# Solvay on Spacetime Quantum Structure (1 Viewer)

### Users Who Are Viewing This Thread (Users: 0, Guests: 1)

#### marcus

Gold Member
Dearly Missed
23rd Solvay Conference is 1-3 December 2005 in Brussels and the official title is The Quantum Structure of Space and Time
The unofficial theme could be "Look who didn't get invited!".
Who might have something new to say about the emergence of 4D spacetime? (Loll maybe? Nope, not there. landscapers instead.)
Who might legitimately have something to say about quantum cosmology? (Bojowald there? Nope. stringy-vacua-inflation-landscapers instead.)
The organizers were short-sighted. In the long run it won't help to shut the new approaches out.
Code:
Opening (Henneaux, Gross)
Day 1  Morning: History (Henneaux chair, Galison)
-               Quantum Mechanics (Gross, Hartle, 't Hooft)
Day 1 Afternoon: Singularities (Horowitz chair, Gibbons, Ashtekar,
-               Damour, Shenker, Silverstein, Turok)
Day 2 Morning: Mathematical Structures (Ooguri chair, Dijkgraaf, Atiyah,
-               Douglas, Kallosh, Nekrasov, Nicolai, Strominger, Yau)
Day 3 Morning: Emergent Spacetime (Harvey chair, Seiberg, Banks,
-               Klebanov, Maldacena, Polyakov)
Day 3 Afternoon: Cosmology (Shenker chair, Polchinski, Banks, Guth,
-               Kachru, Kallosh, Linde, Steinhardt, Weinberg)
Concluding remarks (Gross)
My wild guess is that there will be a moment in the proceedings when someone who understand the situation, say Hermann Nicolai, or Andy Strominger, or Gerard 't Hooft, will wonder why some people are not present. Like, are we doing science? Or is this a prestige pie-eating party where the important thing is how we slice the prestige pie?

Here's the Scientific Program for December 1-3
http://tena4.vub.ac.be/23Solvay/qsst/18-11-2005ScientificProgramme.pdf [Broken]

The Public Program for December 4 is something else.
http://europa.eu.int/comm/research/conferences/2005/solvay/pdf/progr_en.pdf [Broken]
http://europa.eu.int/comm/research/conferences/2005/solvay/index_en.htm [Broken]

Last edited by a moderator:

#### marcus

Gold Member
Dearly Missed
just for contrast, this past weekend there was a workshop at Perimeter called Emergence of Spacetime
http://perimeterinstitute.ca/activities/scientific/PI-WORK-5/schedule.php [Broken]
Let's compare programs.
==============================
Workshop on Emergence of Spacetime
November 18 - 20, 2005

Friday: Talks

11:00 Grigori Volovik Momentum-space topology and universality classes of quantum vacua
11:40 Renate Loll Emergence of quantum spacetime from causal dynamical triangulations
12:20 Lunch
1:20 Xiao-Gang Wen An origin of light and electrons -- a unification of gauge interaction and Fermi statistics
2:00 Fotini Markopoulou Error free quantum gravity
2:40 Peter Horava Emergent Spacetime in Noncritical String and M-Theory
3:20 Break
4:15 Seth Lloyd Computing the universe.

Saturday: Discussions

9-12 Quantum gravity approaches, including causal dynamical triangulations, spin foams and strings.
12:30-1:30 Lunch
1-3 Condensed matter and statistical physics approaches
3-5 Quantum information approaches
5-6 Comparisons of approaches

Sunday: Continuing discussions

9-12 Common issues, including the role of time and the emergence of diffeomorphism invariance.
12-1 Lunch
1-5 Discussion to be determined by participants.
============================

all the talks are available online
http://streamer.perimeterinstitute.ca:81/mediasite/viewer/FrontEnd/Front.aspx?&shouldResize=False

or go to
http://streamer.perimeterinstitute.ca:81/mediasite/viewer/
and click on "Emergence of Spacetime Workshop" in the sidebar menu.

Last edited by a moderator:

#### pelastration

##### multi-layered spacetime
The Brussels conference seems to be sponsored by the European Commission: http://europa.eu.int/comm/research/conferences/2005/solvay/index_en.htm [Broken] .
From the European site:
The Solvay Conference opens its doors to the public!
Indeed, a half-day public event will follow the 23rd Solvay Conference in Physics which will take place in Brussels from 1 to 3 December.
During this afternoon, you will have the possibility to follow the talks given by the famous scientists Robbert Dijkgraaf and Brian Greene on major topics in physics, to meet the Nobel Prize laureates David Gross (2004) and Gerard ’t Hooft (1999) as well as other participants in the 2005 Solvay Conference, and to ask them your questions about the Universe.
* Registration
If you wish to participate in the conference, please register using the form.

Last edited by a moderator:

#### marcus

Gold Member
Dearly Missed
to re-emphasize: real conf is 1-3 and they say explicitly is by invitation only.
very exclusive event.
the public fare on the 4th is popularization, like a talk by Brian Greene on "the Fabric of the Cosmos". usual entertainment.
Robert Dijkgraaf is giving talk with same title as the Public Lecture he gave in Toronto this summer-----recorded talk and slides are already available on line at the Strings '05 website. You can download and watch Dijkgraaf talk ahead of time, and then go hear him live, if you happen to be in Brussels. Nifty graphics, not a lot of content.

the title of his June talk in toronto was something like "Strings black holes and the end of space and time"

Last edited:

#### kleinwolf

marcus do you want to point out that it's like in other systems : even science has it's sort of political internal system...something "the chosen ones"....(in fact I don't know if we choose or if it is a kind of fight...from the "do you know why x is not here....?" we could expect sometimes there should exist like electricity, but we should remain careful because sometimes there are less living reasons...)

Last edited:

#### pelastration

##### multi-layered spacetime
Dimitri Terryn said:
Sorry Dimitri!
There seems to be also an interesting webcast event Dec. 1, 2005. http://beyond-einstein.web.cern.ch/beyond-einstein [Broken]

Last edited by a moderator:

#### marcus

Gold Member
Dearly Missed
kleinwolf said:
... even science has it's sort of political internal system...
whatever happens, let's see if it shows us something. What can we learn from this?

We know there is "politics" in science and that it is a self-selecting self-regulating elite system----this is not news. I like the way the basic system operates very much and cannot imagine a better one. Although it does have problems with how it is supported and the interface with government----funding agencies can be taken over by cliques and so on---it isnt perfect.

We know these things, and we still expect wisdom and clear vision in the leaders. We expect that since they are human they will sometimes play prestige games and grantmanship games and media-showmanship and sometimes struggle to control the funding----sometimes---because they have egos like everyone else. But individual leaders should also have vision and be able to act for the long-term good of science.

Even a Nobel laureate can lack vision and can fail at furthering the long-term good. We have to watch and notice the differences in leadership style. The elite is NOT MONOLITHIC. The outcome could have been different depending on who chaired the organizing committee.

This year there were several big conferences like this. For instance the Einstein Century Conference in Paris, where the scientific meeting lasted a week IIRC and there was a lot of demos and lectures for the public. Much the same TOPICS (spacetime structure) but a very different lineup----broader mix of approaches.

And for example Loll's group was represented. They had a bunch of talks on the emergence of spacetime---but not dominated by any one approach, like string. It was a comparable conference but organized MORE INCLUSIVELY of different approaches to quantizing Einstein's model of spacetime.

So it doesn't have to turn out the way this 23rd Solvay did. For instance if they had given Gerard 't Hooft the job of organizing a "Quantum Structure of Spacetime" conference for this occasion they would have gotten a very different lineup.

't Hooft was involved but it looks like in this case David Gross had the main power---and he used it in a fairly exclusive way. So the 23rd Solvay is a showcase triumph of a certain camp even within string theorists. So far I am just guessing---havent had time to figure out for sure----just saw the program yesterday. First impressions, anyway, since you asked.

I think the outcome is peculiar and so I want to focus attention and learn what I can from it. This 23rd Solvay looks more narrow in its string composition, than this year's main international string conference. I don't yet know what to think about this, but it's interesting to watch!

Yeah Kleinwolf, thanks for asking about the politics issue. Let's see what we can figure out.

Have to go, back later.

Last edited:

Gold Member

#### marcus

Gold Member
Dearly Missed
arivero said:
Some solvay talks are now in the arxiv. to quote a pair:

http://arxiv.org/abs/hep-th/0602011
Beyond Space-Time
A. M. Polyakov

http://arxiv.org/abs/hep-th/0601234
Emergent Spacetime
Nathan Seiberg
thanks for alerting us to these!

Kea made a made a memorable comment about Seiberg's paper a few weeks back on Woit's blog. It was, I believe, the most definite and least mealymouth comment made on the blog that day, but I hesitate to quote.

#### hawk00321

DEAR MARCUS
What is the end of time and space? they will disappear in strings black holes? i can't imagine what happened in that moment,would u explain it for me ? thanks in advanced.
best wishes for u.

#### marcus

Gold Member
Dearly Missed
hawk00321 said:
DEAR MARCUS
What is the end of time and space? they will disappear in strings black holes? i can't imagine what happened in that moment,would u explain it for me ? thanks in advanced.
best wishes for u.
esteemed hawk, I have no idea! I heard Roger Penrose give a slide show talk a month or so ago where he seemed to have some idea, which in itself I found quite astonishing. I do not recommend his ideas, but I believe I can find his slides online at a Penn State website if you are curious.
If you want a taste of penrose very peculiar ideas about the end of time and space (which he think he has a mechanism how it starts over without having a crunch first) let me know and I will look for the slides and try to give a link.

#### hawk00321

dear marcus
we know the black hole has entropy, and we deal with it as the structure of time and space.so i have an idea :the structure of time and space has entropy intrinsicly.when the universe expand,space and time also expand,then the intrinsic entropy will increase.of course ,wo avoid the problem why the low entropy in the early universe. This is the pure geometric viewpiont .But how we deal with the black holes information-loss problem? that is ,black hole evaporated and the structure of time and space deflated.we have known the black hole's entropy is proportional with its square mass by Hawking and Bekenstein.
i am an learner in physics and have no further thoughts ,please piont out my mistakes.thank u very much!!
sincerely hawk.

Last edited:

#### Mike2

hawk00321 said:
dear marcus
we know the black hole has entropy, and we deal with it as the structure of time and space.so i have an idea :the structure of time and space has entropy intrinsicly.when the universe expand,space and time also expand,then the intrinsic entropy will increase.of course ,wo avoid the problem why the low entropy in the early universe. This is the pure geometric viewpiont .But how we deal with the black holes information-loss problem? that is ,black hole evaporated and the structure of time and space deflated.we have known the black hole's entropy is proportional with its square mass by Hawking and Bekenstein.
i am an learner in physics and have no further thoughts ,please piont out my mistakes.thank u very much!!
sincerely hawk.
Quantum gravity is the same as quantum geometry since gravity is described by a background metric which is also its geometry. Now if spacetime/gravity/geometry is quantized, then we have bits of spacetime curvature going this way and that - probably a QM superposition of all possibilities. You've hit on an idea I have also been recently considering.

Occassionally these bits of randomly directed metric curvature bits allign to form a line or loop or surface or closed surface or some other geometric shape which would be a membrane of some sort. It's probably more likely that small geometric shapes would spontaneously emerge than large. And I suppose it would be less probable that they survive for a longer time. In such a superposition, one can construct variously sized geometric objects. That would mean that the vacuum energy of the virtual particles is a manifestation of quantum spacetime, and visa versa.

I wonder if there is some conservation of information required of the universe as a whole, would more bits of spacetime be required to offset the increase of information accompanied by the emergence of these geometric shapes, so that the net information contain of the whole remains constant? This would mean that space expands precisely because particles emerge, and visa versa.

Might it be possible to calculate the number of spacetime quantum states that particle require by knowing the expansion rate and mass of the universe?

Last edited:

#### marcus

Gold Member
Dearly Missed
Mike, thanks for responding to hawk. I will leave it up to you to continue the discussion if Hawk wants, as desired.

Hawk, I don't know enough to reply. and I didnt understand you to make any mistakes which I could correct.

when people say "quantum structure of spacetime" I think they usually mean mostly SMALL SCALE structure------microscopic

cosmologists mostly deal with LARGE SCALE structure, including the ultimate fate of the universe
=======

both kinds of conversation can be extremely vague and speculative

I just attended this talk by Penrose, which he gave where I live and then later gave at Penn State. I found it very frustrating. I almost wish I had not gone to hear the talk. This is an example of what a brilliant creative human can say about the structure of spacetime at this moment in history.

http://www.phys.psu.edu/events/index.html?event_id=1386;event_type_ids=0;span=2005-12-26.2006-05-31 [Broken]

We have a long ways to go. There is an audio that goes with these slides which you can listen to. I dont recommend it but it is available. Good luck.
=======================

Hawk, For contrast you might want to look at two recent papers by Abhay Ashtekar et al which are part of a series called

Quantum Nature of the Big Bang

these are not so speculative, efforts are under way to derive testable conclusions and the models have been tried out in detail by a lot of people-----it does not deal with the overall quantum structure of all spacetime but focuses on the quantum structure of one very particular spacetime event, the transition from contraction to expansion------their model gives the classical answers at all times after the first fraction of a second from the beginning of expansion (it has the correct "classical limit") it only differs from the usual cosmology picture when you get very close to the beginning of expansion

http://arxiv.org/abs/gr-qc/0602086 (February 2006)
http://arxiv.org/abs/gr-qc/0604013 (April 2006)

Last edited by a moderator:

#### Mike2

Mike2 said:
Quantum gravity is the same as quantum geometry since gravity is described by a background metric which is also its geometry. Now if spacetime/gravity/geometry is quantized, then we have bits of spacetime curvature going this way and that - probably a QM superposition of all possibilities. You've hit on an idea I have also been recently considering.

Occassionally these bits of randomly directed metric curvature bits allign to form a line or loop or surface or closed surface or some other geometric shape which would be a membrane of some sort. It's probably more likely that small geometric shapes would spontaneously emerge than large. And I suppose it would be less probable that they survive for a longer time. In such a superposition, one can construct variously sized geometric objects. That would mean that the vacuum energy of the virtual particles is a manifestation of quantum spacetime, and visa versa.

I wonder if there is some conservation of information required of the universe as a whole, would more bits of spacetime be required to offset the increase of information accompanied by the emergence of these geometric shapes, so that the net information contain of the whole remains constant? This would mean that space expands precisely because particles emerge, and visa versa.

Might it be possible to calculate the number of spacetime quantum states that particle require by knowing the expansion rate and mass of the universe?
For example, if a particle consisted of 10 spacetime quantum geometry bits, how many total spacetime bits would it take to make this random emergence inevitable, have probability of 1?

#### hawk00321

dear mike
thank u very much
marcus said that structure of time and space is small scale in quantum theory.i consider that if we can make a small black hole in lab and we suppose it to survive for a longer time,how we detect it's entropy?somebody argue that entropy decrease in detected process in micro-system ,because the states reduced.

i am considering your thougts in these days .if the information is conservation in the whole universe,how we calculate it's change in the inflation process ? of course,we should accept big bang model and inflation model.

if a paticle consisted of 10 spacetime quantum geometry bits,maybe need more bits to make it ,i don't think that is unitary.but how we deal with antiparticles? The information conservation might break down as the matter and antimatter.how we get to it?

indeed, I am not sure......

#### Mike2

hawk00321 said:
dear mike
thank u very much
marcus said that structure of time and space is small scale in quantum theory.i consider that if we can make a small black hole in lab and we suppose it to survive for a longer time,how we detect it's entropy?somebody argue that entropy decrease in detected process in micro-system ,because the states reduced.

i am considering your thougts in these days .if the information is conservation in the whole universe,how we calculate it's change in the inflation process ? of course,we should accept big bang model and inflation model.

if a paticle consisted of 10 spacetime quantum geometry bits,maybe need more bits to make it ,i don't think that is unitary.but how we deal with antiparticles? The information conservation might break down as the matter and antimatter.how we get to it?

indeed, I am not sure......
I have no idea how all of it fits together, yet. I'm just going on the premise that spacetime is quantized, and that spacetime is more fundamental than particles, so that particles must emerge out of the more fundamental building block of quantum bits of spacetime.

But if I were to throw out some guesses, I'd say that perhaps matter is made of spacetime on negative curvature and antimater is made of positive curvature, or perhaps visa versa. Then at lower energies, since the universe would have started with a closed topology, it would have an overall negative curvature (or is it positive; I can't remember). That mean that there is not an exact symmetry between matter and antimatter so that antimatter would have collapsed.

What about electrodynamic and neuclear forces? Where do these forces come from? I speculate in this scenario that it is probably more efficient to bring particles together to reduce entropy than to form new particles, since all of it is considering the probability of forming structures in regions. Perhaps this has something to do with the other forces being so much stronger than gravity?

Last edited:

### The Physics Forums Way

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving