Concluding remarks

The case of the cosmological constant demonstrates that anthropic models can be subjected to observational tests and can be confirmed or ruled out at a specified confidence level. It also illustrates the limitations and difficulties of anthropic predictions.

The situation we are accustomed to in physics is that the agreement between theory and observations steadily improves, as the theoretical calculations are refined and the accuracy of measurements increases. This does not apply in anthropic models. Here, predictions are in the form of probability distributions, having an intrinsic variance which cannot be further reduced.

However, there is ample possibility for anthropic models to be falsified. This could have happened in the case of the cosmological constant if the observed value turned out to be much smaller than it actually is. And this may still happen in the future, with improved understanding of the prior and anthropic factors in the distribution given by Eq. (10.7). Also, there is always a possibility that a compelling non-anthropic explanation for the observed value of pv will be discovered. As of today, no such explanation has been found, and the anthropic model for pv can certainly be regarded a success. This may be the first evidence that we have for the existence of a vast multiverse beyond our horizon.

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