Astroparticle Physics

28714 Astrobiology“In the beginning the universe was created.This has made a lot of people very angryand been widely regarded as a bad move.”Douglas AdamsApart from considering the physical development of our universe,it is interesting to speculate about alternatives to ouruniverse, i.e., whether the evolution in a different universemight have led to different physical laws, other manifestationsof matter, or to other forms of life. Einstein had alreadypondered about such ideas and had raised the questionwhether the necessity of logical simplicity leaves anyfreedom for the construction of the universe at all.The numerous free parameters in the Standard Model ofelementary particles appear to have values such that stablenuclei and atoms, in particular, carbon, which is vital forthe development of life, could be produced. 1 Also the coincidenceof time scales for stellar evolution and evolution oflife on planets is strange. In the early universe, hydrogen andhelium were mainly created, whereas biology, as we knowit, requires all elements of the periodic table. These other elementsare provided in the course of stellar evolution and insupernova explosions. The long-lived, primordial, radioactiveelements ( 238 U, 232 Th, 40 K) that have half-lives on theorder of giga-years, appear to be particularly important forthe development of life. Furthermore, a sufficient amount ofiron must be created in supernovae explosions such that habitableplanets can develop a liquid iron core. This is essentialin the generation of magnetic fields which shield life on theplanets against lethal radiation from solar and stellar windsand cosmic radiation.1 α particles are formed in pp fusion processes. In αα collisions8 Be could be formed, but 8 Be is highly unstable and does notexist in nature. To reach 12 C, a triple collision of three α particleshas to happen to get on with the production of elements.This appears at first sight very unlikely. Due to a curious moodof nature, however, this reaction has a resonance-like large crosssection (see also Problem 2 in this chapter).free parametersearly universedevelopment of lifecosmic radiation