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Speed of Light Inconstant?
DHR writes "Australian scientists have discovered that light isn't quite as fast as it used to be." We've done previous stories on these findings. Those of you with subscriptions to Nature can read the actual paper, the rest of us will just have to suffer.
Well, let's see here:
The speed of light -is- always constant in one sense,
simply because the length of 1 meter is defined by the distance light travels in a set time.
Now, from a more physical standpoint: We need more evidence.
Quite a few measurements of c have been done, and a single measurement isn't about to upend all this.
Extraordinary claims require extraordinary evidence, remember?
Now, nobody says that relativity is a complete and final theory. It probably isn't. But you still need lots
of evidence to replace it with another theory.
Otherwise, we won't even know if the theory we're replacing it with is better!
It's an interesting theory and experiment, but even so, I'd bet on this being a
freak result, for the simple reason that scientific breakthroughs don't come around that often.
If the very early Universe, when all the matter and energy could be contained in a microdot, was such an exotic place that the speed of light approached infinity -- then what happened to the speed of sound?
Two points. First, the idea that the whole mass of the "universe" was contained in a microdot just at the Big Bang isn't really right (depending on what you mean by "universe"). The whole mass of today's observable universe, yes. But if you take the cosmological models at face value, the universe is probably infinite in extent, and always was (at least as far back as you can go without worrying about unknown theories of quantum gravity). It's more accurate to say that the density of the universe approached an arbitrarily large value; then you don't have to worry about a "smaller infinity" or similar.
Now, to what you actually asked: the speed of sound is not a fundamental quantity the way the speed of light is. "Speed of light" generally means "speed of light in a vacuum", which according to standard theory is a fundamental contant. (In material other than vacuum, light tends to travel at speeds less than the "speed of light".) Sound doesn't travel in a vacuum, but needs a medium to travel through. It's speed is entirely dependent on that medium. What we call the "Speed of sound" (when, say, timing distance to lightning strikes based on the delay before we hear the thunderclap) is the speed of sound in air at a typical density and pressure found on the surface of the Earth. The speed of sound in water is a lot higher. In rock, higher still.
In the very early universe, I would expect the speed of sound to be very, very high, but it will always be less than the speed of light in a vacuum (whatever that value happens to be at any given moment).
-Rob
Interesting they suggest that time and motion are different between two frames of reference travelling at different speeds.
Isn't this kinda the idea of relativity? How does it change the speed of light?
The reason Astronomers don't want to accept this is becuase it would change the nature of every cosmological theory they have. They've invested large amounts of time in old theories, why should they learn new ones? It's all about ego for them.
While there is a possible grain of truth in what you say, it's probably vastly overstated.
It would be better to say that extraordinary claims require extraordinary proof. To almost everybody, the claim that the fine structure constant has been changing is pretty extraordinary, and as such requires pretty solid proof before any measurable fraction of people who care about these things will casually accept it.
There is a danger in the iconoclastic argument. Yes, if a new truth is revolutionary and will require everybody to throw out everything they know, everybody will resist accepting that truth. It does not follow that therefore every revolutionary idea which meets widespread resistance must be a new truth.
-Rob
First of all, according to relativity there is no such thing as speed "in absolute terms". Second, all observers, regardless of motion, measure the same value for the speed of light. That is why time and distance will appear differently to two observers in relative motion.
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