Recently by Matin Durrani

By Matin Durrani

Skimming through the latest issue of CavMag — a glossy newsletter about the latest developments at the Cavendish Laboratory, Cambridge — I at first thought I had misread an article that stated: “In 1930, when I gratefully accepted a research studentship from Girton College…”

Marie Constable visiting the Cavendish Laboratory with director of development Malcolm Longair (right) and Geoffrey Constable (right)

In fact, it was not a misprint but part of a wonderful article by Marie Constable, a 101-year-old physicist who had done her PhD at the Cavendish back in the early 1930s.

Constable, who was writing all about her visit to the Cavendish in September last year to attend its Alumni Open Day, gave some marvellous insights into several legendary figures from physics.

Lord Rutherford, she writes, was “a big, bluff and hearty New Zealander”, who was “friendly and helplful”. He would, apparently, make random visits around the lab to his research students, knocking loudly on their door before asking if they needed any help. It was Rutherford, she says, who also instituted the practice of the Cavendish afternoon tea break, serving tea and buns every Wednesday in the library.

James Chadwick, who discovered the neutron and was Rutherford’s effective second-in-command, is described as being “friendly and kind” although he had a reputation for not tolerating silly mistakes and could sometimes “get cross”.

Meanwhile, Constable recalls Patrick Blackett, another Nobel laureate who had served in the Royal Navy, as being “tall, handsome and helpful” and “a remarkable addition to the Cavendish staff”.

Marie also once attended a lecture by Niels Bohr although, perhaps not surprisingly given his taciturnity, she says little about Paul Dirac, other than he “was often seen in the Cavendish and regularly attended the Wednesday afternoon tea-break”.

As for life at the Cavendish, it was apparently “serene and decent” and the atmosphere was “collaborative rather than adverserial”.

But despite being the only female graduate student at the Cavendish at the time, Constable says she did not encounter much discrimination. However, she admits that when she was an undergraduate, women had to sit at the front of the lecture room — “for fear their attention might be distracted by too much male proximity”. And she was later prevented from attending a workshop course for research students, forced to enrol instead at a local technical college instead.

Luckily that worshop experience proved handy and Marie carved out a career as a safety expert.

It’s a great little story and marvellous to see there are still living links with the glory days of Cambridge physics. The full article can be read at CavMag, which will be put online at this link shortly

By Matin Durrani

The physics blogosphere has been wild with rumour in recent days that researchers in the Cryogenic Dark Matter Search (CDMS) in the US may have obtained the first direct evidence for dark matter in the form of Weakly Interacting Massive Particles.

The CDMS group gave simultaneous lectures at SLAC and Fermilab late on Thursday evening UK time that would, or would not, announce major new findings, depending on whose blog you read.

My colleague Michael Banks has been listening in to the webcasts and e-mailed me to say that “the outcome is that it is not conclusive evidence of dark matter, but they did have two events on a background of 0.5… so some signal, but not the five events needed for a discovery”.

An arXiv paper on the new results should be there by early morning.

It appears, Michael tells me, that the first event was detected on 27 October 2007, with a recoil energy of roughly 12 keV, and the second was seen earlier that year at roughly 15 keV. A third event lies just outside their box with recoil of 12 keV. Apparently this gives the lower bound on the WIMP mass for these recoil energies as roughly 0.5 GeV.

CDMS has a neat summary here. This is the key sentence: “We estimate that there is about a one in four chance to have seen two backgrounds events, so we can make no claim to have discovered WIMPs.”

We’ll have more on this later in our news channel so stay tuned. In the meantime,
Cosmic Variance has been doing a live blog, which has lots of as-it-happens stuff to get stuck into to.

Electrons (blue) passing either side of a current-carrying solenoid shows the Aharonov-Bohm effect in action (Courtesy Physics Today)

By Matin Durrani

The Aharonov-Bohm effect is one of those weird, counter-intuitive consequences of quantum mechanics that makes physics the fascinating subject it is.

Discovered 50 years ago by Yakir Aharonov and the late David Bohm at the University of Bristol in the UK, the AB effect, as it is known to insiders, is being celebrated today at a special conference at Bristol.

In case you weren’t aware, the AB effect describes the fact that an electrically charged particle passing through a region where both the magnetic and electric fields are zero is nevertheless affected by the electromagnetic potential in that region.

It can best be understood by considering a beam of electrons passing through two slits and then around either side of a current-carrying solenoid, as shown by the blue lines in the picture above.

Although there is no magnetic field outside the solenoid, the potential is different on the two sides, which means that the wavefunction of the electrons travelling past one side of the solenoid are phase-shifted by a different amount compared with the electrons travelling past the other.

The AB effect can be verified by allowing the electron beams to interfere: the resulting fringe patterns shift depending on whether the solenoid is on or off.

The conference, which also marks the 25th anniversary of Michael Berry’s discovery of the related “Berry phase”, has attracted a crowd of specialists from around the world, including Aharonov himself.

I went to the conference dinner at the university’s Georgian-period Goldney Hall, where guests were treated to a marvellous menu of roast asparagus with goat’s cheese mousse and Serrano ham crisps, slow-cooked rump of lamb with quince sauce, and confit of raspberries.

Spotted among the guests were Bob Chambers, who confirmed the AB effect experimentally back in 1960, former Brookhaven chairman Michael Hart and independent physicist Julian Barbour, author of The End of Time.

Today’s first lecture session back at the university’s physics department was chaired by Murray Peshkin from Argonne National Laboratory in the US, who introduced Sir Michael by saying “he is a man of few words but many syllables – so listen carefully”.

Berry’s lecture was entitled “Semifluxon degeneracy choreography” and he duly proceded to use a fair few long-syllabled words, including “Gaussian random simulation”, “traceless real symmetric 2×2 matrices” and “rearrangements of nodal domains”.

The talk was a bit over my head, but on such occasions I take comfort in Richard Feynman’s famous phrase that “nobody really understands quantum mechanics”.

The conference ends today.

The cover of Graham Farmelo’s biography of Paul Dirac

By Matin Durrani

“Moving, funny, sad and intensely readable, this is a fascinating insight into the psychology of genius.”

No, not a description of this blog entry, but what the judges of the Costa Book Awards had to say about Graham Farmelo’s biography of Paul Dirac, published earlier this year.

The judges have shortlisted his book, entitled The Strangest Man: The Hidden Life of Paul Dirac, Quantum Genius, for the 2009 Costa Biography Award.

As physicists, we’re biased, of course, and so are hoping Graham beats off the other contenders.

(For the record, they are a description by the late playwright Simon Gray of his battle with cancer, a biography by the author William Fiennes of his brother Richard, and a biography of Lucie de la Tour du Pin. No I’ve not heard of her either, but she lived in France at the turn of the 19th century and was, apparently, “the Pepys of her generation”.)

Graham’s shortlisting — announced last night on the BBC Radio 4 show Front Row — is a great opportunity for me to give you a final reminder that he is presenting the inaugural webinar in the physicsworld.com online lecture series tomorrow, Thursday 26 November 2009, at 4p.m. UK time. Graham will be describing Dirac’s life story and outlining his key scientific contributions.

(Profuse apologies again to anyone in the US for the clash with Thanksgiving, but we’re hoping you can log on while popping the turkey in the oven.)

The webinar is free and you can register for the event via this link

Graham was pretty chuffed about the shortlisting. “I’m thrilled,” he e-mailed me today. “I always wanted the book to be read not only by physicists but by people who enjoy biographies. The wonderful thing about prizes like this is that they bring books to new audiences.”

Let’s hope he wins.

Eric Goff testing ball trajectories

By Matin Durrani

Qualification for next summer’s football World Cup in South Africa reaches its climax tomorrow — highlights include France’s return play-off with Ireland and Egypt squaring off against arch-rivals Algeria on the same day.

But some teams, like England, have already secured their passage to the world’s greatest sports tournament and will no doubt be already be dreaming of lifting the famous trophy.

England’s players have a night off tomorrow but if star midfielder David Beckham is feeling a bit bored, he might want to read a new paper in the American Journal of Physics by John Eric Goff of Lynchburg College, Virginia, and Matt Carré of the University of Sheffield in the UK.

Goff and Carré carried out a series of experiments in which soccer balls were launched from a machine while two high-speed cameras recorded portions of their trajectory. The equipment allowed the researchers to vary the balls’ launch speed and spin — balls could be fired either with no spin, topspin, backspin, sidespin or any combination.

From the resulting data, the two physicists then calculated the “lift” drag coefficient on the ball and the “sideways” drag coefficient, C_S. If the ball has pure topspin or pure backspin then C_S is zero, but if the ball has any other spin, the value of C_S is not zero.

All lovely stuff, of course, but where does Beckham come in? Well, Goff and Carré then examined Beckham’s famous 90th-minute free kick taken against Greece in October 2001 that secured England’s qualification for the 2002 World Cup in France. His carefully taken kick bent around the wall before landing plum in the back of the Greek net and secured England a dramatic last-minute equalizer in the 2—2 draw.

Using TV footage of the famous match, the two physicists calculated that the ball left Beckham’s foot at a speed of 36 m/s at which point its “Reynolds number” (air speed times ball diameter, divided by kinematic viscosity) was of 5.1 × 10⁵. The ball had an average rotational velocity of 63 radians per second, rose above the height of the crossbar during the flight and moved about 3 m sideways, before slowing down to about 19 m/s as it dipped into the corner of the goal.

Goff and Carré then did a back-of-the-envelope calculation to estimate a value for C_S, which was found to be about 0.2 for the famous shot.

And the punchline? Sorry folks, there isn’t one. But maybe the paper will persuade Becks, who’s currently on loan from LA Galaxy at AC Milan, to swot up on a bit of simple physics before next summer’s tournament. Assuming he makes the team, that is.

Vitaly Ginzburg in Stockholm in 2003

By Matin Durrani

Vitaly Ginzburg, who turned 93 last month, is without doubt one of the leading Russian theorists of the 20th century, who shared the 2003 Nobel Prize for Physics with Alexei Abrikosov and Tony Leggett for their work on the theory of superconductors and superfluids.

He’s a long-standing admirer of Physics World magazine — having first written for us back in 1997 — and when the opportunity arose to interview him, I jumped at the chance.

Ginzburg gave answers to our questions in Russian, which were then translated into English by Vitaly Kisin, a former colleauge of mine here at Institute of Physics Publishing. I must also thank Maria Aksenteva, who is the managing editor of the journal Uspekhi Fizicheskikh Nauk, which Ginzburg has edited for the last 11 years. She is very much his “eyes and ears”.

In the interview, which you can read by following this link, Ginzburg talks about how his interest in physics developed, why he distrusts the Church’s growing role in Russian society, and how his role in developing a hydrogen bomb for the Soviet Union was what saved his life.:

The interview is in the opinion section of physicsworld.com’s In-depth channel which currently contains a couple other great articles worth checking out.

In How to publish a scientific comment Rick Trebino relives the time he tried - and failed - to have a comment published in a scientific journal. You couldn’t make the story up.

Then as Imperial College London counts down to a debate on the pros and cons of human space flight on 12 November, the two panellists write exclusively for us, presenting their arguments for and against manned or robotic space missions in the article Human spaceflight: science or spectacle? Championing robotic missions is David Clements, a lecturer in astrophysics from Imperial. Making the case for human space flight is Ian Crawford, a reader in planetary science and astrobiology from Birkbeck College, London.

Finally, Robert P Crease probes arguments made by US energy secretary Steven Chu that the next generation of synchrotron sources are an essential tool for meeting the energy challenge — check out his article “The Lure of Synchrotrons” by following this link

By Matin Durrani

A reconstruction of NASA’s Mars Science Laboratory rover at the Quantum to Cosmos festival

I’ve been here at the Perimeter Institute for Theoretical Physics for four days now and I felt it was time I should visit the special “tent” containing hands-on displays and exhibits for the public as part of the Quantum to Cosmos festival .

First up inside is a full-scale model of NASA’s Mars Science Laboratory rover, which is due to take off in autumn 2011 and land on the red planet in summer 2012.

Round the corner were exhibits explaining quantum computing, superconductivity, polarization and more.

In the centre of the tent, meanwhile, was a 3D movie containing simulations of galaxy collisions, black-hole mergers and the early universe, with a voice-over from Stephen Hawking.

A still of the Alice and Bob videos, which can be watched online

There was also face-painting corner for children, with special paint that only shows up under ultraviolet light.

Visitors could also watch a great series of one-minute cartoons about quantum mechanics, featuring two characters called Alice and Bob.

All good stuff - but the question is whether such events will persuade young people to study physics.

Many pupils, and most importantly their parents, decide what to study based on the career opportunities that their chosen field will provide. Somehow we need to show pupils that physics isn’t kids’ stuff - but a decent career move too.

Perimeter Institute director Neil Turok with one of its many blackboards

This is my first visit to the Perimeter Institute for Theoretical Physics in Waterloo, Canada.

Physics World has been following the progress of the institute since it first began in 1999 so I knew what the ethos of it would be like - it encourages staff to work on unorthodox areas that are outside the mainstream, it strives for excellence, and it provides a supportive environment where nothing is taken for read.

There are no big shots whose views cannot be called into question and postdocs are given lots of freedom to pursue the ideas they are most interested in - to do pretty much what they want.

The founders of the institute also knew that a key factor would be the building itself. After spending its first few years in a temporary home — a former red-brick Victorian post office — the Perimeter Institute moved into a brand new building in 2004.

It was specially constructed, and is filled with lots of comfy, low sofas where people can stop and discuss weighty matters. The offices all have glass walls so that you can see if someone is in, and the corridors are deliberately narrow so that people are forced to stop and talk. (And in an amusing in-joke, there are seminar rooms known as the Alice Room and the Bob Room, named after the two people used in thought experiments on quantum cryptography.)

Free coffee is on tap. There are pool tables, stripped floorboards, lots of natural light, real log fires, and blackboards everywhere.

I’d heard about the blackboards. But what it is interesting is that they are actually used. So too are the Blackberries that all staff are given: the institute was founded by Mike Lazaridis, whose company Research in Motion makes these hand-held devices.

What was also nice to see was that the institute’s director, Neil Turok, did not see it beneath himself to make me a cup of tea before sitting down for an interview for an article I will be writing for the December issue of Physics World magazine.

I can’t imagine most lab bosses would pesonally make tea for their visitors. He even washed the cups out beforehand.

I just wish I understood what was on his blackboard.

By Matin Durrani

Enrico Fermi was a real lover of back-of-the-envelope “guestimation” calculations and was fond of posing them to his would-be PhD students.

The Quantum to Cosmos festival is on now in Waterloo, Canada

He famously asked how many piano tuners there are in Chicago and in July 1945 calculated the strength of the first atomic-bomb test blast by dropping pieces of paper before, during and after the explosion.

It is that ability of physicists to make rough “ball-park” estimates, off the cuff, of various quantities that inspired today’s “Art of Guestimation” event at the Quantum to Cosmos festival in Waterloo, Canada.

Holed up in the Princess Twin cinema were three young physicists - Sarah Croke and Robin Blume-Kohout from the Perimeter Institute for Theoretical Physics and Robert McNees from Loyola University in Chicago — who were given 10 minutes to answer various “Fermi questions” put to them by the audience before the gong went.

We had time for five questions, which are listed below, along with the panel’s answers. As with all these things, there are no right or wrong solutions. The point of the session was to show the logical way that physicists think when they want approximate solutions.

How much memory would an individual person need to store everything they could see in a lifetime? About 1 exobyte - on the assumption that the eye works like a movie film, storing visual information at about 30 frames a second, with each frame being stored in high definition (1920 × 1080 pixels) and with each pixel needing 32 bits to store colour. (The panel ignored what happens when you sleep, which would only open another can of worms.)

How many humans have ever lived since Homo Sapiens first walked on the planet? This question has been asked before - it’s about a hundred billion. Very roughly speaking, there as many people alive now as have ever lived.

How many “eh”’s would a typical Canadian say in a lifetime? (Bit of a silly one this - the “joke” is that Canadians say “eh” a lot.) The panel’s answer was seven million, assuming Canadians talk for three hours a day, that each sentence lasts five seconds and one in 10 sentences include the word “eh”. Eh?

How many Loonies are there in circulation? (No, we’re not talking mad people, but Canadian one-dollar coins.) This got the panel really stuck - their final answer was between two and four hundred million before the gong went.

How much salt is there in the Atlantic Ocean? The critical point was knowing how much salt there is in a litre of sea water. Just multiply that number by the volume of the ocean to give, ooh, about 10 to the power 19 kg.

The session was a lot of fun. Although I am not sure if this kind of event has ever been done before, I reckon it could be a winner at other science festivals too. It certainly got the audience involved, which has to be a good thing.

By Matin Durrani

What big question in physics keeps you awake at night?

That was the poser for a nine-strong panel of top physicists taking part in yesterday’s inaugural event of the Quantum to Cosmos 10th anniversary festival here at the Perimeter Institute for Theoretical Physics in Waterloo, Canada.

Sitting in a row of directors’ chairs on the main stage in the institute’s auditorium, the panel gave a range of answers related to pretty fundamental physics — not surprising given their interests and those of the institute itself,

In a nutshell, here are their answers - and apologies in advance if I have glossed over any subtleties. The panel session was only meant to be a bit of fun, after all.

Sean Carroll, Caltech
Why are the laws of physics the way they are?

Katherine Freese, University of Michigan
What is the universe made of?

Leo Kadanoff, University of Chicago
How does complexity develop in the universe?

Lawrence Krauss, Arizona State University
Have we come to the limits of our knowledge?

David Tong, Cambridge University
How will we ever know if string theory is correct?

Neil Turok, Director, Perimeter Institute
What happened at the singularity of the Big Bang?

Andrew White, University of Queensland
What is life?

Anton Zeilinger, University of Vienna
How far are we along the road of scientific discovery?

As for the ninth member of the panel — Gino Segrè from the University of Pennslyvania — I wasn’t quite sure what his answer was. I quizzed him afterwards in the Perimeter Institute’s candle-lit “Black Hole Bistro”, where the panel and special guests, myself included, were fed by the institute’s catering staff with plates of crab cakes and bite-sized pizza slices.

I think Gino was most concerned about the world not having enough young physicists to answer all those big questions that keep the rest of the panel awake

Gino recently reviewed for Physics World a book on how Wolfgang Pauli’s dreams were analyzed by Carl Jung. That got me thinking — what would be really interesting would be to analyze the panel’s dreams after thinking all those big questions.

I just hope they’re not having nightmares.