In April 2018, British cosmologist and astrobiologist Stephen Webb spoke to a Vancouver TedX audience about seeing a UFO as a child. This event, he stated, made him wonder exactly “Where are all the aliens?“, is there life on other planets in other galaxies? How would they exist or would we need to grow life elsewhere? With the latter, Webb warned, however, that there are certain barriers that would need to be overcome in order to create new life on a friendly planet or star. The ability to build and maintain a population has several requirements; habitability with flowing water, abiogenesis, the ability to create life from non-life, technological advancements and ability to communicate across space. While this formula may seem simple in relative terms, it’s unclear how to make these things happen.
The basic building blocks of life aren’t unique to Earth: amino acids have been found in comets,
complex organic molecules in interstellar dust clouds, water in exoplanetary systems.The ingredients are there, we just don’t know how they combine to create life, and presumably there will be worlds on which life doesn’t start. …As for the height of the barriers, your guess is as good as anyone’s. In my experience, when people sit down and do the math, they typically conclude there are thousands of civilizations in the galaxy. But then we’re back to the puzzle: Where is everybody?