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Message: <blockquote data-quote="freyar" data-source="post: 6547932" data-attributes="member: 40227">Yes and no.  We have learned a lot about what physical theories are even possible from string theory.  Particle physicist (not string theorist) Matt Strassler wrote a really lovely series of blog posts about this (nine in all, I think), starting <a href="http://profmattstrassler.com/2013/09/23/quantum-field-theory-string-theory-and-predictions/" target="_blank">here</a>.  Well worth reading all of those.String theory as a theory of everything is guilty as charged.  However, it seems people -- scientists, as well as non-scientist EN World members and the rest of society -- are genuinely interested in understanding what a complete theory of quantum gravity might be like.  Every charge you levy against string theory is just as true for any theory of quantum gravity (or theory of everything) for exactly the same reasons --- the energy scales needed to make such tests are beyond human technology for the foreseeable future.  And, by and large, the indirect tests people come up with for any other theory of quantum gravity look a lot like the tests for string theory.  String theory has what is both the advantage and disadvantage of being mathematically rich, rigorous, and precise (when we have the skill to do it properly).So I guess my question is, do you think it is unfruitful scientifically to think about quantum gravity or theories of everything?  If so, that's just something we can disagree about.  But if you think those are valuable questions, then it seems a bit silly to pick out string theory as being unfruitful, since it's been a lot more productive than other theories.Actually, no, not at all.  You seem not to have understood what I was saying, and I'll take the blame for a poor explanation and try again.  What you're saying is applicable to string theory as a theory of everything.  Any theory of our universe must surely reduce to what we already know, of course (well, or just be a toy model of some particular aspect).  But, since string theory is a theory of quantum gravity, it can also describe other universes very different from ours.  Hold that thought for now.Something that happens to be true from time to time in physics is that two very different looking theories end up actually being the same.  One way to think about it is that there is really one theory, but the two theories we know are different projections of that one theory, like the shadows being projections of the blocks on the <a href="http://en.wikipedia.org/wiki/G%C3%B6del,_Escher,_Bach#mediaviewer/File:GEBcover.jpg" target="_blank">cover of Godel, Escher, Bach</a>.  The shadows look different, but they represent the same thing.One of the great surprises of theoretical physics at the end of the 20th century is that theories of particle physics that are similar to the theory of the strong nuclear force in our universe are actually the same as string theories in special universes that look nothing like ours at all!  So when people were doing new nuclear physics experiments 10 or so years ago and not understanding some results, it was string theorists who were able to provide an explanation, since nuclear physics in our world is roughly similar to string theory in a very different type of universe.  I'll repeat for emphasis: string theory as a calculational tool was the first way to understand real experiments in nuclear physics, which were at that time otherwise baffling.  And it's important to note that this is all true even if string theory is not the description of quantum gravity in our universe at all.  It's a totally separate question.</blockquote>

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