Okay, so I'm learning some QFT, I read through Bogoliubov, Shirkov Introduction to Quantized Fields up to the section on renormalization, and then wanted to see a more modern point of view- so I started a-googling and now I'm coming to understand a bit more about gauge theories and what exactly the Standard Model is.

ANYWAY- I'm still a bit troubled and confused about the basis of the whole theory. So many physically 'real' phenomena arise out of pure formalisms involved with perturbation, such as the actual interactions mediated by gauge bosons which, in a way, are just pieces of terms in a perturbative expansion- correct? They're also, conveniently and beautifully, artifacts emerging from the structure of gauge formalism.

Now, I do quite love this abstract nonsense, but isn't this fundamentally different from the physical reality arising in other branches of physics? In GR, another (gauge?) field theory, the stance on reality is quite different.

That is- How does one place QFT's reality in context with that of other areas of physics?

EDIT- By 'reality' I mean those phenomena exhibited by the formalisms that are to be considered physical, as opposed to unphysical. For example, again in GR there is a consensus that some regions of Schwarzschild are not 'real', so we concern ourselves with the dynamics of the other regions. Trying to weed through QFT with this sort of logic seems very difficult.


closed as not a real question by David Z Aug 7 '11 at 3:12

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  • $\begingroup$ Since you wrote "(gauge?)," with a question mark, I'll just comment that GR is indeed a gauge theory. The gauge group is the group of changes of coordinates (a.k.a. diffeomorphisms). $\endgroup$ – Ben Crowell Aug 7 '11 at 3:05
  • $\begingroup$ I've read that, and I really like that take on it, actually. However, aren't diffeomorphisms a little different from other gauge transformations? For instance, QED is globally invariant under U(1), and we get the actual niceties in making that global invariance local. But a diffeomorphism is always local, and frequently ONLY local- correct? (At least mathematically this is how I've thought of them) $\endgroup$ – specterhunter Aug 7 '11 at 3:11
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    $\begingroup$ What exactly do you mean by "physical reality" in this question? Are you asking why GR doesn't arise from a perturbative expansion as the standard model interactions do? Basically, I think that needs to be clarified, otherwise this question doesn't seem nearly clear enough. (Once you take care of that I'll be happy to reopen the question) $\endgroup$ – David Z Aug 7 '11 at 3:11
  • $\begingroup$ Good point. I'm not even quite sure how to phrase what I mean- I guess I mean real phenomena as opposed to unphysical phenomena. $\endgroup$ – specterhunter Aug 7 '11 at 4:22
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    $\begingroup$ QFTs arise all the time in condensed matter physics, and I don't think there's any doubt that condensed matter physics has physical reality. I think experience shows that if you start looking at complicated enough quantum systems, you will start finding quantum field theories. Given how ubiquitous they are, it's not really surprising that the Standard Model is a quantum field theory. $\endgroup$ – Peter Shor Aug 8 '11 at 1:18