New Scientist - Physics and Math - 2010 Apr 07
On time dilation in quasar light curvesWHY do distant galaxies seem to age at the same rate as those closer to us when big bang theory predicts that time should appear to slow down at greater distances from Earth? No one can yet answer this new question, but one controversial idea is that the galaxies' light is being bent by intervening black holes that formed shortly after the big bang.
Space has been expanding since the big bang, stretching light from distant objects to longer, redder wavelengths - a process called "red shift". The expansion means that distant events appear to occur more slowly than those nearby. For example, the interval between light pulses leaving a faraway object once per second should have lengthened by the time they reach Earth because space has expanded during their trip.
Supernovae show this "time dilation" in the speed at which they fade - far-off explosions seem to dim more slowly than those nearby. But when Mike Hawkins of the Royal Observatory in Edinburgh, UK, looked at light from quasars he found no time dilation
- Monthly Notices of the Royal Astronomical Society, M. R. S. Hawkins, DOI: 10.1111/j.1365-2966.2010.16581.x
In this paper we set out to measure time dilation in quasar light curves. In order to detect the effects of time dilation, sets of light curves from two monitoring programmes are used to construct Fourier power spectra covering time-scales from 50 d to 28 yr. Data from high- and low-redshift samples are compared to look for the changes expected from time dilation. The main result of the paper is that quasar light curves do not show the effects of time dilation. Several explanations are discussed, including the possibility that time dilation effects are exactly offset by an increase in time-scale of variation associated with black hole growth, or that the variations are caused by microlensing in which case time dilation would not be expected.