 The other way, though, is you can look at this light from the Big Bang. So this noise that Penzias and Wilson discovered in 1964. And by analyzing the patterns in that light, you can work out what the universe was like very early on. So in the first, you know, 400,000 years of universe's history. And then you can use our theory of cosmology to run the clock forward to today and predict how fast the universe should be expanding.