Are we alone in the vast universe? This a very polemic question. Most of Scientist (Astronomers, Physicists, Biologists, etc.) state that no civilization has visited our planet. Nevertheless Prof. Abraham Loeb* has written a book describing the visit of an interstellar object called Oumuamua that passed 15,040,000 miles from Earth; it is opinion of Prof. Loeb that the object is a piece of advanced technology created by a distant alien civilization.
Prof. Loeb based his hypothesis on the facts that Oumuamua was moving to fast along a strange orbit, it left no trail of gas, and the shape of the object was unusual.
Long time before of the discover of Oumuamua, the astronomer Frank Drake** formulated an equation to estimate the number of civilizations in our galaxy that we might be able to communicate with.

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* Abraham Loeb is Israeli American theoretical physicist who works on astrophysics and cosmology.
** Frank Drake is an American astronomer and astrophysicist.
Based on the ideas shared before:

Is there any factual evidence that the Earth have been visited by other civilizations?
Do you think is important to explore the Universe looking for signals from other civilizations?
Make a quick research about SETI institute. Do you consider its mission is important nowadays?

All opinions are important and valid, and as part of this discussion we must not discuss about the religious beliefs of any participant.