Right, but I'm asking if there is a human junkyard of abandoned math, whether constructed or discovered. Because the argument turns on most of math being a junkyard. I'm asking whether this is a hypothetical, or actually historical. — Marchesk
I think this is a great question, and I think it's important to show that, if most of what could-be-math is junk, then we've come across that junk before. One example that I think fits the bill is John Wallis' proof that all negative numbers are - or rather can be construed as - greater than infinity (the reasoning is simple, and I summarized it in a
previous post). The upshot of Wallis' proof is that the number line (which Wallis
invented), which normally looks like this:
-∞ < ... < -1 < 0 < 1 < ... ∞
can look like this:
0 < 1 < 2 < ... < ∞ < ... < -2 < -1
The thing about this is that there's nothing particularly 'wrong' with this way of ordering the integers (
here's a paper that fleshes it out in modern terms). The
reason math doesn't opt for Wallis' construal of the number line - and his conception of infinity - is because Cantors' constural of it (now the canonial treatment of infinity) is much more
productive. Wallis' number line is 'junk math'.
In a physicsforum post that discusses the paper, a commentator makes a point that's almost identical to Rovelli's with respect to Dirac that I quoted earlier: "when Dirac wrote in his book: 'principles of quantum mechanics' that the derivative of Log(x) should contain a term proportional to a so-called 'delta function' that he had just invented out of thin air a few pages back, was complete nonsense too."
(
source); Compare Rovelli: "Dirac, in his book, is basically inventing linear algebra in the highly non-rigorous manner of a physicist. After having constructed it and tested its power to describe our world, linear algebra appears natural to us. But it didn't appear so for generations of previous mathematicians".
The reason it's not very easy to come up with examples of junk-math is precisely because it's... junk math. No one cares for it, and no ones cares to pursue it because its largely useless.
That said, another, perhaps less pertinent example might be geometrical definitions of infinity (i.e. definitions that rely on intuitions about physical space), which in turn relied on the fuzzy concept of the infinitesimal. Until the invention of non-standard analysis in the 60s (which provided a rigorous way of understanding the infinitesimals) mathematicians made a huge effort to understand infinity on a strictly
arithmetic basis (i.e. without reference to physical space), because the logical foundations of 'geometrical infinity' were not considered to be secure. In that time before those foundations were secured, one could say that the concept of infinity teetered on the edge of 'junk math' - being 'saved', ultimately, because it's so damn useful.