Yes, the universe itself will eventually outpace the speed of light.
Just how this will happen is a bit complicated, so let’s begin at the
very beginning: the big bang. Around 14 billion years ago, all matter in
the universe was thrown in every direction. That first explosion is
still pushing galaxies outward. Scientists know this because of the
Doppler effect, among other reasons. 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 cluster of galaxies about three billion light years
away. Astronomers have measured the distance from the Earth to Hydra by
looking at the light coming from the cluster. Through a prism, Hydra’s
hydrogen looks like four strips of red, blue-green, blue-violet and
violet. But during the time it takes Hydra’s light to reach us, the
bands of color have shifted down toward the red end—the low-energy
end—of the spectrum. On their journey across the universe, the
wavelengths of light have stretched. The farther the light travels, the
more stretched it gets. The farther the bands shift toward the red end,
the farther the light has traveled. The size of the shift is called the
redshift, and it helps scientists figure out the movement of stars in
space. Hydra isn’t the only distant cluster of galaxies that displays a
redshift, though. Everything is shifting, because the universe is
expanding. It’s just easier to see Hydra’s redshift because 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, because space itself is stretching, and space is nothing.
Galaxies aren’t moving through space and away from each other but with
space—like raisins in a rising loaf of bread. Some galaxies are already
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 track expands
while you’re running,” Bennett says. “If it expands faster than you can
run, you’ll never get where you’re going."
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