How a photon choose a geodesic?

Question

Suppose we have two point $p$ and $q$ linked by two geodesics $gamma_1$ and $gamma_2$. Now suppose that a photon is emitted at $p$ and received at $q$. How does the photon choose which of the geodesics to follow?

Umaxo · Accepted Answer

If particle is emitted, it is emitted with certain 4-velocity and it follows geodesic for which this is tangent vector. The decision is completely local, photon has no apriori desire to travel to some point q and then looks for the geodesic to follow.
That being said, photon is quantum mechanical object and such does not follow any particular geodesic.

Alexander · Answer

Beside "position" photons also have "momentum". Both impose initial position and direction of propagation. There are no two geodesics that have same direction at the same position.

How a photon choose a geodesic?

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