Question

giving that a photon has mass , and that gavity can speed up or slow down an object with mass how is it that the speed of light remains to be a constant

Answer 1

YES

Answer 2

NO

Answer 3

lol

Answer 4

i hope you're not confusing photons with protons

protons have a mass where photons are believed to be mass less

a mass can be calculated for photons with certain energy but that mass is purely theoretical as in it means absolutely nothing

Answer 5

photons don't have mass. light does not slow down (acc. to our current understanding). but yes gravity can lead to bending of light as a photon has energy which is equable with mass but light does not slow down in any frame of reference or in any conditions whatsoever (c will cease to remain a constant if it did).

Answer 6

light slows down depending on the refractive index of medium it is traveling through
photons only have zero rest mass

Answer 7

Photons are certainly affected by gravity - all particles are. They don't "slow down", but their paths are bent (this is called "gravitational lensing" or, if bent enough, a "black hole") and they can be redshifted or blueshifted.

To know more about gravitational lensing, You can choose to watch this one by the Max Planck Institute of Astrophysics:
http://www.youtube.com/watch?v=yamVbK-J69M

and after watching that, watch this one by Phil Marshall (an astrophysicist at stanford university) :
http://www.youtube.com/watch?v=4qoDHdIsIg4&feature=related

Answer 8

Gravity doesn't slow things down, it just means if they move in opposition to the gravity, they have to lose energy. But slowing down is only one way to lose energy. Photons lose energy when traveling away from a mass by shifting their frequency down, towards the red.