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Quantum physics tells us that even a perfect vacuum be populated by "virtual" pairs of subatomic particles. I have read that these particles are allowed to violate the Conservation of Matter and Energy because they do so for such a short amount of time before annihilation that they don't count. I don't buy it. As we.have established that "Virtual Particles" are "real" (by virtue of the fact that well known processes don't occur with out them) . The question still begs. As no conversion is 100 percent efficient ( a photon is still left in our reality even after annihilation) To preserve the laws of physics, the energy to create them must come from somewhere. * .Given this, I have two questions:

  1. Have " virtual" pairs ever been observed and/or isolated?
  2. Where do "virtual" particles come from? (As they would have to come from somewhere to satisfy conservation; regardless of how short a time they spend in our universe.)

    • post is edited and reflects (to clarify what I am asking) information discussed below where Question 1 is answered. Question 2 remains.
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marked as duplicate by knzhou, Qmechanic Sep 5 '18 at 4:09

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Virtual particle pairs pop spontaneously out of the vacuum and then recombine and disappear; they exist for too short a time for us to isolate the pair, separate them, and then study them. This means there is no way to "see" them directly.

Despite this, their (indirect) influence on experiments is real. There are well-understood problems in QM which, when solved without taking virtual particle effects into account, yield the wrong answer (i.e., the computed prediction does not match experimental data). Take their effects (called "quantum corrections") into account, and you get the right answer.

How good is the match between theory and experiment when quantum corrections are included? Richard Feynman described the match as like predicting the distance between Los Angeles and New York theoretically and having it match the measured answer to within the thickness of a single sheet of paper.

These things furnish physics guys with a high level of confidence that virtual particles are not just theoretical constructs without physical reality, but things that are part of the real world- specifically, what's called the quantum vacuum.

I invite the experts here to weigh in on this with specific examples of the sort I mentioned above.

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    $\begingroup$ Pictures of virtual particles popping in and out of vacuum are gross oversimplifications, cf. some of the linked questions in comments above. At the core, virtual particles are just useful mnemonics when calculating scattering amplitudes in higher order perturbation theory. $\endgroup$ – Avantgarde Sep 4 '18 at 23:31
  • $\begingroup$ Neils: So like dark matter, we "know" fluctuations and virtual particles exist because if they did not. the world will not work. But that still leaves the other question. Since, matter and energy must.be universally conserved, the question begs " Where do they come from? $\endgroup$ – user33995 Sep 4 '18 at 23:42
  • $\begingroup$ the energy required to temporarily create them is borrowed from the vacuum. the loan is returned when they subsequently annihilate. energy conservation holds perfectly on timescales longer that the lifetime of a virtual particle pair. $\endgroup$ – niels nielsen Sep 5 '18 at 0:17
  • $\begingroup$ @Neil I understand that matter can come from energy and vice versa, but it still has to come from somewhere. To say that is comes from the vacuum though sounds a little off. If you will pardon the allegory, It a bit like placing an empty cup in a fish tank and saying the water is coming from the walls. Similarly then where does the energy come from since the vacuum exists in our reality? $\endgroup$ – user33995 Sep 5 '18 at 2:47
  • $\begingroup$ the behavior of what's called the quantum vacuum defies our conventional intuition, which is based on the behavior of things big enough for us to see, which means the quantum effects are ordinarily miniscule in our every day experience. the rules that you and I grew up with that define the behavior of "big" objects simply do not work in the world of the very small. have you read anything about this stuff, or is this your first excursion into this territory? $\endgroup$ – niels nielsen Sep 5 '18 at 5:04

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