Just 100 years ago, Albert Einstein invented a new theory of gravity called “general relativity” and rapidly applied it to the problem of the study of the universe as a whole. To match astronomers’ understanding at the time, he introduced the cosmological constant, a mathematical term that allowed for a static universe. In the following decade, astronomers showed the universe was not static but expanding, and Einstein banished the cosmological term. However, in the past 20 years, astronomers have shown that the universe is not only expanding, but that this expansion is speeding up. What drives this cosmic acceleration? We call it dark energy, but it might be very similar to Einstein’s idea from a century ago.
In this talk, Robert Kirshner will show how we discovered cosmic acceleration and present the evidence that we live in a universe that is only 4 percent ordinary matter, like the atoms of the periodic table, with the balance divided between mysterious dark energy that speeds up cosmic expansion and equally mysterious dark matter that draws matter together.