Right after the Big Bang, the universe had a monstrous growth-spurt called inflation. The whole thing was over in less than a trillionth of a trillionth of a second, but the universe grew exponentially in that brief blip, repeatedly doubling in size. At the end of inflation, although the universe was still smaller than a car, the outer edge had traveled many times faster than the speed of light. Since then, the universe has continued its expansion, but at a more reasonable, steady pace.
This ultra-fast growth seems to contradict what weve just discussed, but it makes sense if you understand the distinction between expansion and motion. When astronomers say that the universe is expanding, theyre talking about the rather abstract concept of space-time. Basically, space-time is the three physical dimensions of our existence-length, breadth and depth-combined with the additional dimension of time; think of it as a wire grid that connects every part of the universe to every other part. When we say an object has motion, were referring to its change in position relative to the space-time grid. The speed of light is only a constraint for objects that exist within space-time, not for space-time itself.
To better visualize the theory, astronomers often illustrate the expanding universe as a loaf of raisin bread rising in the oven. The raisins are galaxies and the rising dough represents space-time. As the dough expands, the raisin galaxies find themselves farther apart from each other, even though they are not moving relative to the dough between them.
Now lets imagine that theres a beetle in the loaf and it starts crawling toward a faraway raisin (dont worry- were not going to eat it anyway). The beetle represents anything within space, such as baseballs, spaceships or photons. When the beetle burrows through the bread, he is moving relative to the dough, and all the other raisins. The speed of light limits how fast the beetle can travel, but not how quickly the bread can rise. Just because the expansion of space can break the speed limit, it doesnt mean that we can go faster than Einstein said we could.
So, while the speed of light remains an unbreakable barrier for those of us within the universe, it cant limit the expansion of space-time itself. The universe keeps right on expanding, but the speed of light limits how much of it we can see, and how fast we can move. It may not be fair, but thats physics.
