Scientists are on the hunt for a 'dark force' of nature that, if found, would open the door to an invisible realm of the universe.

The team hope to uncover a new fundamental force that connects ordinary matter with the elusive dark sector - invisible matter that makes up most of the cosmos.

If successful, the find would fill in substantial holes in our understanding of the universe, making it one of the most dramatic discoveries in the history of physics.

Our best guess at the make-up of the cosmos explains only 4 per cent of the observable universe, with the rest filled in by dark matter and dark energy.

Dark matter and dark energy are among the most perplexing materials in the cosmos, and could explain the movement of stars and the expansion of the universe.

But while this so-called dark sector forms a significant portion of the known universe, scientists have never directly observed it.

Researchers hope finding a new force that connects the dark sector with ordinary matter will finally reveal what dark matter and energy are made of - if they exist at all.

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Using a new instrument in Rome, scientists will begin a hunt this month for a fifth fundamental force of nature. It is hoped that this theoretical force, which connects ordinary matter with the so-called dark sector, will answer key questions about dark matter (artist's impression)

'At the moment, we don't know what more than 90 per cent of the universe is made of,' Dr Mauro Raggi, a scientist at Sapienza University in Rome, which is leading the project, told the Guardian.

'If we find this force it will completely change the paradigm we have now.

'It would open up a new world and help us to understand the particles and forces that compose the dark sector.'

Researchers will turn on an instrument at Italy's National Institute of Nuclear Physics in Rome this month in search of a fifth fundamental force.

The four basic forces physicists know of include the electromagnetic force and gravity, as well as the strong force - which holds atoms together - and the weak force, which is involved in radiation.

It is believed that a fifth force control dark matter and dark energy, and may exert subtle effects on the other four forces that scientists currently struggle to explain.

Our best guess at the make-up of the cosmos explains only 4 per cent of the observable universe, with the rest filled in by dark matter and dark energy (artist's impression)

WHAT IS DARK MATTER? Dark matter is a hypothetical substance said to make up roughly 27 per cent of the universe. The enigmatic material is invisible because it does not reflect light, and has never been directly observed by scientists. Astronomers know it to be out there because of its gravitational effects on known matter. The European Space Agency says: 'Shine a torch in a completely dark room, and you will see only what the torch illuminates. Dark matter is a hypothetical substance said to make up roughly 27 per cent of the universe. It is thought to be the gravitational 'glue' that holds the galaxies together (artist's impression) 'That does not mean that the room around you does not exist. 'Similarly we know dark matter exists but have never observed it directly.' The material is thought to be the gravitational 'glue' that holds the galaxies together. Calculations show that many galaxies would be torn apart instead of rotating if they weren't held together by a large amount of dark matter. Just five per cent the observable universe consists of known matter such as atoms and subatomic particles. Advertisement

The Positron Annihilation into Dark Matter Experiment, or Padme for short, will record what happens when antimatter particles called positrons are fired into a fragment of diamond just a tenth of a millimetre thick.

When positrons hit the diamond, they merge with its electrons, releasing two particles of light called photons in a burst of energy.

If the theorised dark force exists, then instead of producing two visible photons, the experiment will only release one regular light particle.

The other will be a so-called dark photon that is invisible to the experiment's instruments.

This hypothetical particle is the dark sector's equivalent to a photon, and will be measured by comparing the energy and direction of photons fired in, with whatever comes out.

By measuring the energy of dark photons, scientists can figure out their mass, which the scientists predict is around 50 times that of an electron.

Knowing the mass of the dark photon, if it exists, would allow scientists to figure out what particles it breaks down into, providing a first look at the dark sector.

Other laboratories around the world are also looking for dark photons. Bryan McKinnon, a research fellow at Glasgow University, is involved in the search for the particle at the Thomas Jefferson national accelerator facility in Virginia.

'The dark photon, if it exists, is effectively a portal,' said Glasgow University research fellow Dr Bryan McKinnon, who is not involved in the research.

'It lets us peer into the dark sector to see what is happening. It won't open the floodgates, but it will allow us to have a little look.'