Anthropic principle

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The Anthropic Principle is a loosely structured set of ideas which attempts to explain why certain observable features of the universe are the way that they are, and in particular why the values of particular universal constants seem to have been 'calibrated' so as to maximise the possibility of intelligent life coming into existence (see also: Intelligent design).

Dr. Jonathan Sarfati wrote:

Strong evidence for a Designer comes from the fine-tuning of the universal constants and the solar system, e.g.
  • The electromagnetic coupling constant binds electrons to protons in atoms. If it was smaller, fewer electrons could be held. If it was larger, electrons would be held too tightly to bond with other atoms.
  • Ratio of electron to proton mass (1:1836). Again, if this was larger or smaller, molecules could not form.
  • Carbon and oxygen nuclei have finely tuned energy levels.
  • Electromagnetic and gravitational forces are finely tuned, so the right kind of star can be stable.
  • Our sun is the right colour. If it was redder or bluer, photosynthetic response would be weaker.
  • Our sun is also the right mass. If it was larger, its brightness would change too quickly and there would be too much high energy radiation. If it was smaller, the range of planetary distances able to support life would be too narrow; the right distance would be so close to the star that tidal forces would disrupt the planet’s rotational period. UV radiation would also be inadequate for photosynthesis.
  • The earth’s distance from the sun is crucial for a stable water cycle. Too far away, and most water would freeze; too close and most water would boil.
  • The earth’s gravity, axial tilt, rotation period, magnetic field, crust thickness, oxygen/nitrogen ratio, carbon dioxide, water vapour and ozone levels are just right.

Former atheist Sir Fred Hoyle states, ‘commonsense interpretation of the facts is that a super-intelligence has monkeyed with physics, as well as chemistry and biology, and that there are no blind forces in nature.’[1]

The nub of the argument is that these constants could, in principle, have had any value and are effectively random. The fact that we see them as having these values is simply because we are here to see them. If the constants were otherwise, we would not exist, and there would be no observer to observe the values, and no questioner to pose the question.

Although they were not the first to suggest the idea, three separate versions of the Anthropic Principle were proposed by Barrow & Tipler (1986); these versions come in Weak, Strong and Final forms.

The Weak Anthropic Principle

In this version of the principle, Barrow & Tipler [2] suggest that the values of physical and cosmological quantities may be random, but are not equally probable; The values that they can adopt are governed by two separate requirements:

  1. That in the Universe there are places where carbon-based life can evolve
  2. That the Universe is old enough for it to have already done so.

In essence this simply says that we are here, therefore there must have been some way to get us here. We should not be surprised to find that any universal constants we observe would be configured in such a way as to allow for our existence.

The Strong Anthropic Principle

In this version of the Principle, Barrow & Tipler suggest that regardless of whether or not we are here to observe the fact, the Universe must (by necessity) have those properties which allow life to develop within it at some stage in its history.

In other words, in this principle, it is no coincidence that we are here; the Universe is expressly configured so as to enable and encourage the prospects of our existence.

The Final Anthropic Principle

In the most extreme version of the principle, Barrow & Tipler suggest that intelligent life (or something akin to it) is a necessary feature of the universe, and once it is created it can never be become extinct.

This version of the principle seems almost to imply that the sole purpose of the Universe is to create & sustain intelligent life; not only are the values of constants arranged to do this, but there seems almost to be some unseen force driving the Universe towards its goal.

Theistic Implications

The anthropic principle is commonly interpreted as evidence of an intelligent designer. Physicist Robin Collins said, "The extraordinary fine-tuning of the laws and constants of nature, their beauty, their discoverability, their intelligibility - all of this combines to make the God hypothesis the most reasonable choice we have. All other theories come short." [3] However, this is only evidence for ID if the strong/final versions of the anthropic principle are accepted, since the weak version makes sense without needing an intelligent designer.

Criticisms of the Anthropic Principle

In his web-page on The Anthropic Principle, the transhumanist philosopher Nick Bostrom suggests that the the Anthropic principle is only one manifestation of a much larger theory concerning self-location and observation. Within this he argues that the stronger versions of anthropic principles are simply confused, and while the weaker versions might be sound, they are in fact too weak to be useful. He argues that the current formulations of the principles are not formulated in any way as to yield observational consequences.

See also


  1. The universe is finely tuned for life by Jonathan Sarfati
  2. John D. Barrow and Frank J. Tipler (1986). The Anthropic Cosmological Principle. Oxford Univ. Press, ISBN 0-19-282147-4.
  3. Lee Strobel, The Case for a Creator, Zondervan 2004