Astroparticle Physics

290 14 Astrobiologybeen the result of a selection effect on the plethora of uni-verses in a multiverse. It is also conceivable that there couldexist even a diversity of physical laws in other universes.Only in universes where the conditons allow life to develop,questions about the specialness of the parameters can beposed. As a consequence of this anthropic principle thereis nothing mysterious about our universe being special. Itmight just be that we are living in a most probable universewhich allows life to develop.Nevertheless, it is the hope of particle theorists and cosmologiststhat a Theory of Everything can be found suchthat all sensitive parameters are uniquely fixed to the valuesthat have been found experimentally. Such a theory mighteventually also require a deeper understanding of time. Tofind such a theory and also experimental verifications of it,is the ultimate goal of cosmoparticle physics.This is exactly what Einstein meant when he said: “WhatI am really interested in, is whether God could have madethe world in a different way; that is, whether the necessity oflogical simplicity leaves any freedom at all.”plethora of universesmultiverseanthropic principlecosmoparticle physics14.1 Problems1. Estimate the maximum stable size of a human in theEarth’s gravitational field. What would happen to thisresult if the acceleration due to gravity would double?Hint: Consider that the weight of a human is proportionalto the cube of a typical dimension, while itsstrength only varies as its cross section.2. What are the conditions to synthesize carbon in stars?Hint: The detailed, quantitative solution of this problemis difficult. To achieve carbon fusion one has to havethree alpha particles almost at the same time in the sameplace. Consequently high alpha-particle densities are required,and high temperatures to overcome the Coulombbarriers. Also the cross section must be large. Checkwith the web pageshttp://www.campusprogram.com/reference/en/wikipedia/t/tr/triple_alpha_process.html,http://en.wikipedia.org/wiki/Triple-alpha_process,and nucl-th/0010052 onhttp://xxx.lanl.gov/.