Over in Europe, scientists are getting ready to turn on a huge underground machine. In fact, it is the biggest machine that human beings have ever built. And it's one of the most expensive. The machine is called the Large Hadron Collider, or LHC, and scientists hope that it will help them unlock some of the deepest, darkest secrets of the universe.

What are some of these secrets? It turns out that there are all sorts of things that scientists don't know about the universe. For example, where does "mass" come from? We know that all things made of atoms have mass, but we don't actually know where mass comes from. And speaking of mass, why can't we see lots of it? When we try to measure the mass of the universe, it seems to be a lot heavier than it should be. There seems to be lots of matter in the universe that we can't see. What is this "dark matter," and where is it hiding? And what about black holes? Can we create tiny black holes, and if we can, how do they behave? What can we learn from them? We may be able to answer all of these questions and many more using the LHC.

What is the LHC, and how does it work? It is an incredibly complex machine. But if we start with the basics, we can understand the essence of the LHC.

Diagram © CERN/Philippe Mouche The Large Hadron Collider is the biggest particle accelerator ever built, and it will create the fastest protons human beings have ever created. Its ring is more than five miles in diameter, has a tube 17 miles long and it's so large, it crosses the border between France and Switzerland.

We have all heard of atoms. We can make water, for example, by combining hydrogen atoms with oxygen atoms. That's easy enough. What is inside an atom? Using fairly simple experiments at the beginning of the 20th century, scientists were able to discover electrons, protons and neutrons. By the way, protons and neutrons are known as hadrons.

The next question that comes to mind is obvious, "What is inside a hadron?" This is not so easy a question to answer. But scientists discovered that they could bash two protons together to learn what's inside. The machine that does the bashing is called a particle accelerator, also known as an atom smasher.

The earliest particle accelerators were very simple and could fit in the palm of your hand. By building bigger and bigger particle accelerators, scientists could learn more and more. The basic idea behind a particle accelerator is simple. You take a particle like a proton, and you put a group of them in a sealed tube. You take all the air out of the tube using a vacuum pump, so the protons don't have anything to run into. Then, using microwave energy (a lot like the energy used in a microwave oven), you accelerate the protons.

Image © CERN/ Maximilien Brice; Claudia Marcelloni The central piece of the Compact Muon Solenoid (CMS) particle detector weighs 1920 tons -- the same as five jumbo jets.

Most particle accelerators are shaped like rings, and they contain magnets that steer the protons around the ring and keep the protons bunched together. As the protons accelerate, their speed gets closer and closer to the speed of light.

Protons are incredibly tiny, but at the speed of light, they have a lot of energy. To understand this, think about a baseball. If a little kid throws a baseball at you, it probably won't even hurt. If a major league pitcher throws a 100-mph fast ball at you, it will hurt a lot. If someone shoots a baseball out of a cannon at 500 mph and it hits you, it will likely kill you. A proton in a particle accelerator is going 186,000 mph, and it has a lot of energy despite its tiny size.

Image © CERN/ Laurent Guiraud Inside one of the beam magnets

The LHC actually has two tubes, so that two groups of protons can accelerate in opposite directions. The scientists will then slam the two streams of protons together in some of the biggest head-on collisions ever.

The collisions will happen in underground detector rooms that are as big as warehouses. The detectors are basically gigantic, specialized movie cameras that can sense all of the debris that flies out from the collision. The debris contains the particles that make up the protons – things like quarks and leptons. The only reason that we know that quarks and leptons exist is because we have particle accelerators.

Image © CERN/ Maximilien Brice The huge ATLAS detector will measure the energies of particles produced when protons collide in the center.

Because the collisions in the LHC will be so massive, scientists are hoping that they will see new particles that no one has ever seen before. For example, scientists think there's a particle inside atoms called the Higgs Boson, and that this particle is the thing that gives atoms mass. But scientists have never witnessed a Higgs Boson, so they don't know if it exists or not. Scientists also hope that the LHC will have enough energy that they are able to create mini black holes, which will then immediately evaporate because they are so small. And maybe scientists will find new particles that no one has ever imagined before.

Image © CERN/ Maximilien Brice; Claudia Marcelloni. Engineers check the tunnel magnets that form the accelerator ring.

Because of these possibilities, scientists all over the planet are excited about the LHC, and thousands of scientists are working on the project. With luck, they can start accelerating their first protons sometime in 2008 and begin making new discoveries. We should learn many new things about how the universe works from the LHC.

Beam Dump The Large Hadron Collider is accelerating protons, which are incredibly tiny and incredibly light. But it is accelerating them so fast that they have a giant amount of energy. If it ever needs to get rid of the protons, it sends them to a device called the beam dump. The dump is made of a block of graphite. Magnets sweep the beam across the block so that all the protons do not land on the same spot. There are also sheets of graphite in the tunnel leading to the block to slow down and spread out the protons. Even so, the temperature of the block of graphite rises thousands of degrees when the protons hit. Ultimately, the beam dump absorbs the energy equivalent of several hundred pounds of TNT.