Shengwang Du is a professor in the department of physics at The University of Texas at Dallas. He is noted for having led a team that performed an experiment showing individual photons cannot travel faster than the speed of light (''c'') in a vacuum, thus apparently removing one approach to time travel. Du claims in a peer reviewed journal to have observed single photons'

precursors Precursor or Precursors may refer to: * Precursor (religion), a forerunner, predecessor ** The Precursor, John the Baptist Science and technology * Precursor (bird), a hypothesized genus of fossil birds that was composed of fossilized parts of un ...

, saying that they travel no faster than ''c'' in a vacuum. His experiment involved

slow light Slow light is the propagation of an optical pulse or other modulation of an optical carrier at a very low group velocity. Slow light occurs when a propagating pulse is substantially slowed by the interaction with the medium in which the propagatio ...

as well as passing light through a vacuum. He generated two single photons, passing one through rubidium atoms that had been cooled with a laser (thus slowing the light) and passing one through a vacuum. Both times, apparently, the precursors preceded the photons' main bodies, and the precursor traveled at ''c'' in a vacuum. According to Du, this implies that there is no possibility of light traveling faster than ''c'' (and, thus, violating causality). Some members of the media took this as an indication of proof that time travel to the past using superluminal speeds was impossible.

References

Living people Year of birth missing (living people) Hong Kong physicists Academic staff of the Hong Kong University of Science and Technology Fellows of the American Physical Society {{physicist-stub