Here is the full transcript of cosmologist Sean Carroll’s TEDx Talk on Cosmology and the Arrow of Time at TEDxCaltech conference.
Sean Carroll – TRANSCRIPT
The Universe is really big. We live in a galaxy, the Milky Way Galaxy. There are about a hundred billion stars in the Milky Way Galaxy, and if you take a camera and you point it at a random part of the sky, and you just keep the shutter open, as long as your camera is attached to the Hubble Space Telescope it will see something like this. Every one of these little blobs is a galaxy, roughly the size of our Milky Way. A hundred billion stars in each of those blobs, there are approximately a hundred billion galaxies in the observable Universe. A hundred billion is the only number you need to know, the age of the Universe between now and the Big Bang is a hundred billion in dog years which tells you something about our place in the Universe.
One thing you can do with a picture like this is simply admire it, it’s extremely beautiful, and I’ve often wondered what is the evolutionary pressure that made our ancestors develop, adapt, and evolve to really enjoy pictures of galaxies, when they didn’t have any. But we would also like to understand it, as a cosmologist I want to ask, “Why is the Universe like this?” One big clue we have is that the Universe is changing with time.
If you looked at one of these galaxies and measured its velocity, it would be moving away from you, and if you look at a galaxy even further away, it will be moving away faster. So we say that the Universe is expanding. What that means, of course, is that in the past, things were closer together. In the past, the Universe was more dense, and it was also hotter, if you squeeze things together the temperature goes up. That makes sense to us.