Do Aliens exist?

To answer this question, it has to be cleared first if the wellknown laws of science are also valid in far regions of the cosmos. Dark Energy and Dark Matter seem to exist in the universe, their physical nature, however, is unknown. Astrophysicists assume that the same physical laws on earth are also valid in other regions of the cosmos. This means, for example, that all common elements exist also in other parts of the universe. However, unknown molecules may exist. To construct organic life, elements like Hydrogen (H), Carbon (C), Oxygen (O) and Nitrogen (N) are necessary. So, one should look for these elements on strange planets (exo-planets). Best of all it would be to look for the molecule Ozon (O3). This gas originates by interaction between hydrocarbons and molecules of the atmosphere. May be one can detect this gas in the atmosphere of exo-planets. This, however, is not a proof of the existence of extraterrestric life, but makes it possible. If there should be organic life on strange planets, it is not sure, that one has found Aliens, i.e. higher developed species. This question is still without answer!