Since light bend in gravitational fields in line with the general relativity , does the speed of light slows down? or is it always constant and never change?
Light does not change speed in a vacuum, it just follows the local geodesic, which makes it look bent in terms of Euclidean geometry. A geodesic is a straight line in space-time (Riemann geometry).Since light bend in gravitational fields in line with the general relativity , does the speed of light slows down? or is it always constant and never change?
As seen locally, the speed of light is always the same everywhere.Since light bend in gravitational fields in line with the general relativity , does the speed of light slows down? or is it always constant and never change?
As i understood, that will not affect the fixed speed of light, i wonder what kind of engergy drives light to maintain it's speed?the speed of light relative to the coordinate system at a lower potential is effectively slightly slower than it is at a higher potential.
As light climbs out of a gravitational potential, it doesn't lose speed, but it does lose energy. This is the gravitational red shift.Since light is a form of energy, and can be measured in energy units (joules, or quanta), therefore what cause , feed, create or drive that energy to maintain a fixed and constant speed, it baffled me
This question is a little nuanced in GR. One could roughly say yes, the presence of a gravitational field "increases the path length" taken by the light ray and thereby accounts for the Shapiro delay. Alternatively, one can think of the Shapiro delay in terms of time dilation within the gravitational field. Which view to take is...as far as I know, personal preference. Kip Thorne, for example, takes the former view in his description of Shapiro delay in The Science of Interstellar (I know it's not a physics text or anything, but I think we can trust the great Kip Thorne on this part of GR), but Wikipedia takes the latter view in its description of Shapiro delay. The photon's path is of course null, and the proper length along its world line is 0.While light may not lose speed coming out of a gravity well, does it have a longer path to take than it would otherwise?
While light may not lose speed coming out of a gravity well, does it have a longer path to take than it would otherwise?
In GR, where the space is curved, how would you like to define the "straight path of light"? The light will never take that "straight path" as gravitational lensing is a real thing, so the only thing you can compare is "how long would light take to go from A to B if there were no central mass compared with how long would light take to go from A to B with the presence of the central mass?" The answer to that is "without the central mass, the light takes a slightly shorter time to get from A to B, the longer time required in the presence of the central mass is the Shapiro delay". http://en.wikipedia.org/wiki/Shapiro_delayView attachment 76766
This Quote addresses the heart of my question,
Fig 1 is a straight path of light
Fig 2 is a path of light that is bent by Gravity
the question is will both rays of light reaches from (a) to (b) at the same time?