A new experiment conducted in Hong Kong has shown that time travel is even less likely than it was previously thought to be. Sorry, Back to the Future fans.
One theory of time travel goes something like this: if it were possible for something to travel faster than the speed to light, it might be able to arrive before it left. In other words, in order to go back in time, you would have to travel faster than the fastest known speed in the universe.
Some scientists in recent years have believed this might be possible. They have done experiments with photons (tiny wave-particles of light) where waves of light seemed to move ahead of the photons themselves. However, a group of scientists from the Hong Kong University of Science and Technology, led by Professor Shengwang Du, have found that this is just an optical illusion. Photons cannot move faster than the speed of light—300,000km per second.
All is not lost: there are still other possible explanations for why time travel might work. This new discovery makes it that much more improbable, though. Now, if only we could hop into the TARDIS and turn back time to before this experiment was conducted!