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Constancy of the Speed of Light

Submitted by D. Kiran (EEE IV/IV)

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Editor's Note: As a related article, please see this technical article on the Speed of Light - it deals with the more technical aspects the subject. Kiran can also be contacted at his email address for information on this topic.

Is the velocity of light a fixed constant of nature, invariant over time?

"A Time Varying Speed of Light as a Solution to Cosmological Puzzles"

Is Einstein About to be Dethroned?

"A Physical theory based solely on the first postulate of relativity"

"It is remarkable when you can find one simple idea that has so many appealing consequences"

This report presents the available measurements of c and several statistical studies, which suggest that c has decreased in the past 300 years. What other "constants" of physics might prove to be non-fixed? How would a non-constant c affect physical laws? Possible consequences for cosmology and the age of the universe are discussed.

The possibility that the velocity of light, c, is not a fixed constant is reconsidered by statistical analysis of the historical measurements collected from various sources. Testing of the selected data shows the measured value of the velocity of light has decreased over the past 250 years. Furthermore, the probability of some systematic or experimental problem was found to be low. Brief analysis of constants other than c suggests that those constants that involve atomic phenomena and units of time are also apparently changing. Another set of constants with no obvious dependence on c were analyzed and show no apparent variability with time. A variable velocity of light implies that atomic clocks and dynamical clocks do not run in step - that atomic time has been decreasing with respect to dynamical time.

The speed of light - the fastest thing in the universe - is getting slower. Physicists have devised a new theory to explain how the cosmos emerged from the big bang, which overturns one of the central pillars of modern scientific belief - that the speed at which light travels has always been the same. The idea, proposed by two experts from Britain and America, could rewrite the textbooks and challenge Einstein's theory of relativity if space observations reveal evidence to support it.

Some scientists say the speed of light immediately after the universe was born may have been far faster than its present-day value of 186,000 miles a second. They say it has been slowing down ever since.

One mystery that it seems to be able to explain is why the universe is so uniform - why opposite extremes of the cosmos that are too far apart to have ever been in contact with each other appear to obey the same rules of physics and are even at about the same temperature. It would only be possible for light to cross from one side to the other if it travelled much faster than today moments after the universe was created, between 10 billion and 15 billion years ago. Their hypothesis suggests it was so fast that it could have been travelling at 186,000 miles a second multiplied by a figure with 70 zeroes after it.

Calculations based on the theory also give the most elegant explanation for the speed at which the universe appears to be expanding, which is thought to be just fast enough to avoid an eventual collapse to a big crunch. Instead, the universe would simply grow forever though at a decreasing rate, and its ultimate fate would be a slow, lingering death as all the stars burn out and every particle of matter within it separates.

This page last modified on 25/03/2002