The Anthropic Cosmological Principle and Related Issues

I originally wrote this in the 1990’s, before the discovery of the accelerating expansion of the universe. As noted below, that discovery has falsified some of the theories assciated with the anthropic principle.

The anthropic cosmological principle asserts that the laws, constants and basic structure of the universe are not completely arbitrary. Instead they are contrained by the requirement that they must allow for the existence of intelligent observers, ourselves.

Example: Why is the visible universe about 14 Billion light years in diameter? Because that means the universe is about 14 billion years old. Our sun is at least a second generation star because it contains Carbon, Oxygen, Silicon and other elements. It had to get them from earlier stars that had exploded–they were not available just after the big bang (which could only have produced Hydrogen and Helium). Hence the sun as we know it could not have existed much earlier in the history of the universe. Since we in turn require those elements, we could not have existed in a much earlier phase of the universe. You also have to allow a few billion years for evolution. We see a universe that is 15 billion light years across because the universe had to grow to that size to permit us to exist. We could not, incidentally, observe a universe that was a lot older, since by that time the stars will have burned out and there will be no available energy to support life. Many other examples are discussed in the following references.

There are lots of other facts in physics, astronomy, and chemistry, that can be interpreted in this manner. You can argue that this is all coincidence, and some of these observations have been referred to as “cosmic coincidences”. You can also argue that this is obvious–nothing else would be possible. The subject is very controversial.

One aspect of this is that the Principle asserts that there is something special about our place in the universe. The example above shows that we must live in a particular segment of cosmic history. This goes against the general trend of science since Copernicus; that there is nothing special about our place. This makes a lot of scientists uncomfortable, but I think it is hard to dispute.

It may be that all of this is unnecessary, and that the cosmic coincidences can be derived from a physical theory, such as superstrings. This is the view of “The Beginning of the End of the Anthropic Principle”. Thanks to Bernard Leong for bringing this paper to my attention.

Theologically, the anthropic principle has led to a revival of the argument from design, which had lost its intellectual respectability when Darwin came along. I think the mainstream theological community was taken by surprise when the physicists came up with this. John Polkinghorne has some good discussions of the theological issues. See, for example, The Faith of a Physicist (Polkinghorne was a prominent theoretical physicist before becoming an Anglican priest).

Fundamentalists with intellectual pretenses also like the anthropic principle, but they conveniently omit the relationship between the human evolutionary time scale (billions of years) and that of the universe (also billions).

The Future of the Universe and Life.

  1. Freeman Dyson began the modern analysis of the topic with his paper “Time without end: Physics and Biology in an Open Universe” , Reviews of Modern Physics 51, 447-460 (1979). This paper was based on series of lectures given at New York University in 1978. Dyson said that:

    I hope with these lectures to hasten the arrival of the day when eschatology, the study of the end of the universe, will be a respectable scientific discipline and not merely a branch of theology.

  2. Frank Tipler of Tulane University has proposed the Omega Point Theory. It appears in the final chapter of ACP in a largely mathematical form. The broader implications are mentioned, but not emphasized.

    Tipler has insisted that what he is proposing is a scientific theory, i.e. that it makes predictions that can be tested. This first of these is the the universe is closed: The Hubble expansion of the the universe that began with the Big Bang will eventually cease, and be replaced by a contraction ending in a final singularity. This is a necessary condition for Tipler’s Omega point. It now appears that this is not correct: See, for example The End of the Universe or (highly recommended) The End of Everything: (Astrophysically Speaking).

Since 1998 observations have indicated that the universe will expand forever and that Einstein’s cosmological constant is positive. Hence it can be argued that it will not be possible for life to survive indefinitely. See