Number 161 (Story #1), January 24, 1994 by Phillip F. Schewe and Ben Stein GAMMA RAY BURSTS MAY BE EXHIBITING TIME DILATION owing to the expansion of the universe. The powerful gamma ray bursts studied over the past few years by the Gamma Ray Observatory (GRO) are sprinkled uniformly across the sky, suggesting that they come not from our galaxy but from beyond, perhaps in some cases from the distant edge of the universe. At the recent meeting of the American Astronomical Society in Virginia, Jay Norris of NASA Goddard announced that from among the more than 700 bursts seen so far dim bursts are typically twice as long as brighter bursts and, furthermore, that the dim bursts lie more toward the "red" end of the gamma-ray range. The cosmological explanation of this pattern would proceed as follows: the theory of relativity holds that a time interval measured in one frame of reference will be different for an observer in another frame of reference. The difference (or time dilation) will increase as the relative velocity of the two frames increases. Thus gamma sources near the edge of the universe would be receding from Earth at a greater velocity than closer sources, and consequently the length of a far-out burst would appear to be longer than for near-in bursts. Radiation from the cosmic microwave background (which is presumably even more redshifted) streams in on us unabated and therefore, unlike the gamma bursts, has no beginning, middle, or end. Norris admits that the cosmological hypothesis is still tentative because the relation between burst energy and duration is not yet calibrated.