That's not true, here's an example where it's billiard balls: https://en.wikipedia.org/wiki/Novikov_self-consistency_principle https://en.wikipedia.org/wiki/No

That's not true, here's an example where it's billiard balls: https://en.wikipedia.org/wiki/Novikov_self-consistency_principle https://en.wikipedia.org/wiki/Novikov_self-consistency_princ...