#2217 - Brian Cox

5924.952 - 5947.841 Brian Cox

And so the universe has been expanding for a billion years, so the light will be stretched. And so you can measure how much stretch there is. You just measure the color of the light from the supernova. So you can argue that maybe if you go for light that's been traveling 12 billion years across the universe, then maybe there was something different. Maybe the light was emitted a bit different.