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Virtual particles colliding with other virtual particles

  1. Nov 7, 2011 #1
    Forgive that to many here this will sound like a dumb question. I have searched and searched and failed to find an answer.

    Give the constant creation/annihilation of all forms of particles in ZPE, it seems likely to me that some among them would collide with each other before either had a chance to annihilate. When such collision occurs, does any energy get transferred to the "real" world and not get annihilated?

    Has any calculation ever been made as to how often such collisions are likely to occur?

    Thanks for your help.
     
  2. jcsd
  3. Nov 7, 2011 #2
    That virtual particles exist at all, except as far as their virtualness is perhaps an artifact of calculation or something, is/has been a hotly debated topic in physics forums. The 'evidence' of the widely referenced, including by some highly-credentialed physics boffins, Casimir effect has been interpreted otherwise:

    http://en.wikipedia.org/wiki/Casimir_effect

    Therefore, before speculating on the interactions of virtual particles, we must establish whether they necessarily exist. Or else the discussion becomes crudely analogous to what happens every time a flying saucer collides with Santa Claus.
     
  4. Nov 7, 2011 #3
    Dan...

    Thank you for your response. I am familiar with your point of view on virtual particles. There is another view however, that regards them as particles in all regards for the short time they exist.

    It is to these people that my question should have been specifically addressed.
     
  5. Nov 7, 2011 #4
    Very well, and I have nothing further to add, except my concern for those who, as I once did, are eager to join in a discussion about things only because they are so blithely discussed in popular magazines, treated as a given on the same level as c-invariance, evolution, and the like; and the less parsimonious view has perversely risen to the top of legitimacy.
     
  6. Nov 7, 2011 #5

    Bill_K

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    josephwouk, Your understanding of virtual particles as real particles that exist only a brief time is correct, and is the majority point of view.

    In answer to your question, while virtual particle can interact with each other, the laws of conservation of energy and momentum are obeyed at every vertex. If the state in question is the vacuum state, the amount of energy available is zero, and consequently any particles that are created will be virtual.

    On the other hand in a collision additional energy is available, and interactions between virtual particles can lead to additional particles in the final state.

    As an example, among the leading production modes expected for Higgs bosons are gluon fusion and vector boson fusion. Here, two quarks (which themselves are virtual) produce a pair of virtual bosons (such as W or Z) which then collide to form a Higgs boson. The Higgs (also virtual!) decays, perhaps into a pair of photons, or by other modes into leptons.
     
  7. Nov 7, 2011 #6
    Maybe of interest: Virtual particle pair production in the vacuum, photon scattering, Unruh radiation, Schwinger effect ("virtual electron-positron pairs will be able to separate and become real") etc will be experimentally investigated by the (European) Extreme Light Infrastructure project in the next few years http://www.extreme-light-infrastructure.eu/High-field_5_2.php
     
  8. Nov 8, 2011 #7
    I've said this before in another post. You can scatter of virtual b quarks in the proton during high energy physics experiments (like at the LHC), which produce b jets. These b jets will leave a unique signature in your detector. So from an experimentalist point of view, virtual particles do exists, and you can measure the consequences of their existence. They are not a mere calculation tool. Also, all "real" particles are slightly off shell, and eventually end their existence at a vertex of another interaction, so they are in essence virtual as well. What is a mere calculation tool and an idealization is the idea of a free particle, since by definition they ever interact, and hence can never be studied or detected.
     
  9. Nov 8, 2011 #8

    Thank you for your reply. It is precisely these "additional particles" that I'm referring to.

    Assuming that they indeed survive, I was wondering whether any statistical calculation has been or even can be made to estimate how often virtual particles collide and produce additional particles.

    My guess/hope is that it would only be a tiny percentage.
     
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