> Why? We learn about the past by looking at the present all the time. We also learn about the future by looking at the present.

The original comment's was in a differnt spirit or at least how I interpreted it. It was more implying by looking at a very small slice of reality you should in theory be able to re-construct the whole universe because every particle and space quantum is being influenced (to tiniest degrees) by every other particle in the universe, which will not work if you dont know all the rules, no determinism and T_zero.

The rules are presumably also gleanable from looking at the small speck of dust.

I don't know why you want to know T_zero. I assume T means time here, not temperature or so?

If you have eg randomness as your non-determinism, you can still build probability distributions of the rest of the universe and the rest of time. (And honestly, even if you have determinism in the laws, you always have measurement errors. Even in classical mechanics.)