Abhay Ashtekar (Physics Department, Penn State, US  and Perimeter Institute, Canada)

Our notions of space and time underwent a radical change just over a 100 years ago. Through general relativity, gravity ceased to be a force and became a manifestation of space-time geometry. This paradigm shift opened unforeseen perspectives in our understanding of the physical universe: possibility of ripples in space-time geometries that manifest themselves as gravitational waves; of black holes, representing geometries that trap not only matter but also light; and of the Big Bang, the primordial explosion marking the birth of the space-time continuum itself. However, through black holes and the big bang we also learnt that Einstein’s equations predict the presence of space-time singularities: rugged edges where the space-time continuum tears and all of classical physics comes to an abrupt halt. These singularities are the gates to physics beyond Einstein – i.e., to unification of general relativity with quantum physics. Construction of this desired theory of quantum gravity is a truly challenging task because it requires an entirely new syntax to formulate concepts that are sufficiently adequate to describe the extreme universe. We now need the quantum analog of Riemannian geometry that serves as the syntax for general relativity. After a brief discussion of why several distinct approaches are being pursued, I will focus on loop quantum gravity, based on a specific theory of Riemannian quantum geometry. I will explain how it leads to quantum space-times that extend Einstein’s classical continuum beyond its singularities. While this conceptual framework is rather abstract and involves novel mathematics, it also leads to predictions that can be tested observationally.

Language: English

Participation via Zoom:
https://uni-bonn.zoom.us/j/94919053391?pwd=d3RjYm5RTy9BVnZUeTlhS0YrOXhMdz09
Meeting ID: 949 1905 3391
Passcode: 729340

The full schedule of the Bonn History and Philosophy of Physics Research seminar can be found here:
 https://www.history-and-philosophy-of-physics.com/events.html