Speed of light may have changed recently

The speed of light, one of the most sacrosanct of the universal physical constants, may have been lower as recently as two billion years ago - and not in some far corner of the universe, but right here on Earth.

The controversial finding is turning up the heat on an already simmering debate, especially since it is based on re-analysis of old data that has long been used to argue for exactly the opposite: the constancy of the speed of light and other constants.

A varying speed of light contradicts Einstein's theory of relativity, and would undermine much of traditional physics. But some physicists believe it would elegantly explain puzzling cosmological phenomena such as the nearly uniform temperature of the universe. It might also support string theories that predict extra spatial dimensions.

The threat to the idea of an invariable speed of light comes from measurements of another parameter called the fine structure constant, or alpha, which dictates the strength of the electromagnetic force. The speed of light is inversely proportional to alpha, and though alpha also depends on two other constants (see graphic), many physicists tend to interpret a change in alpha as a change in the speed of light. It is a valid simplification, says Victor Flambaum of the University of New South Wales in Sydney.

It was Flambaum, along with John Webb and colleagues, who first seriously challenged alpha's status as a constant in 1998. Then, after exhaustively analysing how the light from distant quasars was absorbed by intervening gas clouds, they claimed in 2001 that alpha had increased by a few parts in 105 in the past 12 billion years.

But then German researchers studying photons emitted by caesium and hydrogen atoms reported earlier in June that they had seen no change in alpha to within a few parts in 1015 over the period from 1999 to 2003 (New Scientist, 26 June) though the result does not rule out that alpha was changing billions of years ago.

Throughout the debate, physicists who argued against any change in alpha have had one set of data to fall back on. It comes from the world's only known natural nuclear reactor, found at Oklo in Gabon, West Africa.

The Oklo reactor started up nearly two billion years ago when groundwater filtered through crevices in the rocks and mixed with uranium ore to trigger a fission reaction that was sustained for hundreds of thousands of years. Several studies that have analysed the relative concentrations of radioactive isotopes left behind at Oklo have concluded that nuclear reactions then were much the same as they are today, which implies alpha was the same too.

That is because alpha directly influences the ratio of these isotopes. In a nuclear chain reaction like the one that occurred at Oklo, the fission of each uranium-235 nucleus produces neutrons, and nearby nuclei can capture these neutrons.

For example, samarium-149 captures a neutron to become samarium-150, and since the rate of neutron capture depends on the value of alpha, the ratio of the two samarium isotopes in samples collected from Oklo can be used to calculate alpha.

A number of studies done since Oklo was discovered have found no change in alpha over time. "People started quoting the reactor [data] as firm evidence that the constants hadn't changed," says Steve Lamoreaux of Los Alamos National Lab (LANL) in Albuquerque, New Mexico.

Now, Lamoreaux, along with LANL colleague Justin Torgerson, has re-analysed the Oklo data using what he says are more realistic figures for the energy spectrum of the neutrons present in the reactor. The results have surprised him. Alpha, it seems, has decreased by more than 4.5 parts in 108 since Oklo was live (Physical Review D, vol 69, p121701).

That translates into a very small increase in the speed of light (assuming no change in the other constants that alpha depends on), but Lamoreaux's new analysis is so precise that he can rule out the possibility of zero change in the speed of light. "It's pretty exciting," he says.

So far the re-examination of the Oklo data has not drawn any fire. "The analysis is fine," says Thibault Damour of the Institute of Advanced Scientific Studies (IHES) in Bures-sur-Yvette in France, who co-authored a 1996 Oklo study that found no change in alpha. Peter Moller of LANL, who, along with Japanese researchers, published a paper in 2000 about the Oklo reactor that also found no change in alpha, says that Lamoreaux's assumptions are reasonable.

The analysis might be sound, and the assumptions reasonable, but some physicists are reluctant to accept the conclusions. "I can't see a particular mistake," says Flambaum. "However, the claim is so revolutionary there should be many independent confirmations."

While Flambaum's own team found that alpha was different 12 billion years ago, the new Oklo result claims that alpha was changing as late as two billion years ago. If other methods confirm the Oklo finding, it will leave physicists scrambling for new theories. "It's like opening a gateway," says Dmitry Budker, a colleague of Lamoreaux's at the University of California at Berkeley.

Some physicists would happily accept a variable alpha. For example, if it had been lower in the past, meaning a higher speed of light, it would solve the "horizon problem".

Cosmologists have struggled to explain why far-flung regions of the universe are at roughly the same temperature. It implies that these regions were once close enough to exchange energy and even out the temperature, yet current models of the early universe prevent this from happening, unless they assume an ultra-fast expansion right after the big bang.

However, a higher speed of light early in the history of the universe would allow energy to pass between these areas in the form of light.

Variable "constants" would also open the door to theories that used to be off limits, such as those which break the laws of conservation of energy. And it would be a boost to versions of string theory in which extra dimensions change the constants of nature at some places in space-time.

But "there is no accepted varying-alpha theory", warns Flambaum. Instead, there are competing theories, from those that predict a linear rate of change in alpha, to those that predict rapid oscillations. John Barrow, who has pioneered varying-alpha theories at the University of Cambridge, says that the latest Oklo result does not favour any of the current theories. "You would expect alpha to stop [changing] five to six billion years ago," he says.

Before Lamoreaux's Oklo study can count in favour of any varying alpha theory, there are some issues to be addressed. For one, the exact conditions at Oklo are not known. Nuclear reactions run at different rates depending on the temperature of the reactor, which Lamoreaux assumed was between 227 and 527°C.

Damour says the temperature could vary far more than this. "You need to reconstruct the temperature two billion years ago deep down in the ground," he says.

Damour also argues that the relative concentrations of samarium isotopes may not be as well determined as Lamoreaux has assumed, which would make it impossible to rule out an unchanging alpha. But Lamoreaux points out that both assumptions about the temperature of the Oklo reactor and the ratio of samarium isotopes were accepted in previous Oklo studies.

Another unknown is whether other physical constants might have varied along with, or instead of, alpha. Samarium-149's ability to capture a neutron also depends on another constant, alpha(s), which governs the strength of the strong nuclear attraction between the nucleus and the neutron.

And in March, Flambaum claimed that the ratio of different elements left over from just after the big bang suggests that alpha(s) must have been different then compared with its value today (Physical Review D, vol 69, p 063506).

While Lamoreaux has not addressed any possible change in alpha(s) in his Oklo study, he argues that it is important to focus on possible changes in alpha because the Oklo data has become such a benchmark in the debate over whether alpha can vary. "I've spent my career going back and checking things that are 'known' and it always leads to new ideas," he says.

Lower? Wasn't it supposed to have been faster 6000 years ago?

From the Article:

Horizon problem

Some physicists would happily accept a variable alpha. For example, if it had been lower in the past, meaning a higher speed of light, it would solve the "horizon problem".

However, a higher speed of light early in the history of the universe would allow energy to pass between these areas in the form of light.

The speed of light and the color of light are related.
I know I'm opening myself up here, but IF I remember my physics correctly the color's visible have to do with the frequency, of oscillation, not the speed of travel.
Be easy on me, I've not been through this stuff in quite a while AND my memory is pretty full. Consequently, when I have something new to store in memory, I have to find something old and unused to throw out. I could have thrown this information out.

However, a higher speed of light early in the history of the universe would allow energy to pass between these areas in the form of light.

IOW, a faster light-speed (lower alpha) would be useful in the very earliest (pre-inflation) nanoseconds of the universe, yes. Useful in explaining the large-scale uniformity of the universe we see now. However, this does not help what some people are trying to do with this story.

Not exactly a big help for the Young Earth Creationists, is it?
Very interesting article. Again, thanks for the ping.
It's not a problem at all. Everything that the scientists are saying is based on their (commonly accepted assumptions I'll agree) assumption. I'll reiterate, they were not there and do not know. I'll still accept Gods word on it, which has NOT changed, before I'll accept the word of scientists who don't even know how much there is to know, much less how much they do know.

Regards,
GE

I know I'm opening myself up here, but IF I remember my physics correctly the color's visible have to do with the frequency, of oscillation, not the speed of travel.

Other things being held equal, a change in the speed of light would change the frequency of arrival of the peaks and valleys in the waveform.

Other things are not exactly equal, however, as it appears space and the light waveforms within have been stretched over time. Assuming the speed of light to be constant, that would red-shift light in transit so that objects appear redder the farther away they are. Since we indeed see a correlation between distance and redshift, it appears the universe has been expanding.

Experiments in the last decade have managed to slow light down, in some cases to as little as ten miles per hour...

Ah ha! This would explain why I am having greater difficulty driving at night. I just need faster headlights. And all this time I thought I needed glasses or something. hmmm . . . and maybe all this time has not really been that much time.

Must be global warming... Oh, yeah, caused by the Bush Administration. (hee hee)

It was written in the 1500's by a Bishop James Ussher. It is generally considered the basis for the 4004 b.C. creation date. He took Gods word and put it in historical context. He took biblical events and historical events and wrote a history book that chronologically discusses both historical and Biblical events; putting them on a time scale. For example, you can see what was happening in the rest of the world when the Jewish people left Egypt for the promised land.
It is extremely fascinating to me. I am still reading it and have only finished about 1/3'rd of it.
It had not been printed for several hundred years until AIG (Answers In Geneses) reprinted it (with updated English - the English of the 1500's is nearly unreadable today). They have two bindings - the leather one is very expensive, but the regular hardback is around $60.00 or so.

Two other guys names Lorentz and Fitsgerald developed a relationship that quantified how much things at very high speed behaved differently than those at normal speeds. This 'Lorentz-Fitgerald contraction' was SQRT(1 - V**2/C**2).

Actually, it was Heaviside who first calculated the distortion of the electromagnetic fields of a moving charge.

One good thing about the General Theory of Relativity is that it provided an explanation for gravity. It was always a challenge to conventional physics to explain action at at distance without an interaction phenomenon. How does the earth know the sun is over there pulling on us? And how does the sun manage to grab the earth and yank it around without a string between the two?

Heaviside published the first serious post-Newtonian gravitational theory in 1893, his "A Gravitational and Electromagnetic Analogy" in Electromagnetic Theory Vol I. He introduced the concept of mass currents, gravitomagnetic fields, and gravity waves. Not coincidentally, Einstein's GR reduces to Heaviside's theory in the weak field limit.

However, this does not help what some people are trying to do with this story.

I think the point of the article and what we need to take away from it is that there is evidence that the speed of light itself is relative and variable. There is evidence that it at one time was faster and at another time was slower than it is now. So the real possibility exists that it was, at one time in the history of this universe, infinitely faster than it is now and that at another point, the brakes could have been put on it and it could have slowed to a level perhaps significantly if not infintely slower than it is now. But at all times the speed of light was the speed of light.

Now if the speed of light was at one time faster than it is now, what would that do to time? If the speed of light is variable, as is suggested by this article, then what, if anything, is constant?

As best I can figure, the speeding of light in "recent" times (i.e, post-emission along the way) would BLUE-shift the light as we see it here and now compared to how it would have looked to someone near the emitting object back when.

My understanding is very different. Light moves at the speed of light (in a vacuum), and this is true regardless of its color. The color we see is the result of the wavelength, and that's determined by whether the source of the light is moving away from us (stretched out, thus red) or moving toward us (compressed, thus blue).

If light has been speeding up, but not the rate of expansion of the universe, then the degree of redshifting (or blueshifting) probably wouldn't change (I'm winging it here). There is also the independent line of evidence provided by the brightness of Cepheid variables. This always corresponds with observed redshifts, and it was Hubble's big clue that redshift and distance were related. Yet another line of evidence is the absorption of light as it passes through the Lyman alpha forest, which I don't fully understand, but I'm told it independently confirms all the other observations about the distance of stars and the rate of expansion of the universe.

The speed of light and the color of light are related. If the speed of light has increased, would the old light from galaxies long ago and far away appear to be redshifted?

I think it would depend on how the observer is affected by the changed speed of light. Put yourself in the position of a omniscient being who is unaffected by the change. To you, the speed of light has changed and you could measure the difference in light travel time from point A to point B. But to the non-omniscient who are affected by the light speed change, their concept of distance would change with the speed of light. I think the change in distance would be proportional to the change in the speed of light: ie. no net change in measured frequency. Think of the Doppler Effect where only relative motion can be detected (to the first order).

I think a far more interesting concept is the idea of an anisotropic speed of light. Local differences could be measured.

Perhaps I will read it! I usually stick to fiction, but who knows?

I wish to clear something up that may be confusing, which is my fault. I am a firm believer in evolution. On earlier posts I was simply joshing some of the regular posters on these threads - spicing things up if you will. If I have misled you, forgive me.

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