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I think it may have been Witten (perhaps somebody can correct me) who suggested that a TEO might not actually exist. Just as we might never, even in principle, posses the mathematics that can interpolate between the strongly coupled and free limits of QCD, it might not be possible to write down one set of equations that describes one corner of a TEO, say, ...


4

First of all, there is a quantum field theory on a curved background, even though it is not perfect. There are problems with global definitions of spinors, vacua, particle numbers etc. and this all seems to be a consequence of the core properties of GR such as no privileged definition of time or "global God observer". But the main issue of the theory is ...


20

One thing that stops us from having a theory of everything is actually quite simple. Gravity as we understand it, thanks to the strong equivalence principle, is not a force. It is entirely geometrizable because there is actually no coupling constant between a physical object and the "gravitational field". This means that there is no a priori way to ...


1

It is not true that these theories cannot coexist. To put things in context: Ever since Newton's time we have been thinking of things taking place in locations in space and time. Special relativity (SR) showed us that these are connected, and we really should be thinking of spacetime as the theater in which we live. General relativity (GR) simply gave some ...



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