August Monthly Meeting – Is it just me or has gravity become less attractive? by Dr Leonardo Giani

Our meetings include brief business, a main presentation and items of astronomical news or learning from members.

The August Main Item will be: Is it just me or has gravity become less attractive? by Dr Leonardo Giani
A synopsis of the talk ,and details on the speaker, are below.

The August 2023 meeting is planned to be a face-to-face meeting; attendees can also join in online via Zoom. Details emailed to members. Guests/visitors can contact us for Zoom details at .
Visitors are welcome to join our face-to-face or online meetings.

Synopsis – Is it just me or has gravity become less attractive? by Dr Leonardo Giani

What do we know about Gravity? Back in the time of Aristotle, scholars had decided that apples fall from the tree because they want to return to their “natural” place. The heavier the object, the faster it will try to return to its natural place, which for earth and water is our planet, the centre of the Universe around which stars and planets revolve. Something was still unclear: a swinging pendulum does not stop in the centre (when it is the closest to its natural place), but keeps oscillating symmetrically around it. The Aristotelian response to this enigma was rather unimpressive: “mysterium”.
Roughly 2000 years later, Galileo and Newton delivered better explanations for these phenomena based on simple empirical evidence: Gravity is an attractive force. Whilst the latter principle is at the basis of the layman’s understanding of gravitation, discoveries made at the dawn of the 20th century showed that it might not be the case. Einstein’s General Relativity describes the fabric of space-time as a dynamic entity and predicts that a Universe filled with ordinary matter will expand. However, in agreement with the idea that Gravity is attractive, it also indicates that the expansion could slow down eventually.

However, on the other hand in 2011, Perlmutter, Schmidt and Riess were awarded the Nobel Prize for the discovery that the expansion of the Universe has recently (roughly 6 billion years ago) started accelerating, challenging our understanding of Gravity once again. What is the source of such accelerated expansion? Why did the gravitational interaction change behaviour only recently? Why does gravity behave so differently in the Universe and on Earth?
In this talk I will review the most popular attempts to address these questions and where they fall short. I will also try to convince you that, despite its phenomenology, gravity (or better Gravitation) has never been more attractive.

Biography:  Leo graduated in theoretical physics at the University of Bologna (Italy) in 2016, and then joined an international Ph.D. program at the University of Vitoria (Brazil) under the supervision of Professors Oliver Piattella and Luca Amendola. With assistance from a grant from the DAAD (German funding agency), he spent the last year of his Ph.D. working at the University of Heidelberg (Germany). His Ph.D. was awarded in 2020 for a thesis on geometrical models of Dark Energy, which received an honourable mention at the 2021 ICTP-SAIFR Prize for Classical Gravity and Applications, an annual competition for Ph. D. students in all South American institutions.
Leo arrived in Brisbane in 2022 to take up a postdoctoral fellowship at the University of Queensland working with Tamara Davis. His research focuses on Dark Energy phenomenology, gravity tests and theoretical Cosmology.