Back into the swing of things in Maynooth, getting ready for the repeat examinations that start next month, I realized that I had forgotten to pass on an interesting paper that I found out about a few weeks ago but was reminded of while in London so I’m remedying my omission now. The title is The Coherence Principle: A Falsifiable Prior for Model Selection from the Grammar of Theories by Raul Jimenez, Carlos Peña Garay, Fergus Simpson, and Licia Verde. It addresses the issue of how to assign prior probabilities. We know how to do this in cases where the models concerned belong to a family differentiated by relatively simple parameters (as is the case in the standard cosmological framework), but for more complex differences the appropriate prior is difficult to choose. I see the paper as an attempt to extend the work of Ed Jaynes, though I’m not sure the authors see it quite in those terms!
Here is the abstract:
Bayesian model selection in cosmology and particle physics is often performed where posterior odds inherit a strong, often unacknowledged dependence on the prior assigned to competing models. Standard responses — reference priors, hierarchical priors, or appeals to naturalness — ignore relevant theoretical knowledge or rely on criteria hard to define operationally. We propose the Coherence Principle: a reproducible prescription for assigning model priors according to compatibility with the validated structure of an existing theory. This structure, grammar, includes symmetries, conservation laws, locality, Lorentz invariance, and universality patterns. Unmotivated violations of these rules incur a coherence cost, converted into a prior weight through a maximum-entropy exponential form controlled by one calibratable parameter α. The resulting prior is distinct from both the Bayesian Occam factor and naturalness: it penalizes not parameter volume or fine tuning, but departures from validated theoretical grammar. We illustrate the principle with examples from cosmology and fundamental physics: neutrino mass mechanisms, dark energy and modified gravity, inflation, beyond-Standard-Model sectors, and hierarchical astrophysical inference. We test it also on four historical cases — general relativity, Pauli’s neutrino, parity violation, and special relativity — where evidential and theoretical contexts can be reconstructed. These examples show that it favors the historically successful choice when the proper grammar is defined in the correct domain and time. The Coherence Principle makes explicit a common but usually tacit part of physical reasoning: trust in validated structural rules. It turns this judgment into a transparent, testable, and overrulable component of Bayesian inference, leaving empirical likelihoods free to dominate when data are sufficiently constraining.
I was very sad this morning to read the news that Sam Neill has passed away at the age of 78. He was a very fine and exceptionally versatile actor. Among many other roles I remember him well as the sadistic and corrupt Chief Inspector Chester Campbell in Peaky Blinders. I was impressed by his convincing Ulster accent but then found out he was actually born in Omagh, County Tyrone.
About 25 years ago (!) I made a very brief appearance in a BBC documentary series called Space for which Sam Neill (left) was the narrator. Apparently he only agreed to do the job on condition that they would film his segments at his home in New Zealand. I remember talking to the production team about Sam Neill and they all said he was not only very professional in his work but also a very nice man. These things don’t always go together…
After the episode I was in – the last of six – was broadcast, my Mam rang me. She didn’t mention my part at all, but asked “That Sam Neill, is he nice?”. I had to explain that I never met him, as they filmed his segments after all the other location sequences. “Oh well,” she said. “At least he knows your name”.
The following clip shows the item I took part in. Originally we were going to demonstrate wormholes using a snooker table, clever editing and reversed video. The producer, Jeremy Turner, decided that wouldn’t look spectacular enough so instead we went to St Anton in Austria: I was flown over the Alps in a helicopter and then driven through the Arlberg tunnel in an impressively fast car. Well worth the cost to license fee payers, I’m sure, even if the three-day trip to Austria by me and a crew of six as well as the hire of the helicopter ended up as a mere three minutes of screen time.
The item is daft, I know, and I don’t really believe any of that stuff about wormholes. It was great fun doing it, but hard work. I remember after the shoot we had a few drinks to wrap it up then left on a very early flight the next morning to the UK. I got back to Nottingham University just in time for a 10am lecture.
Anyway, the episode I was in was called To Boldly Go. I remember suggesting to the producer that the only way to travel faster than light in the manner required was with a split infinitive drive, but they didn’t use that in the final script.
Notice how, in the helicopter sequence, I give the appearance of being completely terrified. A fine piece of acting by me, I thought. *Cough*
The Book of Evidence, by Irish author John Banville, isn’t a new novel – it was published in 1989 – but it was recommended to me a couple of years ago by an Irish friend and was in my pile of books to read until I took it with me on a recent trip.
I wasn’t sure what to expect of this book, but found it an intriguing and unsettling read. Shortlisted for the Booker Prize in 1989, The Book of Evidence is the tale of a dark journey into the mind of a murderer.
The story revolves around Freddie Montgomery who is an educated man – a scientist – but an unsympathetic and unsavoury character. I’d say he is a borderline sociopath, actually. He is the (evidently unreliable) narrator of the story, which is essentially that he tries to steal a painting in order to sell it and settle a debt, but in the course of the attempted robbery he kills a young servant girl in a very brutal way. He is eventually arrested and tells his story on remand awaiting trial. The plot is apparently based on a true story.
This isn’t a whodunnit at all, as the killer tells us what he did. There is a puzzle, though, which is why he killed the girl. The reader never finds out, but that’s probably because Freddie Montgomery himself doesn’t know. In his account he looks back over his entire life, he comes across as an aimless drifter who seems confused by many of the things he has done. It’s only at the very end that he shows any remorse for the murder he committed. At least he realises that he can’t blame his actions on anyone but himself (although he would obviously like to).
We never find out what happens at his trial, as the account finished before it starts. So it’s not a courtroom drama.
In some ways this book echoes The Outsider by Albert Camus as well as Crime and Punishment and Notes from the Underground by Fyodor Dostoevsky. The confessional nature of the account in this book is given authenticity by Banville by making the narration dense and loquacious, with frequent detours and peppered with long words. Montgomery seem to be trying to impress the reader with his erudition but he just comes across as a narcissist. The cumbersome prose style is essential for conveying Montgomery’s inner voice, but it doesn’t make for easy reading. It’s not supposed to. I was intrigued enough to want to read more by Banville, including a sequel to this novel, Ghosts.
P.S. For non-Irish readers it is perhaps worth spelling out that, in Irish criminal law, the “Book of Evidence” is a mandatory set of documents the prosecution must serve to the defence before a trial in a higher court. It’s a term one finds quite often in media reporting of court cases in Ireland.
I took another ferry back from Holyhead to Dublin last night. The outbound journey was via Irish Ferries but I returned on the Stena Line. I left Holyhead at 22.15 and arrived at the Ferry Terminal at Dublin Port at 1.45am. I was a bit unsure what it would be like on such a late-night trip but the trip was uneventful. I’d had a very tiring day getting to Holyhead so I toyed with the idea of sitting in the bar and having a few drinks, but I thought better of that. Instead I found a quiet corner in one of the lounges where there was a bench seat, and managed to stretch out enough to get about an hour’s sleep.
I think quite a few passengers had booked cabins for the crossing. I didn’t think it was worth doing that for less than four hours aboard, but I will consider that next time I take a late-night ferry. There’s not much to see out of the window in the dark!
The disadvantage of being a foot passenger on these ferries is that you have to wait until all the people with vehicles have disembarked before getting a bus back to the terminal building, which adds about 30 minutes to the time. Anticipating the probability that I would be knackered topo fed up to try getting home by public transport with all my luggage in the early hours of the morning, I had booked a taxi to meet me at 1.45, the scheduled arrival time, but I didn’t actually meet the driver until after 2am. Sitll, I got home to Maynooth quickly and was tucked up in bed by 3am. I had to open all the windows as the house was very stuffy, but other than that all was well.
While I was staying in London I took a few trips by train here and there, most of them very shambolic. All the direct trains from London Paddington to Oxford were cancelled, so passengers had to get on very overcrowded trains that went through Oxford to other destinations. To get back to London I used a train to Marylebone which I didn’t know existed. It was slow, but got me back.
With these problems in mind I took an earlier train from Euston to Holyhead than I originally intended. I’m glad I decided that because even the earlier train was delayed by > 45 minutes leaving Euston. Worse, some other trains goint to Manchester and beyond were cancelled so passengers were advised to get on the train I was on and change at Crewe or Chester. The seat reservations weren’t working so the result was a very sweaty overcrowded train with standing room only, at least until Chester where many people got off. The uncomfortable journey made me break a 195-day blogging streak as I just couldn’t be bothered even when I got a seat. Instead I just relaxed and looked out of the window as we travelled along the coast of North Waves.
My train from Holyhead to London was delayed by over an hour as was the train back yesterday. The upshot of all that is that I get a 100% refund of the fare for the entire journey so it was effectively free (if you don’t count the cost of the stress and discomfort).
Anyway, this trip was my first experience of ferry+train to the UK and back. My summary of the experience is “Ferry Good, Train Bad”.
Back home to Maynooth, just in time for another Saturday update of activity at the Open Journal of Astrophysics. Since the last update we have published a further nine papers, bringing the number in Volume 9 (2026) to 145 and the total so far published by OJAp up to 593.
I will 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, published on Tuesday 7th July, is “The Information Content of Quasar Variability Light Curves: How Well Can we Infer Stochastic Model Parameters?” by Brendon Brewer (U. Auckland, NZ), Geraint F. Lewis (U. Sydney, AU), Xiang Yu & Yuan Li (Auckland). Published in the folder Astrophysics of Galaxies, this study suggests that quasar variability studies should focus on the short term volatility parameter, as it’s more informative than the variability timescale. Volatility decreases with redshift suggesting intrinsic effects.
The overlay for this paper is here
You can find the officially accepted version on arXiv here and the announcement on Fediverse here:
New Publication at the Open Journal of Astrophysics: "The Information Content of Quasar Variability Light Curves: How Well Can we Infer Stochastic Model Parameters?" by Brendon Brewer (U. Auckland, NZ), Geraint F. Lewis (U. Sydney, AU), Xiang Yu & Yuan Li (Auckland)
The second paper for this week, also published on Tuesday 7th July, but in the folder High-Energy Astrophysical Phenomena, is “Cygnus X-3 as a PeVatron and the LHAASO 2025 data” by Michael Kachelriess & E. Lammert (NTNU, Trondheim, Norway). This paper suggests that the high-mass X-ray binary Cygnus X-3 can accelerate cosmic rays beyond PeV energies, contributing to a photon flux peaking around PeV energies.
The overlay looks like this:
The official version of the paper can be found on arXiv here and the Fediverse announcement here:
New Publication at the Open Journal of Astrophysics: "Cygnus X-3 as a PeVatron and the LHAASO 2025 data" by Michael Kachelriess & E. Lammert (NTNU, Trondheim, Norway)
New Publication at the Open Journal of Astrophysics: "The DESI DR1 Peculiar Velocity Survey: growth rate measurements from galaxy and momentum correlation functions" by Ryan J Turner (Swinburne Institute of Technology, Australia) and 63 others from around the world.
New Publication at the Open Journal of Astrophysics: "On the effective spin-mass ratio relation of binary black hole mergers that evolved in isolation" by Sambaran Banerjee (Helmholtz-Instituts für Strahlen und Kernphysik, Germany) and Aleksandra Olejak (MPA Garching, Germany)
The fifth paper of the week, also published on Wednesday 8th July but in the folder Astrophysics of Galaxies, is “On the connection between galaxy orientation and halo absorption properties” by Rohan Venkat, Soo May Wee, and Hsiao-Wen Chen (U. Chicago, USA). This article investigates the azimuthal dependence of metal-line absorption in the circumgalactic medium of 87 isolated galaxies. The results show no significant correlation between absorption strength and azimuthal angle.
The overlay for this one is here:
You can read the final version of this one on arXiv here and the Mastodon announcement is here:
The sixth paper of this week is “Searching for Periodicity in FRB 20240114A” by Jonathan I Katz (Washington U., USA). This was published on Thursday 9th July in the folder High-Energy Astrophysical Phenomena. The study described in this paper observed FRB 20240114A, an active Fast Radio Burst, but found no significant periodicity in its bursts, contradicting magnetar models predictions.
The overlay for this one is here:
You can find the final accepted version on arXiv here and the Mastodon announcement is here:
The seventh article for this week is “Multiphase gas in Circumgalactic cloud complexes: Insights from kiloparsec-scale Magnetohydrodynamic Turbulence Simulations” by Rajsekhar Mohapatra (Princeton U., USA), Alankar Dutta (MPA Garching, Germany) and Prateek Sharma (Indian Institute of Science, Bangalore). This -paper was also published on Thursday 9th July, in the folder Astrophysics of Galaxies. This paper uses high-resolution simulations to investigate the mass distribution of the circumgalactic medium (CGM), a diffuse gas surrounding a galaxy’s halo with small-scale clumps of cold gas forming in quiescent regions.
The overlay for this one is here:
You can find the final accepted version of this one on arXiv here and the Mastodon announcement is here:
New Publication at the Open Journal of Astrophysics: "Multiphase gas in Circumgalactic cloud complexes: Insights from kiloparsec-scale Magnetohydrodynamic Turbulence Simulations" by Rajsekhar Mohapatra (Princeton U., USA), Alankar Dutta (MPA Garching, Germany) and Prateek Sharma (Indian Institute of Science, Bangalore)
The (penultimate) eighth article for this week is “Line-of-sight shear in SLACS strong lenses I: shear and mass model parametrisations” by Natalie B. Hogg (U. Cambridge, UK), Daniel Johnson (U. Montpellier, France), Anowar J. Shajib (U. Chicago, USA) and Julien Larena (Montpellier). This was also published on Thursday 9th July, but in the folder Cosmology and Nongalactic Astrophysics. This article studies models of 23 strong gravitational lenses to measure line-of-sight shear for the first time, providing potential new constraints on cosmological parameters.
The overlay for this one is here:
You can find the final accepted version on arXiv here and the Mastodon announcement is here:
New Publication at the Open Journal of Astrophysics: "Line-of-sight shear in SLACS strong lenses I: shear and mass model parametrisations" by Natalie B. Hogg (U. Cambridge, UK), Daniel Johnson (U. Montpellier, France), Anowar J. Shajib (U. Chicago, USA) and Julien Larena (Montpellier)
The ninth and last article for this week is “Current and future constraints on the expansion history of the GREA model” by Irene Graziotti (INAF-Osservatorio Astronomico di Capodimonte, Italy), Chiara De Leo (Sapienza University of Rome, Italy) and Matteo Martinelli (INAF-Osservatorio Astronomico di Roma, Italy). This study explores the General Relativistic Entropic Acceleration (GREA) framework, comparing it to the standard description of the universe. Current data favors the standard model, but GREA remains competitive.
The overlay for this one is here:
You can find the officially-accepted version on arXiv here and the Mastodon announcement here:
New Publication at the Open Journal of Astrophysics: "Current and future constraints on the expansion history of the GREA model" by Irene Graziotti (INAF-Osservatorio Astronomico di Capodimonte, Italy), Chiara De Leo (Sapienza University of Rome, Italy) and Matteo Martinelli (INAF-Osservatorio Astronomico di Roma, Italy)
As you can see, it has been a bumper week, especially when you consider that there was no arXiv mailing om Monday July 6th owing to the July 4th holiday in the USA. I should have known this would happen while I was travelling!
I’m not in Maynooth right now, but I gather it’s warm there. Not perhaps as warm as here in London (34°C), bit still a bit warm to be wearing a fur coat. Still, it seems that Maynooth Library Cat is surviving…
Today has been a very frustrating day from the point of view of travel – apparently it’s too hot for trains to function – but at least that gave me time to read the book Invisible Rainbows by Dr Alfredo Carpineti (left). This is an engaging and nicely written tour of what we know (and don’t know) about the Universe organized by wavelength of electromagnetic radiation, from radio through microwaves and infrared, to ultraviolet and X-rays to gamma rays. All the wavebands outside the range of human perception, in fact.
What makes this book different from others that have taken the same general approach is that he builds that fairly conventional narrative around conversations with LGBTQIA+ scientists to demonstrate how diverse perspectives have contributed to the advancement of astronomy, astrophysics and cosmology.
There are even a couple of quotes from yours truly, but it’s not just for vanity’s sake that I’m very happy to see this book published. It’s very nicely written and offers a very new perspective on science as a human endeavour. This definitely the first astrophysics book I’ve seen with a dedication “For all the queer kids reaching for the stars”. I guess I was one of those once! The book is at times humorous, even cheeky, but always driven by a passion for astrophysics and the celebration of human diversity. I wish I had I time to read it before Pride Month, but I’m nevertheless very proud to have featured even in a tiny way in such a delightful book.
It’s been three days now since Pride in London and I think it’s time to post a few pictures to show I was actually there.
My partner took a bit of persuading to come along – he’s not out (for good reasons) and does not like the idea of having pictures on the internet. He detests social media too and, unusually for a person his age, has no instagram or tiktok or anything else.
He thought it would be hard to avoid being pictured. Anyway, we found a fairly unobtrusive spot and although he was a bit nervous at first he soon relaxed and started to enjoy it. Some people took pics of the crowds lining the route, but there was a convenient tree for him to hide behind. We stayed several hours, actually, and the parade was still passing our place at the end of Piccadilly when we left, so it must have been a very long parade.
A wonderful thing happened, halfway through our stay at the Parade: we held hands in public for the first time. That may not seem much but it meant a great deal to me. I often hear people saying that Pride is no longer needed, but remember that not everyone has an understanding family or grew up in an accepting environment. It’s taken two and a half years to get this far. It’s not the sort of “progress” that the “pride progress” flag is supposed to represesent, but it’s progress nonetheless.
Another warm day in London found us taking the shortish trip by Tube to Kew to see not only the magnificent botanical gardens but also the large collection of sculptures by Henry Moore dispersed throughout. Here are a few snaps I took on the way around. As you can see in the pictures, the gardens are looking a bit parched.
Cynara Cardunculus, in Kew Gardens, a large thistle plant which is very pollinator-friendly
It’s more than 30 years since I was last at Kew Gardens, so I didn’t remember the way round very well. We ended up spending about four hours there, including a stop for tea at the Orangery which, I’m delighted to say, was served properly, in a pot, with nice cups and saucers and milk in a little jug. The last time I saw works by Henry Moore in an outdoor setting was back in 2011; see this post.
Though not many people have gardens as extensive as Kew, they are very helpful in assisting domestic gardeners with hints and suggestions of things to plant in different spaces: dry, damp, sunlit, shady, you name it.
Anyway, it was a really lovely day for all kinds of reasons. I know it’s corny but I was reminded of that song by Lou Reed:
just a perfect day you make me forget myself I thought I was someone else someone good
After picking up his things from the hotel we went to Paddington where I saw my weekend companion onto the train for Heathrow. I’m a bit sad to be on my own again, but it won’t be long until the next time…and the next place.
Back to the hotel for a short siesta after spending most of the day at Tate Britain, where there is a special exhibition of works by and about James McNeill Whistler. The main collection at Tate Britain is free, but the Whistler exhibition costs £24 to see. It’s well worth it though.
The first picture shows Whistler’s famous portrait of his mother, who seems to be holding court. My favourite pieces, however, the Nocturnes, two of which I have mentioned on this blog before. There are three shown below, but photographs don’t do them justice at all. The appearance of the paint when seen close up is quite remarkable, a sort of translucent quality to it even when the picture is very dark. Whistler was one of the first artists to really master painting in the dark without using moonlight or other obvious illumination.
The last of these is particularly interesting to me. When the great American songwriter Billy Strayhorn saw the beautifully evocative painting (above) of one of the bridges over the River Thames, it inspired him to write an equally evocative song to be performed by his longstanding musical collaborator and friend Duke Ellington. The song was written in 1941, but it was only years later that he realized that he had named it after the wrong bridge. The painting was of Battersea Bridge; but he had named the song Chelsea Bridge, a much less romantic location. Chelsea Bridge is an intriguing tune, based on minor sixth chords voiced via their third inversions, it sounds almost atonal but very evocative, just like the painting.
In one of the video segments played during the exhibition we hear the actor Anton Lesser quoting Whistler with words the effect that he saw colours like notes on a keyboard; he started naming his paintings after musical works, e.g. “Symphony in White” before he got to his masterpieces, the Nocturnes.
I wrote about another of the Nocturnes here. Nocturne in Black and Gold, in the same series as the third picture above, is famous for having been at the centre of a libel case. The influential art critic John Ruskin hated it and accused Whistler of “flinging a pot of paint in the public’s face”. Whistler sued for damages (though he couldn’t really afford to). He won the case against Ruskin, but the outcome was financially disastrous for him because he was awarded only one farthing in damages and was bankrupted.
Tate Britain has an extensive permanent collection of primarily English art from about 1600 onwards, not least a huge collection of works by J.M.W. Turner. It’s fascinating to see so many of these together, charting this extraordinary artist’s evolution from brilliant if conventional upstart to pioneering impressionist. Along the way Turner’s interest in conventional themes began to wane in favour of the interplay between sea and clouds, to the extent that his works began to look like abstracts. There is in my mind a strong influence on Whistler. This one, ostensibly a seascape with a distant shore, reminds me of Rothko.
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In the Dark 