#cosmologicalprinciple — Public Fediverse posts

Weekly Update from the Open Journal of Astrophysics 15/08/2026

Although it’s still holiday season for some, it’s time once more for another Saturday update of activity at the Open Journal of Astrophysics. Since the last update we have published a further four papers, bringing the number in Volume 9 (2026) to 171 and the total so far published by OJAp up to 619.

I continue to include the posts made on our Mastodon account (on Fediscience); these announcements also show the DOI for each paper.

The first paper to report this week was published on Monday 10th August in the folder High-Energy Astrophysical Phenomena. “Search for neutrino emission from blazar γ-ray flares accounting for possible neutrino time delays” by Egor Podlesny & Foteini Oikonomou (Norwegian University of Science & Technology, Trondheim, Norway) investigates high-energy neutrino emissions associated with blazar flares, using data from IceCat-1, MOJAVE, CGRaBS, and Fermi-LAT. A slight correlation was found, consistent with the null hypothesis.

You can find the officially accepted version on arXiv here and the announcement on Fediverse here:

https://fediscience.org/@OJ_Astro/117069981161677800

The second paper for this week, published on Tuesday 11th August in the folder Cosmology and Nongalactic Astrophysics is “The velocity coherence scale: a novel probe of cosmic homogeneity and a potential standard ruler” by Leonardo Giani (Swinburne University of Technology), Cullan Howlet (U. Queensland), Chris Blake (Swinburne), Ryan J. Turner (Australia National University) and Tamara M. Davis (U. Queensland) – all in Australia. This paper argues that velocity coherence scale, a measure that identifies the transition point of galaxy motion from correlated to anti-correlated, could potentially characterize the onset of cosmic homogeneity.

The overlay looks like this:

The official version of the paper can be found on arXiv here and the Fediverse announcement here:

https://fediscience.org/@OJ_Astro/117075588846174571

The third paper of the week, also published on Tuesday 11th Augus, but in the folder Astrophysics of Galaxies, is “A GLIMPSE of the 99%: a census of the faintest galaxies during the epoch of reionization and its implications for galaxy formation models” by Hakim Atek (Sorbonne Université, Paris, France) and 21 others based around the world.

The overlay is here:

The official version of the paper can be found on arXiv here and the Fediverse announcement here:

https://fediscience.org/@OJ_Astro/117075737363441518

The fourth and final paper of the week was published on Wednesday 12th August in the folder Astrophysics of Galaxies: “Dust and Grain Size Evolution in Galaxy Simulations: What Matters and What Does Not” by Massimiliano Parente & Desika Narayanan (U. Florida, USA) and Paul Torrey (U. Virginia, USA) presents the first implementation of an evolving dust grain size distribution within a model of galaxy evolution, successfully reproducing key observational constraints and exploring the mechanisms shaping galaxies.

The overlay is here:

The officially-accepted version of the paper can be found on arXiv here and the Fediverse announcement here:

https://fediscience.org/@OJ_Astro/117081036416703046

That’s all for this week. We’re just ticking over at the moment, and steadily building up a backlog of papers to publish while we wait for authors to put their final versions on arXiv. I have a feeling there’s going to be a big splurge sometime. Will it be next week? We’ll find out next Saturday!

Weekly Update from the Open Journal of Astrophysics 15/08/2026

Although it’s still holiday season for some, it’s time once more for another Saturday update of activity at the Open Journal of Astrophysics. Since the last update we have published a further four papers, bringing the number in Volume 9 (2026) to 171 and the total so far published by OJAp up to 619.

I continue to include the posts made on our Mastodon account (on Fediscience); these announcements also show the DOI for each paper.

The first paper to report this week was published on Monday 10th August in the folder High-Energy Astrophysical Phenomena. “Search for neutrino emission from blazar γ-ray flares accounting for possible neutrino time delays” by Egor Podlesny & Foteini Oikonomou (Norwegian University of Science & Technology, Trondheim, Norway) investigates high-energy neutrino emissions associated with blazar flares, using data from IceCat-1, MOJAVE, CGRaBS, and Fermi-LAT. A slight correlation was found, consistent with the null hypothesis.

You can find the officially accepted version on arXiv here and the announcement on Fediverse here:

https://fediscience.org/@OJ_Astro/117069981161677800

The second paper for this week, published on Tuesday 11th August in the folder Cosmology and Nongalactic Astrophysics is “The velocity coherence scale: a novel probe of cosmic homogeneity and a potential standard ruler” by Leonardo Giani (Swinburne University of Technology), Cullan Howlet (U. Queensland), Chris Blake (Swinburne), Ryan J. Turner (Australia National University) and Tamara M. Davis (U. Queensland) – all in Australia. This paper argues that velocity coherence scale, a measure that identifies the transition point of galaxy motion from correlated to anti-correlated, could potentially characterize the onset of cosmic homogeneity.

The overlay looks like this:

The official version of the paper can be found on arXiv here and the Fediverse announcement here:

https://fediscience.org/@OJ_Astro/117075588846174571

The third paper of the week, also published on Tuesday 11th Augus, but in the folder Astrophysics of Galaxies, is “A GLIMPSE of the 99%: a census of the faintest galaxies during the epoch of reionization and its implications for galaxy formation models” by Hakim Atek (Sorbonne Université, Paris, France) and 21 others based around the world.

The overlay is here:

The official version of the paper can be found on arXiv here and the Fediverse announcement here:

https://fediscience.org/@OJ_Astro/117075737363441518

The fourth and final paper of the week was published on Wednesday 12th August in the folder Astrophysics of Galaxies: “Dust and Grain Size Evolution in Galaxy Simulations: What Matters and What Does Not” by Massimiliano Parente & Desika Narayanan (U. Florida, USA) and Paul Torrey (U. Virginia, USA) presents the first implementation of an evolving dust grain size distribution within a model of galaxy evolution, successfully reproducing key observational constraints and exploring the mechanisms shaping galaxies.

The overlay is here:

The officially-accepted version of the paper can be found on arXiv here and the Fediverse announcement here:

https://fediscience.org/@OJ_Astro/117081036416703046

That’s all for this week. We’re just ticking over at the moment, and steadily building up a backlog of papers to publish while we wait for authors to put their final versions on arXiv. I have a feeling there’s going to be a big splurge sometime. Will it be next week? We’ll find out next Saturday!

Weekly Update from the Open Journal of Astrophysics 15/08/2026

Although it’s still holiday season for some, it’s time once more for another Saturday update of activity at the Open Journal of Astrophysics. Since the last update we have published a further four papers, bringing the number in Volume 9 (2026) to 171 and the total so far published by OJAp up to 619.

I continue to include the posts made on our Mastodon account (on Fediscience); these announcements also show the DOI for each paper.

The first paper to report this week was published on Monday 10th August in the folder High-Energy Astrophysical Phenomena. “Search for neutrino emission from blazar γ-ray flares accounting for possible neutrino time delays” by Egor Podlesny & Foteini Oikonomou (Norwegian University of Science & Technology, Trondheim, Norway) investigates high-energy neutrino emissions associated with blazar flares, using data from IceCat-1, MOJAVE, CGRaBS, and Fermi-LAT. A slight correlation was found, consistent with the null hypothesis.

You can find the officially accepted version on arXiv here and the announcement on Fediverse here:

https://fediscience.org/@OJ_Astro/117069981161677800

The second paper for this week, published on Tuesday 11th August in the folder Cosmology and Nongalactic Astrophysics is “The velocity coherence scale: a novel probe of cosmic homogeneity and a potential standard ruler” by Leonardo Giani (Swinburne University of Technology), Cullan Howlet (U. Queensland), Chris Blake (Swinburne), Ryan J. Turner (Australia National University) and Tamara M. Davis (U. Queensland) – all in Australia. This paper argues that velocity coherence scale, a measure that identifies the transition point of galaxy motion from correlated to anti-correlated, could potentially characterize the onset of cosmic homogeneity.

The overlay looks like this:

The official version of the paper can be found on arXiv here and the Fediverse announcement here:

https://fediscience.org/@OJ_Astro/117075588846174571

The third paper of the week, also published on Tuesday 11th Augus, but in the folder Astrophysics of Galaxies, is “A GLIMPSE of the 99%: a census of the faintest galaxies during the epoch of reionization and its implications for galaxy formation models” by Hakim Atek (Sorbonne Université, Paris, France) and 21 others based around the world.

The overlay is here:

The official version of the paper can be found on arXiv here and the Fediverse announcement here:

https://fediscience.org/@OJ_Astro/117075737363441518

The fourth and final paper of the week was published on Wednesday 12th August in the folder Astrophysics of Galaxies: “Dust and Grain Size Evolution in Galaxy Simulations: What Matters and What Does Not” by Massimiliano Parente & Desika Narayanan (U. Florida, USA) and Paul Torrey (U. Virginia, USA) presents the first implementation of an evolving dust grain size distribution within a model of galaxy evolution, successfully reproducing key observational constraints and exploring the mechanisms shaping galaxies.

The overlay is here:

The officially-accepted version of the paper can be found on arXiv here and the Fediverse announcement here:

https://fediscience.org/@OJ_Astro/117081036416703046

That’s all for this week. We’re just ticking over at the moment, and steadily building up a backlog of papers to publish while we wait for authors to put their final versions on arXiv. I have a feeling there’s going to be a big splurge sometime. Will it be next week? We’ll find out next Saturday!

Weekly Update from the Open Journal of Astrophysics 15/08/2026

Although it’s still holiday season for some, it’s time once more for another Saturday update of activity at the Open Journal of Astrophysics. Since the last update we have published a further four papers, bringing the number in Volume 9 (2026) to 171 and the total so far published by OJAp up to 619.

I continue to include the posts made on our Mastodon account (on Fediscience); these announcements also show the DOI for each paper.

The first paper to report this week was published on Monday 10th August in the folder High-Energy Astrophysical Phenomena. “Search for neutrino emission from blazar γ-ray flares accounting for possible neutrino time delays” by Egor Podlesny & Foteini Oikonomou (Norwegian University of Science & Technology, Trondheim, Norway) investigates high-energy neutrino emissions associated with blazar flares, using data from IceCat-1, MOJAVE, CGRaBS, and Fermi-LAT. A slight correlation was found, consistent with the null hypothesis.

You can find the officially accepted version on arXiv here and the announcement on Fediverse here:

https://fediscience.org/@OJ_Astro/117069981161677800

The second paper for this week, published on Tuesday 11th August in the folder Cosmology and Nongalactic Astrophysics is “The velocity coherence scale: a novel probe of cosmic homogeneity and a potential standard ruler” by Leonardo Giani (Swinburne University of Technology), Cullan Howlet (U. Queensland), Chris Blake (Swinburne), Ryan J. Turner (Australia National University) and Tamara M. Davis (U. Queensland) – all in Australia. This paper argues that velocity coherence scale, a measure that identifies the transition point of galaxy motion from correlated to anti-correlated, could potentially characterize the onset of cosmic homogeneity.

The overlay looks like this:

The official version of the paper can be found on arXiv here and the Fediverse announcement here:

https://fediscience.org/@OJ_Astro/117075588846174571

The third paper of the week, also published on Tuesday 11th Augus, but in the folder Astrophysics of Galaxies, is “A GLIMPSE of the 99%: a census of the faintest galaxies during the epoch of reionization and its implications for galaxy formation models” by Hakim Atek (Sorbonne Université, Paris, France) and 21 others based around the world.

The overlay is here:

The official version of the paper can be found on arXiv here and the Fediverse announcement here:

https://fediscience.org/@OJ_Astro/117075737363441518

The fourth and final paper of the week was published on Wednesday 12th August in the folder Astrophysics of Galaxies: “Dust and Grain Size Evolution in Galaxy Simulations: What Matters and What Does Not” by Massimiliano Parente & Desika Narayanan (U. Florida, USA) and Paul Torrey (U. Virginia, USA) presents the first implementation of an evolving dust grain size distribution within a model of galaxy evolution, successfully reproducing key observational constraints and exploring the mechanisms shaping galaxies.

The overlay is here:

The officially-accepted version of the paper can be found on arXiv here and the Fediverse announcement here:

https://fediscience.org/@OJ_Astro/117081036416703046

That’s all for this week. We’re just ticking over at the moment, and steadily building up a backlog of papers to publish while we wait for authors to put their final versions on arXiv. I have a feeling there’s going to be a big splurge sometime. Will it be next week? We’ll find out next Saturday!

Weekly Update from the Open Journal of Astrophysics 15/08/2026

Although it’s still holiday season for some, it’s time once more for another Saturday update of activity at the Open Journal of Astrophysics. Since the last update we have published a further four papers, bringing the number in Volume 9 (2026) to 171 and the total so far published by OJAp up to 619.

I continue to include the posts made on our Mastodon account (on Fediscience); these announcements also show the DOI for each paper.

The first paper to report this week was published on Monday 10th August in the folder High-Energy Astrophysical Phenomena. “Search for neutrino emission from blazar γ-ray flares accounting for possible neutrino time delays” by Egor Podlesny & Foteini Oikonomou (Norwegian University of Science & Technology, Trondheim, Norway) investigates high-energy neutrino emissions associated with blazar flares, using data from IceCat-1, MOJAVE, CGRaBS, and Fermi-LAT. A slight correlation was found, consistent with the null hypothesis.

You can find the officially accepted version on arXiv here and the announcement on Fediverse here:

https://fediscience.org/@OJ_Astro/117069981161677800

The second paper for this week, published on Tuesday 11th August in the folder Cosmology and Nongalactic Astrophysics is “The velocity coherence scale: a novel probe of cosmic homogeneity and a potential standard ruler” by Leonardo Giani (Swinburne University of Technology), Cullan Howlet (U. Queensland), Chris Blake (Swinburne), Ryan J. Turner (Australia National University) and Tamara M. Davis (U. Queensland) – all in Australia. This paper argues that velocity coherence scale, a measure that identifies the transition point of galaxy motion from correlated to anti-correlated, could potentially characterize the onset of cosmic homogeneity.

The overlay looks like this:

The official version of the paper can be found on arXiv here and the Fediverse announcement here:

https://fediscience.org/@OJ_Astro/117075588846174571

The third paper of the week, also published on Tuesday 11th Augus, but in the folder Astrophysics of Galaxies, is “A GLIMPSE of the 99%: a census of the faintest galaxies during the epoch of reionization and its implications for galaxy formation models” by Hakim Atek (Sorbonne Université, Paris, France) and 21 others based around the world.

The overlay is here:

The official version of the paper can be found on arXiv here and the Fediverse announcement here:

https://fediscience.org/@OJ_Astro/117075737363441518

The fourth and final paper of the week was published on Wednesday 12th August in the folder Astrophysics of Galaxies: “Dust and Grain Size Evolution in Galaxy Simulations: What Matters and What Does Not” by Massimiliano Parente & Desika Narayanan (U. Florida, USA) and Paul Torrey (U. Virginia, USA) presents the first implementation of an evolving dust grain size distribution within a model of galaxy evolution, successfully reproducing key observational constraints and exploring the mechanisms shaping galaxies.

The overlay is here:

The officially-accepted version of the paper can be found on arXiv here and the Fediverse announcement here:

https://fediscience.org/@OJ_Astro/117081036416703046

That’s all for this week. We’re just ticking over at the moment, and steadily building up a backlog of papers to publish while we wait for authors to put their final versions on arXiv. I have a feeling there’s going to be a big splurge sometime. Will it be next week? We’ll find out next Saturday!

The local galaxy distribution does not violate the #CosmologicalPrinciple: https://arxiv.org/abs/2607.01172 -> thread https://bsky.app/profile/seshnadathur.bsky.social/post/3mpqaru6xg223 - that's vs. some paper hidden behind a paywall and thus irrelevant anyway, but if you must know https://www.cref.it/en/news-en/anisotropic-structures-identified-on-a-cosmic-scale-new-results-from-desi-data-published-in-nature/ described it.

The local galaxy distribution does not violate the #CosmologicalPrinciple: https://arxiv.org/abs/2607.01172 -> thread https://bsky.app/profile/seshnadathur.bsky.social/post/3mpqaru6xg223 - that's vs. some paper hidden behind a paywall and thus irrelevant anyway, but if you must know https://www.cref.it/en/news-en/anisotropic-structures-identified-on-a-cosmic-scale-new-results-from-desi-data-published-in-nature/ described it.

The local galaxy distribution does not violate the #CosmologicalPrinciple: https://arxiv.org/abs/2607.01172 -> thread https://bsky.app/profile/seshnadathur.bsky.social/post/3mpqaru6xg223 - that's vs. some paper hidden behind a paywall and thus irrelevant anyway, but if you must know https://www.cref.it/en/news-en/anisotropic-structures-identified-on-a-cosmic-scale-new-results-from-desi-data-published-in-nature/ described it.

The local galaxy distribution does not violate the #CosmologicalPrinciple: https://arxiv.org/abs/2607.01172 -> thread https://bsky.app/profile/seshnadathur.bsky.social/post/3mpqaru6xg223 - that's vs. some paper hidden behind a paywall and thus irrelevant anyway, but if you must know https://www.cref.it/en/news-en/anisotropic-structures-identified-on-a-cosmic-scale-new-results-from-desi-data-published-in-nature/ described it.

The local galaxy distribution does not violate the #CosmologicalPrinciple: https://arxiv.org/abs/2607.01172 -> thread https://bsky.app/profile/seshnadathur.bsky.social/post/3mpqaru6xg223 - that's vs. some paper hidden behind a paywall and thus irrelevant anyway, but if you must know https://www.cref.it/en/news-en/anisotropic-structures-identified-on-a-cosmic-scale-new-results-from-desi-data-published-in-nature/ described it.

Structures on Gigaparsec Scales

The latest in a sequence of claims of very large scale structures in the distribution that violate the cosmological principle emerged a week or so ago with a paper in Nature. The paper is behind a paywall but here is the abstract:

I’ve been nudged a few times by various people to comment on that but I’ve been busy recently and didn’t have time to look at the paper in detail. I had a quick look today and the thing that immediately struck me was that I didn’t understand the mock catalogues they used to compare the ΛCDM model with the observations. I still don’t understand that but I’ve stopped worrying about it because today I received a preprint (not behind a paywall, but on arXiv) from Till Sawala with the title The local galaxy distribution does not violate the cosmological principle and the (rather devastating) abstract:

The cosmological principle, which states that the Universe is statistically homogeneous and isotropic on sufficiently large scales, is a foundational assumption of the standard cosmological model. A recent analysis of DESI DR1 galaxy samples reported coherent anisotropic features in the local galaxy distribution extending to gigaparsec scales. If correct, this result would directly contradict the cosmological principle and motivate inhomogeneous cosmologies. Here I analyse the same data and compare them with galaxy distributions predicted by the FLAMINGO cosmological hydrodynamic simulation, performed in the standard ΛCDM paradigm. I show that the apparent anomaly disappears when the correct comoving distance scale is used. I also show that, rather than violating the cosmological principle, the observed structures are consistent with those expected in a ΛCDM Universe.

Here’s Figure 9 of the Sawala paper.

It seems that the authors of the Nature paper, Francesco Sylos Labini and Marco Galoppo, misinterpreted the distances of galaxies in the DESI DR1 sample in a way which boils down to an error of a factor (1+z), where z is the redshift. This hugely increases the scale and distorts the pattern of galaxy clustering. Using the correct comoving distance the measured structures are completely consistent with ΛCDM.

Oops!

P.S. I’ve stopped worrying about the mock surveys…

Structures on Gigaparsec Scales?

The latest in a sequence of claims of very large scale structures in the distribution that violate the cosmological principle emerged a week or so ago with a paper in Nature. The paper is behind a paywall but here is the abstract:

I’ve been nudged a few times by various people to comment on that but I’ve been busy recently and didn’t have time to look at the paper in detail. I had a quick look today and the thing that immediately struck me was that I didn’t understand the mock catalogues they used to compare the ΛCDM model with the observations. I still don’t understand that but I’ve stopped worrying about it because today I received a preprint (not behind a paywall, but on arXiv) from Till Sawala with the title The local galaxy distribution does not violate the cosmological principle and the (rather devastating) abstract:

The cosmological principle, which states that the Universe is statistically homogeneous and isotropic on sufficiently large scales, is a foundational assumption of the standard cosmological model. A recent analysis of DESI DR1 galaxy samples reported coherent anisotropic features in the local galaxy distribution extending to gigaparsec scales. If correct, this result would directly contradict the cosmological principle and motivate inhomogeneous cosmologies. Here I analyse the same data and compare them with galaxy distributions predicted by the FLAMINGO cosmological hydrodynamic simulation, performed in the standard ΛCDM paradigm. I show that the apparent anomaly disappears when the correct comoving distance scale is used. I also show that, rather than violating the cosmological principle, the observed structures are consistent with those expected in a ΛCDM Universe.

Here’s Figure 9 of the Sawala paper.

It seems that the authors of the Nature paper, Francesco Sylos Labini and Marco Galoppo, misinterpreted the distances of galaxies in the DESI DR1 sample in a way which boils down to an error of a factor (1+z)/h, where z is the redshift and h represents the Hubble constant. This hugely increases the scale and distorts the pattern of galaxy clustering. Using the correct comoving distance the measured structures are completely consistent with ΛCDM.

Oops!

P.S. I’ve stopped worrying about the mock surveys…

Structures on Gigaparsec Scales

The latest in a sequence of claims of very large scale structures in the distribution that violate the cosmological principle emerged a week or so ago with a paper in Nature. The paper is behind a paywall but here is the abstract:

I’ve been nudged a few times by various people to comment on that but I’ve been busy recently and didn’t have time to look at the paper in detail. I had a quick look today and the thing that immediately struck me was that I didn’t understand the mock catalogues they used to compare the ΛCDM model with the observations. I still don’t understand that but I’ve stopped worrying about it because today I received a preprint (not behind a paywall, but on arXiv) from Till Sawala with the title The local galaxy distribution does not violate the cosmological principle and the (rather devastating) abstract:

The cosmological principle, which states that the Universe is statistically homogeneous and isotropic on sufficiently large scales, is a foundational assumption of the standard cosmological model. A recent analysis of DESI DR1 galaxy samples reported coherent anisotropic features in the local galaxy distribution extending to gigaparsec scales. If correct, this result would directly contradict the cosmological principle and motivate inhomogeneous cosmologies. Here I analyse the same data and compare them with galaxy distributions predicted by the FLAMINGO cosmological hydrodynamic simulation, performed in the standard ΛCDM paradigm. I show that the apparent anomaly disappears when the correct comoving distance scale is used. I also show that, rather than violating the cosmological principle, the observed structures are consistent with those expected in a ΛCDM Universe.

Here’s Figure 9 of the Sawala paper.

It seems that the authors of the Nature paper, Francesco Sylos Labini and Marco Galoppo, misinterpreted the distances of galaxies in the DESI DR1 sample in a way which boils down to an error of a factor (1+z), where z is the redshift. This hugely increases the scale and distorts the pattern of galaxy clustering. Using the correct comoving distance the measured structures are completely consistent with ΛCDM.

Oops!

P.S. I’ve stopped worrying about the mock surveys…

Structures on Gigaparsec Scales

The latest in a sequence of claims of very large scale structures in the distribution that violate the cosmological principle emerged a week or so ago with a paper in Nature. The paper is behind a paywall but here is the abstract:

I’ve been nudged a few times by various people to comment on that but I’ve been busy recently and didn’t have time to look at the paper in detail. I had a quick look today and the thing that immediately struck me was that I didn’t understand the mock catalogues they used to compare the ΛCDM model with the observations. I still don’t understand that but I’ve stopped worrying about it because today I received a preprint (not behind a paywall, but on arXiv) from Till Sawala with the title The local galaxy distribution does not violate the cosmological principle and the (rather devastating) abstract:

The cosmological principle, which states that the Universe is statistically homogeneous and isotropic on sufficiently large scales, is a foundational assumption of the standard cosmological model. A recent analysis of DESI DR1 galaxy samples reported coherent anisotropic features in the local galaxy distribution extending to gigaparsec scales. If correct, this result would directly contradict the cosmological principle and motivate inhomogeneous cosmologies. Here I analyse the same data and compare them with galaxy distributions predicted by the FLAMINGO cosmological hydrodynamic simulation, performed in the standard ΛCDM paradigm. I show that the apparent anomaly disappears when the correct comoving distance scale is used. I also show that, rather than violating the cosmological principle, the observed structures are consistent with those expected in a ΛCDM Universe.

Here’s Figure 9 of the Sawala paper.

It seems that the authors of the Nature paper, Francesco Sylos Labini and Marco Galoppo, misinterpreted the distances of galaxies in the DESI DR1 sample in a way which boils down to an error of a factor (1+z), where z is the redshift. This hugely increases the scale and distorts the pattern of galaxy clustering. Using the correct comoving distance the measured structures are completely consistent with ΛCDM.

Oops!

P.S. I’ve stopped worrying about the mock surveys…

Structures on Gigaparsec Scales?

The latest in a sequence of claims of very large scale structures in the distribution that violate the cosmological principle emerged a week or so ago with a paper in Nature. The paper is behind a paywall but here is the abstract:

I’ve been nudged a few times by various people to comment on that but I’ve been busy recently and didn’t have time to look at the paper in detail. I had a quick look today and the thing that immediately struck me was that I didn’t understand the mock catalogues they used to compare the ΛCDM model with the observations. I still don’t understand that but I’ve stopped worrying about it because today I received a preprint (not behind a paywall, but on arXiv) from Till Sawala with the title The local galaxy distribution does not violate the cosmological principle and the (rather devastating) abstract:

The cosmological principle, which states that the Universe is statistically homogeneous and isotropic on sufficiently large scales, is a foundational assumption of the standard cosmological model. A recent analysis of DESI DR1 galaxy samples reported coherent anisotropic features in the local galaxy distribution extending to gigaparsec scales. If correct, this result would directly contradict the cosmological principle and motivate inhomogeneous cosmologies. Here I analyse the same data and compare them with galaxy distributions predicted by the FLAMINGO cosmological hydrodynamic simulation, performed in the standard ΛCDM paradigm. I show that the apparent anomaly disappears when the correct comoving distance scale is used. I also show that, rather than violating the cosmological principle, the observed structures are consistent with those expected in a ΛCDM Universe.

Here’s Figure 9 of the Sawala paper.

It seems that the authors of the Nature paper, Francesco Sylos Labini and Marco Galoppo, misinterpreted the distances of galaxies in the DESI DR1 sample in a way which boils down to an error of a factor (1+z)/h, where z is the redshift and h represents the Hubble constant. This hugely increases the scale and distorts the pattern of galaxy clustering. Using the correct comoving distance the measured structures are completely consistent with ΛCDM.

Oops!

P.S. I’ve stopped worrying about the mock surveys…

https://www.europesays.com/ie/565530/ The universe isn’t as uniform as we thought #BigBang #CosmologicalPrinciple #cosmology #DarkMatter #Éire #EnricoFermiResearchInstitute #HubbleTension #IE #Ireland #JamesWebbTelescope #Physics #Science #ScienceAndTechnology #TheConversation #UniverseMeasurement

Fundamental principles of the universe called into question by two physicists

One of the most basic and accepted truths about the universe is that it’s pretty much the same…
#NewsBeep #News #Physics #AU #Australia #cosmologicalprinciple #DarkEnergySpectroscopicInstrument #DavidSpergel #desi #FrancescoSylosLabini #JohnPeacock #KatherineFreese #Science
https://www.newsbeep.com/au/760341/

Fundamental principles of the universe called into question by two physicists

One of the most basic and accepted truths about the universe is that it’s pretty much the same…
#NewsBeep #News #Physics #AU #Australia #cosmologicalprinciple #DarkEnergySpectroscopicInstrument #DavidSpergel #desi #FrancescoSylosLabini #JohnPeacock #KatherineFreese #Science
https://www.newsbeep.com/au/760341/

https://www.europesays.com/uk/1050067/ Fundamental principles of the universe called into question by two physicists #CosmologicalPrinciple #DarkEnergySpectroscopicInstrument #DavidSpergel #DESI #FrancescoSylosLabini #JohnPeacock #KatherineFreese #Physics #Science #UK #UnitedKingdom

Fundamental principles of the universe called into question by two physicists

One of the most basic and accepted truths about the universe is that it’s pretty much the same…
#NewsBeep #News #Physics #cosmologicalprinciple #DarkEnergySpectroscopicInstrument #DavidSpergel #DESI #FrancescoSylosLabini #JohnPeacock #KatherineFreese #Science #UK #UnitedKingdom
https://www.newsbeep.com/uk/658190/

https://www.europesays.com/ie/554189/ Fundamental principles of the universe called into question by two physicists #CosmologicalPrinciple #DarkEnergySpectroscopicInstrument #DavidSpergel #DESI #Éire #FrancescoSylosLabini #IE #Ireland #JohnPeacock #KatherineFreese #Physics #Science

Fundamental principles of the universe called into question by two physicists

One of the most basic and accepted truths about the universe is that it’s pretty much the same…
#NewsBeep #News #US #USA #UnitedStates #UnitedStatesOfAmerica #Physics #cosmologicalprinciple #DarkEnergySpectroscopicInstrument #DavidSpergel #DESI #FrancescoSylosLabini #JohnPeacock #KatherineFreese #Science
https://www.newsbeep.com/us/725934/

Fundamental principles of the universe called into question by two physicists

One of the most basic and accepted truths about the universe is that it’s pretty much the same…
#NewsBeep #News #US #USA #UnitedStates #UnitedStatesOfAmerica #Physics #cosmologicalprinciple #DarkEnergySpectroscopicInstrument #DavidSpergel #DESI #FrancescoSylosLabini #JohnPeacock #KatherineFreese #Science
https://www.newsbeep.com/us/725934/

The Cosmological Principle holds that the universe, at large scales, is homogeneous and isotropic for all observers—implying no location is special. It is the foundational assumption of modern cosmology.

#Cosmology #CosmologicalPrinciple

The Cosmological Principle holds that the universe, at large scales, is homogeneous and isotropic for all observers—implying no location is special. It is the foundational assumption of modern cosmology.

#Cosmology #CosmologicalPrinciple

The Cosmological Principle holds that the universe, at large scales, is homogeneous and isotropic for all observers—implying no location is special. It is the foundational assumption of modern cosmology.

#Cosmology #CosmologicalPrinciple

The Cosmological Principle holds that the universe, at large scales, is homogeneous and isotropic for all observers—implying no location is special. It is the foundational assumption of modern cosmology.

#Cosmology #CosmologicalPrinciple

Astronomy is facing a real #Cosmology crisis. New observations clash with theory: vast structures defy the #CosmologicalPrinciple, the #HubbleTension persists, and #JWST reveals mature galaxies far earlier than expected. Combined with puzzles in #DarkMatter and #DarkEnergy, the evidence suggests our standard model is incomplete. Rather than doom, this may be a historic “#MercuryMoment” — a rare phase where contradictions drive breakthroughs and reshape our view of the universe.

JWST’s Deep Field Observations Contravene Cosmological Principle
James Webb Space Telescope’s deep field observations under JWST Advanced Deep Extragalactic Survey (JADES)...........
#CosmologicalPrinciple #galaxy #JADES #JWST #JWSTAdvancedDeepExtragalacticSurvey #milkyway
Umesh Prasad

https://www.scientificeuropean.co.uk/sciences/space/jwsts-deep-field-observations-contravene-cosmological-principle/

JWST’s Deep Field Observations Contravene Cosmological Principle
James Webb Space Telescope’s deep field observations under JWST Advanced Deep Extragalactic Survey (JADES)...........
#CosmologicalPrinciple #galaxy #JADES #JWST #JWSTAdvancedDeepExtragalacticSurvey #milkyway
Umesh Prasad

https://www.scientificeuropean.co.uk/sciences/space/jwsts-deep-field-observations-contravene-cosmological-principle/

JWST’s Deep Field Observations Contravene Cosmological Principle
James Webb Space Telescope’s deep field observations under JWST Advanced Deep Extragalactic Survey (JADES)...........
#CosmologicalPrinciple #galaxy #JADES #JWST #JWSTAdvancedDeepExtragalacticSurvey #milkyway
Umesh Prasad

https://www.scientificeuropean.co.uk/sciences/space/jwsts-deep-field-observations-contravene-cosmological-principle/

JWST’s Deep Field Observations Contravene Cosmological Principle
James Webb Space Telescope’s deep field observations under JWST Advanced Deep Extragalactic Survey (JADES)...........
#CosmologicalPrinciple #galaxy #JADES #JWST #JWSTAdvancedDeepExtragalacticSurvey #milkyway
Umesh Prasad

https://www.scientificeuropean.co.uk/sciences/space/jwsts-deep-field-observations-contravene-cosmological-principle/

JWST’s Deep Field Observations Contravene Cosmological Principle
James Webb Space Telescope’s deep field observations under JWST Advanced Deep Extragalactic Survey (JADES)...........
#CosmologicalPrinciple #galaxy #JADES #JWST #JWSTAdvancedDeepExtragalacticSurvey #milkyway
Umesh Prasad

https://www.scientificeuropean.co.uk/sciences/space/jwsts-deep-field-observations-contravene-cosmological-principle/

Timescape versus Dark Energy?

Just before the Christmas break I noticed a considerable amount of press coverage claiming that Dark Energy doesn’t exist. Much of the media discussion is closely based on a press release produced by the Royal Astronomical Society. Despite the excessive hype, and consequent initial scepticism, I think the paper has some merit and raises some interesting issues.

The main focus of the discussion is a paper (available on arXiv here) by Seifert et al. with the title Supernovae evidence for foundational change to cosmological models. This paper is accompanied by a longer article called Cosmological foundations revisited with Pantheon+ (also available on arXiv) by a permutation of the same authors, which goes into more detail about the analysis of supernova observations. If you want some background, the “standard” Pantheon+ supernova analysis is described in this paper. The reanalysis presented in the recent papers is motivated an idea called the Timescape model, which is not new. It was discussed by David Wiltshire (one of the authors of the recent papers) in 2007 here and in a number of subsequent papers; there’s also a long review article by Wiltshire here (dated 2013).

So what’s all the fuss about?

In the standard cosmological model we assume that, when sufficiently coarse-grained, the Universe obeys the Cosmological Principle, i.e. that it is homogeneous and isotropic. This implies that the space-time is described by a Friedmann–Lemaître–Robertson–Walker metric (FLRW) metric. Of course we know that the Universe is not exactly smooth. There is a complex cosmic web of galaxies, filaments, clusters, and giant voids which comprise the large-scale structure of the Universe. In the standard cosmological model these fluctuations are treated as small perturbations on a smooth background which evolve linearly on large scales and don’t have a significant effect on the global evolution of the Universe.

This standard model is very successful in accounting for many things but only at the expense of introducing dark energy whose origin is uncertain but which accounts for about 70% of the energy density of the Universe. Among other things, this accounts for the apparent acceleration of the Universe inferred from supernovae measurements.

The approach taken in the Timescape model is to dispense with the FLRW metric, and the idea of separating the global evolution from the inhomogeneities. The idea instead is that the cosmic structure is essentially non-linear so there is no “background metric”. In this model, cosmological observations can not be analysed within the standard framework which relies on the FLRW assumption. Hence the need to reanalyse the supernova data. The name Timescape refers to the presence of significant gravitational time-dilation effects in this model as distinct from the standard model.

I wrote before in the context of a different paper:

….the supernovae measurements do not directly measure cosmic acceleration. If one tries to account for them with a model based on Einstein’s general relativity and the assumption that the Universe is on large-scales is homogeneous and isotropic and with certain kinds of matter and energy then the observations do imply a universe that accelerates. Any or all of those assumptions may be violated (though some possibilities are quite heavily constrained). In short we could, at least in principle, simply be interpreting these measurements within the wrong framework…

So what to make of the latest papers? I have to admit that I didn’t follow all the steps of the supernova reanalysis. I hope an expert can comment on this! I will therefore restrict myself to some general comments.

• My attitude to the standard cosmological model is that it is simply a working hypothesis and we should not elevate it to a status any higher than that. It is based not only on the Cosmological Principle (which could be false), but on the universal applicability of general relativity (which might not be true), and on a number of other assumptions that might not be true either.
• It is important to recognize that one of the reasons that the standard cosmology is the front-runner is that it provides a framework that enables relatively straightforward prediction and interpretation of cosmological measurements. That goes not only for supernova measurements but also for the cosmic microwave background, galaxy clustering, gravitational lensing, and so on. This is much harder to do accurately in the Timescape model simply because the equations involved are much more complex; there are few exact solutions of Einstein’s equations that can help. It is important that people work on alternatives such as this.
• Second, the idea that inhomogeneities might be much more important than assumed in the standard model has been discussed extensively in the literature over the last twenty years or so under the heading “backreaction”. My interpretation of the current state of play is that there are many unresolved questions, largely because of technical difficulties. See, for example, work by Thomas Buchert (here and, with many other collaborators here) and papers by Green & Wald (here and here). Nick Kasiser also wrote about it here.
• The new papers under discussion focus entirely on supernovae measurements. It must be recognized that these provide just one of the pillars supporting the standard cosmology. Over the years, many alternative models have been suggested that claim to “fix” some alleged problem with cosmology only to find that it makes other issues worse. That’s not a reason to ignore departures from the standard framework, but it is an indication that we have a huge amount of data and we’re not allowed to cherry-pick what we want. We have to fit it all. The strongest evidence in favour of the FLRW framework actually comes from the cosmic microwave background (CMB) with the supernovae provide corroboration. I would need to see a detailed prediction of the anisotropy of the CMB before being convinced.
• The Timescape model is largely based on the non-linear expansion of cosmic voids. These are undoubtedly important, and there has been considerable observational and theoretical activity in understanding them and their evolution in the standard model. It is not at all obvious to me that the voids invoked to explain the apparent acceleration of the Universe are consistent with what we actually see in our surveys. That is something else to test.
• Finally, the standard cosmology includes a prescription for the initial conditions from which the present inhomogeneities grew. Where does the cosmic web come from in the Timescape model?

Anyway, I’m sure there’ll be a lot of discussion of this in the next few weeks as cosmologists return to the Universe from their Christmas holidays!

Comments are welcome through the box below, especially from people who have managed to understand the cos.

#arXiv241215143 #CosmicWeb_ #cosmologicalPrinciple #DarkEnergy #Pantheon #supernovae #Timescape #timescapeModel

Timescape versus Dark Energy?

Just before the Christmas break I noticed a considerable amount of press coverage claiming that Dark Energy doesn’t exist. Much of the media discussion is closely based on a press release produced by the Royal Astronomical Society. Despite the excessive hype, and consequent initial scepticism, I think there are some interesting issues.

The main focus of the discussion is a paper (available on arXiv here) by Seifert et al. with the title Supernovae evidence for foundational change to cosmological models. This paper is accompanied by a longer article called Cosmological foundations revisited with Pantheon+ (also available on arXiv) by a permutation of the same authors, which goes into more detail about the analysis of supernova observations. If you want some background, the “standard” Pantheon+ supernova analysis is described in this paper. The reanalysis presented in the recent papers is motivated an idea called the Timescape model, which is not new. It was discussed by David Wiltshire (one of the authors of the recent papers) in 2007 here and in a number of subsequent papers; there’s also a long review article by Wiltshire here (dated 2013).

So what’s all the fuss about?

In the standard cosmological model we assume that, when sufficiently coarse-grained, the Universe obeys the Cosmological Principle, i.e. that it is homogeneous and isotropic. This implies that the space-time is described by a Friedmann–Lemaître–Robertson–Walker metric (FLRW) metric. Of course we know that the Universe is not exactly smooth. There is a complex cosmic web of galaxies, filaments, clusters, and giant voids which comprise the large-scale structure of the Universe. In the standard cosmological model these fluctuations are treated as small perturbations on a smooth background which evolve linearly on large scales and don’t have a significant effect on the global evolution of the Universe.

This standard model is very successful in accounting for many things but only at the expense of introducing dark energy whose origin is uncertain but which accounts for about 70% of the energy density of the Universe. Among other things, this accounts for the apparent acceleration of the Universe inferred from supernovae measurements.

The approach taken in the Timescape model is to dispense with the FLRW metric, and the idea of separating the global evolution from the inhomogeneities. The idea instead is that the cosmic structure is essentially non-linear so there is no “background metric”. In this model, cosmological observations can not be analysed within the standard framework which relies on the FLRW assumption. Hence the need to reanalyse the supernova data. The name Timescape refers to the presence of significant gravitational time-dilation effects in this model as distinct from the standard model.

I wrote before in the context of a different paper:

….the supernovae measurements do not directly measure cosmic acceleration. If one tries to account for them with a model based on Einstein’s general relativity and the assumption that the Universe is on large-scales is homogeneous and isotropic and with certain kinds of matter and energy then the observations do imply a universe that accelerates. Any or all of those assumptions may be violated (though some possibilities are quite heavily constrained). In short we could, at least in principle, simply be interpreting these measurements within the wrong framework…

So what to make of the latest papers? I have to admit that I didn’t follow all the steps of the supernova reanalysis. I hope an expert can comment on this! I will therefore restrict myself to some general comments.

• My attitude to the standard cosmological model is that it is simply a working hypothesis and we should not elevate it to a status any higher than that. It is based not only on the Cosmological Principle (which could be false), but on the universal applicability of general relativity (which might not be true), and on a number of other assumptions that might not be true either.
• It is important to recognize that one of the reasons that the standard cosmology is the front-runner is that it provides a framework that enables relatively straightforward prediction and interpretation of cosmological measurements. That goes not only for supernova measurements but also for the cosmic microwave background, galaxy clustering, gravitational lensing, and so on. This is much harder to do accurately in the Timescape model simply because the equations involved are much more complex; there are few exact solutions of Einstein’s equations that can help. It is important that people work on alternatives such as this.
• Second, the idea that inhomogeneities might be much more important than assumed in the standard model has been discussed extensively in the literature over the last twenty years or so under the heading “backreaction”. My interpretation of the current state of play is that there are many unresolved questions, largely because of technical difficulties. See, for example, work by Thomas Buchert (here and, with many other collaborators here) and papers by Green & Wald (here and here). Nick Kasiser also wrote about it here.
• The new papers under discussion focus entirely on supernovae measurements. It must be recognized that these provide just one of the pillars supporting the standard cosmology. Over the years, many alternative models have been suggested that claim to “fix” some alleged problem with cosmology only to find that it makes other issues worse. That’s not a reason to ignore departures from the standard framework, but it is an indication that we have a huge amount of data and we’re not allowed to cherry-pick what we want. We have to fit it all. The strongest evidence in favour of the FLRW framework actually comes from the cosmic microwave background (CMB) with the supernovae provide corroboration. I would need to see a detailed prediction of the anisotropy of the CMB before being convinced.
• The Timescape model is largely based on the non-linear expansion of cosmic voids. These are undoubtedly important, and there has been considerable observational and theoretical activity in understanding them and their evolution in the standard model. It is not at all obvious to me that the voids invoked to explain the apparent acceleration of the Universe are consistent with what we actually see in our surveys. That is something else to test.
• Finally, the standard cosmology includes a prescription for the initial conditions from which the present inhomogeneities grew. Where does the cosmic web come from in the Timescape model?

Anyway, I’m sure there’ll be a lot of discussion of this in the next few weeks as cosmologists return to the Universe from their Christmas holidays!

Comments are welcome through the box below, especially from people who have managed to understand the cos.

#arXiv241215143 #CosmicWeb_ #cosmologicalPrinciple #DarkEnergy #Pantheon #supernovae #Timescape #timescapeModel

Timescape versus Dark Energy?

Just before the Christmas break I noticed a considerable amount of press coverage claiming that Dark Energy doesn’t exist. Much of the media discussion is closely based on a press release produced by the Royal Astronomical Society. Despite the excessive hype, and consequent initial scepticism, I think there are some interesting issues.

The main focus of the discussion is a paper (available on arXiv here) by Seifert et al. with the title Supernovae evidence for foundational change to cosmological models. This paper is accompanied by a longer article called Cosmological foundations revisited with Pantheon+ (also available on arXiv) by a permutation of the same authors, which goes into more detail about the analysis of supernova observations. If you want some background, the “standard” Pantheon+ supernova analysis is described in this paper. The reanalysis presented in the recent papers is motivated an idea called the Timescape model, which is not new. It was discussed by David Wiltshire (one of the authors of the recent papers) in 2007 here and in a number of subsequent papers; there’s also a long review article by Wiltshire here (dated 2013).

So what’s all the fuss about?

In the standard cosmological model we assume that, when sufficiently coarse-grained, the Universe obeys the Cosmological Principle, i.e. that it is homogeneous and isotropic. This implies that the space-time is described by a Friedmann–Lemaître–Robertson–Walker metric (FLRW) metric. Of course we know that the Universe is not exactly smooth. There is a complex cosmic web of galaxies, filaments, clusters, and giant voids which comprise the large-scale structure of the Universe. In the standard cosmological model these fluctuations are treated as small perturbations on a smooth background which evolve linearly on large scales and don’t have a significant effect on the global evolution of the Universe.

This standard model is very successful in accounting for many things but only at the expense of introducing dark energy whose origin is uncertain but which accounts for about 70% of the energy density of the Universe. Among other things, this accounts for the apparent acceleration of the Universe inferred from supernovae measurements.

The approach taken in the Timescape model is to dispense with the FLRW metric, and the idea of separating the global evolution from the inhomogeneities. The idea instead is that the cosmic structure is essentially non-linear so there is no “background metric”. In this model, cosmological observations can not be analysed within the standard framework which relies on the FLRW assumption. Hence the need to reanalyse the supernova data. The name Timescape refers to the presence of significant gravitational time-dilation effects in this model as distinct from the standard model.

I wrote before in the context of a different paper:

….the supernovae measurements do not directly measure cosmic acceleration. If one tries to account for them with a model based on Einstein’s general relativity and the assumption that the Universe is on large-scales is homogeneous and isotropic and with certain kinds of matter and energy then the observations do imply a universe that accelerates. Any or all of those assumptions may be violated (though some possibilities are quite heavily constrained). In short we could, at least in principle, simply be interpreting these measurements within the wrong framework…

So what to make of the latest papers? I have to admit that I didn’t follow all the steps of the supernova reanalysis. I hope an expert can comment on this! I will therefore restrict myself to some general comments.

• My attitude to the standard cosmological model is that it is simply a working hypothesis and we should not elevate it to a status any higher than that. It is based not only on the Cosmological Principle (which could be false), but on the universal applicability of general relativity (which might not be true), and on a number of other assumptions that might not be true either.
• It is important to recognize that one of the reasons that the standard cosmology is the front-runner is that it provides a framework that enables relatively straightforward prediction and interpretation of cosmological measurements. That goes not only for supernova measurements but also for the cosmic microwave background, galaxy clustering, gravitational lensing, and so on. This is much harder to do accurately in the Timescape model simply because the equations involved are much more complex; there are few exact solutions of Einstein’s equations that can help. It is important that people work on alternatives such as this.
• Second, the idea that inhomogeneities might be much more important than assumed in the standard model has been discussed extensively in the literature over the last twenty years or so under the heading “backreaction”. My interpretation of the current state of play is that there are many unresolved questions, largely because of technical difficulties. See, for example, work by Thomas Buchert (here and, with many other collaborators here) and papers by Green & Wald (here and here). Nick Kasiser also wrote about it here.
• The new papers under discussion focus entirely on supernovae measurements. It must be recognized that these provide just one of the pillars supporting the standard cosmology. Over the years, many alternative models have been suggested that claim to “fix” some alleged problem with cosmology only to find that it makes other issues worse. That’s not a reason to ignore departures from the standard framework, but it is an indication that we have a huge amount of data and we’re not allowed to cherry-pick what we want. We have to fit it all. The strongest evidence in favour of the FLRW framework actually comes from the cosmic microwave background (CMB) with the supernovae provide corroboration. I would need to see a detailed prediction of the anisotropy of the CMB before being convinced.
• The Timescape model is largely based on the non-linear expansion of cosmic voids. These are undoubtedly important, and there has been considerable observational and theoretical activity in understanding them and their evolution in the standard model. It is not at all obvious to me that the voids invoked to explain the apparent acceleration of the Universe are consistent with what we actually see in our surveys. That is something else to test.
• Finally, the standard cosmology includes a prescription for the initial conditions from which the present inhomogeneities grew. Where does the cosmic web come from in the Timescape model?

Anyway, I’m sure there’ll be a lot of discussion of this in the next few weeks as cosmologists return to the Universe from their Christmas holidays!

Comments are welcome through the box below, especially from people who have managed to understand the cos.

#arXiv241215143 #CosmicWeb_ #cosmologicalPrinciple #DarkEnergy #Pantheon #supernovae #Timescape #timescapeModel

Timescape versus Dark Energy?

Just before the Christmas break I noticed a considerable amount of press coverage claiming that Dark Energy doesn’t exist. Much of the media discussion is closely based on a press release produced by the Royal Astronomical Society. Despite the excessive hype, and consequent initial scepticism, I think the paper has some merit and raises some interesting issues.

The main focus of the discussion is a paper (available on arXiv here) by Seifert et al. with the title Supernovae evidence for foundational change to cosmological models. This paper is accompanied by a longer article called Cosmological foundations revisited with Pantheon+ (also available on arXiv) by a permutation of the same authors, which goes into more detail about the analysis of supernova observations. If you want some background, the “standard” Pantheon+ supernova analysis is described in this paper. The reanalysis presented in the recent papers is motivated an idea called the Timescape model, which is not new. It was discussed by David Wiltshire (one of the authors of the recent papers) in 2007 here and in a number of subsequent papers; there’s also a long review article by Wiltshire here (dated 2013).

So what’s all the fuss about?

In the standard cosmological model we assume that, when sufficiently coarse-grained, the Universe obeys the Cosmological Principle, i.e. that it is homogeneous and isotropic. This implies that the space-time is described by a Friedmann–Lemaître–Robertson–Walker metric (FLRW) metric. Of course we know that the Universe is not exactly smooth. There is a complex cosmic web of galaxies, filaments, clusters, and giant voids which comprise the large-scale structure of the Universe. In the standard cosmological model these fluctuations are treated as small perturbations on a smooth background which evolve linearly on large scales and don’t have a significant effect on the global evolution of the Universe.

This standard model is very successful in accounting for many things but only at the expense of introducing dark energy whose origin is uncertain but which accounts for about 70% of the energy density of the Universe. Among other things, this accounts for the apparent acceleration of the Universe inferred from supernovae measurements.

The approach taken in the Timescape model is to dispense with the FLRW metric, and the idea of separating the global evolution from the inhomogeneities. The idea instead is that the cosmic structure is essentially non-linear so there is no “background metric”. In this model, cosmological observations can not be analysed within the standard framework which relies on the FLRW assumption. Hence the need to reanalyse the supernova data. The name Timescape refers to the presence of significant gravitational time-dilation effects in this model as distinct from the standard model.

I wrote before in the context of a different paper:

….the supernovae measurements do not directly measure cosmic acceleration. If one tries to account for them with a model based on Einstein’s general relativity and the assumption that the Universe is on large-scales is homogeneous and isotropic and with certain kinds of matter and energy then the observations do imply a universe that accelerates. Any or all of those assumptions may be violated (though some possibilities are quite heavily constrained). In short we could, at least in principle, simply be interpreting these measurements within the wrong framework…

So what to make of the latest papers? I have to admit that I didn’t follow all the steps of the supernova reanalysis. I hope an expert can comment on this! I will therefore restrict myself to some general comments.

• My attitude to the standard cosmological model is that it is simply a working hypothesis and we should not elevate it to a status any higher than that. It is based not only on the Cosmological Principle (which could be false), but on the universal applicability of general relativity (which might not be true), and on a number of other assumptions that might not be true either.
• It is important to recognize that one of the reasons that the standard cosmology is the front-runner is that it provides a framework that enables relatively straightforward prediction and interpretation of cosmological measurements. That goes not only for supernova measurements but also for the cosmic microwave background, galaxy clustering, gravitational lensing, and so on. This is much harder to do accurately in the Timescape model simply because the equations involved are much more complex; there are few exact solutions of Einstein’s equations that can help. It is important that people work on alternatives such as this.
• Second, the idea that inhomogeneities might be much more important than assumed in the standard model has been discussed extensively in the literature over the last twenty years or so under the heading “backreaction”. My interpretation of the current state of play is that there are many unresolved questions, largely because of technical difficulties. See, for example, work by Thomas Buchert (here and, with many other collaborators here) and papers by Green & Wald (here and here). Nick Kasiser also wrote about it here.
• The new papers under discussion focus entirely on supernovae measurements. It must be recognized that these provide just one of the pillars supporting the standard cosmology. Over the years, many alternative models have been suggested that claim to “fix” some alleged problem with cosmology only to find that it makes other issues worse. That’s not a reason to ignore departures from the standard framework, but it is an indication that we have a huge amount of data and we’re not allowed to cherry-pick what we want. We have to fit it all. The strongest evidence in favour of the FLRW framework actually comes from the cosmic microwave background (CMB) with the supernovae provide corroboration. I would need to see a detailed prediction of the anisotropy of the CMB before being convinced.
• The Timescape model is largely based on the non-linear expansion of cosmic voids. These are undoubtedly important, and there has been considerable observational and theoretical activity in understanding them and their evolution in the standard model. It is not at all obvious to me that the voids invoked to explain the apparent acceleration of the Universe are consistent with what we actually see in our surveys. That is something else to test.
• Finally, the standard cosmology includes a prescription for the initial conditions from which the present inhomogeneities grew. Where does the cosmic web come from in the Timescape model?

Anyway, I’m sure there’ll be a lot of discussion of this in the next few weeks as cosmologists return to the Universe from their Christmas holidays!

Comments are welcome through the box below, especially from people who have managed to understand the cos.

#arXiv241215143 #CosmicWeb_ #cosmologicalPrinciple #DarkEnergy #Pantheon #supernovae #Timescape #timescapeModel

in the #arXiv

Investigating Ultra-Large Large-Scale Structures: Potential Implications for Cosmology

by Alexia Lopez @morninglopez and co-authors
https://arxiv.org/abs/2409.14894

#cosmology #bigring #giantarc #galaxies #ΛCDM #CosmologicalPrinciple #LSS #LargeScaleStructure #Universe #astrodon #astronomy #astrophysics #science #STEM #RoyalSociety

in the #arXiv

Investigating Ultra-Large Large-Scale Structures: Potential Implications for Cosmology

by Alexia Lopez @morninglopez and co-authors
https://arxiv.org/abs/2409.14894

#cosmology #bigring #giantarc #galaxies #ΛCDM #CosmologicalPrinciple #LSS #LargeScaleStructure #Universe #astrodon #astronomy #astrophysics #science #STEM #RoyalSociety

in the #arXiv

Investigating Ultra-Large Large-Scale Structures: Potential Implications for Cosmology

by Alexia Lopez @morninglopez and co-authors
https://arxiv.org/abs/2409.14894

#cosmology #bigring #giantarc #galaxies #ΛCDM #CosmologicalPrinciple #LSS #LargeScaleStructure #Universe #astrodon #astronomy #astrophysics #science #STEM #RoyalSociety

in the #arXiv

Investigating Ultra-Large Large-Scale Structures: Potential Implications for Cosmology

by Alexia Lopez @morninglopez and co-authors
https://arxiv.org/abs/2409.14894

#cosmology #bigring #giantarc #galaxies #ΛCDM #CosmologicalPrinciple #LSS #LargeScaleStructure #Universe #astrodon #astronomy #astrophysics #science #STEM #RoyalSociety

in the #arXiv

Investigating Ultra-Large Large-Scale Structures: Potential Implications for Cosmology

by Alexia Lopez @morninglopez and co-authors
https://arxiv.org/abs/2409.14894

#cosmology #bigring #giantarc #galaxies #ΛCDM #CosmologicalPrinciple #LSS #LargeScaleStructure #Universe #astrodon #astronomy #astrophysics #science #STEM #RoyalSociety

@GravityGrinch Excellent presentation! The 'unterbestimmtheitsproblem' 😍 [42:00] is particularly relevant! [also discussed in 1st question]
Without the #CosmologicalPrinciple , #Cosmology becomes much more complex than the current model based on simple assumptions that are used in #LCDM right now.

@GravityGrinch Excellent presentation! The 'unterbestimmtheitsproblem' 😍 [42:00] is particularly relevant! [also discussed in 1st question]
Without the #CosmologicalPrinciple , #Cosmology becomes much more complex than the current model based on simple assumptions that are used in #LCDM right now.

@GravityGrinch Excellent presentation! The 'unterbestimmtheitsproblem' 😍 [42:00] is particularly relevant! [also discussed in 1st question]
Without the #CosmologicalPrinciple , #Cosmology becomes much more complex than the current model based on simple assumptions that are used in #LCDM right now.

@GravityGrinch Excellent presentation! The 'unterbestimmtheitsproblem' 😍 [42:00] is particularly relevant! [also discussed in 1st question]
Without the #CosmologicalPrinciple , #Cosmology becomes much more complex than the current model based on simple assumptions that are used in #LCDM right now.

@GravityGrinch Excellent presentation! The 'unterbestimmtheitsproblem' 😍 [42:00] is particularly relevant! [also discussed in 1st question]
Without the #CosmologicalPrinciple , #Cosmology becomes much more complex than the current model based on simple assumptions that are used in #LCDM right now.

#GeorgeSmoot III - Did Our #Universe Have a #Beginning?

https://www.youtube.com/watch?v=S2jnk3ZfUME

#Philosophy #PhilosophyOfScience #Science #PhilosophyOfCosmology #Cosmology #BigBang #CMB #CosmicMicrowaveBackground #CosmologicalPrinciple #Astronomy #Astrophysics #Complexity #Inflation #Curvature #Flatness #Geometry #Spacetime #GeorgeSmootIII #CloserToTruth #RobertKuhn

#GeorgeSmoot III - Did Our #Universe Have a #Beginning?

https://www.youtube.com/watch?v=S2jnk3ZfUME

#Philosophy #PhilosophyOfScience #Science #PhilosophyOfCosmology #Cosmology #BigBang #CMB #CosmicMicrowaveBackground #CosmologicalPrinciple #Astronomy #Astrophysics #Complexity #Inflation #Curvature #Flatness #Geometry #Spacetime #GeorgeSmootIII #CloserToTruth #RobertKuhn

#GeorgeSmoot III - Did Our #Universe Have a #Beginning?

https://www.youtube.com/watch?v=S2jnk3ZfUME

#Philosophy #PhilosophyOfScience #Science #PhilosophyOfCosmology #Cosmology #BigBang #CMB #CosmicMicrowaveBackground #CosmologicalPrinciple #Astronomy #Astrophysics #Complexity #Inflation #Curvature #Flatness #Geometry #Spacetime #GeorgeSmootIII #CloserToTruth #RobertKuhn

#GeorgeSmoot III - Did Our #Universe Have a #Beginning?

https://www.youtube.com/watch?v=S2jnk3ZfUME

#Philosophy #PhilosophyOfScience #Science #PhilosophyOfCosmology #Cosmology #BigBang #CMB #CosmicMicrowaveBackground #CosmologicalPrinciple #Astronomy #Astrophysics #Complexity #Inflation #Curvature #Flatness #Geometry #Spacetime #GeorgeSmootIII #CloserToTruth #RobertKuhn

#GeorgeSmoot III - Did Our #Universe Have a #Beginning?

https://www.youtube.com/watch?v=S2jnk3ZfUME

#Philosophy #PhilosophyOfScience #Science #PhilosophyOfCosmology #Cosmology #BigBang #CMB #CosmicMicrowaveBackground #CosmologicalPrinciple #Astronomy #Astrophysics #Complexity #Inflation #Curvature #Flatness #Geometry #Spacetime #GeorgeSmootIII #CloserToTruth #RobertKuhn

#RobertLaughlin - What's #Fundamental in the #Cosmos?

https://www.youtube.com/watch?v=7Jya_lmQuvw&ab_channel=CloserToTruth

#Philosophy #PhilosophyOfScience #PhilosophyOfCosmology #Science #Cosmology #Metaphysics #Einstein #GR #GeneralRelativity #SpecialRelativity #EquivalencePrinciple #Gravity #BlackHoles #CosmologicalPrinciple #Spacetime #Time #Space #Emergence #QM #QuantumMechanics #CloserToTruth #RobertKuhn

#RobertLaughlin - What's #Fundamental in the #Cosmos?

https://www.youtube.com/watch?v=7Jya_lmQuvw&ab_channel=CloserToTruth

#Philosophy #PhilosophyOfScience #PhilosophyOfCosmology #Science #Cosmology #Metaphysics #Einstein #GR #GeneralRelativity #SpecialRelativity #EquivalencePrinciple #Gravity #BlackHoles #CosmologicalPrinciple #Spacetime #Time #Space #Emergence #QM #QuantumMechanics #CloserToTruth #RobertKuhn

#RobertLaughlin - What's #Fundamental in the #Cosmos?

https://www.youtube.com/watch?v=7Jya_lmQuvw&ab_channel=CloserToTruth

#Philosophy #PhilosophyOfScience #PhilosophyOfCosmology #Science #Cosmology #Metaphysics #Einstein #GR #GeneralRelativity #SpecialRelativity #EquivalencePrinciple #Gravity #BlackHoles #CosmologicalPrinciple #Spacetime #Time #Space #Emergence #QM #QuantumMechanics #CloserToTruth #RobertKuhn

#RobertLaughlin - What's #Fundamental in the #Cosmos?

https://www.youtube.com/watch?v=7Jya_lmQuvw&ab_channel=CloserToTruth

#Philosophy #PhilosophyOfScience #PhilosophyOfCosmology #Science #Cosmology #Metaphysics #Einstein #GR #GeneralRelativity #SpecialRelativity #EquivalencePrinciple #Gravity #BlackHoles #CosmologicalPrinciple #Spacetime #Time #Space #Emergence #QM #QuantumMechanics #CloserToTruth #RobertKuhn

#RobertLaughlin - What's #Fundamental in the #Cosmos?

https://www.youtube.com/watch?v=7Jya_lmQuvw&ab_channel=CloserToTruth

#Philosophy #PhilosophyOfScience #PhilosophyOfCosmology #Science #Cosmology #Metaphysics #Einstein #GR #GeneralRelativity #SpecialRelativity #EquivalencePrinciple #Gravity #BlackHoles #CosmologicalPrinciple #Spacetime #Time #Space #Emergence #QM #QuantumMechanics #CloserToTruth #RobertKuhn

#CosmologicalPrinciple
"Cosmological models are built on a simple, century-old idea, but new observations demand a radical rethink"
🔗 https://phys.org/news/2023-06-cosmological-built-simple-century-old-idea.html

#CosmologicalPrinciple
"Cosmological models are built on a simple, century-old idea, but new observations demand a radical rethink"
🔗 https://phys.org/news/2023-06-cosmological-built-simple-century-old-idea.html

#CosmologicalPrinciple
"Cosmological models are built on a simple, century-old idea, but new observations demand a radical rethink"
🔗 https://phys.org/news/2023-06-cosmological-built-simple-century-old-idea.html