If you’ve always dreamed of using your neighborhood mad scientist’s DeLorean to go back in time, meet your nerdy dad, and make sure he falls in love with Lea Thompson…you’re out of luck. Physicists at the Hong Kong University of Science and Technology have proved that nothing can travel faster than the speed of light — not even using black-market Libyan plutonium and a flux capacitor — and therefore time travel is impossible.

“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 [Shengwang]’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.”

Du measured the speed of a single photon — which had never been done before — and proved Einstein’s theory that protons have to adhere to a universal speed limit. Therefore, the university said, “an effect cannot occur before its cause.”

This matches up with another, less technical proof: If time travel were possible, wouldn’t someone from the future have showed up to tell us about it?