The question of whether there is intelligent life elsewhere in the universe has been asked by people for many years.
But if we hear something, should we answer? In the absence of any signal from them, should we try to make our presence known?
One of those asking these questions is Stephen Hawking, the British cosmologist with many deep thoughts and a good sense of humour.
Unlike many celebrity scientists, Hawking's provocative, news-grabbing statements almost always have some content worth pondering.
Looking for ET
Hawking is part of a Breakthrough Listen project to develop more sensitive radio receivers and listen in on the alien civilisations of the cosmos.
There is another project called Breakthrough Message to design a digital message that could be transmitted from Earth to an extraterrestrial civilisation. The message should be "representative of humanity and planet Earth".