Physicists have built a ring in which pulses of light whip circles around each other and the normal rules that govern light’s behavior no longer apply.
By Rafi Letzter | SPACE.com
Under normal circumstances, light displays certain kids of physical symmetry. First, if you were to play a tape of light’s behavior forward and then backward, you would see it behave in the same way moving in both directions in time. This is called time-reversal symmetry. And second, light, which can move through the world as a wave, has what is called polarization: how it oscillates relative to the motion of the wave. That polarization usually stays the same, providing another type of symmetry.
But inside this ring-shaped device, light both loses its time-reversal symmetry and changes its polarization. Inside the ring, light waves turn circles and resonate with one another, producing effects that don’t normally exist in the outside world. [The 10 Most Outrageous Military Experiments]