How You Can Change the Past - The Quantum World

A repost from New Scientist 4 January 2013

Does objective reality exist? Is there an underlying truth that doesn't depend on the observer?
According to quantum physics, there may be no consistent reality. Not only do we change the outcome of experiments by what we choose to measure, but we can alter those results after they've already happened.
In this animation, find out how our choices of what to observe can change what actually happens, and what that means for our understanding of reality. A classic experiment illustrates the conundrum by attempting to measure whether a photon behaves as a particle or a wave. It turns out that it can be either, or a mixture of both, depending on how the experiment is set up.