Anonymous asked in Science & MathematicsPhysics · 10 years ago

Why pair production can not take place in vacuum?

3 Answers

  • 10 years ago
    Favourite answer

    Photons, from which pairs are created, have both energy & momentum, neither of which can be zero.

    When a pair is created from the photon the total energy of the pair must equal the original photon energy, which is fine.

    But also the total momentum of the pair must equal the original photon momentum. Since this process can be viewed from any frame of reference it is always possible to find a frame of reference in which the total momentum of the pair is zero. Since there is no frame of reference in which the photon momentum is zero, you then have a violation of conservation of momentum.

    There must always be another particle present which can be manipulated so the total momentum of all particles is conserved before & after pair production.

  • 10 years ago

    Sounds like you're asking about what are known as "virtual particles." Quantum physics has revealed that at the tiniest imaginable scale (0.000000000000000000000000000000000016 meters), space isn't flat, but more like a seething quantum foam of energy. It's that energy that produces virtual particles. They always come in pairs, each being the anti-particle of the other which means they almost instantaneously self-annihilate.

  • Anonymous
    10 years ago

    It is because a gamma-ray cannot create electron-positron pairs in a

    vacuum that is why pair production cannot takes place in vaccume.

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