# Photon not actually massless

1. Jul 18, 2012

### Allojubrious

Because light bends due to gravity, as can be seen in Gravitational Lensing, if gravity responds to mass and light is bent by gravity, does that not imply that the photon is NOT 100% massless?? That the photon indeed has a very tiny amount of mass?? Because if light bends due to gravity, then light must have a some mass right?? If one could explain this phenomenon, that would be great!

Thanks,
Al

2. Jul 18, 2012

### phinds

Photons are NOT "bent" in the way you seem to think. Photons follow a spacetime "straight line" (aka "geodesic").

3. Jul 18, 2012

### Mark M

No. In general relativity, the strength of gravity is determined not by mass, but energy-momentum. So, light interacts gravitationally even though it has zero mass.

4. Jul 18, 2012

### Allojubrious

Oh ok yeah that makes sense, well thank you!

Thanks,
Al