When Descartes famously equated thinking with existing, the idea of existence meant something very different from today. He lived in a world before quantum mechanics and wave-particle duality, indeed even before Newtonian mechanics.
To Descartes and his contemporaries human existence was as solid as the rocks of the earth, as permanent as the stars in heaven. True, people died eventually in Descartes’s world, but they were assumed merely to travel off to another and better place.
For Descartes, to say ‘I think therefore I am’, was to say, ‘I have a permanent place in the cosmos: I belong: I am here to stay.’
Yet almost every discovery of physics and chemistry since Descartes has confirmed not how permanent we are, but how temporary. As the universe runs down, its energy randomly rearranges first one group of atoms, then another, like raindrops on a window pane. Sometimes natural laws conspire to impose patterns on the raindrops and for a moment they appear to have a unique and lasting identity. But the moment passes – whether it is a moment measured in nanoseconds or millennia – and the kaleidoscope patterns swirl into another new randomness.
Sometimes the accidental rearrangements are simple and commonplace – clouds of hydrogen condensing into stars. Sometimes the accidents are more complex. In Dorset’s Chesil Beach, the stones have been re-arranged by the tides and their relative buoyancy so that they are finely graded along an 18-mile stretch, from tiny pebbles at one end to large boulders at the other.
It may well be that similar processes in chemistry have caused self-replicating molecules to form spontaneously – though as yet we have no direct evidence of this process happening naturally.
But no matter how complex the patterns and no matter how long lasting they are in human term, they remain accidents, nothing more than epiphenomena of the giant switchback ride that is the universe, as the energy of the Big Bang is dissipated.
To say “I think, therefore I am”, means nothing more than to say, “I think, therefore I am like the little dot that glows for a moment on the TV screen after it has been switched off.”