Greetings from the afterlife.

It isn't what you expect. There are no puffy clouds, no beautiful landscapes, no children hugging lions like they do in Jehovah's Witness magazines, and that's because this is my version of the afterlife. After death, I will live here, and you will live somewhere else.

That's how life after death works, or at least it might be how it works. In his book Sum, the neuroscientist David Eagleman imagines 40 different versions of life after death and this week his theories – or possibilities as Eagleman prefers to call them – have been turned into a piece of performance art at the Royal Opera House.

The scope of Eagleman's possibilities is fascinating. In one version of the afterlife, he says, we might meet multiple versions of ourselves, some more successful than we were in life, some less so. In another, there would only be people we remember. There would be no possibility of ever meeting anyone new. Imagine that hell.

What Eagleman is doing with all these lives after death is using them as a way to make us evaluate life before death. That's why there are pleasant versions of the afterlife, and unpleasant ones. Which makes sense. Would you want your life, or your afterlife, to be 100% pleasant? The pleasant bits are only pleasant because we can compare them to the unpleasant ones. As the great philosopher and starship captain, James T Kirk, once said: "I need my pain."

And so what would my version of the afterlife be like? For a start, it would smell of cat fur, and I would be permanently six years old. I say six because that's the time before responsibility. But more importantly, it's the time before the doubt arrives – the horrible, nagging, persistent doubt that says: maybe there is no afterlife.