Decelerating Universe

As every astronomer knows, the latest news from the edge of the known universe is more than a billion years old. The current Yearbook of the Carnegie Institution reports that the most distant observable galaxies, whose light started toward the earth more than a billion years ago, are not receding quite as fast as was expected. This conclusion is preliminary, but if it stands up to all tests, it will set the cosmological thinkers into a fresh flurry of figuring.

One of the solidest rules in cosmology (a field where solid rules are not prevalent) is that the universe is expanding, and that far-distant galaxies are receding at speeds proportionate to their distance. Repeated observations indicate, for example, that galaxies 300 million light-years (1,800 million trillion miles) away from the earth are receding at about 10,000 miles per second. Many sweeping systems of cosmology have been based on this "linear" (directly proportionate) relationship between the distance of galaxies and their speed.

The shattering news came from Palomar Mountain, where more and more distant galaxies are being studied with the 200-in. Hale telescope. The most distant ones whose speeds can be measured convincingly are apparently receding at almost 40,000 miles per second, more than one-fifth of the speed of light (or were receding at that rate more than a billion years ago). But even this fantastic speed is not great enough to fit the "linear" speed-distance rule. The newly observed galaxies, judged by their brightness, are so far away that they ought to be moving considerably faster than they are.

In the guarded language of the report: "The . . . data . . . show an apparently significant departure from linearity in the direction which indicates deceleration." In simpler words, galaxies do not increase their speed at a constant rate as they get more distant. Far beyond the boundaries of present observation, they may slow down or even come to a stop.

People who have found the expanding universe hard to take philosophically will find little comfort in the latest news from Palomar. The universe is (or was) still expanding, but it is not (or was not) obeying the simple rules that cosmologists drew up to account for it.

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