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Sesh Nadathur

@seshnadathur.bsky.social
676 followers 424 following 1.1K posts

Professor of Cosmology at Portsmouth. "Cosmic cartographer": I make and use 3D maps of the Universe from galaxy redshift surveys, with telescopes on desert mountaintops and in space. Dad, occasional climber, likes cricket. Occasionally I have opinions.

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Mike Cook @mtrc.bsky.social · 22/09/2026
New Post: Why I Love AI Next month it'll be twenty years since I went to university, learned to program, and studied AI. I wrote about why I loved it, why I still love it, and why, unfortunately, it no longer exists. www.possibilityspace.org/blog/posts/i...
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Stephen Morgan MP @stephenmorganmp.bsky.social · 21/09/2026
The RNLI's people represent the very best of society and our city. They dedicate themselves to rescuing people they've never met before, without judgment, fear or favour👇🏻 www.portsmouth.co.uk/news/portsmouth-mp-backs-rnli-volunteers-after-threats-9128353
portsmouth.co.uk
Portsmouth MP thanks RNLI volunteers with public letter after threats made to crews
RNLI volunteers have faced threats and abuse
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Sesh Nadathur @seshnadathur.bsky.social · 21/09/2026
7.4k applicants the year I applied (2014), 7k in 2022, suddenly triple the application rate since then. I wonder what could have caused that? 🤔 Purely in terms of the number of human hours of effort wasted on unsuccessful applications, it may actually be better now than then ... !
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Lev Parikian @levparikian.bsky.social · 19/09/2026
Well it’s about that time again – the time when grown adults all over the country say “right, time for bed” with a sense of purpose and then sit slumped on the sofa for another 53 minutes, scrolling through the random drivellings of total strangers.
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Anthony Painter @anthonypainter.bsky.social · 19/09/2026
"Reindustrialisation" could take us into some pretty dangerous territory. Manufacturing is an important part of our economic future but elevating it above all else is extremely high risk. Latest Substack. anthonypainter.substack.com/p/wrong-left...
anthonypainter.substack.com
Wrong left turn
Why “reindustrialisation” could lead us down a very wrong path even if a noble aspiration.
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James Ball @jamesrball.com · 18/09/2026
It is incredibly important that political violence does not succeed. The far-right mob that shut down Portsmouth wanted this outcome. If the state wishes to avoid more of these actions, it needs to make sure this RNLI branch reopens *immediately*, or as close to that as humanly possible.
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Sesh Nadathur @seshnadathur.bsky.social · 14/09/2026
My random Monday reflection, driven by family conversations over the weekend, is that UK schools really provide an excellent education. My kids (6 & 8) just started chatting to me about Picasso, and Andy Warhol, and local Portsmouth street artists - all based on stuff they've learned at school.
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Charles Fourier @charlesfourier.bsky.social · 08/09/2026
Bill Bryson’s words seem appropriate to post right now
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Sesh Nadathur @seshnadathur.bsky.social · 08/09/2026
I don't think they actually are denying it as strongly as you think. Read the OpenAI statement, it is quite carefully worded. In particular this bit: "While unlikely, we cannot rule out that de-identified data derived from their usage of our products helped improve our models⁠."
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Quantian @quantian.bsky.social · 08/09/2026
Dancing very very VERY close to saying “OpenAI stole our almost-complete proof of Navier-Stokes from internal access to our ChatGPT sessions because they were desperate to scoop Anthropic” which is absolutely 100% a believable thing OpenAI would do right now cims.nyu.edu/~tristanb/st...
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Sesh Nadathur @seshnadathur.bsky.social · 07/09/2026
A colleague went to the National Air and Space Museum in Washington DC which has a beautiful #cosmology exhibition on "Discovering Our Universe" featuring many telescopes, several historically important astronomers, and also ... me?! I'm described as a Cosmic Cartographer, which is awesome 🤩 🔭🧪
Picture of a museum exhibit about the Sloan Digital Sky SurveyA section of a museum display with an information label titled "Seshadri Nadathur, Cosmic Cartographer"
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Sesh Nadathur @seshnadathur.bsky.social · 05/09/2026
The astrophysics facts in this monumental thread are great, but the shark facts are even better.
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The Author, Séamas O'Reilly @seamas.bsky.social · 01/09/2026
TL:DR, in 2020, I got to ask Werner Herzog whether the story about him being forced to speak French to some child soldiers was true, and he gave me the most poetic, most Herzogian response I could ever have hoped for.
“Hello. Can you hear me?” asks a black screen on my laptop. I am using Zoom for the 4,000th time since the beginning of the pandemic and enjoying approximately the 4,000th technical glitch in the same time period. A few seconds later, Werner Herzog bursts into view, his familiar face framed by bookshelves and sliding drawers, which I long to believe contain a spear and the animatronic prostheses of a fully working Loch Ness Monster. For 20 minutes, I withstand the ego-shredding horror of a five-second delay in video communication, which leaves my every question stranded in total silence as if the stupidity has rendered him dumbstruck.Feeling increasingly stupid myself, I bite the bullet. “Werner,” I ask, “were you really held at gunpoint and made to speak a few regrettable sentences in French?” Is the story you tell in the Incident at Loch Ness outtake real?
“No,” he says. “Look, I do speak those languages, sure. I mean, I do not speak Latin or ancient Greek because they are dead languages, but I can read them. It’s of minor importance; as always, there’s some layers, few facts, a few distortions. It’s inventive. I do have fundamental problems with speaking French because I am very Bavarian, and it’s a very different attitude to spoken language or discourse. Discourse is different from French. I did have to do with child soldiers in Honduras and Nicaragua for one film. I’m actually planning a project in Sierra Leone with child soldiers — completely staged, of course — but it concerns some U.N. troops and a small group of child soldiers who hold a checkpoint at a bridge. So, of course, child soldiers have always had a certain appeal to me because something deep comes across there.”Perhaps sensing my dejection at his runaround answer and the end of our allotted time together on Zoom, Herzog launches into an unbroken paean to fakery’s favorable position over the so-called truth, citing the French Nobel Prize winner André Gide and William Shakespeare, two figures who’ve expressed a preference for feigning. “Only those who are deeply religious would tell you what the truth is,” he says at one point. “And they are obviously as wrong as it gets because the biggest of all fake news is religion.”
And what of this outtake, I ask. Is it not itself, for all the joy of its execution, merely fake news of the same order?
“I always quote Michelangelo as my key witness” he replies, “whose Pietà is in Rome. When you look at the statue, you see the dead body of Jesus in Mary’s lap. Jesus’ face is the tormented face of a 33-year-old man. And when you look at the face of his mother, she is 15. So my question is, Did Michelangelo try to cheat us? Did he try to give us fake news? Did he try to defraud us, lie to us? No. I think he made a clear statement.”
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Sesh Nadathur @seshnadathur.bsky.social · 01/09/2026
Finally something maybe/possibly resembling a positive result from a dark matter detection experiment? Much too early to get excited - but at least it isn't another definite null result, and more data should arrive to adjudicate relatively soon!
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Sesh Nadathur @seshnadathur.bsky.social · 01/09/2026
Some personal/professional news: as of today, I am now a Professor of Cosmology. 🔭 The journey to professorship over the last decade+ required support from many people along the way, not least those who wrote positive assessments of my work for the panel, so many thanks to all of them!
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KarSteN Haustein @khaustein.bsky.social · 31/08/2026
Globally, the hottest August in observed history is just about to end. In Western Europe, the summer of 2026 (June, July, August) has been the warmest as well. Compared to this year, 1976 (the famous UK summer) and 2003 (the hottest EU summer so far) look like amateurs in terms of heat (1/2)
Global map of temperature departures with most continental regions as well as the tropical Pacific in red (hot). Parts of Antarctica in blue (cold)

Source: http://www.karstenhaustein.com/climateMap of Europe with blue and cold patches for cold and hot temperature departures from the long-term climate average (1961-1990). France and the UK in red. All else rather blue.Map of Europe with blue and cold patches for cold and hot temperature departures from the long-term climate average (1961-1990). All of central Europe in red. Parts of the Atlantic in blueMap of Europe with blue and cold patches for cold and hot temperature departures from the long-term climate average (1961-1990). All of central and Southern Europe in red. No blue left anymore.
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Sesh Nadathur @seshnadathur.bsky.social · 30/08/2026
An amusing story (with a very on-the-nose final sentence) - but some might wonder what is new. That particular code has had "subtle" errors that add up to it being "very wrong" since it was first written, by humans, back in 2012. I wrote a paper about it at the time! Not sure AI was needed for that
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Sesh Nadathur @seshnadathur.bsky.social · 25/08/2026
When I was younger I never paid much attention to Dolly's music though I was vaguely aware of her. But I remember exactly where I was and what I was doing the first time I ever heard Jolene youtu.be/Ixrje2rXLMA?...
youtu.be
Dolly Parton - Jolene (Official Audio)
YouTube video by DollyPartonVEVO
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Kyle Griffin @kylegriffin1.bsky.social · 25/08/2026
Reminder: Dolly Parton helped fund the Moderna vaccine for COVID.
nytimes.com
Dolly Parton, who helped fund the Moderna vaccine, gets a ‘dose of her own medicine.’ (Published 2021)
The country music star broke into song before she was inoculated, and urged her fans to “get out there and get your shot.”
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Sesh Nadathur @seshnadathur.bsky.social · 25/08/2026
RIP Dolly Parton. A great human.
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Sesh Nadathur @seshnadathur.bsky.social · 20/08/2026
Big day on my cricket club's WhatsApp group, containing as it does a mix of school teachers, parents, and teens getting their GCSE results today ...
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Sesh Nadathur @seshnadathur.bsky.social · 19/08/2026
Anyone who signs petitions or open letters from the Good Law Project should have a good think about what they are doing, IMO
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Sesh Nadathur @seshnadathur.bsky.social · 16/08/2026
Great performance to get silver, so clearly the visualisation worked! And a good interview afterwards as well
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Sesh Nadathur @seshnadathur.bsky.social · 16/08/2026
Absolutely loving Jaz Sawyers' style in the long jump!
Jaz Sawyers on the long jump runway visualising before her first jump, wearing a funky pair of sunglasses and with a colourful blanket wrapped around her waist
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Grumpy Philosopher @stevecooke.org · 13/08/2026
A direct result of government policy: 1) a disastrous funding system, 2) removal of student recruitment quotas, 3) restricting overseas recruitment. Now, the richest universities are over-recruiting, to the detriment of students & every other university. A problem that’s been known about for years.
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852dude @852dude.bsky.social · 13/08/2026
Bro. People are cool as fuck.
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Gabe Lynch @gpxl.bsky.social · 04/08/2026
You can think of this disagreement as a sort of "matter density deficit" — DESI BAO data prefer a lower matter density than the CMB infers to be in cold dark matter and baryons. As pointed out by other authors though, this can be explained if we have the reionization optical depth (τ) wrong... 2/n
A figure from Sailer et al. 2025, showing constraints on the matter fraction and optical depth from different data sources. There is a second panel which shows constrains on the combination of the Hubble constant and the sound horizon, which is measured by baryon acoustic oscillation data, and the matter matter fraction.

In the first panel, there is an ellipse representing constraints from the cosmic microwave background, and a band showing constraints from DESI BAO data. The two are in better agreement if the value of the optical depth is higher.
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Sesh Nadathur @seshnadathur.bsky.social · 12/08/2026
Well I thought that was amazing! I managed to get some remarkably decent photos just by sticking my eclipse glasses in front of my phone camera, plus the colander trick worked nicely too.
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Sesh Nadathur @seshnadathur.bsky.social · 12/08/2026
I thought I didn't have any eclipse glasses but my wife found an old pair lying in a drawer!
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Stephen Bush @stephenkb.bsky.social · 12/08/2026
I don’t mean to suggest that either of these individual professors are mere victims of the system, but I also think it is worth noting that “ask questions of us? We’ll turn the investigation onto you” appears to be Cambridge’s preferred response:
theguardian.com
University of Cambridge whistleblower who reported alleged bullying wins employment tribunal
Prof Wyn Evans, who raised concerns over treatment of female staff at Institute of Astronomy, was subject to ‘baseless’ investigation, judge rules
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Sesh Nadathur @seshnadathur.bsky.social · 10/08/2026
Watching the athletics on catch-up, and it is so good to see Jakob Ingebritsen back. What a great final lap.
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Sesh Nadathur @seshnadathur.bsky.social · 10/08/2026
I see people are talking about Harry Potter for some reason, so here are my thoughts: my kids, who are 6 and 8, have absolutely loved reading them (3 and 4 books in, respectively). But that's roughly their level: as a grown adult if you are arguing on the internet about them, what are you doing?
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Sesh Nadathur @seshnadathur.bsky.social · 03/08/2026
What an excellent and thought-provoking set of slides!
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Mike Boylan-Kolchin @mbkplus.bsky.social · 02/08/2026
For the academics out there who are wondering about how to deal with rejection (and aren’t we all):
Rejected Rejection
(Contributed by Gretchen F. Stoloti)
Herbert A. Millington
Chair - Search Committee
412A Clarkson Hall
Whitson University
College Hill, MA 34109
Dear Professor Millington,
Thank you for your letter of March 16. After careful consideration, I regret to inform you that I am unable to accept your refusal to offer me an assistant professor position in your department.
This year I have been particularly fortunate in receiving an unusually large number of rejection letters. With such a varied and promising field of candidates it is impossible for me to accept all refusals.
Despite Whitson's outstanding qualifications and previous experience in rejecting applicants, I find that your rejection does not meet my needs at this time. Therefore, I will assume the position of assistant professor in your department this August.
I look forward to seeing you then.
Best of luck in rejecting future applicants.
Sincerely,
Chris L. Jensen
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Sam Freedman @samfr.bsky.social · 03/08/2026
Why do so many progressives want this? I just don't get it.
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Sesh Nadathur @seshnadathur.bsky.social · 02/08/2026
This post makes some interesting and correct points that I haven't seen mentioned anywhere else.
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Rob Jacques @knutcrosswords.bsky.social · 30/07/2026
UEFA spokesperson Dietmar Fumm said to reporters "This decision effectively signals that Gianni Infantino is an enemy of world football". tl;dr: FIFA "foe" - Fumm
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Sesh Nadathur @seshnadathur.bsky.social · 29/07/2026
At Arundel today with a group of lads from my cricket club, watching Sussex v Essex. Very good turnout, in the 4000s I'd say. Festival atmosphere. Essex got 316/6, probably a good score but they looked on course for much more at one point!
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Kirsty Grainger @kirstygrainger.bsky.social · 27/07/2026
Earlier this year UKRI launched a funding call to invest £40M in ONE AI lab. www.ukri.org/opportunity/... For some unknown reason they decided to fund TWO AI labs at the cost of £60M. An extra £20M. Just found. That's the equivalent of 7 more years of Jodrell Bank. www.ukri.org/news/ukri-la...
ukri.org
UKRI launches two AI research labs to stay ahead in global race
Two new labs will back British researchers to develop next generation artificial intelligence (AI) systems, helping secure the UK’s position as a global leader.
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Harry Cliff @harrycliff.bsky.social · 27/07/2026
It’s official: UKRI has defunded the LHCb upgrade, which would have run at the High Luminosity LHC (currently under construction). This is a disaster for UK physics. We’ve rightly invested heavily in the HL-LHC but without LHCb, we’re throwing away crucial science that can’t be done anywhere else.
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Chris Lintott @chrislintott.bsky.social · 27/07/2026
Short-sighted, stupid cuts to the UKRI budget include shutting down Jodrell Bank, the icon of British astronomy. (Many other cuts too, including 20% to our brand new @vrubinobs.bsky.social). Interesting politically to shut down a major facility in...um..Manchester 🔭 www.bbc.co.uk/news/article...
bbc.co.uk
Jodrell Bank's Lovell telescope faces axe in science cuts, BBC understands
Astronomers warn it would tear the heart out of UK science, and leave a generation untrained.
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Greg Egan @gregegansf.bsky.social · 27/07/2026
While the Fields Medal celebrates the under-40s, the mathematician Joan Birman has, at the age of 99, solved a major open problem in representations of the Braid groups, a topic she has worked on for more than 60 years.
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Sesh Nadathur @seshnadathur.bsky.social · 26/07/2026
Well, that was quite good www.maptap.gg July 26 99🎯 96🔥 99🎯 99🎯 100🎯 Final score: 990
maptap.gg
🎯MapTap Daily Geography Game
Play MapTap - the daily geography game! Find 5 world locations on a 3D globe with historical stories. Free browser-based daily game for geography lovers.
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NSF–DOE Rubin Observatory @rubinobservatory.org · 24/07/2026
Talk about a cosmic glow-up✨📸 This progression of images of galaxy group RSCG 55 shows the evolution of ground-based sky surveys spanning more than three decades🤯, ending with NSF–DOE Rubin Observatory's view. 🔭🧪
Five-panel image showing the progressive evolution of sky surveys from 1994 to 2025, revealing more and more detail in a triple merging galaxy system and the surrounding sky.
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Sesh Nadathur @seshnadathur.bsky.social · 22/07/2026
Graduation ceremony day for my former PhD student Dr Nathan Findlay! Nathan's (excellent) thesis was titled "Novel clustering methods for cosmology with the Dark Energy Spectroscopic Instrument" and he defended it a few weeks ago.
Two men wearing academic doctoral gowns (one scarlet and blue, the other scarlet and purple with white trim) and hats, standing in front of a building with stone steps and pillars. One of them is also wearing a tartan kilt.
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Sesh Nadathur @seshnadathur.bsky.social · 19/07/2026
Well that was quite a fun game. And really a great day of sport all round.
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Tony Tassell @tonytassell.bsky.social · 17/07/2026
A reminder when Gary Sobers hit six sixes in an over h/t @jderbyshire.ft.com www.youtube.com/watch?v=8u7A...
youtube.com
Sir Garfield Sobers hits 6 Sixes in an over
YouTube video by Kalyan Verma
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Sesh Nadathur @seshnadathur.bsky.social · 17/07/2026
What a man he was.
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Sesh Nadathur @seshnadathur.bsky.social · 13/07/2026
Very sorry to see this. He was a great actor and, from what I could tell from his social media, a lovely and funny guy.
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Sesh Nadathur @seshnadathur.bsky.social · 12/07/2026
On the train to Durham, where, if the weather reports are to be believed, it is only 21 degrees. Can't remember the last time I experienced that kind of temperature!
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