My coworker told me gravity isn’t a force it’s an effect mass has on space time, like falling into a hole or something. We’re not physicists, I don’t understand.
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A force is often defined as a mass that changes speed and/or direction (i.e. accelerates). Gravity has no mass so it’s not a force. It just causes things that already have mass to attract each other.
A ripple in a pond isn’t a force. It’s a wave and water is its medium.
Gravity also isn’t a force. It’s more like the wave in the pond. But instead of water it’s space-time that’s the medium.
Objects with high mass warp space-time similarly to how a boat might warp the surface of a lake as it moves through it.
It’s easier to think of gravity as an acceleration field, not a force field. It still isn’t strictly correct but insofar as it matters to normal people it’ll be more correct if you understand the relationship acceleration and force have.
Objects with mass distort space-time. More mass, bigger distortion. As a 2d analogy, picture spacetime as being like the surface of a trampoline. If you drop a bunch of marbles they wont move quickly, but will *eventually* come together. Now instead drop a handfull of marbles and a single bowling ball. It’s gonna look like the marbles are all getting pulled towards the bowling ball.
The space time distortion model is called the theory of general relativity, and it fills in the holes where Newton’s equations break down. This is usually where enormous masses, distances, and velocities come into play, like planetary motions.
However, relativity breaks down when things get incredibly small, and this is what physicists are currently attempting to solve using quantum mechanics.
What does it feel like to gently float down a moving river?
Unless you bump into something, it actually doesn’t feel like anything at all. You’re moving along with the water. You don’t really feel the water “pushing” on you, like some kind of force. You don’t need to push against the water to be moving. You and the water move along together.
But what if you bump into a rock and get stuck? Now you can’t move along with the river. Now, you suddenly very much feel the force of the water pushing on you, and the force of your body pushing against the rock.
Gravity is like water in a river. It is *space itself* being bent in a way that it basically continually “flows” towards things with mass. If you simply flow along with it, you don’t feel a thing. You don’t even feel like you’re falling, or speeding up. There’s no force. You just float along with it, even though you’re “at rest.”
But when you hit the rock in the stream (in this case, the surface of the earth), now suddenly it feels like space itself is some “force” pushing you towards the center of the earth, and the earth is pushing back on you. But that is an illusion. Nothing is pushing you downwards.
Your body, “at rest,” with no effort or force acting on it, wants to move towards the center of the earth. But it can’t. The actual force you feel is the ground is stopping it, as space continues to “flow” towards the center of the earth, right through you, and your chair, and the ground.
Astrophysicist here. Gravity is a force. Force is something that causes an acceleration which can be a change of speed or a change of direction. Your coworker is wrong.
I like this YouTube video explaining it:
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