The problem of dark energy and dark matter was first tackled by Albert Einstein, while working on The Theory of General Relativity. His calculations showed that the universe should present one of the two possible states: either expanding, or contracting. Unwilling to believe his own work, regardless of the results, he introduced a constant to make the universe after his liking - static, that is.

However, twelve years later, Edwin Hubble showed that the universe was not static, but expanding in space. Even more, it seemed that the speed at which it was expanding was growing exponentially. The concept of dark energy was introduced only a decade ago, to resolve the paradox. Estimations on the mass of the universe calculated to match the expanding rate, suggested that more than three quarters of the mass is represented by this mysterious form of matter, that presents a repulsive gravitational force towards normal matter.

In the issue of this months "Physics World" magazine, Eric Linder and Saul Permutter from the university of California, reveal how little we know about dark energy. Permutter proved Hubble right once again by observing distant supernovae explosions, that confirm the idea that the effect of gravitational fields on the matter present in the visible universe does not slow the speed of the expansion.

To explain the phenomena of dark energy action, the team constructed a so-called 'concordance model' of the universe, that predicts that the other quarter of the universe is represented by 21 percent dark matter, and only 4 percent of the normal matter which we experience on a daily basis.

They believe that dark energy merely represents a kind of 'cosmological constant' specific to the universe, that has similar energy to the elementary sub-atomic particle while popping in and out of existence.

Though it has never been directly observed, the galaxies and the cosmic microwave background radiation could provide some clues to its nature. The technology currently available can make clear comparisons between the positions of the galaxies and the thermal fluctuations seen in the CMB, to reveal the pattern of galaxy formation.

However, the universe we live in is still mostly unknown, as are its nature, its birth and its future, and there might be a possibility that we may never make the difference between the dark matter as a cosmological constant or something more exotic that we might never be able to comprehend.