Imagine shining a torch on a wall of a large dark room. The further away from the wall you are the larger and dimmer the circle of light will be. A normal light source spreads out with distance, an effect known as diffraction.
A coherent light source, such as a laser pointer, diffracts considerably less. It would throw a bright spot of light anywhere in the same room. However, the same spot would be 100 km wide by the time it reached the Moon.
Two scientists, Michael Berry and Nandor Balazs, predicted the existence of light beams that do not diffract at all in 1979. They named these beams “Airy beams” after the British astronomer Sir George Airy. Last year a group led by Georgios Siviloglou from the CREOL-University of Central Florida produced Airy beams for the first time. They showed that Airy beams could be curved.
The St Andrews team has now shown that curved Airy beams can be used to push particles along curved paths. They created what team member Joerg Baumgartl called, “a small snow-blower.” They used it clear a chamber of microscopic particles. This could be the basis of micro-engineering devices that could move and sort particles or cells.
Professor Dholakia said, “our understanding of how light moves and behaves is challenged by such beams and it is exciting to see them move into the interdisciplinary arena – light has thrown us a curve ball!”
The world survives the start-up of the biggest ever scientific experiment
September saw the start-up of the Large Hadron Collider (LHC), the world’s biggest, most complex and most expensive scientific experiment ever built. Situated beneath the Franco-Swiss border near Geneva, it has been over a decade in construction. The European Organization for Nuclear Research (CERN) has 15 years of experiments planned, with a price tag of 6.5 billion Euros (US$9 billion).
The LHC is the world’s most powerful particle smasher. Its 27-kilometre circumference ring comprises 1,600 superconducting magnets, most weighing over 27 tonnes. Approximately 96 tonnes of liquid helium keep the magnets at their operating temperature of minus 271.3 degrees centigrade. That is colder than outer space. When operational, the various experiments will produce roughly 10 petabytes of data a year. If recorded onto data CDs, the stack would be nearly 20 kilometres tall.
The LHC accelerates protons (a type of hadron) to 99.999 percent of the speed of light. Two beams of protons, travelling in opposite directions around the ring, collide in four detectors. By examining the debris from these collisions, scientists will try to answer five important questions.
1) What gives things mass?
Under Earths gravity, you experience mass as weight. But, what exactly is mass? In 1964, Professor Higgs proposed the mechanism that gives rise to mass. The particle involved is known as the Higgs boson. It is also known as the ‘God Particle’, much to his disgust of the atheist Higgs.
No one has ever detected the Higgs boson. Scientists hope to detect it in the debris of the LHC collisions.
2) What is dark matter made of?
Scientists attempting to understand the nature of the universe have an embarrassing problem; they cannot see 96 percent of it. They know it is there because they can see its affects on the motions of galaxies, but they cannot see it directly. They call the missing stuff ‘dark matter’ and ‘dark energy.’
Different theories have been proposed to explain this dark stuff, predicting different results for the LHC. Therefore, the results from the LHC will eliminate some of the competing theories.
3) What was matter like at the beginning of the Universe?
Current theories describing the birth of the Universe, say it exploded into existence about 13.7 billion years ago in an event known as the Big Bang.
In the first microseconds after the Big Bang, the Universe was so hot, that matter as we know it could not exist. Instead, there would have been a soup of fundamental particles known as quark-gluon plasma. The collisions in the LHC will produce similar quark-gluon plasmas, allowing scientists to explore the nature of the very early Universe.
4) Where has all the anti-matter gone?
Everything in the Universe is made of matter. The opposite of matter, known as anti-matter, has the same properties of matter, but with the opposite electrical charge. When matter and anti-matter come into contact, they mutually annihilate.
Current theories predict that equal amounts of matter and anti-matter were created in the Big Bang, and then destroyed each other. In other words, we should not be here. However, as we self-evidently are here, there must have be a bias in favour of matter. Results from the LHC will help discover the differences between matter and anti-matter.
5) Are there extra dimensions?
We experience the universe in four dimensions, three of space and one of time. Scientists propose there are may be more dimensions that may are detectable using the LHC. At the very high energies involved in the LHC collisions, particles may travel into these other dimensions so apparently disappearing.
For a great description of how the LHC works, see the following video, produced by CERN.
The LHC is not without controversy. A few scientist worry the high-energy collisions at the LHC could lead to the destruction of the Earth. A legal challenge was mounted to try to stop the LHC from being switched on. CERN maintains, and nearly all scientists agree, that there is no danger, not least because such high-energy collisions happen all the time in the Earth upper atmosphere.
The LHC shut down shortly after start-up, when liquid helium coolant leaked from the one of the superconducting magnets. It takes a month to warm the machine up for repairs, and then a further month to cool in down again, so repairs will run into the scheduled winter break. CERN cannot afford the electricity to run the LHC during the winter.
The LHC will be up running again, spring 2009. With luck, it will begin to answer some of those questions within the year.
From the BBC
A space mission that will be critical to our understanding of climate change has launched from California.
The Jason-2 satellite will become the primary means of measuring the shape of the world’s oceans, taking readings with an accuracy of better than 4cm.