PHOTONS from a distant galaxy have shed light on theories of quantum
gravity.
According to these theories, space-time is a seething mess on tiny scales
(Â鶹´«Ã½, 19 June, p 28). This “foam” should slow down
high-energy photons slightly more than low-energy ones. Using the Whipple
telescope in Arizona, however, Steve Biller of Oxford University and his
colleagues found that high- and low-energy gamma rays from flares in the distant
galaxy Markarian-421 arrived on Earth at about the same time (Physical
Review Letters, vol 83, p 2108).
The observations rule out theories that predict the biggest space-time
fluctuations. A proposed replacement for Whipple, called VERITAS, could test
ideas about quantum gravity even more sternly.
