# September 22, December 5, Science Cafe "Universe"

August 3, 2020

Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)

Enjoy a cup of tea or juice while interacting with scientific experts in our upcoming Science Cafe series.

The Kavli IPMU is proud to announce the dates for our annual Science Cafe series "Universe", co-hosted with the Tamarokuto Science Center. This year's events will be held on Sep 22 and December 5. Event will be in English.

Interested in testing you knowledge of the latest advances in mathematics and astronomy? We look forward to seeing you there. Pre-registration is required.

## Science Cafe 2020 "Universe"

**Date & Time:** 14:00 - 15:30 September 22 (Tue/Public holiday)

**Venue:** Online

**The Dehn invariant: let's understand why a certain problem is impossible**

Speaker: Dinakar Muthiah (Kavli IPMU Project Researcher）

**Difficulty level:** Recommended for junior high school students and above (the lecture itself has been made with high school level science knowledge in mind. The lecture will be in English with no interpretation services available on the day)

**Seats:** 40 (prior registration required. If the number of registrants exceeds the number of seats, participants will be drawn from a lottery.)

**Admission:** Free

**Introduction**

In mathematics, we are often curious whether a problem is possible or impossible to solve. To prove that a problem is possible to solve, you just solve it! But how would you prove there is no solution? This is harder, but can be more interesting. One way to show that a task is impossible is by discovering a good "invariant".

We will consider the problem of "equidecomposability of polyhedra". Given two shapes of equal size, can we cut the first one into pieces and reassemble the pieces to get the second? Each shape is a polyhedron, and we allow cuts along straight lines. In the two-dimensional plane the answer is yes: this is always possible. However, in the three dimensional space, the answer is no! This task in general is impossible. We will talk about the invariant, discovered by Dehn, which shows us why.

**About the speaker:**

Muthiah joined Kavli IPMU in 2018 as a project researcher. His field of expertise is Mathematics.

**Date & Time:** December 5 (Saturday)/ Time will be announced later.

**Venue:** Tama Rokuto Science Center or Online

**The Universe at the largest scales: The Cosmic Web**

Speaker: Robin Kooistra (Kavli IPMU Project Researcher）

Details and registration will be ready on this Autumn.

**Introduction**

After the Big Bang, the distribution of matter in the Universe has evolved through gravity to form a complex pattern of filaments, walls, voids and nodes.These encompass the largest scales we can observe and are collectively known as the Cosmic Web.

In this talk I will give a brief overview of our current understanding of these structures.

This will include a discussion on the available observations, as well as some of the theoretical work that has been performed by making use of computer simulations.

**About the speaker:**

Kooistra joined Kavli IPMU in 2019 as a project researcher. His field of expertise is Astronomy.