Here's another way to think about it, that is mathematically frightening for the people who think that the aliens are out there and they're going to visit us at some time in the future.

We were talking earlier about trillions of planets that exist throughout the known universe that might even be friendly for life to arise.

Imagine that between us as intelligent human beings and the most simple form of bacteria that we can imagine,

there are only 100 independent evolutionary steps. Now that's not true, it's probably a million or more different mutations that had to happen and were favourable allow any organism to survive such that we exist today.

But just make it only a hundred. And imagine that each of those independent steps had a probability of just one in ten of happening.

Now in fact, it's probably more like one in a million, but we'll be generous, we'll say one in ten. So now what we have is a chain of probability, one in ten times, one in ten times, one in ten a hundred times.

And if you know how to do mathematics, you'll realise that this is one over ten, all to the power of one hundred, which is one over one followed by a hundred zeros.

That number swamps the astronomical number I was talking about with planets earlier on. In other words, the probability of us arising on this particular argument is infinitesimally small.

The fact that it's happened once should blow up behind.