Posted by Davis Landstrom (195.93.32.153) on August 13, 2002 at 11:05:00:
The whole concept that the speed of light may be decaying is an interesting one.
It is also interesting that some creationists attempted to use this as evidence that the universe is only 6,000 to 10,000 years old (as it indicates in the Bible), their 'evidence' however was like most creationist 'evidence' against evolution and an ancient universe, unfounded and flawed.
But, I heard something interesting recently, namely that the speed of light may have bee infinite at the begining of the universe, this may well have ramifications for the age of the universe, the universe may be many millions if not billions of years younger than we previously thought. I don't think for one minuit that the universe is 6 to 10,000 years old, but it is a little un-nerving to think that the creationists who advocated c-decay might have got it marginally correct.
In answer to the question about where light gets the energy to 'speed up' after it vacates a medium like water or air that 'decelerates it:
Firstly let us look at light in a perfect vacume, it travels as an electromagnetic photon, pure energy unintrupted and unable to loose that energy.
When the photons enter a substance that has transmitance like water or air, collisions occur between these photons and particles in that medium. Should these photons of light collide with electrons they transfer their entire energy to these electrons causing them to 'jump' in their orbits, for a brief period of time these electrons are excited, then they 'jump' back down to their what is known as ground state which was the state they were in before the photons collided with them, as a result of jumping back down to their ground states these electrons re-emit the photons, and the re-emmited photons go on to collide with more electrons in the medium which do exactly the same thing, and so on.
The reason as to why there is an apparent 'slowing down' effect is simply because of the time delay involved in raising the energy states of these electrons to re-emit the photons, between electrons the photons travel at light speed. The speed of light within the medium isn't realy different, what you are measuring is simply the 'electron excitation delay'.
Of course a 'ray' of light consisting of many photons will loose alot of energy traveling through air or water simply because not every particle in air or water is an electron, there are baryons (nuclear particles) like protons and neutrons as well, and these tend to absorb light photons rather than re-emit them.
There is no energy lost when an electron absorbs and re-emits a photon, the system is 100% efficient this is because of quantum theory. A single photon of Electromagnetic energy represents the lowest possible quantity (quantum) of energy, you can not have less that 1 quantum of energy, in other words you can not have half or a quarter of a photon, it is either a whole photon or nothing, when the photon is absorbed by the electron, the electrons energy is raised by exactly 1 quantum, so when the electron goes back to ground state it is only going to emit 1 quantum of energy nothing less, nothing more.
I hope that this answers the question.