The scientific way

Scientific rules, like all rules, must be applied intelligently.

Last week we pointed out that sets of rules varied in how they should be used. Sometimes they’re best as a checklist, sometimes as a point of departure; sometimes adhered to closely, sometimes as a reminder of what you should not be doing.  Well, we expect that the rules of science should be more rigorous that those of Photographic Composition or the Art of War, and require less judgement in their application.  That’s a big part of the difference between art and science.  Scientific laws are just that.

But it might be hard to convince a High School Chemistry students of the truth of that statement.  At that level the subject seems to consist chiefly of a set of rules-of-thumb, each with its exceptions.  Worse, from the point of view of our tutor, the exact wording of the rule and what is contained in the exceptions will vary depending on which particular course the student is taking (normal, Honors, AP or whatever).  All atoms will build molecules with eight electrons in the valence shell; except hydrogen, which is content with two, and the boron family, each of which is satisfied with six; but for the upper level classes only, the transition metals will sometimes have ten or twelve in their valence shells.  The Noble Gases do not form molecules; except the upper-level classes may mention xenon hexafluoride, and no one talks about helium hydride.  All the nitrates are soluble in water, except silver nitrate.  And so on.

At a more advanced level of study, many of these seemingly arbitrary collections of rules become unified with a deeper level of understanding.  Unfortunately, that requires much more mathematical physics than can be expected even of college students who are not Physics or Chemistry majors.  These privileged few can see how the s, p, d and f orbitals emerge from solving the Schrödinger Equation for a one-electron atom.

Unfortunately, once you get away from the simplest situations even these initiates are back on rules of thumb.  To calculate even a small molecule ab initio is extremely hard, so we try combinations of the single-atom orbitals as a first guess, then adjust as our judgement directs.

Is Physics, then, more regular than Chemistry?  Someone studying turbulence might not immediately agree.  And at the basic level Physics splits up into the Newtonian kind, which is fine below a certain speed and larger than a certain scale; Quantum Mechanics, below that certain scale and below that certain speed;  Special Relativity, above that scale and above that speed; Quantum Field Theory, below that scale and above that speed; and General Relativity, when gravity gets strong.  A physicist starting work on a problem must judge which area his problem lies in.  And trying the most general theory that can possibly be applied can be a recipe for frustration.  There are calculations that are relatively easy and straightforward in Newtonian physics, but can only be done in General Relativity with enormous difficulty and lots of computer time (if at all).

And do we really need to consider magnetic fields?