Quantum physics is a brain-breakingly difficult discipline. Really, the only thing that quantum physicists have been able to rely on is uncertainty, namely the Heisenberg uncertainty principle.
For those who don’t spend their time reading about quantum physics, and really what’s wrong with you, the uncertainty principle can be summed up as the more we know about a particle’s position, the less we know about its velocity, and vice versa. There’s an actual equation involved, but that’s the summary.
This is where the idea that observing a particle changes it comes from. The thinking is that we can’t measure the particle, but we can measure the disturbance created by trying.
So what happens when you don’t measure the particle enough to disturb it?
Apparently, you violate Heisenberg’s uncertainty principle! The team measured the system in a “weak” manner before and after measuring it. They got a general idea of a photon’s orientation, and then measured it in a more disruptive way and found that they were getting about half of the disturbance they should be.
The basic idea of the uncertainty principle is still correct, so SF writers and pretentious indie filmmakers take heart: Your big idea/cheap attempt at philosophizing is safe. But the uncertainty principle is, perhaps unsurprisingly, a bit less certain than we thought.