• Quick note - the problem with Youtube videos not embedding on the forum appears to have been fixed, thanks to ZiprHead. If you do still see problems let me know.

Speed of light

karros

Student
K
Joined
Sep 7, 2005
Messages
49
has or is the speed of light a constant? Has the speed of light slowed down any since the big bang? And finally is there a formula that shows the rate of speed decrease of light over time?

Thanks in advanced.
 
I don't have all the answers to your questions, but 'c' is the speed of light through a vacuum. When it passes through different media, ie: air, water, glass, etc. it has a slower speed, owing to the more circuitous path it must take to pass through the material. In laboratory settings, scientists have slowed down light considerably by having it pass through certain exotic materials, reaching 40 miles and hour vs. the 186,000 miles/sec light travels through a vacuum. In regards to your queries about the speed of light slowing over time, I don't have any definitive answer, but my initial thoughts are that this is highly unlikely.
 
I've read some articles in SCIAM and Discover that stated a theory that in the first brief moments after the Big Bang, light did travel faster than it does now. I'm not certain what issues these articles were in or if they've been refuted since then, this was about 3-4 years ago. However, I'm sure SCIAM or Discover's websites would be a great starting point. You can search their issues online.
 
It depends on what you mean by the speed of light. The value of "c", which happens to match the speed of light through a vacuum right now is a fundamental constant. There are GUTs that do predict that the speed of light could have varied over time, but there are no conclusive measurements that either prove or disprove any of these theories at the present time. As for a formula to describe how the speed of light might have changed over time, it would depend on which particular GUT you were interested in looking at.
 
Thanks

I am doing a study for Dr. Hovind since he finds it easier just to make claims without backing them up. This info has helped so far.
 
Cyphermage said:
Egads. Roy Masters, of the Foundation for Human Understanding. I remember the hilarious debates between him and the late Walter Martin, "The Bible Answer Man."
Click to expand...

As a matter of fact, the debates with Walter Martin are available on cassette on his website. I haven't heard it myself but I know Roy can be very funny at times and seemingly without any effort on his part. Did you listen to his radio program at one time? His meditation exercise, Be Still and Know can be downloaded for free.

www.fhu.com
http://www.fhu.com/shopping_audios04.html
 
Last edited:
If the "speed of light" appeared to be "changing", precisely which metric is actualy changing?

Velocity? (contraction/expansion of space-time)
Distance? (contraction/expansion of space)
Time? (contraction/expansion of time)

Some food for thought anyways...
 
Hardenbergh said:
As a matter of fact, the debates with Walter Martin are available on cassette on his website. I haven't heard it myself but I know Roy can be very funny at times and seemingly without any effort on his part. Did you listen to his radio program at one time? His meditation exercise, Be Still and Know can be downloaded for free.

www.fhu.com
http://www.fhu.com/shopping_audios04.html
Click to expand...

Yes, I've listened to his program. Many many years ago, I left a religious radio station on for several months, and caught the daily performances of all the biggies. Dr. Walter Martin, Marylin Hickey, Roy Masters, Elizabeth Claire Prophet, Bob Larson, James Dobson, and others too numerous to mention.

I eventually tired of it, but it was amusing while it lasted.
 
karros said:
has or is the speed of light a constant? Has the speed of light slowed down any since the big bang? And finally is there a formula that shows the rate of speed decrease of light over time?

Thanks in advanced.
Click to expand...

C is constant, per se. Of course, since the universe is expanding, I suppose you could say it's actually accelerating, not that we'd ever notice that, really.
 
rockoon said:
If the "speed of light" appeared to be "changing", precisely which metric is actualy changing?

Velocity? (contraction/expansion of space-time)
Distance? (contraction/expansion of space)
Time? (contraction/expansion of time)

Some food for thought anyways...
Click to expand...
I was thinking along these lines with regard to this question.

It seems that if there was such a thing as a meter stick that didn't expand along with space then we might detect a change in the speed of light over time because we could compare the fixed length meter stick with the normal meter stick thats length is changing with time and we might detect some kind of change in the speed of light over time.

But it seems that as space expands locally all the relevant parameters change just so, so that we think the speed of light is constant. But we realize that this isn't quite so because we can detect that space is expanding by the red shift of electromagnetic radiation coming from stars far away from us.

But, we might be able to detect this expansion of space locally because the time it takes a light beam to travel one meter should be slightly less than half as much time as it takes a light beam to travel two meters.

This site, http://scienceworld.wolfram.com/physics/HubbleConstant.html ,
lists one value for hubble's constant as 83 km/sec per megaparsec. Assuming that my math and unit conversion is roughly correct this means that the light flight path past the two meter stick will be about 10^-28 meters longer than twice the length of the one meter stick so it seems like we arent going to be detecting a change in the speed of light because of the expansion of space based on local measurements any time soon. The size of atoms are roughly 10^-10 meters.

I'm not sure its completely impossible though. Imagine a long tunnel with an almost perfect vacuum and two nearly perfect mirrors at each end bouncing light back and forth billons of times. Would we ever get to the point that detecting a local expansion of space was remotely in the realm of possible because of an apparent change in the velocity of light from the speed measured for one trip to the average speed measured for billions of reflections. Now I think about this a little bit more it seems we wouldn't have to directly measure the speed, we could just look for a red shift in the light beam that had been reflected back and forth billions of times.
 
Last edited:
karros said:
I am doing a study for Dr. Hovind since he finds it easier just to make claims without backing them up. This info has helped so far.
Click to expand...

Hovind will never ever ever listen to reason. He's a quack, a liar, and a fraud. When proven wrong, he will flimflam and ignore. Rather than debate with him, you might look into doing something more useful, like bashing your head against a brick wall.
 
When we talk about changes in a universal constant, it really makes sense only to talk about dimensionless constants. Otherwise, you can fudge other things to make the change unnoticable.

The simplest dimensionless constant which contains "c" is the Fine Structure Constant.

alpha = k*e/hbar*c

So the question we want to ask is given two regions of spacetime continuum, one from our universe, and one from a universe where alpha has some other value, how do they differ?

What property of spacetime carries the value of this constant.

This is not something that is predicted by the standard model, and since everything we can observe about our universe indicates that this dimensionless constant has the same value everywhere, there really aren't a whole lot of experiments we can do to answer this question.

One question we might ask is whether this constant has changed over time, and whether it had a value in the early universe which is different than the value it has today.

We can examine the value of the Fine Structure Constant in prior cosmological epochs by looking at the fine structure splitting of certain spectral lines in distant quasars and radio galaxies.

The latest such studies suggest that if there is a change, it is very slow, and is less than a part in 10^13 per year.
 
karros said:
I am doing a study for Dr. Hovind since he finds it easier just to make claims without backing them up. This info has helped so far.
Click to expand...
[swiki]Kent Hovind[/swiki]

Hovind debates Ross : "Einstein’s theory was that the speed of light is a constant. Time is the variable. Maybe he was wrong. Maybe time is the constant and light is the variable."

:jaw-dropp

Time ... a constant.
 
Heres a very recent blog posting by someone reputable for anyone interested. As mentioned above, an evolving dimensionful thing such as the speed of light is somewhat poitless to think about - but the speed of light appears in the denominator of the fine structure constant, which is dimensionless, and so it makes sense to ask if that is evolving...

http://motls.blogspot.com/2006/05/evolving-fine-structure-constant.html
 
You must log in or register to reply here.

Back
Top Bottom