Monday, November 29, 2010
The ten most important questions for astrobiology: Number 3
Is this universe particularly suited for the phenomenon of life?
Because this is a bit ambiguous there are some necessary qualifications. First, implicit in the way I've phrased this question is the idea that 'this universe' is either one of many or that it represents an instance of a phenomenon that somehow reoccurs. Second, and this is really just an expansion of the question, it suggests that life requires a particular range of physical laws and/or 'contents' in a universe to happen. Third, this question hits the button to sound the anthropic principle klaxon, opening a Pandora's box of weak and strong arguments about the timing of life, its privileged position and even its necessity for the existence of the universe in the first place.
It can be quite a morass, so I'll try to stick to the easy bits. The second item above can also be rephrased as a question about what the minimum requirements are for life to show up at some point, and whether some physical laws are more or less important. If we stick with carbon-based life then there's a ready laundry list, not least of which is the need for carbon in the first place. Carbon comes from the triple-alpha process in stellar nucleosynthesis. Intriguingly this set of nuclear reactions hinges critically on resonances between nuclear energy levels, allowing beryllium and helium nuclei to gracefully flop into forming a new carbon-12 nuclei. Without that coincidence then carbon would be little abundant in the universe, rather than the 4th most abundant element in the universe - after hydrogen, helium and oxygen. This resonance hinges in turn on the value of the fine-structure constant, describing the universal strength of electromagnetic interaction. Change this constant by a few percent and among the consequences you can kiss carbon goodbye.
Even if you feel you can do without carbon - preferring some alternative life chemistry - then a different fine structure constant also messes up things like covalent bonds in molecules, at least compared to the way they are around us. Before even getting to details like this if the universe had a different overall composition, or differing gravitational constant, or differing CP violation, then it could be radically different from the outset - perhaps never making any structures beyond individual atoms. In brief, there are a lot of things that seem to have to fall into place for something like us to come along.
Because we feel (rightly) incredibly uncomfortable with any notion we might be special to the universe (the universe clearly being special to us) then things get sticky, and answering question 3 hits a wall....unless we get to the first qualification I give above: the universe is one of many, whether contemporaneous (multiverses) or one of an endless succession (cyclical). An infinite number of universes, or quantum realities, are like the infinite number of monkeys with typewriters - somewhere amongst them will be the ones that can produce life like us. Much like the realization that carbon production requires something special - and indeed how Fred Hoyle came up with the physics for it - it may be that a version of the anthropic principle is actually telling us that there must be multiple universes, or else things are even more bizarre.
Astrobiology can't answer 3 yet, at least not in any satisfactory way. But finding out more about life in the universe, carbon-based or otherwise, could just possibly nudge us in the right direction.