title: Shengwang Du
text: # Shengwang Du
  
  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, saying that they travel no faster than c in a vacuum. His experiment involved slow light 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.
  
  