Video: The Problem of Time in Quantum Gravity and Cosmology

  1. marcus

    marcus 24,302
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    This could be good
    http://pirsa.org/08010033

    ==quote==
    PIRSA:08010033
    Title: Lecture 1 ( Windows Media , Macromedia Flash , MP3 Audio , PDF)
    Speaker(s): Lee Smolin
    Abstract: The Problem of Time in Quantum Gravity and Cosmology
    Date: 09/01/2008 - 7:00 pm
    Location: 405
    URL: http://pirsa.org/08010033/
    ==endquote==

    what i see coming out of both Loll's Triangulations gravity
    and Smolin's discovery of matter in the twists and braids of the geometry state (the spin network)
    is that both of these ways of representing the quantum state of geometry-matter EVOLVE BY LOCAL MOVES
    where the spinnetwork is locally rearranged, or the triangulation simplices (triangular building blocks) rearrange themselves
    and I see TIME becoming realized as the process of these local moves rearranging the state of geometry+matter
    (which are aspects of the same thing, same underlying degrees of freedom)

    have to go, back later
     
    Last edited: Jan 11, 2008
  2. jcsd
  3. Regardless of the choice of microstructure, this sounds principally very plausible to me and I like it.

    I think of time as a relative measure of distinguishable change, and the "direction of time" is thus related to the direction of expected change. If it's not possible to distinguish a asymmetric rating the direction of change, I think is similar to not be able to define time.

    This is how i personally imagine how the measure of the measure possibly diminishes in the domain where time is hard to define. So the loss of the arrow of time, is explained by a diminishing confidence measure of the time measure.

    /Fredrik
     
  4. marcus

    marcus 24,302
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    A practical question about time, as opposed to a theoretical one, is when do we expect the next lecture in this series?

    I believe on Wednesday 16 January, and the plan is for the lectures to be 3 hours, with a break, every Wednesday for the next few weeks.
     
  5. Here is an old 1997 paper from Smolin, but since he is doing the lecture on marcus link and this paper is relevant to the topic I thought it might be interesting to add. He makes some reflections in that paper.

    "A possible solution to the problem of time in quantum cosmology"
    http://arxiv.org/abs/gr-qc/9703026

    Edit: I personally think the conceptual reflections are very good in this 1997 paper of Smolin. I suspect it's good to read for anyone intending to follow the upcoming lectures. When I read his suggestions to resolution, I see that it is very close to my preferred thinking. He clothes it in other words, but the physical meaning are very similar.

    (I think this _strongly_ connects to the (somewhat diverged, but still) discussion in the CDT study group thread )

    /Fredrik
     
    Last edited: Jan 15, 2008
  6. In the mentioned paper, Smolin in the "conclusion" makes these excellent key reflections that are right on the money worth thinking about once of twice


    "If the configuration space or state space is not constructible, then it is not clear that the ergodic hypothesis is well defined or useful."

    Edit: Here is a paper with a historical perspective on the ergodic hypothesis, connecting to classical systems that might be worth skimming. http://library.lanl.gov/cgi-bin/getfile?00285754.pdf

    "What is then needed is a new approach to statistical physics based only on the evolving set of possibilities generated by the evolution from a given initial state."

    " Finally, we may note that there are other reasons to suppose that a quantum cosmological theory must incorporate some mechanisms analogous to the self-organization of complex systems"

    The second quote above is my favourite and I couldn't agree more.

    /Fredrik
     
    Last edited: Jan 15, 2008
  7. Marcus, I hope I'm not violating any unspoken rules again. if you want to keep this thread clean from discussion let me know! I thought that reflections of the topic of the course might be relevant here?

    I the light of the other thread, my question on Rovelli's book Quantum Gravity, and reflections that appear during reading Rovelli's words in the LQG summary from 1997, and combining that with some impression that Smolin and Rovelli once upon a time sort of worked in similar ideas... I start to wonder.

    I get the impression, especially from Rovelli's note that LQG does not address some unclear foundational issues of QM. Maybe I am reading too much out of Smolins comment above, but as I read his comment on the quest for new statistical physics, this does not seem to be in line with Rovelli's program.

    With the foundational issues of QM I'm not talking about restoring classical realism or consciousness issues. I mean the proper attachment to reality of the measure we call probability, that is well defined mathematically, but less so physically, and it's relation to bayesian vs frequentis interpretation, and the retention of measurement results? I personally have hard to see how this does NOT touch this topic? I thought this what was Smoling meant with his comment above?

    Does anyone know if Smolin and Rovelli had differing opinions in 1997?

    /Fredrik
     
  8. marcus

    marcus 24,302
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    I don't know. I will try to make sense of this and reply soon. But right now I want to say that the second lecture is available online. It was given 16 january but it takes a while for them to get it ready for download and put it out, so it showed up the next morning.

    http://pirsa.org/08010034

    In general if you want to look for PIRSA video lectures here's the link
    http://www.perimeterinstitute.ca/Scientific/Seminars/PIRSA/

    About Smolin and Rovelli they have different and in a sense complementary personalities. I have never noticed them to be in CONFLICT where one say A and one says NOT-A. But I have always seen them to be interested in different things and contributing differenty to the research effort.

    I don't know how much anyone can say about the opinions of a creative researcher, a stranger cannot look inside the mind. Unless it is in the special case where someone writes a review paper that survey's the field, like Rovelli's 1997, or his book.

    If it is not impolite of me, i will make a kind of cartoon sketch or caricature of their two personalities. I think Smolin likes to take risks and to foster creative young people who will take risks. If some program he sees is going along all right with lots of people helping, then he will go off in wild unexplored territory and SCOUT some new idea. I think Rovelli is more with the main body of the research, like a conventional leader. He always keeps a strategic picture in mind. He plans logically. If he sees a small gap, he tries to fill it. If he sees a major objective for the program he gathers people and attacks that goal. He is somewhat more orderly and predictable. This does not mean any less creative.
    So one can make a cartoon picture of these two ways of behaving that recalls the covered wagons of the Old West in North America where you have one kind of leader who stays with the wagons and is more central, and you have another person who is a scout and explorer. sometimes he is in advance, other times he may be trying some new path that might not work.

    I wouldn't say that the two have different opinions, because I don't know their opinions except as shown in survey papers. they behave differently, they have different kinds of vision. they emphasize different stuff and work on different stuff, but all this seems complementary in the sense of fitting together rather well.

    Look at what Starodubtsev did. In 2004 he was at Perimeter collaborating on one or more papers with Smolin, then he continues at perimeter and collaborates with Freidel, then in 2006 he goes to postdoc in LOLL's group at Utrecht. Now he is in Rovelli's group at Marseille.
    Now Staro is giving seminar talks on a way to LINK UP the Triangulations approach with LQG.
    In some sense the work of somebody in Rovelli or Smolin's position is to build up a research community that is innovative and focused on the important problems. Part of the output is people. This is another form of collaboration.

    I'm sorry I cant say much definite about differences of opinion. Of course Smolin's main work since 2005 has been on incorporatiing MATTER as topological aspects of the spinnetwork quantum state of geometry. This is avant guard and high risk. Rovelli is focused on the main problem of perfecting the LQG dynamics, working out the classical limit, just for pure gravity. He is more deliberate and gradual, doing things in logical order instead of jumping ahead.

    But it would be very nice if, by the time Rovelli et al are finished getting the LQG spinnetwork dynamics and the classical limit, that already some progress has been made of realizing different particles as the braids and twists in the spinnetwork. So I do not see a conflict, but more a kind of division of labor.
     
    Last edited: Jan 17, 2008
  9. Thanks for your expansions, I appreciate it! When I read something longer written by someone, a picture of that author somehow "involuntarily" forms in the readers mind and an impression of liking or not liking his general style of reasoning forms. I have probably so far skimmed more of Smolins papers, than Rovelli's. I like many of the "key questions" Smolin has expressed, they give the impression of someone with quite an open mind, I like that alot.

    /Fredrik
     
  10. marcus

    marcus 24,302
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    I just watched Lecture 2A
    each Wednesday there's roughly 3 hours and it's divided into two sections with a break in between.

    ========
    EDIT TO REPLY TO NEXT POST
    Jim, last time I checked they had not posted 2B
     
    Last edited: Jan 17, 2008
  11. Where's 2B? Have they posted it yet Marcus
     
  12. marcus

    marcus 24,302
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  13. I am following this lecture as well. At least as long as I understand something.
    One thing which surprised me was to hear that diffeomorphism invariance is something substantially different as coordinate invariance.

    Otherwise I am too lazy to really try to calculate the examples of constraint systems with invariance of time reparametrization Smolin gives because I get the rough idea without them. Probably this will kill me, when he moves on to general relativity.
     
    Last edited: Jan 18, 2008
  14. marcus

    marcus 24,302
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    As usual, there were two lectures on Wednesday and the video was posted the next day.

    PIRSA:08010035 Lecture 3
    Speaker(s): Lee Smolin
    Abstract: The Problem of Time in Quantum Gravity and Cosmology
    Date: 23/01/2008 - 7:00 pm
    URL: http://pirsa.org/08010035/

    PIRSA:08010041 Lecture 3B
    Speaker(s): Lee Smolin
    Abstract: The Problem of Time in Quantum Gravity and Cosmology
    Date: 23/01/2008 - 8:00 pm
    URL: http://pirsa.org/08010041/
     
  15. Thanks for the updates Marcus!

    I thought I was going to follow these but I'm lagging alot. 3 hours in one go is too long, I only had time to see half fraction of the first one. But I'm saving the lectures along with the pdfs and hopefully get time to watch them later.

    /Fredrik
     
  16. marcus

    marcus 24,302
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    Looks now like it is more like 2 hours a week, than three. So when and if you get to it, watching will not be as much work as you expected. Just my rough estimate.

    I sometimes turn on the slide archive and look at the slides, then I can JUMP to a slide I'm interested in and start the video playing there. Are you able to do that?

    It means you don't have to watch the whole (approx. one-hour) talk in one sitting.
     
  17. Yes, I can do that. But I was worried that they were going to remove the online clips before I got to it though? But now I found the clip data stream so I have at least saved them in case they are removed before I get the time, but then I loose the automatic synch to the slides.

    I guess everybodies problem is time, not only Smolins :) It's frustrating to realize that new ideas are generated at a rate that exceeds the evaluation capabilities so the rating systems becomes even more important as a selective tools. And now I got Rovelli's book too, I'll get it tonight. So I'll probably try to read a few pages in that when I get to it, and look at Smolins lectures later. I was hoping to initiate reading it before my attention gets stuck on something more interesting.

    I did some pre-reading of his other texts, and I already sense some from my personal viewpoint, severe issues with the ideas, but I'm still curious to see if my first impression will last. The first issues I've seen is not technical, rather having todo with the general strategy, and the choice of "variables". I've got a feeling that there is no solid arguments for this proceudre, and it seems to be somewhat arbitrary and strange. This is disturbing me, and I hope that starting to read Rovellis book may provide some more info.

    This is all deeply interesting stuff for sure!

    /Fredrik
     
  18. I watched the new lectures and I also had a look at Dirac's small book recommended by Smolin. I am following the progress (if you can always call it like that) of theoretical physics only as a hobby, so I should be careful, what I say.
    But let me say, that having seen a little bit of QFT in the Lagrangian and path integral approach before, I am not overly impressed by the elegance of say electrodynamics in the classical Hamiltonian picture as presented by Smolin. The single most important feature of classical electrodynamics is Lorentz invariance and going back to a language, where the symmetry between space and time is broken, feels somehow like a regression.
    From what I read about Smolin's views about a relational view of space and time in the tradition of Leibnitz it seems like giving up symmetry is not an accident but part of the program Smolin has. Maybe it is the right approach, but I am not feeling great about it right now.
    Dirac writes in the introduction to his book, that the best working way to a quantum theory leads from the Lagrangian (to ensure Lorentz invariance) to the Hamiltonian and from there to the quantum theory via canonical quantization. I think Feynman has shown that you can read off the Feynman rules directly from the Lagrangian. So if I understand correctly this is no longer true.
    In LQG space and time are something totally different. But for me to the question "What is time?" also belongs the question, why it "almost" looks like a spatial dimension in special relativity.
     
    Last edited: Jan 29, 2008
  19. I haven't been able to see any more lectures yet due to time :( Instead I decided to analyze Rovelli's thinking slowly. But somehow, it feels that it's more or less conceptually connected questions, seen from different angles. So I might as well anything in the ballpark and the same part of my brain starts spinning in the same mode.

    I personally dig the "relational ideas", and I think in this picture symmetries are dynamical things. The use of symmetries in the classical thinking is IMO more like tools for reasoning. By assuming symmetry one can obviously draw far reaching conclusions, but if this assumption is dynamical to start with, the conclusions are misleading. So if the degress of symmetry are dynamical and quantified, it can translate into emergent tools of reasoning which comes out as very plausible and deep scientific framework that is also deeply satisfactory from my philosophical point of view of science.

    /Fredrik
     
  20. marcus

    marcus 24,302
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    Last edited: Jan 31, 2008
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    Last edited: Jan 31, 2008
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