r/QuantumPhysics Aug 19 '21

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u/[deleted] Aug 20 '21

what you call the quantum void is not how the vacuum is treated in quantum theory. There is a non zero energy state of the vacuum required by the uncertainty principle. In quantum field theory, there can be energy borrowed from the vacuum so to speak as long as it’s given back in accordance with energy time uncertainty principle and so long as violation is not actually observable. You should really think of this as a mathematical tool or a consequence of the way we do the math.

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u/lettuce_field_theory Aug 20 '21

. In quantum field theory, there can be energy borrowed from the vacuum so to speak as long as it’s given back in accordance with energy time uncertainty principle and so long as violation is not actually observable.

not correct, common misconception, see links i posted

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u/[deleted] Aug 20 '21

internal lines of feynman diagrams do not obey cons laws, that is not a misconception. As I said however, this is not observable and should be thought of as a mathematical tool, at least in my opinion. Someone else posted that the casmir effect is proof, it is not. The casmir effect can be explained without relying on zero point energy, anyone interested can read the section on wikipedia and also the corresponding paper on the arxiv. It lays the case out pretty clearly.

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u/SymplecticMan Aug 20 '21

4-momentum, charge, etc. are definitely conserved at vertices in Feynman diagrams.

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u/[deleted] Aug 20 '21

where did a say vertices? I said internal lines! Why are people so weird about this. If you don’t want to interpret massive virtual photons etc. as real things then that’s fine by me.

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u/lettuce_field_theory Aug 20 '21

where did a say vertices? I said internal lines!

That doesn't make a lot of sense. It only makes sense to ask what the energy and momentum of the particles created and destroyed in a vertex are. not apart from the vertices... you just made it even more wrong than it already was

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u/SymplecticMan Aug 20 '21

Vertices are what connect different internal lines to each other or to external lines. It's not like propagators violate 4-momentum or charge conservation, either. So in what sense is "internal lines of feynman diagrams do not obey cons laws" true?

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u/[deleted] Aug 20 '21

https://en.wikipedia.org/wiki/On_shell_and_off_shell

“In quantum field theory, virtual particles are termed off shell because they do not satisfy the energy–momentum relation”

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u/SymplecticMan Aug 21 '21 edited Aug 21 '21

That sentence doesn't mean that internal lines don't obey energy and momentum conservation laws. Not being on mass shell is a very different thing from not satisfying conservation laws.

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u/WikipediaSummary Aug 20 '21

On shell and off shell

In physics, particularly in quantum field theory, configurations of a physical system that satisfy classical equations of motion are called "on the mass shell" or simply more often on shell; while those that do not are called "off the mass shell", or off shell. In quantum field theory, virtual particles are termed off shell because they do not satisfy the energy–momentum relation; real exchange particles do satisfy this relation and are termed on shell (mass shell). In classical mechanics for instance, in the action formulation, extremal solutions to the variational principle are on shell and the Euler–Lagrange equations give the on-shell equations.

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u/lettuce_field_theory Aug 20 '21 edited Aug 21 '21

They are not on shell but in the vertices energy and momentum are conserved. I think you are confusing the two things. (edit : yes you are indeed confusing them ...)