One theory which can no longer be taken very seriously is that UFOs are interstellar spaceships.

Only feeble minds are paralyzed by facts.

I believe any malevolent supercivilisation would have rapidly self-destructed as we may be in the process of doing ourselves. If we do have contact, physical contact with aliens, I think it will be benign.

No communication technology has ever disappeared, but instead becomes increasingly less important as the technological horizon widens.

Those wanderers must have looked on Earth, circling safely in the narrow zone between fire and ice, and must have guessed that it was the favourite of the Sun's children.

The exploration of the planets is now closer to us in time than the exploration of Africa by Stanley and Livingstone.

I will not be afraid because I understand ... And understanding is happiness.