Sad news for those with a flux capacitor and some plutonium to spare. Hong Kong scientists now say that time travel is impossible.

Dashing the hopes of "Back to the Future" and "Bill and Ted" fans alike, a group of Hong Kong scientists claims that recent research proves that time travel is impossible.

A team at the Hong Kong University of Science and Technology, led by Professor Shengwang Du, has concluded that single photons cannot travel faster than the speed of light in a vacuum. Unfortunately for time travel buffs, photons apparently obey the laws of physics, regardless of whether you have a magic phone booth or can get that DeLorean up to 88 miles per hour.

"The results add to our understanding of how a single photon moves. They also confirm the upper bound on how fast information travels with light," Professor Du said in a statement. "By showing that single photons cannot travel faster than the speed of light, our results bring a closure to the debate on the true speed of information carried by a single photon. Our findings will also likely have potential applications by giving scientists a better picture on the transmission of quantum information."

According to Du, the scientific community got all excited about time travel several years ago with the discovery of "superluminal propagation of optical pulses," which basically said that a group of optical pulses could move faster than the speed of the light. Du, however, said this was only a visual effect and could not actually be used to transmit real information. People then focused on a single photon moving faster than the speed of light, but "because of lack of experimental evidence of single photon velocity, this is also an open debate among physicists," Du said.

As a result, Du's team measured the maximum speed of a single proton, which showed that it obeys the universe's speed limit and "confirms Einstein's causality; that is, an effect cannot occur before its cause," researchers said.

In their tests, researchers managed to separate the optical precursor, a wave-like structure at the front of an optical pulse, from the rest of the photon wave packet. To accomplish this, Du's team created a pair of photons and passed one of them through a group of laser-cooled rubidium atoms, which allowed them to observe optical precursors for the first time.

"The team found that, as the fastest part of a single photon, the precursor wave front always travels at the speed of light in vacuum," researchers said. "The main wave packet of the single photon travels no faster than the speed of light in vacuum in any dispersive medium, and can be delayed up to 500 nanoseconds in a slow light medium. Even in a superluminal medium where the group velocity (of an optical pulse peak) is faster than the speed of light in vacuum, the main part of the single photon has no possibility to travel faster than its precursor."

So, until someone came come up with something that travels faster than the speed of light, it looks like time travel will be confined to movies and TV.