July 14, 2006

How Constant are 'Physical Constants'?

MSNBC is reporting on rising doubts among scientists - particularly Cambridge Univeristy astronomer Michael Murphy - as to whether key physical constants are actually constant. The new evidence goes beyond c-decay or the variable speed of light cosmology, and posits changes in the constants governing the four fundamental forces. (Side-note: does anyone know why Wikipedia describes c-decay as a crackpot, pseudo-science claim, and even Answers in Genesis is skeptical about it, but the 'variable speed of light cosmology' is considered to be a real scientific theory, and in description Wikipedia says "The idea is that light propogated as much as sixty times faster in the distant past?" Which Wikipedia article is in error, or is there some difference between the two accounts that I am not seeing?) In particular, it appears that the spectrum of light may have been different billions of years ago, based on analysis of light emitted from distant quasars, and this can be explained by minute decreases in c, the speed of light, and increases in α, the electro-magnetic force constant. If string theory is correct, these variations could be explained by slight changes in the geometry of the invisible string-theoretic dimensions. More info at SPACE.com.

(HT: slashdot)

Posted by Kenny at July 14, 2006 11:19 AM
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A couple of comments (as if you expected otherwise from me)-

First of all, questioning whether physics constants are constant is NOT new- in fact, as the universe expands, some of them (Hubble's constant) are even expected to change. Others, however, (like G) we're not sure, but it is not unlikely that they could change slowly as the universe changes, since a lot of physicists expect them to be determined by the make-up of the universe. For example, as the mass density decreases, they think it is at least possible for them to change.

Now as for light. The answer to which wikipedia article is right is both. c-decay is very specific "conjecture"- it's used by young earth creationists, and needs to light to decay by a certain amount and at a certain rate, which physicists are fairly certain is wrong (unless for some reason light has stopped decaying at this substantial rate). (To be fair, I should say physicists as a group tend to strongly dislike young earth creationists.) However, variable speed of light cosmology is more general ("the speed of light can change"), and is not so specific. In general, the changes tend to be much, much smaller.

As I'm sure you're aware, the postulate that the speed of light is constant for all observers is one of the fundamental postulates of relativity. Relativity has been pretty well verified experimentally, and there is no CONCLUSIVE experimental/theoretical reasons as yet to reject that the speed of light was constant in the past. There are questions as to the accuracy of the people measuring the quasars, and factors such as intersteller dust need to be accounted for before we start changing our fundamental understanding of the universe, although as you correctly noted string theory allows for the possibility and even explains it.

(If you're interested, I have an elementary book on the how/why some physical constants can change under conventional theories that you can borrow, since I'm always trying to get you to read more physics.)

Posted by: Lauren at July 14, 2006 12:33 PM

PS- I should say that even if the speed of light was varying over time, relativity would still hold, with a few alterations in the math.

Posted by: Lauren at July 14, 2006 12:34 PM

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