I often hear that gravity is not a force, but simply the curvature of spacetime. A common example given is having a heavy ball placed on a rubber sheet. The ball sinks, distorting the sheet. Therefore, other “orbiting” objects will also tend to roll towards the sunken part.
What I can’t understand is, what causes the objects to “fall” anyway? On earth, that’s just the planet’s gravity. If you did the same experiment on space the objects wouldn’t roll down. So how is this an explanation of gravity as a curvature, when it requires a *force* to work? Is there a better explanation? Am I just missing something?
In: Physics
The rubber sheet analogy is somewhat useful but not super accurate because, as you said, it only makes sense in the presence of gravity.
Think of it this way. All things in the universe travel in a straight line, unless acted upon by an outside force. This makes sense but then how do you explain the orbits of planets, right? They certainly seem to be going around in circles and not in a straight line.
The explanation is that they ARE going in a straight line, but spacetime itself is curved. The objects in the gravity well are following a geodesic. So, the straight line ends up curving when the spacetime it’s moving through is curved by gravity.
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