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Can Anything Move faster than Light?

Yes, the cosmos itself will ultimately outpace the speed of light. Just how this will take place is a little complex, so let's start at the very foundation: the big bang. About 14 billion years ago, all matter in the universe was thrown in every direction. That first explosion is still pushing galaxies outward. Researchers know this since of the Doppler Effect, among other causes. The wavelengths of light from other galaxies shift as they move away from us, just as the pitch of an ambulance siren changes as it moves past.

Take Hydra, a group of galaxies around three billion light years away. Astrophysicists have calculated the distance from the Earth to Hydra by observing the light coming from the cluster.

Through a prism, Hydra's hydrogen appears like four strips of red, blue-green, blue-violet and violet. But in the time it takes Hydra's light to reach us, the bands of colour have moved down toward the red end—the low-energy end—of the spectrum. On their voyage across the cosmos, the wavelengths of light have stretched. The farther the light travels, the more stretched it gets. The distant the bands shift toward the red end, the farther the light has travelled. The size of the shift is called the redshift, and it helps researchers figure out the movement of stars in space. Hydra is not the only distant cluster of galaxies that shows a redshift, however. Everything is shifting, because the cosmos is expanding. It's just easier to see Hydra's redshift as the farther a galaxy is from our own, the faster it is moving away.

There is no limit to how fast the universe can expand, says physicist Charles Bennett of Johns Hopkins University. Einstein's theory that nothing can travel faster than the speed of light in a vacuum still holds true, since space itself is stretching, and space is nothing. Galaxies are not moving through space and away from each other but with space—like raisins in a rising loaf of bread. Some galaxies are at present so far away from us, and moving away so quickly, that their light will never reach Earth. "It's like running a 5K race, but the pathway expands while you are running," Bennett says. "If it expands faster than you can run, you will never get where you are going."

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