Neutrino telescopes under the ocean: The case for ANTARES

High energy cosmic neutrinos should provide a new means to explore the sky. Due to the weakness of their interaction with matter and the absence of their interaction with the electromagnetic radiations, neutrinos can travel in the Universe without being absorbed. On the contrary, because photons interact with matter, with the infra-red (IR) radiation and with the cosmic microwave background (CMB), the Universe is opaque for high energy gamma rays. Charged cosmic rays such as protons are deflected by the galactic and extra-galactic magnetic fields. So, only UHE protons, above 10 eV, are rigid enough to point back to their source. Nevertheless, at these extreme energies protons also suffer from interactions with IR radiations and with the CMB which limit their free pathlength to about 50Mpc. At greater distances protons continuously lose energy and become less and less rigid. Therefore, it appears that the only way to explore the Universe in the high energy range and at great distances is to detect neutrinos.