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.
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 Meditationsof 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.
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.
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 at NASA, 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)…
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.
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.
Once again it’s time to introduce first-year Mathematical Physics students to the joy of vectors, or specifically Euclidean vectors. Some of my students have seen them before, but probably aren’t aware of how much we use them theoretical physics. Obviously we introduce the idea of a vector in the simplest way possible, as a directed line segment. It’s only later on, in the second year, that we explain how there’s much more to vectors than that and explain their relationship to matrices and tensors.
Although I enjoy teaching this subject I always have to grit my teeth when I write them in the form that seems obligatory these days.
You see, when I was a lad, I was taught to write a geometric vector in the following fashion:
This is a simple column vector, where are the components in a three-dimensional cartesian coordinate system. Other kinds of vector, such as those representing states in quantum mechanics, or anywhere else where linear algebra is used, can easily be represented in a similar fashion.
This notation is great because it’s very easy to calculate the scalar (dot) and vector (cross) products of two such objects by writing them in column form next to each other and performing a simple bit of manipulation. For example, the scalar product of the two vectors
and
can easily be found by multiplying the corresponding elements of each together and totting them up:
showing immediately that these two vectors are orthogonal. In normalised form, these two particular vectors appear in other contexts in physics, where they have a more abstract interpretation than simple geometry, such as in the representation of the gluon in particle physics.
Moreover, writing vectors like this makes it a lot easier to transform them via the action of a matrix, by multipying rows in the usual fashion, e.g.
which corresponds to a rotation of the vector in the plane. Transposing a column vector into a row vector is easy too.
Well, that’s how I was taught to do it.
However, somebody, sometime, decided that, in Britain at least, this concise and computationally helpful notation had to be jettisoned and students instead must be forced to write a vector laboriously in terms of base vectors:
Some of you may even be used to doing it that way yourself. Why is this awful? For a start, it’s incredibly clumsy. It is less intuitive, doesn’t lend itself to easy operations on the vectors like I described above, doesn’t translate easily into the more general case of a matrix, and is generally just …well… awful. The only amusing thing about this is that you get to tell students not to put a dot on the “i” or the “j” – it always gets a laugh when you point out that these little dots are called “tittles“.
Worse still, for the purpose of teaching inexperienced students physics, it offers the possibility of horrible notational confusion. In particular, the unit vector is too easily confused with , the square root of minus one. Introduce a plane wave with a wavevector and it gets even worse, especially when you want to write , and if you want the answer to be the current density then you’re in big trouble!
Call me old-fashioned, but I’ll take the row and column notation any day!
(Actually it’s better still just to use the index notation, which generalises easily to and, for that matter, .)
Or perhaps being here in Ireland we should, in honour of Hamilton, do everything in quaternions.
This week’s veggie box included the following beauty
The vegetable in the picture is called Romanesco. I’ve always thought of it as a cauliflower but I’ve more recently learned that it’s more closely related to broccoli. It doesn’t really matter because both broccoli and cauliflower are forms of brassica, which term also covers things like cabbages, kale and spinach. All are very high in vitamins and are also very tasty if cooked appropriately. Incidentally, the leaves of broccoli and cauliflower are perfectly edible (as are those of Romanesco) like those of cabbage, it’s just that we’re more used to eating the flower (or at least the bud).
A while ago, inspired by a piece in Physics World, I wrote an item about Romanesco, which points out that a “head” of Romanesco displays a form of self-similarity, in that each floret is a smaller version of the whole bud and also displays structures that are smaller versions of itself. That fractal behaviour is immediately obvious if you take a close look. Here’s a blow-up so you can see more clearly:
There is another remarkable aspect to the pattern of florets, in that they form an almost perfect golden spiral. This is a form of logarithmic spiral that grows every quarter-turn by a factor of the golden ratio:
.
Logarithmic, or at least approximately logarithmic, spirals occur naturally in a number of settings. Examples include spiral galaxies, various forms of shell, such as that of the nautilus and in the phenomenon of phyllotaxis in plant growth (of which Romanesco is a special case). It would seem that the reason for the occurrence of logarithmic spirals in living creatures is that such a shape allows them to grow without any change in shape.
Although it is rather beautiful, the main attraction of Romanesco is that it is really delicious. It can be eaten like cauliflower (e.g. in a delicious variation of cauliflower cheese) but my favourite way of cooking it is to roast it with a bit of olive oil, lemon juice and garlic. Yum!
Just to mention that tomorrow morning (October 5th 2021) will see the announcement of this year’s Nobel Prize for Physics. I must remember to make sure my phone is fully charged…
I was, however, a guest of the Nobel Foundation rather than a prizewinner, so my medal is made of chocolate rather than gold. I think after 15 years the chocolate is now inedible, but it serves as a souvenir of a very nice weekend in Stockholm!
I have a spectacular bad track record at predicting the Physics Nobel Prize winner. Most pundits have, actually. I certainly didn’t see the last two coming. I couldn’t resist having a go again however.
It’s been a good few years for cosmology and astrophysics, with Jim Peebles (2019), Roger Penrose, Andrea Ghez & Reinhard Genzel (2020) following on from Kip Thorne, Rainer Weiss and Barry Barish (2017) for the detection of gravitational waves. Although I said so last year only to be proved wrong, I think it’s very unlikely that it will be in this area again. I have no idea who will win but if I had to take a punt I would suggest Alain Aspect, Anton Zeilinger and John Clauser for their Bell’s inequality experiments and contributions to the understanding of quantum phenomena, including entanglement. I’m probably wrong though.
Feel free to make your predictions through the comments box below.
To find out you’ll have to wait for the announcement, around about 10.45 (UK/Irish time) tomorrow morning. I’ll update tomorrow when the wavefunction has collapsed.
Anyway, for the record, I’ll reiterate my opinion that while the Nobel Prize is flawed in many ways, particularly because it no longer really reflects how physics research is done, it does at least have the effect of getting people talking about physics. Surely that at least is a good thing?
UPDATE: Unsurprisingly, I was wrong again. The 2021 Nobel Prize for Physics goes to Syukuro Manabe and Klaus Hasselmann (1/4 each) and Giorgio Parisi (1/2). Manabe and Hasselmann were cited for their work in “the physical modeling of Earth’s climate, quantifying variability and reliably predicting global warming”. The second half of the prize was awarded to Parisi for “the discovery of the interplay of disorder and fluctuations in physical systems from atomic to planetary scales.” Congratulations to them all!
Just time today to pass on the news that the University of Cork is advertising a Professorship “with a specialism in astrophysics, gravitational physics or cosmology”. More details can be found here.
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. It’s nice to see the University of Cork investing in astrophysics too. I had a quick look at their Physics department webpage and it seems their main interest at the moment is in radio astronomy and Active Galactic Nuclei so presumably they are looking for something to complement this activity. There is a follow-up position in theoretical astrophysics in the pipeline too.
P.S. I’ve never been to Cork, actually, but I’ve heard very good things about the city and it’s high on my list of places to visit when travel becomes more feasible than it is at the moment.
The views presented here are personal and not necessarily those of my employer (or anyone else for that matter).
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On a vu souvent
Rejaillir le feu
De l'ancien volcan
Qu'on croyait trop vieux 27 minutes ago
RT @hi_its_rebz: Cannot stop thinking about Adam Tickell leaning heavily on his commitment to equality, diversity and inclusion when announ… 2 hours ago
are the components in a three-dimensional cartesian coordinate system. Other kinds of vector, such as those representing states in quantum mechanics, or anywhere else where 
and 
plane. Transposing a column vector into a row vector is easy too.
is too easily confused with 
, the square root of minus one. Introduce a plane wave with a wavevector 
and it gets even worse, especially when you want to write 
, and if you want the answer to be the current density 
then you’re in big trouble!
which generalises easily to 
and, for that matter, 
.)
.
