19656

This article states that the early universe expanded “from subatomic scales to the size of a grapefruit in less than a trillionth of a second” or one picosecond. This would correspond to a velocity many times the speed of light (light only travels about 0.012 inch in a picosecond). How can this statement be reconciled with Einstein’s general theory of relativity that limits matter to a speed less than the speed of light?

Eric Rosenfeld
Gloucester Point, Va.

Researcher David N. Spergel agrees that general relativity requires that no object move through space faster than light. He adds, however, “General relativity also predicts that space itself can expand. . . . We can actually point to distant galaxies, on opposite sides of the sky, that are moving apart from each other at faster than the speed of light.” —R. Cowen