It’s a quote by Albert Einstein, which is where we left off last time. Comprehensible translates to, for example, mathematically intelligible, regular or lawful. These are different ways to say that it is possible to arrive at descriptions of the world that allow us to understand it and make predictions. Einstein’s point was that there is no particular reason to expect the universe to be the way it is, i.e. following elegant mathematical laws. It could have just as well been a chaotic mess impossible to make sense out of.
It’s hard to tell whether it’s even meaningful to speak of the way the universe could have been without speaking of how the universe and its characteristics arise. Indeed, one of the deepest questions in physics is, why does the universe have the laws it has? (Second only to why is there something rather than nothing?)
But imagine for the moment that the universe was in fact a messy chaos. Well, one thing seems clear, that kind of universe would not contain life, because life is one of the most obvious examples of order and regularity (or if you like, life requires order and regularity to exist), and intelligent life is precisely the kind of life that requires most order.
The point is that our very existence screens off the possibility of a non-regular universe, it is impossible for us to observe anything different because we would not have existed under those circumstances. This point is known as the anthropic principle. Does it answer the question? Not really; the anthropic principle has been labeled as unscientific and metaphysical by critics. You have to be careful to not take the point too far. In this case I’m just saying that life implies a selection effect to the universe it inhabits.
But again, that does not answer the question. However, if we additionally postulate that there isn’t one universe, but many, the situation makes some sense:
Alice: Why is the universe comprehensible?
Bob: The thing is, there isn’t just one, there are many, so it turns out that some of them are comprehensible, just like in a lottery someone must end up winning.
Alice: But what about the coincidence that we landed precisely on a comprehensible one?
Bob: That’s not a coincidence, our very existence implies that the universe we are in must be orderly. We couldn’t have landed in any other one.
Alice: So it’s a combination of those two things that answers the question, the anthropic principle is not enough..
Although in fact the question is still not answered because we had to postulate the existence of many universes, and we could in turn ask ourselves why that is the case. Oh well.