#cosmological-constant — Public Fediverse posts

https://www.europesays.com/uk/994557/ The Force That Holds Atoms Together May Be Driving the Universe Apart #BindingQuarks #ColdDarkMatter #CosmologicalConstant #DarkEnergy #EdwinHubble #HubbleConstant #KnownUniverse #Physics #RateOfExpansion #Science #StrongNuclearForce #UK #UnitedKingdom

The Force That Holds Atoms Together May Be Driving the Universe Apart

Here’s what you’ll learn when you read this story: The universe is expanding faster every second, and physicists…
#NewsBeep #News #Physics #AU #Australia #bindingquarks #Colddarkmatter #cosmologicalconstant #Darkenergy #EdwinHubble #Hubbleconstant #knownuniverse #rateofexpansion #Science #strongnuclearforce
https://www.newsbeep.com/au/704331/

The Force That Holds Atoms Together May Be Driving the Universe Apart

Here’s what you’ll learn when you read this story: The universe is expanding faster every second, and physicists…
#NewsBeep #News #Physics #AU #Australia #bindingquarks #Colddarkmatter #cosmologicalconstant #Darkenergy #EdwinHubble #Hubbleconstant #knownuniverse #rateofexpansion #Science #strongnuclearforce
https://www.newsbeep.com/au/704331/

The Force That Holds Atoms Together May Be Driving the Universe Apart

Here’s what you’ll learn when you read this story: The universe is expanding faster every second, and physicists…
#NewsBeep #News #Physics #bindingquarks #Colddarkmatter #cosmologicalconstant #DarkEnergy #EdwinHubble #HubbleConstant #knownuniverse #rateofexpansion #Science #strongnuclearforce #UK #UnitedKingdom
https://www.newsbeep.com/uk/612022/

https://www.europesays.com/ie/509637/ The Force That Holds Atoms Together May Be Driving the Universe Apart #BindingQuarks #ColdDarkMatter #CosmologicalConstant #DarkEnergy #EdwinHubble #Éire #HubbleConstant #IE #Ireland #KnownUniverse #Physics #RateOfExpansion #Science #StrongNuclearForce

Could a cosmic uncertainty principle help explain dark matter?

When you buy through links on our articles, Future and its syndication partners may earn a commission. A…
#NewsBeep #News #Physics #AU #Australia #AxelMellinger #CentralMichiganUniversity #cosmicmicrowavebackground #cosmologicalconstant #Darkenergy #darkmatter #quantummechanical #rateofexpansion #SavvasKoushiappas #Science #StandardModel
https://www.newsbeep.com/au/696893/

Could a cosmic uncertainty principle help explain dark matter?

When you buy through links on our articles, Future and its syndication partners may earn a commission. A…
#NewsBeep #News #Physics #AU #Australia #AxelMellinger #CentralMichiganUniversity #cosmicmicrowavebackground #cosmologicalconstant #Darkenergy #darkmatter #quantummechanical #rateofexpansion #SavvasKoushiappas #Science #StandardModel
https://www.newsbeep.com/au/696893/

https://www.europesays.com/ie/504405/ Could a cosmic uncertainty principle help explain dark matter? #AxelMellinger #CentralMichiganUniversity #CosmicMicrowaveBackground #CosmologicalConstant #DarkEnergy #DarkMatter #Éire #IE #Ireland #Physics #QuantumMechanical #RateOfExpansion #SavvasKoushiappas #Science #StandardModel

https://www.europesays.com/uk/986987/ Could a cosmic uncertainty principle help explain dark matter? #AxelMellinger #CentralMichiganUniversity #CosmicMicrowaveBackground #CosmologicalConstant #DarkEnergy #DarkMatter #Physics #QuantumMechanical #RateOfExpansion #SavvasKoushiappas #Science #StandardModel #UK #UnitedKingdom

Scientists Think Ghost Particles Could Be Storing Their Mass in a Hidden Dimension

“Hearst Magazines and Yahoo may earn commission or revenue on some items through these links.” Here’s what you’ll…
#NewsBeep #News #US #USA #UnitedStates #UnitedStatesOfAmerica #Physics #cosmologicalconstant #KATRIN #Science
https://www.newsbeep.com/us/615902/

Scientists Think Ghost Particles Could Be Storing Their Mass in a Hidden Dimension

“Hearst Magazines and Yahoo may earn commission or revenue on some items through these links.” Here’s what you’ll…
#NewsBeep #News #US #USA #UnitedStates #UnitedStatesOfAmerica #Physics #cosmologicalconstant #KATRIN #Science
https://www.newsbeep.com/us/615902/

https://www.europesays.com/ie/462078/ Scientists Think Ghost Particles Could Be Storing Their Mass in a Hidden Dimension #CosmologicalConstant #Éire #IE #Ireland #KATRIN #Physics #Science

Scientists Think Ghost Particles Could Be Storing Their Mass in a Hidden Dimension

“Hearst Magazines and Yahoo may earn commission or revenue on some items through these links.” Here’s what you’ll…
#NewsBeep #News #Physics #AU #Australia #cosmologicalconstant #KATRIN #Science
https://www.newsbeep.com/au/641305/

Scientists Think Ghost Particles Could Be Storing Their Mass in a Hidden Dimension

“Hearst Magazines and Yahoo may earn commission or revenue on some items through these links.” Here’s what you’ll…
#NewsBeep #News #Physics #AU #Australia #cosmologicalconstant #KATRIN #Science
https://www.newsbeep.com/au/641305/

Scientists Think Ghost Particles Could Be Storing Their Mass in a Hidden Dimension

“Hearst Magazines and Yahoo may earn commission or revenue on some items through these links.” Here’s what you’ll…
#NewsBeep #News #Physics #cosmologicalconstant #Katrin #Science #UK #UnitedKingdom
https://www.newsbeep.com/uk/559309/

https://www.europesays.com/uk/929204/ Scientists Think Ghost Particles Could Be Storing Their Mass in a Hidden Dimension #CosmologicalConstant #KATRIN #Physics #Science #UK #UnitedKingdom

https://www.europesays.com/ie/458146/ The universe may end trillions of years sooner than we thought #BigCrunch #CosmologicalConstant #DarkEnergy #Éire #ExpansionRate #FateOfTheUniverse #IE #Ireland #Science #Space #TheUniverse

The universe may end trillions of years sooner than we thought

When you buy through links on our articles, Future and its syndication partners may earn a commission. Astronomers…
#NewsBeep #News #Space #bigcrunch #cosmologicalconstant #DarkEnergy #expansionrate #fateoftheuniverse #Science #TheUniverse #UK #UnitedKingdom
https://www.newsbeep.com/uk/555298/

The #CosmologicalConstant from a Quantum Gravitational θ-Vacua and the Gravitational Hall Effect: https://arxiv.org/abs/2506.14886 -> Could the mathematical ‘shape’ of the universe solve the cosmological constant problem? https://www.brown.edu/news/2026-04-20/cosmological-constant-problem

The #CosmologicalConstant from a Quantum Gravitational θ-Vacua and the Gravitational Hall Effect: https://arxiv.org/abs/2506.14886 -> Could the mathematical ‘shape’ of the universe solve the cosmological constant problem? https://www.brown.edu/news/2026-04-20/cosmological-constant-problem

The #CosmologicalConstant from a Quantum Gravitational θ-Vacua and the Gravitational Hall Effect: https://arxiv.org/abs/2506.14886 -> Could the mathematical ‘shape’ of the universe solve the cosmological constant problem? https://www.brown.edu/news/2026-04-20/cosmological-constant-problem

The #CosmologicalConstant from a Quantum Gravitational θ-Vacua and the Gravitational Hall Effect: https://arxiv.org/abs/2506.14886 -> Could the mathematical ‘shape’ of the universe solve the cosmological constant problem? https://www.brown.edu/news/2026-04-20/cosmological-constant-problem

The #CosmologicalConstant from a Quantum Gravitational θ-Vacua and the Gravitational Hall Effect: https://arxiv.org/abs/2506.14886 -> Could the mathematical ‘shape’ of the universe solve the cosmological constant problem? https://www.brown.edu/news/2026-04-20/cosmological-constant-problem

While the holy grail of #InhomogeneousCosmology is to explain #DarkEnergy as an epiphenomenon of the cosmologically recent formation epoch of #CosmicVoids and other #LargeScaleStructure, #YonadavBarryGinat and #PedroGFerreira have gone for a more modest goal: keeping the #CosmologicalConstant but tacking on void formation to get a sort-of #BeyondLCDM inhomogeneous model that better matches #DES and #DESI results [1].

#ArXiv_2601_20633
@cosmology #Cosmology #LCDM

[1] https://arxiv.org/abs/2601.20633

While the holy grail of #InhomogeneousCosmology is to explain #DarkEnergy as an epiphenomenon of the cosmologically recent formation epoch of #CosmicVoids and other #LargeScaleStructure, #YonadavBarryGinat and #PedroGFerreira have gone for a more modest goal: keeping the #CosmologicalConstant but tacking on void formation to get a sort-of #BeyondLCDM inhomogeneous model that better matches #DES and #DESI results [1].

#ArXiv_2601_20633
@cosmology #Cosmology #LCDM

[1] https://arxiv.org/abs/2601.20633

While the holy grail of #InhomogeneousCosmology is to explain #DarkEnergy as an epiphenomenon of the cosmologically recent formation epoch of #CosmicVoids and other #LargeScaleStructure, #YonadavBarryGinat and #PedroGFerreira have gone for a more modest goal: keeping the #CosmologicalConstant but tacking on void formation to get a sort-of #BeyondLCDM inhomogeneous model that better matches #DES and #DESI results [1].

#ArXiv_2601_20633
@cosmology #Cosmology #LCDM

[1] https://arxiv.org/abs/2601.20633

While the holy grail of #InhomogeneousCosmology is to explain #DarkEnergy as an epiphenomenon of the cosmologically recent formation epoch of #CosmicVoids and other #LargeScaleStructure, #YonadavBarryGinat and #PedroGFerreira have gone for a more modest goal: keeping the #CosmologicalConstant but tacking on void formation to get a sort-of #BeyondLCDM inhomogeneous model that better matches #DES and #DESI results [1].

#ArXiv_2601_20633
@cosmology #Cosmology #LCDM

[1] https://arxiv.org/abs/2601.20633

While the holy grail of #InhomogeneousCosmology is to explain #DarkEnergy as an epiphenomenon of the cosmologically recent formation epoch of #CosmicVoids and other #LargeScaleStructure, #YonadavBarryGinat and #PedroGFerreira have gone for a more modest goal: keeping the #CosmologicalConstant but tacking on void formation to get a sort-of #BeyondLCDM inhomogeneous model that better matches #DES and #DESI results [1].

#ArXiv_2601_20633
@cosmology #Cosmology #LCDM

[1] https://arxiv.org/abs/2601.20633

Outer Space Is a Viscous Fluid, New Paper Claims

There’s endless debate among cosmologists about what really makes up the emptiness of outer space, though many believe…
#NewsBeep #News #Space #AU #Australia #cosmologicalconstant #Darkenergy #darkmatter #expansionoftheuniverse #GreekletterLambda #IndianInstituteofTechnology #intriguingtheory #MuhammadGhulamKhuwajahKhan #OuterSpace #Science #viscousfluid
https://www.newsbeep.com/au/438533/

Outer Space Is a Viscous Fluid, New Paper Claims

There’s endless debate among cosmologists about what really makes up the emptiness of outer space, though many believe…
#NewsBeep #News #US #USA #UnitedStates #UnitedStatesOfAmerica #Science #cosmologicalconstant #DarkEnergy #Darkmatter #expansionoftheuniverse #GreekletterLambda #IndianInstituteofTechnology #intriguingtheory #MuhammadGhulamKhuwajahKhan #OuterSpace #viscousfluid
https://www.newsbeep.com/us/420775/

Outer Space Is a Viscous Fluid, New Paper Claims

There’s endless debate among cosmologists about what really makes up the emptiness of outer space, though many believe…
#NewsBeep #News #US #USA #UnitedStates #UnitedStatesOfAmerica #Science #cosmologicalconstant #DarkEnergy #Darkmatter #expansionoftheuniverse #GreekletterLambda #IndianInstituteofTechnology #intriguingtheory #MuhammadGhulamKhuwajahKhan #OuterSpace #viscousfluid
https://www.newsbeep.com/us/420775/

Fractal-Weighted Holographic Universe

https://pastebin.com/giakNwEr

#physics #holographicprinciple #cosmologicalconstant #fractal

Fractal-Weighted Holographic Universe

https://pastebin.com/giakNwEr

#physics #holographicprinciple #cosmologicalconstant #fractal

Fractal-Weighted Holographic Universe

https://pastebin.com/giakNwEr

#physics #holographicprinciple #cosmologicalconstant #fractal

Fractal-Weighted Holographic Universe

https://pastebin.com/giakNwEr

#physics #holographicprinciple #cosmologicalconstant #fractal

https://www.europesays.com/ie/186540/ You’re Living Alongside Invisible Wormholes, Scientists Say—and They May Be Warping Your Reality #AmericanPhysicalSociety #CosmologicalConstant #DarkEnergy #Éire #IE #Ireland #OrdersOfMagnitude #Science #Scientists #Space

You’re Living Alongside Invisible Wormholes, Scientists Say—and They May Be Warping Your Reality

Churning nano-wormholes could explain the clash in our cosmological constants. The wormholes add magnitude to a math parameter…
#NewsBeep #News #US #USA #UnitedStates #UnitedStatesOfAmerica #Science #AmericanPhysicalSociety #cosmologicalconstant #DarkEnergy #ordersofmagnitude #scientists
https://www.newsbeep.com/us/298368/

You’re Living Alongside Invisible Wormholes, Scientists Say—and They May Be Warping Your Reality

Churning nano-wormholes could explain the clash in our cosmological constants. The wormholes add magnitude to a math parameter…
#NewsBeep #News #US #USA #UnitedStates #UnitedStatesOfAmerica #Science #AmericanPhysicalSociety #cosmologicalconstant #DarkEnergy #ordersofmagnitude #scientists
https://www.newsbeep.com/us/298368/

https://www.europesays.com/ie/167557/ Scientists Think They Figured Out How and When the Universe Will End #BigCrunch #CosmologicalConstant #DarkEnergy #DarkMatter #Éire #IE #Ireland #OurUniverse #Science #Scientists #Space #TheUniverse

Scientists Think They Figured Out How and When the Universe Will End

Here’s what you’ll learn when you read this story: A new paper adjusts an equation that defines our…
#NewsBeep #News #US #USA #UnitedStates #UnitedStatesOfAmerica #Science #bigcrunch #cosmologicalconstant #DarkEnergy #Darkmatter #ouruniverse #scientists #TheUniverse
https://www.newsbeep.com/us/275536/

Scientists Think They Figured Out How and When the Universe Will End

Here’s what you’ll learn when you read this story: A new paper adjusts an equation that defines our…
#NewsBeep #News #US #USA #UnitedStates #UnitedStatesOfAmerica #Science #bigcrunch #cosmologicalconstant #DarkEnergy #Darkmatter #ouruniverse #scientists #TheUniverse
https://www.newsbeep.com/us/275536/

Physicists Predict When The Universe Will End in a Reverse Big Bang

If recent discoveries that dark energy is evolving hold any water, our Universe will collapse under its own…
#NewsBeep #News #Physics #AU #Australia #BigCrunch #cosmologicalconstant #Darkenergy #expansionoftheuniverse #HenryTye #Science #TheUniverse
https://www.newsbeep.com/au/199127/

https://www.europesays.com/uk/358747/ Will our universe rip apart or expand forever? Dark energy holds the answer | Technology News #BigBang #CosmicAcceleration #CosmologicalConstant #DarkEnergy #DarkEnergySurvey #DESI #EuclidTelescope #Physics #Science #TypeIaSupernovae #UK #UnitedKingdom #UniverseExpansion #WillTheUniverseEnd

Men will contemplate the existence of 10^120 multiple infinite universes rather than admit there might be a god. #cosmologicalconstant

Men will contemplate the existence of 10^120 multiple infinite universes rather than admit there might be a god. #cosmologicalconstant

Men will contemplate the existence of 10^120 multiple infinite universes rather than admit there might be a god. #cosmologicalconstant

Men will contemplate the existence of 10^120 multiple infinite universes rather than admit there might be a god. #cosmologicalconstant

Men will contemplate the existence of 10^120 multiple infinite universes rather than admit there might be a god. #cosmologicalconstant

Here is my next YouTube short about the great discovery by David Benisty et al. that the cosmological constant can be inferred from the Milky Way and Andromeda system! This is so important because it's a complementary probe to the CMB (Planck, ACT, etc.).
https://youtube.com/shorts/mwF0HhSu5yM?si=vT-Swj-nqEHMlihk

#astronomy #astrophysics #scicomm #outreach #CosmologicalConstant #YouTube

Here is my next YouTube short about the great discovery by David Benisty et al. that the cosmological constant can be inferred from the Milky Way and Andromeda system! This is so important because it's a complementary probe to the CMB (Planck, ACT, etc.).
https://youtube.com/shorts/mwF0HhSu5yM?si=vT-Swj-nqEHMlihk

#astronomy #astrophysics #scicomm #outreach #CosmologicalConstant #YouTube

Here is my next YouTube short about the great discovery by David Benisty et al. that the cosmological constant can be inferred from the Milky Way and Andromeda system! This is so important because it's a complementary probe to the CMB (Planck, ACT, etc.).
https://youtube.com/shorts/mwF0HhSu5yM?si=vT-Swj-nqEHMlihk

#astronomy #astrophysics #scicomm #outreach #CosmologicalConstant #YouTube

Here is my next YouTube short about the great discovery by David Benisty et al. that the cosmological constant can be inferred from the Milky Way and Andromeda system! This is so important because it's a complementary probe to the CMB (Planck, ACT, etc.).
https://youtube.com/shorts/mwF0HhSu5yM?si=vT-Swj-nqEHMlihk

#astronomy #astrophysics #scicomm #outreach #CosmologicalConstant #YouTube

Huh, we may live in the Boondocks of the Universe.

I found it really interesting, but we may be in the middle of the largest known super void in the universe.

Recent discovery. It's called the KBC void, and is about a billion light-years across or so.

It's the best explanation #astronomy has come up with for the discrepancy in the #CosmologicalConstant and is probably a good thing. Cuz we are less likely to have extreme events happen to us.

#science #randomthoughts #cool

Huh, we may live in the Boondocks of the Universe.

I found it really interesting, but we may be in the middle of the largest known super void in the universe.

Recent discovery. It's called the KBC void, and is about a billion light-years across or so.

It's the best explanation #astronomy has come up with for the discrepancy in the #CosmologicalConstant and is probably a good thing. Cuz we are less likely to have extreme events happen to us.

#science #randomthoughts #cool

Huh, we may live in the Boondocks of the Universe.

I found it really interesting, but we may be in the middle of the largest known super void in the universe.

Recent discovery. It's called the KBC void, and is about a billion light-years across or so.

It's the best explanation #astronomy has come up with for the discrepancy in the #CosmologicalConstant and is probably a good thing. Cuz we are less likely to have extreme events happen to us.

#science #randomthoughts #cool

Huh, we may live in the Boondocks of the Universe.

I found it really interesting, but we may be in the middle of the largest known super void in the universe.

Recent discovery. It's called the KBC void, and is about a billion light-years across or so.

It's the best explanation #astronomy has come up with for the discrepancy in the #CosmologicalConstant and is probably a good thing. Cuz we are less likely to have extreme events happen to us.

#science #randomthoughts #cool

Huh, we may live in the Boondocks of the Universe.

I found it really interesting, but we may be in the middle of the largest known super void in the universe.

Recent discovery. It's called the KBC void, and is about a billion light-years across or so.

It's the best explanation #astronomy has come up with for the discrepancy in the #CosmologicalConstant and is probably a good thing. Cuz we are less likely to have extreme events happen to us.

#science #randomthoughts #cool

Cosmology Results from DESI

Yesterday evening (10pm Irish Time) saw the release of new results from the Dark Energy Spectroscopic Instrument (DESI), completing a trio of major announcements of cosmological results in the space of two days (the Atacama Cosmology Telescope and the Euclid Q1 release being the others). I didn’t see the DESI press conference but you can read the press release here.

There were no fewer than eight DESI papers on the astro-ph section of the arXiv this morning. Here are the titles with links:

• DESI DR2 Results I: Baryon Acoustic Oscillations from the Lyman Alpha Forest
• DESI DR2 Results II: Measurements of Baryon Acoustic Oscillations and Cosmological Constraints;
• Construction of the Damped Lyα Absorber Catalog for DESI DR2 Lyα BAO;
• Validation of the DESI DR2 Lyα BAO analysis using synthetic datasets;
• Validation of the DESI DR2 Measurements of Baryon Acoustic Oscillations from Galaxies and Quasars;
• Extended Dark Energy analysis using DESI DR2 BAO measurements;
• Constraints on Neutrino Physics from DESI DR2 BAO and DR1 Full Shape;
• Data Release 1 of the Dark Energy Spectroscopic Instrument.

You can see from the titles that the first seven of these relate to the second data release (DR2; three years of data) from DESI; the last one listed here is a description of the first data release (DR1), which is now publicly available.

Obviously there is a lot of information to digest in these papers so here are two members of the DESI collaboration talking with Shaun Hotchkiss on Cosmology Talks about the key messages from the analysis of Baryon Acoustic Oscillations (the BAO in the titles of the new papers):

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

A lot has been made in the press coverage of these results about the evidence that the standard cosmological model is incomplete; see, e.g., here. Here are a few comments.

As I see it, taken on their own, the DESI BAO results are broadly consistent with the ΛCDM model as specified by the parameters determined by the Cosmic Microwave Background (CMB) inferred from Planck. Issues do emerge, however, when these results are combined with other data sets. The most intriguing of these arises with the dark energy contribution. The simplest interpretation of dark energy is that it is a cosmological constant (usually called Λ) which – as explained here – corresponds to a perfect fluid with an equation-of-state p=wρc2 with w=-1. In this case the effective mass density of the dark energy ρ remains constant as the universe expands. To parametrise departures from this constant behaviour, cosmologists have replaced this form with the form w(a)=w0+wa(1-a) where a(t) is the cosmic scale factor. A cosmological constant Λ would correspond to a point (w0=-1, wa=0) in the plane defined by these parameters, but the only requirement for dark energy to result in cosmic acceleration is that w<0 not that w=-1.

The DESI team allow (w0, wa) to act as free parameters and let the DESI data constrain them, either alone or in combinations with other data sets, finding evidence for departures from the “standard values”. Here’s an example plot:

The DESI data don’t include the standard point (at the intersection of the two dashed lines) but the discrepancy gets worse when other data (such as supernovae and CMB) are folded in, as in this picture. The weight of evidence suggests a dark energy contribution which is decreasing with time.

These results are certainly intriguing, and a lot of credit is due to the DESI collaboration for working so hard to identify and remove possible systematics in the analysis (see the papers above) but what do they tell us about ΛCDM?

My view is that we’ve never known what the dark energy actually is or why it is so large that it represents 70% of the overall energy density of the Universe. The Λ in ΛCDM is really just a place-holder, not there for any compelling physical reason but because it is the simplest way of accounting for the observations. In other words, it’s what it is because of Occam’s Razor and nothing more. As with any working hypothesis, the standard cosmological model will get updated whenever new information comes to light (as it is doing now) and/or if we get new physical insights into the origin of dark energy.

Do the latest observations cast doubt on the standard model? I’d say no. We’re seeing an evolutionary change from “We have no idea what the dark energy is but we think it might be a cosmological constant” to “We still have no idea what the dark energy is but we think it might not be a cosmological constant”.

#baryonAcousticOscillations #cosmologicalConstant #Cosmology #DarkEnergy #DarkEnergySpectroscopicInstrument #OccamSRazor #ShaunHotchkiss

Cosmology Results from DESI

Yesterday evening (10pm Irish Time) saw the release of new results from the Dark Energy Spectroscopic Instrument (DESI), completing a trio of major announcements of cosmological results in the space of two days (the Atacama Cosmology Telescope and the Euclid Q1 release being the others). I didn’t see the DESI press conference but you can read the press release here.

There were no fewer than eight DESI papers on the astro-ph section of the arXiv this morning. Here are the titles with links:

• DESI DR2 Results I: Baryon Acoustic Oscillations from the Lyman Alpha Forest
• DESI DR2 Results II: Measurements of Baryon Acoustic Oscillations and Cosmological Constraints;
• Construction of the Damped Lyα Absorber Catalog for DESI DR2 Lyα BAO;
• Validation of the DESI DR2 Lyα BAO analysis using synthetic datasets;
• Validation of the DESI DR2 Measurements of Baryon Acoustic Oscillations from Galaxies and Quasars;
• Extended Dark Energy analysis using DESI DR2 BAO measurements;
• Constraints on Neutrino Physics from DESI DR2 BAO and DR1 Full Shape;
• Data Release 1 of the Dark Energy Spectroscopic Instrument.

You can see from the titles that the first seven of these relate to the second data release (DR2; three years of data) from DESI; the last one listed here is a description of the first data release (DR1), which is now publicly available.

Obviously there is a lot of information to digest in these papers so here are two members of the DESI collaboration talking with Shaun Hotchkiss on Cosmology Talks about the key messages from the analysis of Baryon Acoustic Oscillations (the BAO in the titles of the new papers):

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

A lot has been made in the press coverage of these results about the evidence that the standard cosmological model is incomplete; see, e.g., here. Here are a few comments.

As I see it, taken on their own, the DESI BAO results are broadly consistent with the ΛCDM model as specified by the parameters determined by the Cosmic Microwave Background (CMB) inferred from Planck. Issues do emerge, however, when these results are combined with other data sets. The most intriguing of these arises with the dark energy contribution. The simplest interpretation of dark energy is that it is a cosmological constant (usually called Λ) which – as explained here – corresponds to a perfect fluid with an equation-of-state p=wρc2 with w=-1. In this case the effective mass density of the dark energy ρ remains constant as the universe expands. To parametrise departures from this constant behaviour, cosmologists have replaced this form with the form w(a)=w0+wa(1-a) where a(t) is the cosmic scale factor. A cosmological constant Λ would correspond to a point (w0=-1, wa=0) in the plane defined by these parameters, but the only requirement for dark energy to result in cosmic acceleration is that w<0 not that w=-1.

The DESI team allow (w0, wa) to act as free parameters and let the DESI data constrain them, either alone or in combinations with other data sets, finding evidence for departures from the “standard values”. Here’s an example plot:

The DESI data don’t include the standard point (at the intersection of the two dashed lines) but the discrepancy gets worse when other data (such as supernovae and CMB) are folded in, as in this picture. The weight of evidence suggests a dark energy contribution which is decreasing with time.

These results are certainly intriguing, and a lot of credit is due to the DESI collaboration for working so hard to identify and remove possible systematics in the analysis (see the papers above) but what do they tell us about ΛCDM?

My view is that we’ve never known what the dark energy actually is or why it is so large that it represents 70% of the overall energy density of the Universe. The Λ in ΛCDM is really just a place-holder, not there for any compelling physical reason but because it is the simplest way of accounting for the observations. In other words, it’s what it is because of Occam’s Razor and nothing more. As with any working hypothesis, the standard cosmological model will get updated whenever new information comes to light (as it is doing now) and/or if we get new physical insights into the origin of dark energy.

Do the latest observations cast doubt on the standard model? I’d say no. We’re seeing an evolutionary change from “We have no idea what the dark energy is but we think it might be a cosmological constant” to “We still have no idea what the dark energy is but we think it might not be a cosmological constant”.

#baryonAcousticOscillations #cosmologicalConstant #Cosmology #DarkEnergy #DarkEnergySpectroscopicInstrument #OccamSRazor #ShaunHotchkiss

Cosmology Results from DESI

Yesterday evening (10pm Irish Time) saw the release of new results from the Dark Energy Spectroscopic Instrument (DESI), completing a trio of major announcements of cosmological results in the space of two days (the Atacama Cosmology Telescope and the Euclid Q1 release being the others). I didn’t see the DESI press conference but you can read the press release here.

There were no fewer than eight DESI papers on the astro-ph section of the arXiv this morning. Here are the titles with links:

• DESI DR2 Results I: Baryon Acoustic Oscillations from the Lyman Alpha Forest
• DESI DR2 Results II: Measurements of Baryon Acoustic Oscillations and Cosmological Constraints;
• Construction of the Damped Lyα Absorber Catalog for DESI DR2 Lyα BAO;
• Validation of the DESI DR2 Lyα BAO analysis using synthetic datasets;
• Validation of the DESI DR2 Measurements of Baryon Acoustic Oscillations from Galaxies and Quasars;
• Extended Dark Energy analysis using DESI DR2 BAO measurements;
• Constraints on Neutrino Physics from DESI DR2 BAO and DR1 Full Shape;
• Data Release 1 of the Dark Energy Spectroscopic Instrument.

You can see from the titles that the first seven of these relate to the second data release (DR2; three years of data) from DESI; the last one listed here is a description of the first data release (DR1), which is now publicly available.

Obviously there is a lot of information to digest in these papers so here are two members of the DESI collaboration talking with Shaun Hotchkiss on Cosmology Talks about the key messages from the analysis of Baryon Acoustic Oscillations (the BAO in the titles of the new papers):

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

A lot has been made in the press coverage of these results about the evidence that the standard cosmological model is incomplete; see, e.g., here. Here are a few comments.

As I see it, taken on their own, the DESI BAO results are broadly consistent with the ΛCDM model as specified by the parameters determined by the Cosmic Microwave Background (CMB) inferred from Planck. Issues do emerge, however, when these results are combined with other data sets. The most intriguing of these arises with the dark energy contribution. The simplest interpretation of dark energy is that it is a cosmological constant (usually called Λ) which – as explained here – corresponds to a perfect fluid with an equation-of-state p=wρc2 with w=-1. In this case the effective mass density of the dark energy ρ remains constant as the universe expands. To parametrise departures from this constant behaviour, cosmologists have replaced this form with the form w(a)=w0+wa(1-a) where a(t) is the cosmic scale factor. A cosmological constant Λ would correspond to a point (w0=-1, wa=0) in the plane defined by these parameters, but the only requirement for dark energy to result in cosmic acceleration is that w<0 not that w=-1.

The DESI team allow (w0, wa) to act as free parameters and let the DESI data constrain them, either alone or in combinations with other data sets, finding evidence for departures from the “standard values”. Here’s an example plot:

The DESI data don’t include the standard point (at the intersection of the two dashed lines) but the discrepancy gets worse when other data (such as supernovae and CMB) are folded in, as in this picture. The weight of evidence suggests a dark energy contribution which is decreasing with time.

These results are certainly intriguing, and a lot of credit is due to the DESI collaboration for working so hard to identify and remove possible systematics in the analysis (see the papers above) but what do they tell us about ΛCDM?

My view is that we’ve never known what the dark energy actually is or why it is so large that it represents 70% of the overall energy density of the Universe. The Λ in ΛCDM is really just a place-holder, not there for any compelling physical reason but because it is the simplest way of accounting for the observations. In other words, it’s what it is because of Occam’s Razor and nothing more. As with any working hypothesis, the standard cosmological model will get updated whenever new information comes to light (as it is doing now) and/or if we get new physical insights into the origin of dark energy.

Do the latest observations cast doubt on the standard model? I’d say no. We’re seeing an evolutionary change from “We have no idea what the dark energy is but we think it might be a cosmological constant” to “We still have no idea what the dark energy is but we think it might not be a cosmological constant”.

#baryonAcousticOscillations #cosmologicalConstant #Cosmology #DarkEnergy #DarkEnergySpectroscopicInstrument #OccamSRazor #ShaunHotchkiss