I don’t know if you saw it, but I happened to catch the last two talks of the Strings 2008 conference, via live webcast. They were summary talks. Hirosi Ooguri did an excellent job of summarizing all the main themes in various talks during the conference, and the David Gross summed it all up, took stock of where we are, and where we aren’t, and looked forward. A sort of “state of the union” speech if you like. And the state is good. Very good indeed.
I found these two talks to be excellent, informative, and very interesting. I recommend them to people interested in research in strings and related topics. I can’t see a link to a video archive of talks on the official site, so I hope something will appear later. Right now, there’s a link to a pdf of Hirosi’s slides, but I really hope you can see the video eventually, since the slides don’t show the humour and wit with which it was all delivered. Also, David presented no slides, and spoke off the cuff, so without video archive, there’s nothing to see yet. Check back there.
Enjoy!
-cvj
Hi Clifford,
Thanks for summarizing your point of view. Opportunely I will search on our blog about other specific issues.
Best wishes,
Christine
Well, I could do a long list, but the main underlying problem is simply: We don’t know what it really is.
Non-perturbatively, string theory stops being a theory of strings. We don’t know what it is a theory of. We have lots of marvellous hints (such as powerful dualities of various sorts), and can do amazing things with some of the things we have worked out, but that’s not enough. We need a constructive definition. That, I think, will help with lots of other issues such as understanding how to control time dependence (watching spacetimes change from one form to another as a function of time…. an almost tautological problem at times), how to figure out which apparent solutions are really solutions, and so forth.
There’s lots more to be said, but I’ve said it many times before in other posts and comments.
Cheers,
-cvj
The best attempt so far does not mean it is the only attempt and it does not mean it is the right approach. It could turn out to be wrong, ultimately, and others could develop further their ideas and approaches to become more promising.
I agree with you.
What are, in your opinion, the main problems in string theory today?
Thanks.
About the latter part of the comment. I don’t see any confusion. The best attempt so far does not mean it is the only attempt and it does not mean it is the right approach. It could turn out to be wrong, ultimately, and others could develop further their ideas and approaches to become more promising. Right now however, the situation is as I said.
About the first question. This is question-dependent, and also I don’t think it really should be thought of in terms of there being a precise cutoff. In the same way that it wouldn’t make sense in the water discussion. I also don’t think it is a good idea to obsess about that particular distance. It is possible that the Planck scale may be elsewhere, and not that particular scale. The key idea to take away is simply that there is a scale below which it certainly would not make sense to discuss spacetime, just as there is a scale below which there is no sense in taking about the fluid properties of water. There is no sharp point at which you suddenly go from one description to another. Physics does not really work that way, generally (leaving aside a phase transition, which …well… let’s leave it at that).
Best,
-cvj
Hi,
But I have 2 other questions:
Firstly, it states that the ”structure of nature will terminate at 10-35meter” So that implies that >10-35 we have general relativity. <10-35 we have quantum theory. So my question is what is ‘happening’ precisely at the cut off point at x=10^-35?
You say that string theory is the best attempt so far, but there are quite a few professors such as John Baez who have chosen to go in another direction using other approaches. How there be such a divide in physics, if one approach is said to be ‘the best’?
Thats something I dont understand. Either string theory ‘is’ the only hope, or it isn’t.
Thanks
Hi,
It’s not to hard to explain the idea. I’m not a mathematician either, and anyway, this is a physics topic, not a mathematical one, so it would he wrong to explain it in mathematical terms.
Consider a glass of water. You can pour it, splash it around, wet things with it, and so forth. It has a very familiar fluid property to it. There are lovely equations that describe the properties of fluids, how they flow, how that flow depends on measurable properties such as viscosity, etc. All good.
But what is water? Well, it is made of atoms of hydrogen and oxygen, bound together and interacting according to the rules of quantum mechanics into molecules, which then, in huge numbers, interact together in a conglomerate, bouncing off each other and so forth. Yet no atom or molecule has any trace of the things we know as wetness, fluidity, viscosity, etc. The properties of water that we know about do not exist at the scale of atoms and molecules. They emerge from the collective properties and behaviour of the interacting aggregate.
Now compare to the statement you quoted above. Same thing. Spacetime and its smooth properties are like water and its nice smooth properties. Things like classical gravity according to Einstein or Newton are a lot like the equations of fluid dynamics. All of that needs replacing when you get down to the Planck scale where quantum gravity rules and smooth spacetime is no longer a good description. This is why some of us work on string theory. It simply is the best and most workable attempt so far to understand the above issues in concrete terms. It is incomplete, but we are learning a lot every day.
Best,
-cvj
I visited ooguris webpage and here it states: ”Surprisingly, there are reasons to think that the hierarchical structure of nature will terminate at 10-35meter, the so-called Planck length. Space and time do not exist beyond the Planck scale, and they should emerge from a more fundamental structure.”
Professor Clifford could you explain to me what it means to say that spacetime does not exist and emerge from a fundamental structure?
I will not understand the technical details, given that I’m not a mathematician however I would like to know what this means.
Thanks
Thanks! He always gives great talks…
-cvj
Until the Strings ’08 videos are available, one can also kill an idle hour with this talk by Rajagopal (4 June 2008) on applying AdS/CFT to quark-gluon plasmas and cold fermion gases.