Does space itself exist? This question has concerned the greatest minds of physics. Simply put:
If every matter object in the universe disappeared, would space still be there?
Newton saw space as the canvas upon which God painted, so it would still exist even without objects. In contrast Leibniz considered a substance without properties unthinkable so to him space was based on object relations, just as a meter was defined as the distance between two marks on a platinum-iridium bar in Paris. If objects only move with respect to each other, he concluded that without matter there would be no space.
Newton’s reply to Leibniz was a hanging bucket of water that spun around (Figure 2.2). 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 when it initially spins relative to the water the surface is flat, and when later it is concave, the bucket and the water spin at the same speed. In a universe where all movement is relative, a spinning bucket should be indistinguishable from one that is still. If an ice skater spins in a stadium his arms splay out by the spin. One could see this as relative movement, as the stadium spinning round the skater, but why then do the skater’s arms splay? He concluded that the skater really is spinning in space (Greene, 2004) p32.
This seemed to settle the matter until Einstein showed that objects actually do move relative to each other. Mach then resurrected Leibniz’s idea, arguing that the water in Newton’s bucket rotated with respect to all the matter of the universe. In a truly empty universe, Newton’s bucket would stay flat and a spinning skater’s arms would not splay, but this isn’t testable as one can’t empty the universe. This resort to speculation reflects how disturbing some physicists find the idea of a space that is:
“…substantial enough to provide the ultimate absolute benchmark for motion.” (Greene, 2004) p37
How then could a virtual space handle object interactions? There are two options:
1. Centralized. Give each particle an absolute position then compare all positions every cycle and if any are equal, then a collision has occurred. To the inhabitants of this virtual reality, space would indeed be truly nothing and potentially continuous. Yet as the particles increase the interactions grow geometrically, as each point must be compared to every other point every cycle. For a simulation the size of our universe, the processing required is unimaginable.
2. Distributed. Let each point of space be a node with a pre-allocated processing capacity. Now a collision is when a node gets more processing than it can handle. To the inhabitants of this virtual reality, space isn’t continuous and does exist apart from the objects in it. This tactic seems wasteful as empty space is allocated null processing but has the advantage that expanding the system also adds more processing.
Reverse engineering prefers the distributed option because the processing is finite. It implies that a point of empty space can show a dot or “nothing”, just like a screen point, where showing nothing is null processing. This means that if every object in our space disappeared, it would still exist, just as a screen still exists even if no image is shown, supporting the current verdict of physics that:
“space-time is a something” (Greene, 2004) p75
Empty space as null processing is neither the passive canvas of Newton nor the nothing of Leibniz because null processing is something not nothing and it is active not passive.