Is 2015 the year that the mysteries of dark matter and supersymmetry are solved?

Scientists are excited at the prospect of uncovering what the universe is made of. They are preparing to fire up the Large Hadron Collider to recreate cosmic energies from 14 billion years ago that could unravel the mystery, writes Robert Matthews

By using the Large Hadron Collider, above, to smash particles into one another with energies that prevailed in the first moments of the Big Bang, scientists hope to catch glimpses of the existence of Show more

There is a real buzz of excitement among scientists that this year will be the one they solve one of the biggest cosmic mysteries – and one of the most basic: what is the universe made of?

Researchers are preparing to fire up the colossal machine that they believe has the best shot at finding the answer.

Bizarrely, it is not pointed at the heavens; in fact, it is buried deep underground. Stranger still, it is best known for its discoveries about the smallest scales of matter.

The machine is the Large Hadron Collider (LHC), the famous 27-kilometre-long particle accelerator near Geneva, Switzerland.

In 2013 it made international headlines for discovering the so-called Higgs particle, the final piece of the theory describing all the known matter in the universe.

Now, after a two-year shutdown, the LHC is about to spearhead the search for a far more mysterious quarry: dark matter.

The first hints of this enigmatic material emerged in the 1930s, during studies of galaxies. These vast collections of stars, gas and dust move through space in gigantic clusters, held together by their mutual gravity.

Yet observations of galaxies’ internal motion revealed a puzzling fact: there just were not enough stars to generate the gravity needed to stop the clusters from flying apart.

Although galaxies are made up of more than just bright stars, even including reasonable amounts of dark gas and dust lurking in the galaxies failed to solve the enigma.

The mystery deepened when astronomers began work on the origin of the chemical elements in the universe.

Using the known properties of protons and neutrons, which form atomic nuclei, theorists succeeded in getting almost perfect agreement between their calculations and the observed amounts of hydrogen and helium, the two most common cosmic elements. Yet that success vanished if they assumed that the enigmatic dark matter in galaxies was also made from protons and neutrons.

This did, at least, give some insight into the nature of dark matter: whatever else it was, it could not be the stuff found in atoms.

All hope that the mystery of dark matter would just fade away vanished in the 1990s, when satellites observing the distant universe confirmed not only that dark matter exists, but that it is five times more abundant than ordinary matter.

So if dark matter is not made from atoms, what is it? That is what the LHC is being powered up to find out over the coming months.

Although the LHC is renowned for its discovery of the Higgs particle, this may yet prove to be just the warm-up act for a far more impressive performance.

Few scientists doubted that the Higgs boson existed, as it was the sole remaining piece of an amazingly successful account of the sub-atomic world, known as the Standard Model.

It has been clear for years that the Standard Model cannot be the final word in scientific description of matter and forces.

Various anomalies and gaps have been found in both the theory and observation that hint of more to come.

At the top of the “most wanted” list is a phenomenon called supersymmetry.

Put simply, this is a hidden connection between the two most basic types of particle: those that make up matter – such as protons and neutrons – with those carrying forces between them, such as photons.

At first sight, these two particle families have nothing in common. Yet, according to supersymmetry, they share an underlying unity – one that manifested itself in the first moments of the Big Bang 14 billion years ago, but which has since faded from view.

The most obvious way to look for supersymmetry is to recreate the incredible energies of the early universe.

That is exactly what the LHC will do over the coming months.

By smashing particles into one another with energies that prevailed in the first moments of the Big Bang, scientists hope to catch glimpses of the existence of supersymmetry by using the LHC.

The most basic symptom of supersymmetry is the creation of types of particle not seen since the earliest days of the universe. And it is these that provide the link with the mystery of dark matter.

Being unlike any particle that makes up conventional matter, these supersymmetric particles will not wreck the neat agreement between observation and the theory of how the elements were created in the Big Bang.

But because they have mass, they could generate the gravity needed to prevent galaxy clusters from flying apart from each other.

Theorists think that even the lightest of the particles predicted by supersymmetry may be enough to do the trick. If they are right, a major cosmic mystery will have been solved.

But accounting for dark matter would be just the start. Supersymmetry promises to resolve other long-standing problems with current theories of how the universe is put together.

One of the most notorious problems centres on the theory for how light interacts with matter.

Developed in the 1920s, its predictions have been confirmed with astonishing precision. Yet to extract those predictions, theorists have to perform mathematical trickery that suggests something vital is missing from the basic theory. Add supersymmetry to the mix, and the trickery is no longer needed.

Undoubtedly, the biggest pay-off from the discovery of supersymmetry would be the boost it would give to the quest for the ultimate “theory of everything” – a single set of equations describing all matter and forces in the cosmos.

The search for this theory defeated even Albert Einstein, who was still scribbling down his ideas for it on his deathbed.

Since then, theorists and experimentalists have uncovered tantalising hints that Einstein’s quest was not wholly misguided.

Particle accelerators such as the LHC have found evidence that all the sub-atomic forces merge into a single “superforce” at incredibly high energies.

Once again, supersymmetry plays a key role in explaining how this happens.

This year marks the centenary of Einstein’s greatest achievement: the publication of his theory of gravity, known as general relativity.

His intellectual heirs at the LHC are hoping that it will also be the year when our understanding of the cosmos moves up to the next level.

Robert Matthews is a visiting reader in science at Aston University, Birmingham