According to the Hong Kong University of Science and Technology research team led by Du Shengwang, they had proved that a single photon, or unit of light, “obeys the traffic law of the universe”.

“Einstein claimed that the speed of light was the traffic law of the universe or in simple language, nothing can travel faster than light,” the university said on its website.

“Professor Du’s study demonstrates that a single photon, the fundamental quanta of light, also obeys the traffic law of the universe just like classical EM (electromagnetic) waves,” it added. “The study, which showed that single photons also obey the speed limit c, confirms Einstein’s causality; that is, an effect cannot occur before its cause.”