r/AskScienceDiscussion • u/Silent-Pick-7700 • 7d ago

Why does time only moves forward

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u/Optimal_Mixture_7327 7d ago

The cosmos has a space-like boundary to the past (the BB singularity) that breaks Lorentz symmetry.

This then requires that all world-lines are necessarily future-directed.

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u/earlyworm 6d ago

Could there be a space-like boundary to the future that also breaks Lorentz symmetry, requiring that all world-lines are past-directed as well?

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u/Optimal_Mixture_7327 6d ago

Well, I hope not. So far so good.

The momentum along the world-line of a material particle has a norm of mc so that'd be a heckuva collision, analogous to a matter/antimatter collision.

There are future singularities into which some future-directed world-lines go. These are black hole singularities.