Does the Grand Canyon Exist?

An image of the Grand Canyon showing clearly that what we see is merely the absence of the rock which was previously there.

An image of the Grand Canyon showing clearly that what we see is merely the absence of the rock which was previously there. Picture from NASA Earth Observatory.

The wonder-ful NASA Earth Observatory this week sent me an image of the Grand Canyon created by overlaying satellite imagery with a detailed topographic map. And as I stared in wonder I could see clearly that the Grand Canyon did not in fact exist!

What I saw was that the Grand Canyon was a phenomenon defined by absence – the absence of the rock which has been removed. The rock which has been removed was – if you like – the ‘positive’ – the actual ‘stuff’ which exists. And what remains is the ‘negative’ a phenomenon made entirely out of… absence! And this made me think about electrons…

As you may know, Dirac’s conception of particles and anti-particles imagines a vacuum state, geographically analogous to the elevated high plains. He imagined that things could be added to this vacuum state to create a phenomenon we call a ‘particle’ , for which the geographic analogy would be a mountain. Nobody could doubt that a mountain exists!

But in Dirac’s conception, something can also be subtracted from this vacuum state to make an anti-particle, for which the geographic equivalent would be a valley. Or a canyon. Anti-particles would be defined by absence.

Staring at the undeniable existence of the Grand Canyon and realising that it didn’t really exist, I felt something click. I felt that the wonders and mysteries of the  microscopic world were somehow being played out at another scale – a scale so large that this time I almost failed to recognise them for a different reason!

It’s a funny old world.

Goodnight

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