Online registration is closed for this event. If available, tickets on the day of the event may incur an additional charge.

Math Encounters — Online:

“Number Theory Problems: From Easy to Undecidable”
with Bjorn Poonen

Wednesday, August 5 at 4:00 pm EDT (New York)

Rational numbers are fractions such as -2/7.  It turns out that the circle x2+y2=3 has no points whose coordinates are rational numbers, while the circle x2+y2=5 has infinitely many.  Why do these equations behave so differently?  What about more complicated equations: is there a method to decide whether there are any solutions in rational numbers?  Join Bjorn Poonen, Distinguished Professor in Science at MIT, as a search for answers leads to questions about prime numbers, geometry, and problems that a computer will never be able to solve.

Special introduction by C. Kenneth Fan, President of Girls’ Angle.

This is a live-streamed event.  Occasional video recordings are made available for a fee at

This page is for the 4:00 pm EDT (New York) session.  Click here to register for the 7:00 pm EDT (New York) session instead.

By registering for a Math Encounters presentation, you agree that you may be photographed or videotaped by Museum staff and associates.

Math Encounters is MoMath’s popular free public presentation series celebrating the spectacular world of mathematics, produced with support from the Simons Foundation.

For further information, call the National Museum of Mathematics at 212-542-0566 or e-mail

Please check our online shop for books by Math Encounters presenters.

August 5th, 2020 from  4:00 pm to  5:30 pm
MoMath Online
United States