# Fundamental question

Why must the 4-momentum for photons $$p^\mu =(\frac{h\nu}{c},\frac{h\nu}{c} \textbf{e})$$ transform as a 4-vector in Special Relativity?

Dale
Mentor
2020 Award
I don't understand the question. The four-momentum transforms as a four-vector for all particles, not just photons.

CompuChip
You can even derive it (Let $p^\mu = (p^0, \vec{p})$, apply a Lorentz transformation and you will see what p0 should be).