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The degree of fine-tuning in our universe — and others (paper)

Quote:Both the fundamental constants that describe the laws of physics and the cosmological parameters that determine the properties of our universe must fall within a range of values in order for the cosmos to develop astrophysical structures and ultimately support life. This paper reviews the current constraints on these quantities. The discussion starts with an assessment of the parameters that are allowed to vary. The standard model of particle physics contains both coupling constants and particle masses, and the allowed ranges of these parameters are discussed first. We then consider cosmological parameters, including the total energy density of the universe, the contribution from vacuum energy, the baryon-to-photon ratio, the dark matter contribution, and the amplitude of primordial density fluctuations. These quantities are constrained by the requirements that the universe lives for a sufficiently long time, emerges from the epoch of Big Bang Nucleosynthesis with an acceptable chemical composition, and can successfully produce large scale structures such as galaxies. On smaller scales, stars and planets must be able to form and function. The stars must be sufficiently long-lived, have high enough surface temperatures, and have smaller masses than their host galaxies. The planets must be massive enough to hold onto an atmosphere, yet small enough to remain non-degenerate, and contain enough particles to support a biosphere of sufficient complexity. These requirements place constraints on the gravitational structure constant, the fine structure constant, and composite parameters that specify nuclear reaction rates. We then consider specific instances of possible fine-tuning in stellar nucleosynthesis, including the triple alpha reaction that produces carbon, the case of unstable deuterium, and the possibility of stable diprotons. For all of the issues outlined above, viable universes exist over a range of parameter space, which is delineated herein. Finally, for universes with significantly different parameters, new types of astrophysical processes can generate energy and thereby support habitability.

Interesting paper I found and thought I'd share. It seems that contrary to some common philosophical claims that our universe is strongly fine-tuned for life, many fundamental parameters could be changed significantly and the universe could still be habitable, as best as we can tell. Some areas of parameter space are seemingly even more habitable than our own universe - such as "dark matter" interactions generating energy and allowing for habitable planets far away from stars, or changes in gravity allowing for bigger terrestrial planets with more surface area and thus more room for evolutionary innovation and complexity.

From an in-setting perspective, perhaps universes more amenable to computation or complexity are desired by the highest archai and what they seek to create; perhaps those who posit that the universe is a simulation suggest that the base reality is a universe even more compatible with running enormous simulations.

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