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Shakespeare's_Fool comments on No Evolutions for Corporations or Nanodevices - Less Wrong

28 Post author: Eliezer_Yudkowsky 17 November 2007 02:24AM

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Comment author: Shakespeare's_Fool 17 November 2007 04:21:38AM 0 points [-]

Eliezer,

The theory of change in stars over time that I am familiar with says that early stars were nearly pure hydrogen. Heavier elements were formed in them as they burned and when they became nova. Subsequent stars created and were composed of increasing concentrations of increasingly heavy elements. Did this not change the life span of stars? Did I misunderstand your point?

Also, is there an equation that is claimed to describe the change in the entropy of the universe?

Can it be used to figure out if the increase in entropy caused by a star going nova would cause an increase in entropy in the universe as a whole? If one nova is insufficient, how many would have to go nova simultaneously to cause an increase? How long would the increase last?

John

Comment author: bigjeff5 05 January 2012 11:36:31PM 3 points [-]

The theory that you are familiar with is a little off. What stars can produce is solely a function of size, not generation. Already fused material from a previous star does not allow the new star to fuse more elements. Likewise, the longevity of stars is solely a function of size. It's a balance between the heat of fusion and the pressure of gravity. More matter in the star means more pressure, which means the rate of fusion increases and more elements can be fused, but the fuel is consumed significantly faster.

The smaller a star is the longer it burns, because there is less pressure being exerted by gravity to drive the fusion process. Big stars don't last long (the biggest only a few million years), but they produce the all of the naturally occurring elements - up to iron via normal fusion, and the heavier elements during supernova that occurs after iron fusion begins. Smaller stars like our sun will never get past the carbon stage and will never go supernova, and smaller stars still like brown dwarfs will never get past the hydrogen stage. These small stars last the longest because their rate of fusion is incredibly slow.