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Originally Posted by [1ponders]
3. Also isn't light redshifted when it moves through this field implying it costs it energy to escape from it. If e=mc sq then if the photon had mass to start with it would have less mass after leaving the field as it cost it energy to do so. If it had less mass then it would be less effected by subsequent gravitational field as the force applied to this photon mass by another would less (by the formula F = G m1 m2 / r2) This observationally doesn't apply. Light reacts consistantly with one gravitational field after another. Hence there is no mass loss. But there is energy loss, more red shifting. Therefore light has energy but no mass.
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If e=mc2 then aren't they interchangeable, energy is mass and mass is energy, if energy is lost wouldn't mass be lost as well ie m=e/c2, so if energy is lost, this would represent an equivalent loss of mass equal to the amount of energy lost divided by c2. There is no observed deviation of gravitaional effects on light after light experiences a gravity field so there is no loss of mass. IE If a photon had mass then by lossing energy in a gravity field it would also loose mass. If it lost mass then it would be effected differently by subsequent gravity fields by F = G m1 m2 / r2. There is no observed difference so there is no mass.
The marble wouldn't loose any mass as the energy it lost in its ejection into space is the energy applied to it to get it there in the first place. If we were able to get the marble to self propell itself into space then yes it would loose mass.
Another thing to think about it that experimentally it has been shown that as objects increase in velocity they increase in mass. The closer to light speed the larger the mass increase. So at light speed an object would have infinite mass. And would require infinite energy to get it there. It could be simplistically argued that the energy is being converted into mass. Then why doesn't a photon have infinite mass. It is travelling at lightspeed.
