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Feynman's perspective on negative energy states and pair creation

  1. Jul 5, 2008 #1
    Dirac's theory of the electron predicted that there were identical particles of equal mass but of negative energy.

    He appealed to the Pauli exclusion principle and proposed that there was a negative energy 'sea' of electrons that was full up to -2mc^2 in order to answer critics that positive energy electrons described by the Dirac electron theory would simply decay down to -infinity.
    With this description pair creation is described by absortion of a photon (where the energy of the photon E_p > 2mc^2) by a negative energy electron that scatters up to a poitive energy state leaving behind a hole.

    This hole is the negative energy 'sea' has equal but opposite charge to the electron and is commonly known as a positron.

    I believe that this description is somewhat old hat and not used anymore in modern QFT circles. Can anybody give me a not too technical explanation to why the 'old hat' qualitative explanation is unsatisfactory and how Feynman's resolution works, i.e. negative-energy particles can only travel backward in time.
  2. jcsd

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