MNb wrote on 04/12/10 at 15:00:01:
That's a question physicists don't bother to answer. They are only interested in mathematical equations that correctly describe experimental results. A question like "does energy exist?" is too difficult.
The great Ernst Mach thought very seriously about these issues, and I find his ideas very attractive. When I was young I read
The Analysis of Sensations with great interest.
Following Mach, you reach the conclusion that the "existence" of an atomic particle, even the if "seen" in a cloud chamber, is not quite the same as that of a table or a chair. If I understand him correctly, the atomic theory is a complicated circumlocution, whereby assertions that seem to be about particles are in fact assertions, though quite complicated ones, about mundane experience. We believe that tables exist because we can knock on them and say, "See? This is a table." We can't do that with an electron, so the quality of an electron's existence is obviously different.
Some students of physics that I knew at the time found this line of reasoning preposterous. They would say things like, "You do not directly experience the table, either, but reflected light etc.." They were missing the point that what we experience
directly of the table, not the collegination of atoms and electrical fields and so forth, of which they suppose the table to consist, is the data. The rest is but theory.
I noticed that on wikipedia it is asserted that Mach denied the atomic theory. If he did, he didn't make that plain in
The Analysis of Sensations as I recall it. It was only that he drew an epistomological distinction about it.