Though it sounds like something straight out of science fiction, controlling the speed of light has in fact been a long-standing challenge for physicists. In a study recently published in Communications Physics, researchers from Osaka University generated light bullets with highly controllable velocities.

According to Albert Einstein’s principle of relativity, the speed of light is constant and cannot be exceeded; however, it is possible to control the group velocity of optical pulses.

Currently, the spatiotemporal coupling of optical pulses provides an opportunity to control the group velocity of three-dimensional non-diffraction optical wave-packets, known as “light bullets,” in free space.