14 DAY TRIAL // The last of the 1624 main superconducting magnets for the Large Hadron Collider (LHC) was delivered on 27 November. The construction is coordinated by CERN and it involves more than 200 manufacturers around the world, producing vast quantities of complex components to tight precision. The LHC was conceived 22 years ago and approved for build 10 years later.
"The present achievement is an essential milestone. The successful completion of all main magnets for the LHC accelerator results from the dedication and efficient collaboration of teams from CERN, other laboratories and many European industries. This is a promising step towards achieving the three pillars of the LHC - the accelerator, experiments, and computing - and the ultimate goal of scientific discoveries," said CERN's Director General Robert Aymar.
The LHC is located in a circular underground tunnel of 27 km circumference approximately 100 meters beneath the surface near the border between Switzerland and France. The existing CERN accelerator, similar in size, collides electrons with positrons while the LHC will collide protons accelerated near the speed of light. Such collisions will involve much higher energies, seven times higher than the most powerful particle accelerator currently in use.
The biggest challenge faced by engineers was that the magnets have to be chilled at very low temperatures to get them in a superconducting state. This allows them to work without losses. The temperature has to be around -271?C which is even colder than outer space.
"We introduced new techniques that were not yet standard in industry, including a new welding method for special stainless steel," said Lucio Rossi, head of the Magnets, Cryostats and Superconductors group at CERN. Lyn Evans, LHC project leader, added, "This is the end of more than six years of industrial production under very tight quality control. It has required a very close collaboration between the magnet manufacturers and CERN."
The challenges faced by the CERN's industrial partners required plenty of research and development which resulted in all sorts of innovations that are likely to find applications in many other areas, from magnetic resonance imaging (MRI) machines to car manufacturing.
The construction of LHC is expected to be finished by mid-2007 and the accelerator will be ready to start its first experiments around November 2007. The detailed results should be available around 2010. It takes a few years of experiments to draw any definite conclusions because one has to observe a large number of collisions in order to be able to classify them.
What discoveries are hoped from LHC?
The most important discovery that is expected from the LHC is either the detection or the non-detection of the Higgs boson. This particle is predicted by the Standard Model of elementary particles (which describes quarks, electrons and so on) and it's a very important part of the model. The Higgs boson is supposed to interact with all the massive particles and to be responsible for their masses. The non-detection of the Higgs boson would come as a total blow to the Standard Model as well as to all the present contenders to the status of "grand unified theory of everything" - theoretical constructions like "superstring theory", "quantum loop gravity", "process physics" and so on.
In 1998, the Kamiokande experiment has proved that neutrinos can oscillate from one form to another. This had solved the longstanding mystery that the Sun seemed to emit only a third of the number of neutrinos it had to emit according to theory. In fact, the Sun emits the correct number of neutrinos, but until recently, scientists have only detected a third of them - the other two thirds transform into other kinds of neutrinos which have been neglected. This discovery however, also implies that the neutrinos have masses - otherwise, the interactions that mediate the transformations wouldn't be available.
But the Standard Model used to consider that neutrinos have no mass - and thus do not interact with the Higgs boson. The model however can be changed by simply adding to the theory a new set of possible interactions - and thus raising the number of supposed "constants of nature" (which describe the strengths of the interactions) from 18 to 25. (An additional "constant of nature" comes from general relativity - the cosmological constant.) The Higgs boson is behind all but three of these "constants of nature", so its non-detection will be devastating to the theory.
Physicists wonder whether the somewhat ad hoc change to the Standard Model forced by the Kamiokande discovery that neutrinos have mass is good enough. Maybe more fundamental changes are needed. How can we tell? The LHC experiments will offer clues in this respect and maybe will also offer clues about how gravity could be incorporated into quantum mechanics.
"The Standard Model describes all the forces except gravity using quantum mechanics. General relativity describes gravity, ignoring quantum mechanics. General relativity is a beautiful work of pure thought. The Standard Model is a baroque mess: we live in an interesting world," said John Baez from the Faculte des Sciences de Luminy. "While it seems to have been designed by a committee, the Standard Model works quite well - too well for frustrated physicists who want to find something simpler."
Hopefully, the LHC will discover the limitations of the Standard Model because insofar all its predictions (except that of the neutrinos mass) fitted the experimental results to a degree that no one really expected.
The LHC will also be able to verify or put to rest the speculations about the existence of extra dimensions of space. String theories, or just "string hunches" as some have called them, claim that space has up to 22 extra spatial, yet invisible, dimensions! These extra-dimensions are supposed to be curled up like some small circles. Supposedly, we're not seeing them because they are curled like that. (In principle, string theory could still survive in the minds of the most devoted string theorists even if LHC fails to find the predicted extra-dimensions because they could simply claim that the extra-dimensions are even more tightly curled - but that would deliver a serious blow to the already diminishing respectability of this line of theoretical research.)
Finally, due to the huge energies created by the accelerator, it will be able to simulate the conditions present in the early universe and it just might reveal the nature of dark matter - an assumed type of matter that doesn't interact with light and which cannot find any place inside the Standard Model. Dark matter was invented to explain "the mystery of the missing mass", as Baez calls it.
This mystery appears both when one looks at galaxy's rotation and at the larger structures comprised of many galaxies. The galaxies rotate in a way that makes one think that there must be a lot of additional mass besides the mass of the visible stars. (Read more.)
Our galaxy is part of a larger structure. Most astronomers think that this structure, called the Virgo Supercluster (image, Milky Way is on the left), is bound together only by gravity. But when one measures the mass of this Supercluster and compares it to the total mass of the visible stars, one gets a huge difference.
"The Virgo Supercluster contains about 200 galaxy clusters, with a total of about 2,500 large galaxies and 25,000 small ones," Baez said. "The Virgo Supercluster contains about 200 trillion (2*10^14) stars. But, its mass is about 10^15 times that of the Sun. Since most stars are not huge, there are not enough stars to explain the mass of the Virgo Supercluster!"
There seems to be about 5 times more dark matter than standard matter (the stuff described by the Standard Model). Insofar, nobody knows what this matter is made of. Some speculate that maybe the general theory of relativity is wrong at such huge distances and no dark matter is actually needed. However, some observations seem to deny this possibility.
So, as the LHC starts producing data in the following years, we can say that there is going to be a lot of excitement for the field of high energy physics. For the past 30 years, since the Standard Model was created, the field of fundamental theoretical physics has yielded no significant result whatsoever and people are still asking the same questions Einstein was worrying about more than 50 years ago. Moreover, when it was discovered that the expansion of the universe is actually accelerating, rather than decelerating under the influence of gravitation, every theorist was taken by surprise. As Lee Smolin has said, everybody feels that they are missing something big. But maybe theoretical physics will soon exit this unprecedented dark cloud. After all, physicists will finally have access again not only to endless mathematical speculations but also to some relevant experimental results.
See more pictures of the LHC here.
