The Unknowable Universe

Cosmologists are becoming increasingly confident of their ability to fathom the secrets of the universe. Indeed there are scientists who believe that the cosmologists are too cocky. Last week in Nature, the University of London's William Hunter McCrea examined cosmology with a mathematician's skeptical eye. His conclusion: a built-in mystery to the universe will forever keep cosmologists from knowing what it is really like.

The root of the problem, says McCrea. is that light does not travel at infinite speed, and other influences such as gravitation are presumably just as slow. So when distant parts of the universe interact by attracting or irradiating each other, they do so only after a long delay.

In a classic paragraph, McCrea asks his readers to consider a remote part, P, of the universe. "We see no other part of the universe," he says, "in the state in which it influences P. For example, if P is one billion light-years away, and Q is a part of the universe one billion light-years away in the opposite direction, then, if the universe is static, whatever influence Q has on P when we observe P depends on the state of Q at a time two billion years before Q was in the state in which we observe Q. But the universe is not static, and so we know nothing from observation about the state of Q when Q influenced the state of P in which we observe P."

If the universe were of finite size, says McCrea, man might learn about it by continuing his observations for a long but finite time. But since the universe is al most certainly unbounded, even a very long period of observation, say ten billion years, would be insufficient. He thinks that cosmologists should include a factor of unavoidable uncertainty in their theories. "Thus we should be asserting almost nothing about what the universe is like at great distances in space or time. This provides a view of cosmology that essentially leaves room for endless observational surprises. It seems more satisfactory than the recent trend towards a belief that the nature of the 'whole' universe has already been discovered."

This file is automatically generated by a robot program, so reader's discretion is required.