If matter exists, and space is just its absence, is it nothing at all? The greatest minds of physics have wondered whether space exists, and in particular:
If all the matter in the universe disappeared, would space still exist?
If space is something it would, but if it is nothing at all, it wouldn’t. For Newton, space was the canvas upon which God painted, so it would still exist without matter, but Leibniz disagreed. He couldn’t imagine a thing with no properties and so defined space relative to matter, just as distance is defined by two marks on a platinum-iridium bar in Paris. If objects only move with respect to each other, without matter there would be no space.
Newton’s reply to Leibniz was a bucket of water that is spun around (Figure 2.2). At first the bucket spins not the water, then the water also spins and presses up against the side to make a concave surface. If the water spins with respect to another object, what is it? It can’t be the bucket because initially, when it spins relative to the water, the surface is flat, and later, when it is concave, the bucket and the water spin at the same speed. In a universe where all objects move relative to other objects, a spinning bucket should be indistinguishable from one that is still. And when an ice skater spins in a stadium, their arms splay out by the spin. If this is movement relative the stadium, why then do the skater’s arms splay? Such examples suggest that the skater really is spinning in space (Greene, 2004) p32.
This seemed to settle the matter. Space is something, but then Einstein showed that objects actually do move relative to each other, so Mach resurrected Leibniz’s idea. He claimed that the water in Newton’s bucket rotated with respect to all the matter of the universe, so in a truly empty universe, Newton’s bucket would stay flat and the spinning skater’s arms wouldn’t splay. This theory isn’t testable because we can’t empty the universe but his willingness to rely on speculation shows how disturbing some physicists find the idea that space is:
“…substantial enough to provide the ultimate absolute benchmark for motion.” (Greene, 2004) p37.
Hence, the current verdict of physics is that “space-time is a something” (Greene, 2004) p75. This property of causing object movement could be provided by a network, but how would it register object collisions? Modern networks provide two feasible options:
1. Centralized. A central processor registers each object’s absolute position and direction and compares them every cycle to deduce a collision for those at the same point. To its inhabitants, this space would seem to be continuous and to have no existence in itself, but the processing required increases geometrically with the particles, as each one must be compared to every other particle. Even for the atoms in our universe, the processing required is unimaginable, so the system as a whole could overload.
2. Distributed. Each network point is allocated a finite processing capacity to handle local objects, and a collision occurs when it gets more processing than it can handle and overloads. To its inhabitants, this space would seem to be not continuous and to exist apart from the objects in it. This approach seems to waste processing on empty space but has the advantage that the system as a whole never fails.
Current computing prefers the distributed option, which is how our Internet works, because it doesn’t let the whole system fail. If our space is virtual, it has run for fourteen billion years without failing, so this option is preferred. Empty space is then null processing not nothing. It follows that if every object disappeared, our space would still exist, just as a screen still exists even when it shows no image.
Quantum realism concludes that empty space isn’t the passive canvas of Newton because null processing is active, nor is it the nothing at all of Leibniz because null processing is something not nothing.