## Ligatures, Diphthongs and Supernovae

Posted in History, Pedantry, The Universe and Stuff with tags , , , , , , , , on January 18, 2016 by telescoper

At the weekend I noticed a nice article by John Butterworth on his Grauniad blog about where Gold comes from. Regular readers of this blog (Sid and Doris Bonkers) know that I am not at all pedantic but my attention was drawn to the plural of supernova in the preamble:

I have to confess that I much prefer the latin plural “supernovae” to the modernised “supernovas”, although most dictionaries (including the One True Chambers) give these both as valid forms.  In the interest of full disclosure I will point out that I did five years of Latin at school, and very much enjoyed it…

When I tweeted about my dislike for supernovas and preference for supernovae some replied that English words should have English plurals so that supernovas was preferred (although I wonder if that logic extends to, e.g. datums and phenomenons). Others said that supernovae was fine among experts but for science communication purposes it was better to say “supernovas” as this more obviously means “more than one supernova”. That’s a reasonable argument, but I have to admit I find it a little condescending to assume that an audience can cope with the idea of a massive star exploding as a consequence of gravitational collapse but be utterly bewildered by a straightforward latin plural.

One of the reasons I prefer the Latin plural – along with some other forms that may appear archaic, e.g. Nebulae – is that Astronomy is unique among sciences for having such a long history. Many astronomical terms derive from very ancient sources and in my view we should celebrate this fact because it’s part of the subject’s fascination. That’s just my opinion, of course. You are welcome to disagree with that too.

Anyway, you might be interested to know a couple of things. One is that the first use of “super-nova” recorded in the Oxford English Dictionary was in 1932 in a paper by Swedish astronomer Knut Lundmark. This word is however formed from “nova” (which means “new” in Latin) and the first use of this term in an astronomical setting was in a book by Tycho Brahe, published in 1573:

(I’ll leave it as an exercise to the student to translate the full title.)

Nowadays a nova is taken to be a much lower budget feature than a supernova but the “nova” described in Tycho’s book was was actually a supernova, SN1572 which he, along with many others, had observed the previous year. Historical novae were very often supernovae, in fact, because they are much brighter than mere novae. The real difference between these two classes of object wasn’t understood until the 20th Century, however, which is why the term supernova was coined much later than nova.

Anyway, back to pedantry.

A subsequent tweet from Roberto Trotta asserted  that in fact supernovae and supernovas are both wrong; the correct plural should be supernovæ, in which the two letters of the digraph “ae” are replaced with a single glyph known as a ligature. Often, as in this case, a ligature stands for a diphthong, a sort of composite vowel sound made by running two vowels together.   It’s one of the peculiarities of English that there are only five vowels, but these can represent quite different sounds depending on the context (and on the regional accent). This  means that English has many hidden diphthongs. For example,  the “o” in “no” is a diphthong in English. In languages such as Italian, in which the vowels are very pure, “no” is pronounced quite differently from English. The best test of whether a vowel is pure or not is whether your mouth changes shape as you pronounce it: your mouth moves as you say an English “no”, closing the vowel that stays open in the Italian “no”…

So, not all diphthongs are represented by ligatures. It’s also the case that not all ligatures represent diphthongs. Indeed some are composed entirely of consonants. My current employer’s logo features a ligature formed from the letters U and S:

The use of the ligature æ arose in Mediaeval Latin (or should I say Mediæval?). In fact if you look at the frontispiece of the Brahe book shown above you will see a number of examples of it in its upper-case form Æ. I’m by no means an expert in such things but my guess is that the use of such ligatures in printed works was favoured simply to speed up the typesetting process – which was very primitive – by allowing the compositor to use a single piece of type to set two characters. However, it does appear in handwritten documents e.g. in Old English, long before printing was invented so easier typesetting doesn’t explain it all.

Use of the specific ligature in question caught on particularly well in Scandinavia where it eventually became promoted to a letter in its own right (“aesc”) and is listed as a separate vowel in the modern Danish and Norwegian alphabets.  Early word-processing and computer typesetting software generally couldn’t render ligatures because they were just too complicated, so their use fell out of favour in the Eighties, though there are significant exceptions to this rule. Latex, for example, always allowed ligatures to be created quite easily. Software – even Microsoft Word – is much more sophisticated than it used to be, so it’s now not so much of a problem to use ligatures in digital text. Maybe they will make a comeback!

Anyway, the use of æ was optional even in Mediaeval Latin so I don’t think it can be argued that supernovæ is really more correct than supernovae, though to go back to a point I made earlier, I do admit that a rambling discussion of ligatures and diphthongs would not add much to a public lecture on exploding stars.

## The Nobel Prize for Neutrino Oscillations

Posted in The Universe and Stuff with tags , , , , , , , , on October 6, 2015 by telescoper

Well the Nobel Prize for Physics in 2015 has been announced. It has been awarded jointly to Takaaki Kajita and Arthur B. McDonald for..

the discovery of neutrino oscillations, which prove that neutrinos have mass.

You can read the full citation here. Congratulations to them both. Some physicists around here were caught by surprise because the 2002 Nobel Prize was also awarded for neutrino physics, but it is fair because this award goes for a direct measurement of neutrino oscillations, which is an important breakthrough in its own right; the earlier award was for measurements of solar neutrinos. For a nice description of the background you could do worse than the Grauniad blog post by Jon Butterworth about neutrino physics.

In brief the a process in which neutrinos (which have three distinct flavour states, associated with the electron, mu and tau leptons) can change flavour as they propagate. It’s quite a weird thing to spring on students who previously thought that lepton number (which denotes the flavour) was always conserved. I remember years ago having to explain this phenomenon to third-year students taking my particle physics course.  I decided to start with an analogy based on more familiar physics, but it didn’t go to plan.

A charged fermion such as an electron (or in fact anything that has a magnetic moment, which would include, e.g. the neutron)  has spin and, according to standard quantum mechanics, the component of this in any direction can  can be described in terms of two basis states, say $|\uparrow>$ and $|\downarrow>$ for spin in the $z$ direction. In general, however, the spin state will be a superposition of these, e.g.

$\frac{1}{\sqrt{2}} \left( |\uparrow> + |\downarrow>\right)$

In this example, as long as the particle is travelling through empty space, the probability of finding it with spin “up” is  50%, as is the probability of finding it in the spin “down” state. Once a measurement is made, the state collapses into a definite “up” or “down” wherein it remains until something else is done to it.

If, on the other hand, the particle  is travelling through a region where there is a  magnetic field the “spin-up” and “spin-down” states can acquire different energies owing to the interaction between the spin and the magnetic field. This is important because it means the bits of the wave function describing the up and down states evolve at different rates, and this  has measurable consequences: measurements made at different positions yield different probabilities of finding the spin pointing in different directions. In effect, the spin vector of the  particle performs  a sort of oscillation, similar to the classical phenomenon called  precession.

The mathematical description of neutrino oscillations is very similar to this, except it’s not the spin part of the wavefunction being affected by an external field that breaks the symmetry between “up” and “down”. Instead the flavour part of the wavefunction is “precessing” because the flavour states don’t coincide with the eigenstates of the Hamiltonian that describes the neutrinos’ evolution. However, it does require that different neutrino types have intrinsically different energies  in quite  a similar way similar to the spin-precession example. In the context of neutrinos however the difference in energy means a difference in mass, and if there’s a difference in mass then not all flavours of neutrino can be massless.

Although the analogy I used isn’t a perfect, I thought  it was a good way of getting across the basic idea. Unfortunately, however, when I subsequently asked an examination question about neutrino oscillations I got a significant number of answers that said “neutrino oscillations happen when a neutrino travels through a magnetic field….”. Sigh. Neutrinos don’t interact with  magnetic fields, you see…

Anyway, today’s announcment also prompts me to mention that neutrino physics is one of the main research interests in our Experimental Particle Physics group here at Sussex. You can read a recent post here about an important milestone in the development of the NOvA Experiment which involves several members of the Department of Physics and Astronomy in the School of Mathematical and Physical Sciences here at the University of Sussex. Here’s the University of Sussex’s press release on the subject. In fact Art McDonald is a current collaborator of our neutrino physicists, who have been celebrating his award today!

Neutrino physics is a fascinating subject even to someone like me, who isn’t really a particle physicist. My impression of the field is that was fairly moribund until about the turn of the millennium  when the first measurement of atmospheric neutrino oscillations was announced. All of a sudden there was evidence that neutrinos can’t all be massless (as many of us had long assumed, at least as far as lecturing was concerned).  Now the humble neutrino is the subject of intense experimental activity, not only in the USA and UK but all around the world in a way that would have been difficult to predict twenty years ago.

But then, as the physicist Niels Bohr famously observed, “Prediction is very difficult. Especially about the future.”

## Neutrini via NOVA

Posted in The Universe and Stuff with tags , , , , on October 9, 2014 by telescoper

There’s been quite a lot of discussion at this meeting so far about neutrino physics (and indeed neutrino astrophysics) which, I suppose, is not surprising given the proximity of my current location, the city of L’Aquila, to the Gran Sasso Laboratory which is situated inside a mountain a few kilometres away. If I were being tactless I could at this point mention the infamous “fast-than-light-neutrino” episode that emanated from here a while ago, but obviously I won’t do that.

Anyway, I thought I’d take the opportunity to put up this video which describes how neutrinos are detected at the NOVA experiment on which some of my colleagues in the Department of Physics & Astronomy at the University of Sussex work and which is now up and running. If you want to know how to detect particles so elusive that they can pass right through the Earth without being absorbed, then watch this:

## NOvA and Neutrinos

Posted in The Universe and Stuff with tags , , , , on March 11, 2014 by telescoper

Yesterday’s Grauniad blog post by Jon Butterworth about neutrino physics reminded me that I forgot to post about an important milestone in the development of the NOvA Experiment which involves several members of the Department of Physics and Astronomy in the School of Mathematical and Physical Sciences here at the University of Sussex. Here’s the University of Sussex’s press release on the subject, which came out a couple of weeks ago.

The NOvA experiment consists of two enormous  particle detectors, one at the Fermi National Accelerator Laboratory “Fermilab” near Chicago and the other in Minnesota. The neutrinos are actually generated  at Fermilab; the particle beam is then aimed  at the detectors the, one near the source at Fermilab, and the other in Ash River, Minnesota, near the Canadian border. The particles, sent in their billions every couple of seconds, complete the 500-mile trip in less than three milliseconds.

The point is that the experiment has managed for the first time to actually detect neutrinos through the 500 miles of rock separating the two ends of the experiment. This is obviously just a first step, but it’s equally obviously a crucial one.

Colleagues from Sussex University are strongly involved in  calibrating and fine-tuning the detector, which produces light when particles pass through it. Dr Abbey Waldron and PhD student Luke Vinton have developed a calibration procedure that uses known properties of  muons to calibrate precise measurements of the neutrinos, which are less well understood.  The detector sees 200,000 particle interactions a second, produced by cosmic rays bombarding the atmosphere, and scientists can’t record every single one. Sussex’s Dr Matthew Tamsett has developed a trigger algorithm that searches for events that look like neutrinos among the billions of other particle interactions.

Neutrino physics is an interesting subject to someone like me, who isn’t really a particle physicist. My impression of the field is that was fairly moribund until 1998 when the first measurement of atmospheric neutrino oscillations was announced. All of a sudden there was evidence that neutrinos can’t all be massless (as many of us had long assumed, at least as far as lecturing was concerned).  Now the humble neutrino is the subject of intense experimental activity, not only in the USA and UK but all around the world in a way that would have been difficult to predict twenty years ago.

But then, as the physicist Niels Bohr famously observed, “Prediction is very difficult. Especially about the future.”

## Neutrino Physics in a Small Universe

Posted in Biographical, The Universe and Stuff with tags , , , , , , , on April 23, 2013 by telescoper

I’ve only just got time for a quick lunchtime post before I head off to attend an afternoon of Mathematics presentations, but it’s a one of those nice bits of news that I like to mention on here from time to time.

It is my pleasure to pass on the wonderful news that one of my colleagues in the School of Mathematical and Physical Sciences here at the University of Sussex,  Dr Jeff Hartnell,. has been awarded  the High Energy Particle Physics prize of the Institute of Physics, which means that his name has now been added to the illustrious list of previous winners. The prize is awarded annually by the HEPP Group, a subject group in the Nuclear and Particle Physics Division of the IOP, to a researcher in the UK who has made an outstanding contribution to their field of study early in their career (within 12 years of being awarded their first degree).

There’s a very nice piece about this award here which reveals, amongst other things, that many moons ago at Nottingham I was Jeff’s undergraduate tutor! In fact Jeff also attended a third-year course on Theoretical Elementary Particle Physics I taught in those days. That he survived those experience and went on to be a world-leading physicist speaks volumes! Not only that, it’s also evidence that the world of physics is smaller than we sometimes suppose. I’ve crossed paths with a number of my new colleagues at various times in the past, but it’s particularly rewarding to see someone you taught as an undergraduate go on to a highly successful career as a scientist. Jeff was awarded a prestigious ERC grant this year too!

Jeff is currently in the USA helping to set up the largest-ever experiment in neutrinos to be built there, called NOvA. You can click on the preceding links for more technical details, and I also found this interesting video showing the NOvA detector being assembled. Particle physics experiments are never small, are they?

p.s. Why do they insist on writing “metric ton” instead of “tonne”?