I like your original comment further up, but disagree with the following bit: > We can still talk about the causal effect of lunch on what I wrote before lunch

I like your original comment further up, but disagree with the following bit: > We can still talk about the causal effect of lunch on what I wrote before lunch. To the extent that the situation occurs in the physical universe, that is meaningless. The future can never be a causal parent of the past. That says there is much more to the typical causality question than just the direction of time. The difference between the “time reversibility” in physics and the typical ML example is that once you’ve decided on something as the effect, the other thing must be the cause. So the problem is quite simple if you’re not trying to figure out the nature/direction of time, and especially not with microscopic physics. Anyone curious about the relation between time reversibility in physics and causal reasoning could look at Scholkopf+Janzing 2016 for an interesting line of thought. Somebody should tell Yann Lecun that a little knowledge is dangerous.