Page 1514 – Physics World

Home » Page 1514

Ask a Nobel laureate

Questions please

By Hamish Johnston

Would you like to ask Nobel laureate John Mather a question?

Maybe you want to know why he decided to study the temperature distribution of the cosmic microwave background — which won him a share in the 2006 prize for physics

Or perhaps you want to ask him what it the most important challenge facing cosmologists today?

Or you could ask him how he spent his prize money!

The Nobel Foundation has joined forces with YouTube to allow you to upload a video of your question — and Mather will answer a selection of queries on video. You can find out more here.

The deadline for questions is 30 October, and you can post as many questions as you like.

Electrons reveal DNA without destroying it

The recent winners of this year’s Nobel Prize for Chemistry join a famous lineage of scientists who have shed light on the biomolecular world by using X-ray crystallography. However, new research published this week unveils an alternative to this famous technique that could reveal the structure and properties of biomolecules in much finer detail. According to its creators in Switzerland, the new method has the potential to revitalize biophysics, biochemistry and molecular biology.

Award-winning research

Developed by physicists, X-ray crystallography determines the structure of crystalline materials by scattering a beam of X-rays from the electrons within a material and measuring the diffraction pattern that results. James Watson and Francis Crick at the University of Cambridge, with the help of Maurice Wilkins and Rosalind Franklin at King’s College London, famously used this technique to determine the double-helix structure of DNA molecules. Similarly, this year’s Nobel Prize for Chemistry was awarded to the trio of biophysicists who used X-ray crystallography to determine the atomic structure of ribosome – the sites in cells where proteins are produced.

Despite all its successes, however, the ultimate limitation of this technique is that it works by averaging over millions of molecules in a crystal. This inevitably means that some of the finer details of the molecular world could remain undiscovered. Moreover, there are many protein molecules that are very difficult or impossible to crystallize.

The obvious technological solution for researchers is to replace their X-ray crystallography with high-energy electron microscopes, which physicists are already using to peer into the inanimate, atomic world. The trouble is that biological matter can be very delicate and so the radiation used in these techniques can damage or destroy the biomolecules under observation.

Electrons slow down

Now, Hans Werner-Fink and his team at the University of Zurich have suggested a way around this problem by creating a form of microscopy that utilizes lower-energy electrons. To demonstrate their new technique, the researchers isolated a strand of DNA and exposed it to a beam of low-energy electrons over the course of 70 min. By tracking the electrons that are scattered elastically, the researchers were able to build up holographic images of the DNA.

Underlying the new technique is the fact that, at certain energies, the electron radiation causes no damage to the DNA. In this way, Fink and his colleagues report successful imaging at a number of discrete energy points up to 230 eV. They admit that they do not fully understand why these “energy windows” exist but they conclude that elastic scattering must dominate at these frequencies.

Fink told physicsworld.com that, although the holography technique is simple in principle, there have been a number of technical challenges to overcome in realizing the technology. The researchers are now working with industrial partners in Germany to improve the design of their electron detector as well as their miniaturized electron lens. “We are convinced that our technique has the potential to offer the most detailed images yet of single biomolecules,” Fink said.

The related research paper is currently under review for publication in Physical Review Letters and an advance copy is available on the arXiv preprint server.

Canadian theory institute honours Stephen Hawking

The Perimeter Institute for Theoretical Physics in Waterloo, Canada, has announced that a major new extension to the building will be known as the Stephen Hawking Centre. The extension, which is currently being built, is due to open in 2011 and will double the size of the institute. It will also provide a home for the institute’s Master’s students, the first of whom joined the Perimeter Institute this autumn as part of its Perimeter Scholars international programme.

The announcement was made on 17 October at a special ceremony in the institute’s auditorium, held to mark the theory centre’s 10th anniversary. The ceremony was attended by Mike Lazaridis, who founded the institute in 1999 using money that he had made from Research in Motion – the Waterloo-based firm that makes Blackberry handheld devices. Although Hawking himself was unable to attend as intended, he did provide a video-recorded message.

“Theoretical physics has been the most successful and cost-effective in all of science,” said Hawking. “Many great challenges lie ahead. Where this new understanding will lead is impossible to say for sure. What we can say with confidence is that expanding the perimeter of our knowledge will be the key to our future.”

10 new distinguished research chairs

The Perimeter Institute has also announced 10 new distinguished research chairs, in addition to the 10 who were unveiled earlier this year. They will be Dorit Aharonov (quantum computing), Patrick Hayden (quantum communication), Leo Kadanoff (complex systems), Chris Isham (particle theory), Renate Loll (quantum gravity), Malcolm Perry (strings), Sandu Popescu (quantum fundamentals), Bill Unruh (gravitational physics), Guifre Vidal (quantum information) and Mark Wise (particle theory). The chairs will visit the Perimeter Institute for about a month each year.

The Perimeter Institute’s research chairs are the idea of the institute’s director Neil Turok, who took over last year. Turok was previously based at Cambridge, where he was a colleague of Hawking in the Department of Applied Mathematics and Theoretical Physics. Turok told physicsworld.com that Hawking, whom he last saw in September, appeared to be recovering well from the flu that he had suffered from earlier in the year. Hawking said in his pre-recorded message that he looked forwarding to visiting the Perimeter Institute in summer 2010.

More than just wonderland

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.

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.

Blackboards and Blackberries

By Matin Durrani

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.

The art of guestimation

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 x 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.

Questions, questions, questions

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.

Enter the yoctosecond

Light pulses emitted by an exotic state of matter known as a quark–gluon plasma last for just a few yoctoseconds – according to calculations by physicists in Germany. One yoctosecond is one trillionth of a trillionth of a second (10^–24 s) and is comparable to the time it takes light to cross an atomic nucleus. Indeed, the researchers say that such pulses could be used to study the ultrafast processes taking place inside nuclei.

Standard ultrafast lasers can produce pulses no shorter than a few femtoseconds (10^–15 s) long. It is, however, possible to generate attosecond (10^–18 s) pulses by combining the frequency harmonics that result from the nonlinear interaction of femtosecond pulses with various atoms.

Now, Jörg Evers and colleagues at the Max Planck Institute for Nuclear Physics in Heidelberg have worked out that it should be possible to extend this lower limit down by a further factor of a million.

Free soup

Their approach uses the light emitted by a quark–gluon plasma, a soup of free quarks and gluons, the force carriers that normally bind quarks together inside protons and neutrons. This state of matter is believed not to have existed naturally since the universe was just a millionth of a second old but can be recreated by smashing heavy ions into one another at extremely high energies inside particle accelerators. It is currently produced by the Relativistic Heavy Ion Collider (RHIC) at the Brookhaven Laboratory in New York and will also be created inside the Large Hadron Collider, due to switch on shortly at CERN in Geneva.

Evers and co-workers argue that a quark–gluon plasma naturally generates extremely brief photon pulses as it cools down. The plasma is initially very hot but then cools rapidly as it expands to about the size of a nucleus, at which point it turns back into normal matter. High-energy photons can only be emitted by the hot plasma itself and not the resulting normal matter, which means that pulses of such high-energy photons cannot last for longer than the lifetime of the plasma itself – which is just a few yoctoseconds. The trick is to simply focus on these photons, rather than those with a lower energy.

Two pulses are better than one

Establishing whether or not a quark–gluon plasma produces yoctosecond pulses is, however, not enough to show that it could be used to actually measure such brief intervals of time. This requires a double pulse: one to prepare the system and the other to carry out the measurement. Evers illustrates this with reference to a sprint race, in which the sound of a starter pistol sets the runners off and a photograph taken a few seconds later then establishes their position after that time.

Fortunately, a quark–gluon plasma could produce such a double pulse as it expands. Evers explains that initially the plasma emits light in all directions but then a competition of two mechanisms sets in. The rapid expansion of the plasma along the original collision axis of the heavy ions dictates that after some time most of the remaining particles within the plasma should move at right angles to this axis, which also constrains the light to be emitted in this direction. But a few moments later the complex internal dynamics of the plasma renders the motion, and with it the light emission, isotropic again. This should mean that a detector placed close to the collision axis will register a signal at the beginning and end of the plasma’s expansion, but not in-between: this is the double pulse.

According to Evers, this technique could shed light on the very dynamics inside a quark–gluon plasma that generates the double pulse. He says it could also be used to study processes inside atomic nuclei, perhaps improving our understanding of the reactions inside compact stars or supernovae, or helping us to design better fusion reactors. Indeed, he notes that measurements on the femtosecond timescale have already been used in industrial applications, such as investigating combustion processes when designing new engines.

Measurement technology needed

John Tisch, a laser physicist at Imperial College London questions how easy it will be to build the technology to measure yoctosecond pulses but adds that people had similar doubts about attosecond technology. “The key to unlock attosecond science was to utilize aspects of the generation process itself to measure the pulses,” he said. “So I would anticipate that yoctosecond pulses – if they ever materialize – might be measured by turning some of the same physics governing their generation back on itself.”

Evers says that he and his colleagues are currently developing yoctosecond detector technology but are not giving any secrets away.

The research is published in Physical Review Letters.

Chemical signature could help locate Earth-like planets

New insights into the Sun’s chemical composition may provide a new way to search for Earth-like planets orbiting distant stars – claims an international team of astrophysicists.

Astronomers have already discovered hundreds of planets (called exoplanets) orbiting stars other than the Sun. However, most of the known exoplanets are gas giants like Jupiter – rather than rocky Earth-like worlds. This is probably because the two techniques currently used to find exoplanets work best on large planets.

Now a team led by Jorge Meléndez of the University of Porto believes that the Sun’s unusual chemical composition could be related to the formation of Earth and the other rocky planets – and this chemical fingerprint could be used to identify other stars with rocky satellites.

‘Excellent news’

“Very excitingly, the star most similar to the Sun in this respect that we have found so far is Alpha Centauri A, the second nearest star,” said Martin Asplund, team member and director of Germany’s Max Planck Institute for Astrophysics. He said that this is “excellent news” because, if Earth-like planets do exist in that system, it is close enough for them to be observed directly.

The team came up with this idea after comparing absorption spectra of the Sun with that of 11 “solar twins” – stars that are physically similar to the Sun – and 10 “solar analogues”, which are slightly less similar. The measurements were made using the Magellan telescope at Las Campanas Observatory in Chile and the Keck telescope in Hawaii.

Whereas previous, less accurate, studies had suggested that the Sun’s chemical composition is typical of stars, Meléndez and Asplund say that in fact the sun’s composition is “quite unusual”. Compared to the solar twins, the team found that it has about the same amount of light elements like carbon and oxygen. Heavier elements, such as aluminium, iron and nickel, show a 10–20% lower abundance.

Dust-cleansed gas

Meléndez points out that this distribution in elemental abundances correlates strongly with their condensation temperatures. He suggests that the higher condensation temperature elements – referred to as refractory elements – were involved in the planet-forming process in our solar system. “The scenario we are proposing is that during the formation of the Sun some of the gas condensed into dust and eventually became the planets,” Asplund told physicsworld.com. “The largely dust-cleansed gas then continued being sucked into the Sun.”

About 10–20% of the stars in the study have a close chemical resemblance to the Sun. However, stars with giant planets orbiting round them are not chemically similar to the Sun, according to Meléndez.

Other characteristics of the solar system add to the argument that the Sun’s lack of refractory elements could be tied to the presence of rocky planets. For example, the total mass of elements missing from the Sun is similar to the total found in its four rocky planets. Also, the Earth’s crust contains relatively fewer light elements and more refractory ones compared with the Sun.

However, José Robles, a researcher at the Kennedy Space Centre in Florida who previously worked with Meléndez to identify solar twins, calls into question how significant the difference between the Sun and the average of the 11 twins is. Together with Australian National University astronomer Charles Lineweaver he points out that the amount of lighter, more volatile, elements in stars is known to vary. “Their statement that the Sun is depleted in refractories could probably more legitimately be described as the average twin being more depleted in volatiles than the Sun is,” said Robles.

‘Work in progress’

Robles applauds the accuracy of the measurements and describes the idea that the abundance differences between the Sun and solar-twins might be explained by planet formation as “thought-provoking”. According to Robles, using this approach to spot terrestrial planets “is an interesting idea that we may be able to do someday, but not yet. It is a work in progress.”

Meléndez’s team will now go on to study a further 100 stars in search of similarities with the Sun, having been allocated three nights’ observing time with the European Southern Observatory’s Very Large Telescope in Chile.

This work was published in The Astrophysical Journal Letters.

Inside the Perimeter

By Matin Durrani

The Perimeter Institute for Theoretical Physics in Waterloo, Canada, which kicks off its 10th anniversary festival today

“Make sure you don’t blow the world up!”

That was the parting shot from one of my fellow passengers as the minibus we were sharing from Toronto airport dropped him off outside his house here in Waterloo, Canada.

It took me a while to realise what the guy was on about. You see, I had mentioned to him that I was travelling to Waterloo to attend the 10th anniversary celebrations of the Perimeter Institute for Theoretical Physics.

In passing, I had also talked about the Large Hadron Collider at CERN and it was only later that I twigged what he meant: he had obviously assumed that the only thing physicists are hell bent on doing is making potentially life-threatening black holes.

All of which underlines the importance of Perimeter Institute’s 10-year bash, which focuses on explaining to the public what the institute and its physicists are trying to do.

The festival, entitled From Quantum to Cosmos, contains a string of exciting public events, ranging from panel debates and exhibitions to film screenings and a science-fiction workshop.

The first event takes place tonight, featuring an all-star list of physicists including Lawrence Krauss, Anton Zeilinger and Sean Carroll who will discuss the small matter of “what lies ahead in physics”. It will be streamed live on the web from the festival website

The Perimeter Institute, in case you weren’t aware, was set up in 1999 by Mike Lazaridis – the man who founded the company that makes Blackberry handheld phones.

The institute focuses on basic topics like particle physics, string theory and cosmology as well as quantum information, quantum gravity and the fundamentals of quantum mechanics.

I’m here for the next few days so I’ll keep you posted on life inside the Perimeter. One thing’s for sure: there’s no-one here planning to blow up the world. I just hope that guy on the minibus is here to find out what they really do.

Browse articles by content type

Ask a Nobel laureate