Outdated, still in use

We look for reasons to teach things that aren’t true.

Our tutor was approached recently by a sometime student of his who asked, “Is it really true that when you move fast you change shape?”  It was pretty clear that the student was being introduced to some of the strange effects of Special Relativity.  It seems like one hardly learns to grasp the ins and outs of Newtonian physics before learning that it’s actually not true.  The assumptions that one makes for the textbook problems on inclined planes and the orbits of planets don’t really hold, especially when you move at high speeds or in strong gravity, and Newtonian predictions can be wildly wrong in areas where Quantum Mechanics holds sway (which is pretty much all of Chemistry).  Well, if it’s wrong, why teach it at all?

One reason, and this is the one most scientists would produce, is that for almost all of science it’s not very wrong; and for much of it, any errors are undetectable.  You can securely board an airplane designed using Newtonian calculations, and even calculate the motions of most planets and galaxies without problems.

Another, very practical reason is that the mathematics required for quantum or relativistic calculations is more advanced and difficult than Newtonian differential equations.  Indeed, some figuring that appears in introductory Physics textbooks cannot be done at all in the higher theories, or must be delegated to a powerful computer.  So if you wanted to start your students with the “true” theories you would have to wait until several years later in their studies, when they have the mathematical background.  [Richard Feynman tried to include at least a bit of everything in an introductory course at Caltech in the 1960s, and concluded that it was not a success.  The course in book form, The Feynman Lectures on Physics, remains a wonderful resource for Physics teachers.  But it’s generally agreed to be an aspirational textbook that is too difficult to base a course on.]

We put forth here a third reason, especially for scientists, for being conversant with both the old approximations and the new.  As we noted recently, our astronomer was working out a problem in Special Relativity for his own information.  Before that he had been helping our tutor teach Newtonian Physics for some time, and for his calculation kept having to work out which basic assumptions were discarded when working relativistically.

To make the transition to 20th-century science many apparently obvious assumptions had to be discarded and basic ideas modified.  If we are to make further progress there is no question that some things everyone assumes now, perhaps without thinking of them, will have to go.  If scientists keep the example of the previous transition always before them, there is less of a danger that current thinking will stifle the scientific imagination.