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I have a question. In string theory, what is the nature of time? Is it universal and absolute, like QM, or dynamic like relativity, or yet something else?
by woodandsteel 10y ago
I have a question. In string theory, what is the nature of time? Is it universal and absolute, like QM, or dynamic like relativity, or yet something else?
- marcosdumay 10y agoNormal QM is what you get when you do quantization of Newtonian Mechanics, that's why it has an absolute time. If you quantize General Relativity instead, you'll get a variant of QM with relative times. But it's much more complex, and useless for most daily applications¹, so people don't use it often. 1 - X-ray measurements and nuclear physics are two important exceptions.
- contravariant 10y agoDid you mean special relativity? Or is there some limited way in which you can quantize general relativity?
- marcosdumay 10y agoYep, I meant special relativity.
- smallnamespace 10y agoAre you talking about the semiclassical approximation when talking about quantized GM?
- millstone 10y agoMark Srednicki's Quantum Field Theory book has a very nice and often quoted passage in its introduction regarding two approaches to incorporating time in a relativistic theory. The problem is that non-relativistic QM treats space (position) as an operator while time as a sort of label. But relativity demands that space and time be on equal footing. So we can either make space a label (as is done in QFT), or time an operator (leading to string theory). The passage is long, but here is a Quora article that excerpts it: https://www.quora.com/Why-is-time-not-an-operator-in-quantum-mechanics-even-though-it-seemingly-is-an-observable https://www.quora.com/Why-is-time-not-an-operator-in-quantum...
- woodandsteel 10y agoThank you, I, who have not had a course in QM, actually managed to understand that link at a minimal level.
- walrus1066 10y agoActually, time is relativistic in quantum field theory (QFT), the framework upon which the standard model is built. It has special relativity baked in, but not general relativity (which describes how gravity works). Unifying QFT and general relativity is a holy grail of physics. R.e. String theory, I would think time is relativistic also, it is a direct consequence of the speed of light being constant in all frames of reference, which is a fact consistently proven by many experiments over the last 100+ years.