| Mark Vernon | Comment is free | guardian.co.uk
Imagine Stephen Hawking is reincarnated, and this time round his father is a philosopher. One day, when little Stephen is about five years old, they're sitting in the summer house with Fido, their pet dog. And Stephen asks one of those questions children love to repeat.
Daddy. Yes Stephen? Why is Fido? Well, Stephen, Fido had a mummy and daddy like you.
Yeah but, why is Fido? Err, you mean why is he a dog? That's because his parents were dogs, and his parent's parents were dogs too. They belong to what we call the same species. (Stephen is precocious in this life too.)
But why is Fido? Well, we know that Fido's parent's parent's parent's parents – a long way back – were not dogs, but were wolves. That was before human beings made them pets.
Oh. Why is Fido? Before there were wolves there was another species out of which wolves grow. We call it evolution, Stephen, and it's a very important process in the natural world.
Ev-o-lu-tion. (Stephen likes the feel of that word.) But why is Fido? Before that species, there was another, and another, and another, all the way back to tiny animals we call cells.
Why IS Fido? You're asking about biochemistry now. Err, roughly you can say that when the stuff of which everything is made is put together in a very complicated way – like a fantastic lego puzzle – then it takes on this very special property we call life.
WHY IS FIDO? Before life, there was just stuff – matter. It hung around for many billions of years on planet earth.
But why is FIDO? Before the earth, there were stars, and galaxies, subatomic particles and strange things like black holes. (Stephen has the very strange feeling that he knows all about black holes, even though he's only five.)
Yeah but, why is Fido? Scientists think it all started with a big bang, Stephen, a kind of spontaneous eruption out of which everything came.
Wow! Why is Fido? The big bang must have happened because of the laws of physics.
BUT WHY IS FIDO?
(At this point Stephen's father pauses. Being a philosopher, he realises that Stephen is now asking a very different question to all the ones he's asked before. You see, before, his questions could be answered with reference to some preceding state of affairs, out of which Fido can be said to have come. Now, though, he is asking about where everything came from, and being everything, there is no antecedent reality to refer to. To start to talk of nothing, not even abstract laws of nature, let alone wildly compressed energy, is to try to put everything in the context of nothing. But nothing is precisely that: not a quantum field fluctuating in the vacuum, not one universe springing out of a multiverse. Nothing is more radical than that. It is nothing. It's impossible to conceive of, in fact. It's no wonder Stephen's father pauses.)
I'm not sure we can ask that question, Stephen. It makes no sense.
But I want to know: why is Fido?
Well, some say the universe just is. There's a famous philosopher from about 100 years ago, Bertrand Russell, and he thought that.
(Stephen harrumphs.) But why is Fido?
There is another answer.
Yes? (Stephen sits up.)
Well, it's not exactly an answer.
Oh?
More like a mystery.
I like mysteries.
But I'm not sure you're going to like this one.
Tell me!
Well, there was another philosopher who was a friend of Bertrand Russell, in fact. He was called Ludwig Wittgenstein, and he said, "Not how the world is, but that it is, is the mystery."
Wow!
And the mystery is sometimes given a name.
What's the name?
It's called God.
(With thanks to Herbert McCabe)