Why are second order partial differential equations able to model such a wide variety of physical phenomena? Why do we never need to go to third or fourth order ?It seems just about everything can be described with such equations, as if physical reality is just second order in nature. Is there a reason for this?
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6$\begingroup$ Possible duplicate of Why are differential equations for fields in physics of order two? and Why are there only derivatives to the first order in the Lagrangian?. $\endgroup$ – AccidentalFourierTransform Jan 15 '17 at 9:33
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1$\begingroup$ As one of the 9 answers on the first duplicate points out, the Dirac equation does not follow the pattern, being first order. $\endgroup$ – user140606 Jan 15 '17 at 12:13
