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You might be tempted to leave out concise (because completeness is a tempting thing to have!), but then, as Godel proved, you literally need an infinite number of axioms. If you leave out consistent, you can prove that 0 = 1, so that's not very useful. Godel's incompleteness theorem in a nutshell: I don't understand Gödel's Incompleteness Theorem so I've stopped at that. Anyho, I made-up the above dialogue between a layman and a physicist to keep my wife from dozing-off while I waxed on and on about cats and strings. Often, the beauty has proved to be a reliable guide to Reality. String Theory is beautiful (so I hear, unfortunately, the math is beyond me). To me, 'by definition' is equivalent to a big acknowledgment - atleast among peers - that is not based on a proven fact. Consider the question: Are the Strings in String Theory fundamental? By definition Strings are fundamental.
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In many ways, it surely is (and personally for me, to acknowledge this is to make peace with myself). So, I re-read Physicist Edward Witten's beautiful article on String Theory yesterday night and kept thinking about what Wittgenstein said: Knowledge is in the end based on acknowledgment. Gödel's Incompleteness Theorem has seen to that. Physicist: He said it before, not anymore. I think he said we would know Everything. I don't think he meant to say we know a lot. Hawking says a Theory of Everything is just around the corner. Layman: I suppose this is your personal view. A Theory of Everything is a grand way of saying we know a lot. We can never be sure if a theory explains everything in the Universe because we don't and can't possibly know all that the Universe is made of. Physicist: Well, a Theory of Everything is a linguistic construct, not a physical one. Everything is provisional? There will never be a Theory of Everything? Layman: Nothing is really fundamental then.
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Scientific progress is this continuous illumination of newer vistas, the lighting of hidden parts of an inexhaustibly large picture. The earlier theories are still true but they are now a small part of a bigger picture. New models of reality that change our conception fundamentally are found and we begin again. Sometimes, we have breakthroughs: times such as when Newton published his Principia, when Einstein published his Theory of Gravitation or when Quantum Mechanical Laws were published. Physicist: You see, physics usually advances gradually, building upon our earlier understanding. Layman: Like how sometime back protons were fundamental, and then how quarks were fundamental? Physicist: Well, they are not made of anything. Layman: What are the strings in String Theory made of?
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