Life in the universe is a fascinating topic. The simplest question: Are we alone? It breeds so many deeper and more profound scientific questions, like “How many habitable planets are there?” “How likely is life to develop on any given planet?” and “How long can a civilization survive?” We can’t answer them definitively, but we can narrow it down.
The Drake equation, shown above, was first developed by Frank Drake, the head of the Search for Extraterrestrial Intelligence (SETI), in 1961. He took the question of are we alone and made it quantifiable, in a probabilistic way. It lets us test out ideas about life and allows us to use our scientific advancement to update our answer to our big question: Are we alone?
It starts off broadly with the number of new stars forming, and the number of stars that have planets, before restricting these huge numbers to just habitable planets. This is an active area of research in astronomy, and so we are slowly pinning down the number of habitable planets per star. This number can create wild variations in the final answer, giving a universe with no life, or one with plentiful life.
From there we reach the tough questions. How many of those habitable planets that can support life will actually go on to develop life? And how many of those will develop intelligent life? And of those, how many will develop the technology to communicate? The first question is difficult, and one that biologists and biochemists are trying to answer in a laboratory setting. But left to natural events, it’s reasonable to think a planet that can support life inevitably will develop life. It’s possible that it takes a long time – life on Earth developed roughly 1.5 billion years after the Earth formed, and if a planet can’t maintain the conditions for life to develop for a long time, maybe it will never develop.
The second question seems simple, that if life develops, intelligence should invariably follow. It may take more or less time than it did here on Earth, but I think it’s a natural consequence. The third also seems like a natural consequence to me, but it partly depends on natural resources. Earth has plenty of elements and materials that we have found uses for as we develop technology. Most planets should have some amount of raw material necessary to advance technology, but if a planet is lacking in some of them, it may take longer to reach the level of technology required to communicate.
Finally, the last term, and arguably the most thought-provoking term, is L – the length of time a civilization spends sending signals to space. Essentially this asks the question “How long does a civilization last?” This creates a lot of thought about the current state of humanity. With so much war among our own species, how long before we destroy each other and the world we’ve built? Would another species be so aggressive? Could they last longer? The answer to this, sadly, seems to be no. If a civilization did become everlasting, they would have likely had to spread out among the stars to surpass the longevity of their home planet. If this was the case, wouldn’t we have encountered such a civilization? Or multiple civilizations? With radio silence in our neck of the woods, it loosely guides us toward a universe full of short-lived civilizations.
One of the ways the entire Drake equation can be simplified, is by instead asking the question “What are the odds that humanity is the only intelligent civilization to have ever arisen in the Universe?” This is called the ‘pessimism line,’ and when putting our best guess together, it gives an interesting answer. Among all the stars, galaxies, and planets, humanity could be alone only if the odds of a habitable planet developing life are less than 1 in 1022. That is a staggeringly small probability, and so it’s very likely that we aren’t alone.
However, there is a down side. If an advanced civilization only lasts as long as human civilization has, around 10,000 years, it gives a very small window for life to communicate. Combine this with the fact that the universe is 13.7 billion years old, and you end up with a bleak outlook: That there are a huge number of long-dead civilizations in the universe.
I could go on, but I could write a novel about this subject, and I like the idea of debate and hearing the thoughts of others. So what do you think?
Note: I am by no means an expert on the Drake equation, so please feel free to disagree with me and debate my thoughts on what each term could be. I love having these types of discussions, especially when it’s such a fundamental question.