The mass of the photon is zero. The end.

Relativistic mass is a hazardous concept, and many authors refuse to use it. Accepting the concept implies, for example, that if you stand on a weighing machine connected to a bomb that blows up if your weight exceeds 100kg, and you're in a uniform gravitational field, you'll eventually blow up in the lab frame as you accelerate. That obviously contradicts the fact that you'll watch yourself remain intact in the rest frame. See also this question on SE.

The mass of the photon is zero. The end.

Relativistic mass is a hazardous concept, and many authors refuse to use it. It makes the increase in kinetic energy of an object with velocity appear to be connected with some change in the internal structure of the object. See also this question on SE.

The mass of the photon is zero. The end.

Relativistic mass is a hazardous concept, and many authors refuse to use it. Accepting the concept implies, for example, that if you stand on a weighing machine connected to a bomb that blows up if your weight exceeds 100kg, you'll eventually blow up in the lab frame as you accelerate. That obviously contradicts the fact that you'll watch yourself remain intact in the rest frame. See also this question on SE.

The mass of the photon is zero. The end.

Relativistic mass is a hazardous concept, and many authors refuse to use it. Accepting the concept implies, for example, that if you stand on a weighing machine connected to a bomb that blows up if your weight exceeds 100kg, and you're in a uniform gravitational field, you'll eventually blow up in the lab frame as you accelerate. That obviously contradicts the fact that you'll watch yourself remain intact in the rest frame. See also this question on SE.