Krister Shalm, a physicist, gave a talk about the "double-slit experiment" - described by Richard Feynman as the "very heart of quantum mechanics".
The phenomenon may be understood as the following: When firing balls or marbles through a slit, the formation on the back wall is a line, two slits yield two lines. If, however, we were to push a wave through two slits the waves meet coming through the slits and form an interference pattern of many lines seen on the back wall.
On a quantum level, if we imagine light or photons to be particle like material and fire these through a double slit we see the interference pattern instead of the two lines we had been expecting. Thus, photons seem to behave like waves. It was thought photons were colliding and therefore affecting eachother but even when firing only one photon at-a-time the same interference pattern emerged. To fix the problem, a measuring device was placed close to the one slit to check which one it went through but this time the pattern changed forming two lines rather than the interference pattern.
Given this dual quantum event, the researchers asked: "Would it be possible to see what happens in-between these states?". The solution they came up with is known as "weak measurement". In brief, this meant making the measuring device that changes the pattern have a weaker role in the experiment - or take less measurement. Building on the work of Yakir Aharonov's group at Tel Aviv University, the Toronto University group experimentally reconstruct the full trajectory light takes using modern measuring equipment and showed that the average light photon undergo a change from behaving like a particle to behaving like a wave.