Or is it just straight out of the equations? has it been detected?
The Casimir effect:
Is a test for the existance of virtual particles. This effect has been measured.
You can't detect them.That's what they are called virtual.Duhhhh !!
However,you needn't go to Casimir effect to prove that Feynman diagrams are a correct symbolical representation of reality,i think a Compton effect is much easier to test/measure.
Also the Lamb Shift.
Well,let's see.1922 vs 1947.
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