Why the Universe is Just So

Abstract

Some properties of the world are fixed by physics derived from mathematical symmetries, while others are selected from an ensemble of possibilities. Several successes and failures of ``anthropic'' reasoning in this context are reviewed in the light of recent developments in astrobiology, cosmology and unification physics. Specific issues raised include our spacetime location (including the reason for the present age of the universe), the timescale of biological evolution, the tuning of global cosmological parameters, and the origin of the Large Numbers of astrophysics and the parameters of the Standard Model. Out of the twenty parameters of the Standard Model, the basic behavior and structures of the world (nucleons, nuclei, atoms, molecules, planets, stars, galaxies) depend mainly on five of them: $m_e,m_u,m_d,\alpha ,$ and ${\alpha }_G$ (where $m_{proton}$ and ${\alpha }_{QCD}$ are taken as defined quantities). Three of these appear to be independent in the context of Grand Unified Theories (that is, not fixed by any known symmetry) and at the same time have values within a very narrow window which provides for stable nucleons and nuclei and abundant carbon. The conjecture is made that the two light quark masses and one coupling constant are ultimately determined even in the ``Final Theory'' by a choice from a large or continuous ensemble, and the prediction is offered that the correct unification scheme will not allow calculation of $(m_d-m_u)/m_{proton}$ from first principles alone.

23 pages, RevTex, one figure, revised version submitted to Reviews of Modern Physics Colloquia

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• A Large Mass Hierarchy from a Small Extra Dimension
• A Flat Universe from High-Resolution Maps of the Cosmic Microwave Background Radiation
• A Measurement of the Angular Power Spectrum of the CMB from l = 100 to 400
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Cited by in corpus (110)

• Dynamics of dark energy
• Extended Theories of Gravity
• The Cosmological Constant
• Search for New Physics with Atoms and Molecules
• The fundamental constants and their variation: observational status and theoretical motivations
• Supersymmetric Unification Without Low Energy Supersymmetry And Signatures for Fine-Tuning at the LHC
• Varying constants, Gravitation and Cosmology
• Aspects of Split Supersymmetry
• The Mathematical Universe
• Dimensionless constants, cosmology and other dark matters
• Measuring and Understanding the Universe
• Implications of Gauge Unification for Time Variation of the Fine Structure Constant
• Inflationary paradigm after Planck 2013
• Quark mass dependence of the rho and sigma from dispersion relations and Chiral Perturbation Theory
• Axions as Quintessence in String Theory
• A Finely-Predicted Higgs Boson Mass from A Finely-Tuned Weak Scale
• Quantum order from string-net condensations and origin of light and massless fermions
• Splitting Supersymmetry in String Theory
• Strange and non-strange quark mass dependence of elastic light resonances from SU(3) Unitarized Chiral Perturbation Theory to one loop
• Life at the Interface of Particle Physics and String Theory
• Perspective: Tipping the scales - search for drifting constants from molecular spectra
• Varying the light quark mass: impact on the nuclear force and Big Bang nucleosynthesis
• Physical Theories, Eternal Inflation, and Quantum Universe
• Evidence for the Multiverse in the Standard Model and Beyond
• Stars In Other Universes: Stellar structure with different fundamental constants
• Dark Energy in Practice
• What can the observation of nonzero curvature tell us?
• The Cold Big-Bang Cosmology as a Counter-example to Several Anthropic Arguments
• A 119-125 GeV Higgs from a string derived slice of the CMSSM
• The Degree of Fine-Tuning in our Universe -- and Others
• Anthropic Reasons for Non-Zero Flatness and Lambda
• Cosmological Constraints on a Dynamical Electron Mass
• The Intermediate Scale MSSM, the Higgs Mass and F-theory Unification
• Gedanken Worlds without Higgs: QCD-Induced Electroweak Symmetry Breaking
• Neutrino 2004: Concluding Talk
• Anthropic predictions for neutrino masses
• Quark and lepton masses and mixing in the landscape
• Likely values of the Higgs vev
• Anthropic tuning of the weak scale and of m_u/m_d in two-Higgs-doublet models
• Nuclear Astrophysics of Worlds in the String Landscape
• Dynamics of M-theory vacua
• The Beginning of the End of the Anthropic Principle
• Producing the Deuteron in Stars: Anthropic Limits on Fundamental Constants
• The Multiverse and Particle Physics
• Tracing the cosmic history by Gauss-Bonnet gravity
• Spatial gradients in the cosmological constant
• Planets in Other Universes: Habitability constraints on density fluctuations and galactic structure
• Editorial note to "Large number coincidences and the anthropic principle in cosmology"
• $\theta$-dependence of light nuclei and nucleosynthesis
• Drake Equation for the Multiverse: From the String Landscape to Complex Life
• Constraints on Alternate Universes: Stars and habitable planets with different fundamental constants
• A Solution to the electroweak horizon problem in the R_h=ct universe
• The Standard Cosmological Model
• Vacuum Energy Density Measured from Cosmological Data
• Spontaneous Symmetry Breaking as a Basis of Particle Mass
• Galaxy Formation Efficiency and the Multiverse Explanation of the Cosmological Constant with EAGLE Simulations
• Towards a Coherent Theory of Physics and Mathematics: The Theory-Experiment Connection
• Fundamental constants and tests of general relativity - Theoretical and cosmological considerations
• On the Habitability of Universes without Stable Deuterium
• Computational and Biological Analogies for Understanding Fine-Tuned Parameters in Physics
• Galactic Habitability Re-Examined: Indications of Bimodality
• Alpha-alpha scattering in the Multiverse
• The fine-tuning problems of particle physics and anthropic mechanisms
• Sensitivity of Carbon and Oxygen Yields to the Triple-Alpha Resonance in Massive Stars
• Properties of Gravitationally Bound Dark Compact Ultra Dense Objects
• Viscosity and diffusion in life processes and tuning of fundamental constants
• Properties of condensed matter from fundamental physical constants
• Binding the Diproton in Stars: Anthropic Limits on the Strength of Gravity
• Why the laws of physics are just so
• Issues in the Philosophy of Cosmology
• Stellar Helium Burning in Other Universes: A solution to the triple alpha fine-tuning problem
• On making predictions in a multiverse: conundrums, dangers, and coincidences
• Exotic Rotational Correlations in Quantum Geometry
• Constraints on fundamental physical constants from bio-friendly viscosity and diffusion
• Large Mixing Angles From Many Right-Handed Neutrinos
• Retrofitted Natural Supersymmetry from a U(1)
• Let's talk about varying G
• Universes without the Weak Force: Astrophysical Processes with Stable Neutrons
• Higgs Bosons, Electroweak Symmetry Breaking, and the Physics of the Large Hadron Collider
• Multiversality
• The Fine Structure Constant and Habitable Planets
• Constraints on Vacuum Energy from Structure Formation and Nucleosynthesis
• Nuclear Processes in Other Universes: Varying the Strength of the Weak Force
• A New Approach to Flavor Symmetry and an Extended Naturalness Principle
• Anthropics of Aluminum-26 Decay and Biological Homochirality
• High-scale SUSY from an R-invariant New Inflation in the Landscape
• Life, the Universe, and almost Everything: Signs of Cosmic Design?
• Cosmological Constant in Coherent Quantum Gravity
• Dark Energy density in models with Split Supersymmetry and degenerate vacua
• Multiverse Scenarios in Cosmology: Classification, Cause, Challenge, Controversy, and Criticism
• Probing nuclear observables via primordial nucleosynthesis
• Effects of Bound Diprotons and Enhanced Nuclear Reaction Rates on Stellar Evolution
• The Electroweak Horizon Problem
• Dark Energy Density in SUGRA models and degenerate vacua
• Improved Constraints on the Variation of the Weak Scale from Big Bang Nucleosynthesis
• Congeniality Bounds on Quark Masses from Nucleosynthesis
• Quantum field theory and classical optics: determining the fine structure constant
• Extrinsic and intrinsic effects setting viscosity in complex fluids and life processes: the role of fundamental physical constants
• Lectures on Naturalness, String Landscape and Multiverse
• The Fine-Tuning Argument
• Fundamental physical constants, operation of physical phenomena and entropy increase
• Possible Solution to the Triple Alpha Fine-Tuning Problem: Spallation Reactions during Planet Formation
• Anthropic Origin of the Neutrino Mass from Cooling Failure
• Quantum Mechanics, Gravity, and the Multiverse
• Quasiparticle Cosmology
• Naturalness as a reasonable scientific principle in fundamental physics
• Quark Masses: An Environmental Impact Statement
• The Eventual Quintessential Big Collapse of the Closed Universe with the Present Accelerative Phase
• On a Relation of Vacuum Energy to the Hierarchy of Forces
• The Emperor's Last Clothes?