Why is there a limit to the speed of light?

Question

Why doesn't light travel twice as fast as it normally does ?

Answer 1

Scientists have apparently broken the universe's speed limit.

For generations, physicists believed there is nothing faster than light moving through a vacuum -- a speed of 186,000 miles per second.

But in an experiment in Princeton, New Jersey, physicists sent a pulse of laser light through cesium vapor so quickly that it left the chamber before it had even finished entering.

The pulse traveled 310 times the distance it would have covered if the chamber had contained a vacuum.

Researchers say it is the most convincing demonstration yet that the speed of light -- supposedly an ironclad rule of nature -- can be pushed beyond known boundaries, at least under certain laboratory circumstances.

Not so impossible

"This effect cannot be used to send information back in time," said Lijun Wang, a researcher with the private NEC Institute. "However, our experiment does show that the generally held misconception that `nothing can travel faster than the speed of light' is wrong."

The results of the work by Wang, Alexander Kuzmich and Arthur Dogariu were published in Thursday's issue of the journal Nature.

The achievement has no practical application right now, but experiments like this have generated considerable excitement in the small international community of theoretical and optical physicists.

"This is a breakthrough in the sense that people have thought that was impossible," said Raymond Chiao, a physicist at the University of California at Berkeley who was not involved in the work. Chiao has performed similar experiments using electric fields.

In the latest experiment, researchers at NEC developed a device that fired a laser pulse into a glass chamber filled with a vapor of cesium atoms. The researchers say the device is sort of a light amplifier that can push the pulse ahead.

Previously, experiments have been done in which light also appeared to achieve such so-called superluminal speeds, but the light was distorted, raising doubts as to whether scientists had really accomplished such a feat.

The laser pulse in the NEC experiment exits the chamber with almost exactly the same shape, but with less intensity, Wang said.

The pulse may look like a straight beam but actually behaves like waves of light particles. The light can leave the chamber before it has finished entering because the cesium atoms change the properties of the light, allowing it to exit more quickly than in a vacuum.

The leading edge of the light pulse has all the information needed to produce the pulse on the other end of the chamber, so the entire pulse does not need to reach the chamber for it to exit the other side.

The experiment produces an almost identical light pulse that exits the chamber and travels about 60 feet before the main part of the laser pulse finishes entering the chamber, Wang said.

Wang said the effect is possible only because light has no mass; the same thing cannot be done with physical objects.

The Princeton experiment and others like it test the limits of the theory of relativity that Albert Einstein developed nearly a century ago.

According to the special theory of relativity, the speed of particles of light in a vacuum, such as outer space, is the only absolute measurement in the universe. The speed of everything else -- rockets or inchworms -- is relative to the observer, Einstein and others explained.

Application: faster computers?

In everyday circumstances, an object cannot travel faster than light. The Princeton experiment and others change these circumstances by using devices such as the cesium chamber rather than a vacuum.

Ultimately, the work may contribute to the development of faster computers that carry information in light particles.

Not everyone agrees on the implications of the NEC experiment.

Aephraim Steinberg, a physicist at the University of Toronto, said the light particles coming out of the cesium chamber may not have been the same ones that entered, so he questions whether the speed of light was broken.

Still, the work is important, he said: "The interesting thing is how did they manage to produce light that looks exactly like something that didn't get there yet?"
http://www.cnn.com/2000/TECH/space/07/20/speed.of.light.ap/
http://home.sunrise.ch/schatzer/space-time.html
http://csep10.phys.utk.edu/guidry/violence/lightspeed.html
http://www.livescience.com/technology/050819_fastlight.html
http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/ltrans.html
http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/speed_of_light.html
http://www.physicsforums.com/showthread.php?t=71234

Answer 2

From a classical standpoint, the permittivity and permeability of free space set the speed of light. Since these two parameters have to ultimately have quantum mechanical roots, the explanation ultimately lies in the answer to the question of why all the physical constants take onthe values that they have. So at this point in time, we don't know the fundamental reason for the speed of light being what it is - that's the y way the universe is constructed but we can't yet explain why.

The effect another poster talked about has been well know for years - it's called a precursor wave. You can't transmit information with it and the reasons why materials exhibit this behavior is rather complex and off-topic.

Answer 3

You could have worded your question a lot better. "Why doesn't light travel twice as fast as it normally does ?" Because that could cause a paradox, the light speed would double, then the doubled speed would become the normal speed, and have to double again. ect.

But until we are able to reach the speed of light, we may never be able to tell why it travels at the speed it does. And really, why would light need to go any faster/slower? Do you ask the wind how it moves mountains?

Answer 4

There is no limit that's how fast it wants to go. Light speed is the speed of electromagnetic radiation or anything with zero resting mass. Something with no mass goes pretty darn fast, I think it would be taking it to a quantum level if it went any faster.

Answer 5

Because Planck's Constant is not zero.

Although your question seems more metahysical, and we can't really figure out a "why" to most things, as much as figure out how it works, and etc.

Answer 6

Because it has no mass.