DISCOVERY?

Is causality an inherent property of our universe, or only an illusion which emerges from how we interpret the world?

The Scotish philospher David Hume proposed the latter view. In his opinion, we can never do more than merely observe that two events A and B regularly follow one another, and cannot say why the cause A leads to the result B.

According to Hume's sceptical interpretation the notion of causality is an invention of our minds, which has no counterpart expressed in the real world.

[Czepel has a link to an online encylopedia of philosophy here]

LARGE AND SMALL IN A SINGLE THEORY

A current study by the three physicists comes close to suggesting that Hume might just have been a little too skeptical. Renate Loll at the University of Utrecht, together with two collaborators, has designed a model which describes space and time as an assemblage of extremely small quantum particles.

[this is not quite true but Czepel is a journalist]

This is already of considerable interest because the principles of large scale physics (General Relativity Theory) on the one hand, and small scale physics (Quantum Mechanics) on the other, have until now scarcely been brought under one roof.

The two theories, although both well verified by experiment, do not immediately let themselves be "married"---that is, combined in a single coherent theoretical concept...

...
...
[there is lots more in case anyone else is curious, or wants to translate it for us.)

 

[marcus]

Last update was 8 august, time to update again

At the July Paris ("Einstein Century") conference Stefan Zohren presented a Loll-Westra-Zohren paper about "sum over topologies"---how to incorporate topology change into the nonperturbative quantum gravity path integral. Here's a snapshot of Stefan

[PLAIN]http://www1.phys.uu.nl/wwwitf/fotopagina's/Studenten/Stefan%20Zohren.htm[/URL] [/PLAIN]

there has been some delay in posting the schedule for October's Loops 05 conference. It should eventually appear at this site:
http://loops05.aei.mpg.de/
possibly at this page
http://loops05.aei.mpg.de/index_files/Programme.html

These are CDT papers that have come out in the past 12 months.
http://arxiv.org/find/grp_physics/1...gravity+AND+Lorentzian+quantum/0/1/0/past/0/1

There is a paper in the works by Loll with Dario Benedetti and Francesco Zamponi. I would like to see another from Loll/Dittrich on Black Holes but I don't know of one in the works, and it would be exciting to get a new paper from Loll/Westra about sum-over-topologies.

This thread, Quantum Grafitti, is mainly about the people doing Loll-type quantum gravity, with random news and gossip. To get an idea of the CDT (Causal Dynamical Triangulations) scene check out Loll's website at the Uni Utrecht in Holland. Here is a list of Loll graduate students/postdocs:

http://www.phys.uu.nl/~loll/Web/students/students.html

Here are some snapshots mostly from the Utrecht Inst. of Theor. Physics:

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Renate.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Willem1.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Dario.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Johan.jpg

http://www.phys.uu.nl/~helios/commissies.php#kas (Jaap)

[PLAIN]http://www1.phys.uu.nl/wwwitf/fotopagina's/Studenten/Stefan%20Zohren.htm[/URL] [/PLAIN]

here is the whole staff of the Utrecht ITP (inst. theor. phys.) where Loll and co-workers and students are based.
http://www1.phys.uu.nl/wwwitf/Members/members.staff.htm

Here is Loll homepage:
http://www.phys.uu.nl/~loll/Web/title/title.html

A clear brief non-technical description of CDT approach, written by Loll for general audience is here
http://www.phys.uu.nl/~loll/Web/research/research.html

CDT coverage in press here:
http://www.phys.uu.nl/~loll/Web/press/press.html

A commissioned general audience article on CDT, in English, is expected to appear in a forthcoming issue of Contemporary Physics
and should eventually be listed here
http://www.ingentaconnect.com/content/tandf/tcph

We have a PF a thread polling people's predictions about whether the QG path integral including sum over topologies will prove extendable from the 2D case up to 3D and 4D. the thread is here:
https://www.physicsforums.com/showthread.php?t=81626

 

[marcus]

this thread is to keep track of the news/current events/essential links about Loll triangle gravity. (CDT path integral)
see preceding post for basix

something interesting I just became aware of:

people who have been watching CDT (since that April 2004 paper) know that one of the surprises is that microscopically the CDT spacetime continuum has this "fractal-like" highly non-classical stucture with dimensionality going down steadily from macro 4D down to 3.5 down to 2.9 etc etc down to (at very small scale) sort of 1.9 to 2.1----roughly 2D.

this is measured by creating a spacetime by Monty Sims in the computer and then RUNNING A RANDOM WALK DIFFUSION PROCESS in that spacetime
the dimension you measure that way is called the "spectral" dimension.
to distinguish it from the "hausdorff" dimension that you measure by comparing radius and volume.

this business is summarized in the paper I've had in my sig for much of this year:
http://arxiv.org/hep-th/0505154
and also in this other short paper http://arxiv.org/hep-th/0505113

So probably others, I for one at least, were thinking it was pretty weird that Loll gravity has a fractally wrinkly feathery kinky smallscale spacetime structure.

the thing about it is that with Loll gravity you DON'T PRESUPPOSE HOW SPACETIME IS GOING TO LOOK, you set up a dynamic action principle of how little spacetime chunks arrange themselves together and stick together and LET IT RUN and SEE what kind of continuum comes out, whatever comes out that's it, and if it doesn't look and act like our space macroscopically, then you did something wrong.

so you can't be sure you are going to get a nice smooth spacetime or even something that is four dimensional! for some 10 years they were trying to do this and the dimension kept coming out really wrong. But now by the grace of nature and the coolness of Renate Loll you do get something that is largescale 4D. however as we learned earlier this year, it is kinky at microscopic scale

OK NOW SOMEONE USING AN ENTIRELY DIFFERENT APPROACH at the University of Mainz, a guy named Martin Reuter HAS ALSO FOUND A KINKY FRACTALLY MICROSCOPIC STRUCTURE

he is coming from an entirely different direction and he says he has "MADE CONTACT" with Loll results.

so I am paying attention to this and emphasizing it. I think it could be significant.
Here is Martin Reuter paper that came out today. I already put it on the Rovelli thread

http://www.arxiv.org/abs/hep-th/0508202
Fractal Spacetime Structure in Asymptotically Safe Gravity
O. Lauscher, M. Reuter
20 pages

"Four-dimensional Quantum Einstein Gravity (QEG) is likely to be an asymptotically safe theory which is applicable at arbitrarily small distance scales. On sub-Planckian distances it predicts that spacetime is a fractal with an effective dimensionality of 2. The original argument leading to this result was based upon the anomalous dimension of Newton's constant. In the present paper we demonstrate that also the spectral dimension equals 2 microscopically, while it is equal to 4 on macroscopic scales. This result is an exact consequence of asymptotic safety and does not rely on any truncation. Contact is made with recent Monte Carlo simulations."

Reuter approach is so different that the fact that the two approaches CONVERGE and actually AGREE on something makes me wonder if maybe in some sense REAL spacetime continuum could be micro-fractally, and only have the illusion at large scale, that we see, of having 4 nice dimension

in other words wondering if maybe it is not just the MODEL but the actual real continuum that is like this---but what that could mean is a relational thing. spacetime is the web of spatial relations and causalities among things and for it to be microfractally must have to do with how things can relate to each other at very close quarters---how they can be on top of each other and beside and between and inside and around, but at very small scale. these possibilities of relationship ARE space. and if Loll and Reuter picture is true (which would be pretty surprising because physics theories turn out so often to be false) then these possibilities of relation would have to be DIFFERENT at very small scale than over larger reaches.
well it is a lot of stuff to be puzzled with.

 

[arivero]

The original argument leading to this result was based upon the anomalous dimension of Newton's constant.

Yep, this makes such kind of results intuitive. G is an area, as Fermi constant. All the others are adimensional.

 

[Sam Owen]

What is meant by spacetime is a fractal, fractal like or has a kinky fractally structure ?

I know what a fractal is and what they look like, so is it an appearance of fracticality or actually fractal and does the reductablity of the pattern ever stop at a cut off volume ?

also how does one get half a spatial dimension or half a temporal dimension surely a half is still a whole when talking of dimensions ?

 

[marcus]

In her papers (like e.g. http://arxiv.org/hep-th/0505154 and the earlier http://arxiv.org/hep-th/0505113 ) Loll says "fractal-like". and "evidence of a fractal structure" --- she never says that spacetime actually turns out to BE a fractal. I think she is speaking more carefully than Reuter---who says his picture predicts that at small scales it IS a fractal. I think he is using word in a more general sense or just being careless. but I do not know reuter work at all well, so cannot be sure. Let us assume that he also means "fractal-like"

I am starting an auxilliary thread to talk about what fractal-like
versus just plain "fractal"
could mean. That way, discussing what is a fractal or what it means to say something is "like a fractal" will not gum up this CDT news-and-gossip thread.

Here is the auxilliary thread
https://www.physicsforums.com/showthread.php?t=86751

I hope it helps get some answers about what is means to not actually be a fractal but to be "like a fractal".

 

[marcus]

Hanno Sahlmann (the Sahlmann algebra is basic in LQG) is now a postdoc at Utrecht ITP
http://www1.phys.uu.nl/wwwitf/fotopagina's/Medewerkers/Hanno.htm
(earlier he was at AEI-Potsdam and at Penn State, if I remember correctly.
Here is Hanno's Penn State webpage:
http://cgpg.gravity.psu.edu/people/igpg_hsahlmann.shtml )

Sergei Alexandrov is at Utrecht as well. He has done both string and LQG research. Some of his LQG research was with Etera Livine (now at Perimeter). Sergei Alexandrov used to be at Paris. after PhD he came to Utrecht.
http://www1.phys.uu.nl/wwwitf/fotopagina's/Medewerkers/Serguei.htm

Utrecht has a capability in at least 3 kinds of quantum gravity research: string, LQG and CDT (Renate Loll's specialty). this is interesting because not very many places have this kind of diversity.


Stephon Alexander is now faculty in Abhay Ashtekar's department at Penn State (he was a postdoc at SLAC-Stanford)

 

[marcus]

because of Fall term changes, here's a CDT update:

schedule for October's Loops 05 conference should eventually appear here:
http://loops05.aei.mpg.de/

These are CDT papers that have come out in the past 12 months.
http://arxiv.org/find/grp_physics/1...gravity+AND+Lorentzian+quantum/0/1/0/past/0/1

I believe there is a paper in the works by Loll with Dario Benedetti and Francesco Zamponi.

http://www.phys.uu.nl/~loll/Web/students/students.html

Here are some snapshots mostly from the Utrecht Inst. of Theor. Physics:

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Renate.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Willem1.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Dario.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Johan.jpg

http://www.phys.uu.nl/~helios/commissies.php#kas (Jaap)

http://www.phys.uu.nl/~0404985/ (Stefan Zohren, alt. at Aachen)

here is the whole staff of the Utrecht ITP (inst. theor. phys.) where Loll and co-workers and many of her students are based.
http://www1.phys.uu.nl/wwwitf/Members/members.staff.htm

Here is Loll homepage:
http://www.phys.uu.nl/~loll/Web/title/title.html

A clear brief non-technical description of CDT approach, written by Loll for general audience is here
http://www.phys.uu.nl/~loll/Web/research/research.html

An excellent survey article for wide audience ("The Universe from Scratch") is here
http://arxiv.org/hep-th/0509010

CDT coverage in press here:
http://www.phys.uu.nl/~loll/Web/press/press.html

We have a PF a thread polling people's predictions about whether the QG path integral including sum over topologies will prove extendable from the 2D case up to 3D and 4D. the thread is here:
https://www.physicsforums.com/showthread.php?t=81626

It is interesting that Hanno Sahlmann is now listed as postdoc at Utrecht. Here is his earlier web page, describing his research interests, with sketches of ideas, from when he was at Penn State:
http://cgpg.gravity.psu.edu/people/igpg_hsahlmann.shtml .

 

[marcus]

...It is interesting that Hanno Sahlmann is now listed as postdoc at Utrecht. Here is his earlier web page, describing his research interests, with sketches of ideas, from when he was at Penn State:
http://cgpg.gravity.psu.edu/people/igpg_hsahlmann.shtml .

Hanno Sahlmann postdoc is working for Loll (!)

http://www.phys.uu.nl/~loll/Web/group/group.html

 

[marcus]

it looks like one of the best available LQG postdocs has just crossed the border over into CDT. I do not think this is bad luck for LQG, on the contrary it could be good luck.


hanno casts a wide net of ideas. the LQG uniqueness theorem associated with Lewandowski Okolow Sahlmann Thiemann actually started out with two solo papers by Hanno.

then it was picked up by Lewandowski Okolow (who called the algebra the "Sahlmann algebra") and carried further by them and by Sahlmann-Thiemann collaboration. So he is able to work at an efficient level of abstraction and connect the dots. It seems exciting to me that hanno should decide to work postdoc with Loll. things could come of it that one didn't expect. I don't want to say that he might see a connection between some variant of LQG-spinfoam and CDT because maybe that is the wrong idea to be thinking. but something valuable is likely to come from his crossing the border. I think it is a lucky move, him going to work with Loll!



OTHER NEWS BIANCA DITTRICH HAS JUST MOVED FROM POTSDAM TO PERIMETER

if she decides to do some CDT while she's there it will make a stronger CDT presence at Perimeter.

 

[marcus]

Frank Saueressig is also at Utrecht

an interesting group of people is assembled at Utrecht (at the ITP and the Spinoza Institute there)

Sahlmann has been giving seminars about LQG
and Saueressig about (Reuter asympt. safe) QEG

Saueressig was at Mainz working with Reuter in 2001, for instance
http://www.arxiv.org/abs/hep-th/0110054
Renormalization Group Flow of Quantum Gravity in the Einstein-Hilbert Truncation
M. Reuter, F. Saueressig
58 pages, 24 figures
Phys.Rev. D65 (2002)

mostly by cleverness, I suppose, the Utrecht people have assembled a Quantum Gravity group that is strong in LQG/CDT/QEG
It would be difficult to do it just by spending money.

In 2002 Saueressig went to Jena, in 2003 he was still collaborating with Reuter:
http://www.arxiv.org/abs/hep-th/0311056
Nonlocal Quantum Gravity and the Size of the Universe
M. Reuter, F. Saueressig

In spring 2004 he was still at Jena, and doing some string papers with Thomas Mohaupt, but in fall 2004 he was already at Utrecht.

some science historian could someday write how this Utrecht combination was assembled (if they get results) and by what chain of decisions.

Here are recent seminar talks there:
http://www1.phys.uu.nl/wwwitf/Seminars/seminars.html
http://www1.phys.uu.nl/spinoza/seminars.html
http://www1.phys.uu.nl/spinoza/seminars/Grafiti.html

especially in this last link notice 12 Sept Renormalization Group improved cosmologies: no strings attached by Frank Saueressig, and two seminars on Loop Quantum Gravity on 19 Sept and 26 Sept given by Hanno Sahlmann Loop Quantum Gravity, an (un-)conventional QFT

You see also that Bojowald spoke in March, and Kiril Krasnov in April, and Renate Loll in June (Kiril Krasnov, of Nottingham, does Laurent Freidel type stuff---more or less simultaneous with Freidel)

So if Loll wants to talk to someone about QEG and fractally smallscale structure of spacetime, she does not have to email Reuter at Mainz, she can just walk down the hall to Saueressig. If there is any new development in LQG, Sahlmann can tell her about it. very good place. I will get a picture of Frank Saueressig to help thicken the soup.

 

[marcus]

Here is Frank Saueressig 12 September talk abstract:

Renormalization Group improved cosmologies: no strings attached

"It is generally believed that in the very early universe, at times smaller than the Planck time, quantum gravity effects play a crucial role. Since the physics in the Planck era prepares the initial conditions for the subsequent classical evolution of the universe it is desirable to gain some understanding of the quantum gravitational processes which took place immediately after the Big Bang. Based on the Einstein-Hilbert approximation of asymptotically safe quantum gravity we discuss a consistent renormalization group based framework which allows for the inclusion of such quantum gravitational effects into the cosmological field equations and applies to all stages of the cosmological evolution. The very early universe is found to contain a period of "oscillatory inflation". Later on the cosmological evolution is classical and asymptotes to a de Sitter era at cosmologically late times."


Here is a snapshot:
http://www1.phys.uu.nl/spinoza/members/Frank.htm

 

[marcus]

More Utrecht gossip:

Abhay Ashtekar will be teaching a course there Spring 2006 term.
http://www1.phys.uu.nl/wwwitf/courses/main.htm

It is a regular course for credit, with exam. Now is fall semester which runs thru the first week of January. So he is teaching NEXT semester which goes
February--June 2005

The course is Black holes in fundamental physics
lectures are Wednesday 9-11, with a tutorial on Monday.
A course description is available at the above link.

what intelligence is getting all these people together? As I said earlier, I don't think you could do it with just money---no matter how well funded Harvard or Princeton are, I don't think they are currently in position to assemble such a group. Or Stanford or UCSB-Kavli. What good is cash if you hire the wrong people? It is good luck for the graduate students at Utrecht---they can see several paths to QG where progress is being made and there are suggestions of convergence.

 

[Timbuqtu]

It's good to hear such positive things about Utrecht. I'm one of the students who enrolled in the Master's programme in Theoretical Physics in Utrecht this year. And I really enjoy the courses taught at the moment (QFT, Statistical Field Theory, GR) and I'm looking forward to next semester's courses (Cosmology, String, Black holes, Standard model, etc.). Certainly I will attend Ashtekar's course next semester.

Keep up the good work, Marcus! Your announcements are really useful.

 

[marcus]

.. And I really enjoy the courses taught at the moment (QFT, Statistical Field Theory, GR) :

interesting, if you go to GR lecture at 9 Thursday morning then you may be hearing classical GR from someone who has an idea of what could replace it.

 

[Spin_Network]

I would give anything to get into the lecture by :prof. dr.ir. P. Grassberger,:NS-TP450M: Kramers course: Phase transitions and anomalous scaling in non-equilibrium systems

then:NS-TP453M: Soft condensed matter theory:lecturer : dr. R.H.H.G. van Roij,

Great place to be!

 

[marcus]

Timbuqtu, I have a suggestion for you
the October 10-14 conference at potsdam could be historically significant
it might IMHO be of interest to you later to have been there and seen it.
I suggest you consider doing this:
go to Loll, or Westra and say "can you get me in as an observer to this conference? I know the registration is past, but i think it might be
a memorable conference and I would like to have seen it. would that work?"
http://loops05.aei.mpg.de

 

[marcus]

Perimeter is inviting applications for postdoc positions for 2006
http://www.perimeterinstitute.ca/index.php?lang=en
application must be done online (they supply a link)
and the deadline---in November 2005---will be extended until
all positions are filled.

 

[Timbuqtu]

interesting, if you go to GR lecture at 9 Thursday morning then you may be hearing classical GR from someone who has an idea of what could replace it.

It is interesting . But let me ask you something else: can you imagine Gerard 't Hooft, being one of the big string opponents, teached String theory for couple of years (until 2003/2004) here?

Timbuqtu, I have a suggestion for you
the October 10-14 conference at potsdam could be historically significant
it might IMHO be of interest to you later to have been there and seen it.
I suggest you consider doing this:
go to Loll, or Westra and say "can you get me in as an observer to this conference? I know the registration is past, but i think it might be
a memorable conference and I would like to have seen it. would that work?"
http://loops05.aei.mpg.de

Probably it's too late now (Potsdam is not exactly around the corner). But there will be enough oppurtunaties to see (some of) these people around here I think. And I guess I wouldn't understand a lot of what they are saying. But it sure must be impressive to see all these guys together.

 

[marcus]

It is interesting . But let me ask you something else: can you imagine Gerard 't Hooft, being one of the big string opponents, teached String theory for couple of years (until 2003/2004) here?

Yes Timbuqtu!
I think Gerard 't Hooft should be the perfect person to teach a course about String ideas.

I think that to all approaches to bring quantum physics together with GR he would be encouraging them to do their best. but I think he is also realistic and I like the quote where he is explaining that String ideas are not yet a Theory----that there is so far no scientific theory called String Theory, that makes predictions by which it can be tested---and he says in his book In Search of the Ultimate Building Blocks:

Actually, I would not even be prepared to call string theory a “theory” rather a “model” or not even that: just a hunch. After all, a theory should come together with instructions on how to deal with it to identify the things one wishes to describe, in our case the elementary particles, and one should, at least in principle, be able to formulate the rules for calculating the properties of these particles, and how to make new predictions for them. Imagine that I give you a chair, while explaining that the legs are still missing, and that the seat, back and armrest will perhaps be delivered soon; whatever I did give you, can I still call it a chair?


https://www.physicsforums.com/showthread.php?p=755232#post755232

https://www.physicsforums.com/showthread.php?p=761411#post761411

My impression of 't Hooft (please tell me if I am way off the mark) is that he wants people to get a quantum theory of spacetime, AND HE DOES NOT CARE WHO, OR HOW, OR BY WHAT METHOD IT COMES. So he is not protecting the interest or prestige of this method or that method, or the authority of this person or that person. I like to imagine that 't Hooft says to all the methods "go for it! go get 'em". And if this is his attitude and also the attitude of De Wit, then those people stand a good chance.]

 

[marcus]

here is a general question to anybody

Renate Loll has a new snapshot of herself at her website

http://www.phys.uu.nl/~loll/Web/title/title.html

and she is holding a doll.

Identify this doll.

 

[Kalimaa23]

Isn't that the Einstein action figure they realized for the 2005 World Year of Physics?

 

[marcus]

Isn't that the Einstein action figure they realized for the 2005 World Year of Physics?

Thank you Dimitri! Stupid me, I could tell it was Einstein but I didn't know there was an Official Horrible Taste Kitsch doll created especially for the World Year of Physics. what will they think of next.

 

[marcus]

this photo troubles me

maybe it is a good photo. what do you think? anybody.

what I see in the person at that moment is a mixture of
dignity and impudence

and maybe the picture is iconic, or symbolic of a true relationship, that already at this moment we (in combination with her) hold Gen Rel in the palm of a new model.
and that Gen Rel is the artifact of the quantum theory we watch developing

 

[selfAdjoint]

Seems more like the chip on her shoulder is aimed out at the viewer rather than at the Einstein doll. Like "Yes, I have an Einstein doll. You want to make something of it?"

 

[Spin_Network]

this photo troubles me

maybe it is a good photo. what do you think? anybody.

what I see in the person at that moment is a mixture of
dignity and impudence

and maybe the picture is iconic, or symbolic of a true relationship, that already at this moment we (in combination with her) hold Gen Rel in the palm of a new model.
and that Gen Rel is the artifact of the quantum theory we watch developing

The photographer ( likes to put something "extra" into his images, for instance here:http://www.fjodor.nl/manipulation_mariecarmenoudendijk_gb.html

His webpage here:http://www.fjodor.nl/biografie_gb.html

I do not think Loll would have just picked up the Doll,that was just laying around in the room she was having her picture taken, and holding Einstein thus?

She is reaching out to Einstein?..Holding Einsten in the palm of her hand?..or just simply, she is holding out a "model of Einstein", wherby she is symbolically an "extension" of Einstein?

 

[marcus]

She is reaching out to Einstein?..Holding Einsten in the palm of her hand?..?

her theory, CDT, is aimed at comprehending and containing Einstein Gen Rel. if it were right then she would be the "super-Albert"

and CDT would provide a dynamical principle by which spacetime operates at very very small scale
and this quantum dynamical principle, by operating everywhere at very small scale, would GIVE RISE at large scale to the behavior described by the Einstein equation of general relativity.

so Gen Rel would come out of Loll CDT as a large scale limit.

you know this Spin_N, I just want to have it explicitly said. this is what CDT aims to do. It aims to have a micro-scale dynamic principle that DOES NOT EVEN ASSUME THAT THE MACRO-SPACETIME IS FOUR DIMENSIONAL. Even something as basic as the dimensionality is supposed to arise from the working of a simple Planckscale mechanism.

So if one can make CDT work, then one "explains" Einstein Gen Rel. One has a model that can reproduce it from something simpler and more basic.

the photo concept, symbolism (even tho daring), layout and composition is OK, what bothers me is the absurdist streak of the photographer, because the doll is such a Barby caricature of Einstein. But I am gradually getting over the shock and will be all right soon

 

[Spin_Network]

her theory, CDT, is aimed at comprehending and containing Einstein Gen Rel. if it were right then she would be the "super-Albert"

and CDT would provide a dynamical principle by which spacetime operates at very very small scale
and this quantum dynamical principle, by operating everywhere at very small scale, would GIVE RISE at large scale to the behavior described by the Einstein equation of general relativity.

so Gen Rel would come out of Loll CDT as a large scale limit.

you know this Spin_N, I just want to have it explicitly said. this is what CDT aims to do. It aims to have a micro-scale dynamic principle that DOES NOT EVEN ASSUME THAT THE MACRO-SPACETIME IS FOUR DIMENSIONAL. Even something as basic as the dimensionality is supposed to arise from the working of a simple Planckscale mechanism.

So if one can make CDT work, then one "explains" Einstein Gen Rel. One has a model that can reproduce it from something simpler and more basic.

the photo concept, symbolism (even tho daring), layout and composition is OK, what bothers me is the absurdist streak of the photographer, because the doll is such a Barby caricature of Einstein. But I am gradually getting over the shock and will be all right soon

Marcus, I left the reply for a while hoping that you would re-look at the Loll/Einstein MODEL picture?

Take another look?...what do you see?..specifically, what pose/stance is the Einstein Model Loll is holding in?..look really closely!

Scale Model

 

[marcus]

...

Scale Model

maybe I understand you Spin_N. if you had been the photographer then the Albert doll would have his left hand extended palm up supporting a tiny figure of Newton. and Newton would have been in a similar stance...

well, here is the link, in case anyone else is curious
http://www.phys.uu.nl/~loll/Web/title/title.html