Is the Earth common, but life unique?

We know from the recent years of research on exoplanets (i.e. planets orbiting other stars than the Sun), that there are approximately 10 billion stars in the Milky Way alone with planets similar to Earth in both size and temperature.

If life arose on just a fraction of them and in just a few cases developed intelligent beings with a technical civilization, we have to expect that they will travel to the nearest planets, just as we will do in the future. So why haven’t aliens from one of these planets visited Earth? Is the universe filled with planets where life never arises? Or are other Earths constantly bombarded with devastating asteroids? Or why are we apparently so alone in the universe?

Host: Uffe Gråe Jørgensen, Astronomer, Niels Bohr Institute
Produced with support from: the Danish Agency for Science, Technology and Innovation.
Produced by: The Compound for the Niels Bohr Institute, 2013 
Length: 11:56