# Public Lecture

## Overview

During this year's meeting of the Australian Mathematical Society in Adelaide, French mathematician Professor Étienne Ghys will give a public lecture with the title "The shape of our planet Earth: a mathematical challenge!" Professor Ghys is well-known for his clear explanations of mathematics to non-experts, and has won many prizes for his popular talks, books and movies. In this lecture, he will explain why the earth is not exactly round, and the mathematical questions that arose from attempts to determine the earth's precise shape. Everyone who is interested is cordially invited to attend this lecture.

The lecture will take place in the Braggs Lecture Theatre on the North Terrace campus of the University of Adelaide, from 7 pm to 8 pm on Wednesday, the 5th of December. Before the lecture, there will be a reception from 6 pm to 7 pm in the atrium of the Ingkarni Wardli building, to which all are welcome.

## Talk Description

### The shape of our planet Earth: a mathematical challenge!

Our planet Earth is rotating. The centrifugal force produces some equatorial bulge so that the Earth is not exactly spherical. The mathematical question of the determination of the shape of a rotating body has been central in the development of mathematics for several centuries. Newton was the first to get an estimate of the flattening of the Earth by a purely theoretical reasoning, "without having to get out of his home", as Voltaire wrote. I will discuss historical developments, like for instance the surprising discovery by Poincaré of rotating bodies having the shape of a pear! This topic is indeed a wonderful example of the interaction between pure and applied science. Even though the question has been studied by the greatest mathematicians since 350 years and many discoveries have been made, many important questions still remain open.

## Speaker Biography

Étienne Ghys is a professor of mathematics at the École Normale Supérieure de Lyon in France. He works in the area of geometry and dynamical systems. He has received many prizes for his research, but he is also very active in popularising mathematics by talks, books and movies. His talent for explaining maths to non-experts is a reason why he was asked to give a public lecture at this year's International Congress of Mathematicians in Brazil, the world's largest mathematics conference. This lecture about the geometry of snowflakes was attended by a large audience of school teachers and high school students.

He has produced two series of short films explaining the fourth dimension and chaos theory to the general public. His movie "Dimensions: A walk through mathematics!” has received the d’Alembert Prize for the dissemination of mathematics to the general public of the French Mathematical Society and he has received the Award for Dissemination of Mathematical Knowledge of the Clay Mathematics Institute.