So anything that has two states corresponds to one bit. Heads or tails, as well as true or false, zero or one. If you have four states, that corresponds to two bits. But now what corresponds to three bits? Would it be six states? No, actually what happens is that you have eight states. That corresponds to three bits. So why is this so? So if I look at three bits, I can have zero zero zero, zero zero one, zero one zero, zero one one, one zero zero, one zero one, one one zero and one one one. Three bits, eight states. All I'm doing is just counting out and here you see me counting in binary notation. These are just the numbers zero, one, zero one zero is two in binary notation, zero one one is three, one zero zero is four, one zero one is five, one one zero is six, one one one is seven, which shows the rationale behind the old joke, which is that there are ten different kinds of people in the universe. Those who understand binary notation and those who don't. If I go to more bits, so if I have n bits, where n is equal to one, two, three, et cetera, what it means is that I have two to the n different possibilities. Or sometimes called states. So I can have 00....0, 00....1, 00....10, 00....11, you can tell, there's a heck of a lot of possibilities here, and end up going 11111....1. So this is zero, this is one, this is two, this is three and this is two to the n minus one, because two to the n would be 1000.....0, which is two to the n. So when you are counting in binary, when you have bits, you have for a relatively small number of bits, you can have a very very very large number of possible states, possible things that you could label with these bits. In fact, it's an interesting question to ask how many bits are there in the universe? How many bits in the universe? Well, this seems kind of a crazy question, you would think. There's an infinite number of bits in the universe. But actually this is not so, if you look at it in our universe, which is the part that we have access to since the Big Bang, which was, last time I read, 13 * 10^9 years ago. So the part of the universe that could be within 13 billion light years in any direction, this amount is actually finite. This is a rather surprising result that the amount of information in the universe is finite. It comes from the laws of quantum mechanics, but it turns out that within the universe, there are 10^90 particles, most of these are microwave photons from the black body, radiation that is left over from the Big Bang. They are all over the place, they are around us right now. There are particles of light, wavelength is roughly about that size. There are 10^90 of them, so this is a one followed by 90 zeros, in ordinary digital notation, and each of these particles carries a few bits of information with it. And in fact, if you go to the absolute limits that are allowed by the Laws of Physics, the total number of bits that could be allowed would be 10^120, which is a one followed by 120 zeros. These are large numbers of bits, but they're not infinite. They're big numbers, but I could think of much bigger numbers. For instance, 10 to the 120 plus one is bigger than 10 to the 120. Or 10 to the 220, or 10 to the 240. There are large numbers, but there's a finite number of bits, and a large number of bits but it's finite. Now what does this mean?