We Have No Idea: A Guide to the Unknown Universe

by Jorge Cham

Shortly after realizing this, two teams of scientists raced against each other to measure the rate of expansion of the universe. But finding supernovae is not easy because they are short-lived explosions. To catch one, you have to constantly scan the sky for stars and spot the ones that suddenly get much brighter and then dimmer so it took a while. The two teams assumed that the expansion of the universe should either be slowing down or staying the same. This is a reasonable assumption. If the universe exploded, and gravity is trying to pull everything back in, then there are only two options: either gravity wins and things get pulled back in, or it loses and everything keeps expanding steadily. When the scientists measured these supernovae and calculated the rate at which the universe was expanding, they expected gravity to be winning. That is, they expected to find that more distant stars (the ones in the past) were moving away more quickly than closer stars (the ones closer to the present). Instead, they were flummoxed to discover the opposite: that stars seem to be moving away from us more quickly now than they were in the past. In other words, the universe is expanding faster now than it was before.