Comments on: Would String Theory Truly Realize Einstein’s Dream? http://sciencewriter.org/2006/10/string-theory-and-einstein/ Davide Castelvecchi, Freelance Science Writer: Physics, Astronomy, and Math Sat, 31 Jul 2010 15:10:19 +0000 http://wordpress.org/?v=2.6.5 By: Aaron Bergman http://sciencewriter.org/2006/10/string-theory-and-einstein/#comment-147 Aaron Bergman Mon, 23 Oct 2006 17:41:39 +0000 http://sciencewriter.org/2006/10/string-theory-and-einstein/#comment-147 I'm sorry, but this is wrong. String perturbation theory makes sense (although can be difficult to quantize) on any background that satisfies the Einstein field equations, not just Minkowski space. Even in this context, string theory does explain "that heavy objects curve space", at least perturbatively. Within more nonperturbative approaches (the main example being AdS/CFT), one can go much further. In AdS/CFT, there is no background dependence except at the boundary of spacetime. You also say that "Initially, string theory only seemed compatible with a “flat” universe. When physicists showed in the late 1990s that there were a few other possibilities for string-compatible universes, that was seen as a huge breakthrough". The existence of multiple solutions was well-known back to the dawn of string theory; as mentioned above, string perturbation theory is compatible with any solution to the appropriate Einstein field equations. What was accomplished in the late 1990s was the issue of moduli fixing. The previous geometries all could deform continuously in such a way that led to massless fields that we do not observe. The accomplishment was to get rid of those fields and to make plausible that one could obtain solutions with a positive cosmological constant. I’m sorry, but this is wrong. String perturbation theory makes sense (although can be difficult to quantize) on any background that satisfies the Einstein field equations, not just Minkowski space. Even in this context, string theory does explain “that heavy objects curve space”, at least perturbatively.

Within more nonperturbative approaches (the main example being AdS/CFT), one can go much further. In AdS/CFT, there is no background dependence except at the boundary of spacetime.

You also say that “Initially, string theory only seemed compatible with a “flat” universe. When physicists showed in the late 1990s that there were a few other possibilities for string-compatible universes, that was seen as a huge breakthrough”. The existence of multiple solutions was well-known back to the dawn of string theory; as mentioned above, string perturbation theory is compatible with any solution to the appropriate Einstein field equations. What was accomplished in the late 1990s was the issue of moduli fixing. The previous geometries all could deform continuously in such a way that led to massless fields that we do not observe. The accomplishment was to get rid of those fields and to make plausible that one could obtain solutions with a positive cosmological constant.

]]> By: James R http://sciencewriter.org/2006/10/string-theory-and-einstein/#comment-142 James R Fri, 20 Oct 2006 17:22:56 +0000 http://sciencewriter.org/2006/10/string-theory-and-einstein/#comment-142 Nice post, Davide. You certainly cleared up some of my misconceptions about what String Theory is doing. I'm going to read it over again, and maybe we can talk about it next week. (I took off today to go skateboarding). -Buzz Skyline Nice post, Davide. You certainly cleared up some of my misconceptions about what String Theory is doing.

I’m going to read it over again, and maybe we can talk about it next week. (I took off today to go skateboarding).

-Buzz Skyline

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