Sesh Nadathur
@seshnadathur.bsky.social
Astronomer, Associate Professor of cosmology at Portsmouth. Works on galaxy redshift surveys, from telescopes on remote mountaintops or in space. Dad, occasional climber, likes cricket. Occasionally has opinions.
Apropos of nothing in particular, two cosmology questions for my followers:
- in the first figure, are the black or blue contours in better agreement with the pink ones?
- in the second figure, are the black or blue contours in better agreement with (w0,wa)=(-1,0)?
🔭🧪☄️
- in the first figure, are the black or blue contours in better agreement with the pink ones?
- in the second figure, are the black or blue contours in better agreement with (w0,wa)=(-1,0)?
🔭🧪☄️
November 14, 2025 at 7:26 PM
Apropos of nothing in particular, two cosmology questions for my followers:
- in the first figure, are the black or blue contours in better agreement with the pink ones?
- in the second figure, are the black or blue contours in better agreement with (w0,wa)=(-1,0)?
🔭🧪☄️
- in the first figure, are the black or blue contours in better agreement with the pink ones?
- in the second figure, are the black or blue contours in better agreement with (w0,wa)=(-1,0)?
🔭🧪☄️
The net result of these changes is to slightly change the cosmology implications: reducing the 4.2σ significance of the evidence for evolving DE to just 3.2σ. Compare the shift in the small blue and grey contours in the zoomed in second figure here:
November 12, 2025 at 12:08 PM
The net result of these changes is to slightly change the cosmology implications: reducing the 4.2σ significance of the evidence for evolving DE to just 3.2σ. Compare the shift in the small blue and grey contours in the zoomed in second figure here:
This new paper from the Dark Energy Survey team reanalyses their data, changing (hopefully improving) various different aspects of the analysis, and finds that as a result the data points shift a bit, in different directions at different redshifts
arxiv.org/abs/2511.07517
arxiv.org/abs/2511.07517
November 12, 2025 at 12:00 PM
This new paper from the Dark Energy Survey team reanalyses their data, changing (hopefully improving) various different aspects of the analysis, and finds that as a result the data points shift a bit, in different directions at different redshifts
arxiv.org/abs/2511.07517
arxiv.org/abs/2511.07517
So back in March we showed that if you combine BAO data from DESI with supernova data from the Dark Energy Survey and CMB data from Planck and other experiments, evolving dark energy is preferred over the standard cosmological constant model, at the 4.2σ level.
November 12, 2025 at 11:50 AM
So back in March we showed that if you combine BAO data from DESI with supernova data from the Dark Energy Survey and CMB data from Planck and other experiments, evolving dark energy is preferred over the standard cosmological constant model, at the 4.2σ level.
Aren't languages wonderful? Here's an example of Deutsche Bahn not only borrowing from English but also "verbing" a noun in a way that Calvin and Hobbes would respect!
November 4, 2025 at 4:01 PM
Aren't languages wonderful? Here's an example of Deutsche Bahn not only borrowing from English but also "verbing" a noun in a way that Calvin and Hobbes would respect!
Fourth location is the Kobayashi Maskawa Institute at Nagoya University, where I will give a seminar that is also part of an HSC medium band workshop. Nagoya is nice but also very hot and humid, 40C yesterday 🥵
August 6, 2025 at 3:16 AM
Fourth location is the Kobayashi Maskawa Institute at Nagoya University, where I will give a seminar that is also part of an HSC medium band workshop. Nagoya is nice but also very hot and humid, 40C yesterday 🥵
Third conference location is Saitama in Japan, at the RIKEN institute where I gave a talk today (this photo is from dinner afterwards). I also learned that the special long-flowering sakura varieties growing near here were genetically modified at the particle accelerator in the lab at RIKEN 🤔
August 4, 2025 at 2:44 PM
Third conference location is Saitama in Japan, at the RIKEN institute where I gave a talk today (this photo is from dinner afterwards). I also learned that the special long-flowering sakura varieties growing near here were genetically modified at the particle accelerator in the lab at RIKEN 🤔
We had a good discussion session yesterday in Benasque about the DESI data and evidence for evolving dark energy, ending with asking people if they agreed with John Peacock's quote in the Guardian saying he would bet £1000 on it. More even split than I expected, but a plurality disagreed.
July 29, 2025 at 1:21 PM
We had a good discussion session yesterday in Benasque about the DESI data and evidence for evolving dark energy, ending with asking people if they agreed with John Peacock's quote in the Guardian saying he would bet £1000 on it. More even split than I expected, but a plurality disagreed.
Second conference location of the week is Benasque in the Spanish Pyrenees. I had a nice chat about cosmology with Oliver Philcox and Antony Lewis while hiking up a small hill above the town this morning.
July 24, 2025 at 2:40 PM
Second conference location of the week is Benasque in the Spanish Pyrenees. I had a nice chat about cosmology with Oliver Philcox and Antony Lewis while hiking up a small hill above the town this morning.
I'm in Durham today, having just given a talk at the PASCOS 2025 conference. This kicks off a crazy three weeks of travel for me, covering 4 separate conferences...
July 21, 2025 at 12:10 PM
I'm in Durham today, having just given a talk at the PASCOS 2025 conference. This kicks off a crazy three weeks of travel for me, covering 4 separate conferences...
I love observing how phonics teaching works on the brain of a 5-year-old - she's got the building blocks to go and be creative, and the end result isn't really any stranger than standard English spelling.
July 15, 2025 at 8:06 AM
I love observing how phonics teaching works on the brain of a 5-year-old - she's got the building blocks to go and be creative, and the end result isn't really any stranger than standard English spelling.
We took the kids to the Vitality Blast game today where they got to actually meet Ellyse Perry! As well as go out on the pitch for the toss and be interviewed "on TV".
Big shout out to Rhianna Southby for being very nice to them at the start, and for batting well to get Hampshire the win.
Big shout out to Rhianna Southby for being very nice to them at the start, and for batting well to get Hampshire the win.
July 6, 2025 at 4:17 PM
We took the kids to the Vitality Blast game today where they got to actually meet Ellyse Perry! As well as go out on the pitch for the toss and be interviewed "on TV".
Big shout out to Rhianna Southby for being very nice to them at the start, and for batting well to get Hampshire the win.
Big shout out to Rhianna Southby for being very nice to them at the start, and for batting well to get Hampshire the win.
A bit late to this, but - today is the birthday of Paul McCartney, surely the greatest living Briton. A life to be grateful for, if ever there was one.
June 18, 2025 at 6:34 PM
A bit late to this, but - today is the birthday of Paul McCartney, surely the greatest living Briton. A life to be grateful for, if ever there was one.
I had a fantastic day at Lord's today, an enthralling day of cricket with very high quality fast bowling from both sides. The last time I was at Lord's was Steve Smith's debut Test match, 15 years ago!
June 11, 2025 at 9:43 PM
I had a fantastic day at Lord's today, an enthralling day of cricket with very high quality fast bowling from both sides. The last time I was at Lord's was Steve Smith's debut Test match, 15 years ago!
Very proud of my wife, who has just run her first ever marathon - BigSea Trails in Dorset - up and down some crazy hills and along beaches. The nutcase! ❤️
June 8, 2025 at 4:48 PM
Very proud of my wife, who has just run her first ever marathon - BigSea Trails in Dorset - up and down some crazy hills and along beaches. The nutcase! ❤️
The case against AI, as summarised by the Daily Star ...
April 27, 2025 at 5:27 PM
The case against AI, as summarised by the Daily Star ...
Meh. As shown in arxiv.org/abs/2503.14743, you can use an even more general non-parametric Gaussian process regression, and if you think the result of that is consistent with w=-1 LCDM then we should have a discussion ...
April 2, 2025 at 9:12 AM
Meh. As shown in arxiv.org/abs/2503.14743, you can use an even more general non-parametric Gaussian process regression, and if you think the result of that is consistent with w=-1 LCDM then we should have a discussion ...
Here's the photo I managed to get:
March 29, 2025 at 11:28 AM
Here's the photo I managed to get:
1. Doesn't make sense to *add* BOSS data (lots of overlap in galaxies). Can *replace* DESI with BOSS, then constraints are weaker but still in the same place (see figure)
March 25, 2025 at 5:23 PM
1. Doesn't make sense to *add* BOSS data (lots of overlap in galaxies). Can *replace* DESI with BOSS, then constraints are weaker but still in the same place (see figure)
This (very information-dense) figure gives a good idea of where the evidence comes from, I think. Fig. 13 in the paper.
March 19, 2025 at 10:54 PM
This (very information-dense) figure gives a good idea of where the evidence comes from, I think. Fig. 13 in the paper.
While the headline takeaway from the ACT results yesterday was "LCDM is fine", the headline from DESI is quite different - evidence for evolving dark energy, at up to 4.2 sigma, and over 3 sigma even without any supernovae, which persists with many different combinations of datasets. 🧪🔭
March 19, 2025 at 10:15 PM
While the headline takeaway from the ACT results yesterday was "LCDM is fine", the headline from DESI is quite different - evidence for evolving dark energy, at up to 4.2 sigma, and over 3 sigma even without any supernovae, which persists with many different combinations of datasets. 🧪🔭
And here is a webpage with a guide to papers and nice summaries of the results: www.desi.lbl.gov/2025/03/19/d...
March 19, 2025 at 10:07 PM
And here is a webpage with a guide to papers and nice summaries of the results: www.desi.lbl.gov/2025/03/19/d...
My 4-year-old and I were discussing Orion tonight and I started to point out Betelgeuse. She said "I know, it's going to explode soon!" And then she said "It will explode near our house and then we'll have to move, coz stars are full of fire." Unsure where she gets her astronomy knowledge from 🔭
March 1, 2025 at 9:25 PM
My 4-year-old and I were discussing Orion tonight and I started to point out Betelgeuse. She said "I know, it's going to explode soon!" And then she said "It will explode near our house and then we'll have to move, coz stars are full of fire." Unsure where she gets her astronomy knowledge from 🔭
So it is ridiculous to post a QR code because it is harder to follow than a link, but it turns out you can get a clickable link out of it on your phone. On Android if you have this enabled you can use it on the QR code on your screen and it will give you a link.
February 18, 2025 at 7:26 PM
So it is ridiculous to post a QR code because it is harder to follow than a link, but it turns out you can get a clickable link out of it on your phone. On Android if you have this enabled you can use it on the QR code on your screen and it will give you a link.
Here are four of my favourite photos from things I did/places I visited in 2024:
December 31, 2024 at 6:44 PM
Here are four of my favourite photos from things I did/places I visited in 2024: