A high energy photon, like $E_\gamma \geq m_ec^2 + m_{\bar e}c^2$ where $m_e, m_{\bar e}$ is the mass of an electron and positron respectively, can spontaneously create an electron-positron pair.


Is there a moment when this high energy particle is both a photon and an electron-positron pair?

More specifically, once a photon is high enough energy that it can turn into massive particles, is it still a photon or is it more like a probability of being a photon or other particle?


I am reading about stars and my book says that high energy photons need a massive nucleus for the simultaneous conservation of momentum and energy. I feel like adding a bystanding nucleus to my question does not change what I am asking.


1 Answer 1


Since high energy photons propagate with the same velocity (c) as low energy photons, they cannot be a superposition of a photon and a state involving massive particles. Placed within a medium including massive charged particles, however, they can interact, and/or scatter which permits them to create particle anti-particle pairs and also slows down their velocity of propagation.

  • $\begingroup$ Then what does is mean that light is a "quantum superposition of excited matter states and pure photons"? $\endgroup$
    – Tsangares
    Commented Jul 6, 2017 at 23:26

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