This is a revisitation of a post that I published in 2011, with the title “The Hubbert hurdle: revisiting the Fermi Paradox“ Here, I am expanding the calculations of the previous post and emphasizing the relevance of the paradox on the availability of energy for planetary civilizations and, in particular on the possibility of developing controlled nuclear fusion. Of course, we can’t prove that nuclear fusion is impossible simply because we have not been invaded by aliens, so far. But these considerations give us a certain feeling on the orders of magnitude involved in the complex relationship between energy use and civilization. Despite the hype, nuclear energy of any kind may remain forever a marginal source of energy.

Post revised and readapted from “The Hubbert hurdle: revisiting the Fermi Paradox” — Published on “Cassandra’s Legacy” in May 2011

https://cassandralegacy.blogspot.com/2011/10/hubbert-hurdle-revisiting-fermi-paradox.html //

It seems clear that planets are common around stars and, with about 100 billion stars in our galaxy, organic life cannot be that rare. Of course, “organic life” doesn’t mean “intelligent life,” and the latter doesn’t mean “technologically advanced civilization.” But, with so many planets, the galaxy may well be teeming with alien civilizations, some of them technologically as advanced as us, possibly much more.

The next step in this line of reasoning is called the “Fermi Paradox,” said to have been proposed for the first time by the physicist Enrico Fermi in the 1950s. It goes as, “if aliens exist, why aren’t they here?” Even at speeds slower than light, nothing physical prevents a spaceship from crossing the galaxy from end to end in a million years or even less. Since our galaxy is more than 10 billion years old, intelligent aliens would have had plenty of time to explore and colonize every star in the galaxy. But we don’t see aliens around and that’s the paradox.

Paradoxes are often extremely useful scientific tools. They state that two contrasting beliefs cannot be both true and that’s usually powerful evidence that some of our assumptions are not correct. The Fermi paradox is not so much about whether alien civilizations are common or not, but about the idea that interstellar travel is possible. //

But let’s imagine that an alien civilization, or our own in the future, avoids an irreversible collapse and that it moves to nuclear energy. Let’s assume it can avoid the risk of nuclear annihilation. Can nuclear energy provide enough energy for interstellar travel? There are many technological problems with nuclear energy, but a fundamental one is the availability of nuclear fuel. Without fuel, not even the most advanced spaceship can go anywhere.