It Simply Is

Gravity simply is, and it's merely that the equations that describe General Relativity are geometric in nature. The idea that mass-and-energy curves space can be right, even though this naive visualization must be wrong.

Statements that say, "this simply is" invariably mean, "we do not yet understand why this happens." This is, however, very different from saying that we have no knowledge at all.

But under no circumstances should you conceive of space as though it's a material, physical thing; it isn't. This is only a mathematical structure that we can write down equations to describe: the equations of Einstein's General Relativity. The fact that matter and radiation respond to that curvature in the exact ways that the equations predict validates this theory, but it doesn't mean that space is actually a fabric.

We also talk about the expanding Universe in the context that 'the fabric of space is stretching,' even though there is no fabric and it isn't really stretching, or for that matter, changing in any way. What's happening is simply that the distance between any two points in the Universe is changing according to a particular set of rules in the context of General Relativity. Galaxies, like raisins embedded in a loaf of baking bread, expand away from one another. The wavelength of radiation gets longer too, as though the length of the wave crests and troughs expanded away from one another too.

I dunno... are non physical things still things ? If they are, then I have no problem with saying that space is expanding and thus changing; space is a relational thing. And if space isn't a thing, how can gravity be described as the curvature of space ?

One of the most paradoxical ideas to wrap your head around in all of physics is that the equations that describe the Universe are just that: equations describing things we can physically observe. We can no more observe the 'fabric of space' than we can observe the nothingness of empty spacetime; it simply exists. Any visualization we attempt to assign to it, whether it's a 2D fabric, a 3D grid, or a baking ball of dough, is just that: a human-inspired creation. The theory itself doesn't demand it.

I think I'll stick to pretending that space is a sort of non-physical fabric, accept that I don't understand what that is, and "shut up and calculate" as a wise man once said. Easier that way. Otherwise I'm likely to explode in a shower of Zeno's Paradoxes as I struggle to contemplate the formless, infinite nothingness that apparently divides me from measurable reality.

Science is hard.


https://www.forbes.com/sites/startswithabang/2018/08/11/ask-ethan-is-spacetime-really-a-fabric/