Fine-tuned universe

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Table of contents

1 What is a "Fine-tuned universe" ?
2 Does "Fine-tuning" need an explanation ?
3 What are the possible explanations ?
4 How can we choose between the competing explanations ?
5 See also
6 Source

What is a "Fine-tuned universe" ?

Our universe seems to be fine-tuned (for intelligent life), because any small changes in the 20 or so physical constants would make it very different, and presumably not hospitable to intelligent life.

For example, stars would not be able to burn hydrogen and helium if the electric charge of the electron had been only slightly different. So our sun would not be able to give us the energy that we need.

Does "Fine-tuning" need an explanation ?

Some, like Stephen Jay Gould, believe that fine-tuning does not need any more explanation than a particular roll of dice that would result in a double six. Our universe had to have physical constants, and it just happened to be the ones that allowed our existence.

Moreover, any other combinations of physical constants may have resulted in a very different universe, one in which a human-like civilisation may not emerge, but who is to say that it would not be hospitable to other, very different, forms of intelligent life ?

However, the observation that no other forms of life have yet been observed in our universe allows us to think that indeed our universe is incredibly fine-tuned for intelligent life, and that it is a surprising fact that needs an explanation.

What are the possible explanations ?

There are actually 2 broad types of explanations: the Great Architect, and the Multiverse. While they are not incompatible with each other, accepting one of them makes the other one less necessary.

The Great Architect explanation assumes the existence of a being, principle or mechanism with the purpose to create a universe with intelligent life. It would thus somehow set the physical constants as we know them. This agent could of course be a God-like being, but it need not be.
The Multiverse explanation assumes the existence of a mechanism that has created many universes with different physical constants, some of which are hospitable to intelligent life. And because we are an intelligent being, we would happen to be in a hospitable one. This approach has led to a lot of research in the anthropic principle.

How can we choose between the competing explanations ?

The usual test for a satisfactory explanation is that it fits all known observations, and that it can make testable predictions. It remains to be seen whether the fine-tuned universe enigma can be resolved satisfactorily.

Source

Nick Bostrom (2002) "Anthropic Bias: Observation Selection Effects in Science and Philosophy", Routledge, New York