Archive for April, 2019

Flamenco Sketches for International Jazz Day

Posted in Jazz with tags , , , , , on April 30, 2019 by telescoper

I discovered only this morning that today, April 30, is International Jazz Day 2019 so I thought I’d post a track to mark the occasion. This is from the all-time classic album Kind of Blue featuring the Miles Davis Sextet and it was recorded on April 22, 1959 – just over 60 years ago! This album appears very frequently in lists of top jazz records, but it’s so good I don’t think there’s any risk of getting bored with it no matter how often you hear it.

Flamenco Sketches involves a series of solos each improvised on a set of five scales; it’s the fourth section that hints at the Spanish influence alluded to in the title. The tempo is very slow, which contributes the air of solemnity as does the absolute perfection of the solos. In that respect it has clear parallels with some of Duke Ellington’s work. Miles Davis, who opens and closes the track on muted trumpet, and Bill Evans on piano are absolutely faultless but I particularly enjoy John Coltrane’s playing on tenor saxophone: his tone is as bleak and austere as an Arctic sunrise, and just as wonderful and he conjures up an absolutely beautiful improvised melody. Other members of the band are Cannonball Adderley (as), Paul Chambers (b) and Jimmy Cobb (d).

Enjoy! And a Happy International Jazz Day to you all!

Job in Theoretical Physics at Maynooth!

Posted in Maynooth with tags , on April 30, 2019 by telescoper

Just a short post passing on the information that we have a fixed-term job available in the Department of Theoretical Physics at Maynooth University. You can find the details here.

The position is for 5 months, starting in September 2019, and it to basically to provide teaching cover for Dr Jonivar Skullerud who will be on sabbatical for a Semester. I know it is a short appointment, but it seems to me that it would provide a good opportunity for an early-career academic, perhaps someone straight out of a PhD, to gain some teaching experience.

The deadline for applications is 23.30 on Sunday May 26th, i.e. about 4 weeks away, and you should apply through the jobs portal here.

If you’d like to know any more please feel free to contact me privately.

Oh, and please feel free to pass this on to anyone who may be interested!

Redshift and Distance in Cosmology

Posted in The Universe and Stuff with tags , , , , , on April 29, 2019 by telescoper

I was looking for a copy of this this picture this morning and when I found it I thought I’d share it here. It was made by Andy Hamilton and appears in this paper. I used it (with permission) in the textbook I wrote with Francesco Lucchin which was published in 2003.

I think this is a nice simple illustration of the effect of the density parameter Ω and the cosmological constant Λ on the relationship between redshift and (comoving) distance in the standard cosmological models based on the Friedman Equations.

On the left there is the old standard model (from when I was a lad) in which space is Euclidean and there is a critical density of matter; this is called the Einstein de Sitter model in which Λ=0. On the right you can see something much closer to the current standard model of cosmology, with a lower density of matter but with the addition of a cosmological constant. Notice that in the latter case the distance to an object at a given redshift is far larger than in the former. This is, for example, why supernovae at high redshift look much fainter in the latter model than in the former, and why these measurements are so sensitive to the presence of a cosmological constant.

In the middle there is a model with no cosmological constant but a low density of matter; this is an open Universe. Because it decelerates much more slowly than in the Einstein de Sitter model, the distance out to a given redshift is larger (but not quite as large as the case on the right, which is an accelerating model), but the main property of interest in the open model is that the space is not Euclidean, but curved. The effect of this is that an object of fixed physical size at a given redshift subtends a much smaller angle than in the cases either side. That shows why observations of the pattern of variations in the temperature of the cosmic microwave background across the sky yield so much information about the spatial geometry.

It’s a very instructive picture, I think!

University News

Posted in Education, Politics with tags , , , , , , on April 28, 2019 by telescoper

As we stagger towards Week 11 of this twice-interrupted Semester I’m back in the office preparing stuff for another set of lectures. This term seems to have gone on forever, largely because of the two breaks (one at half-term around St Patrick’s Day, and other other for Easter). Now, though, the end is in sight. Or at least the examination period is: there are just two more weeks of lectures, ending on 10th May then a short break, then examinations start (on 17th May). Then, of course, there is marking, checking, conflating exam grades with coursework marks, examination boards, and all the other stuff that go on behind the scenes.

I noticed that this weekend’s edition of the Irish Times included a hard copy of a report called Delivering for Ireland: The Impact of Irish Universities which was produced by the Irish Universities Association. In fact the thing given away with the paper is just a summary report (you can download it in PDF format here). The full report (all 86 pages of it) can be downloaded here.

The report is full of interesting information, including this (which I didn’t know before):

The report was produced with the aim of making the case for further investment in Ireland’s universities. It remains to be seen whether the current Irish government will be persuaded. I’m not holding my breath. right-wing governments never seem to be interested in investing in the future. I think the best we can hope for is that Ireland does not continue its policy of slavishly copying English Higher Education policy, especially with the introduction of student loans and high tuition fees.

And talking of the idiocies of the English University system, there is a story going around that the UK Government is planning to make EU students pay full `Overseas’ fees after Brexit. Actually, Higher Education policy is a devolved matter so this can only be directly enforced on English universities. It will, however, be hard for Scottish Welsh and Northern Irish institutions to resist the consequences.

In fact I’ve long felt that the existing system – in which Home and EU students have to be treated the same way as a matter of law but non-EU students can be charged different (i.e. higher) fees is completely immoral. Once at university students are all taught the same way so why should some be charged more than others because they happen to come from China? What would you think of a shop that tried to charge people different prices for the same goods depending on the nationality of the customer?

This decision is of course an inevitable consequence of Theresa May’s interpretation of the EU referendum result as a mandate for policies of extreme xenophobia, as is the withdrawal from Erasmus. It is just another symptom of the UK’s descent into narrow-minded insularity. The message this decision sends out is that Britain hates foreigners but it likes their money so the rich ones who can pay extortionate fees will be graciously allowed to come here to get fleeced. Does the government really think that EU citizens are daft enough to come to a country that identifies itself in such a way? I don’t think they are. They’ll just find somewhere else to go, and the consequence for UK universities will be severe. I am confident this will push more than one UK higher education institution into bankruptcy.

Anyway, even if the the Irish university continues to be under-resourced, it will at least continue to welcome students from the EU on the same basis as before. So if you’re a European student who was thinking about studying in England, why not come to Ireland instead? It’s far cheaper, and we even have the same weather…

The Bloody History of Mount Street Bridge

Posted in History with tags , , , on April 27, 2019 by telescoper

Easter was quite late this year, as it was in 1916, the year of the Easter Rising: Easter Monday fell on 22nd April 2019, and on 24th April 1916 – the day that the uprising started. People who were brought up in Ireland would have learnt much events of 1916 at School, and through the annual commemorations, but we weren’t taught anything about the Easter Rising in Britain, so I’ve just picked up bits and pieces here and there from reading about it. This week one of the articles that particularly struck me was about the Battle of Mount Street Bridge so I thought I’d write a little bit about it here.

To begin with, here is an old map I came across a while ago that shows the extent of the area of Dublin seized by the rebels in 1916:

You can click on the map to make it clearer. The area of interest here is towards the right of the map, inside the blue perimeter marked ‘3rd Battalion’. The road marked in red leading North West to the Mount Street Bridge past the Beggars Bush Barracks (also marked in red) is Northumberland Road. It changes name to Mount Street on the other (NW) side of the bridge. Northumberland Road forms a junction with Haddingdon Road near the Barracks.

Most of the city’s street layout has survived intact so it is possible to walk around and visit many of the locations on this map, many of which still bear the scars of the Easter Rising. It’s quite a strange feeling doing that, as it brings the violence of the past rather too close for comfort. I think Mount Street Bridge is a good illustration. I walked through the area last year without knowing that it had such a bloody history, but now I don’t think I’ll ever be able to visit it again without getting the shivers. Still, at least it makes one feel grateful to be living in a time of peace though some people don’t seem to think that’s very important these days.

Anyway, the large area surrounded by the blue line to the right of the map was occupied on the 24th April 1916 by the 3rd Battalion of the Irish Volunteers under the command of one Éamon de Valera. De Valera commanded a relatively small contingent of fewer than 150 rebels, with a headquarters in Boland’s Bakery.

At 11am on 24th April 1916, acting under de Valera’s instructions, Lieutenant Michael Malone led 16 Volunteers from the 3rd battalion towards Mount Street Bridge, a key crossing point over the Grand Canal for a road that leads directly into the heart of Dublin. Their task was to stop British reinforcements entering Dublin from the South East. They set up several strong points either side of the bridge, marked on the map by the sold blue circles.

Meanwhile, British High Command in England received an urgent request from Ireland for reinforcements needed to put down the uprising. On the evening of 24th April 1916, the 59th North Midland Division received orders from Brigade HQ to ‘stand to’ for an immediate move. The division consisted of three brigades; 176th (2/5th, 2/6th South Staffordshire regiment, 2/5th, 2/6th North Staffordshire regiment); 177th (2/4th, 2/5th Lincolnshire regiment, 2/4th, 2/5th Leicestershire regiment) and the 178th infantry division (2/5th, 2/6th, 2/7th and 2/8th battalions of the Sherwood Forester regiment). The men were apparently enthusiastic at the thought of active service overseas and believed they were on their way to France or Flanders. In fact the Division began immediate embarkation for Kingstown (now Dun Laoghaire), Ireland.

Lieutenant Malone was still fortifying his post in a house at 25 Northumberland Road on 24th April when his attention was drawn to the sound of soldiers advancing towards his position. Assuming this was the anticipated British counter-attack, Lieutenant Malone, together with James Grace and three others, opened fire on the troops as they reached the junction of Northumberland Road and Haddington Road. The British soldiers were caught completely by surprise. They were not, as it turned out, attempting to assault the rebel positions; they were just returning to their barracks after weekend manoeuvres. Many men fell where they were hit, others ran for cover. They were all unable to return fire, as their rifles were unloaded. After the gunfire had ceased, the street was littered with the dead and dying. Local civilians – the vast majority of whom wanted nothing to do with the uprising – ran from their houses to help the wounded British soldiers.

It was not until early on Wednesday morning (April 26th 1916) that the newly arrived troops from England had disembarked and assembled on the quayside in Kingstown. They were mostly raw recruits who had only just completed six weeks of basic training, and many of them had never even fired a rifle. Orders were received that two battalions were to make their way towards the Royal Hospital Kilmainham. Two more were to make their way to Trinity College. The other battalions were to remain in reserve. Carrying their full military kit, the Sherwood Foresters began to march towards the city centre.

On Tuesday 25th April, Malone had sent away three of his companions as they were `only boys’, leaving just himself and James Grace to defend the position on Northumberland Road. On 26th April, as the British troops reached the junction of Northumberland Road and Haddington Road, these two opened fire into the ranks of the oncoming Sherwood Foresters. The first hail of bullets claimed the lives of ten men.

Following instructions they would have been given in basic training, the British soldiers dropped to the ground in response to the gunfire. That would have been a good tactic to have employed when coming under fire in open countryside – such as they might have experienced in Flanders – as they would have had a chance of crawling for cover in a trench or ditch or hedgerow. In this situation, however, it was just about the worst thing they could have done. They lay prone in the middle of the road and were easily picked off by Malone and Grace, firing down on them from the windows of a house on Northumberland Road. To be fair to the British officers in command, urban warfare was a new thing in 1916 – the horrors of, e.g., Stalingrad were still to come – so they didn’t really know what to do.

The British troops regrouped and tried to charge the position where the gunfire was coming from, but were repulsed, suffering heavy casualties. Even more casualties were sustained when they tried to encircle the building. Finally, using grenades, they managed to blow in the front door of 25 Northumberland Road at the same time as others gained entry to the rear of the house via Percy Lane.

A barricade constructed of household furniture blocked those soldiers attempting to gain entry through the front door. As Malone descended the stairs towards the hall, he was confronted by the British soldiers who entered through the back door and was shot dead. In order to clear the house the military threw grenades into the basement but Grace, who was hiding there, had taken cover behind a metal oven and avoided serious injury. He stayed put, and wasn’t found until after the battle. He was arrested by the British authorities, but released at Christmas 1916.

Altogether the fighting at Mount Street resulted in almost two-thirds of the total British casualties during the Easter Rising. A total of four officers and 216 other ranks were killed or wounded during this bloody episode.

This short video gives some more details:

A Short (Physical Review) Letter!

Posted in History, Maynooth, The Universe and Stuff with tags , , , , on April 26, 2019 by telescoper

I think it is Blaise Pascal who is to be credited with the quote frequently paraphrased as “I didn’t have time to write a short letter so here’s a long one instead” but, whoever it was, this afternoon’s interesting theoretical physics seminar at Maynooth University about Magnetic Molecules by Jürgen Schnack of Bielefeld University provided a great example of how a short letter can pay off.

William Giauque was awarded the Nobel Prize for Chemistry in 1949 for his work on the properties (including magnetic properties) of matter at very low temperatures. Among the many achievements that led to this award Giauque was the first person to generate matter in a laboratory with a temperature below 1 Kelvin. This result was described in a publication in Physical Review Letters in 1933. Here is the letter in full:

I’ve seen a number of surprisingly short short communications from this era, but I think this one is the record. I’m not sure how many marks this would get as a lab report from an undergraduate physics student, but it doesn’t seem to have done Giauque any harm to keep it extremely brief!

While I’m here I’ll also mention that this also the common practice of awarding the Nobel Prize for Chemistry on the basis of work that is really Physics is clearly not a recent innovation!

Dos and Don’ts of reduced chi-squared

Posted in Bad Statistics, The Universe and Stuff with tags , , on April 26, 2019 by telescoper

Yesterday I saw a tweet about an arXiv paper and thought I’d share it here. The paper, I mean. It’s not new but I’ve never seen it before and I think it’s well worth reading. The abstract of the paper is:

Reduced chi-squared is a very popular method for model assessment, model comparison, convergence diagnostic, and error estimation in astronomy. In this manuscript, we discuss the pitfalls involved in using reduced chi-squared. There are two independent problems: (a) The number of degrees of freedom can only be estimated for linear models. Concerning nonlinear models, the number of degrees of freedom is unknown, i.e., it is not possible to compute the value of reduced chi-squared. (b) Due to random noise in the data, also the value of reduced chi-squared itself is subject to noise, i.e., the value is uncertain. This uncertainty impairs the usefulness of reduced chi-squared for differentiating between models or assessing convergence of a minimisation procedure. The impact of noise on the value of reduced chi-squared is surprisingly large, in particular for small data sets, which are very common in astrophysical problems. We conclude that reduced chi-squared can only be used with due caution for linear models, whereas it must not be used for nonlinear models at all. Finally, we recommend more sophisticated and reliable methods, which are also applicable to nonlinear models.

I added the link at the beginning; you can download a PDF of the paper here.

I’ve never really understood why this statistic (together with related frequentist-inspired ideas) is treated with such reverence by astronomers, so this paper offers a valuable critique to those tempted to rely on it blindly.



Silhouettes of Gustav Mahler – Otto Böhler

Posted in Art, Music with tags , , , , on April 25, 2019 by telescoper

Schattenbilder (Silhouettes) of Gustav Mahler conducting, by Otto Böhler (1847–1913), published posthumously in 1914.

More Order-of-Magnitude Physics

Posted in Cute Problems with tags , , , on April 25, 2019 by telescoper

A very busy day today so I thought I’d just do a quick post to give you a chance to test your brains with some more order-of-magnitude physics problems. I like using these in classes because they get people thinking about the physics behind problems without getting too bogged down in or turned off by complicated mathematics. If there’s any information missing that you need to solve the problem, make an order-of-magnitude estimate!

Give  order of magnitude answers to the following questions:

  1. What is the maximum distance at which it could be possible for a car’s headlights to be resolved by the human eye?
  2. How much would a pendulum clock gain or lose (say which) in a week if moved from a warm room into a cold basement?
  3. What area would be needed for a terrestrial solar power station capable of producing 1GW of power?
  4. What mass of cold water could be brought to the boil using the energy dissipated when a motor car is brought to rest from 100 km/h?
  5. How many visible photons are emitted by a 100W light bulb during its lifetime?

There’s no prize involved, but feel free to post answers through the comments box. It would be helpful if you explained a  bit about how you arrived at your answer!

The First Bookie

Posted in Football, mathematics, Sport with tags , , , , , , on April 24, 2019 by telescoper

I read an interesting piece in Sunday’s Observer which is mainly about the challenges facing the modern sports betting industry but which also included some interesting historical snippets about the history of gambling.

One thing that I didn’t know before reading this article was that it is generally accepted that the first ever bookmaker was a chap called Harry Ogden who started business in the late 18th century on Newmarket Heath. Organized horse-racing had been going on for over a century by then, and gambling had co-existed with it, not always legally. Before Harry Ogden, however, the types of wager were very different from what we have nowadays. For one thing bets would generally be offered on one particular horse (the Favourite), against the field. There being only two outcomes these were generally even-money bets, and the wagers were made between individuals rather than being administered by a `turf accountant’.

Then up stepped Harry Ogden, who introduced the innovation of laying odds on every horse in a race. He set the odds based on his knowledge of the form of the different horses (i.e. on their results in previous races), using this data to estimate probabilities of success for each one. This kind of `book’, listing odds for all the runners in a race, rapidly became very popular and is still with us today. The way of specifying odds as fractions (e.g. 6/1 against, 7/1 on) derives from this period.

Ogden wasn’t interested in merely facilitating other people’s wagers: he wanted to make a profit out of this process and the system he put in place to achieve this survives to this day. In particular he introduced a version of the overround, which works as follows. I’ll use a simple example from football rather than horse-racing because I was thinking about it the other day while I was looking at the bookies odds on relegation from the Premiership.

Suppose there is a football match, which can result either in a HOME win, an AWAY win or a DRAW. Suppose the bookmaker’s expert analysts – modern bookmakers employ huge teams of these – judge the odds of these three outcomes to be: 1-1 (evens) on a HOME win, 2-1 against the DRAW and 5-1 against the AWAY win. The corresponding probabilities are: 1/2 for the HOME win, 1/3 for the DRAW and 1/6 for the AWAY win. Note that these add up to 100%, as they are meant to be probabilities and these are the only three possible outcomes. These are `true odds’.

Offering these probabilities as odds to punters would not guarantee a return for the bookie, who would instead change the odds so they add up to more than 100%. In the case above the bookie’s odds might be: 4-6 for the HOME win; 6-4 for the DRAW and 4-1 against the AWAY win. The implied probabilities here are 3/5, 2/5 and 1/5 respectively, which adds up to 120%, not 100%. The excess is the overround or `bookmaker’s margin’ – in this case 20%.

This is quite the opposite to the Dutch Book case I discussed here.

Harry Ogden applied his method to horse races with many more possible outcomes, but the principle is the same: work out your best estimate of the true odds then apply your margin to calculate the odds offered to the punter.

One thing this means is that you have to be careful f you want to estimate the probability of an event from a bookie’s odds. If they offer you even money then that does not mean they you have a 50-50 chance!