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That'd be spacetime, from Einstein's general relativity. I suppose different names for the dimensions are warranted, since we can move freely forwards and backwards in the space dimensions, but the same does not apply for time. I can't go backwards with that, or stop. It's all part of one thing, thoigh. Or at least solving gravity made Einstein realize space and time are connected.
Special relativity came first, and it was actually to solve paradoxes relating to fast-moving magnets. Maxwell's equations produce a fixed speed of light, which breaks Galilean relativity, but they have Lorentz symmetry baked in. Just gluing them on to Newtonian mechanics can cause problems.
His solution was to work out a weird, different but observationally equivalent mechanics that would work. Decades later, it was realised matter is waves which internally move at the speed of light as well, so it's not that weird after all.
Weirdly, the math at the quanta level works in both directions (time-wise).
I guess something happens when you get a few atoms together that changes this.
Maybe AbouBenAdam has some insight.
Isn't that when people always start talking about entropy and how that gives us an arrow of time?
And I think whether math "works" within an incomplete model isn't really proof. I mean I can calculate a negative amount of people on the bus... But that alone doesn't make it possible/real.
Not with that attitude
It still can't be rigorously proven that thermodynamics works - if you look at the statistical mechanics papers on it they basically assume something is random that is not to do it. TBF, the empirical evidence is convincing, and the assumptions they do make are small, even infinitely small.
The second law probably relates to pseudorandomness and P=NP, in the end, but that's a big unsolved problem.