Posted on 06/30/2004 1:35:28 PM PDT by NukeMan
Speed of light may have changed recently
19:00 30 June 04
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 fine structure constant
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.
Natural nuclear reactor
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.
Energy spectrum
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.
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".
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.
Reaction rate
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.
Eugenie Samuel Reich
The Top 20 Cool Things About a Car that Goes Faster than the Speed of Light
20 Sleep 'til noon. Still get to work by 8:00am!
19 Doppler shift makes red traffic lights look green.
18 Breaking laws of physics only a misdemeanor in most states.
17 Never in car long enough to hear an entire Madonna song.
16 Carl Sagan and Stephen Hawking keep bugging you to carpool.
15 No one can see you pick your nose while you drive.
14 Lunch breaks in Paris, circa 1792.
13 LA to Vegas in 2 nanoseconds.
12 You can stop worrying about being sucked into a black hole driving home from work.
11 You'll be so thin while driving it you can even wear horizontal stripes.
10 That deer in your headlights is actually behind you.
9 Kid from Mentos commercial almost guaranteed to lose a limb if he tries to duck through back seat.
8 Traffic enforcement limited to cops with PhD's in Quantum Physics.
7 Bugs never see you comin'.
6 You can get to the good hookers before Charlie Sheen.
5 Can make a fortune delivering pizza with the slogan "It's there before you order or it's free!"
4 Car makes it from Hollywood to London fast enough to not arouse suspicions of Elizabeth Hurley.
3 License plate: "Me=mc2"
2 Cigarette butts don't land in the backseat -- they land in last week!
and the Number 1 Cool Thing About a Car that Goes Faster than the Speed of Light...
1. drive-by shooting stars
http://hagen.let.rug.nl/peterm/jokes/joke40.htm
This is really posted at 5:02:30.
Two billion years ago ... wasn't that when we switched to Universal Savings Time? In order to conserve energy, if memory serves.
Keep thinking she is my stepdaughter, at least that is what I tell the neighbors. They are beginning to wonder how I came up with a new stepdaughter without getting married.
PS: Keep this to yourself.
I think he deduced it as a consequence of Maxwell's equations. That's where he got the symbol "c" from, I'm told. But as always, I'll yield to the experts, who often correct my babblings.
Faster? No, they are SLOWER. At least in my kitchen. I'll check the bathroom tonight.
I first notice it with the refrigerator light.
"A varying speed of light contradicts Einstein's theory of relativity, and would undermine much of traditional physics." I'm no physicist, but that assertion seems a stretch because if the 'constant is sliding upward, the relative 'whole-universe' relationship would be the same at any given temporal point. Am I confused or what?
I wasn't around then. You're the expert.
Faster or slower in the fridge? Inquiring minds want to know!
The Theory is okay. If the speed of light is not constant, and of course it isn't at all, results may lie outside the Theory rather than contradict it.
Probably. But so am I. If the speed of light is variable, I'll need to rethink just about everything.
I know nothingk...nothingk!
This happens every time I get a new set of tires for my truck.
Too bad Mallomar season just ended !
Finding the Speed of Light with
Marshmallows-A Take-Home Lab
Robert H. Stauffer, Jr., Cimarron-Memorial High School, Las Vegas, Nevada, USA
I have heard that at 16 years old, Albert Einstein constantly wondered what it would be like to ride on a beam of light. Students in physics always seem to be fascinated by the properties of light. However, speed-of-light demonstrations often require extensive preparation or expensive equipment. I have prepared a simple classroom demonstration that the students can also use as a take-home lab.
The activity requires a microwave oven, a microwave-safe casserole dish, a bag of marshmallows, and a ruler. (The oven must be of the type that has no mechanical motion-no turntable or rotating mirror. If there is a turn-table, remove it first.) First, open the marshmallows and place them in the casserole dish, completely covering it with a layer one marshmallow thick. Next, put the dish of marshmallows in the microwave and cook on low heat. Microwaves do not cook evenly and the marshmallows will begin to melt at the hottest spots in the microwave. (I leaned this from our Food Science teacher Anita Cornwall.) Heat the marshmallows until they begin to melt in four or five different spots. Remove the dish from the microwave and observe the melted spots. Take the ruler and measure the distance between the melted spots. You will find that one distance repeats over and over. This distance will correspond to half the wavelength of the microwave, about 6 cm. Now turn the oven around and look for a small sign that gives you the frequency of the microwave. Most commercial microwaves operate at 2450 MHz.
All you do now is multiply the frequency by the wavelength. The product is the speed of light.
Example:
Velocity = Frequency ´ Wavelength
Velocity = 2450 MHz ´ 0.122 m
Velocity = 2.99 ´ 108 m/s
This works in my physics class, often with less than 5% error. Then the students can eat the marshmallows.
(Reprinted with permission from The Physics Teacher, vol. 35, April 1997, p. 231. Copyright 1997 American Association of Physics Teachers )
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