6th EPS Conference on Gravitation

Jun 1, 2026, 8:00 AM → Jun 3, 2026, 2:00 PM Europe/Oslo

Ullandhaug Campus, AR Ø-110 (University of Stavanger )

Sigbjørn Hervik (University of Stavanger), Renate Loll (Radboud University)

Aim and Motivation

Gravity impacts all stages of the evolution of the universe, but the precise role of fundamental gravity in modeling cosmology remains to be understood. Current cosmological tensions may be related to an incomplete or oversimplified treatment of gravity and spacetime in the ΛCDM model, and highlight the need for quantifying the influence of initial conditions, local effects of gravity and backreaction beyond a perturbative analysis on FLRW backgrounds.

Recent advances in numerical and analytical methods and a wealth of astrophysical precision data allow for new, systematic studies of the interplay of matter, geometry and inflationary expansion, and open new pathways for a model-independent analysis. Research that exploits the interwovenness of gravity and cosmology includes the proposed use of gravitational wave observations to elucidate the extreme physics of the early universe, and of cosmological probes to constrain modified gravity theories. The big underlying challenge – besides unraveling the complexities of the history of our universe and the nature of its initial big-bang singularity – is to come up with clear evidence for new (quantum) physics beyond general relativity and the standard model of particle physics.

Gravity & Cosmology: Searching for Concordance  brings together researchers working on different aspects of the cosmology-gravity interface, who may not necessarily meet at more specialized, subcommunity-oriented events, to exchange views on what are the most feasible and promising ways forward and explore how they relate to each other. Our keynote speakers are leading experts on numerical and mathematical relativity, modified gravity, quantum cosmology, cosmography, gravitational wave cosmology, cosmological tensions, backreaction and phase transitions, and on foundational aspects. We aim for an interactive meeting and for constructive and respectful dialogue, including organized discussions on future challenges and opportunities. We invite the submission of abstracts for contributed talks and posters and encourage especially junior researcher to participate.

Confirmed Invited Speakers

• Martin Bojowald (Penn State)
• Chris Clarkson (Queen Mary)
• Ed Copeland (Nottingham)
• Eleonora Di Valentino (Sheffield)
• Ruth Durrer (Geneva)
• Grigorios Fournodavlos (Crete)
• Cristiano Germani (Barcelona)
• Mark Hindmarsh (Helsinki)
• Alexander Kamenshchik (Bologna)
• Sofie Marie Koksbang (Odense)
• Marek Lewicki (Warsaw) 
• Eugene Lim (King's College)
• David Mota (Oslo)
• Zoe Wyatt (Cambridge)

Discussion Conveners

• Giulia Gubitosi (Naples)
• Mercedes Martín-Benito (Madrid)

Location and Venue

The location of the conference is in Stavanger, located on the coast in south-western part of Norway. Western part of Norway is famous for its spectacular fjords, and the Stavanger region is particularly known for its Pulpit Rock situated at the Lysefjord, see conference picture. 

Stavanger has coastal climate being a result of being by the relatively temperate North Sea. The city typically experience mild winters and cool summers, and the average day temperature in June is around 15ºC. 

The venue for the conference is at the University of Stavanger (UiS), campus Ullandhaug, which is just a couple of kilometers from the city centre, and 7km from Stavanger Airport. There are direct flights to Stavanger from several European cities like Amsterdam, Copenhagen, London, Frankfurt and Helsinki. 

CRUISE WEDNESDAY:
Everyone could book their own ticket, and there are two departure times, 14:30 and 15:30. 
Link to the Lysefjord cruise:
Rødne fjordcruise

Mon, June 1

8:15 AM Registration

8:50 AM Welcome

1 Dark energy: A cosmological constant, quintessence or something else?

Dark Energy is the term given to the dominant energy density in the universe today which appears to be causing it to accelerate. A key question then is what is responsible for the dark energy? There are three favoured candidates: a cosmological constant which has a fixed constant energy density, a quintessence field which has an energy density which varies with time or a modification of Einstein's General Theory of Relativity, where the presence of extra curvature terms could lead to the observed acceleration. We will discuss these options, and their problems (they all have some!), and comment on the recent tentative evidence emerging from the DESI collaboration of dynamical dark energy - exciting but not as you would expect from quintessence!

Speaker: Ed Copeland (U Nottingham)

2 Early-universe cosmology with LISA

The Laser Interferometer Space Antenna (LISA) offers a unique opportunity to probe the early universe through the detection of stochastic gravitational wave backgrounds. In this talk, I will review recent progress within the LISA Cosmology Working Group in analyzing these signals as probes of physics beyond the Standard Model. I will focus on early-universe sources such as first-order cosmological phase transitions and cosmic strings, highlighting their predicted signatures and the key challenges that must be addressed to fully exploit LISA’s scientific potential.

Speaker: Marek Lewicki (U Warsaw)

10:10 AM Coffee Break

3 Cosmological tests of gravity beyond general relativity

Several modifications to General Relativity have been proposed to explain the nature of dark energy and the observed accelerated expansion of the Universe. However, such theories are stringently constrained by local tests of gravity and by observations of gravitational waves. In this talk, I begin by outlining the conditions under which theories beyond General Relativity can remain viable in light of these constraints, and by describing how they are expected to manifest across different astrophysical systems and in their cosmological signatures. Building on this framework, I will present a range of observational tests that exploit current and next‑generation astronomical surveys to probe gravity on multiple scales. In particular, I will show how the nonlinear dynamics and observable properties of galaxies and galaxy clusters provide especially promising avenues for constraining theoretical models of modified gravity.

Speaker: David Mota (U Oslo)

4 Testing general relativity with cosmological observations

General Relativity (GR) is immensely successful. With the late discovery of gravitational waves from black hole and neutron star mergers, it has passed all the tests with flying colors. But so far, all observations have mainly tested the vacuum equations of GR. The most important non-vacuum case, cosmology, is in agreement with GR only after the introduction of two otherwise unknown components, 'Dark Matter' and 'Dark Energy' which amount to about 95% of the total energy budget of the present Universe. This led people in the field to question the validity of GR for cosmology. Might it be that GR is flawed on large, cosmological scales? Or in the presence of matter in general? But how can we test Einstein's equation in the presence of matter? Can't we simply move any modification of the Einstein tensor to the right hand side and call it a 'dark matter/energy' component? In my talk I shall discuss possible ways (partially) out of this dilemma. How to test both, the left and the right hand side of Einstein's equations with cosmological observations.

Speaker: Ruth Durrer (U Geneva)

5 The relativistic galaxy bispectrum

The galaxy bispectrum will play an important role for future galaxy surveys. On large scales it will be a key probe for measuring primordial non-Gaussianity, and hence help discriminate between different inflationary models and other theories of the early universe. On these scales, a variety of relativistic effects come into play once the galaxy number-count fluctuation is projected onto the past light cone. The Fourier-space galaxy bispectrum is complex, with the imaginary part arising from leading-order relativistic corrections. Detection of the imaginary part is potentially a smoking gun signal of relativistic contributions. We will discuss whether next-generation surveys could make such a detection. Further, we will discuss how relativistic effects break parity invariance of the observed trispectrum.

Speaker: Chris Clarkson (Queen Mary U of London)

12:25 PM Lunch Break

6 A status on cosmic backreaction and its relation to model-independent cosmology

The structures of the Universe can affect the large-scale cosmic dynamics. This effect is known as cosmic backreaction. Although the effect has been known and studied for decades, it is still unclear how important the effect is in our Universe. One can attempt to quantify the effect in several different ways, but the resulting estimates vary wildly, depending on the introduced approximations. It is therefore unclear to what extent (if at all) backreaction is related to dark energy, cosmological tensions and how important it is in relation to testing theories of gravity beyond general relativity. In this talk, I will present the concept of cosmic backreaction and how it may be related to dark energy and cosmic tensions, as well as why it may be particularly important when studying gravity beyond general relativity. I will also review why backreaction is so difficult to quantify and discuss the necessary steps remaining before we can make truly trustworthy theoretical predictions of its importance in our universe. Lastly, I will discuss the possibility of quantifying backreaction through observations and how this fits into a larger strategy of studying observations model-independently.

Speaker: Sofie Marie Koksbang (U Southern Denmark)

Contributed Talks: Monday I

7 TBA

Speaker: Germano Nardini (U Stavanger)

8 Extended quintessence

In this talk, I will discuss a model of extended quintessence in which a scalar field is non-minimally coupled to gravity, serving as a candidate for dark energy. I will present its properties at both the background and linear perturbation levels. While the non-minimal coupling is constructed to satisfy local tests of gravity without need to introduce screening mechanisms, the model exhibits interesting features in both regimes, including phantom crossing and the potential to alleviate the Hubble tension. All computations are performed using a modified version of the Boltzmann code hi_class.

Speaker: Abdolali Banihashemi (U Oslo)

9 Stochastic scalar-tensor theories

Previous work on Stochastic Inflation in full General Relativity is extended to any dark energy model described by the Effective Field Theory of Dark Energy. The recipe to obtain the dynamics of a any such nonlinear and nonperturbative long-wavelength scalar-tensor theory, when dynamically sourced by classicalised fluctuations of the short modes, is explained, proved and illustrated with a few examples of matchings. These include Gauss-Bonnet, Brans-Dicke, Horndeski theories and beyond. The separate universe approximation is also provided and commented for each of those. A final discussion on the validity of the approach is provided, as well as other natural extensions to provide a phenomenologically complete stochastic framework, and potential applications beyond the realm of inflation.

Speaker: Yoann Launay (U Cambridge)

3:30 PM Coffee Break

Contributed Talks: Monday II

10 Tests of general relativity with the gravitational wave transient catalog 4.0

The worldwide LIGO-Virgo-KAGRA (LVK) network of gravitational-wave (GW) detectors continues to increase in sensitivity, thus increasing the quantity and quality of the detected GW signals from compact binary coalescences. These signals allow us to perform ever-more sensitive tests of general relativity (GR) in the dynamical and strong-field regime of gravity. We present the results of a suite of tests of GR using the binary signals included in the fourth GW Transient Catalog (GWTC-4.0), i.e., up to and including the first part of the fourth observing run of the detectors (O4a). We restrict our analysis to the 91 confident signals, that were measured by at least two detectors, and have false alarm rates ≤ 10^−3 yr^−1. These include 42 events from O4a. We discuss the results and their implications for GR and alternatives/extensions, as well as the challenges and state of the field going forward. Based on: [arXiv:2603.19019] GWTC-4.0: Tests of General Relativity. I. Overview and General Tests [arXiv:2603.19020] GWTC-4.0: Tests of General Relativity. II. Parameterized Tests [arXiv:2603.19021] GWTC-4.0: Tests of General Relativity. III. Tests of the Remnants. This talk is on behalf of the LVK Collaboration

Speaker: Ofek Birnholtz (Bar-Ilan U)

11 Measuring cosmic expansion with gravitational waves: hints from binary black hole-galaxy cross-correlations

The most debated crisis in cosmology today is, perhaps, the inconsistency of the estimated value of the current expansion rate of the Universe (known as the Hubble constant, H0) between different probes using high redshift and low redshift observations. Gravitational wave (GW) emitting sources, which are routinely observed nowadays through the ground-based LIGO-Virgo-KAGRA detector network, could serve as an independent probe shedding light on this crisis. Such sources, also called the “standard sirens”, provide us with a direct measure of the cosmological distances through the observed gravitational wave strain. When accompanied by an electromagnetic counterpart, such as Gamma Ray bursts, the redshift of the source can also be determined, thus offering a new avenue to probe the cosmic expansion. However, the majority of the detected GW events do not have an associated electromagnetic signal. For such sources, one can make use of their clustering properties with respect to the observed galaxies and the underlying dark matter distribution, since they are part of the same large-scale structure and are thus correlated with each other through structure formation history. In this talk, I will discuss how the angular correlation between gravitational-wave standard sirens and galaxies allows an unbiased inference of the Hubble constant. With the growing number of such events in future observations, this technique will be imperative for a robust cosmological inference using GWs.

Speaker: Sayantani Bera (Aix-Marseille U)

12 High precision predictions for next generation gravitational wave observatories: the post-Newtonian frontier at the seventh order

Next generation gravitational wave detectors, such as the Einstein Telescope and LISA, require an improvement of two orders of magnitude in waveform accuracy to control systematic effects. Therefore, completing the seventh post-Newtonian order (7PN) is critical for robust inference of cosmological parameters and tests of general relativity. This talk presents recent high order PN computations for compact binaries using Effective Field Theory and multi-loop integration techniques. The talk focuses on the static sector of the 6PN and 7PN gravitational potential, which is the most technically challenging barrier to determining the full potential. We first present the 6PN static potential, highlighting the techniques that enabled the evaluation of six-loop Feynman diagrams. Next, we introduce a novel correlation function framework for the computation of static two-body interactions. This approach demonstrates that the static PN factorization theorem stems from a $\mathbb{Z}_2$ symmetry, enabling the direct determination of odd-PN static contributions from lower order data. Using this framework, we derive a closed all order formula encoding the structure of static PN corrections, and determine the complete 7PN static potential. We conclude by discussing extensions to this framework. These advancements will enable more accurate measurements with future observatories, while offering a new perspective on the classical two-body problem. Talk based on 2512.19498 and 2604.14134.

Speaker: Matteo Pegorin (U & INFN Padova)

Session on Future Challenges: Bridging Planckian physics to cosmological observables (convener: Mercedes Martin-Benito)

Conveners: Ed Copeland, Germano Nardini, Giulia Gubitosi, Marek Lewicki, Sofie Marie Koksbang

Reception / Poster session

Tue, June 2

13 General aspects of quantum cosmology

Quantum cosmology is often analyzed in a model-dependent way, following specific quantization schemes. This talk instead focuses on general properties and related questions implied by the common separation of modes into an expanding background and evolving perturbations. While this separation is well-understood classically, it gives rise to important questions about Casimir energies, covariance, and modified dynamics on the quantum level.

Speaker: Martin Bojowald (Penn State U)

14 Singularities and their crossing in gravity and cosmology

We discuss the nature of singularities and possibility of their crossing in gravity and cosmology. We study at which conditions singularities can disappear in quantum cosmology and how quantum particles behave in the vicinity of singularities. Some attempts to develop general approach to the connection between the field reparametrization and the elimination of singularities is presented as well.

Speaker: Alexander Kamenshchik (U & INFN Bologna)

10:10 AM Coffee Break

15 The initial boundary value problem for the Einstein vacuum equations with umbilic boundary

In this talk, we will discuss the initial boundary value problem in general relativity from a mathematical point of view. We will first make the analogy to the classical Cauchy problem for the Einstein equations, first resolved by Yvonne Choquet-Bruhat in 1952, and highlight some desired properties that a potential treatment of timelike boundaries should have. Then, we will go over the various technical difficulties that arise in such an endeavor. The main result that we will present in the end concerns the local well-posedness of the problem for homogeneous Neumann conditions, in geometric terms, when the boundary is umbilic. This is joint work with Jacques Smulevici.

Speaker: Grigorios Fournodavlos (U Crete)

16 Structures and dynamics in slowly expanding cosmological spacetimes

I will survey some recent joint work studying the dynamics of relativistic and non-relativistic fluids on cosmological FLRW spacetimes. Interesting nonlinear features arise from the dynamics, that can lead to finite-time shock formation in a mechanism unlike the classical Jeans instability.

Speaker: Zoe Wyatt (U Cambridge)

17 Gravitational waves from early universe phase transitions

In extensions of the Standard Model of particle physics, phase changes associated with symmetry-breaking or confinement could have been first order transitions, featuring the nucleation, expansion and merger of bubbles of the newly stable phase. The resulting sound waves would have been a powerful source of gravitational radiation, containing information about the thermodynamic parameters of the transition. I will review ongoing work on characterising the spectrum of gravitational radiation from early universe phase transitions and prospects for observing an electroweak-scale transition at the future space-based gravitational wave detector LISA.

Speaker: Mark Hindmarsh (U Helsinki & U Sussex)

12:25 PM Lunch Break

18 Cracks in the standard cosmological model: Anomalies, tensions, and hints of new physics

The ΛCDM model has long served as the standard paradigm in cosmology, offering a remarkably successful description of the Universe’s evolution. Yet, as observational precision continues to improve, persistent tensions have emerged across a range of probes, including the well-known Hubble constant discrepancy. While individual datasets may each align with ΛCDM, their collective interpretation reveals significant discordances that challenge the model’s internal consistency. In this talk, I will review the most prominent tensions in modern cosmology and assess their implications. I will present recent results pointing to hints of dynamical dark energy and interactions within the dark sector. I will also reflect on the growing influence of methodological choices, such as dataset selection and model assumptions, in shaping our cosmological conclusions.

Speaker: Eleonora Di Valentino (U Sheffield)

Contributed Talks: Tuesday I

19 Heisenberg dynamics of quantum particle in curved spacetime

The quantum dynamics of a particle, with or without spin, in curved spacetime is analyzed from the Heisenberg picture, hence with a focus on the observables. It is based on a covariant Hamiltonian formulation. For the spin-zero particle, quantum geodesic equations are obtained as differential equations governing the evolution of the position observables. The formulation is not compatible with the usual approach based on the Schrödinger wavefunction representation, and has theoretically desirable features over the latter. Our approach suggests an alternative path to quantum gravitation based on the observables. While the classical, commutative, limit of the equations gives the geometric geodesic equation of real-number manifolds, the noncommutativity of the quantum observables gives a nontrivial form of the results. The (Weak) Equivalence Principle is maintained. Generalization to include spin is straightforward. Interesting conceptual implications and some results under black hole metrics will be discussed. (Class. Quantum Grav. 41, 085013 (2024) ; Chin. J. Phys. 96, 690-699; 97, 1293-1305 (2025); manuscript in preparation.)

Speaker: Otto Kong (NCU Taiwan)

20 Quantum measure in Regge calculus

A. D’Adda (2021) has shown that by assigning a length to each link and coordinates to each labelled vertex, one can define a non-Euclidean flat metric and a reference frame within each simplex that is invariant under GL(n,R). In this formulation, the metric tensor is a function of both the link lengths and the vertex coordinates. In this talk, we show that by performing an appropriate gauge fixing of the metric tensor, it is possible to compute explicitly the Faddeev–Popov determinant entering the quantum measure of Regge calculus. The determination of this measure has been a longstanding open problem, and our results represent a step toward its resolution. A well-defined quantum measure has important implications for numerical investigations of quantum gravity. In particular, our approach may lead to improved simulations in Quantum Regge Calculus and could also have consequences for Dynamical Triangulations and, potentially, for Causal Dynamical Triangulations.

Speaker: Gabriele Gionti (Vatican Observatory)

21 When dimensions become quantum: Toward a new approach to quantum gravity

In a number of different approaches to quantum gravity, the effective number of spatial dimensions has been found to change with energy scale. Motivated by this phenomenon, we propose quantum systems in which the number of spatial dimensions is promoted to a dynamical quantum variable. This opens new avenues for constructing gravitational systems in which the very notion of dimensionality becomes quantum. During the talk, we will discuss the fundamentals of our formalism and its possible applications to quantum gravity and cosmology.

Speaker: Mikolaj Myszkowski (U Southern Denmark)

3:30 PM Coffee Break

Contributed Talks: Tuesday II

22 Late-time phase transitions in cosmological simulations

Recent cosmological data from DESI motivate modelling of extensions to the standard model that modifies late-time phenomenology, while maintaining concordance with early Universe, local laboratory and solar system experiments. One promising way to do so is to have additional cosmologically relevant degrees of freedom that are negligible until they are activated in underdensities of the late-time Universe by a phase transition governed by the ambient matter density. The interplay with nonlinearities in late-time matter structures provides new signatures, such as environment-dependent clustering. Finding predictions requires numerical simulations. I will present results on the matter 1-point function, gravitational wave emission and some future directions.

Speaker: Øyvind Christiansen (Czech Academy of Sciences)

23 Cosmological first-order phase transitions with large bubbles: Beyond conformal fluid and flat spacetime

Using semi-analytical models, we investigate the power spectrum of gravitational waves generated by sound waves in the plasma during a first-order phase transition in new unexplored scenarios. (i) The phase transition is accompanied by a change of the equation of state from that of pure radiation. This modifies the shape of the gravitational wave power spectrum as a consequence of both sound and gravitational waves propagating across a non-conformal fluid. (ii) In addition, we investigate the novel limit where the phase transition completes with large bubbles, by which we mean that the mean bubble spacing R∗​ is a non-negligible fraction of the Hubble length 1/H∗. Since the amplitude of the gravitational wave signal increases with R∗H∗​, this is also the loud signal regime. In this regime the effects of gravity, hitherto neglected, become relevant. We here consider the first general relativistic corrections beyond the Universe expansion. This work improves the current estimation of the gravitational waves power spectrum from first order phase transitions and expands the possible scenarios of transitions that can be tested by gravitational wave detectors.

Speaker: Lorenzo Giombi (U Helsinki)

24 Gravitational wave signals from cosmic strings with backreaction

Cosmic strings are one-dimensional topological defects, which are formed during symmetry-breaking phase transitions with a non-simply connected vacuum manifold. If they exist, they are expected to generate gravitational waves, which we might be able to detect with future gravitational wave observatories such as LISA or Einstein Telescope. In particular, local features on the strings, such as kinks and cusps, would produce distinctive gravitational waveforms. The evolution of these strings can be approximately modelled using Nambu-Goto dynamics, which can then be used to calculate the gravitational wave signals they emit. In previous such calculations the effect of the gravitational backreaction of the string onto itself was neglected. However, since the gravitational self-force is particularly important for kinks and cusps we would expect it to especially affect the gravitational waves produced by these features. By modelling how simple cosmic string loops evolve under the effect of their own gravity we find that the gravitational backreaction suppresses the formation of cusps. This subsequently leads to a high-frequency cut-off in the gravitational wave signal they produce, which has important implications for detecting such signals with future observatories.

Speaker: Lasse Gerblich (U Cambridge)

Session on Future Challenges: Cosmology beyond ΛCDM - What should theory do next? (convener: Giulia Gubitosi)

Conveners: Eleonora Di Valentino, Ruth Durrer, Eugene Lim, David Mota

Conference dinner

Conference dinner at the restaurant Phileas Fogg.
Address: Skagen 27, 4006 Stavanger

Wed, June 3

25 Primordial black holes: formation and statistics

I will present the latest understanding on black hole´s formation in an expanding universe and discuss the statistics of Type I black holes.

Speaker: Cristiano Germani (U Barcelona)

26 Probing the big bang with numerical relativity

I will talk about how numerical relativity is now being used to solve hitherto intractable strong gravity and highly complex systems in the early universe. As examples, I will discuss on how we are using numerical relativity to understand how inflation may or may not occur, and also how we are now using numerical relativity to probe the stability of compact extra dimensions.

Speaker: Eugene Lim (King's College London)

10:10 AM Coffee Break

Contributed Talks: Wednesday

27 On the diversity of dwarf galaxies in multi-component dark matter scenarios

The observed diversity of small-scale structures suggests that dark matter may be multi-component. Ultra-faint dwarf spheroidal galaxies exhibit both cored and cuspy density profiles, which are difficult to reconcile if all dark matter components share purely adiabatic initial conditions. In this work, we investigate a scenario in which a subdominant dark matter component carries isocurvature perturbations. Using N-body simulations, we explore whether such perturbations can influence the formation of satellite galaxies and contribute to diversity in halo properties at small scales. This framework provides a potential connection between early-universe physics and the structure of dwarf galaxies.

Speaker: Jessica Lopez-Sanchez (CEICO Prague)

28 Non-linear dynamics during kination

We investigate the effects of large scalar inhomogeneities during the kination epoch, a period in which the universe’s dynamics are dominated by the kinetic energy of a scalar field, by fully evolving the Einstein equations using numerical relativity. By tracking the non-linear growth of scalar perturbations with both sub-horizon and super-horizon initial wavelengths, we are able to compare their evolution to perturbative results. Our key findings show that in the deep sub-horizon limit, the perturbative behaviour remains valid, whereas in the super-horizon regime, non-linear dynamics exhibit a much richer phenomenology. Finally, we discuss the possibility of primordial black hole formation from the collapse of such perturbations and assess whether this process could serve as a viable mechanism to reheat the universe in the post-inflationary era.

Speaker: Panagiotis Giannadakis (King's College London)

29 Real-time cosmology in relativistic N-body simulations

The current generation of telescopes will be able to detect the real-time change of cosmological observables, in particular the change in redshift and position of sources. This will provide direct dynamical insight into the evolution of the universe and its structures, including the first direct evidence of its accelerated expansion. To interpret these extremely precise measurements, it is essential to understand the influence of cosmic structures on these observables. I will present results from fully relativistic N-body simulations, studying these observables directly on the past light cone, including all effects from light propagation and the structures in the universe.

Speaker: Alexander Oestreicher (U Southern Denmark)

30 Warp drive: A gedankenexperiment taken too far

In this talk, I provide a systematic classification and critical evaluation of warp-drive spacetimes within General Relativity (GR). Moving beyond the popular "creative" approach, I adopt a rigorous "agonistic" methodology to address the recent renaissance of claims regarding physically feasible, positive-energy warp drives. By applying a basic principle, which mandates mathematical consistency within GR prior to physical speculation, we identified fundamental errors and misconceptions in existing literature. I will present a model hierarchy distinguishing between Restricted Warp (R-Warp)--encompassing most proposals--and more generalized configurations. The presentation focuses on demystifying these models through several no-go theorems, e.g.: 1) It is impossible to construct a superluminal R-Warp model that is globally hyperbolic. 2) The ADM energy for R-Warp models is generically zero, exposing the mathematical ambiguity of "total mass" calculations used in many studies. 3) I will contrast the "creative" approach (Synge G-method) with the "realistic" one, highlighting how the former often leads to "fantastic" but unphysical results. Finally, by recalling a proof that R-Warp models fundamentally violate the null energy condition (due to Santiago et al. 2022), we conclude that warp drives are best viewed as Gedankenexperiments for probing the boundaries of GR rather than viable technological blueprints. Time permitting, I will link these spacetimes to cosmological models.

Speaker: Hamed Barzegar (ENS de Lyon)

31 Gravity and topological field theory

Speaker: Eirik Svanes (U Stavanger)

32 Conference Wrap-Up

12:30 PM Lunch Break