Welcome to Gaia! :: Varying Speed of Light?

Well, I'm currently reading a book about whether the speed of light is either constant or varies.

Care to enlighten me on this subject?

I think the OP is asking about whether or not the value of c varies over time.

I don't really feel like info dumping now so pleh.

Never heard of the speed of light changing. But I know that the wavelength changes...

scream

Imagine identical glass bulbs filled with various different gases, all connected to identical devices to measure their pressure (or a mercury tube to measure deviations in height of the mercury column instead). In apparently identical regimes, they give somewhat different readings, although they are close. However, scientists discover a curious pattern: given a fixed reference regime, the ratios of the pressures at arbitrary regimes to the reference one get closer and closer the less gas there is in the bulb--extrapolated, they converge. So they decide to call this ratio limit "temperature", scaled by some unit, and proceed to have many a fruitful and successful theory.


"But wait," an objector appears, "how can we measure this 'temperature' if to do the experiment we always need some gas in the bulb, so that we always fall short of our limit?"
The scientists look at him as if he had grown a second head. The theorists don't understand why idealization is a problem, while the experimenters have a well-defined procedure for measuring it to an arbitrary accuracy. And of course they fall short of perfect accuracy, but is this man's objection really just "experiments are never ideal"?

Suddenly, a troll appears.

"The speed of light does vary in these cases!" they cry. "We've even theories to describe how it varies, and our latest proved to be extremely precise under every environment we could throw at it. But c itself is an idealization of no energy density, and it can at least be approached to very impressive accuracy..." But there's no hope. They've tried explaining all of this to the troll before, but it is impervious to facts.

---

Alright, enough melodrama. But seriously, one would have to have a seriously warped view of relaity before Kaz-Balan's arguments even begin to make sense. And it's not just a warped view of scientific theories, but people as well. Kaz-Balan and his ilk appear to be under the impression that scientists simply love to make assumptions for no reason other than possibly making their jobs easier. In reality, science is a rather competitive game and the pressure to publish papers is high, so you can bet that whenever a scientist makes an assumption taken completely out of his rear end, there are other scientists scribbling furiously to see how it can be checked or to prove him wrong. Because, hey--research paper.

Take QFT, for instance. It is an essential component that photons (light) has no rest mass. But how do we know that photons have no mass? Well, a simple kind of approach would be to just say that our theory is highly successful in its predictions and it says so (an abductive sort of argument: why is our theory predictively successful if it is wrong?), but in case it isn't enough to satisfy, rest assured that it isn't enough for some scientists as well. So, then, what are the consequences of having a massive photon? Those can be analyzed and are found to be a frequency-dependent speed of light, even in vacuum (how apropos). There was no such dependence observed to within experimental limits, which bounds photon mass to be extremely close to zero.

Why? You are not a very interesting troll.


I see the point flies over you head, as usual: for every scientist, it is in his or her best interests to publish on new phenomena, and papers arguing against portions of other scientists' work are in fact very common.


Ah, the conspiracy mindset. How typical.


Hmm... a complete dismissal of quantitative concerns. This was certainly expected.


There is no dark matter or dark energy in the standard model.


Oh, really? If that's so, try the following experiment (please bear with me for a moment): out of two initially synchronized clocks at the same place on Earth, one remains at the same position (on Earth) while the other is flown across the world at a constant speed. GTR predicts that the clocks will differ by some specific amount, and when the experiment was performed, the prediction turned out to be correct to high accuracy.

Now, since you say you have no complaints against the results, I hope you will grant that the GTR prediction was meaningful at least in the minimal sense that it produced the correct result. Perhaps you just don't like its ontological terms, and would prefer some other framework. I don't know what it is, but presumably you do, so for now I'll call it the "Kaz-Balan Ontology" (KBO), and I'll call the standard interpretations (involving four-vectors and time dilation and everything else) the "standard model ontology" (SMO). Queries:

In SMO, we attribute the difference in initially synchronized clocks to time dilation. What is the proper explanation in KBO?

The SMO intepretation directly corresponds to the mathematics of GTR. Is there a mathematical framework for KBO that can be used to calculate the correct difference in the clock readings?

If there isn't, then what is the point of having KBO in the first place, since all our nitty-gritty calculations are done through SMO anyway?

You claim that your interpretation predicts the precession of Mercury. Fine, show me. Make a detailed analysis in your own framework that shows it should precess, and by roughly how much. Alternatively, show me how to calculate the difference in clocks (in a general situation of the type stated above) in your framework. I do not believe you can do it, although I'm curious enough to hope that you prove me wrong in this matter.


In the end, science is about things we can measure. And clocks are observed to differ when in different states of motion, even though whenever they are side-by-side, no such difference occurs. We call this "time dilation" because time is what clocks measure. Maybe you can re-intepret as something else, but if you're not questioning that the clocks are observed to differ (as you say, you consider experimental results valid), then your entire objection are a at best a quibble over terminology--just a question of what we call things.