L'éléphant n°8 will be out tomorrow (more about this later), and it reminds me of a nice discussion with philosopher Karine Prévot about whether outsiders in a field are more likely to make unexpected breakthroughs. This seems to be a widely held belief, but it could easily be a myth kept alive by some spectacular but in fact very uncommon examples.
There are indeed arguments going in either direction. On one hand it seems reasonable that outsiders bring with them some fresh air and a new way of looking at old unsolved problems. On the other hand, why someone lacking a thorough education in a given field would ever come up with interesting ideas ? Spending years working on a subject would be pointless: just wait for an outsider to come and solve the problem. This seems ridiculous.
Still, there are some significant examples. The question is how much significant they are. Surprisingly, I did not find any research paper on this question.
Anyway, below is a little list I have compiled (with the help of many people at mathoverflow, may they be thanked) of famous scientists who made some important contribution in a field other than their own. Feel free to expand it.
From physics to biology:
Erwin Schrödinger: the famous physicist wrote "What is life ?", a book which has been very influential in the biology community, in particular on James Watson.
Francis Crick : speaking about Watson, Crick was primarily educated as a physicist, and only began studying biology in 1947, according to his wikipedia entry.
Max Delbrück was a theoretical physicist who came to be more and more interested in biology. He earned the Nobel prize in physiology and medicine in 1969.
From Chemistry to biology:
Louis Pasteur is best remembered for his invaluable contributions to microbiology and the prevention of diseases, but, as is well-known, he began his scientific career as a chemist.
Linus Pauling could also be put in this section, with his discovery of a new kind of disease.
From mathematics to biology:
Alan Turing is justly known for his contributions to mathematics and computer sciences. Maybe less widely known is his seminal work on morphogenesis.
Also in this section (maybe) is Norbert Wiener for his foundation of cybernetics.
From mathematics to physics, froms physics to mathematics: this is trickiest than one can think. Those disciplines are so close together that a mathematician could be argued not to be an outsider in physics, even less so the other way round. However, it might still come as a surprise that the logician Kurt Gödel discovered one of the very few known exact solutions to the equations of general relativity. And guess what ? It has paradoxical properties...
Also I can't resist mentioning Alain Connes work on the spectral standard model. Aftel all, it was not so obvious that a specialist in functional analysis could come up with entirely new ideas on the unification of the fundamental forces.
In the other direction, it is impossible not to mention Edward Witten. Not only was he the first physicist ever to win the Fields medal, but he did so because he could apply physical intuition from quantum field theory to topological questions. And this exactly the kind of examples I am looking for.