The levels of civilization in the universe (Kardashev scale)
Up to now, mankind has achieved many great scientific achievements. From the time of hunting, gathering until the first steps on the MoonAliens can be as heavy as polar bears
A Spanish scientist thinks alien creatures can be as heavy as a polar bear and over two meters tall, but are unlikely to be smarter than humanity.Scientists call for active contact with aliens
American space experts say it is time for people to actively communicate with aliens, not just receiving signs of extraterrestrial life.