Lucas Lombriser

Last updated

Lucas Lombriser (born 12 April 1982) is a Swiss National Science Foundation Professor at the Department of Theoretical Physics, University of Geneva. [1] His research is in Theoretical Cosmology, Dark Energy, and Alternative Theories of Gravity. In 2020 [2] [3] [4] [5] [6] [7] [8] [9] and 2021 [10] [11] [12] Lombriser proposed that the Hubble tension and other discrepancies between cosmological measurements imply significant evidence that we are living in a Hubble Bubble of 250 million light years in diameter which is 20% less dense than the cosmic average and lowers the locally measured cosmic microwave background temperature over its cosmic average. Previously, in 2019, he has proposed a solution to the cosmological constant problem from arguing that Newton's constant varies globally. [13] [14] [15] [16] [17] [18] [19] In 2015 and 2016, Lombriser predicted the measurement of the gravitational wave speed with a neutron star merger and that this would rule out alternative theories of gravity as the cause of the late-time accelerated expansion of our Universe, [20] [21] [22] [23] [24] a prediction that proved true with GW170817. Lombriser is a member of the Romansh-speaking minority in Switzerland.

Contents

Education and career

Lombriser did a Master in Physics at ETH Zurich in 2008 and completed his PhD at the Institute for Theoretical Physics, University of Zurich in 2011. [1] His thesis advisor was Uroš Seljak. [25] Lombriser did postdoctoral research at the Institute of Cosmology and Gravitation, University of Portsmouth and the Institute of Astronomy, Royal Observatory Edinburgh, University of Edinburgh. He joined the Department of Theoretical Physics, University of Geneva in January 2018 on a Swiss National Science Foundation Professorship.

He is an Affiliate Member of the Higgs Centre for Theoretical Physics, University of Edinburgh. [26]

Research

Lombriser's research is in Theoretical Cosmology, Dark Energy, and Alternative Theories of Gravity. In 2010 he was part of a research group that succeeded in making the first measurement of the quantity, a model-independent estimator for gravitational interactions at cosmological distances. [27] [28] In 2015 and 2016, Lombriser predicted the measurement of the gravitational wave speed with a neutron star merger and that this would rule out alternative theories of gravity as the cause of the late-time accelerated expansion of our Universe. [20] [21] [22] [23] [24] This prediction and its implications became reality with GW170817. In 2019, he proposed the additional global variation of the General Relativistic Einstein-Hilbert action with respect to Newton's constant. [13] [16] [14] [15] [17] [18] This leads to a constraint equation upon Einstein's field equations which, after evaluation over the observable Universe, provides a solution to the decades-old cosmological constant problem. In March 2020 Lombriser proposed that the much-debated Hubble tension implies significant evidence that we are living in a Hubble Bubble that is 250 million light years in diameter and is 20% less dense than the cosmic average. [2] [3] [4] [5] [6] [7] In April 2021 his team showed that this results in a higher cosmic microwave background temperature than measured locally, which eases further cosmological tensions. [10] [11] [12]

Lombriser is involved in the Euclid space telescope mission of the European Space Agency (ESA) and the Euclid Consortium. He is also involved in the ESA Laser Interferometer Space Antenna (LISA) gravitational wave observatory. [29] He is the PI of the DeepThought Project. [30]

In June 2023, Lombriser reported an alternative way of interpreting the available scientific data which suggested that the notion of an expanding universe may be more a "mirage" than an actuality. [31] [32]

Media

Lombriser has given several interviews on his research work and life in the Swiss Romansh-speaking media, including TV, [33] radio, [34] and newspaper articles. [35] [36] [37] He has also spoken on BBC Radio Scotland. [38] His research works from 2010, [27] [28] 2016, [20] [21] [22] [23] [24] 2019, [13] [14] [15] [16] [17] [18] 2020, [2] [3] [4] [5] [6] [7] and 2021 [10] [11] [12] have received broad attention by news outlets worldwide.

Related Research Articles

<span class="mw-page-title-main">Big Bang</span> How the universe expanded from a hot, dense state

The Big Bang event is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models of the Big Bang explain the evolution of the observable universe from the earliest known periods through its subsequent large-scale form. These models offer a comprehensive explanation for a broad range of observed phenomena, including the abundance of light elements, the cosmic microwave background (CMB) radiation, and large-scale structure. The overall uniformity of the Universe, known as the flatness problem, is explained through cosmic inflation: a sudden and very rapid expansion of space during the earliest moments. However, physics currently lacks a widely accepted theory of quantum gravity that can successfully model the earliest conditions of the Big Bang.

<span class="mw-page-title-main">Physical cosmology</span> Branch of cosmology which studies mathematical models of the universe

Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of fundamental questions about its origin, structure, evolution, and ultimate fate. Cosmology as a science originated with the Copernican principle, which implies that celestial bodies obey identical physical laws to those on Earth, and Newtonian mechanics, which first allowed those physical laws to be understood.

In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the early universe. The inflationary epoch is believed to have lasted from 10−36 seconds to between 10−33 and 10−32 seconds after the Big Bang. Following the inflationary period, the universe continued to expand, but at a slower rate. The acceleration of this expansion due to dark energy began after the universe was already over 7.7 billion years old.

<span class="mw-page-title-main">General relativity</span> Theory of gravitation as curved spacetime

General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. General relativity generalises special relativity and refines Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time or four-dimensional spacetime. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of second order partial differential equations.

<span class="mw-page-title-main">Cosmological constant</span> Constant representing stress–energy density of the vacuum

In cosmology, the cosmological constant, alternatively called Einstein's cosmological constant, is the constant coefficient of a term that Albert Einstein temporarily added to his field equations of general relativity. He later removed it. Much later it was revived and reinterpreted as the energy density of space, or vacuum energy, that arises in quantum mechanics. It is closely associated with the concept of dark energy.

<span class="mw-page-title-main">Accelerating expansion of the universe</span> Cosmological phenomenon

Observations show that the expansion of the universe is accelerating, such that the velocity at which a distant galaxy recedes from the observer is continuously increasing with time. The accelerated expansion of the universe was discovered in 1998 by two independent projects, the Supernova Cosmology Project and the High-Z Supernova Search Team, which used distant type Ia supernovae to measure the acceleration. The idea was that as type Ia supernovae have almost the same intrinsic brightness, and since objects that are farther away appear dimmer, the observed brightness of these supernovae can be used to measure the distance to them. The distance can then be compared to the supernovae's cosmological redshift, which measures how much the universe has expanded since the supernova occurred; the Hubble law established that the farther away that an object is, the faster it is receding. The unexpected result was that objects in the universe are moving away from one another at an accelerating rate. Cosmologists at the time expected that recession velocity would always be decelerating, due to the gravitational attraction of the matter in the universe. Three members of these two groups have subsequently been awarded Nobel Prizes for their discovery. Confirmatory evidence has been found in baryon acoustic oscillations, and in analyses of the clustering of galaxies.

The ultimate fate of the universe is a topic in physical cosmology, whose theoretical restrictions allow possible scenarios for the evolution and ultimate fate of the universe to be described and evaluated. Based on available observational evidence, deciding the fate and evolution of the universe has become a valid cosmological question, being beyond the mostly untestable constraints of mythological or theological beliefs. Several possible futures have been predicted by different scientific hypotheses, including that the universe might have existed for a finite and infinite duration, or towards explaining the manner and circumstances of its beginning.

<span class="mw-page-title-main">Big Crunch</span> Theoretical scenario for the ultimate fate of the universe

The Big Crunch is a hypothetical scenario for the ultimate fate of the universe, in which the expansion of the universe eventually reverses and the universe recollapses, ultimately causing the cosmic scale factor to reach zero, an event potentially followed by a reformation of the universe starting with another Big Bang. The vast majority of evidence indicates that this hypothesis is not correct. Instead, astronomical observations show that the expansion of the universe is accelerating rather than being slowed by gravity, suggesting that the universe is far more likely to end in heat death. However, there are new theories that suggest that a "Big Crunch-style" event could happen by the way of a Dark energy fluctuation, however this is still being debated amongst scientists.

The Big Bounce is a hypothesized cosmological model for the origin of the known universe. It was originally suggested as a phase of the cyclic model or oscillatory universe interpretation of the Big Bang, where the first cosmological event was the result of the collapse of a previous universe. It receded from serious consideration in the early 1980s after inflation theory emerged as a solution to the horizon problem, which had arisen from advances in observations revealing the large-scale structure of the universe. In the early 2000s, inflation was found by some theorists to be problematic and unfalsifiable in that its various parameters could be adjusted to fit any observations so that the properties of the observable universe are a matter of chance. Alternative pictures, including a Big Bounce may provide a predictive and falsifiable possible solution to the horizon problem, and are under active investigation as of 2017.

Brane cosmology refers to several theories in particle physics and cosmology related to string theory, superstring theory and M-theory.

In particle physics, the hypothetical dilaton particle is a particle of a scalar field that appears in theories with extra dimensions when the volume of the compactified dimensions varies. It appears as a radion in Kaluza–Klein theory's compactifications of extra dimensions. In Brans–Dicke theory of gravity, Newton's constant is not presumed to be constant but instead 1/G is replaced by a scalar field and the associated particle is the dilaton.

<span class="mw-page-title-main">False vacuum decay</span> Hypothetical vacuum, less stable than true vacuum

In quantum field theory, a false vacuum is a hypothetical vacuum that is relatively stable, but not in the most stable state possible. In this condition it is called metastable. It may last for a very long time in this state, but could eventually decay to the more stable one, an event known as false vacuum decay. The most common suggestion of how such a decay might happen in our universe is called bubble nucleation – if a small region of the universe by chance reached a more stable vacuum, this "bubble" would spread.

<span class="mw-page-title-main">Paul Steinhardt</span> American theoretical physicist (born 1952)

Paul Joseph Steinhardt is an American theoretical physicist whose principal research is in cosmology and condensed matter physics. He is currently the Albert Einstein Professor in Science at Princeton University, where he is on the faculty of both the Departments of Physics and of Astrophysical Sciences.

The expansion of the universe is the increase in distance between gravitationally unbound parts of the observable universe with time. It is an intrinsic expansion; the universe does not expand "into" anything and does not require space to exist "outside" it. To any observer in the universe, it appears that all but the nearest galaxies recede at speeds that are proportional to their distance from the observer, on average. While objects cannot move faster than light, this limitation only applies with respect to local reference frames and does not limit the recession rates of cosmologically distant objects.

An inhomogeneous cosmology is a physical cosmological theory which, unlike the currently widely accepted cosmological concordance model, assumes that inhomogeneities in the distribution of matter across the universe affect local gravitational forces enough to skew our view of the Universe. When the universe began, matter was distributed homogeneously, but over billions of years, galaxies, clusters of galaxies, and superclusters have coalesced, and must, according to Einstein's theory of general relativity, warp the space-time around them. While the concordance model acknowledges this fact, it assumes that such inhomogeneities are not sufficient to affect large-scale averages of gravity in our observations. When two separate studies claimed in 1998-1999 that high redshift supernovae were further away than our calculations showed they should be, it was suggested that the expansion of the universe is accelerating, and dark energy, a repulsive energy inherent in space, was proposed to explain the acceleration. Dark energy has since become widely accepted, but it remains unexplained. Accordingly, some scientists continue to work on models that might not require dark energy. Inhomogeneous cosmology falls into this class.

In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. Its primary effect is to drive the accelerating expansion of the universe. Assuming that the lambda-CDM model of cosmology is correct, dark energy is the dominant component of the universe, contributing 68% of the total energy in the present-day observable universe while dark matter and ordinary (baryonic) matter contribute 26% and 5%, respectively, and other components such as neutrinos and photons are nearly negligible. Dark energy's density is very low: 6×10−10 J/m3, much less than the density of ordinary matter or dark matter within galaxies. However, it dominates the universe's mass–energy content because it is uniform across space.

<span class="mw-page-title-main">Nikodem Popławski</span> Polish physicist

Nikodem Janusz Popławski is a Polish theoretical physicist, most widely noted for the hypothesis that every black hole could be a doorway to another universe and that the universe was formed within a black hole which itself exists in a larger universe. This hypothesis was listed by National Geographic and Science magazines among their top ten discoveries of 2010.

A black hole cosmology is a cosmological model in which the observable universe is the interior of a black hole. Such models were originally proposed by theoretical physicist Raj Pathria, and concurrently by mathematician I. J. Good.

The asymptotic safety approach to quantum gravity provides a nonperturbative notion of renormalization in order to find a consistent and predictive quantum field theory of the gravitational interaction and spacetime geometry. It is based upon a nontrivial fixed point of the corresponding renormalization group (RG) flow such that the running coupling constants approach this fixed point in the ultraviolet (UV) limit. This suffices to avoid divergences in physical observables. Moreover, it has predictive power: Generically an arbitrary starting configuration of coupling constants given at some RG scale does not run into the fixed point for increasing scale, but a subset of configurations might have the desired UV properties. For this reason it is possible that — assuming a particular set of couplings has been measured in an experiment — the requirement of asymptotic safety fixes all remaining couplings in such a way that the UV fixed point is approached.

The Buchalter Cosmology Prize, established in 2014, is a prestigious annual prize bestowed by Dr. Ari Buchalter.

References

  1. 1 2 "Lucas Lombriser | Cosmology and Astroparticle Physics - University of Geneva". cosmology.unige.ch.
  2. 1 2 3 Lombriser, Lucas (2020). "Consistency of the local Hubble constant with the cosmic microwave background". Physics Letters B. 803: 135303. arXiv: 1906.12347 . Bibcode:2020PhLB..80335303L. doi: 10.1016/j.physletb.2020.135303 . S2CID   195750638.
  3. 1 2 3 "Solved: The mystery of the expansion of the universe". phys.org.
  4. 1 2 3 swissinfo.ch, S. W. I.; Corporation, a branch of the Swiss Broadcasting. "Womöglich leben wir in einer "Hubble-Bubble"". SWI swissinfo.ch.
  5. 1 2 3 Ferreira, Becky (March 11, 2020). "We Actually Live Inside a Huge Bubble in Space, Physicist Proposes".
  6. 1 2 3 "¿Resuelto el misterio de la velocidad de expansión del Universo?". abc. March 12, 2020.
  7. 1 2 3 red, science ORF at/Agenturen (March 11, 2020). "Leben wir in einer "Hubble-Bubble"?". science.ORF.at.
  8. ↑ "Is our galaxy in a cosmic 'bubble?'". RT America youtube.
  9. ↑ "Best of Last Year: The top Phys.org articles of 2020". phys.org.
  10. 1 2 3 "L'univers serait plus chaud qu'on croyait". Le Matin. 25 May 2021.
  11. 1 2 3 "Expansion des Universums: "Simple Theorie" löst Diskrepanz bei Hubble-Konstante". heise.de.
  12. 1 2 3 "L'Univers serait plus chaud que prévu". sciencesetavenir.fr. June 2021.
  13. 1 2 3 Lombriser, Lucas (2019). "On the cosmological constant problem". Physics Letters B. 797: 134804. arXiv: 1901.08588 . Bibcode:2019PhLB..79734804L. doi: 10.1016/j.physletb.2019.134804 . S2CID   119274583.
  14. 1 2 3 "Providing a solution to the worst-ever prediction in physics". phys.org.
  15. 1 2 3 Lea, Robert (September 10, 2019). "Tackling Cosmological Constant Problem with a new approach". Medium.
  16. 1 2 3 Childers, Tim (6 September 2019). "'Einstein's Biggest Blunder' May Have Finally Been Fixed". livescience.com.
  17. 1 2 3 "Una solución para la peor predicción de la historia de la Física". abc. September 1, 2019.
  18. 1 2 3 "El error más grave de Einstein puede que haya sido al fin resuelto". El Confidencial. September 11, 2019.
  19. ↑ "A new generation takes on the cosmological constant problem". Physics World. 3 March 2021.
  20. 1 2 3 Lombriser, Lucas; Taylor, Andy (2016). "Breaking a dark degeneracy with gravitational waves". Journal of Cosmology and Astroparticle Physics. 2016 (3): 031. arXiv: 1509.08458 . Bibcode:2016JCAP...03..031L. doi:10.1088/1475-7516/2016/03/031. S2CID   73517974.
  21. 1 2 3 Lombriser, Lucas; Lima, Lima (2017). "Challenges to self-acceleration in modified gravity from gravitational waves and large-scale structure". Physics Letters B. 765: 382–385. arXiv: 1602.07670 . Bibcode:2017PhLB..765..382L. doi: 10.1016/j.physletb.2016.12.048 . S2CID   118486016.
  22. 1 2 3 "Challenges to Cosmic Self Acceleration in Modified Gravity from Gravitational Waves and Large-Scale Structure". YouTube . IPhT-TV. 26 September 2017.
  23. 1 2 3 Rzetelny, Xaq (February 25, 2017). "Theoretical battle: dark energy vs. modified gravity". Ars Technica.
  24. 1 2 3 "Quest to settle riddle over Einstein's theory may soon be over". phys.org.
  25. ↑ "Lucas Lombriser - The Mathematics Genealogy Project". www.genealogy.math.ndsu.nodak.edu.
  26. ↑ "Higgs Centre for Theoretical Physics". higgs.ph.ed.ac.uk.
  27. 1 2 Reyes, Reinabelle; Mandelbaum, Rachel; Seljak, Uroš; Baldauf, Tobias; Gunn, James; Lombriser, Lucas; Smith, Robert (2010). "Confirmation of general relativity on large scales from weak lensing and galaxy velocities". Nature. 464 (7286): 256–258. arXiv: 1003.2185 . Bibcode:2010Natur.464..256R. doi:10.1038/nature08857. PMID   20220843. S2CID   205219902.
  28. 1 2 "Ein weiterer Triumph für Einstein | NZZ". Neue Zürcher Zeitung.
  29. ↑ "lombriser | Lisamission.org". www.elisascience.org.
  30. ↑ "The DeepThought β Collaboration". deepthought-beta.net.
  31. ↑ Lea, Robert (20 June 2023). "The expansion of the universe could be a mirage, new theoretical study suggests - New research looking at the cosmological constant problem suggests the expansion of the universe could be an illusion". Live Science . Archived from the original on 20 June 2023. Retrieved 20 June 2023.
  32. ↑ Lombriser, Lucas (2 June 2023). "Cosmology in Minkowski space". Classical and Quantum Gravity . arXiv: 2306.16868 . doi:10.1088/1361-6382/acdb41. Archived from the original on 20 June 2023. Retrieved 20 June 2023.
  33. ↑ "Lucas Lombriser cumprova teoria da Einstein - TV". Play RTR.
  34. ↑ "Bunura: Lucas Lombriser e la cosmologia - Radio". Play RTR.
  35. ↑ "In skywalker da la scienza perscrutescha undas da gravitaziun, La Quotidiana, 2 October 2017" (PDF).
  36. ↑ Astrofisicher Lucas Lombriser, La Quotidiana, 4 June 2018
  37. ↑ "Cosmologia - In sguard en la vita da l'astrofisicher Lucas Lombriser". Radiotelevisiun Svizra Rumantscha (RTR). December 10, 2019.
  38. ↑ "BBC Radio Scotland - Newsdrive - Available now". BBC.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.