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Say a e-, e+ virtual pair is created in the vicinity of a star.

During the short period of their existence they felt the gravitational field and picked up a net momentum towards the star. Now they can't annihilate into nothing because it would violate momentum conservation, is this correct?

I know I'm not supposed to see this problem using classical physics, but I'm not sure what's the correct quantum perspective.

seilgu
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  • Virtual pairs are not actually ever "created". – ACuriousMind Sep 04 '16 at 18:18
  • But they do contribute to the Feynman diagram right? – seilgu Sep 04 '16 at 18:22
  • Yes, but the Feynman diagram is just a calculational tool, and the internal lines do not represent actual particles. Search other questions about [tag:virtual-particles] for more on this. – ACuriousMind Sep 04 '16 at 18:23
  • And they could interact with gravitons in some diagrams so there's a real effect. – seilgu Sep 04 '16 at 18:23
  • IF it's only a calculational tool, then what about Hawking radiation ? – seilgu Sep 04 '16 at 18:26
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    What about it? If you read the original paper by Hawking, he pretty clearly states the "virtual particles getting separated" is just an analogy. His actual derivation doesn't use the notion at all. – ACuriousMind Sep 04 '16 at 18:28
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    https://profmattstrassler.com/articles-and-posts/particle-physics-basics/virtual-particles-what-are-they/ as they are not real, you (and I) will have to check what Hawking Radiation actually consists of... Physical insight into the process may be gained by imagining that particle-antiparticle radiation is emitted from just beyond the event horizon. This radiation does not come directly from the black hole itself, but rather is a result of virtual particles being "boosted" by the black hole's gravitation into becoming real particles. https://en.wikipedia.org/wiki/Hawking_radiation –  Sep 04 '16 at 19:08
  • I'm voting to close this question as off-topic because it is based upon a misunderstand of virtual particles. – John Rennie Sep 05 '16 at 06:29
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    I'm voting to leave open, because a question based on a misunderstanding is answerable -- the answer is "this is the misunderstanding..." –  Sep 05 '16 at 07:22
  • Perhaps there is a simply way to explain why virtual particles doesn't have any effects? Or does it require a through calculation to prove that the effect is zero? – seilgu Sep 05 '16 at 11:51
  • For example, perhaps there is a Feynman diagram in which a graviton enters and interacts with virtual pairs and then emits two particles? (such that energy and momentum is both conserved) – seilgu Sep 05 '16 at 12:01
  • Such diagrams could of course contribute to the graviton propagator, but since the diagram has to overall conserve momentum, and the graviton is the only incoming and outgoing particle, it is impossible for the graviton to impart momentum onto such a pair. – ZachMcDargh Sep 06 '16 at 18:26

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