Shengwang Du is a professor in the Elmore Family School of Electrical and Computer Engineering, and also the Department of Physics and Astronomy, at Purdue University.
He is noted for having led a team that performed an experiment[1] showing individual photons cannot travel faster than the speed of light (c) in a vacuum, thus apparently removing one approach to time travel.
[2][3] Du claims in a peer reviewed journal to have observed single photons' precursors, saying that they travel no faster than c in a vacuum.
According to Du, this implies that there is no possibility of light traveling faster than c (and, thus, violating causality).
[4] Some members of the media took this as an indication of proof that time travel to the past using superluminal speeds was impossible.