[leptons]

>Mass is not required for gravity; only energy is.

E = MC^2

Can't have energy without mass, and mass leads to gravity.

[elashri]

Actually it is

E^2 = (MC)^2 + (PC^2)^2

The first term is describing the rest mass. You can redefine the mass term to make it E=mc^2 but now this mass does not correspond to the rest mass. And for sure you can have energy without having a rest mass. Actually for the early universe all you had was a form of radiation and energy.

[itishappy]

The full equation is: E^2 = (p*c)^2 + (m0*c^2)^2.

https://en.wikipedia.org/wiki/Energy%E2%80%93momentum_relati...

[damiankennedy]

This ignores Planck's energy-frequency relation. Things like photons are affected by gravity as well.

[pdonis]

> E = MC^2

Is only an approximation for particular cases, not a general law.