Gravity and How to Intuitively Visualize It

Recently, I came upon a reddit post asking the simple and perfectly reasonable, and rather all-too common question:

Why do gravity make thing fall?

Well, not really. Their question was more focused on the mass of objects and why it “projects” gravitational force. I don’t claim to be a physicist (yet), but I think I have a pretty solid grasp on this particular intuition. Another user criticized the typical “Bowling ball on a trampoline” intuition, saying that it merely kicked the question down the road. That’s not entirely untrue, but the point of that particular intuition is not to serve as the all-encompassing view of gravity and the geodesics of spacetime, but to get you framing and relating gravity and geodesics.

We cannot intrinsically determine our position in spacetime and thus we cannot realistically manipulate it, and if we could, we couldn’t generate the energy to freely do so. We don’t actually travel along spacetime, but through it.

Objects proceed through spacetime not of their own volition, but because they are forced to do so due to all the external forces of the universe.

Even the “why” of this is relatively simple. Because things exist, they do stuff (entropy and enthalpy and all that) until the energy distribution is so complete that no further work can be done. No energy gradients, no deltas, and thus no where to go and no where to motivate motion in the sense we are used to. Just think of floating adrift through space. Thats really how we are currently moving through spacetime. We know that in a vacuum, without a medium to act against, we lack the energy to displace ourselves. Similarly, as we exist in spacetime, we lack the capacity to affect our trajectory in any meaningful way. Our motion is entirely passive, which is difficult for us to understand.

A ball would roll along due to laws of motion and angular momentum in a scenario in which work can still be done. Thus, as it travels and depresses spacetime, its natural trajectory is altered by any outside entity’s curving the spacetime it travels along, while it also curves that spacetime in some way as well. This is more to get the mental image of us and the geodesics framed rather than to be the be-all end-all mental model of gravity and spacetime.

So, the ultimate goal is to realize that gravity is more like a bowling ball moving through the ocean. It displaces the water slightly where it is, which does, although incredibly slightly, deform the medium in which it exists. It has no agency over its own movement, and simply proceeds along the gradient according to the forces acting upon it.