[wongarsu]

That's the acceleration you feel on the surface of the earth. But that's not an inertial reference frame. In an inertial reference frame gravity doesn't cause acceleration (kind of by definition).

The argument is that gravity doesn't cause acceleration, resisting gravity does. Kind of how spinning an object doesn't cause a centrifugal force, the real force is whatever forces it to stay on a circular path instead of continuing straight

[toast0]

> Kind of how spinning an object doesn't cause a centrifugal force, the real force is whatever forces it to stay on a circular path instead of continuing straight

Let's say the Moon is in a circular orbit around the Earth (close enough), what's the real force that's forcing it to stay on that path? If it's not gravity, what is it?

[dreamcompiler]

Great question. The answer is nothing. There is no force making the moon follow a circular path. The moon "thinks" it's moving in a Newtonian, inertial "straight line." Because the spacetime around the earth and moon is curved, the moon moves in a straight line through that curved space.

Caution: The circular path we see the moon follow is not the curvature of spacetime itself. Rather it's a zero-force iso-line along that 4D spacetime. This is also called a geodesic.

[xpl]

The Moon moves not in circles but rather along a straight line in curved spacetime. It doesn't require any force to stay on this path — it is in free fall.