Photo by Cristofer Maximilian on Unsplash
The Fermi Paradox highlights the contradiction between the high likelihood of intelligent extraterrestrial life and the absence of any evidence of intelligent extraterrestrial life.
The paradox is named after the physicist Enrico Fermi, who posed the question in 1950. It should be noted that when Fermi wondered why we hadn’t seen any evidence of extraterrestrial life, the only planets we had discovered were in our solar system.
The universe should be teaming with life.
It was thought that our universe is approximately 13.8 billion years old. However, images that have come back from the James Webb telescope may call that number into question, hinting that the universe may be even older than originally thought.
The exact age of the universe isn’t the point here. What matters more in this discussion is the age of Earth.
Earth is estimated to have formed about 4.5 billion years ago. Our sun formed about 4.6 billion years ago. So, if the universe is about 13.8 billion years old, earth wasn’t here for most of that time. Other galaxies, stars, and planets were around long before the Earth. It is estimated that the first stars formed around 100 to 200 million years after the universe began, so about 13.6 to 13.7 billion years ago. Those first stars that formed then died and seeded the elements of the universe. You and I are indeed made of stardust.
Scientists believe that about 4.3 billion years ago, Earth may have developed conditions suitable to support life. The ball of molten rock had to cool for 200 million years or so before life was even possible. The oldest fossils on Earth are about 3.7 billion years old and estimates are that life started on Earth between 3.7 and 4.0 billion years ago. So, our best guess is that life formed relatively quickly on Earth when conditions were right.
The first possibility of life anywhere in the universe wouldn’t have been right after the Big Bang but after a generation or two of stars dying and forming the elements needed for life. The absolute earliest this could have been was about 13 billion years ago. If you want to take another billion years just to be conservative and say it wouldn’t have been possible until 12 billion years ago, fine, let’s work with that number.
It took about 4 billion years from the start of life on Earth. Only then did our civilization travel out into space and send messages to other potential civilizations.
Remember, life started on Earth pretty quickly after it became possible. If we assume that was the case on any other planet anywhere in the universe, life that could send messages out into space and begin traveling in space should have been possible about 8 billion years ago.
So where is everyone?
The numbers.
· Earth is just one planet orbiting one star in our solar system.
· There are about 400 billion stars in the Milky Way Galaxy.
· The Milky Way could have 60 billion planets with habitable zones.
· There are estimated to be about 2 trillion galaxies in the observable universe.
· There may be 50 sextillion potential habitable planets in the universe.
From our little science experiment on Earth, we know that life can start soon after conditions allow for life. And there are about 60 billion planets just in our Milky Way that are in habitable zones. Even if only 1/3 of these planets can harbor life, that still leaves hundreds of millions of planets that may have the conditions to support life in the Milky Way.
The famous “Drake Equation” that estimates the number of extraterrestrial civilizations in our galaxy estimated that there should be a minimum of 1,000 and a maximum of 100,000,000 civilizations in the Milky Way.
So where is everyone?
Maybe space is just too vast.
One possible answer is that space is just so vast that there is no real way to get anywhere. The closest star to us, Proxima Centauri is 4.2 light years away. This means that if we could travel at the speed of light, it would take about 8.5 years for a round trip. But we can’t travel at the speed of light. If we could hop aboard the fastest spacecraft technology humans have ever developed, it would take us at least 19,000 years to get there. Round trip about 40,000 years.
So, hoping on a spacecraft to visit our celestial neighbors isn’t going to happen anytime soon.
Still, assuming an advanced civilization could have emerged 8 billion years ago somewhere in the universe, you would have to think spacecraft design could have been improved a bit in 8 billion years.
The laws of physics would still apply, so it would take 4.2 years minimum to travel from Alpha Centauri to our neighborhood.
If you then assume that intelligent life is possible, but still rare in the universe, it may be no surprise that no one has visited because of the vastness of space.
But we don’t have to be visited by little green men or women to know that intelligent life exists. Intelligent life could have been sending radio signals and other markers of technology out into space for billions of years. But space is eerily quiet. The SETI Institute has had its instruments pointed to the heavens for forty years now. They haven’t heard anything.
So where is everyone?
The great filter.
The great filter is the idea that the development of life from its earliest stage to the levels of development that would allow for a spacefaring intelligence has to pass through some filters that make the development of intelligent life very rare.
The idea of the great filter comes from Robin Hanson’s essay “The Great Filter – Are We Almost Past It?”
Hanson proposes nine steps that a civilization must get through before it can colonize the observable universe. Hanson may have missed something, but the list is a pretty solid one. Here it is:
1. The right star system, including habitable planets
2. Reproductive molecules
3. Simple single-cell life
4. Complex single-cell life
5. Sexual reproduction
6. Multi-cell life
7. Tool using animals with intelligence
8. Civilization advancing to the potential for colonization explosion (you are here)
9. Colonization explosion
The great filter posits that one of these steps, or multiple steps, is improbable, which is why we don’t see anyone else around. For example, the element Phosphorus is relatively rare in the universe, the rarest of the elements required for life on Earth. The dearth of phosphorus in the universe may eliminate most habitable planets – and stop most potential civilizations at square one. But with 60 billion planets in the habitable zone in the Milky Way, surely many of them have enough phosphorus.
The mindboggling high number of habitable planets in the Milky Way, much less the universe, makes it quite likely that there are enough planets out there that meet the first seven criteria on Hanson’s list.
Perhaps civilization itself is the greatest filter.
That leaves us with where we are today. We live in a very advanced civilization that can put a name to the Fermi paradox and can understand the great filters that we have passed on the way to the civilization we have.
But perhaps the civilization we have is the greatest filter. Perhaps civilizations elsewhere in the universe just haven't gotten past this filter. Perhaps creating civilizations inevitably leads to self-destruction through things like climate change, pollution, and resource depletion that destroy the ability of a civilization to ever get to a colonization explosion.
Perhaps intelligent life ultimately is a little too intelligent for its own good. Perhaps it is inevitable that civilizations discover the means of their destruction on their climb up the technology ladder and ultimately succumb to something like climate change, nuclear war, or overconsumption of their resources.
Look at where we are here on Earth:
- We have pushed past 6 of the 9 planetary boundaries that sustain life on Earth.
- We aren’t acting nearly fast enough to address these problems.
- Our leadership focuses more on growth than on the degrowth needed.
- Our leadership focuses on consolidating power and wealth, not leadership.
- Some people try to change things but may not be able to do so in time.
- Civilization moves toward disaster that compromises our ability to survive.
Maybe this article I’m writing has already been written, many times, on many worlds. Maybe none of them got past the great filter of civilization.
Maybe that's not what's happening.
But if it isn't, where is everybody?
Thanks Nigel. I too would get a chuckle out of politicians trying to tackle the Fermi paradox. Have Neil deGrasse Tyson or Brian Cox interview their politician of choice about it.
Thanks for the comment MonkeyBalandingBuddha,
One potential explanation that I didn't mention is the "Dark Forest Hypothesis" which goes something like this: "No one wants to advertise they are around once they are smart enough to do so, because they don't want to draw the attention of anyone out there looking for resources."
We aren't that smart ... yet.