COBE produced a map that included ripples, or amplitude fluctuations, in the structure of space-time across billions of light years. Those ripples are the largest structures humans ever will be able to see, Hogan said. But they also are greatly magnified images of the smallest structures ever visible – the same fluctuations that started out smaller than a subatomic particle at the Big Bang, then were frozen into the fabric of space-time and stretched as inflation expanded the universe to its current size.