Archive for the The Universe and Stuff Category

Cosmology Talks: Julien Lesgourgues on Neutrino Masses

Posted in The Universe and Stuff with tags , , , on April 3, 2020 by telescoper

If you are missing your regular seminar experience because of the Coronavirus lockdown, Shaun Hotchkiss has set up a YouTube channel just for you!

The channel features technical talks rather than popular expositions so it won’t be everyone’s cup of tea but for those seriously interested in cosmology at a research level they should prove interesting.

Here’s an example in which Julien Lesgourgues talks about (not measuring neutrino masses with cosmological data.

Early Dark Energy and Cosmic Tension

Posted in The Universe and Stuff with tags , , , , , on March 19, 2020 by telescoper

To avoid talking any more about you-know-what I thought I would continue the ongoing Hubble constant theme. Rhere is an interesting new paper on the arXiv (by Hill et al.) about the extent to which a modified form of dark energy might relieve the current apparent tension.

The abstract is:


You can click on this to make it bigger; you can also download the PDF here.

I think the conclusion is clear and it may or may not be related to a previous post of mine here about the implications of Etherington’s theorem.

Here’s my ongoing poll on the Hubble constant poll. Feel free to while away a few seconds of your time working from home casting a vote!



New Publication at the Open Journal of Astrophysics!

Posted in Open Access, The Universe and Stuff with tags , , , , , , , on March 13, 2020 by telescoper

Well Maynooth University may have shut down but the The Open Journal of Astrophysics certainly has not.

In fact we have just published another paper! This one is called Halo Spins from Primordial Inner Motions and the first author is Mark Neyrinck (based in Bilbao). The other authors are Miguel Aragon-Calvo (based in Mexico), Bridget Falck and Alex Szalay (based in the USA) and Jie Wang (China).

Here is a grab of the overlay:

You can find the arXiv version of the paper here.

As an added bonus there are some groovy videos to go with this paper:

You might have to read the paper, however, to understand exactly what they mean (although they are very pretty anyway).

An Astronomical Anniversary

Posted in Biographical, History, The Universe and Stuff with tags , , on March 10, 2020 by telescoper

I was reminded via Twitter that today is the 200th anniversary of the first formal meeting of the Astronomical Society of London which took place on 10th March 1820. This society turned into the Royal Astronomical Society when it was given a Royal Charter in 1831. Here is the first page of the the Minutes of that first meeting:

Those of you who have been paying attention will recall that the decision to form the Society was taken at a dinner in January 1820 and the bicentenary of this event was celebrated in January by the RAS Dining Club (of which I am a member).

Club Dinners usually take place after the Open Meetings of the Royal Astronomical Society on the second Friday of the month. Sadly, however, there won’t be a Club Dinner this Friday as it has been cancelled owing to the Coronavirus emergency. I’ll have to make do with beans on toast again then.

Incidentally, I thought I’d share this list of the first 200(ish) members of the Royal Astronomical Society (PDF) kindly sent to me by former Cardiff colleague Mike Edmunds. There are some illustrious names among the early members, including Laplace and Bessel, as well as some oddities, such as His Excellency Alexis Greig (Vice Admiral of the Imperial Russian Navy) and Edward Riddle, Esq. (First Mathematical Master, the Royal Naval Asylum).



Maynooth’s Creation

Posted in Maynooth, Music, The Universe and Stuff with tags , , , , on March 8, 2020 by telescoper

As it was foretold, this afternoon to the College Chapel at Maynooth, which looks like this inside:

This was in fact the first time I’ve set foot inside the Chapel. The occasion was the annual Spring Concert by Maynooth University Choral Society, accompanied by the Irish Choral Sinfonia, in a performance of Haydn’s great oratorio The Creation.

It’s worth mentioning that Haydn started preparing to write his Creation in 1796, which is just a year after St Patrick’s College in Maynooth was established (as the National Seminary of Ireland). This work was therefore was a good choice for the year in which the College celebrates the 225th year of its own creation.

Although the College Chapel is quite large it provided a very intimate setting for this great masterpiece (in that the audience was very close to the musicians and singers) and provided a very distinctive acoustic. Curiously, this was the first time I had heard this work performed in English.

The solo vocalists – Claudia Boyle (soprano), Andrew Gavin (tenor) and Simon Morgan (bass) – were all excellent, as were the choir and orchestra. All in all it was a hugely enjoyable experience, even if the wooden seats were a bit unforgiving!

After the performance there was a Buffet Supper in Pugin Hall, which I had assumed would just be sandwiches but which turned out to be a very nice meal with wine at which I got chatting to some very friendly people. Admission to the event was by invitation only, but the guest list was not restricted to folk from Maynooth University.

As the token astrophysicist present a few people asked me what was shown in the picture on the cover of the programme. Not being a proper astronomer I didn’t know but I am reliably informed that it is the Eagle Nebula (M16), though it is reversed left to right which I claim as an excuse for not recognising it…

From the Inventor of the H-index

Posted in Biographical, The Universe and Stuff with tags , , , , on March 5, 2020 by telescoper

My third-year students are busily engaged with a Computational Physics class test so I thought I’d occupy myself for a few minutes by sharing an interesting little paper that appeared on the arXiv a few weeks ago. The paper is by Jorge Hirsch, the inventor of the (in)famous H-index.

Here is the abstract:

A magnetic field H is expelled from the interior of a metal becoming superconducting. Everybody thinks the phenomenon is perfectly well understood, particularly scientists with the highest H-index think that. I don’t. I will explain why I believe that without Holes, conceptualized by Heisenberg in 1931 fifty years after Hall had first detected them in some metals, neither magnetic field expulsion nor anything else about superconductivity can be understood. I have been a Heretic in the field of superconductivity for over 30 years, and believe that Hans’ little story about the emperor perfectly captures the essence of the situation. Here is (a highly condensed version of) the wHole story.

You will see that, despite the liberal sprinkling of letters H, the paper isn’t ostensibly about the H-index, but it does contain some interesting comments thereon, including:

I proposed the H-index hoping it would be an objective measure of scientific achievement. By and large, I think this is believed to be the case. But I have now come to believe that it can also fail spectacularly and have severe unintended negative consequences. I can understand how the sorcerer’s apprentice must have felt.

I think the opinion of a scientist about the value of the H-index roughly speaking divides according to whether a said scientist has a big one or a small one. Those lucky enough to have a high H-index probably think it is fine, while those who have a low value can probably find a reason why it is flawed. My own H-index (42 according to Google Scholar) is mediocre, which I reckon is a fair reflection of my status.

R.I.P. Freeman Dyson (1923-2020)

Posted in The Universe and Stuff with tags , on February 29, 2020 by telescoper

I was just about to leave work last night when I heard via social media the sad news of the death at the age of 96 of the theoretical physicist Freeman Dyson.

Overnight the regular media have been running tributes to him, and various friends and colleagues have been posting their own personal recollections of a remarkable scientist who also seems to have been a kind and generous human being.

I never had the opportunity to meet, or even correspond with, Freeman Dyson myself but I do recall from Nottingham times being told that both Dyson and Julian Schwinger visited and gave lectures for the bicentennial celebrations of the birth of George Green. People there remembered him with fondness.

Please feel free to share any personal reminiscences through the Comments Box below.

Freeman Dyson was an original and creative thinker who was by no means always right but I’ve always felt that scientists should be judged by their best work rather that their worst, and Dyson was a wonderful generator of ideas and made important and influential contributions across a wide range of fields from Quantum Electrodynamics and Solid State Physics to Astronomy and Cosmology.

Rest in peace, Freeman Dyson (1923-2020).