[dataflow]

I understand what you're writing (I think), but I don't think I understand how the implications would be consistent with relativity unfortunately. I thought gravity is (supposedly) caused by the deformation of space. If your space isn't flat, then you're going to experience acceleration (aka gravity) at that point, right? And if this deformation is permanent, then its source is already long gone - meaning that when you look down to see why you're falling, you see that there's no matter or energy causing you to fall. Which seems weird to me because I thought you need some kind of matter/energy to cause space to curve (and hence feel gravity/acceleration). Is that not the case?

[simonh]

These distortions are predicted by relativity. They’re a consequence of it, not a problem with it.

Objects influenced by a gravitational field don’t feel an acceleration. Astronauts in orbit round the earth don’t feel anything even though they are going round in circles. It’s only when something gets in the way that you feel an acceleration from the thing stopping your trajectory, like the surface of the earth.

The distortions were talking about are created by a mass though, the mass that created the original gravity wave.

[dataflow]

> Objects influenced by a gravitational field don’t feel an acceleration.

We don't feel velocity but we do feel acceleration, whether it's due to gravity or anything else. I still don't follow the logic unfortunately.

[ravi-delia]

You don't feel acceleration either, you feel the normal force of an object against you. If you're in freefall you feel nothing (or really, you do feel the absence of a normal force you're used to).

However, that's not what the comment you replied to was saying. Gravity doesn't apply a force at all! A force is when your worldline gets pushed around, but an object undergoing gravity is actually still going "straight", it's spacetime that's deformed.

[dataflow]

Ohh, right! Interesting! I think I'm finally seeing what's going on. Thanks!

[simonh]

One problem is that a lot of simplifications get layered on in pop science explanations of relativity, or actually deep science of any kind. We often talk about the force of gravity, but the thing is it's actually not a force, or even a field, in the same way as other forces and fields in physics.

This is why Einstein is so revered in Physics. He didn't just explain a force, otherwise why would he be given pre-eminence over Maxwell who explained electromagnetism? Relativity is something else completely.

Here's a really good explanation of what's actually going on when gravity influences an object. Hold on to your chair.

https://www.youtube.com/watch?v=UKxQTvqcpSg&t=19s

[ravi-delia]

> it's actually not a force, or even a field, in the same way as other forces and fields in physics

That's why (for anyone who's still reading this old thread) gravity is treated separately from the other three "fundamental" forces. We can explain pretty much everything in physics with the tools of Quantum Field Theory, even if there's still some gaps, but relativity is a whole other ballgame. Not only is it totally resistant to the mathematical techniques (quantum operations are linear, relativity is very much not, to name just one issue), but it's sort of unclear what QFT looks like without spacetime as a stage to act on. If the properties of spacetime emerge from some simpler, presumably more quantum, system, we have next to no idea how.