@ScienceBiker -- Only works as a rhetorical comment because 'wet' is a subjective adjective that applies to any liquid where the molecular cohesive force is lower than the adhesive force, but I get it.

You're welcome. I'm here from time to time, usually when I'm dry.

@ScienceBiker -- The world would be a sad place indeed without such exchanges, my friend. Never hold back for there are many of us who appreciate it.

There is no special reason to suppose that the speed of light has always had the value that it has now.

@Coffeo nor is there any reason at all to suppose that the speed of light has ever varied from what it is today, don't you agree?

@NDEer -- According to Answers in Genesis's astronomer Lisle, there is. Everybody knows his reckoning is accurate because it agrees to the letter with the good book.

Read the following and be "enlightened"....

[answersingenesis.org]

@evidentialist oh of course, that authoritative site proves it so beyond doubt, how could I have even questioned it?

@NDEer -- you are a gentleman indeed.

@NDEer There are, I think, some reasons for thinking it might have changed. [livescience.com]

@Coffeo that's an interesting article, thanks for the link. It's pure speculation and no evidence, but that's where all science starts. I'd like to see someone test it experimentally:

"To find this tiny fluctuation, the researchers say, one could measure how light disperses at long distances. Some astronomical phenomena, such as gamma-ray bursts, produce pulses of radiation from far enough away that the fluctuations could be detected."

But would this really be a valid way to test it? We know that the conventional standard is 'the speed of light in a vacuum' and that light slows down when it passes through transparent matter (solid, liquid, or gas), with the higher-energy light (which in the visible range is toward the blue end of the spectrum) slowing down more. This is what makes a prism separate light into its component wavelengths. The amount that any given wavelength of light slows down in matter is also dependent upon the density of the matter, with higher densities slowing light down more.

The problem is, space isn't a perfect vacuum. There are atoms and occasionally molecules and even dust-like particles floating around in it everywhere, giving it a certain amount of density. A very low density to be sure (on the order of an atom or two in every cubic centimeter but higher or lower in different regions) so especially over vast distances that should have some effect on the speed of light in the kind of astronomical experiment the article suggests, and invalidate the experiment.

[hypertextbook.com]

@NDEer Sure. My point is simply that we can't, at present, be sure one way or the other.

@Coffeo Well sure, essentially that's always the case in science because everything is always open to being reevaluated in the light of new evidence, so nothing can be said to be forever and truly 'sure' in an absolute sense -- continuing to be 'believed in', in the face of damning evidence against it and in support of something else. Somebody comes up with an idea challenging the existing dogma, and if their idea proves right, new dogma replaces the old, that's how science works (using 'dogma' loosely here). So if someone could scientifically prove the world was really flat and at the center of the universe, science would have to go with it and abandon all that old-fashioned Copernican and and Galilean dogma, right? Just like if someone could prove the speed of light in a vacuum is not a constant.

@NDEer Science is not about proof. Proof is a mathematical thing.

@Coffeo hairsplitting over word definitions gets us nowhere; sufficient evidence constitutes 'proof' in science. The fact that the word has a more specialized meaning in mathematics circles does not change that.

Here's an interesting report about the speed of light: [phys.org]

@NDEer Sorry, but word definitions are important. Also, a demonstration that photons cannot travel faster than light is not sufficient to demonstrate that the velocity of light is constant at all times and in all places. Of course, it might be: I'm not claiming that it isn't.

@Coffeo, if word definitions are important to you, you look them up, don't make them up. Then they don't need to be quibbled over like armchair philosophers get off on. Here's Google's defintion of the word Proof in the context of science as used here, with some examples. You should be able to easily tell from this that there are many ways science is about proof of things:

[google.com]

proof
pro͞of
noun

evidence or argument establishing or helping to establish a fact or the truth of a statement.

"you will be asked to give proof of your identity"

synonyms:
evidence, verification, corroboration, authentication, confirmation, certification, documentation, validation, attestation, substantiation

"proof of ownership"

@NDEer / @Coffeo -- Yes, indeed, the definitions and connotations of words are incredibly important. Unfortunately, the Google definition is limited to the general use for the word whereas in given disciplines the word 'proof' takes an entirely different turn. The following is an article that should 'prove' useful in your future pursuits:

[forbes.com]

You may also find the following videos of some interest, oh, and please forgive the simplistic nature of the videos, they were quick and easy to find: