The fine structure constant and habitable planets

Sandora, McCullen

doi:10.1088/1475-7516/2016/08/048

Cited by 8 publications

(8 citation statements)

References 65 publications

(85 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This coincidence was investigated in detail in Reference [45], where it was found that, since the radioactive heat is generated by alpha decays, which are tunneling processes, their lifetime depends exponentially on the fine structure constant (and to a lesser degree on the other parameters). If α were increased to a value of 1{136, all possibly relevant alpha decays would occur with half lives of less than Gyr timescales, and so would have decayed by this point, leaving the Earth cool and stagnant.…”

Section: Does Life Need Plate Tectonics?mentioning

confidence: 99%

Multiverse Predictions for Habitability: Fraction of Planets that Develop Life

Sandora

2019

Universe

Self Cite

View full text Add to dashboard Cite

In a multiverse context, determining the probability of being in our particular universe depends on estimating its overall habitability compared to other universes with different values of the fundamental constants. One of the most important factors in determining this is the fraction of planets that actually develop life, and how this depends on planetary conditions. Many proposed possibilities for this are incompatible with the multiverse: if the emergence of life depends on the lifetime of its host star, the size of the habitable planet, or the amount of material processed, the chances of being in our universe would be very low. If the emergence of life depends on the entropy absorbed by the planet, however, our position in this universe is very natural. Several proposed models for the subsequent development of life, including the hard step model and several planetary oxygenation models, are also shown to be incompatible with the multiverse. If any of these are observed to play a large role in determining the distribution of life throughout our universe, the multiverse hypothesis will be ruled out to high significance.

show abstract

Section: Does Life Need Plate Tectonics?mentioning

confidence: 99%

Multiverse Predictions for Habitability: Fraction of Planets that Develop Life

Sandora

2019

Universe

Self Cite

View full text Add to dashboard Cite

show abstract

“…For tractability, we note that in [43], when this sum was performed in earnest, the resultant heat resembled a Gaussian which peaked at α " 1{144 at a value 2.7 times our observed heat. This allows us to use a simplified expression…”

Section: Glaciationsmentioning

confidence: 62%

“…Indeed, these two sources of heat are comparable [42]. Given this intriguing fact, along with the high sensitivity of this latter form of heat to the fine structure constant uncovered in [43], it is worth thoroughly investigating the interplay between these two quantities for generic values of the parameters.…”

Section: Glaciationsmentioning

confidence: 99%

Multiverse Predictions for Habitability: Fraction of Life That Develops Intelligence

Sandora

2019

Universe

Self Cite

View full text Add to dashboard Cite

Do mass extinctions affect the development of intelligence? If so, we may expect to be in a universe that is exceptionally placid. We consider the effects of impacts, supervolcanoes, global glaciations, and nearby gamma ray bursts, and how their rates depend on fundamental constants. It is interesting that despite the very disparate nature of these processes, each occurs on timescales of 100 Myr-Gyr. We argue that this is due to a selection effect that favors both tranquil locales within our universe, as well as tranquil universes. Taking gamma ray bursts to be the sole driver of mass extinctions is disfavored in multiverse scenarios, as the rate is much lower for different values of the fundamental constants. In contrast, geological causes of extinction are very compatible with the multiverse. Various frameworks for the effects of extinctions are investigated, and the intermediate disturbance hypothesis is found to be most compatible with the multiverse.

show abstract

“…At the more fundamental level, nuclei themselves must be stable (Section 2). In addition, if habitable planets require particular nuclear structures, such as iron being the most stable nucleus and/or particular types of radioactivity, then even tighter constraints on the fundamental parameters (e.g, α) can be derived [462,463].…”

Section: Planetsmentioning

confidence: 99%

The Degree of Fine-Tuning in our Universe -- and Others

Adams

2019

Preprint

View full text Add to dashboard Cite

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 (α, α s , α w ) and particle masses (m u , m d , m e ), and the allowed ranges of these parameters are discussed first. We then consider cosmological parameters, including the total energy density of the universe (Ω), the contribution from vacuum energy (ρ Λ ), the baryon-to-photon ratio (η), the dark matter contribution (δ), and the amplitude of primordial density fluctuations (Q). 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 (α G ), the fine structure constant (α), and composite parameters (C ) 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.

show abstract

The fine structure constant and habitable planets

Cited by 8 publications

References 65 publications

Multiverse Predictions for Habitability: Fraction of Planets that Develop Life

Multiverse Predictions for Habitability: Fraction of Planets that Develop Life

Multiverse Predictions for Habitability: Fraction of Life That Develops Intelligence

The Degree of Fine-Tuning in our Universe -- and Others

Contact Info

Product

Resources

About