The world's biggest and most expensive scientific experiment is ready to re-start

Underneath some nondescript farmland near Geneva, on the border of France and Switzerland, the world's biggest and most expensive scientific experiment is ready to re-start.

The Large Hadron Collider (LHC) at Cern will help scientists investigate some of the biggest mysteries in the universe.

In 2012, after the first run of the machine, the scientists here made headlines when they discovered the Higgs boson - a fundamental particle that has a role in giving other particles mass and which had been predicted to exist by theoretical physicists Peter Higgs,François Englert and Robert Brout almost 50 years earlier.

Higgs and Englert would go on to share the Nobel Prize in physics in 2013 (Brout was left off the list because he died in 2011 and the prize cannot be awarded posthumously).

For the past two years, the collider has been shut down and engineers have been upgrading every element of the accelerator and its detectors. When it starts again, it'll be able to reach twice the energy as it could before, allowing it to reach further into unknown areas of physics.

It will accelerate protons around a 27-kilometre ring underground to nearly the speed of light and then collide them in the centre of one of four huge detectors - Atlas, CMS, LHCb and Alice. Whenever the protons smash together, they explode into a shower of new particles. Sifting through that debris can give scientists a window into new, as-yet-undiscovered, areas of nature.

In Run 2, as the next phase of operation is known, the scientists want to go into the complete unknown. During the first phase of operation, many scientists were almost certain they would find the Higgs boson. That particle filled in the last piece of the Standard Model of particle physics, which describes all the particles and forces in the universe - including electrons, quarks and photons.

But, as successful as it has been, scientists know that the Standard Model is not a complete picture of the universe. It doesn't include a description of the force of gravity, for example, and can only account for around 4% of the mass of the universe. The remaining 96% of our cosmos is dark matter and dark energy and no-one knows what any of those things might be.

The Standard Model also cannot explain why we don't see antimatter in the universe.

Antimatter is the same as normal matter except it has the opposite electrical charge. A positively-charged electron is known as a positron, for example, and when it comes into contact with an electron, the two particles annihilate into pure energy. At the beginning of the universe, a fractional amount more matter than antimatter seems to have come into existence from the big bang.

All the antimatter and most of the matter came together and annihilated - we and everything we see today is made from the matter that remained.

Scientists at the LHCb experiment at Cern will investigate why that might have happened.

Professor Tara Shears of the University of Liverpool explains what the LHCb experiment is designed to do:

"We can't explain the difference we need to in order to explain how the universe evolved so we have a really big mystery to solve here," says Professor Tara Shears of the University of Liverpool, who works on the LHCb experiment. "And we are hoping in the next run we will see something that illuminates that difference for us and shows us what the deep underlying explanation is."

One of the leading candidates to plug some of these holes in the Standard Model is called "supersymmetry". An idea that was first formulated in the early 1970s, it suggests that all the fundamental particles we know about so far have heavier, as-yet-undiscovered "superpartner" particles. Some of these heavier particles could be candidates for dark matter, for example. If the LHC can find evidence for these superpertner particles in its collisions, scientists would be well on their way to proving that supersymmetry was real.

Sudan Paramesvaran of Bristol University, who works on the CMS experimentat Cern, and Professor Tara Shears told me what their experiments could mean for the public:

"We don’t know what we are going to find," says Sudan Paramesvaran of Bristol University, who works on the CMS experimentat Cern. "If we did find supersymmetry or dark matter it would have such wide ranging implications not just for particle physics but for the universe in its entirety and astrophysics - it would be one of the most seminal moments of the 21st century."

Particle beams will soon start to circulate regularly once again around the LHC, for the first time in years. They'll be more powerful than ever and they'll give us a window onto a whole new era of physics.