Creating Energy as We Roll Downhill to Iron

If you put a bunch of random nuclei in a box and rattle very hard and for a very long time, eventually all the atoms would transmute into iron.  The lighter elements would undergo fusion to fall into lower and lower energy states while the heavier elements would undergo fission to fall into lower and lower energy state.  All the energy being created in the universe since the big bang is coming from this big squeeze.  The iron nucleus has the strongest bonds between its nucleons and is thus at the bottom of the energy hill that other nuclei can roll down by fusing and fissing.

Something has long bothered me about the classic binding energy/nucleon chart we all first see in chemistry class:

The problem is, simply, that this is upside down.  I have written before about the problems people have with bond energy and the problems that people have with negative numbers, but it didn't click with me at those times that this chart is a classic example.  The top of this curve represent the most binding energy, which means it take the most work to tear those nucleons apart, which means they are sitting at the bottom of a very deep well (negative potential energy).  When you look at this chart, it is not clear that everything lighter releases energy when undergoing fusion and everything above can releases energy via fission.

The curve should be presented more like this all the time:

(from The Essential Cosmic Perspective, Bennett et al.)

 

Why is the first chart more popular?  Because people want things to be taller when they are stronger, not deeper.  This is yet another example of the deep problems people have with negative numbers.  Read the first few paragraphs of this great New York Times blog entry for more examples.  Sorry folks, bigger bond energy means a bigger negative number and things just make more sense when you picture it that way.