Coragyps

Bud - the measurement I think I remember was on the accretion disk on some galaxy's central black hole. The approaching edge was blueshifted, the receding edge reddened, so the rotational velocity was measurable. The transverse movement of a "knot" in the disk was measured by radio interferometry over a few years, so that the distance was purely trigonometrically determined. Maybe not strictly parallax, but pretty much pure Euclid. I'll try rooting around for the citation.

Principia

<a href="http://news.yahoo.com/news?tmpl=story2&cid=570&ncid=753&e=1&u=/nm/20020807/sc_nm/science_light_dc_1" target="_blank">Relevant article?</a>

ohwilleke

One way to go after the speed of light issue is to say that if the speed of light is changing, then the electromagnetic force wouldn't work in prior eras.

Pantera

Oops - this is a pretty classic creationist howler I'm afraid. Obviously he knows practically nothing about the science he is attempting to criticise. Carbon dating is not used to date fossils. Carbon-14 has a half life of just under 5000 years, and after about ten half-lives its concentration drops to essentially unmeasurable levels, thus making the technique useless for dating anything older than about 50,000 years. Dating of geological samples makes use of other techniques, such as the potassium argon method, which use isotopes with much longer half-lives.

Still, perhaps the rate of radioactive decay has dropped generally over time - let's do what creationists would rather we didn't and actually think through what this would mean. Well, if the amount of decay required to make the world look 4.5 billion years old has actually taken place in about six thousand years then (removes shoes and socks to helpwith counting) the amount of background radiation in the past would have to have been at least six million times higher than it is now. In fact, assuming an exponential decay curve, it would have to have been many, many times higher than that in the early days of the world. Conclusion: Even if Adam and Eve hadn't been instantly fried, any children them managed to have would have had three heads. Time for a new theory creationists!

Axiom of Choice

As Scientiae pointed out, there is some new support for the changing speed of light arguement coming out soon. So, I guess I must say the question isn't as cut and dried as I originally thought. However, I'm still really skeptical of this, since it seems to me that alot of other measurements must be wrong for this one to be right. Additionally, I'm a little suspicious of any attempt to throw out relativity without a really good explaination of why relativity is right in so many other cases. However, can't say too much for sure until the experts start coming out with their positions on the matter.

Philosoft

Bingo. It really shouldn't have to go any farther than this.

beausoleil

I freely admit to not having thought this through completely. However it seems to me that relativity requires the speed of light to be constant for observers in all reference frames. So if 2 observers in two different reference frames measure the speed of a particular light pulse, they will get the same answer irrespective of their relative velocities (special) and accelerations (general). This is what 'the speed of light is constant' means.

It doesn't mean that the value the observers determine is the same now as it was a few microseconds after the big bang. I haven't read the recent Nature paper yet, but I doubt Paul Davies is repudiating general relativity.

beausoleil

Jus goes to show how wrong I can be!

<a href="http://news.bbc.co.uk/1/hi/sci/tech/2181455.stm" target="_blank">http://news.bbc.co.uk/1/hi/sci/tech/2181455.stm</a>

Nonetheless, I think what I said above makes some sense. I suspect Prof Davies of seeking some publicity.

Bluenose

Note that the article does not provide much detail on the John Webb research on quasars.

The quotes from Paul Davies may not reveal the full context of his explanation of his teams research.

I will try to find a better explanation for what appears at first blush to be less than exact reporting.

Bluenose

Note where it says further work is needed.