The Heisenberg Uncertainty Principle
is one of the most well-known and dearly held tenets of modern quantum physics. It's one of those things about science you totally know, even if you don't know you know it. The principle states that on a quantum level, you can't directly measure anything without changing something about it.
Thus, it is impossible to measure a particle's position without affecting its velocity, and vice versa. Still confused? Us to, but luckily this Futurama clip explains the matter brilliantly in the first 30 seconds or so. Go ahead, we'll wait. Back? Great. Now that you understand the uncertainty principle, it's time for the news about it. Thanks to new measurement techniques, physicists are no longer certain that the theory holds up.