Speed of Light Questions

[Kewell]

How much does speed of light slow down when traveling in water compared to the light that travels in a vacuum?

Is it possible to travel faster than light or at least the same speed when it is traveling through water and we are traveling above the water?

And there are articles going around saying that Speed of Light is not actually a constant and its slowing down, and has been ever since the beginning of time. If this is true and light was faster in the past wouldnt this totally alter our concepts of time and the age of the universe?

 

[baulten]

How much does speed of light slow down when traveling in water compared to the light that travels in a vacuum?

Light does not slow down. It appears to because it refracts off the various water molecules and hence-forth takes more time to cross the water, but the wave is still propagating at the speed of light. It just runs into things on the way :lol:

Is it possible to travel faster than light or at least the same speed when it is traveling through water and we are traveling above the water?

Well, I suppose it would be possible to travel at the same apparent speed. Of course this all depends on temperature and density of the water.

And there are articles going around saying that Speed of Light is not actually a constant and its slowing down, and has been ever since the beginning of time. If this is true and light was faster in the past wouldnt this totally alter our concepts of time and the age of the universe?

Yes, it would. There are a few papers on these theories, but the majority of scientists do not believe that the speed of light has ever varied.

 

[Kewell]

So if we are able to travel at the same apparent speed, does that mean we would be able to see the actual end of the light beam?

And if the light wave is propagating at the speed of light in water.. and we are above the water traveling at the same speed wouldnt we have to be traveling the same speed as the light in water. Isnt that impossible?

 

[derekmcd]

How much does speed of light slow down when traveling in water compared to the light that travels in a vacuum?

Is it possible to travel faster than light or at least the same speed when it is traveling through water and we are traveling above the water?

And there are articles going around saying that Speed of Light is not actually a constant and its slowing down, and has been ever since the beginning of time. If this is true and light was faster in the past wouldnt this totally alter our concepts of time and the age of the universe?

The refractive index of a vacuum should be 1. The refractive index of water is 1.33. The speed of light in a vacuum (C) is 3*10^8 meters per second. Simply divide the speed of light by the refractive index of the medium it is traveling through. In the case of water, the phase velocity of the beam of light would be 2.25*10^8 meters per second or 225,000 km per second.

So, in theory, you could travel faster than a beam of light in water. However, I wouldn't hold your breath waiting for this technology.

As was pointed out, the photons are always travelling at C. When a photon hits an atom, it can transfer its momentum to the atom which puts the electron into a higher energy state by absorbing the photon. The same electron will re-emit a photon in order to return to its original state. It is the amount of time between the absorption/emission cycle that gives the appearance that a photon can be slowed down.

A perfect example of this is photons generated in the Sun's core. It can take them up to one million years to fight their way through the sun before they hit the photosphere at which point, it only takes them a bit over 8 minutes to reach the Earth.

One way you could look at it is by stating the beam of light has to travel a longer distance to get to the other side. Sort of like walking through a maze.

 

[origin]

And if the light wave is propagating at the speed of light in water.. and we are above the water traveling at the same speed wouldnt we have to be traveling the same speed as the light in water. Isnt that impossible?

First, can matter travel faster than the speed of light in water, the answer is yes. Look up http://www.physlink.com/Education/AskExperts/ae219.cfm, the VERY important key is that the electrons are traveling faster than the speed of light in WATER, which is slower than the speed of light in a vacuum.

This does not violate special relativity becasue special relativity says that nothing can travel faster than light in a vacuum. In fact no mass can even travel at the speed of light in a vacuum.

 

[therocketjohn]

Sometimes light just looks like it is slowing down because Chuck Norris is running next to it.