I live in Australia. As a non-scientist or mathematician cosmology can be hard to understand. This is particularly so when a much loved and respected local Nobel laureate, Brian Schmidt says, “The universe is infinite and it is expanding”.
If the universe is infinite it never ends - I assume it goes on forever!
I can understand infinite in mathematics, the square root of two is a number that, like the size of the universe, goes on forever. But the square root of two is not like the infinity of adding numbers together. The square root of two is infinite but always stays less than one number and bigger than another - it is as if infinity has been constrained.
If you have an infinite universe how can it only point one way? If you look inwards should it not get infinitely smaller? As you look inward, however, the standard model cuts you off – everything seems to just disappear fromview. It is just like the universe - after 13 billion light years or so it also fades from sight! Now, string theory would say it gets a lot smaller still but even string theory has a size that is way bigger than infinitely small.
I find the concept of an infinite universe really confusing.
Having said that I think of the anthropic principle as a basis to explain the existence of life. Our entire universe, the one we can actually see, seems to be perfect for it because even if we are alone somebody is here? It seems you need water, a star for some heat, a steady temperature, a rocky planet and presto it can happen. And so on the basis of all the hundreds of trillions of stars and planets out there you get the numbers you need for life. The problem is I have also heard that the universe does not need to be the way it is. The laws of physics need only be slightly different and all of a sudden you get no stars and I assume life. If you apply the anthropic principle to our whole universe, the one we can see that is, there has got to be more than one because you cannot expect to get all the laws of physics spot on with just the one roll of the dice. All of a sudden infinity is looking good again!
So my question to those who believe in an infinite universe derives from the square root of two. An infinite universe, maybe but it is nevertheless smaller than one thing and bigger than another! Without this constraint sooner or later you end up with an earth like planet that is an exact replica of our own. Moreover, once you get one, by definition there must be an infinite number of them. How do you defend a model that says there must be an infinite number of infinite universes, when just like the string theorists, you know the model can never be seen or empirically tested.