What Is “Fundamental”I couldn't get too excited about this essay, because "fundamental" is a subjective and ill-defined term. Nevertheless, I did post about 5 times in the last years on this subject, primarily in response to philosophers posting ridiculous opinions about what is fundamental in physics.
October 28, 2017 to January 22, 2018
Interesting physical systems can be described in a variety of languages. A cell, for example, might be understood in terms for example of quantum or classical mechanics, of computation, or information processing, of biochemistry, of evolution and genetics, or of behavior and function. We often consider some of these descriptions “more fundamental” than other more “emergent” ones, and many physicists pride themselves on pursuing the most fundamental sets of rules. But what exactly does it mean?
Are “more fundamental” constituents physically smaller? Not always: if inflation is correct, quanta of the inflaton field are as large as the observable universe.
Are “less fundamental” things made out of “more fundamental” ones? Perhaps – but while a cell is indeed "made of" atoms, it is perhaps more so “made of" structural and genetic information that is part of a long historical and evolutionary process. Is that process more fundamental than the cell?
Does a “more fundamental” description uniquely specify a “less fundamental” one? Not in many cases: consider string theory, with its landscape of 10500 or more low-energy limits. And the same laws of statistical mechanics can apply to many types of statistically described constituents.
Is “more fundamental” more economical or elegant in terms of concepts or entities? Only sometimes: a computational description of a circuit may be much more elegant than a wavefunction one. And there are hints that even gravity, a paragon of elegance, may be revealed as a statistical description of something else.
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