Quantum mechanics are cool, and these experiments boggle the mind. However, the specific interpretation of the future determining the past only comes out as surprising when you assume a non-deterministic universe in the first place. By opening and shutting the second slit "randomly", we assume that there is true randomness in the world. If we consider instead that randomness is just a determined process on which we lack information, what we actually observe here is two events always fitting each other: Light always behaves as a wave if it has to do so in order to suit the opening of the second slit. So I think there are at least two viable interpretations: The only thing this proves is that we are not in a non-deterministic universe with temporally unidirectional causation. We might be instead in a non-deterministic universe with the future determining the past, or simply in a fully deterministic universe, full stop.
This reminds me that history isn't really known or understood until those of us in the future describe it, using the results that followed the initial event. Perhaps science will next conduct a test to determine whether the quantum events can change again when some future scientist observes and describes the initial observation.
I'm not that good with pictures, but think of it as arrows: In their non-deterministic interpretation, there is an arrow from the future event (C: opening the second slit) to the earlier event (B: helium atoms behaving like waves). In my proposed alternative deterministic interpretation, there are two arrows starting from a third point, before B and C, namely A (a set of prior circumstances leading both to the helium atoms behaving like waves, and to the second slit opening). One arrow leads from A to B, the other from A to C. Only arrow AC is greyed out, and the scientists call this process "random".
I suppose there are other interpretations. For example, we regard the observable present as THE present, but what if it lags behind, only manifesting once the fuzz of quantum interactions sorts itself out, as if were living some small epsilon T after those interactions? Or perhaps time itself is organized into quanta that have kind of a foam.
Can't one say that in a sense then that all possible future events then do have an existence of their own? Kind of like multi worlds theory. Anything that is possible actually does exist.
I seem to remember reading this before, in regards to light which originates in the far reaches of the universe. This light "chose" to behave as a wave or a particle all of those light years ago, based on our measurements in the here and now. Pretty staggering. It feeds into relativity too. There's no "now" that is a privileged frame of reference.
Whether or not the future determines the past or not still doesn't answer why some people's future totally sucks.
