Mass of Photon: What's the Proper Explanation?

[swampwiz]

I read an internet meme:

Photons have mass? I didn't even know they were Catholic.

I was going to respond that photons are "massless" particles, but then I realized that photons have energy, and thus must have mass.

What's the proper explanation here?

 

[berkeman]

I read an internet meme:
I was going to respond that photons are "massless" particles, but then I realized that photons have energy, and thus must have mass.

What's the proper explanation here?

Some INSIGHTS reading for you...

https://www.physicsforums.com/insights/?s=mass

 

[Herman Trivilino]

then I realized that photons have energy, and thus must have mass.

What's the proper explanation here?

The mass $m$ is not equivalent to the energy $E$. In other words, $m \neq E/c^2$. Instead, $m^2=(E/c^2)^2-(p/c)^2$

A system consisting of a single photon has zero mass because its energy $E$ is equal to its momentum $pc$.