It is the greatest scientific experiment in the world. It will help explain what happened as the universe was born in the Big Bang. Some fear it could trigger a black hole that would devour the Earth in a nanosecond. And it is back bigger and stronger than ever.
We're talking about the Large Hadron Collider, the largest subatomic particle smasher in the world. It is based at Cern, the European Organisation for Nuclear Research, and has been switched off for the past two years to allow a major refit and modernisation, and will be ready to start sending packets of particles spinning around its 27km circuit from March 23rd.
The collider already holds all the records for generating the massive energies needed to crack open individual protons (the nuclei of hydrogen atoms). In 2013 it confirmed that the theoretical Higgs Boson was real, a serious achievement. But now the collider will enter a new frontier, as its power level is increased by more than 60 per cent, which opens up possibilities.
The unimaginably small particles travel around the ring at close to the speed of light, so tremendous energies are released when they are allowed to collide. This breaks them down into their constituent parts, and these more fundamental particles are detected and measured by various experiments placed around the ring.
The goal is to discover new things, such as the Higgs Boson, but the ability to see this particle only came about when the collider was able to produce energies reaching 8TeV (trillion electron volts, a way to measure energy). The collider now moves to a higher energy plane, reaching 13TeV. This will open up the potential for important discoveries, including the revelation of new kinds of fundamental particles.
The collider already broke new physics ground during its first run from 2010 to 2013, and fears that the machine could produce a black hole were shown to be nonsense.
Physicists are excited about the new science the improved collider is likely to reveal. Director-general Rolf-Dieter Heuer offers his own wish list, and it echoes the hopes of many physicists.
1 A clean restart
Cern wants the collider to come back into service without incident, unlike the major system failure in 2008 that caused a two-year delay in getting the machine into service. Heuer wants good, intense, high-energy beams that will deliver quality data for physics from the
2 The direct detection of dark matter
Dark matter is the invisible skeleton of the universe and makes up 25 per cent of the universe’s mass. We know it is there, but we have no idea what it is.
All that we know about fundamental particles is bound up in what is known as the Standard Model; the Higgs Boson is the last missing part of this puzzle. It is also called "the theory of almost everything", which is more accurate given that we know nothing about particles that might make up dark matter. The collider's higher energy levels might take us over the threshold needed to see and record some of the particles associated with dark matter.
3 The indirect detection of dark matter
There is more than one way to skin a cat and more than one way to learn about dark matter, and it could come down to the Higgs Boson. The particle was discovered in 2012 and was declared the Higgs in 2013.
It allowed physicists to fill in a final gap in the Standard Model, but they have seen only a few thousand such particles, and interesting questions remain. Such as this one: it is definitely a Higgs Boson, but is it the Higgs that belongs to the Standard Model or a Higgs that lives in the world of dark matter particles?
We know far too little about the particle to make assumptions, but now that Cern is moving up to higher energies, these may tell us much more and clarify where the Higgs belongs. Physicists are excited about the possibility that this might shake up the Standard Model.
4 Matter versus antimatter
When the Big Bang happened, it should have produced equal amounts of matter and its oppositely charged reflection, antimatter. So how come today when we look out at the universe we only see matter: us and the Earth and galaxies and everything else?
Something happened to give matter the edge, but this also caused an antimatter wipe-out, and physicists want to understand why this happened.
Answers may come from one experiment at Cern, the LHCb, which can record particle events down to parts per billion. It has already watched the behaviour of matter and antimatter created by collisions, and while these reinforce the Standard Model, they don’t tell us why the universe is mostly matter. Perhaps the higher energy levels will help to solve this mystery.
5 A universe from primordial soup
The Big Bang was not your common-or-garden firework; it caused unimaginable energy to occur at a point, and the matter that formed from this energy zipped around first as fundamental particles, such as quarks and electrons. After about a millionth of a second, the universe had cooled so much that quarks could only exist in a primordial state of matter as a quark-gluon plasma, a perfect fluid.
The question is: how did the soup made from these ingredients end up delivering the non-fluid main courses and dessert – regular matter – that we are familiar with today? The collider could answer that; it is designed to deliver mini-Big Bangs that can be studied as they dissipate.
ONE LAST WISH: THE UNEXPECTED
The Standard Model has been under construction for more than half a century, and in particular since the 1970s, when quarks were confirmed to exist. Having built it with care, physicists would now like nothing better than to kick a few holes in it.
It is hoped that in this new energy realm, unexpected doors will open to reveal whole new families of particles, maybe from dark matter or the Higgs or something else that has yet to be imagined.
New discoveries may cause a few cracks in the Standard Model, but maybe that will give way to a new “model of everything” that is not limited by the term “almost”.