In order to better understand the universe and its evolution, one needs to be able to interpret all the messages received from the outer space.

Electromagnetic radiations, by far the main astronomical observational mean, are generated by the excitation of atomic particles. On the contrary, gravitational waves have a totally different nature, being generated by the motion and variations of masses of celestial bodies. In a way, today’s astronomical observation is like watching a concert on TV with the volume completely turned off. Detecting gravitational waves may be compared to turning on the volume and listening to something never heard before.

The observation of gravitational waves will therefore significantly complement the observation of electromagnetic waves (light, radio, micro-waves, X and gamma rays) and of astro-particles (cosmic rays, neutrinos). It will reveal aspects of the Universe not reachable by these means and will extend the observable domain even in the cosmic zones darkened by dust and masked by other phenomena.
The most dramatic processes of the cosmos such as supernova explosions, catastrophic collisions, fusion of binary systems, rotation of pulsars, interaction of black-holes or the original big-bang generate gravitational waves. Observing gravitational waves emitted during these violent processes is the only way to obtain information on the masses involved.

The total mass of the universe, evaluated from the mass of observable bodies, cosmic dust and gases, is less than 10% of the mass necessary to explain the motion of the galaxies. Because gravitational waves are generated by the motion of large masses, their observation is likely to provide fundamental information on this puzzling problem.

Every new instrument to observe nature has permitted unforeseen discoveries, which have enriched our knowledge and often revolutionized our image of the world. Gravitational wave detectors are likely to reveal unsuspected aspects of the Universe.
Another aspect to be considered is that, unlike telescopes, which can only look at a very small portion of the sky at a time, gravitational waves detectors are by nature non-directional, they are constantly “listening” to the whole Universe. This gives the possibility to observe cataclysmic phenomenon such as the explosion of supernovas from the very first moment whereas they are usually discovered by telescopes well after the crucial moment.