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Asked by 07gilpinm to Amy, Drew, Julia, Kimberley, Sara on 21 Jun 2011.
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Drew Rae answered on 20 Jun 2011:
Hi there. You ask some interesting questions. Entropy is a pretty well established principle. The laws of thermodynamics only hold in closed systems though. Earth isn’t a closed system, because the sun is providing energy from outside.
Whether all life formed from one cell is a different question. We know of lots of different pre-cellular life, and I think the current understanding is that cells might have come about several times independently. One of the other scientists should be able to say more than me about this.
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Amy MacQueen answered on 20 Jun 2011:
Hi – this is a really good question…which I am less than qualified to answer! Entropy does tend towards disorder which flies in the face of order formation at a concept level. Although as Drew says entropy only applies in a closed system. I would like to question Drew on the many different forms of pre-cellular life…what are you referring to here?
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Sara Imari Walker answered on 21 Jun 2011:
Hi 07gilpinm!! This is a really wonderful question! I grapple with these issues on a daily basis at work =) This is one of my favorites.
To clarify, there is nothing about the existence of life which violates the Second Law of Thermodynamics (i.e. that the entropy of a closed system must always increase). This is a common misconception! Life obeys the law just like everything else in the universe. But, just because the net entropy of a system is increasing doesn’t mean that locally it can’t decrease. Your refrigerator operates on this principle – it makes a locally cold state, increasing the order/decreasing the entropy, at the expense of doing a lot of work and making a lot of heat out the backside in the process. No one would claim that a refrigerator violates the 2nd Law. The point is that this is ok because the refrigerator may locally decrease entropy, but the entropy of the refrigerator + room + electrical wires + etc SYSTEM still increases entropy as a whole. Refrigerators are clearly not living, but the entropy of living systems operates in the same manner. Life locally decreases entropy to make all sorts of beautiful and highly ordered things like organelles, cells, and DNA. But, it does so at the expense of actually increasing the entropy of the whole system (i.e. organism + its environment). In fact, one may argue (and a lot of high level physicists do) that life actually increases entropy faster in a system than if it were absent! There’s a great book by Schrodinger called “what is life?” that is old, but still amazing if you want a really well written but technical treatise on the subject. He started the whole debate.
On the subject of whether or not life is common in the universe – well that’s another question! That is exactly what my field of research – known as astrobiology – aims to address. My research is in fact specifically focused on trying to figure out how life can get started. We have A LOT of clues, but we still haven’t pieced it all together quite yet. But we are working on it! Without a working theory for life’s origin (trust me its a pretty tough physics question!) its hard to say how likely life is to have arisen here more than once or anywhere else for that matter. There are a lot of bio and chem arguments out there for why life may or may not be common in the universe. However, since we’re on the topic of physics here’s something interesting to think about. If life actually locally decreases entropy so that the system as a whole can create even more of it – perhaps life is a very clever way of the universe figuring out how to increase its entropy! Does that mean life is common? Well maybe, but it certainly doesn’t make it any less special. Life is amazing. In my opinion it is the most amazing thing there is. =)
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