It is a given that the speed of light in a vaccuum is c.
ravelling through a denser medium, like water, it is about 75% of c.
Now, lets say light crosses a gravity well, like around a massive body of a planet (Better yet, a black hole):
Is the warped space/time considered a dense medium, therefore, the speed of light slows down?
Is the warped space/time considered a dense medium, therefore, the speed of light slows down?
Well no, the warped space/time is not considered a dense medium - it’s not even a medium. Note that the individual photon always travels at c - it’s the beam of light the changes speed.
As measured from where?
If you’re hitching a ride on the back of a photon in a gravity well, the speed of light you would measure is still c.
To an observer some considerable distance away the speed of light in the gravity well would appear to be somewhat less than c.
Check out this link to hear it from “the man” himself:
http://www.itba.edu.ar/cargrado/fismat/fismod/transf/htm/einstein_5.htm
Are you sure? I’m not a physicist, but it seems to me that you would keep the speed of light constant, and dilate time and space as necessary.
Or does that apply only in inertial frames of reference?
lucwarm,
Well, not having validated the results personally, I can’t say I’m sure. However there are a lot of guys that I trust (Einstein, et. al.) who say it’s so.
Special Relativity makes the claim that the speed of light is the same for all observers in inertial frames of reference. However General Relativity amends that slightly to say that the speed of light is the same for all observers in local inertial frames of reference.
The paper that I pointed you to is one of Einstein’s first publications on the theory (even before he formulated the General Theory of Relativity). Since that time, the experiments that he proposed have been done over and over (though, admittedly not by me) and the results support his thesis.
i thought that the reduction in speed by a beam of light in a medium was because the individual photons were interfacing with the electrons in the medium and being absorbed, only to be released after an infintesimal amount of time. so, the delays of the absorbtions and releasures adding up to create a 25% delay in the motion of the total beam, rather than the individual photons when passing through water.
that is also the same way that that light-freezing experiment worked. it stopped the condition of the light beam by halting the process of releases at the positive stage, holding the beam, but not the photons, in a state of suspension.
anyway, if my understanding is correct, a gravity well will not slow a light beam, it will only arc it’s path along the curved space-time provided by the gravity.
The speed of light is constant in Special Relativity, but not in General Relativity. SR assumes inertial reference frames. In General Relativity, where general reference frames are allowed, the speed of light is not constant. Consider a beam of light traveling outward at the event horizon of a black hole. It will be stationary. Light trying to leave a gravity well is slowed down. Light falling into a gravity well travels faster than c. In order to have an inertial reference frame where you have gravity, your reference frame must to be free-falling. The speed of light is constant only in inertial reference frames where Special Realtivity holds. In fact not only is the speed of light that is constant in SR, but the velocity. That is, both the speed and direction of light is constant in inertial frames. But you must apply General Relativity whenever you need to consider gravity.
Thanks ACoverofNoise and DrMatrix.