Much of modern physics hinges on the notion of a smooth ‘continuum’. But as Professor of Theoretical Physics Sumati Surya argues, our lived experience point to something else: discreteness. Surya argues that spacetime isn’t infinitely divisible but instead built from discrete elements and their causal relationships – there is a “fundamental minimal size below which spacetime loses its meaning”.

What is the ‘substance’ of spacetime?

We are schooled early on, to imagine the ‘real line’, by inserting between any two points on the number line, an uncountable infinity of numbers, the so-called ‘irrationals’. Even as children we are aware that physical objects have an atomicity – if broken too fine, they lose any semblance of self. A continuum-like sheet of paper can only withstand so much tearing or folding, before it gives way to dust. Yet, we are told, there is a reality beyond this, literally that of the ‘reals’, where every division offers an uncountable infinity of further divisions, which never ever stops. Thus, the platonic ‘reality’ of a continuum overrides the physical, experiential reality of finiteness and discreteness.

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At the Planck scale, spacetime comes into its own, as physical substance, the point at which the myth of the continuum dissolves into the dust of spacetime. Yet, most theories of quantum spacetime are framed in the continuum, where spacetime can be broken into bits, ad-nauseam, at scales arbitrarily smaller than the Planck scale.

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