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Re: Landau letter, Re: Mathematica as a New Approach...

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  • Subject: [mg127871] Re: Landau letter, Re: Mathematica as a New Approach...
  • From: John Doty <noqsiaerospace at>
  • Date: Tue, 28 Aug 2012 04:53:42 -0400 (EDT)
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On Wednesday, August 15, 2012 1:31:53 AM UTC-6, Andrzej Kozlowski wrote:
> I agree with your interpretation of Landau's letter but I also think your
> remarks about mathematics miss the point of what mathematicians do.

I know what mathematicians do. Finding connections between ideas is at the core of mathematics. The best mathematicians (von Neumann, for example)follow those connections wherever they lead, and don't stop at arbitrary borders. has some relevance here.

> Mathematicians do not concern themselves with the physical universe - if
> they did they would be something else. The results which they prove are
> meaningful within their own realm. The exact nature of this "meaning" is
> complicated, but it essentially relates to "procedures" (how arguments
> are conducted) than any physical reality. A great deal of mathematics
> (for example, almost all of probability theory) is concerned with
> "infinity", which arguably has no physical meaning at all.

Except that in many cases, it has been physical scientists who *introduced*mathematicians to various uses of infinity (differentials, Fourier analysis, delta functions, ...). But that's history.

It is also clear from history that mathematics developed from very concrete foundations in things like counting and measurement. It is incomprehensible to me that many mathematicians wish to deny this, preferring to believe in Platonic fairy tales. A nasty consequence of this denial was the 1960's "New Math" curriculum for American schoolchildren. Supposed to strengthen math comprehension, it did exactly the opposite.

I cringe when I hear a mathematician talk about Fourier analysis as being about functions in L2. That notion ignores out a large part of the application space: "carrier waves", "flicker noise", delta functions, ... Here we see mathematicians willfully avoiding *meaningful* infinity.

> In 1910 the mathematician Oswald Veblen and the physicist
> James Jeans were discussing the mathematics curriculum for physicists at
> Princeton university. "We can safely omit group theory" argued Jeans,
> "this theory will never have any significance for physics". Veblen
> resisted and it is well known that this fact had a certain influence on
> the future history of physics.
> This example is, in fact, an excellent illustration of the main point
> that people who argue like you do not get.

Actually, this is a rather poor example for your argument. But first, to sh ow you that I'm partially on your side here, let me give you a better one.

Non-Euclidean geometry was one of the great mathematical developments of the nineteenth century. It was driven entirely by the interests of mathematicians: it had no physical motivation. At the same time, the development of quaternions, their subsequent evolution into vector analysis, and the tremendously successful application of these developments to physics (especially electrodynamics) further entrenched three dimensional Euclidean space as *the* model for physical space.

Then everything changed. Poincar=E9 and Minkowski reformulated Lorentz/Einstein special relativity as non-Euclidean geometry. Einstein then combined Minkowski's geometry with Riemann's, added some physics and came up with his general relativity. GR was such a huge intellectual leap that it seems inconceivable that he could have taken it without the foundation provided by "pure" mathematicians. Without that foundation, I don't think that even now, a century later, we'd have an adequate theory of gravity for astrophysics.

But group theory? For half a century after the discussions you describe group theory had little influence on physics. Then, it made its big splash with Gell-Mann and Ne'eman's SU(3) theory of the hadron spectrum. But how much insight really emerged from group theory here? I recall Victor Weisskopf explaining the theory to a group of freshman (of which I was one). The gist was "the hadrons are the states of a spectroscopy, and they exhibit the patterns to be expected for a three particle spectroscopy". No group theory, all physics

OK, you might say. The discovery passed through group theory to mechanism. Group theory was therefore important. The problem with this idea is that a number of other physicists were hot on the trail here, and there was no barrier to skipping straight to mechanism. Gell-Mann and Ne'eman got there first, and they happened to be unusually committed to mathematical abstraction, but a more concretely-minded physicist could have found the mechanism directly: it was not deeply hidden.

The subsequent influence of the SU(3) abstraction on the development of this theory was negative. While Gell-Mann was certainly aware of the three-particle mechanism (he coined the term "quark"), he believed that mechanism was unnecessary. The trouble was that physical mechanisms have consequences beyond symmetry. In particular, if you hit a blob of particles with a probe of sufficiently small wavelength, you'll see that it's lumpy. And that's exactly what experiments revealed. Hadrons are not content-free consequences of SU(3) symmetry: they are composite objects, and the SU(3) symmetry is a consequence of their composition.

This reveals the trouble with group theory here: it obfuscates the underlying physics. SU(3) could as easily represent the organizing principle behind somebody's stamp collection. The distinction between stamps and particles might not matter to mathematics, but it's a big deal in physics.

But one good way to win a Nobel is to win the race. Gell-Mann and Ne'eman were the first ones to completely work out hadron spectroscopy: they won. A (to me unfortunate) consequence was that group theory has gained prominence in physics that goes far beyond its capacity for providing insight. For example, in place of Minkowski's clever geometry, the abstractionists now try to sell us the "Lorentz group". But the fact that Lorentz transforms form a group is trivial and unenlightening: it's the geometry that captures the physical essence here.

> So one reason why existence and non-existence theorems are important is
> that solving them leads to much deeper understanding of mathematics,
> which in turn turns out often to involve unexpected applications in
> other areas.

But many presentations of theorems by mathematicians are unenlightening symbol manipulation. That seems to me to be at the core of Landau's complaint.

> There is also another, more direct reason. Knowing that
> there cannot be a general formula in radicals for the roots of a
> polynomial equation means that we no longer need to try to find one and
> instead can turn our attentions to other approaches. This is itself also
> useful in applications (just this of the number of people who post to
> this forum asking for "explicit" solutions of some equation or other).

Indeed this is a very important result, but Galois theory itself is even less enlightening than other applications of group theory.

> Finally, where on earth did you get the idea that "philosophers have
> comprehensively demolished mathematical Platonism" or indeed that
> philosophers have "comprehensively demolished" any philosophical idea in
> the entire history of philosophy (including, of course, the idea of the
> Creator)? This is an astounding news to not only to me, but also news to
> my wife, who has been a professor of philosophy at one of the world's
> leading universities, has a PhD in the subject from Oxford University,
> etc, etc. It also would be of interest to physicists like Roger Penrose
> who, obviously in blissful ignorance of this great news, remain
> unabashedly "mathematical platonists".

Penrose's Platonism is the source of his bizarre pseudophysical theory of how the mind works. To me, it is profoundly unscientific, based in faith in his subjective experience rather than objective evidence.

> Could you please let us know the name of the philosophers who have
> performed this amazing feat?

There's a *lot* of literature here: I'm surprised you are unfamiliar with it. Let's start with  this paper:

You also might read "Philosophy of Mathematics (5 Questions)", edited by Hendricks and Leigeb, "18 Unconventional Essays on the Nature of Mathematics", edited by Hersh, and Hersh's book "What is Mathematics, Really?".

There are a variety of good arguments against Platonism in the works above, but to me one seems especially unanswerable: mathematical Platonism requires that mathematicians possess a supernatural sense that connects them to an objective reality outside the physical world. There is neither any scientific evidence for this nor any explanation for what biological function such a sense would serve.

On the other hand, I'm very impressed by N=FA=F1ez and Lakoff's idea that mathematics is a phenomenon that emerges naturally from sufficiently sophisticated embodied cognition.  Based in actual science (experimental psychology), this is a very plausible approach to understanding the true nature of mathematics.

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