The European research facility which helped shape our understanding of the fundamentals of matter and invented the world wide web is exactly 50 years old.
The future of Cern is with the LHC
The European Organization for Nuclear Research (Cern), based at Geneva in Switzerland, is the world's largest lab dedicated to particle physics.
It has a massive underground complex in which matter - atoms and their parts - can be smashed together at high speed.
Wednesday's celebrations will be marked by a 27km-long ring of light.
The floodlights in this circle will draw the circumference of the tunnel to be used for the Large Hadron Collider (LHC), a new experimental tool that will collide protons and other particles at very high energies.
Scientists believe this machine, due to come online in 2007, will enable them finally to understand why all the things we can see and touch have mass.
This is a big gap in our description of the Universe - and it is not the only one.
At the moment, the so-called Standard Model of particles and their interactions gives us only a glimpse into the true nature of what one might call "normal matter" and the forces that hold it together.
Measurements of far-distant exploding stars, for example, have led physicists to the knowledge that the cosmos is actually dominated by a mysterious "dark matter" and "dark energy".
A full explanation for these phenomena may be many decades away.
Cern is supported by 20 European member states, but it operates with the participation of scientists from all over the world.
It was opened in 1954 to attract back the European researchers who had fled to North America during World War II and to retain those looking to make a career in physics.
Today it employs 9,000 people, of whom 6,500 are scientists.
Three Cern scientists - Carlo Rubbia and Simon van der Meer in 1984, and Georges Charpak in 1992 - have received the Nobel Prize for work undertaken at the facility.
In terms of spin-offs, sensors that track particles at Cern have been adapted for medical applications, notably positron emission tomography (Pet) scanners used to detect cancer and other diseases.
It is, however, for the realisation of the web that most people probably know Cern and have reason to celebrate its jubilee.
The web was made possible through a hypertext program created by Sir Tim Berners-Lee some 15 years ago. The program made it much easier to organise, link and browse information on the internet.
The purpose of Berners-Lee's work was to give scientists a user-friendly means of sharing the results from experiments undertaken at Cern.
Today, the Geneva facility is at the forefront of developing the Grid, a "super-internet" which will enable physicists to handle the surge of data that will come out of the LHC.
"At Cern, physicists from many nations have come together to study the constituents of matter and the forces that control their behaviour at the most fundamental level possible," said former Cern director-general Professor Sir Chris Llewellyn-Smith.
"This is telling us why matter has the form it does and not some other form. And it's also casting light on the entire architecture of the Universe because the conditions that are created at Cern prevailed just after the birth of the Universe. Cern has been very successful at this," he told the BBC.