In a letter to the European Cultural Conference in Lausanne, Switzerland, in December 1949, Louis de Broglie advocated "the creation of a laboratory or institution where it would be possible to do scientific work, but somehow beyond the framework of the different participating states". Endowed with more resources than national facilities, such a laboratory could "undertake tasks, which, by virtue of their size and cost, were beyond the scope of individual countries".


CERN, the European Organization for Nuclear Research, came into being five years later in 1954. Today, 50 years after its foundation, it is reassuring to see that CERN is building the largest and most powerful particle accelerator ever: the Large Hadron Collider (LHC). This 14 TeV proton-proton collider is at the cutting edge of technology, and is a heartening sign of both the public's support for basic science in Europe and beyond, and of the determination of European countries to stay at the forefront of particle physics. I have been asked to imagine what the next 50 years might hold for CERN and for particle physics. I shall take this opportunity to look into a very cloudy crystal ball, with the deep conviction that particle physics will continue to enrich culture and produce knowledge and technology as it has done for a large part of the last century.

In the medium term, CERN's activities will be dominated by the LHC. By modifying the magnetic fields of the collider around the proton-interaction points, we can envisage a luminosity upgrade that would prolong the working life of the accelerator and extend the mass range for discovery. At a much higher cost we can even imagine doubling the collision energy by replacing the present LHC dipoles with higher-field magnets. Indeed, fully exploiting the LHC could easily take us to 2020 or 2025. As a result, there is little chance of CERN being involved in the construction of a 0.5-1 TeV linear electron-positron collider (CERN Courier October 2004 p5).

But what can we say about the more distant future of CERN, say from 2020 onwards, once the results from the LHC and, possibly, the linear collider are known? A linear collider with a length of several tens of kilometres could conceivably be built underground alongside the Jura mountains next to CERN. On the other hand, a big circular tunnel, such as that required by a Very Large Hadron Collider, would have to go below Lake Geneva or below the Jura (or both). Either option would be simply too expensive to consider. This is why a 3-5 TeV Compact Linear Collider (CLIC) would be the project of choice for the CERN site. A CLIC project could be launched in about 2015, when the LHC will be operating smoothly at its design luminosity, and data-taking could begin as soon as the early 2020s.

CLIC or a VLHC are enormous projects that will have to be undertaken through worldwide collaboration. But does this mean we should make a further step along the lines advocated 50 years ago by de Broglie and promote a world laboratory? This issue has been widely discussed, but in my view concentrating high-energy particle physics in a single laboratory with worldwide support is not a good idea. It would be too vulnerable to fluctuations in policy and mistakes in management. Moreover, it would not stimulate competition. My preference would be a coordinated global network that includes universities, national laboratories and regional laboratories like CERN and Fermilab.

The International Committee for Future Accelerators has considered the concept of a global accelerator network, although there is no consensus on what such a network might actually be or what it could do for us. As I see it, a global network would essentially be a new way of organizing existing particle-physics centres across the world, and focusing them on projects with a global dimension. For example, it would perform "diffuse" R&D on accelerators and detectors, co-operating on a single project at any one time and providing components for the machines and detectors.

Multinational companies are supposed to do what national companies cannot. Similarly, a global accelerator network only makes sense if it can achieve something that individual regions cannot do by themselves and, moreover, something that is essential to make real progress in particle physics. CLIC at CERN and the VLHC at Fermilab could be among the long-term goals of the global accelerator network, which would keep the world's particle physicists busy until 2050. The transition to such a new organization would probably be similar to the shift in Europe from national laboratories to CERN - it would be difficult but worth trying.

Whatever the next 50 years hold for CERN and particle physics in general, it will almost certainly require countries to pool their resources and work together closely. Some 54 years since de Broglie's letter inspired European scientists to build a single laboratory, his vision of basic science is still as relevant: "The universal and very often disinterested nature of scientific research seems to have predestined it for reciprocal and fruitful collaboration."

• Extracted with permission from "CERN: the next 50 years" in Physics World September 2004 p42.

Luciano Maiani, Universita' di Roma "La Sapienza" and INFN. He was director-general of CERN from 1999 to 2003.