Many people have been arguing for a long time that it doesn't. Of course, they couldn't actually give solid proof for this. They based their theory on the fact that if photons had mass at rest than many laws and theories we know today would be wrong. But the question still remains, if photons have no mass at rest, then why is light sucked into black holes. I mean, if light has no mass at rest, then the concept of gravity doesn't apply to it. Also, where does all the energy and momentum come from. I know about the concept of relative mass, but still, even with this, the energy has to come from a source and in my opinion that source has to be an initial mass.