Archive for the The Universe and Stuff Category

Astrophysics & Cosmology Masterclass at Maynooth!

Posted in Biographical, Education, Maynooth, The Universe and Stuff with tags , , on November 4, 2021 by telescoper

Regular readers of the blog – both of them – may remember that, after a couple of postponements due to Covid-19, we presented a Masterclass in Astrophysics & Cosmology in Maynooth on March 25th 2021. Well, owing to popular demand, we’ve decided to do a re-run of the event on Friday 12th November 2021 ahead of the forthcoming CAO cycle. That’s a week tomorrow!

This will be a half-day virtual event via Zoom. It’s meant for school students in their 5th or 6th year of the Irish system. There might be a few of them or their teachers who see this blog so I thought I’d share the news here. You can find more information, including instructions on how to book a place, here.

Here is the updated official poster and the programme:

I’ll be talking about cosmology early on, while John Regan will talk about black holes. After the coffee break one of our PhD students will talk about why they wanted to study astrophysics. Then I’ll say something about our degree programmes for those students who might be interested in studying astrophysics and/or cosmology as part of a science course. We’ll finish with questions either about the science or the study!

I’m told that with a week still to go we already have over 750 science students based in schools from An Daingean to Arranmore Island, from Monaghan to Mayo and many counties in-between. Fortunately it is online so no travelling is involved. Unfortunately the participants don’t get to see the wonderful campus so here’s a gratuitous picture!

(And at 12 noon I don’t turn into a pumpkin but do have to run off to give a lecture on vector calculus..)

A Question of Balance

Posted in Cute Problems, The Universe and Stuff with tags , , on November 3, 2021 by telescoper

Here’s an interesting physics problem for you, based on the idea that the mass of a set of bodies changes if the energy of their mutual interactions changes according to Einstein’s famous formula “E=mc2“.

Four identical masses are placed at rest in pairs either side of an extremely sensitive balance in a symmetrical way such that the distance between the members of a pair is identical for each pair and the centre of mass of each pair is equally spaced from the fulcrum of the balance. In this configuration the system is in equilibrium and the balance is level.

As illustrated schematically in the graphic, one pair of weights is adjusted by displacing each weight slightly away from the centre of mass of the pair by an equal and opposite distance, thus keeping the position of the centre of mass of the pair constant. The other pair of weights is not adjusted.

Assuming that the balance is sufficiently sensitive to detect the slight change in mass associated with the gravitational interactions between the masses in each pair, does the balance move?

If it does move which pair moves up: the displaced pair or the undisturbed pair?

Citation Metrics and “Judging People’s Careers”

Posted in Bad Statistics, The Universe and Stuff with tags , , , , on October 29, 2021 by telescoper

There’s a paper on the arXiv by John Kormendy entitled Metrics of research impact in astronomy: Predicting later impact from metrics measured 10-15 years after the PhD. The abstract is as follows.

This paper calibrates how metrics derivable from the SAO/NASA Astrophysics Data System can be used to estimate the future impact of astronomy research careers and thereby to inform decisions on resource allocation such as job hires and tenure decisions. Three metrics are used, citations of refereed papers, citations of all publications normalized by the numbers of co-authors, and citations of all first-author papers. Each is individually calibrated as an impact predictor in the book Kormendy (2020), “Metrics of Research Impact in Astronomy” (Publ Astron Soc Pac, San Francisco). How this is done is reviewed in the first half of this paper. Then, I show that averaging results from three metrics produces more accurate predictions. Average prediction machines are constructed for different cohorts of 1990-2007 PhDs and used to postdict 2017 impact from metrics measured 10, 12, and 15 years after the PhD. The time span over which prediction is made ranges from 0 years for 2007 PhDs to 17 years for 1990 PhDs using metrics measured 10 years after the PhD. Calibration is based on perceived 2017 impact as voted by 22 experienced astronomers for 510 faculty members at 17 highly-ranked university astronomy departments world-wide. Prediction machinery reproduces voted impact estimates with an RMS uncertainty of 1/8 of the dynamic range for people in the study sample. The aim of this work is to lend some of the rigor that is normally used in scientific research to the difficult and subjective job of judging people’s careers.

This paper has understandably generated a considerable reaction on social media especially from early career researchers dismayed at how senior astronomers apparently think they should be judged. Presumably “judging people’s careers” means deciding whether or not they should get tenure (or equivalent) although the phrase is not a pleasant one to use.

My own opinion is that while citations and other bibliometric indicators do contain some information, they are extremely difficult to apply in the modern era in which so many high-impact results are generated by large international teams. Note also the extreme selectivity of this exercise: just 22 “experienced astronomers” provide the :calibration” which is for faculty in just 17 “highly-ranked” university astronomy departments. No possibility of any bias there, obviously. Subjectivity doesn’t turn into objectivity just because you make it quantitative.

If you’re interested here are the names of the 22:

Note that the author of the paper is himself on the list. I find that deeply inappropriate.

Anyway, the overall level of statistical gibberish in this paper is such that I am amazed it has been accepted for publication, but then it is in the Proceedings of the National Academy of Sciences, a journal that has form when it comes to dodgy statistics. If I understand correctly, PNAS has a route that allows “senior” authors to publish papers without passing through peer review. That’s the only explanation I can think of for this.

As a rejoinder I’d like to mention this paper by Adler et al. from 12 years ago, which has the following abstract:

This is a report about the use and misuse of citation data in the assessment of scientific research. The idea that research assessment must be done using “simple and objective” methods is increasingly prevalent today. The “simple and objective” methods are broadly interpreted as bibliometrics, that is, citation data and the statistics derived from them. There is a belief that citation statistics are inherently more accurate because they substitute simple numbers for complex judgments, and hence overcome the possible subjectivity of peer review. But this belief is unfounded.

O brave new world that has such metrics in it.

Update: John Kormendy has now withdrawn the paper; you can see his statement here.

Still no Primordial Gravitational Waves…

Posted in Astrohype, Bad Statistics, The Universe and Stuff with tags , , , , , , on October 27, 2021 by telescoper

During March 2014 this blog received the most traffic it has ever had (reaching almost 10,000 hits per day at one point). The reason for that was the announcement of the “discovery” of primordial gravitational waves by the BICEP2 experiment. Despite all the hype at the time I wasn’t convinced. This is what I said in an interview with Physics World:

It seems to me though that there’s a significant possibility of some of the polarization signal in E and B [modes] not being cosmological. This is a very interesting result, but I’d prefer to reserve judgement until it is confirmed by other experiments. If it is genuine, then the spectrum is a bit strange and may indicate something added to the normal inflationary recipe.

I also blogged about this several times, e.g. here. It turns out I was right to be unconvinced as the signal detected by BICEP2 was dominated by polarized foreground emission. The story is summarized by these two news stories just a few months apart:

Anyway, the search for primordial gravitational waves continues. The latest publication on this topic came out earlier this month in Physical Review Letters and you can also find it on the arXiv here. The last sentence of the abstract is:

These are the strongest constraints to date on primordial gravitational waves.

In other words, seven years on from the claimed “discovery” there is still no evidence for anything but polarized dust emission…

New Publication at the Open Journal of Astrophysics

Posted in Open Access, The Universe and Stuff with tags , , , , , on October 20, 2021 by telescoper

Time to announce another publication in the Open Journal of Astrophysics. This one is the 13th paper in Volume 4 (2021) and the 44th in all.

The latest publication is entitled  The LSST-DESC 3x2pt Tomography Optimization Challengeand is in the folder marked Instrumentation and Methods for Astrophysics, and is especially relevant for cosmology. The paper is led by Joe Zuntz of the University of Edinburgh, and there are 27 authors altogether, scattered across the globe, representing the LSST Dark Energy Science Collaboration.

Here is a screen grab of the overlay which includes the abstract:

You can find the paper on the Open Journal of Astrophysics site here and can also read it directly on the arXiv here.

Revision of Lecter Notes

Posted in Film, The Universe and Stuff with tags , , , , , , , , on October 19, 2021 by telescoper

I’ve just finished my 11th Lecture on Mechanics and Special Relativity. The Tuesday lecture is in a 5pm to 6pm slot which means quite a few students need to leave early in order to get buses home. I try therefore to design it in such a way that the last 10 minutes or so is optional, so those that depart before the end don’t miss anything vital. Today I ended with a sort of philosophical aside about the nature of things versus how they interact with other things. I wrote about such thoughts already on this blog but that was almost a decade ago so I reckon enough time has elapsed for me to reiterate it here in a slightly modified form.

The text for this dissertation is a short speech by Hannibal Lecter from the film The Silence of the Lambs (1991), specifically the “quotation” from the Meditations of Roman Emperor and stoic philosopher>Marcus Aurelius.

The quotation by Lecter reads

First principles, Clarice. Simplicity. Read Marcus Aurelius. Of each particular thing ask: what is it in itself? What is its nature? What does he do, this man you seek?

I always felt this would make a good preface to a book on particle physics, playing on the word “particular”, but of course one has to worry about using part of a film script without paying the necessary copyright fee, and there’s also the small matter of writing the book in the first place.

Anyway, I keep the Penguin Popular Classics paperback English translation of the Meditations with me when I go travelling; I can’t read Greek, the language it was originally written in. It is one the greatest works of classical philosophy, but it’s also a collection of very personal thoughts by someone who managed to be an uncompromisingly authoritarian Emperor of Rome at the same time as being a humble and introspective person. Not that I have ever in practice managed to obey his exhortations to self-denial!

Anyway, the first point I wanted to make is that Lecter’s quote is not a direct quote from the Meditations, at least not in any English translation I have found. The nearest I could find in the version I own is Book 8, Meditation X:

This, what is it in itself, and by itself, according to its proper constitution? What is the substance of it? What is the matter, or proper use? What is the form, or efficient cause? What is it for in this world, and how long will it abide? Thus must thou examine all things that present themselves unto thee.

Or possibly, later on in the same Book, Meditation XII:

As every fancy and imagination presents itself to unto thee, consider (if it be possible) the true nature, and the proper qualities of it, and reason with thyself about it.

There are other translated versions to be found on the net (e.g. here), all similar. Thus Lecter’s reference is a paraphrase, but by no means a misleading one.

A more interesting comment, perhaps, relates to the logical structure of Lecter’s quote. He starts by asking about a thing “in itself”, which recalls the ding an sich of Immanuel Kant. The point is that Kant argued that the “thing in itself” is ultimately unknowable. Lecter continues by asking not what the thing (in this case a man) is in itself but what it (he) does, which is not the same question at all.

It has long struck me that this is similar to the way we work in physics. For example, we might think we understand a bit about what an electron is, but actually what we learn about is how it interacts with other things, which of its properties change and which remain the same, i.e. what it does. From such behaviour we learn about what attributes we can assign to it, such as charge, mass and spin, but we know these only through their interactions with other entities. The electron-in-itself remains a mystery.

This is true of mathematical objects too. Objects are defined to do certain things under certain operations. That is the extent of their definition. Physicists tend to think there is a reality beyond the mathematics used to represent it, but can we ever really know anything about that reality?

If the reference to mathematical physics all sounds a bit nerdy, then I’ll make the obvious point that it also works with people. Do we ever really know what another person is in himself or herself? It’s only through interacting with people that we discover anything. They may say kind or nasty things and perform good or evil deeds, or act in some other way that leads us to draw conclusions about their inner nature. But we never really know for sure. They might be lying, or have ulterior motives. We have to trust our judgement to some extent otherwise we’re forced to live in a world in which we don’t trust anyone, and that’s not a world that most of us are prepared to countenance.

Even that is similar to physics (or any other science) because we have to believe that, say, electrons (or rather the experiments we carry out to probe their properties) don’t lie. This takes us to an axiom upon which all science depends, that nature doesn’t play tricks on us, that the world runs according to rules which it never breaks.

Theoretical Astrophysics Job Opportunity in Cork

Posted in The Universe and Stuff on October 18, 2021 by telescoper

Just time today to pass on the news that the University of Cork is advertising a Lectureship in Theoretical Astrophysics “with a specialism in astrophysics, gravitational physics or cosmology (although outstanding candidates from any research area in astronomy can also apply)”. More details can be found here. The deadline for applications is 11th November.

I’m posting this information here to encourage cosmologists and gravitational physicists to apply because I would love to see the community in these areas grown in Ireland. This is a follow-up position to the Professorship in Astrophysics recently advertised.

 

JWST: Nice Telescope, Shame about the Name…

Posted in LGBT, Science Politics, The Universe and Stuff with tags , , , , , , , on October 17, 2021 by telescoper
The JWST deployable mirror undergoing tests

I heard last week that the ship carrying the James Webb Space Telescope (JWST) arrived safely in French Guiana and is now being prepared for launch on an Ariane-5 rocket at the European Space Agency’s facility at Kourou. Since the telescope cost approximately $10 billion there was some nervousness it might have been hijacked by pirates on the way.

I’m old enough to remember JWST when it was called the Next Generation Space Telescope NGST); it was frequently discussed at various advisory panels I was on about 20 years ago. Although the basic concept hasn’t changed much – it was planned to be the successor to the Hubble Space Telescope working in the infrared and with a deployable mirror – at that time it was going to have an even bigger mirror than the 6.5m it ended up with, was going to be launched in or around 2010, and was to have a budget of around $600 million. About a decade ago cost overruns, NASA budget problems, and technical hitches led to suggestions that it should be cancelled. It turned out however that it was indeed too big too fail. Now it is set for launch in December total cost greater than ten times the original estimate.

I know many people involved in the JWST project itself or waiting to use it to make observations, and I’ll be crossing my fingers on launch day and for the period until its remarkable folding mirror is deployed about a fortnight later. I hope it goes well, and look forward to the celebrations when it does.

There is a big problem with JWST however and that is its name, which was changed in 2002 from the Next Generation Space Telescope to the James Webb Space Telescope after James E. Webb, a civil servant who was NASA’s chief administrator from 1961 to 1968.

It’s not uncommon for scientific space missions like this to be named after people once the proposal has moved off the drawing board and into serious planning. That happened with the European Space Agency’s Planck and Herschel to give two examples. In any case Next General Space Telescope was clearly never anything but a working title. Yet naming this important mission after a Government official always seemed a strange decision to me. Then news emerged that James Webb had enthusiastically cooperated in a McCarthyite purge of LGBT+ people working in government institutions, part of a wider moral panic referred to by historians as the Lavender Scare. There have been high-profile protests (see, e.g., here) and a petition that received over a thousand signatures, but NASA has ruled out any change of name.

The main reason NASA give is that they found no evidence that Webb himself was personally involved in discrimination or persecution. I find that very unconvincing. He was in charge, so had responsibility for what went on in his organization. If he didn’t know then why didn’t he know? Oh, and by the way, he didn’t have anything to do with infrared astronomy either…

It’s a shame that this fantastic telescope should have its image so tarnished by the adoption of an inappropriate name. The name is a symbol of a time when homophobic discrimination was even more prevalent than it is now, and as such will be a constant reminder to us that NASA seems not to care about the many LGBT+ people working for them directly or as members of the wider astronomical community.

P.S. As an alternative name I suggest the Lavender Scare Space Telescope (LSST)…

Cosmology Talks: James Alvey on Big Bang Nucleosynthesis in 2021

Posted in The Universe and Stuff with tags , , , , , on October 15, 2021 by telescoper

It’s been a while since I last shared another one of those interesting cosmology talks on the Youtube channel curated by Shaun Hotchkiss. This 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. I found this one particular interesting as it is a field that I lost track of quite a long time ago and it was great to see what has been going on!

Here James Alvey gives a pedagofical overview of the general state of the field of Big Bang Nucleosynthesis (BBN) in 2021, including the basic physics that goes into BBN calculations through each of the relevant epochs (neutrino decoupling, the deuterium bottleneck, etc). He gives particular emphasis to the recent LUNA measurements of the D + p →γ + 3He reaction (or deuterium + proton goes to photon and 3-Helium). This was previously the source of greatest uncertainty in predicting the final deuterium abundance of BBN. He ends by talking about the implications of the LUNA measurements on possible new physics beyond the standard model, in particular possible thermal relics.

There is a Nature paper about the LUNA results here and  two other papers on this topic by James can be found here and here.

Writing Papers for Scientific Journals

Posted in Literature, The Universe and Stuff with tags , on October 14, 2021 by telescoper

Knowing that not all readers of this blog have a flair for writing like what I have got, I thought I’d pass on a link to a paper that appeared on the arXiv earlier this week. Here is the abstract:

Writing is a vital component of a modern career in astronomical research. Very few researchers, however, receive any training in how to produce high-quality written work in an efficient manner. We present a step-by-step guide to writing in astronomy. We concentrate on how to write scientific papers, and address various aspects including how to crystallise the ideas that underlie the research project, and how the paper is constructed considering the audience and the chosen journal. We also describe a number of grammar and spelling issues that often cause trouble to writers, including some that are particularly hard to master for non-native English speakers. This paper is aimed primarily at Master’s and PhD level students who are presented with the daunting task of writing their first scientific paper, but more senior researchers or writing instructors may well find the ideas presented here useful.

Knapen et al. 2021, arXiv:2110.05503

The title of the paper is actually Writing Scientific Papers in Astronomy, which seems curious wording to me – rather like Writing Scientific Papers in French (for example) – which is why I didn’t use it for the title of this post. Not that I’m pedantic or anything.

One of the problems with the scientific literature is that most journals have their own style rules which are often in conflict with one another so the detailed guidance on grammar, etc is probably of lesser value than the good tips on how to structure a paper. Those bits apply to any scientific field really, not just astronomy.

I remember very well what a struggle I found it when I wrote my first scientific paper. I had invaluable help, though, from my supervisor, who was an excellent writer. This is well worth reading for those early career researchers who want to avoid at least some of the pain!

The only tip I can offer to a postgraduate student struggling to write a paper is to think of who is going to be reading it. In most cases that will mainly be other early career researchers, so write in such a way that you can connect with them. That usually means, for example, taking special care to explain the things that you found difficult when you started in the area. In other words, you should put enough in your paper to allow someone else entering the field to understand it.

Other tips are of course welcome through the Comments Box.