Comments on: Douglas at City College http://www.math.columbia.edu/~woit/wordpress/?p=151 Tue, 24 Nov 2009 05:18:29 -0500 http://wordpress.org/?v=2.8.6 hourly 1 By: Not Even Wrong » Blog Archive » This Week’s Hype http://www.math.columbia.edu/~woit/wordpress/?p=151&cpage=1#comment-13464 Not Even Wrong » Blog Archive » This Week’s Hype Thu, 13 Jul 2006 18:56:52 +0000 http://www.math.columbia.edu/~woit/wordpress/?p=151#comment-13464 [...] It’s kind of funny to hear that string theory “predicts” that constants like the fine structure constant will vary in time. When Michael Douglas was here in New York giving a talk last year and was asked about predictions of the string theory landscape, he said that the best one was that the fine structure constant would NOT vary. His argument was that it couldn’t vary since effective field theory arguments would imply a corresponding variation in the vacuum energy, something inconsistent with observation. So string theory both predicts that the fine structure constant will vary, and predicts that the fine structure constant will not vary. [...] [...] It’s kind of funny to hear that string theory “predicts” that constants like the fine structure constant will vary in time. When Michael Douglas was here in New York giving a talk last year and was asked about predictions of the string theory landscape, he said that the best one was that the fine structure constant would NOT vary. His argument was that it couldn’t vary since effective field theory arguments would imply a corresponding variation in the vacuum energy, something inconsistent with observation. So string theory both predicts that the fine structure constant will vary, and predicts that the fine structure constant will not vary. [...]

]]> By: Amsterdammer http://www.math.columbia.edu/~woit/wordpress/?p=151&cpage=1#comment-2293 Amsterdammer Wed, 31 Dec 1969 19:00:00 +0000 http://www.math.columbia.edu/~woit/wordpress/?p=151#comment-2293 Concerning the Feynman quote, accidentally I stumbled upon the following (from http://infoproc.blogspot.com/2005/01/string-theory-quotes.html) "...I do feel strongly that this is nonsense! ...I think all this superstring stuff is crazy and is in the wrong direction. ... I don't like it that they're not calculating anything. ...why are the masses of the various particles such as quarks what they are? All these numbers ... have no explanations in these string theories - absolutely none! ... " --Richard Feynman: in Davies and Brown, Superstrings, Cambridge 1988, pp. 194-195. Concerning the Feynman quote, accidentally I stumbled upon the following (from
http://infoproc.blogspot.com/2005/01/string-theory-quotes.html)

“…I do feel strongly that this is nonsense! …I think all this superstring stuff is crazy and is in the wrong direction. … I don’t like it that they’re not calculating anything. …why are the masses of the various particles such as quarks what they are? All these numbers … have no explanations in these string theories – absolutely none! … ”
–Richard Feynman: in Davies and Brown, Superstrings, Cambridge 1988, pp. 194-195.

]]> By: D R Lunsford http://www.math.columbia.edu/~woit/wordpress/?p=151&cpage=1#comment-2294 D R Lunsford Wed, 31 Dec 1969 19:00:00 +0000 http://www.math.columbia.edu/~woit/wordpress/?p=151#comment-2294 Chris - I was trying to point out that Minkowski space also has features that are not realized in naive experience, but we seem very happy with it and find it "useful". -drl Chris –

I was trying to point out that Minkowski space also has features that are not realized in naive experience, but we seem very happy with it and find it “useful”.

-drl

]]> By: Chris Oakley http://www.math.columbia.edu/~woit/wordpress/?p=151&cpage=1#comment-2295 Chris Oakley Wed, 31 Dec 1969 19:00:00 +0000 http://www.math.columbia.edu/~woit/wordpress/?p=151#comment-2295 Danny - I'm not following you. Mass is not dilatation invariant & therefore a universe with massive particles is not dilatation invariant & therefore not conformally invariant. Why is it more complicated than that? Danny – I’m not following you. Mass is not dilatation invariant & therefore a universe with massive particles is not dilatation invariant & therefore not conformally invariant. Why is it more complicated than that?

]]> By: Chris Oakley http://www.math.columbia.edu/~woit/wordpress/?p=151&cpage=1#comment-2296 Chris Oakley Wed, 31 Dec 1969 19:00:00 +0000 http://www.math.columbia.edu/~woit/wordpress/?p=151#comment-2296 Following on from Peter's point, the twistor theorists I knew at Oxford: Lane Hughston, Paul Tod and William Shaw (a graduate student at the time) were always completely honest about what the framework could and could not do ("Don't ask about massive particles, don't ask about interacting particles" is what I seem to remember William saying to me once). Although they were called the "Mathematical Physics" group they were well aware of the fact that what they were doing was much more mathematics than physics. One thing, though where physicists could learn from them is the elegance with which they deal with the SL(2,C) covering group of the Lorentz group (which of course is one of the steps on the road to Twistors). Following on from Peter’s point, the twistor theorists I knew at Oxford: Lane Hughston, Paul Tod and William Shaw (a graduate student at the time) were always completely honest about what the framework could and could not do (”Don’t ask about massive particles, don’t ask about interacting particles” is what I seem to remember William saying to me once). Although they were called the “Mathematical Physics” group they were well aware of the fact that what they were doing was much more mathematics than physics. One thing, though where physicists could learn from them is the elegance with which they deal with the SL(2,C) covering group of the Lorentz group (which of course is one of the steps on the road to Twistors).

]]> By: Matti Pitkanen http://www.math.columbia.edu/~woit/wordpress/?p=151&cpage=1#comment-2297 Matti Pitkanen Wed, 31 Dec 1969 19:00:00 +0000 http://www.math.columbia.edu/~woit/wordpress/?p=151#comment-2297 I think that the key question is "At what level the conformal invariance is realized?". Assume the representatibility of physically realizable space-times as 4-surfaces of space M^4xS, S some compact space. Assume that 3-D lightlike boundaries of space-time surface act as "causal determinants". Causal determinants could correspond also to light-like surfaces representing "shock waves". From these assumptions you end up with the realization that these light-like 3-surfaces allow generalized conformal invariance by their metric 2-dimensionality. Hence conformal invariance and 4-dimensionality of space-time are very tightly related. This conformal invariance has nothing to do with the rather trivial conformal invariance (as compared to 2-D conformal invariance) of M^4. Best, Matti Pitkanen I think that the key question is “At what level the conformal invariance is realized?”.

Assume the representatibility of physically realizable space-times as 4-surfaces of space M^4xS, S some compact space. Assume that 3-D lightlike boundaries of space-time surface act as “causal determinants”. Causal determinants could correspond also to light-like surfaces representing “shock waves”.

From these assumptions you end up with the realization that these light-like 3-surfaces allow generalized conformal invariance by their metric 2-dimensionality. Hence conformal invariance and 4-dimensionality of space-time are very tightly related. This conformal invariance has nothing to do with the rather trivial conformal invariance (as compared to 2-D conformal invariance) of M^4.

Best,
Matti Pitkanen

]]> By: D R Lunsford http://www.math.columbia.edu/~woit/wordpress/?p=151&cpage=1#comment-2298 D R Lunsford Wed, 31 Dec 1969 19:00:00 +0000 http://www.math.columbia.edu/~woit/wordpress/?p=151#comment-2298 Chris, It's somewhat more subtle than that - as an affine space Minkowski space allows dilations, and we should experience these along with boosts and rotations. Since we don't, we "can't" be in Minkowski space. So the argument goes both ways. I think conformalism will eventually play a crucial role, but the existing approaches based on SO(4,2) will not. -drl Chris,

It’s somewhat more subtle than that – as an affine space Minkowski space allows dilations, and we should experience these along with boosts and rotations. Since we don’t, we “can’t” be in Minkowski space. So the argument goes both ways.

I think conformalism will eventually play a crucial role, but the existing approaches based on SO(4,2) will not.

-drl

]]> By: Peter http://www.math.columbia.edu/~woit/wordpress/?p=151&cpage=1#comment-2299 Peter Wed, 31 Dec 1969 19:00:00 +0000 http://www.math.columbia.edu/~woit/wordpress/?p=151#comment-2299 In a word, no. The idea of using twistors to do fundamental physics has mainly been pursued by people working with Penrose's group at Oxford. It never became very popular outside of people associated with this group. The new work on twistor string theory is a big change, causing a lot more people to learn about twistors. There's been a steady interest in twistor techniques among mathematicians for quite a while. Some of this goes back to the late seventies, when Atiyah and others got interested in the fact that you could use holomorphic techniques on twistor space to get solutions to the YM self-duality equations. There's been a lot of work by Ward and others on using twistors to solve various kinds of equations. Claude leBrun has gotten a lot out of twistor techniques in his work on 4-manifolds, and there are lots of other examples of the idea being useful in mathematics. In a word, no.

The idea of using twistors to do fundamental physics has mainly been pursued by people working with Penrose’s group at Oxford. It never became very popular outside of people associated with this group. The new work on twistor string theory is a big change, causing a lot more people to learn about twistors.

There’s been a steady interest in twistor techniques among mathematicians for quite a while. Some of this goes back to the late seventies, when Atiyah and others got interested in the fact that you could use holomorphic techniques on twistor space to get solutions to the YM self-duality equations. There’s been a lot of work by Ward and others on using twistors to solve various kinds of equations.

Claude leBrun has gotten a lot out of twistor techniques in his work on 4-manifolds, and there are lots of other examples of the idea being useful in mathematics.

]]> By: JC http://www.math.columbia.edu/~woit/wordpress/?p=151&cpage=1#comment-2300 JC Wed, 31 Dec 1969 19:00:00 +0000 http://www.math.columbia.edu/~woit/wordpress/?p=151#comment-2300 Peter, Chris Were twistors ever hyped up in the past in a similar manner to string theory, except maybe at a smaller scale? I vaguely remember a popular press book by Peat which discussed string theory and twistors in the 1980's. Other than that, I don't recall twistors being really excessively hyped up. Peter, Chris

Were twistors ever hyped up in the past in a similar manner to string theory, except maybe at a smaller scale?

I vaguely remember a popular press book by Peat which discussed string theory and twistors in the 1980’s. Other than that, I don’t recall twistors being really excessively hyped up.

]]> By: Peter http://www.math.columbia.edu/~woit/wordpress/?p=151&cpage=1#comment-2301 Peter Wed, 31 Dec 1969 19:00:00 +0000 http://www.math.columbia.edu/~woit/wordpress/?p=151#comment-2301 Hi Thomas, There weren't that many string theorists in the audience. Of those who were there, some of them have told me in the past they're not at all happy with the present state of string theory. I had to leave fairly quickly after the talk, didn't get a chance to talk to too many people afterwards. I can say there definitely were some people in the audience sympathetic to my complaints. By the way, Nair isn't really a string theorist, although he has done some work on string theory. He has worked on a lot of different things over the years. This includes YM amplitudes in twistor space, where 15 years ago, he was one of the first (if not the first, I don't really know the history) to calculate them this way. Before the colloquium we talked about what is going on in twistor string theory, which he's working on (and about "Not Even Wrong", of which he is a reader). Hi Thomas,
There weren’t that many string theorists in the audience. Of those who were there, some of them have told me in the past they’re not at all happy with the present state of string theory. I had to leave fairly quickly after the talk, didn’t get a chance to talk to too many people afterwards. I can say there definitely were some people in the audience sympathetic to my complaints.

By the way, Nair isn’t really a string theorist, although he has done some work on string theory. He has worked on a lot of different things over the years. This includes YM amplitudes in twistor space, where 15 years ago, he was one of the first (if not the first, I don’t really know the history) to calculate them this way. Before the colloquium we talked about what is going on in twistor string theory, which he’s working on (and about “Not Even Wrong”, of which he is a reader).

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