The HKUST researchers reported
they directly observed a single photon's optical precursor, a visual effect that only appears superluminal, demonstrating that this fundamental quantum of light obeys the universal speed limit for information (and everything) that was formulated by Einstein.
Their study, which the team claimed is the first experimental demonstration that optical precursors exist for a single photon (showing no faster-than-light propagation occurs), was published in the American Physical Society's journal Physical Review Letters
, along with a synopsis
Du and his colleagues concluded they have ended the debate over whether it might be possible for single photons to exceed light-speed, by measuring the ultimate speed of a single photon in a vacuum, and determining that the true speed of the information it carries obeys Einstein's c
, the universal light-speed-limit.
Most physicists have agreed that instances of apparent faster-than-light motion
observed in groups of photons were an optical illusion, but some still speculated the situation might be different for a single photon.
If even a quantum
of information -- one photon -- were able to travel faster than light-speed, it would be possible for an effect to overtake, and pull ahead of, its cause. Such happenings, which Du and his team claimed they have proved impossible, would give a green light to time-travel theorists.
The university's written statement explained, "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."
The researchers may have cast serious doubts upon the feasibility of time-machine inventing, but they think their findings will help scientists studying quantum information transmission.
Will humans, who frequently break traffic laws, especially to exceed speed limits, now slam the breaks on further theorizing about time travel?
Digital Journal previously reported:
Physicist Stephan Hawking said
in May 2010 that moving forward -- not backward -- though time is theoretically possible.
Vanderbilt University physicist Tom Weiler theorized
in March 2011 that the Large Hadron Collider (LHC
) could generate time-traveling particles.