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...With those words and images in mind, let me lament our prospective losses, if we adopt anthropic or statistical selection arguments too freely:
1. Loss of precision:
I don’t see any realistic prospect that anthropic or statistical selection arguments – applied to a single sampling! – will ever lead to anything comparable in intellectual depth and numerical precision to what these icons represent. In that sense, intrusion of selection arguments into foundational physics and cosmology really does, to me, represent a genuine lowering of expectations.
2. Loss of targets:
Because the standard models of fundamental physics and cosmology describe the world so well, a major part of what ideas going beyond those standard models could aspire to achieve, for improving our understanding of the world, would be to fix the values of their remaining free parameters. If we compromise on that aspiration, there will be much less about the physical world for fundamental theory to target.
IV. A CLASSIFICATION
Of course, physicists have had to adjust their expectations before. In the development of Copernican-Newtonian celestial mechanics attractive a priori ideas about the perfect shape of planetary orbits (Ptolemy) and their origin in pure geometry (Kepler) had to be sacrificed. In the development of quantum mechanics, ideas of strict determinism (Einstein) had to be sacrificed.
In those cases, sacrifice of appealing philosophical ideas was compensated by the emergence of powerful theories that described many specific features of the natural world and made surprising, impressive predictions. In America we have the saying “No pain, no gain.” There’s a big difference, however, between those episodes and the present one.
Resort to anthropic reasoning involves plenty of pain, as I’ve lamented, but so far the gain has been relatively meagre, to say the least. Even if we can’t be precise in our predictions of fundamental parameters, we can still aspire to clear thinking. Specifically, we can try to be clear concerning what it is we can or can’t be precise about. In this way we can limit our losses, or at least sharpen our discussion. In that spirit, I’d like to suggest a chart (Figures 4 and 5) that draws some helpful boundaries...
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