Life, University of Sydney, Australia, June 11, 2012. P24] the density of the universe at the Planck time must be tuned to 60 decimal places in order for the universe to be life-permitting. [Luke A. Barnes: The Fine-Tuning of the Universe for Intelligent Life, University of Sydney, Australia, June 11, 2012. P27] Can Inflation Explain Fine-tuning? Inflation, to set up a life-permitting universe, must do the following: 1. There must be an inflation field. To make the expansion of the universe accelerate, there must exist a form of energy (a field) capable of satisfying the so-called Slow Roll Approximation (SRA), which is equivalent to requiring that the potential energy of the field is much greater than its kinetic energy, giving the field negative pressure. 2- Inflation must start. There must come a time in the history of the universe when the energy density of the inflation field dominates the total energy density of the universe, dictating its dynamics. 3- Inflation must last. While the inflation field controls the dynamics of the expansion of the universe, we need it to obey the slow roll conditions for a sufficiently long period of time. The "amount of inflation" is usually quantied by Ne, the number of e-folds of the size of the universe. To solve the horizon and flatness problems, this number must be greater than ~ 60. 4- Inflation must end. The dynamics of the expansion of the universe will (if it expands forever) eventually be dominated by the energy component with the most negative equation of state w = pressure / energy density. Matter has w = 0, radiation w = 1/3, and typically during inflation, the inflation field has w = -1. Thus, once inflation takes over, there must be some special reason for it to stop; otherwise, the universe would maintain its exponential expansion and no complex structure would form. 5- Inflation must end in the right way. Inflation will have exponentially diluted the mass-energy density of the universe - it is this feature that allows inflation to solve the monopole problem. Once we are done inflating the universe, we must reheat the universe, i.e. refill it with
Life, University of Sydney, Australia, June 11, 2012. P24] the density of the universe at the Planck time must be tuned to 60 decimal places in order for the universe to be life-permitting. [Luke A. Barnes: The Fine-Tuning of the Universe for Intelligent Life, University of Sydney, Australia, June 11, 2012. P27] Can Inflation Explain Fine-tuning? Inflation, to set up a life-permitting universe, must do the following: 1. There must be an inflation field. To make the expansion of the universe accelerate, there must exist a form of energy (a field) capable of satisfying the so-called Slow Roll Approximation (SRA), which is equivalent to requiring that the potential energy of the field is much greater than its kinetic energy, giving the field negative pressure. 2- Inflation must start. There must come a time in the history of the universe when the energy density of the inflation field dominates the total energy density of the universe, dictating its dynamics. 3- Inflation must last. While the inflation field controls the dynamics of the expansion of the universe, we need it to obey the slow roll conditions for a sufficiently long period of time. The "amount of inflation" is usually quantied by Ne, the number of e-folds of the size of the universe. To solve the horizon and flatness problems, this number must be greater than ~ 60. 4- Inflation must end. The dynamics of the expansion of the universe will (if it expands forever) eventually be dominated by the energy component with the most negative equation of state w = pressure / energy density. Matter has w = 0, radiation w = 1/3, and typically during inflation, the inflation field has w = -1. Thus, once inflation takes over, there must be some special reason for it to stop; otherwise, the universe would maintain its exponential expansion and no complex structure would form. 5- Inflation must end in the right way. Inflation will have exponentially diluted the mass-energy density of the universe - it is this feature that allows inflation to solve the monopole problem. Once we are done inflating the universe, we must reheat the universe, i.e. refill it with
fine-tuning.docx