Put down those dreams of leaping forward in time to see how your children turn out and, of course, enjoy riding around on hoverboards: physicists say they’ve put the nail in time travel’s coffin.() A team of researchers from the Hong Kong University of [Science](http://www.tecca.com/topic/science/) and Technology claims to have measured the speed of a single photon and found that it, just like light in its electromagnetic wave form, obeys the universal “speed limit” postulated by Einstein in the early 20th century.
Led by scientist Du Shengwang, the group explored a still unanswered question about whether or not a single photon — the smallest unit of light — could ever travel faster than the physical constant *c*, representing the speed of light in a vacuum. Published in the U.S. journal *Physical Review Letters*, the study concluded that single photons cannot travel faster than *c*, effectively confirming Einstein’s views that “nothing can travel faster than light” and consequently, “an effect cannot occur before its cause.”
The good news is that we can all still hold out for the discovery of wormholes that might allow for rapid travel to distant parts of the universe, which is perhaps the next best thing to true time [travel](http://www.tecca.com/topic/travel/). The bad news is, now everyone will know *Back to the Future II* wasn’t a documentary.