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devilmech
2004-Feb-19, 02:17 PM
After recently browsing a creationist website for something to laugh at( not that serious creationists are laughable, but the majority of the amateur ones on the internet are), I read an argument stating that the speed of light is slowing, which they claim accounts for the fact that we see light from stars that are billions of years old.

Thinking about this, I decided to research it, and after reading everything I could on the subject, I have yet to come across any definitive empirical data on the subject. The closest I came was the book by Barry Setterfield, The Atomic Constants, Light and Time. However, this raised more questions about the validity of the matter than shed light on the subject.

Also, after thinking about this subject in relation to general relativity, I realized that the absolute speed of light will vary slightly based on the speed of time, which will itself vary according to Einstein's theory on the subject. Hence, I would like to formulate a few opinions on the subject, but cannot because of the fact that I do not know of any instances of the speed of light being measured outside of the earth's gravitational pull, and thus have no frame of reference for this.

My questions then, are these: Is there any empirical evidence showing 'c' decay, and have there ever been any measurements of the speed of light outside of the gravitational pull of the earth?

TheThorn
2004-Feb-19, 05:02 PM
Last question first. Yes there have been measurements of the speed of light outside the earth's gravity. If fact, one of the first relatively accurate measurements of c, (as I mentioned in a different thread on this site) was by a guy named Ole Roemer in 1675, and it was based on observations entirely outside the Earth's gravity.

He observed that transits and eclipses of Jupiter's moon Io seemed to happen earlier than expected sometimes and later than expected at other times. He recognized that the pattern depended on the earth's position relative to Jupiter - when we were in the part of our orbit closest to Jupiter they happened earlier than average, and when we were farther away from Jupiter, they happened later. The "lag" in timing was caused by the extra time it took light to get here when we were farther away from Jupiter, and he used that to calculate a reasonably good value for c.

See This Page (http://www.geocities.com/speed_of_light_quran/speed_of_light_history.htm#1675%20Ole%20Roemer_his tory_speed_light) for more on Roemer.

As for empirical evidence of the decay of "c", I think there is some pretty compelling evidence to the contrary. The most easily understood and compelling single observation to me, comes from supernova 1987A in the Greater Magelanic cloud. This page (http://www.geocities.com/Athens/Thebes/7755/ancientproof/SN1987A.html) describes how the light echo from SN1987a gives us a direct measurement of the distance to the supernova - 168,000 light years, which is in good agreement with the distance to the Greater Magelanic cloud calculated using cepheid variables. This is the sort of distance that cretionists "theory" can't handle - if the universe is only 6000 years or so old, then light hasn't had time to get here from such objects. That's why they invented the idea of "c decay".

The logic involved in calculating the distance to SN1987a uses nothing more than high school geometry and the assumption that the speed of light is a constant. The wonderful thing about this particular case is that if "c" has been decaying, then this particular object is farther away from us than the calculations suggest, and it would actually have taken the light longer to get here. This is not pointed out on that web site, or any other that I'm aware of, so let me explain it in just a little more detail here.

There was a gas ring around the star from a previous episode. When the star exploded in the supernova, the flash of light took .658 years to reach the gas and cause it to "light up". We can measure how big it looks in the sky, and we know how big it really is (.658 light years in radius), so we can calculate how far away it is. (This part is described more fully in the link above).

Now for the good part. If the speed of light has been decaying, then it must have been travelling faster back when that star exploded. Since we measured the actual size of the ring of gas by the time it took the light to get there, light moving faster back then would make the object bigger, and that in turn would make it farther away. The only way light from that particular object could have gotten here in under 6000 years (which is why "c decay" was postulated in the first place) is if light was speeding up, not slowing down.

Perhaps Creationists will now postulate two types of light - "Cepheid variable light" which slows down over time, and "Supernova light" which speeds up over time.
;)

devilmech
2004-Feb-19, 05:35 PM
Thanks much for the reply. Interestingly enough, I was reading this directly before I read your post: http://www.talkorigins.org/faqs/hovind/how...ood-add.html#A6 (http://www.talkorigins.org/faqs/hovind/howgood-add.html#A6)

I am familiar with Ole Roemer, and indeed did some reading on his work just a few days ago. I had passed up his work in favor of another work which used basic Maxwell equations(as laid out by James Clerk Maxwell) to show that, in a vacuum, 'c' must be constant, or electromagnetism could not exist as observed. I was hoping that there would be more corroborating evidence for either theory, although I suppose they stand quite well on their own.

As for 'c' decay, thank you very much for the link. It contained a few new bits of information. I'm well aware of all the evidence debunking 'c' decay by now, I was mainly searching for a text which laid out the actual "evidence" used by the creationists to supposedly prove that light is/can slow down. The reason is that I plan to write an article about it on my upcoming science/astronomy/astrophysics website.

Thank you for your time

TheThorn
2004-Feb-19, 09:56 PM
There isn't any better source on this subject than talk.origins. So there probably isn't much I can add to your understanding.

The Setterfield book you mentioned does attempt to provide some basis in data, but it appears that their analysis was faulty. For the most part, the argument is repeated by creationists with no reference to the data. It is rare for Creationists to subject each other's claims to much scrutiny, but in this case, the ICR has even published an article that questions Setterfield's analysis here. (http://www.icr.org/pubs/imp/imp-179.htm), which includes references to the data, and even an interesting graph. Where Setterfield came up with a decay rate of 38 km/sec/yr, their re-analysis comes up with .000014 km/sec/yr (i.e. close enough to 0 that it don't matter).

There&#39;s probably a link to that article somewhere on talk.origins <grin>. They&#39;re damned comprehensive.