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Questions about mathematics which don't fall into the other arXiv categories. If you have a general question about mathematics but it is not research level, it's off-topic but it might be welcomed on Mathematics Stack Exchange.

12 votes

When is 2 qualitatively different from 3?

Complex numbers exist only in dimension 2. That is the only multiplication laws on $R^n$ which satisfy all field axioms exist for $n=1$ (real numbers) and $n=2$ (complex numbers).
62 votes
Accepted

Is spherical trigonometry a dead research area?

It is not. As a proof, I will mention three relatively recent papers where I am a co-author: M. Bonk and A. Eremenko, Covering properties of meromorphic functions, negative curvature and spherical geo …
Alexandre Eremenko's user avatar
61 votes

Is amateur research in mathematics viable?

This is possible. I have at least two friends who studied mathematics (in the graduate school), did not defend their PhD, and found some jobs not related to mathematics. Still they do research, and pu …
14 votes

What are some examples of understanding a space by studying the functions on this space?

The idea goes back to the 1930s when algebraic geometers understood that points of an algebraic variety "are" maximal (or prime) ideals of the ring of regular functions on it. The counterpart of this …
4 votes

Golden ratio in contemporary mathematics

Yes, it does: Lyubich, Mikhail; Milnor, John The Fibonacci unimodal map. J. Amer. Math. Soc. 6 (1993), no. 2, 425–457. and two more papers of the same authors studying what they call Fibonacci map.
34 votes

Theorems with many distinct proofs

"what is worth proving is worth proving again" (Attributed to N. Katz in D. Ruelle's paper, The nature of properly human mathematics.) You are asking for a very long list: most deep and important th …
5 votes
Accepted

Do mathematicians use notebooks to keep their results these days?

Yes, mathematicians keep notebooks. Sometimes, after their death, notebooks are published. Here is an example: http://www.claymath.org/publications/quillen-notebooks Here is another example, though …
31 votes

Counterexamples against all odds

The most famous example is the so-called Riemann-Hilbert problem, which has a long and complicated history which I don't explain in detail. As it happens Hilbert's own formulation was not very exact, …
30 votes

The origin(s) of the word "elliptic"

The origin of all these uses is very different. Joe Silverman explained the genesis of the sequence ellipse $\rightarrow$ elliptic integral $\rightarrow$ elliptic function $\rightarrow$ elliptic curve …
Alexandre Eremenko's user avatar
7 votes

Recreational mathematical papers

Two of my favorite recreational papers are: J-F Mestre, R Schoof, L Washington and D Zagier, Quotients homophones des groupes libres. Homophonic quotients of free groups Experiment. Math. 2 (1993), …
Alexandre Eremenko's user avatar
20 votes

Is the field of q-series 'dead'?

The opinions that certain areas of mathematics are dead are frequently stated but in many cases incorrect. Some areas experience declines in activity and then revivals. Many examples can be given. On …
23 votes

Fascinating moments: equivalent mathematical discoveries

An example which always puzzled me is J. Milnor's paper entitled Eigenvalues of the Laplace operator on certain manifolds, Proc. Nat. Acad. Sci. U.S.A. 51 1964, 542. The whole paper occupies about ha …
29 votes

Where can square roots come from when they are not distances?

$i=\sqrt{-1}$ has no apparent relation with any distance. Also $\int_{-\infty}^\infty e^{-x^2}dx=\sqrt{\pi}.$
16 votes

A search for theorems which appear to have very few, if any hypotheses

There are infinitely many prime numbers. Every integer is a product of primes, in essentially unique way. (Theorems with NO hypotheses:-)
1 vote

A search for theorems which appear to have very few, if any hypotheses

Every bounded analytic function in the unit disk has radial limits almost everywhere.

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