by Chris Peterson » Mon Feb 01, 2010 3:44 pm
mark swain wrote:How can a Mass less particle, be affected at the speed of light, by Gravity?
A photon is not a massless particle. A photon has a
rest mass of zero, which is a very useful theoretical concept fundamental to understanding it and other particles. But in nature, a photon is never at rest. In every measurable way, it behaves as a particle with mass. This makes sense for multiple reasons. First, it obviously has energy, and anything with positive energy has a mass equivalence. Second, it has momentum. In Newtonian mechanics, that would be defined as P = mass * velocity. In the case of a single particle, a QM definition is used, P = h / lambda. The two momentum values are physically equivalent in terms of mechanical behavior, so possessing momentum is equivalent to possessing mass.
Thus, it becomes perfectly reasonable to expect a photon to be affected by gravity, either using Newtonian mechanics (which does approximately work, but produces a slightly incorrect result), or using GM and relativistic mechanics.
[quote="mark swain"]How can a Mass less particle, be affected at the speed of light, by Gravity?[/quote]
A photon is not a massless particle. A photon has a [i]rest mass[/i] of zero, which is a very useful theoretical concept fundamental to understanding it and other particles. But in nature, a photon is never at rest. In every measurable way, it behaves as a particle with mass. This makes sense for multiple reasons. First, it obviously has energy, and anything with positive energy has a mass equivalence. Second, it has momentum. In Newtonian mechanics, that would be defined as P = mass * velocity. In the case of a single particle, a QM definition is used, P = h / lambda. The two momentum values are physically equivalent in terms of mechanical behavior, so possessing momentum is equivalent to possessing mass.
Thus, it becomes perfectly reasonable to expect a photon to be affected by gravity, either using Newtonian mechanics (which does approximately work, but produces a slightly incorrect result), or using GM and relativistic mechanics.