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Comment by paulddraper | Hacker News Reader

General relativity, which describes the effect of mass on space-time, is a very elegant theory with beautiful maths. The trampoline and ball have incidental similarity, but they're for illustration only.

There's nothing that makes the waterbed theory necessarily wrong, but you'd have to posit some new maths different and more complicated than we have with GR.

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Yeah, I understand that the trampoline analogy is inadequate but I believe that we don't consider empty regions of space to have any type of "opposite" curvature or to exhibit negative gravity. I believe curvature is thought to be [0, black hole], not [-black hole, black hole].

Happy to be corrected on that, IANAP.

The disparity between what GR predicts and what we observe has led to the cosmological constant / dark energy / dark matter. Of course, those aren't really things in themselves, they're just a measure of that disparity, a fudge factor.

I'm suggesting that the disparity could be explained by spacetime "responding" to regions of curvature by mass with an opposite curvature.

Unfortunately I'm not qualified to do anything with that idea. I just wanted to throw it out there. It's something that's been bothering me for a long time.

New ideas in physics cannot start with an analogy - they need to work mathematically with all observed data first.

Didn't plenty of new ideas start with analogies? I can think of Feynman and Einstein who described imagining or noticing things in real life which gave rise new ideas in physics.

Probably just a semantic difference in what they mean by "start." In this instance, the waterbed analogy would suggest some sort of negative mass-energy and a mass-energy conservation law.

They started by observations (e.g. light is constant speed), and using those in thought experiments (e.g. light on a train going 0.5c).

They didn't start by noticing everyday phenomenon and extrapolating those observations.

Similar, but different.

...unless you're talking about string theory. That's a close comparison to the waterbed theory.

You would have to explain to some extent what the analogy is, and what it means for the real world, before we could begin to discuss whether it is in any way correct, let alone useful.

Just to be clear- are you implying that people cannot be inspired by natural events and think of an analogy elsewhere in physics? Or are you saying that an analogy cannot be the firmament of a new theory?

I would agree with the latter, but it sounds like you're stating the former, which is categorically incorrect

Is it a new idea? It sounds pretty similar to dark energy.

(0 to black hole) makes more sense because in this analogy it represents somthing like a length of a vector (which details are lost in the process of constructing analogy). So -42 doesn't make much sense because it's exactly the same as 42 in opposite direction.

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