A Many-Colored Glass: Reflections on the Place of Life in the Universe (Page-Barbour Lectures) by Freeman J. Dyson

Author:Freeman J. Dyson [Dyson, Freeman J.]
Language: eng
Format: epub
Publisher: University of Virginia Press
Published: 2010-02-03T08:00:00+00:00

5

Can Life Go On Forever?

A CLASH OF OPINIONS

The question is whether life and intelligence can survive forever in an expanding universe that is constantly growing colder as time goes on. We cannot hope to answer this question with any certainty. We know very little about the nature of the universe and even less about the nature of life and intelligence. But we know enough to speculate about the problem, and that is what I will do in this chapter. I don’t pretend to be able to predict the future. All I can do is explore the future, to see whether the survival of life is consistent with the laws of physics and the laws of information theory. If we find that the laws of physics and information theory make survival impossible, then we have answered the question in the negative. If we find that the laws do not forbid survival, we still do not know the answer. Survival might be impossible because of accidents of history or geography. We cannot in any case prove that life can survive. The best we can do is show that survival is not forbidden by the laws of nature as we know them today.

There are many uncertainties in our knowledge of the laws of nature. One of the most serious uncertainties is the question of proton decay. The proton is the nucleus of a hydrogen atom, and it is an essential component in the nuclei of all atoms. We have no evidence that the proton is unstable. All that we know for sure is that it lives for a very long time. Various so-called grand unified theories of elementary particles predict that protons should decay into lighter particles, mainly positrons and neutrinos, with a lifetime on the order of 1033 years. For readers who are not familiar with high powers of ten, I should explain that 1033 means a trillion times a trillion times a billion. It is, in short, an inordinately long time, but not too long to be measurable if protons are actually unstable. If the lifetime of a proton were 1033 years, it would mean that in a tank containing ten thousand tons of water three protons would decay each year on the average. With a great deal of care and a lot of heavy equipment, the decay of three protons per year would be detectable. Large underground detectors containing thousands of tons of water were built to observe the protons decaying, and no decay events were seen. The detectors turned out to be wonderful observatories for exploring the universe, since they detect neutrinos coming from the sky, but they have never detected a decaying proton. If the proton is unstable, the underground detectors tell us that its lifetime must be greater than 1033 years.

The majority of particle physicists still believe that protons are unstable. If this is true, all atoms are also unstable, and all matter will disintegrate into electrons and positrons within a finite time. The disappearance of ordinary matter will leave only an electron-positron plasma as a possible embodiment of life.

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