As reported in this Daily Mail article, physicists at the Australian National University may have successfully demonstrated retrocausality, whereby an effect precedes its cause. Their findings were published in the May 2015 issue of Nature Physics.
Thomas Young’s classic 1801 “Double-Slit experiment“, showed that light can behave as a particle or a wave. From the article:
When shone through one slit a single glow on the wall behind appears as if the photons are behaving as particles, when a second slit is introduced, this changes to an interference band as if the photons are behaving as waves.
This experiment instead used a helium atom and a laser grid to produce the same effect. The researchers found that when they added a second grid behind the first, it changed how the beam behaved as it passed through the first one.