RE: No dark matter?
May 9, 2011 at 8:48 am
(This post was last modified: May 9, 2011 at 9:12 am by little_monkey.)
(May 8, 2011 at 11:48 pm)Wormhole199 Wrote:(May 8, 2011 at 5:16 pm)little_monkey Wrote:(May 5, 2011 at 4:31 am)Wormhole199 Wrote:
Sorry for being late on this thread. However, that is totally wrong. The speed of light near a black hole, or anywhere else, is the same. Deny that, and you're denying the foundation of Special and General Relativity.
Inside the black hole, the light doesn't escape because it is bent by gravity into a circle, and so doesn't escape, but its speed remains the same. Outside the BH, your clock will slow down and your ruler will shrink, nevertheless, you will end up measuring the speed of light to be c.
Suppose that you are outside gravitational fields, and that you have a clock and a ruler (which is not rotating with respect to stars), and that you are not accelerating. Based on your clock and ruler what is the measured speed of light near a black hole?
c
(May 9, 2011 at 3:00 am)lilphil1989 Wrote:(May 8, 2011 at 5:16 pm)little_monkey Wrote: Sorry for being late on this thread. However, that is totally wrong. The speed of light near a black hole, or anywhere else, is the same. Deny that, and you're denying the foundation of Special and General Relativity.
Inside the black hole, the light doesn't escape because it is bent by gravity into a circle, and so doesn't escape, but its speed remains the same. Outside the BH, your clock will slow down and your ruler will shrink, nevertheless, you will end up measuring the speed of light to be c.
Actually, this is not quite true.
Which part is not true?
Quote:The problem with general relativity is that things can be coordinate dependant. Take for example the Schwarzschild geometry: from the time Schwarzschild came up with it during the first world war (whilst fighting in the trenches, no less) up until the 1960's, everyone thought that the singularity at the schwarzschild radius was a real physical effect, but it turns out to be just an artifact of the coordinates.
Yes that's true. For an observer falling into a black hole, he would not observe anything significant. He would not realize that any light he would be sending out would never go beyond the event horizon.
Quote:The coordinate speed of light can be non-constant (or =/= c), but the proper speed is always c.The speed of light is always the proper speed, unless specified differently. This means observers can detect when their motion is accelerated by studying light signals.
Quote:An observer that doesn't know about relativity that wants to measure the speed of light in a non-inertial frame will measure (distance travelled by light measured by my ruler) / (time elapsed on my clock) which is the average coordinate speed which could be something other than c.
The speed of light does not vary because some observer happens to be ignorant of the laws of physics. His corrections can amply be supplied by one who does know relativity.
Quote:For the example of a black hole you gave, the coordinate speed of light at the surface of a black hole is zero whereas it's proper speed is c.
The light I referred to in my post was emanating from inside the black hole. If there was anything wrong on that, please enlighten me.
