Crossing the thin black line

By James Dacey at CERN

This chart shows the first of two aborted attempts to collide two 3.5 TeV proton beams here at the Large Hadron Collider (LHC) at CERN.

Today is supposed to mark the beginning of the LHC physics programme, and the world’s press is gathered here at the particle physics laboratory to experience the events as they unfold.

Look closely at the chart and you will see the thin black line – which represents beam energy – plummet just after 6 this morning. This was done intentionally by beam engineers, who noticed that bunches of protons had become unstable, and it was better to “dump” the beams in a controlled manner rather than allow them to capitulate freely, which could damage equipment.

This process occurred again at around 8.45, following a similar fault.

I have been whizzing around the LHC’s experiments on the media bus to get the reaction of CERN scientists.

“You should not be at all surprised by this – there are many things that can go wrong with the beams, but the fundamentals have been set in place over the past few weeks,” said Crispin Williams, a detector scientist at ALICE.

Another scientist, Hans-Peter Beck, at the ATLAS experiment, explained to me the difficulties of trying to collide the two proton beams.

“It is like a set of marbles slipping down a sheet of ice. We know they will get to the bottom, but it is very difficult to predict or control their trajectories.”

The next attempt is expected to take place in around an hour’s time.

Watch the CERN webcast here.

An unassuming setting for such an ambitious project

By James Dacey at CERN

Early tomorrow morning, I will be leaving my roadside hotel and taking the second exit on this roundabout towards CERN where the scientists will embark on an infinitely more exciting journey – the start of the physics programme at the Large Hadron Collider (LHC).

This event is marked by the first particle collisions 7 TeV, which will set yet another impressive benchmark for accelerator physics.

CERN has announced within the last hour that the first attempt at collisions will take place any time from 7 a.m. Central European Summer Time.

I will be reporting from CERN during the day, but if you want to be even closer to the action you can follow events via a live webcast, which will include coverage from the control room as well as step-by-step explanations of the procedures.

Later in the day there will be a number of roundtable discussions as well as broadcasts from the LHC’s four experiments: ATLAS, ALICE, CMS and LHCb.

Steve Jones to head BBC Trust review

By James Dacey

British biologist Steve Jones is to head a review of impartiality and accuracy in the BBC’s coverage of science, called for by the BBC Trust – the BBC’s governing body. The Trust has also published guidelines for this review, which give the scope and the timetable of activities.

The review comes as pressure has mounted on the BBC in recent years due to issues such as climate change, GM crops and stem cell research becoming increasingly politicized.

For example, in 2007 the corporation cancelled a special day of programmes that was to be devoted to climate change when senior news executives questioned the impartiality of this broadcast.

The BBC Trust will assess BBC content across all of its media outlets including the BBC World Service, over the coming months. They say that this will involve a number of public engagement activities.

“It will ask whether the BBC’s coverage of science taken as a whole, presents a partial view of the nature of science and the role science plays within society,” say the review guidelines.

Jones will scrutinize the results of these exercises before writing a final report, which is expected to be published in the first half of 2011.

“I look forward to sampling some of [the BBC’s] huge coverage of physics, chemistry, biology, ecology, geology and more to see how well it is doing its job,” says Jones, who is head of the genetics, environment and evolution department at University College London.

“Science is by nature a field full of dispute; this is how it advances. Dispute is not the same as bias, though: and a bias towards optimism or pessimism is a real danger, both in the public presentation of science, and in the beliefs of scientists themselves.”

In addition to his academic research, which focuses on the evolutionary and genetic aspects of biology, Jones is also a familiar guest in BBC programming. He has made more than 200 appearances on BBC radio and has also been a guest on a number of BBC current affairs programmes including Question Time and Newsnight.

“He was selected on the basis of his academic credentials, of his knowledge of the media and his reputation amongst the scientific community,” says the BBC Trust in a statement.

A more sophisticated approach is needed

By Hamish Johnston

When I was a boy I remember hearing that a tray of hot water in a freezer sometimes freezes before a tray of cold water. Being an accepting child rather than a sceptical scientist, I had no problem embracing this as another example of the weirdness of nature.

Called the Mpemba effect, the curiosity was spotted in 1963 by Erasto Mpemba who was making ice cream for a school project. The Tanzanian teenager was in a hurry and put his boiled milk into the freezer before it cooled to room temperature and found that it froze before his classmate’s cooler samples.

When young Erasto asked a teacher how Newton’s law of cooling could be reconciled with his observations he was famously told, “All I can say is that is Mpemba’s physics and not the universal physics.”

Undeterred, Mpemba carried out further experiments, eventually writing a paper with a physicist at the University of Dar es Salaam. The paper was published in 1969 – the same year that Canadian physicist George Kell published an independent observation of the effect.

It turns out that Mpemba was not the first to ponder this phenomenon. The idea has been around for more than 2000 years and the 1969 papers led to a flurry of claims that the effect can be observed in everything from food preparation to frozen pipes.

The papers also spurred a debate among physicists about whether the effect is real or merely the result of bad experimental technique. Indeed, it turns out that it is incredibly difficult to define and control all the variables involved in deciding which sample freezes first.

Some physicists believe that the effect is related to supercooling – when liquid water is cooled it can remain liquid at temperatures well below zero Celsius. It could be that the smaller temperature difference between freezer and cold water encourages more supercooling, lowering the temperature at which the sample freezes.

However, some experiments suggest the opposite – that it is easier to supercool hot water!

Now, James Brownridge at the State University of New York at Binghamton has done a series of nine carefully controlled experiments to understand the conditions under which the Mpemba effect occurs.

His conclusion “Hot water will freeze before cooler water only when the cooler water supercools, and then, only if the nucleation temperature of the cooler water is several degrees cooler than that of the hot water.” The nucleation temperature is the point at which supercooled liquid actually freezes.

He was able to create these conditions in his lab using sealed vials of water that are immersed in a freezing salt solution. He cycled the samples through 28 freeze/thaw cycles and found that the hot water froze before the cold every time.

What I don’t understand about the experiment is that Brownridge seems to have chosen his samples based on the knowledge that there is a 5.5 degree difference between their nucleation temperatures. Or, in other words, the samples are not identical.

So does this mean that the Mpemba effect doesn’t occur with identical samples, but only with samples that differ in a specific way?

You can read more about the Mpemba effect in this Physics World article: Does hot water freeze first?.

At loggerheads: John Pendry (left) and Ulf Leonhardt (right)

By James Dacey

Everybody loves a good, strong disagreement between two academics at the top of their game, especially when their positions are polar opposites. Two recent papers, by John Pendry of Imperial College, London, and Ulf Leonhardt of St Andrews in Scotland, draw our attention to one such fracas that is really starting to heat up.

The issue in question is quantum friction – does it exist? In a nutshell: Pendry says, absolutely yes; while Leonhardt says, not a chance.

If such a force does prove to exist, as well as crowning a winner in this debate, it could be of great interest to engineers trying to improve the performance of ultra-small mechanical devices.

Let me give you a brief history of the issue…

Over the past few years, Pendry and a number of others have advocated the existence of quantum friction, by building on the pioneering work of Dutch physicist, Hendrick Casimir.

In the mid 20th century, Casimir worked out that two flat surfaces placed in a vacuum should be attracted to one another. This force arises from the fact that, according to quantum mechanics, the energy of an electromagnetic field in a vacuum is not zero but continuously fluctuates around a certain mean value, known as the “zero-point energy”. Casimir showed that the resulting radiation pressure outside the plates will tend to be slightly greater than that between the plates and therefore the plates will be forced together.

Pendry and others became interested in the situation where the first surface is moving relative to the second one, claiming that friction should exist between the two. Pendry, who is chair in theoretical solid-state physics at Imperial College, develops the idea in a new paper in the New Journal of Physics. He argues that fluctuations in the first surface appear to be moving with a Doppler-shifted velocity, relative to the first surface. This Doppler shift destroys the balance between fluctuations as there are now more of them travelling against the relative surface motion than there are heading in the opposite direction. This, he believes, leads to a net frictional force.

This argument, however, is strongly rejected by Leonhardt, who is chair in theoretical physics at the University of St Andrews. In a comment paper submitted to the arXiv preprint server, Leonhardt claims that Pendry has described quantum friction “qualitatively”, but not quantitatively. Leonhardt argues that, “there is no experimental evidence for or against this effect, no facts”. He criticizes Pendry’s idea of quantum friction claiming that “one could apply the same effect to extract an unlimited amount of useful energy from the quantum vacuum”.

Leonhardt contrasts Pendry’s academic efforts with his own approach to this topic, referring to a paper he co-authored last year. In this paper – developing the earlier work of Soviet physicist, Evgeny Lifshitz – Leonhardt carries out an “exact calculation” for a particular configuration of plates, which shows quantum friction to equal precisely zero.

This calculation of Leonhardt is scrutinized in Pendry’s latest paper, and the Imperial researcher is less than impressed by it. Pendry says that Leonhardt has essentially shifted the goalposts on the problem. “[Leonhardt’s team] claim that a moving surface can be replaced by a stationary one that is bianisotropic,” he told me. “Of course, this leads to zero net friction in their theory.”

So, as you can see, the issues that still need to be resolved include: what exactly constitutes a moving surface; and the conditions that could trigger what Pendry refers to as a “Doppler-induced imbalance”.

For now though, the argument rages on.