I believe this phenomenon is also called "quantum post selection"? A team's devised a way to experimentally demonstrate it.
http://secondnexus.com/technology-a...-backward-and-the-future-can-affect-the-past/
(The linked-to site appears to be struggling under load (George Takei linked to them on FaceBook) so don't be surprised if you get 503 errors or the like.)
http://secondnexus.com/technology-a...-backward-and-the-future-can-affect-the-past/
What they found is weirder than anything seen to date: Every time the two grates were in place, the helium atom passed through, on many paths in many forms, just like a wave. But whenever the second grate was not present, the atom invariably passed through the first grate like a particle. The fascinating part was, the second grate’s very existence in the path was random. And what’s more, it hadn’t happened yet.
In other words, it was as if the helium particle “knew” whether there would be a second grate at the time it passed through the first. The possible future presence of that second grate appeared to be determining the past state of the atom as it passed through grate #1. Whether it continued as a particle or changed into a wave depended on something that might happen in the future.
But how could a future event–the insertion of the second grate–determine the past state of the helium atom? Time would have to run backward, or something would have to know in advance that the second grate was going to be in place.
(The linked-to site appears to be struggling under load (George Takei linked to them on FaceBook) so don't be surprised if you get 503 errors or the like.)