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Speed of light

One of the interesting questions to ask fundamentalists is do they believe the speed of light is constant.

This opens up an interesting paradox that if the universe is huge and light travels at a constant speed we would only be seeing a tiny portion of stars in the 6,000 light years from earth range.

I have heard this countered by the suggestion "God created the light on its way to us" but that is really difficult to explain in any reasonable manner.

So far the Hubble telescope has been able to see light from the formation of stars billions of years ago it is an interesting question as to how the light from them has got to us in such a short period of time :-)

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Permalink Reply by Skylar on September 5, 2008 at 12:03am

I've heard the "appearance of age" theory where they say that the speed of light is constant here and now but it wasn't always constant and is actually slowing. (Something like that anyway).

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Permalink Reply by Doug on September 5, 2008 at 12:08am

They are usually short on specifics about how this theory would work :-)

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Permalink Reply by Skylar on September 5, 2008 at 11:20am

Yes, exactly. ;)

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Permalink Reply by David Potter on September 13, 2008 at 5:09pm

So is the speed of light constant, throughout the universe?

That is actually an interesting question.

During the Big Bang, the universe was actually accelerating at faster than light speeds. That actually doesn't contradict Einstein's Special Theory of Relativity - since nothing within the space-time continuum is supposed to be able to go faster than light. But nothing about Einstein's Theory restricts space-time itself from moving faster than light.

Einstein himself had a special name for it. It's called frame dragging.

So the answer might actually be "yes and no."

Galaxies far far away - at the limits of astronomical observation - might actually be younger than we suppose. That still does not support the creationist view, however - because everything in our galaxy - as well as the local galactic cluster - would have a speed of light that remains the same relative to our constant motion.

Locally - throughout the universe - the speed of light would always remain the same.

It is only when we look back through time, to an era when the universe itself was expanding at faster than light speeds, that - relative to our own motion today - light might appear to be moving faster than light; and so - the estimated age of the universe might be off a bit.

It is still much older than 6,000 years, however.

Billions and billions - if not trillions and trillions - of years older.

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Permalink Reply by Joshua1080109 on October 4, 2008 at 7:04am

i have a very radical yet simple theory to answer this question...
light doesnt travel at a constant speed
light is of course a beam and in that beam energy packets travel, so those packets must carry some kind of mass...so wouldnt gravety pull on it?

so if the universe is basically nothing what ever gravity there is would constantly pull on it so light msut travel at a speed unpredictable because it is always changing?

and to counter act that theory to further stenghten it, E=MC squared, so energy is exactly the same matter only moving faster? hmmmmmm

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Permalink Reply by Rikka on October 12, 2008 at 10:04pm

haven't scientists been able to slow and stop light anyway? who says that something in space couldn't do that, or even god itself? :P

http://www.hno.harvard.edu/gazette/1999/02.18/light.html
http://news.bbc.co.uk/2/hi/science/nature/3308109.stm

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Permalink Reply by Karl on April 30, 2009 at 6:02am

Light only travels at a constant velocity in a vacuum, when it travels through any other medium its velocity can change dramatically, which is why when light travels through glass it bends.To answer Josh yes light does have mass and does interact with gravity, which is why there is a special theory of relativity which works when there is no strong gravitational field, and the standard theory of relativity which works in strong gravitational fields such as near stars.
There is an argument for saying that the speed of light in a vacuum has changed over time but not since the first phase change occured after the big bang when matter and radiation became decoupled.
By light I mean any form of electromagnetic radiation, light being just one example of EM radiation.

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Permalink Reply by Polymath on May 4, 2009 at 10:43pm

Some believe that the speed of light is lowing down and and was much faster in the past. They point to early attempts to measure the speed as evidence of this slowing. Funny thing, though. When the methods got accurate, the decrease stopped. Hmmm.....

A rather more sophisticated version uses relativity to suggest that the curvature of the universe allows such travel over short time periods (relative to earth). Again, the problem is that this model has absolutely no evidence to support it and much to show it wrong.