A leading physicist says it's 'childish' to think there are no aliens

Do aliens exist? Carlo Rovelli, a founder of loop quantum gravity theory and author of the best-selling book "Seven Brief Lessons on Physics," says it's an easy question.

"There is so much space up there that it is childish to think that in a peripheral corner of an ordinary galaxy there should be something uniquely special," he writes. "Life on Earth gives only a small taste of what can happen in the universe."

Humans do have a long history of thinking they are special, though we're gradually learning otherwise.

"We believed that we were on a planet at the center of the universe, and we are not," he writes. "We thought that we existed as unique beings, a race apart from the family of animals and plants, and discovered that we are descendants of the same parents as every living thing around us."

As Rovelli charts in "Seven Brief Lessons," we used to think the universe was like this:

Eventually this:

And finally this:

And that picture shows just one of one hundred billion galaxies.

So are there aliens? Almost certainly, but we haven't seen them yet - and people have contorted themselves all which ways to explain this.

When you consider the unimaginable vastness of space and how little we know about it even now, however, it seems inevitable.