To me, it's an "acting out" of Schrodinger's cat. A cat is placed in a box, together with a radioactive atom. If the atom decays, and the Geiger counter detects an alpha particle, the hammer breaks a flask of acid, killing the cat. Before the observer opens the box, the cat's fate is tied to the wave function of the atom, which is itself in a superposition of decayed and undecayed states. Thus, said Schrodinger, the cat must itself be in a superposition of dead and alive states before the observer opens the box, "observes" the cat, and "collapses" its wave function. In other words, if the outcome of a circumstance is presently unknown and by observing the circumstance you will disrupt it, then it exists in all possible states simultaneously until it is observed.
The coin toss, I think, is not about baby vs. abortion. It's Brooklyn vs. Manhattan, as Levitt's character explicitly states. So until the coin lands, so to speak, both realities exist.