Tuesday, September 1st
Maciej Kolanowski, Warsaw UniversityLost in translation -- energy in the de Sitter universe
PDF of the talk (800K)
Audio+Slides of the talk (2600M)
SRT (Subtitles) of the talk (70K)
By Jorge Pullin, LSU
One normally tries to think of space-time as space with an extra dimension. But time has a particular nature. This gives space-time unique properties that ordinary three dimensional space does not have. One of them is the nature of infinity. In space-time there are more than one infinity. Objects that travel at speeds slower than light (like humans) finish their lives in a certain infinity, whereas objects that travel at the speed of light, like electromagnetic or gravitational waves end in a different infinity, known as null infinity.
Infinity is important because it is the point where discussions of energy in gravitational physics are meaningful. By sitting at infinity one ensures that one includes all the energy involved in the universe. Discussions of energy are important, for instance, in the context of gravitational waves. We know that binary systems in astronomy emit gravitational waves that carry energy to infinity and that determines that the systems' orbits inspiral and eventually merge. This has been verified dramatically in the last few years with the discovery of gravitational waves by interferometric detectors like the LIGO detectors.
The discussion of infinity in space-time changes when one has a cosmological constant present. This is important because our best measurements today indicate that indeed we live in a universe with a cosmological constant. This requires revisiting the definitions of energy and conserved quantities in space-time. This talk dealt with this point. It presented new definitions for the emitted energy and compared with other ones already present in the literature.
