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Comment by thatcherc | Hacker News Reader

I'll go in to plug the Clockwork Rocket series (Orthogonal and its sequels) and Incandescence, all of which have much more to do with physics and spacetime than Permutation City and short story collections like Instantiation (which I also love).

I think Incandescence is my favorite book of the physics set, but the Orthogonal books and their corresponding web notes [1] are an absolute tour de force of deriving a whole universe of physics from a tiny modification to the rules we're familiar with. It was wild to read those as a physics undergrad and still very cool to think about today.

[1] -https://www.gregegan.net/ORTHOGONAL/00/PM.html

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If you liked Clockwork Rocket, you'll also like Dichronauts.

Whereas Clockwork is set in a +/+/+/+ universe, Dichronauts is +/+/-/-. Between that and the +/+/+/- of the ones set in our own, he's covered every possibility.

(+/+/+/+ and -/-/-/- being mathematically equivalent.)

Unless it is a complete spoiler, could you elaborate on what those universe designations mean?

IANAP, but those +/+/+/+ are the signs in the distance function of your universe. Specifically ++++ is an Euclidean spacetime where the distance of any point in spacetime is the sum of the squares of the distances in each dimension (including time). Our universe is not Euclidean but Minkowski spacetime where the opposite sign is used for the time-like dimension (which gives origin to special relativity).

Egan explores universes with two timelike dimensions (++--) and all spacelike dimensions (++++).

Besides what sibling said-

In a ++-- universe, you have two timelike dimensions but still just one time dimension. This is to say that one of the space dimensions is timelike, which means you get effects like "time" dilation from ordinary rotation.

Our own universe is +++-. Between Dichronauts and Clockwork Rocket, it's possible to get a good intuition for the underlying geometry that causes special relativity; something none of my physics textbooks even tried.

wouldn't there also be +/-/+/+ for negative space dimention?

Incandescence is my favorite because it makes me cry.

Instantiation does contain a short story (The Gateway) about a space anomaly which, IIRC, had some Didicosm-like properties, like lack of mirroring.

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