Rewinding Time to Explore the Big Bang ｜ Universe ｜ BBC Earth Science

We know the universe is expanding and thanks to Hubble we have evidence that this expansion is accelerating over time. So if you know the universe is expanding you can just do a thought experiment and turn time backward and know that the universe was smaller in the past. We can wind back the clock through thousands of billions of yesterdays, back to a time before our Earth and Sun, to a time before the first galaxies, and finally we can cross the cosmic dark ages to pinpoint the moment the universe began. A moment we know happened 13.8 billion years ago. The Big Bang. The moment when our universe burst into existence. Yet it wasn't anything like an explosion. This is the initial state of the universe which was very hot and very very dense. Everything, the whole universe, was held together in a very tiny region of space. So everywhere in the universe is almost like being inside of a star. All the matter that has ever been produced came from that moment in time. These conditions are unbelievably extreme and they no longer exist in today's universe. It almost seems miraculous, if not ridiculous, that we could study the origin of the universe, right? People say to me all the time, how could you know no one was there? For decades the Big Bang has been science's best estimation of how the universe began. And in 2009 a mission is launched to try to get a better understanding of this time in our universe. The European Space Agency's Planck Telescope is designed to look for the remains of the Big Bang. Not starlight this time, but a different type of light. The afterglow of the Big Bang. The most ancient light in the universe. If we do find it, then that means we can measure the actual conditions of the moment of creation. That's nuts, right? Planck will measure this ancient light with more precision than ever before. 7, 6, 5, 4, 3, 2, 1. The moment of the launch is where everything is at risk. And not just the launch, there's a whole bunch of stages. There was palpable excitement because we knew that this was an amazing shot we had at understanding our universe better.