EVEN a child knows you can’t weigh a ray of light. But that may not always have been the case. Physicists have finally come up with an explanation for one of their most counter-intuitive ideas – that for a tiny fraction of a second following the big bang, light itself had mass.
The idea was born a few years ago, when Tomislav Prokopec of Heidelberg University in Germany and Ola Törnkvist of Imperial College, London, tried to explain why galaxies throughout the Universe are surrounded by magnetic fields. They suggested that the fields might be remnants of photons with mass that…
