Speaker:Prof Kevin Buzzard (Imperial College)
Venue: Winstanley Lecture Theatre
Time: 7/11/2011 20:30, drinks from 20:15

Are there any rational solutions to x²+y²=-1? No, because there are no real solutions. How about x²+y²=3? Again the answer is no, but one way of showing this is by constructing a ‘local field’ — the 3-adic numbers — which contains the rationals as a dense subfield, and in which it’s easy to check that there are no solutions. It is far easier to solve equations in these local fields than in global fields such as the rationals, and conversely, sometimes solutions in all local fields can imply solutions in a global field too.