# Can a photon be split? [duplicate]

1. A photon is pure energy, zero mass.
2. Different photons have different wave length and carry a different amount of energy.

Now, it seems logical that a high energy photon can be split into 2 low energy photons. I don't know if this could happen via some natural decay or under an external influence or not at all.

P.s. this is not a duplicate of the previous similar question about splitting a photon. The other question presents a photon as a particle, where as this one considers a photon as energy. I think this leads to different lines of thought.

Yes, you are right. Spontaneous parametric downconversion is one way that a high - energy photon can be converted into two low-energy photons.

• I think we should stress interaction. OP seems to ask about a particle like decay – Alchimista Oct 29 '19 at 9:32

A free photon cannot split into two or more photons. You can’t conserve energy, momentum, and angular momentum.

By the way, saying that “a photon is pure energy” is meaningless, unless all you mean is it doesn’t have mass-energy. There is no such thing as “pure energy”; energy comes in different kinds, none of them “purer” by any sensible criterion than others. Also, a photon has more properties than just zero mass and nonzero energy, such as momentum and a particular spin value, so a photon has energy but, in terms of what it is, it’s not just energy.

• I guess you could satisfy the conservation laws if they split such that $p=p_1+p_2$ but they are both still going the same direction ($\hat{\bf p}_1=\hat{\bf p}_2$). But the two photons would have zero relative velocity in every reference frame, so it's not much of a split... The two photons would have different frequencies though, so it might be observable as decoherence? – Mario Carneiro Oct 29 '19 at 13:03