Stellar nucleosynthesis is entropic because the proton-proton reaction radiates 0.7% of the original mass as 26.73 MeV energy. Additional reactions produce heavier elements until finally supernova nucleosynthesis produces everything up to uranium in the last few seconds of a star’s life.
We can calculate the entropy cost of the elements to create planets and life forms. Many stars had to die to create enough elements for life. Did life therefore evolve as soon as enough heavy elements were created to sustain sufficient organic chemistry for life? Or maybe life evolved earlier on other planets, but could not reach our level because the element mix lacks sufficient “entropic debt.” Will a more metal-rich universe be suitable for even more complex life, or is there a plateau of the right element mix to construct life?
It’s interesting to think about a brief “habitable era” when there is enough entropy for life, but not so much that there are no more main sequence stars to power life or perhaps other conditions (excess heavy metals, novas, or dwarfs) that inhibit life.
The amazing thing is that every atom in your body came from a star that exploded. And, the atoms in your left hand probably came from a different star than your right hand. It really is the most poetic thing I know about physics: You are all stardust. You couldn’t be here if stars hadn’t exploded, because the elements – the carbon, nitrogen, oxygen, iron, all the things that matter for evolution – weren’t created at the beginning of time. They were created in the nuclear furnaces of stars, and the only way they could get into your body is if those stars were kind enough to explode. So, forget Jesus. The stars died so that you could be here today.
- “A Universe From Nothing” by Lawrence Krauss, AAI 2009 (16:50-17:23)
