By Jim Reed
Technology reporter in Geneva, Switzerland
The CMS magnet is one of four detectors in the LHC experiment
It has cost around £5bn, is colder than outer space and will heat particles to 100,000 times the temperature of the sun.
Oh and it's already seen off legal action from two blokes who reckon it could swallow up the entire world in a giant black hole.
After 25 years of planning and construction, scientists at CERN, the European particle physics laboratory, will switch on a huge experiment this morning which, they say, will tell us more about the origins of the universe and could lead to thousands of new inventions.
The Large Hadron Collider, or LHC, built deep underground in Switzerland, will smash tiny particles into each other at speeds almost as fast as light itself.
Here's Newsbeat's guide to the biggest, and most expensive, physics project of all time.
So what does this machine do?
The LHC is the world's biggest particle accelerator.
A series of superconducting magnets in pipes stored deep underground speed up tiny sub-atomic particles called protons to very near the speed of light.
Part of the LHC particle accelerator in its 17-mile underground tunnel
The particles whizz around a 17-mile tunnel deep underground between the border of France and Switzerland 11,245 times every second.
The first test today will see particles flow one way around this giant pipe.
But, over the next couple of weeks, scientists will start sending two streams of particles around in different directions.
At four points underground those streams will cross, splattering protons into each other at extremely high speeds.
Four highly sensitive cameras the size of cathedrals will capture the collisions.
Sounds fun. But what do the scientists hope to find out?
The idea is to replicate the conditions that existed just after the big bang, the huge explosion that scientists think kick-started our universe 13.7 billion years ago and eventually led to life here on Earth.
They hope to spot more of the building blocks that make up atoms and clear up some of the big questions around the creation of the universe.
The CMS magnet detector weighs 12,500 tonnes
In particular, they are trying to be the first to spot something called the "God Particle" or "Higgs boson", named after a Scottish scientist called Peter Higgs.
Researchers have long speculated that it is the secret to giving everything mass and gravity but have never had a machine powerful enough to see it in real life.
And that's really worth £5bn?
Well, scientists say that this kind of research has already led to a series of inventions that make our lives easier today.
The technology behind particle physics has given us those tube-like medical scanners you see on ER, new forms of radiation treatment that can destroy cancers and smaller microchips that power the latest generation of computers.
Others speculate that research carried out at CERN could eventually lead to futuristic technologies like tractor beams and anti-gravity propulsion.
What else then?
Scientists at CERN say that past research has also thrown up a load of unexpected benefits.
In 1991 a British scientist working there, Tim Berners-Lee, thought up a new way of sharing information with other researchers.
The circle marks the position of the LHC on the Swiss/French border
His system of interlinked hypertext pages eventually became the world wide web.
Now scientists at CERN have developed a new computer network called the Grid to share the vast amounts of data that the LHC is expected to churn out.
It is designed as a "step beyond" the internet, letting researchers share processing power as well as information.
And what's this thing about destroying the Earth?
In March, Walter Wagner, a former nuclear safety officer from Hawaii and six others filed a lawsuit to try and stop the LHC being switched on.
They claim it might create a black hole sucking in the laboratory, Europe or even the whole planet.
Some scientists think the LHC could make destructive black holes
A retired German chemist, Professor Otto Rossler, is also leading a group of scientists concerned about the safety of the project.
He reckons it is possible that black holes created in the LHC will grow uncontrollably and "eat the planet from the inside".
Other way-out-there critics claim the experiment could open the way for aliens from another universe to invade through a worm hole in space-time.
Sounds like a Hollywood blockbuster?
CERN says its staff have been flooded by emails from people worried about the experiment.
But a safety review by scientists in the US, Russia and France gave the experiment a clean bill of health.
Although tiny black holes may be created by the particle collisions, the people working at CERN say they will blink in and out of existence before anything scary can happen.
Robert Aymar, the French scientist who leads the project, said: "The LHC will enable us to study in detail what nature is doing all around us.
"It is safe and any suggestion that it might present a risk is pure fiction."