Guillermo AyalaMartinez asked Henry Gee:

Are we alone in the Universe? Opinion of the scientific community

Henry Gee All the elements for life are fairly common in the Universe. Life began on Earth very soon after the Earth itself formed. There are trillions of other planets in the Universe. That our Earth is the only one with life is extremely unlikely. However, nearly all life elsewhere will be of a very simple kind. Even if it is complicated, it will not look like humans.

So, life is common in the Universe. But is there intelligent life in the Universe? That's harder to answer. First, it depends on what you mean by 'intelligent'. I think that civilisations capable of interstellar communication are very rare. Such civilisations exist so very briefly, on the scale of cosmic time, that having more than one in any given galaxy at any one time is extraordinarily unlikely. Even if that were not the case, I subscribe to Cixin Liu's 'Dark Forest' hypothesis - that civilisations that wish to survive will not advertise their presence.

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