What do they mean when they say space time is curved? I keep hearing a lot of talk about Space Time being the 4th dimension, and no matter how many trampoline examples I see, I just don’t get it.
In: Physics
The trampoline example is useful for demonstrating orbits, but it’s kind of prone to overthinking (“then what’s pulling the bowling ball down?”). The scenario I like better is if you imagine that you and I are standing 1 meter apart at the equator, and we each have a compass, and we’re both going to walk north at the same speed. If the earth was flat, lines of longitude would be parallel, and every time I would look over at you you would be 1 m away. Because the earth is curved though, longitude lines converge at the north pole. This means very gradually we would find each other getting closer and closer together, even though we’re both following our line north. Now if we didn’t *know* the earth was curved, we would have to conclude that there’s some attractive force between us that’s pulling us together.
This is how spacetime is. Everything (even a beam of light) is following it’s own “straight line” (geodesic) but the curve of those lines is what produces gravity, makes light rays bend, etc.
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