The double-slit experiment is the best demonstration of quantum weirdness, in which electrons simultaneously act like particles and waves and seemingly violate basic laws of physics. Now we're trying the triple-slit experiment to see if we can circumvent the strangeness...
...and quantum mechanics absolutely crushed the scientists who were hoping they could find a loophole that could reconcile general relativity with quantum mechanics. The scientists weren't terribly optimistic something as simple as adding a third slit would overturn decades of work on quantum theory - as one observed, "If there was three-path interference, there would be a Nobel prize waiting" - but they also are quick to point out their experiment wasn't a complete waste of time:
"The fact that one does not observe deviations from quantum theory also has profound implications. It suggests that the present theory is a good description of our physical world and that we have to work harder to understand its fundamental message."
Check out Nature for a full explanation of their experiment and what it all means.