Talk:Isolated system
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I deleted the paragraph dealing with background microwave radiation. I think the statement that it permeates every object is mistaken. While the radiation may be ubiquitous, it's still just microwave radiation, and not at all difficult to shield against with any conductive barrier. It might be difficult to build an isolated system without an initial contribution of energy from this background radiation, but that is also not a requirement for an isolated system. As long as it's isolated now, it doesn't matter if some of the energy originally came from an outside source.
I also realize a metal barrier would eventually heat up to 2.7K from the background radiation and emit its own blackbody radiation. In that sense, one could argue that the background radiation has "permeated through the barrier" once equilibrium is achieved, but that time can be made arbitrarily long by using thicker or successive insulating layers. So I agree it's impossible to build a permanently isolated system, but that point has already been addressed in the previous paragraph. It seems pretty clear that like many concepts in science, the isolated system is just a model of an ideal limiting case, and the bulk of the article need not be spent on reasons why the limit can never trully be attained in real life.
