Feasibility of Extraterrestrial Visitations: Distances, Energy Demands, and Earth's Unique Biosphere
To the point
Extraterrestrial visitors to Earth are unlikely because of the vast distances and time required for interstellar travel, the enormous energy and physics barriers involved, and Earth’s unique biosphere that would demand special alien adaptations, even though thousands of exoplanets exist and SETI searches have not found detectable signals.
