Tag Archives: Third level

Freeman Dyson and the Dublin Institute for Advanced Studies

On Monday, I attended the Statutory Lecture of the School of Theoretical Physics of the Dublin Institute for Advanced Studies (DIAS). This is an outreach lecture presented annually by DIAS and this year the lecture took place at University College Dublin. Better known abroad than at home, the Institute has a long and distinguished history of world-class research in fundamental areas of physics (see here), so it was entirely appropriate that the statutory lecture was given by Freeman Dyson, renowned physicist and Professor of Physics at the famous Institute for Advanced Study at Princeton, the college on which DIAS is modeled.

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Freeman Dyson at the DIAS lecture on Monday night  

The title of Freeman’s lecture was  “Are Brains Analog or Digital?” and the abstract is below:

We know that creatures like us have two separate systems for processing information, the genome and the brain. We know that the genome is digital, and we can accurately transcribe our genomes onto digital machines. We cannot transcribe our brains, and the processing of information in our brains is still a great mystery. I will be talking about real brains and real people, asking a question that will have practical consequences when we are able to answer it. I am not able to answer it now. All I can do is to examine the evidence and explain why I consider it probable that the answer will be that brains are analog.

I won’t give more details as Professor Dyson will publish his paper on the subject quite soon. Suffice it to say that tickets for the lecture sold out days in advance and there was quite a buzz on the night. Freeman held the audience spellbound, reading from his paper without the benefit of a single slide.  One could gauge the interest generated from the huge number and variety of questions afterwards. That said, I couldn’t help noticing that the Irish media took no interest whatsoever in the occasion – one wonders if a world-famous  musician or celebrity chef would be similarly ignored.

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Professor Dyson with staff from the School of Theoretical Physics at DIAS: Werner Nahm (Senior Professor and Director ), Arthur Jaffe (Professor of Mathematics at Harvard and Chairman of the board), Freeman Dyson, Vincent Cunnane (Chair of DIAS Council) and Cecil Keaveney (Registrar)

After the lecture, some of us retired to a nearby hotel where Professor Dyson and his wife regaled us with stories from his long and interesting career. Freeman was a close colleague of my late father and was instrumental in bringing Lochlainn and the rest of our family to the Institute for Advanced Study at Princeton many years ago (after this, Lochlainn returned to Ireland to take up a position at DIAS). So it was great to encounter Professor Dyson once again, this time as an adult! Not to mention that Freeman has fascinating and original views on a wide range of topics; from space travel to climate science, he remains a truly deep and original thinker.

Update

The day after the lecture, staff and friends of the Dublin Institute for Advanced Studies were treated to a private recital by the well-known Irish pianist Hugh Tinney. The connection is that Hugh’s late mother, Professor Sheila Tinney, was an accomplished mathematician who spent time at Princeton IAS and studied with Professor Dyson (Hugh himself studied maths at Trinity College Dublin before deciding on a career in music and was in the audience for Freeman’s lecture).

It was an extraordinary occasion. Hugh played beautifully and each piece was prefaced with a short discussion of the interface of mind, memory and music. The intimate setting made for one of the most exciting concerts I have experienced, far more fun than a formal venue such as the National Concert Hall. It didn’t hurt that the programme included three of my all-time favourite works, Beethoven’s ‘Moonlight’ Sonata,  Schubert’s G major Impromptu and *that* Nocturne by John Field (no.5 in B flat). The recital also had a special significance for me as it took place in the Organ Room of the Royal Irish Academy of Music, a venue I spent a great deal of time in as a young music student.

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Each piece was prefaced by a discussion of the role of mind in music

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Hugh Tinney presenting his latest CD to Professor Dyson

After the recital, we retired to dinner in a nearby restaurant. As you can imagine, one subject of conversation was the mysterious connection between maths and music. I have heard one explanation for this strange phenomenon: “People who are good at maths are good at most things!”

P.S. A video of Freeman’s lecture is now available on the DIAS website.

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Summer hols; summer school, swimming and that book

You must be finished for the summer? Like most academics, I get asked this question every day in summer, usually by village acquaintances convinced that college closes the day the students finish their exams.

Some lecturers in the Institutes of Technology do indeed take off from June 20th to September 1st; that is their right, given the heavy teaching load during termtime. However, for those of us who try to keep up the research, the summer months are the time to get something done, just like our colleagues in the universities.

For me, this is no chore  – the sheer bliss of being able to do quiet research without classes, meetings, staff interactions and all the rest of it. Very restful. Also, we’re having a serious heatwave in Ireland this month and I’m happy to escape to the cool, quiet office every day. So I plug away happily during the day and treat myself to a swim in my village in the evenings..

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Tide’s in on Lawlor’s Strand in Dunmore East

Actually, I did give some ‘cameo’ lectures this week and last, to our summer school. We have a very nice bunch of engineering, computing and business students visiting from Kiel in Germany, and I had fun trying to condense my climate science course down to a one-hour presentation for each group. I haven’t given short presentations on climate before, it was very satisfying to prepare (see here for a copy of the talk)  The other thing I noticed was that students from the continent always seem to be very mature, polite and interested. I must look into an exchange sometime, do they have Erasmus for staff?

My main task this summer is to finish my little book on cosmology. It’s based on a course I have taught for some years and it’s been a lot of fun to write. Now I’m finding that it’s one thing to write a book and quite another to get it published! Still, I have plenty of time now to be writing book proposals and writing to publishers. In the meantime, I look forward to a swim in the sea everyday after work and a walk into the village. It’s funny to live in a village where others come for summer holidays!

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Tide’s out on Lawlor’s Strand in Dunmore East

Update

Unfortunately it’s so warm, we’re beginning to get quite a few jellyfish. Hope it cools down a little next week!

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A day in the life

There is a day-in-the life profile of me in today’s Irish Times, Ireland’s newspaper of record. I’m very pleased with it, I like the title  – Labs, lectures and luring young people into scence  – and the accompanying photo, it looks like I’m about to burst into song! This is a weekly series where an academic describes their working week, so I give a day-to-day description of the challenge of balancing teaching and research at my college Waterford Institute of Technology in Ireland.

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Is this person singing?

There is quite  a lot of discussion in Ireland at the moment concerning the role of  institutes of technology vs that of universities. I quite like the two-tier system – the institutes function like polytechnics and tend to be smaller and offer more practical programmes than the universities. However, WIT is something of an anomaly – because it  is the only third level college in a largeish city and surrounding area, it has been functioning rather like a university for many years (i.e. has a very broad range of programmes, quite high entry points and is reasonably research-active). The college is currently being considered for technological university status, but many commentators oppose the idea of an upgrade – there are fears of a domino effect amongst the other 12 institutes, giving Ireland far too many universities.

It’s hard to know the best solution but I’m not complaining – I like the broad teaching portfolio of the IoTs, and there is a lot to be said for a college where you do research if you want to, not because you have to!

Update

I had originally said that the institutes cater for a ‘slightly lower level of student’. Oops! This is simply not true in the case of WIT, given the entry points for many of the courses I teach, apologies Jamie and Susie. Again, I think the points are a reflection of the fact that WIT has been functioning rather like a university simply because of where it is.

Comments on the article are on the Irish Times page

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Last day at Cambridge Infinities Conference

Today was the third and last day of the ‘Infinities and Cosmology’ conference at Cambridge (there is also a workshop tomorrow, see website). Yesterday saw quite a heavy schedule, with part II of George Ellis’s ‘Infinites of Age and Size Including Global Topological Issues’, part II of Anthony Aguirre’s ‘Infinite and Finite State Spaces’ and part II of Michael Douglas’s ‘Can We Test the String Theory Landscape?’ (see previous post for an outline of these topics). We also had a fairly technical talk on ‘Singularities and Cosmic Censorship in General Relativity’ by the Cambridge mathematician Mihalis Dafermos: nuts-and-bolts talks like these are great for non-relativists like me because you get to see the mathematical tools used in GR research.

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The logo for the Infinities in Cosmology conference; an artist’s impression of small universes

Today saw part II of Mihalis’s talk and the lecture ‘Infinite Computations and Spacetime’ by Mark Hogarth, a fascinating exploration of new methods of computation by exploiting relativistic spacetime . I won’t attempt to summarize either, but the lectures should soon be available on the conference website.

For me, the highlight of the day was the talk ‘At Home and At Sea in an Infinite Universe: Newtonian and Machian Theories of Motion’ by Simon Saunders,  the well-known Oxford physicist and philosopher of physics. This was a superb discussion of Newton’s cosmology, in particular the paradox of gravitational instability in the Newtonian universe of infinite size and absolute, fixed space. Did Newton realize that our solar system might possess a net acceleration, or did he assume that external gravitational forces somehow cancel out? Drawing on material from Newton’s Principia and his ‘System of the World’,  Professor Saunders argued that Newton assumed the latter, though whether he attributed such a delicate cosmic balancing act to divine intervention or to unknown forces is not clear. (The possibility of a theological argument is not so fanciful as this work was the first mathematical attempt to try to describe the universe as a whole). Later, Professor Saunders suggested that it is likely Newton declined to spend too much time on the question simply because it was untestable.

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Newton’s famous Principia

There were many other interesting points in this fascinating lecture. Viewing the slides shown from Newton’s Principia, I was struck by the equivalence drawn again and again between bodies at rest and in uniform motion. This anticipates Einstein’s special theory of relativity and is again slightly in conflict with Newton’s assumption of a fixed, absolute space, as Simon pointed out. All this hints at a possible difference in Newton’s philosophy towards the universe at large versus motion on local scales – ironic as he was the first scientist to unite terrestrial and celestial motion in a single framework. I won’t comment further, but the lecture left one eager to read Simon’s recent paper on the subject.

All in all, a superb conference. It was interesting that, even with such distinguished speakers, moderators observed time limits strictly in order to allow plenty of time for questions and comments after the talks. In some ways, this was the best part; it’s not often one gets to hear to-and-fro arguments between scientists like John Barrow, George Ellis, Julian Babour and Simon Saunders, in the lecture theatre and over coffee.

Speaking of coffee, one of the best aspects of the conference was the venue. Cambridge’s Department of Applied and Theoretical Physics forms part of its Centre for Mathematical Sciences and is housed in a lovely modern open-plan building, with the smell of coffee and scones wafting throughout the atrium. What other mathematics institute can boast such a setup?  Not DIAS, I’m afraid. Indeed, I’m writing this post in the quiet atrium/canteen (no annoying background music – that wouldn’t be tolerated here). However, I’ve just realised that we are now finished for the day, so I’m off to do some sight-seeing at last.

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The main atrium in the Center for Mathematical Sciences is one big coffee shop, perfect for group discussions of physics, philosophy and mathematics

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The Department of Applied Mathematics and Theoretical Physics forms part of the Centre for Mathematical Sciences at Cambridge

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Mid-term in Chamonix

Last week was mid-term and I had a few days skiing in Chamonix in the French Alps. Chamonix lies in the shadow of Mont Blanc, the highest of the Alpine peaks, and the area is famous for its challenging snowsports and mountain climbing. It was surprisingly easy to get to (1 hr 30 mins from Geneva airport) and the skiing certainly didn’t disappoint.

I stayed with my brother and his family in a tiny chalet in Les Praz, a small village just outside the town of Chamonix. The great advantage of this village is that it offers easy access to La Flègere, a large ski area on the opposite side of the valley to the crowds at Chamonix. We had one day’s skiing out of Flegère, another at Argentière, the next resort along the valley, and the final day at Le Tour, further down the valley again.

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The village of Les Praz in Chamonix

The skiing was great in each case; lots of snow, steep pistes  and clear skies almost every afternoon. An extra thrill was the fact that one could ski over the Swiss border and have lunch in Switzerland. Of the three resorts, Flegère was my favourite; plenty of trees, nice unpisted runs under the lifts and not too many people.

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The lonely skier

That said, I retain my preference for skiing in Austria. One reason is that, like many French resorts, Chamonix has relatively few gondolas, a large number of button lifts  and uncovered chairlifts. Button lifts are quite tiring on the feet after a while, while exposed chairlifts can get very cold – a concern at altitudes above 1500 m where the midday temperature is often below -10 degrees Celsius. In Austria, almost all the main resorts have installed a healthy distribution of small, efficient gondolas and covered chairlifts (in the latter case, the chairs are heated by solar panels in the plastic cover). There were also far fewer restaurants and cafes on the Chamonix slopes, which I found quite surprising for such a famous resort (coffee breaks are important for the tired skier). So while the French are justifiably proud of their resorts, I still prefer Austria!

All in all a very good ski holiday, highly recommended…

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Resistors in series and parallel

In the last post, we saw that for many materials, the electric current I through a device is proportional to the voltage V applied to it, and inversely proportional its resistance, i.e. I = V/R (Ohm’s law). If there is more than one device (or resistor) in a circuit, the current through each also depends on how the resistors are connected, i.e., whether they are connected in series or in parallel.

In a series circuit (below), the resistors are connected one after the other (just as in a TV series, one watches one episode after another). The same current runs through each device since there is no alternative path or branch, i.e.  I = I1 = I2. From V = IR, we see the voltage across each device will be different; in fact, the largest voltage drop will be across the largest resistance (just as the largest energy drop occurs across the largest waterfall in a river). The total voltage in a series circuit is the sum of the individual voltages, i.e. V = V1+V2. As you might expect, the total resistance (or load) of the circuit is the simply the sum of the individual resistances, R = R1 + R2.

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Series circuit: the current is the same in each lamp while there may be a different voltage drop across each (V = V1+V2 +V3)

On the other hand, resistors in a circuit can be connected in parallel (see below). In this case, each device is connected directly to the terminals of the voltage source and therefore experiences the same voltage (V = V1=V2). Since I = V/R , there will be a different current through each device (unless they happen to be of equal resistance) .The total current in a parallel circuit is the sum of the individual currents, i.e. I = I1+I2. A strange aspect of parallel circuits is that the total resistance of the circuit is lowered as you add in more devices (1/R = 1/r1 + 1/r2). The physical reason is that you are increasing the number of alternate paths the current can take.

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Parallel circuit: the voltage is the same across each lamp but the currents may be different (I = I1+I2)

Confusing? The simple rule is that in a series circuit, the current is everywhere the same because there are no branches. On the other hand, devices connected in parallel see an identical voltage. In everyday circuits, electrical devices such as kettles, TVs and computers are connected in parallel to each other because it is safer if each device sees the same voltage source; it also turns out to be more efficient from the point of view of power consumption (an AC voltage is used, more on this later).

In the lab, circuits often contain some devices connected in series, others in parallel. In order to calculate the current through a given device, redraw the circuit with any resistors in parallel replaced with the equivalent resistance in series, and analyse the resulting series circuit.

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Problem

Assuming a resistance of 100 Ohms for each of the resistors in the combination circuit above, calculate the total resistance of the circuit. If a DC voltage of 12 V is applied, calculate the current in the circuit. (Ans: 133 Ω, 0.09 A)

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Current, voltage and the French resistance

Last week, our 1st science students had their first laboratory session on electrical circuits. They haven’t met electricity in lectures yet, so I spent some time explaining the concepts of current and voltage.

In essence, current is the flow of electric charge around a circuit (measured in amps) while voltage is the energy that drives the current (and is measured in volts). I find it helpful to think of the two in terms of cause and effect; a current will only flow in the circuit if a voltage is applied. In simple circuits, this energy is supplied in the form of a DC battery (or voltage source) that drives the current through some device (or resistor) in the circuit.

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The lamp (or resistor) lights as the current goes through it, completing the circuit

You might expect that there is a simple relation between voltage and current, and sure enough, the German scientist Georg Ohm discovered that, for many materials, there is a linear relationship between the two. Ohm’s law states that the current I passing through a material connected to a voltage V is given by the simple equation I = V/R. Here, 1/R is the constant of proportionality and is called electrical resistance and you can see why from the equation: a material with a very large value of R will pass almost no current (bad conductor), while a material with very small R will yield a large current for the same voltage (good conductor). So the term has exactly the same meaning as it has in ordinary speech, e.g. the French resistance. Resistance is measured in volts per amp, also known as Ohms (Ω).

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Many materials have a linear relation between voltage and current – the slope of the graph is the material’s resistance

In the experiment, the students apply a series of voltages to an unknown resistance in a circuit, and record the corresponding currents. A plot of voltage versus current then allows them to verify the linearity of the relation and the resistance is estimated from the slope of the line. (Strictly speaking, one should really put the voltage on the x-axis as it is the independent variable, but the calculation is simpler if the voltage is on the y-axis).

Measuring current and voltage

All of the above is fine in principle. Yet novices find the measurements quite difficult in practice. They have problems connecting the circuit because they get confused between measuring the current that flows through a device, and the voltage across it. It’s crucial to understand the difference between the two, and I suspect the modern multimeter adds to the confusion.

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The ammeter reads the current running through the resistor while the voltmeter reads the voltage across it. A plot of voltage vs current gives a measurement of the resistance

When I was a student, the current was measured by passing the current through an ammeter (marked A in the diagram), an analog device with a nice big dial calibrated in amps or milliamps. The voltage across the resistor was measured by connecting a different instrument, the voltmeter, across the terminals of the resistor; this voltmeter was a separate meter with a dial calibrated in volts (marked V in the diagram). So an ammeter was always connected in series with the resistor/device, while the voltmeter was always connected across it (in parallel).

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Current is measured by passing it through the ammeter (L) while voltage is measured by connecting across the voltmeter (R)

Nowadays, identical instruments are used for both; to measure current, one passes the current through the terminals marked ‘current’ of a multimeter, and the main dial on the meter is switched to the amp scale. To measure voltage, one connects the ends of the resistor across the terminals marked ‘voltage’ on an identical multimeter, and the dial is switched to volts. It sounds simple, but it’s easy to connect to the wrong terminals, getting no readings or blowing the fuse in the meter. More subtly, I think the clever circuity inside the multimeter hides the fact that current goes through while voltage drops across. All in all, I suspect students would understand circuits better if  we went back to separate instruments for measuring current and voltage….

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The mysterious multimeter. To measure current, leads are connected to the sockets marked ‘common’ and ‘amps'; to measure voltage, one connects to the sockets marked ‘common’ and ‘voltage’.

Notes

1. If a 12-V voltage is applied across a resistor of 15, what current flows in the circuit? How many electrons per second does this current represent? (Ans: 0.8 mA,  5.0 x 1015 electrons)

2. What happens to the current if one end of the resistor accidentally touches the other? (Ans: the circuit resistance drops almost to zero and the current becomes very large – don’t try this in the lab!)

3. Ohm’s law is a misnomer – it is not a universal law of nature but simply a property of some materials (many materials have a nonlinear response to voltage, including your cat).

4. It might seem from Ohm’s law that a material with zero resistance can give infinite current! No such materials are known; the relation is simply not valid for these materials. However, some materials have extremely low resistance at very low temperatures, known as superconductors. A good application of superconductivity can be found at the Large Hadron Collider, where protons are guided around the ring by magnets made of superconducting material: this reduces power consumption enormously but the snag is that the entire accelerator has to be kept at extremely low temperatures during the experiments.

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