July 18, 2017 (Phys.org) -- Mathematicians at the Universities of York, Munich and Cardiff have identified a unique property of quantum mechanical particles -- they can move in the opposite way to the direction in which they are being pushed.
In everyday life, objects travel in the same direction as their momentum -- a car in forward motion is going forwards, and certainly not backwards.
However, this is no longer true on microscopic scales -- quantum particles can partially go into reverse and travel in the direction opposite to their momentum. This unique property is known as "backflow."
This is the first time this has been found in a particle where external forces are acting on it. Previously, scientists were only aware of this movement in "free" quantum particles, where no force is acting on them.