The Large Hadron Collider and (below) Joseph Silk

The universe out there is not just what your teacher may have explained to you. If you thought it consists of only the sun, the Milky Way and numerous other galaxies and their stars that can be seen with the naked eye or its sophisticated extensions such as telescopes, nothing could be farther from the truth. Matter in the “luminous” universe is only a fraction of what is actually out there; the rest comprises a mysterious dark matter that has nothing to do with the objects — which are made of atoms — that we encounter in everyday life.

Still, scientists all over the world are chasing a dream of getting to know this enigmatic matter, which they believe is instrumental in creating all things — visible as well as invisible. Without this special matter, called dark matter, life on this tiny planet called earth would not have been possible, because stars such as the sun or galaxies that brew the stars wouldn’t have existed in the first place.

“We are convinced that it (dark matter) is there, but we still do not have the slightest clue as to what it may be like,” says Joseph Silk, the Savilian Professor of Astronomy at Oxford University, who is regarded as one of the top theoreticians of contemporary cosmology.

Silk, who was recently in India in connection with a workshop organised by the International Centre for Theoretical Sciences (ICTS), a new venture of the Tata Institute of Fundamental Research in Mumbai, believes scientists are “very close” to unravelling this mysterious entity. “If that happens, it will be one of the greatest discoveries of modern times in cosmology,” Silk observes, who was at the Inter-University Centre for Astronomy and Astrophysics, Pune.

If you can’t see something, how do you know it is there? The first conclusive proof for the existence of dark matter came nearly 10-15 years ago. Scientists studying the rotation of spiral galaxies found that such galaxies rotate at a much lower velocity than expected. The scientists would have expected them to revolve five times faster. Instead they rotate as if they are far heavier than the mass of all the luminous objects (such as stars and other celestial bodies) put together. This forced the scientists to conclude there is some invisible matter that holds the universe together.

“It is the most critical missing element in the universe,” says Silk who played a crucial role in advancing humankind’s knowledge about dark matter. As compared to ordinary matter, which is made up of atoms and constitutes just 4 per cent of the universe, dark matter makes up 23 per cent.

Dark matter seems to have provided the gravitational force required for the formation of stars as well as galaxies. “So we must find the dark matter to understand how stars and galaxies are formed,” he says. “We need to know what it consists of.”

The Oxford University astrophysicist is very confident that with so many experiments underway scientists will make a breakthrough within the next few years. “We have the best chance of finding it,” remarks Silk.

A number of theories have been pursued by scientists to explain the existence of dark matter. The most plausible explanation, according to Silk, is the theory of supersymmetry, or SUSY for short. This theory postulates that for every elementary particle known, there is a corresponding “superparticle” (or sparticle). For instance, the “superpartner” of an electron is called a selectron (or s-electron).

According to JoAnne Hewett of the Stanford Linear Accelerator Center in the US, supersymmetry describes a grand dance of particles through the universe, but currently we can see only one partner of each pair. According to this theory, the “unseen” sparticles might be the source of the dark matter.

Scientists are hoping that though such sparticles cannot be observed in nature, they can be created in very powerful accelerators. One of the major objectives of the Large Hadron Collider (LHC), which will be switched on in Geneva early next month, is to attempt to create these sparticles. “If they could do that, we would have proof for supersymmetry,” says Silk. This, in turn, will provide evidence for the existence of dark matter.

One of the biggest investments in the history of science, LHC is a 27-km long ring buried three-quarters of a kilometre deep below the earth’s surface on the outskirts of Geneva. It is scheduled to open on September 10.

There are other ways of detecting dark matter. Trillions of dark matter particles pass through the earth every second. Once in the earth’s atmosphere, they interact very weakly with other particles. “So if we have very powerful detectors and can shield them from the interference caused by cosmic rays that bombard the earth, we can detect them,” Silk says. “The trick is to go deep underground where it is quiet and radiation free. Many countries, including India, are setting up experiments for this.”

Another method of detection of this mysterious matter is to study the changes its particles cause in water and ice when they pass through them. In the Antarctica and underneath the Mediterranean Sea, scientists are already engaged in such experiments.