Counterfactual ice cream
Remember the ice cream that you prevented from melting by putting it back in the freezer? Suppose you hadn’t put it back in the freezer. What then?
Let E be the event of your putting the ice cream back in the freezer. To answer the question, we must remove E from reality. This change logically requires removing the conditions that necessitated E. The conditions that necessitated E reside on the surfaces of spheres, centered on E, that get huge as we go back in time. Six hours before E, the sphere of conditions that necessitated E encompassed our solar system beyond the orbit of Pluto. Eighty thousand years before E, the sphere of necessitating conditions enclosed our whole galaxy. (Section 5.1 of my book explains why.) Remove E, and gigantic volumes of space must be different from what they actually were.
How different? Recall that deterministic, nonlinear systems amplify even the smallest change and that the laws of motion are time-symmetric. Remove E from reality, evolve that change backward using the laws of motion, and the change gets amplified exponentially. The result is an exponentially different past on the scale of at least whole galaxies.
How likely is it that this different past gives rise to a human artifact such as your ice cream? Statistical mechanics tell us. It’s as likely as any antithermodynamic event, such as scooping the same cup of water (to the last molecule) out of the ocean that you threw in there yesterday. Such things never happen. That’s why I say that the ice cream wouldn’t have melted if you hadn’t put it back in the freezer.
