| MadSci Network: Physics |
Dear Ray, This is an interesting question, and it is becoming more interesting the more I think about it. You are correct that even a vacuum seems to be filled with a “quantum soup” of subatomic particles constantly being created and annihilated. But the next question is how these particles affect the speed of light, or the measurement of the speed of light. There does seem to be something about “space” that limits the speed of light. If you look at the equations that describe electric and magnetic fields (these equations are called Maxwell’s Equations) and you solve them for the motion of an electromagnetic wave, out pops the speed of light! This speed ultimately depends on two quantities, the “permittivity of free space” (“free space” means a vacuum) and the “permeability of free space”. These two quantities describe how strong the electric and magnetic fields are, respectively, when created by charges. If these quantities had different values than what they have now, light would travel at a different speed. Apparently there is something about space that determines these numbers. Does it have to do with this background “quantum soup”? That is not so clear. Light is not the only thing that is limited to 300,000km/s; gravity waves also travel at that speed. Perhaps we will really understand from where this number comes only when we have a complete unified theory that combines quantum electrodynamics with gravity, that is, with Einstein’s Theory of General Relativity. Your idea does bring up a very interesting analogy, though. When light enters a medium, water or glass for example, the light slows down and moves at a rate that depends on the permittivity and permeability of that material. Perhaps the existence of the “quantum soup” is what determines the values for the permittivity and permeability of “free space”, which is really the permittivity and permeability of “quantum soup”! One more aspect about your question that I would like to address is whether the speed of light is additive or not. Back when physicists were looking for confirmation for the existence of the aether, two physicists, Michelson and Morley, performed a famous experiment where they measured the speed of light in different directions relative to the direction of the Earth’s motion. If speeds were somehow additive, Michelson and Morley should have detected a difference in the speed of light that depended on the direction of the light. Why? Since the Earth is going around the sun, the sun is going around the galaxy, the galaxy is traveling through space, etc, etc, and if there is an additive component to the way light travels relative to the motion of the source or detector, the Michelson and Morley experiment should have measured it. They didn’t find any difference that depended on direction. Another way of looking at this is to say that there is no preferred reference frame, relative to which the motions of other frames are measured. Any frame is just as good as another. No frame is any more special than another. The “quantum soup” looks exactly the same in one frame as it does in another that is moving relative to the first. To sum up, there does seem to be something about space that determines the limiting speed of light. Would it be different if we could remove the “quantum soup” that seems to fill space? We won’t know that until we have a more complete understanding of space-time. Well, Ray, I hope that answers your question. Please let us know if you would like any more information. Thank you for your interest. Sincerely, Jim Guinn Georgia Perimeter College
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