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Lauren Admire | 1 Feb 2010 16:30

Photon Seemingly Travels Faster Than Light

According to Albert Einstein's theory of special relativity, nothing can exceed the speed of light. It's impossible. As matter speeds up, it gains mass. The more mass it has, the more energy is required to keep the object accelerating. Once it hits the speed of light, the mass is infinite, and thus, the required energy to keep it accelerating would be infinite, as well.

"There is no experiment that has contradicted special relativity," states Donald Schneider, professor of astronomy and astrophysics at Penn State. "We have accelerated sub-atomic particles to well over 99 percent of the speed of light, but not equal or exceeding the speed of light."

However, an experiment by scientists at the Joint Quantum Institute have sped up photons faster than the speed of light by launching them through strategically-placed stacks of material. Or, created the illusion of it, at least.

Researchers placed 30 dielectric (electrically insulating) layers of material, one in front of the other, each 80 nanometers apart. The layers alternated between high (H) or low (L) refractive indices, which caused the light to bend or reflect in varying amounts. When a photon passes through these layers, it has a chance of either being reflected or passing through. When it passes through, it passes through all of the layers in 12.84 femtoseconds (quadrillionths of a second). When the researchers added another H layer, the photon reduced its transit time to about 5.34 fs, so that they seemed to emerge through the stack at faster-than-light speeds.

However, this behavior is easily explained by the wave properties of light. As a photon passes through each layer, it creates a remaining wave, and these waves interfere with one another, combining to give the illusion of photons traveling faster than the speed of light. I'm not exactly sure how that works, but it's still awesome. (::reminds self to get a degree in Quantum Physics::)

A similar thing occurs when photons pass through water. Water is denser than empty space and thus, photons are slowed to three-fourths of their original speed. In a nuclear reactor, photons flying off of radioactive rods also appear to exceed the speed of light. This is a process called the Cherenkov Effect. I don't understand how this works, either, but it does make the water glow a neat, eerie blue color, and so this too, is awesome.

Wormholes, tachyons and warp drives are staples of science fiction, and it looks like they won't become a part of reality anytime soon. But at least we can mimic faster than light travel effectively, and that's half the battle.

Source: Science Daily

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