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A big source of confusion is dimension as mathematical vector element vs spatial dimension. These are different concepts.

Still it is interesting that x, y, and z seem identical while t is intrinsically unidirectional. Why?

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Not a physicist -> My assumption is that this is because x,y,z are just constructs to model physical space. They don't exist and we could just as well describe space with cartisian coordinates or some other system where the dimensions would not be isometric. Meanwhile, as you point out, t as a vector is also itself a convenient model for something, not an actual dimension.

Hmm... if t is also then not a Cartesian dimension, it makes me wonder if the whole Cartesian model isn't a bad model of fundamental reality. Maybe it's just a mathematical shortcut.

It helps me think of it as the iteration number in simulations. The state of the world at every iteration i+1 is a function of the state at i. Therefore it's impossible for a phenomenon in the simulation to alter the previous states.

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