by Scott Teresi
www.teresi.us/writing


In April 2000, a very distant object was discovered—the most distant object known to man at the time, 28 billion light years away. It was a quasar, which is a galaxy at its earliest stages of formation, little more than a black hole sucking in huge amounts of matter and giving off as much light as millions of stars. The quasar we see is less than a billion years old, because it took almost the entire lifetime of the universe for its light to reach earth.

With the commonly-accepted age of the universe set at 14 billion years, though (give or take a few billion), how could light have ever reached us from an object 28 billion light years away? Here’s what happened. When the quasar was less than a billion years old it emitted toward earth (or where earth would eventually be) the light we’re seeing now. In the intervening 13 billion years, space actually expanded between the earth and the quasar so much as to move the two objects apart at a rate of almost twice the speed of light. Now, after a total of 14 billion years, the quasar’s light has finally reached us and we find ourselves 28 billion light years from its source.

You may be puzzled as to how two objects can actually recede from each other at twice the speed of light. Nothing can travel faster than light, right? Well, the earth and the quasar were never actually traveling anywhere near the speed of light. Instead, the intervening space between the two objects was expanding so much as to make it seem like that’s what was happening. The universe has been expanding since its birth at the Big Bang. To this very day, the space between galaxies everywhere is expanding. The objects aren’t being pushed or pulled apart; the actual fabric of space between them is expanding. Space can expand at whatever rate it wants, actually. Meanwhile, however, no object will ever move through that space at faster than the speed of light.

References

Kahney, Leander. "Scoping For Distant Objects." Wired News, April 14, 2000.

Sloan Digital Sky Survey web site.