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Hi, i was just wondering something.If light is affected by gravity like near a black hole, is it possible for gravity to slow down or speed up a wave of lights frequency?

Thanks for the reply. I'm not so good with maths.Are you saying gravity can slow or speed up light? Does a red light move slower than a violet light?

Are you saying gravity can slow or speed up light? Does a red light move slower than a violet light?

Quote from: ...lets split up... on 04/05/2012 13:02:19Thanks for the reply. I'm not so good with maths.Are you saying gravity can slow or speed up light? Does a red light move slower than a violet light?No. The speed of light in a vacuum is a universal constant, regardless of frequency, and does not change. The frequency might be red-shifted and the pathway might appear to be bent, but light does not get slowed or speeded up. Every observer will still measure the speed as c, no matter what frame of reference they are in.

It does, however, depend on the gravittional potential Phi. See derivtion at http://home.comcast.net/~peter.m.brown/gr/c_in_gfield.htm [nofollow] Einstein first proved this in 1907. It was also experimentally proven.

So in the presence of gravity the speed of light becomes relative (variable depending on the reference frame of the observer). This does not mean that photons accelerate or decelerate. This is just gravity causing clocks to run slower and rulers to shrink.

I am quite good with maths, but the meaning of all that is a bit beyond me. Is it saying that as you approach the black hole the local speed of light slows,

...first to walking pace, then finally zero at the event horizon?

The v=Here's another link that explains it more clearly....sorry, you cannot view external links. To see them, please REGISTER or LOGIN

To PmbSo you saying if i were near the black hole the light would appear to travel at the usual speed of "c" because of time being relative to space, but if i were observing from a distance it would appear to travel slower?

The Schwarzschild metric describes a black hole, in fact, it can describe any spherical body of gravitational mass. The equation isI don't expect you to understand the equation, but this describes black holes.

Quote from: Ęthelwulf on 06/05/2012 10:24:58The Schwarzschild metric describes a black hole, in fact, it can describe any spherical body of gravitational mass. The equation isI don't expect you to understand the equation, but this describes black holes. What is the purpose of your post? Everything asked by posters I covered above. They asked bout the speed of light slowing down and speeding up. Your post describes gravitational redshift. By the way, who is you? For the details of gravitational redschift in a Schwarzschild Spacetme please seeSee ...sorry, you cannot view external links. To see them, please REGISTER or LOGINScroll down to where it say Schwarzschild Metric. These equations correctly describes why time slows down near a black hole. The value of dt doesn't have to approach zero or any other value in order to demonstrate. This page also shows that as a beam of light moves through a Schwarzschild Spacetime the energ of the beam is conserved. That is one thing that doesn't change.

I can see that your link does not tackle the same approach as I have made... but I can assure you my approach is the reason why clocks run slower.

Quote from: Pmb on 06/05/2012 11:09:50Quote from: Ęthelwulf on 06/05/2012 10:24:58I don't expect you to understand the equation, By the way, who is you? And what do you mean, who am I?

Quote from: Ęthelwulf on 06/05/2012 10:24:58I don't expect you to understand the equation, By the way, who is you?

I don't expect you to understand the equation,

I'll assume you missed the arguement concerning how time is slowed down.

The slowing down of time is actually quite technical for a black hole --- (inside a black hole, time does not stop... in fact, time becomes what is called, spacelike).

I don't expect you to understand the equation, but this describes black holes.

The you see cropping up is in fact the Horizon.

The coefficient of approaches zero, ...

really has to do with why clocks run slower.

The observer moving towards the black hole will never observe a difference in their clocks, , ...

Quote from: Ęthelwulf on 06/05/2012 10:24:58The slowing down of time is actually quite technical for a black hole --- (inside a black hole, time does not stop... in fact, time becomes what is called, spacelike). Actually the slowing down of time is actually quite simple for a black holes. Arguably, the most simple metric for a spacetime is that of a uniform gravitational field which isds^2 = (1 + gz/c^2)^2 dt^2 - dx^2 - dy^2 - dz^2By the way, in what coordinate system/units did you state the Schwarzschild metric in? In my page I used MKS units (at least I think that they're called that). But you seem to be using two different systems of units. Note - In my page ...sorry, you cannot view external links. To see them, please REGISTER or LOGIN I made a mistake. In Eq. (5) I missed putting a square in the last sin. It reads r^2 sin theta d^2 phi. It should read r^2 sin^2 theta d^2 phiQuote from: Ęthelwulf on 06/05/2012 10:24:58I don't expect you to understand the equation, but this describes black holes.I doubt that anybody here, including the moderators, find it very polite when you state that your expectations is low. In fact there is no valid reason to assume the worst.Last week I myself had to adjust my posting paterns as given by the moderators. It wouldn't be very fun for you to have to go through the same thing and risk getting placed on vacation again. Sometimes we just have to take a step back and readjust out thinking and attitude.We had discussed this kind of thing in the thread On the concept of relativistic masshttp://www.thenakedscientists.com/forum/index.php?topic=44036.0Quote from: Ęthelwulf on 06/05/2012 10:24:58The you see cropping up is in fact the Horizon.Correct.Quote from: Ęthelwulf on 06/05/2012 10:24:58The coefficient of approaches zero, ...That is a misleading statement. is not a coefficient, or if it is then your explanation was a bit poor in explaining yourself. In that part of this thead the topic was the gravitational field changing the speed of light. For no obviois reason you changed the subject to gravitational redschift, for no obvious reading and in not a very good way.Quote from: Ęthelwulf on 06/05/2012 10:24:58 really has to do with why clocks run slower. That expression is not the most obvious or the clearest way to explain gravitational redshift. The dt - > doesn't mean what you seem to think that it means. dt -> 0 only means that the coordinate time interval dt is approaching zero. This doesn't help your argument. The slowing of time is meant by Eq. (3) in my treatment of gravitational redshift/slowing down of time. See Eq. (3) & (4) ...sorry, you cannot view external links. To see them, please REGISTER or LOGINQuote from: Ęthelwulf on 06/05/2012 10:24:58The observer moving towards the black hole will never observe a difference in their clocks, , ...That is not true. In fact if one ship wishes to observe the clock on another shift slow down then what you just showed is how it's done.Whew!!

I can assure you, what I told you is pretty standard.

Hi, i was just wondering something.If light is affected by gravity like near a black hole, is it possible for gravity to slow down or speed up a wave of lights frequency? ...

... dt^0--> 0 really has to do with why clocks run slower. ...

The observer moving towards the black hole will never observe a difference in their clocks, but if someone was sending signals back to an observer safely away from the black hole, there clocks would appear to run slower. The person approaching the horizon it will seem to always take forever to get there.

Leonard Susskind also makes note in the same fashion as I did that this has to do with the slowing down of clocks. I'll find it for you since you are skeptical.

Thanks guys.