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Comment by loblollyboy | Hacker News Reader

I don’t have the details but I’m pretty sure passage of time is due to a tendency for entropy to increase, and that if I go back in time a second by, say, walking backwards, it is no more a violation of the cons of energy as if I walk forward.

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How do you know you aren't walking backwards back in time? To be complete you'll also need to be losing your new memories and becoming younger - it's experimentally undistinguishable.

I think the point about conservation of mass still applies. There are literally 2x yourself at a certain point in time, mass is not conserved.

Always conservation of mass is maintained by broadening the scope of the system under test. You can take matter out of a local system and make that local system less massive, but it’s not a violation of physics because the broader system maintains a steady state.

So isn’t the simple layman’s answer that the “system” also spans the 4th dimension and you are just displacing mass around in a 4D space instead of the typical 3D space?

I dont think conservation of mass works like this between "disparate" points in the 4th dimension. It has to be continuosly connected. Otherwise things could appear out of thin air without causality. Reminds me of this software: https://4dtoys.com/ (4d is time in this case not another spacial dimension but the intuition about discontinuity still applies)

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