Does light only travel at one speed?

vertica said:
I assume he is referring to gravitational lensing
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Which doesn't involve the speed of light changing, it involves the deflection of the paths light moves along so as to bend around an object (typically a galaxy). In actual lenses this is done by changing the speed of the light ray so as to refract it but in gravitational lensing its done by warping space-time.
 
How about when light gets sucked into the black hole? Wouldn't black hole cause the light to accelerate further thus increasing it's speed or will the light get sucked at same speed c?
 
yhack said:
The reason we know dark matter exists is because it 'bends' the light so we can see a ring around stars if there's dark matter between us and the star. I don't think this changes the speed though.
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Well, we know that either dark matter exists or something is up with our theory of mavity. The latter is probable, so it's not a given that dark matter exists.
 
As said, the speed of light can be affected by mavity, but does appear to be constant in a vacumn.

However if light was to encounter the theoretical black hole, then light itself would not just "slow" down, it would not escape even. Thats why black holes have not yet been discovered by astronomers, but for all intents and purposes are accepted to exist in science.

My physics teacher, used to use water (as I am sure nearly all physics teachers do) as a way to explain how light moves around the Universe, it gets dispersed as others have said by glass/prisms and as a wave/particle the photons do seem to remain constant unless they face an obstacle. I resume thats why light from very distant stars is seen as weak, because the energy has been dispersed...

Your idea about light would be an elegant idea, however if it was the case and here is something that really does my head in then the light and and energy created by the Big Bang (Another theory about the creation of the Universe) should still be bouncing around for the human race to witness...Only a remnant of that event exists but not in the form of light, it is called white noise, something that astronomers can pick up with radio telescopes.

Btw according to Wikipedia, light speed is 186,282 miles per second. They used to think it was 188,000!!!

Cheers

Von
 
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WingZero30 said:
How about when light gets sucked into the black hole? Wouldn't black hole cause the light to accelerate further thus increasing it's speed or will the light get sucked at same speed c?
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Because the speed of light is unchanged by gravitational fields. The reason a black hole doesn't let light escape from within the event horizon is not because it 'sucks' the light in but because the warping of space-time means there is no path, no matter the direction you move in, which leads to outside the event horizon.

As you get closer to the event horizon more and more of the trajectories you can take (assuming you're moving without propulsion, for the sake of simplicity) wind up leading into the event horizon. On the event horizon there is one and only one trajectory which doesn't lead further into the black hole and its the one which a ray of light pointed directly away from the singularity would move along and even in that case the light doesn't escape, it remains trapped at the event horizon.

This doesn't mean its stationary, anyone falling into the black hole would 'see' it (as much as you can see a particle of light without it hitting your retina) as moving at the speed of light. This is because the speed of light is always measured locally and even in, on and around black holes and all their extreme effects, space-time is locally flat. This is a fancy way of saying that if you consider a small enough region it appears flat, just like the Earth appears flat if you stand on a hill but from space its obviously curved.
 
VonScar said:
Your idea about light would be an elegant idea, however if it was the case and here is something that really does my head in then the light and and energy created by the Big Bang (Another theory about the creation of the Universe) should still be bouncing around for the human race to witness...Only a remnant of that event exists but not in the form of light, it is called white noise, something that astronomers can pick up with radio telescopes.
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Technically still light, just a different wavelength.
 
SiriusB said:
Technically speaking light waves don't really slow down. It is just an apparent affect caused by atoms absorbing photons and re-emitting them. This lag causes the wavefront to be held back or even advanced [plasma can "speed up" light].

Source: The Internets.
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True,

the slowing down is due to rescattering events, between it travels at c even within materials.
 
VonScar said:
As said, the speed of light can be affected by mavity, but does appear to be constant in a vacumn.
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No, it isn't. It's path is affected, not its speed.

VonScar said:
However if light was to encounter the theoretical black hole, then light itself would not just "slow" down, it would not escape even. Thats why black holes have not yet been discovered by astronomers, but for all intents and purposes are accepted to exist in science.
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As I said in my previous post, that isn't the case. The interplay of photons and black hole event horizons is not something you can view in standard Newtonian terms, as you would throwing a brick in the air. The way in which light behaves around a black hole, or any object for that matter, is determined by the space-time curvature, specifically the null geodesics.

VonScar said:
.Only a remnant of that event exists but not in the form of light, it is called white noise, something that astronomers can pick up with radio telescopes.
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The cosmic microwave background does contribute to the static you see on a TV but not all of it. The CMB is not the remnant of the BB but rather the last scattering surface. It is the redshifted light which was thrown off when the universe cooled enough to deionise and atoms form. Before that (for the first 300,000 years or so) the universe was so hot it was a plasma and light couldn't travel very far due to electrons being all over the place.

VonScar said:
Btw according to Wikipedia, light spped is 186,282 miles per second. They used to think it was 188,000!!!
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It's now defined rather than measured, as we define the metre in terms of wavelengths of a particular frequency of light.
 
Apparently a black hole in every)many galaxies. Thats what helps mantain their structure.

I wonder what would happen if they could look at the centre of the Milky Way with device that could see mavity (doesn't exist.)

Cheers

Von
 
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