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This is a great mental model, but I'm getting hung up on a more minor point. The masses wouldn't be moving around on a static spacetime model because, as the te
by sp332 7y ago
This is a great mental model, but I'm getting hung up on a more minor point. The masses wouldn't be moving around on a static spacetime model because, as the text says, the masses are what bend the spacetime. So spacetime would be more curved close to each mass, which in turn means they would accelerate toward each other even harder as they got closer to each other.
- kazinator 7y agoCurved spacetime is not required to explain anything in classical mechanics. The presented concepts are poorly developed and do not account for forces other than gravity. Suppose A and B are oppositely charged and electrostatically attracted together with great vigor over a considerable distance. Next to A there is a C, which is not charged, and not attracted to B (other than mildly due to gravity). A begins to move toward B rapidly, whereas C hardly moves toward either of them. Are A and C situated in a differently curved spacetime, even though they start off right next to each other in both space and time? You didn't learn it this way in school because it's bunk. The equations of motion together with fields that are responsible for forces provide a coherent theory that actually solves problems.
- billiam 7y agoIt's....complicated. That's why The Three Body Problem is not just a great scifi book, but a real mechanics brain teaser. That doesn't take away from the strength of this illustration, which is explanatory in nature, not authoritative.
- rm445 7y agoThey do! Gravity is an r-squared law. (If you're confused about constant acceleration due to gravity, Galileo's experiment and all that, well different masses fall to earth with the same acceleration from the same height, but g decreases with distance from the Earth. It takes the familiar 9.81 m/s value as an agreed averaged value at the surface).
- sp332 7y agoI know they do in real life. It's the illustrations showing a static curve that the masses slide over that I'm taking issue with.
- rm445 7y agoOh yeah, I see what you mean. I think the models in the article are deliberately simplified. At least some of those plots demonstrate a constant force, rather than a gravitational-type force. And the well-known weights-on-a-rubber-sheet analogy is notoriously unhelpful. I guess the real equations work for real curved spacetime.
- _bxg1 7y agoI noticed that too. Presumably, modeling a dynamic curve over time would have dramatically complicated the diagrams and explanations without really adding much to the core concept. That's at least my assumption for why it was passed over.