From 19 till 22 June the University of Tartu Institute of Physics (UTIP) is hosting an international conference “Geometric Foundations of Gravity 2023”, where gravity theorists, cosmologists, particle physicists and mathematicians gather to discuss what kind of solutions to the contemporary problems in fundamental physics could be found by exploring the less studied possibilities in the geometric description of the spacetime structure.
This is the latest edition of the series of conferences held in Tartu, where in the recent years the gravity theory research group has become a trailblazer in the subject. "Currently, the way science describes the gravitational phenomena ranging from planetary motions to black holes and universe as a whole is based on Einstein's theory of general relativity. It relies on the mathematics of Riemannian geometry, and stipulates how the energy and momentum of matter generate the curvature of spacetime. The theory has proven to be really successful during the last century as it explains many observations and experiments. Yet there are several major open questions concerning the structure of the universe and its origin. In this conference, we have gathered experts from different areas of theoretical physics and mathematics with the aim of exploring new geometrical features that might allow us to address these open questions," explains Dr. Alejandro Jiménez, a postdoctoral fellow in the gravity group.
"Following the spirit Einstein's geometrization of gravity, contemporary theoretical research is interested in the various modifications and extensions that go beyond the usual Riemannian framework," continues Dr. Damianos Iosifidis, also a postdoctoral fellow in the gravity group. "Such extended geometric arenas may be related to the the other properties of matter besides energy and momentum. For instance in the metric-affine theories, the micro-properties of matter (like spin, dilation, and shear) can also play a role and produce additional non-Riemannian effects of spacetime torsion and non-metricity. These features will have an influence on the gravitational phenomena in a non-trivial way and consequently can modify the cosmological evolution or the universe, or alter the subtle properties of stars, black holes, and gravitational waves," elaborates Dr. Iosifidis further.
The current event this year is already the seventh international gravity meeting in a row, tells UTIP associate professor in theoretical physics, head of the Laboratory of Theoretical Physics Dr. Laur Järv. While the recent conferences had to be conducted basically online or in a heavily hybrid format, in this year the conference puts focus on in-person participation. More than 70 participants from 20 countries will come to Tartu, while over 40 more researchers have registered interest to follow the talks online.
General public who finds the fundamental issues of the cosmos interesting, can satisfy the curiosity at the conference public lecture held in the Tartu Old Observatory on Tuesday, 20 June at 18:15. The current President-Elect of the European Physical Society Prof. Mairi Sakellariadou form King's College London will speak on the topic Early Universe Cosmology: a primer, aiming at unraveling the mysteries of our universe and highlighting the need for a theory that will encompass quantum mechanics and general relativity.
See more information on the conference homepage.
From 27 June to 1 July the University of Tartu Institute of Physics (UTIP) is hosting an international conference “Metric-Affine Frameworks for Gravity 2022”, where gravity theorists, cosmologists, particle physicists and mathematicians gather to discuss what kind of solutions to the contemporary problems in fundamental physics could be found by exploring the less studied possibilities in the geometric description of the spacetime structure.
According to one of the conference organizers, UTIP research fellow in theoretical physics Dr. Jorge G. Valcárcel the metric-affine framework offers a modern approach to gravity which attempts to unify the effects of the main fundamental properties of matter, such as the energy, momentum, and spin, into a single geometrical description. Although the mathematical undepinnings of this class of theories date back to the works of Élie Cartan, Hermann Weyl, and Albert Einstein a century ago, a systematic analysis and application of these models in cosmological and astrophysical settings has only become feasible relatively recently with a heavy use of computer algebra to aid the calculations.
Among the different variants in this family of theories, in the last years many research efforts in Tartu have focused and contributed to the development of teleparallel gravity. Also at the conference almost half of the presentations touch the various aspects of these particular kinds of models. As the conference organizer UTIP research fellow in theoretical physics Dr. María José Guzmán explains, teleparallel gravity is interesting because it provides a new landscape for exploring theories that supersede general relativity, for it uses the concept of torsion instead of curvature to describe spacetime. Thereby uncharted avenues open up to understand the observed features of the Universe, along with possible mathematical pitfalls that might render the theory unviable.
The MaffGrav conference belongs to a series of international gravity meetings held in Tartu, the current event this year is already the sixth in a row, tells UTIP associate professor in theoretical physics, head of the Laboratory of Theoretical Physics Dr. Laur Järv. While the last two conferences had to be conducted basically online, this year the conference takes place in a truly hybrid form. Despite the lingering Covid-19 pandemic and potentially threatening security situation, among the almost 120 conference participants roughly half will attend the meeting in-person.
General public who finds the fundamental issues of the cosmos interesting, can satisfy the curiosity at the conference public lecture held in the Tartu Old Observatory on Tuesday, 28 June at 18:15. Prof. Davi Rodrigues will speak on the topic Why galaxies rotate? aiming to explain what are the reasons to postulate the existence of dark matter and whether there are any viable alternatives.
See more information on the conference homepage.
From 28 June to 2 July 2021 the conference "Geometric Foundations of Gravity", organized by the University of Tartu, Institute of Physics, Laboratory of Theoretical Physics, had over 160 registered online participants from 42 countries. Despite the uncertainties related to travel during the lingering pandemic, some researchers still found the opportunity to arrive in Tartu and the conference was held in hybrid form.
While black holes and gravitational waves have provided interesting new observational data in the past few years, in this year the crisis in cosmology in determining the so-called Hubble-Lemaitre parameter H0 started to excite researchers. Comparing the decrease in brightness of distant supernovae with accurate data on background radiation from the early universe, we obtain two predictions for the relative rate of universe expansion that differ far more than the measurement error limits would allow. Thus, it seems that the standard model of cosmology or ΛCDM, whereby the universe is described by general relativity with a cosmological constant and dark matter, does not really hold. Celia Escamilla Rivera, Professor at the Autonomous University of Mexico, gave a conference public lecture on just this topic.
A series of talks at the conference presented the latest advances in extensions and alternatives to Einstein's theory of general relativity, covering not only cosmology and black holes but also models of stars. "Especially when studying theories where other geometric quantities such as torsion or nonmetricity are involved in describing gravity instead of spacetime curvature, Tartu has become in several directions an international pioneer and a center of attraction for scientific thought," explained María José Guzmán, a young researcher from Chile who recently got a postdoc grant in Tartu. Another notable circle of presentations and discussions concerned the quantum effects of gravity and the possibilities for their manifestation in astrophysical observations, where the basic ideas of theorists offer an input into the planning of new observation missions.
"Geometry is beautiful. It is even more beautiful when you realize that it suits to describe the laws of nature. However, there are still blank spots in this particular description, and this is why we are here: to discover," concluded Aneta Wojnar, a University of Tartu research fellow in theoretical physics, one of the conference organizers.
On 15–19 June 2020, the University of Tartu Institute of Physics will host an international online conference on teleparallel theories of gravity, where about 100 theoretical physicists and mathematicians from all continents have registered their interest to attend.
In mathematical terms Einstein's 1915 theory of general relativity describes the force of gravity by spacetime curvature. This explains many astronomical phenomena, and has recently received remarkable confirmation by the observations of gravitational waves as well as the black hole image. Yet the unresolved puzzles of dark matter and dark energy invite the researchers to think beyond general relativity. In fact, Einstein himself in his later years played with the alternative geometric notions of torsion and nonmetricity to model gravity. Such theories where the spacetime has no curvature are called "teleparallel" in the mathematical language.
These early ideas did not receive too much attention, as general relativity seemed to work well, but were later picked up and developed further by other researchers. "Currently we know several alternative formulations leading to the equivalent classical dynamics. The question arises whether the geometry of spacetime can be decided by experiments, or whether it is merely a matter of convention," Tomi Koivisto, Senior Research Fellow of Theoretical Physics at the University of Tartu and one of the conference organisers, explained the crux of the problem.
The conference is already the fourth consecutive international scientific meeting dedicated to the geometric foundations of gravity, organised by the University of Tartu Institute of Physics as a part of the activities of the Centre of Excellence The Dark Side of the Universe. "This conference was initially planned as a relatively small and specialised workshop to discuss some recent results and ponder the open problems, but as the travel restrictions forced the event to go online, the participation numbers tripled," said Laur Järv, Senior Research Fellow of Theoretical Physics and Assistant Director of the institute.
The conference talks and discussions are scheduled to take place in a narrow time frame from 12 to 18, to better accommodate participants from the distant time zones of Asia and America. The welcome event is replaced by a TeleQuiz, and instead of the conference excursion, the participants are invited to visit the virtual exhibition hall of the University of Tartu Museum.
On Tuesday, 16 June at 18, Professor Emmanuel Saridakis of the National Technical University of Athens and Hefei University of Technology, and Lead Researcher at the National Observatory of Athens, delivers a popular lecture describing the most recent insights and discoveries from the cosmos, "Black holes and gravitational waves: a new window to look at the universe". The lecture is held in English and is accessible online for free.
More details are available on the conference webpage.
On 17-21 June 2019 University of Tartu, Institute of Physics will host the 2nd international conference "Geometric Foundations of Gravity", attended by over 60 theoretical physicists and mathematicians from 20 countries.
Einstein's general relativity, which mathematicallly describes the force of gravity by spacetime curvature, explains well many astronomical phenomena, and has recenty acquired remarkable confirmation by the observations of gravitational waves as well as the black hole image. Yet, the unresolved problems of dark matter and dark energy raise the possibility that general relativity is just a limiting case of a more broad theory, that engenders significant effects only on the behaviour of the universe at very large scales. "Fitting together the standard models of particle physics, cosmology, and gravity for a comprehensive description of the universe does not give a fully consistent picture. This motivates the researchers to revisit the geometric foundations and systematically consider all possible alternatives in the formulation of the theory," explains the topic UT IP senior research fellow in theoretical physics Manuel Hohmann, one of the conference organizers.
The conference is run by the UT IP Laboratory of Theoretical Physics, and it is a part of the activities of the Center of Excellence "The Dark Side of the Universe", supported by the European Regional Development Fund. The invited speakers of the conference include Professors Fawad Hassan (Stockholm), Lavinia Heisenberg (ETH Zürich), Jutta Kunz (Oldenburg) and Derek Wise (Concordia, St. Paul). "Tartu has become and internationally recognized hub of gravity theory and it is a pleasure to see that after two years many seasoned experts as well as young researchers in the field have found a possibility to delve with us into the puzzles of universe," rejoices the UTIP assistant director Laur Järv, also a conference organizer.
On the popular level the gravity related topics are explained at a public lecture on Tuesday, 18 June at 6 p.m. at Tartu Old Observatory (on Toomemägi). Professor Lavinia Heisenberg will speak in English under the title "Our Dark Universe".
More details are available on the conference webpage.