All energy is dinosaur energy

A thread running through the morning and afternoon UE1 sessions today is the question of how to temporally bound energy transfer processes.  In describing a series of energetic phenomena (as in the Wallace and Grommit video),  several teachers have wondered aloud about how far back in time one ought to go in order to satisfactorily describe the origin of the process that they are observing.  Wallace obtains energy from the cheese he eats, which in turn sets off a cascade of energetic transfer events that results in sound energy, light energy, and the energy that Grommit himself expends.  But the teachers are quick to ask where that cheese energy itself comes from.  The potential for an infinite regress emerges (turtles all the way down), until one teacher ends puts an end to the regress with the comment that "all energy traces back to the dinosours, from fossil fuels". 

In the afternoon, Sean's group is discussing where the energy to melt ice comes from, and there is a suggestion that the energy originates in the sun.  But this seems to be unsatisfying to Sean, who notes that "most of the energy we have ultimately comes from the sun. But there are other suns. Where did that energy come from? The big bang?"  In Roxanne's group discussing the water cycle, she asks: "If we think of it as a cycle, what is our starting point?  What's the bottom?"

This issue of how to temporally bound an energetic process story seems to me to be analogous to (although not exactly the same as) the issue of how to spatially bound an energetic process, i.e., how to define a system.  The question of how to use the concept of energy in a useful way is intricately tied to the definition of a system, since it is only by knowing where the system boundaries exist that one can talk about energy conservation or energy degradation (where is it conserved?  from where is it degrading?).  Likewise, defining a temporal system involves making an arbitrary decision about what will be relevant or significant for the purpose at hand.  If one does not make that decision, any energetic process is virtually unlimited in scope.  There is nothing absolute about either decision - the temporal bounding decision or the spatial bounding decision - and I suspect that discomfort in making either decision is only overcome with a lot of practice (and perhaps substantial exposure to physics).  Recognizing that the temporal and spatial assignments are arbitrary and chosen based on the particular problem being explored seems like a pretty important step toward developing a working facility with the energy toolbox.