Fact and Fiction

Thoughts about a funny old world, and what is real, and what is not. Comments are welcome, but please keep them on topic.

Tuesday, January 17, 2006

The cosmic landscape: preface

This is my interpretation of the preface to Leonard Susskind's book The Cosmic Landscape: String Theory and the Illusion of Intelligent Design.

How is it that the universe appears to be so well designed for our existence? Here are two possibilities:

  1. The laws-of-nature are unique, so that a priori it is a lucky accident that the universe is hospitable for our existence.
  2. There is an ensemble of many possible laws-of-nature, within which one can find laws-of-nature that happen to be hospitable for our existence.

Historically, physicists have assumed that (1) is the case, even though it would appear to be a stroke of luck that this could lead to our existence. It is an open research question whether (1) is how the universe works, but it may eventually turn out that (1) is indeed true. However, in the meantime, recent results (i.e. an ensemble or landscape of alternative laws-of-nature) from research into string theory open up the possibility that (2) might be the case.

The fact that (2) is now being considered as a realistic possibility has annoyed many physicists who have assumed (1) all along. However, this book describes an interesting type of science (i.e. (2)) that needs to be understood more widely, so that more people can enter into informed discussion about it.

If (2) is true then the ultimate "theory of everything" will have far less predictive power than if (1) is true. There is a sliding scale of possibilities ranging all the way from (1) to (2), and we should not make strong prior judgements about where the universe lies on this scale.

The laws-of-nature appear to be fine-tuned in such a way that they are consistent with the fact of our own existence. This is called the "anthropic principle".

The direction in which one chooses to use the anthropic principle is very important:

  1. The laws-of-nature are fine-tuned a priori so that we can exist. This is the strong anthropic principle, which is also known as "intelligent design".
  2. The universe is such that there is an ensemble of many possible laws-of-nature, amongst which we find one that happens to be fine-tuned a posteriori by the fact of our existence. This is the weak anthropic principle.

Susskind's book uses the weak version of the anthropic principle, as (potentially) applied to the rich landscape of laws-of-nature that emerges from string theory. His aim is to show that there is no need for the strong version of the anthropic principle, so "intelligent design" in superfluous.

In fact Susskind makes his intentions clear with this quotation from Laplace at the front of the book:

Your Highness, I have no need of this hypothesis.

Laplace said this to Napolean in response to being asked why he didn't mention God in his book on the System of the World.


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