I have always been bothered by the seeming perplexity that people have about the fact that we have yet to encounter intelligent life beyond planet Earth.
It doesn’t seem weird to me at all, even though I suspect life–even intelligent life–is not that uncommon in the universe.
Enrico Fermi–a great physicist from the mid-20th century– expressed the perplexity that many people have in what has come to be known as the “Fermi Paradox.”
At its most simple, the paradox is this: if the development of intelligent life is even moderately likely, why haven’t we seen evidence of intelligent life elsewhere in the universe? There are so many suns, so many planets, and there has been so much time since the universe began that it is a mystery why we have seen no evidence that life exists off the Earth.
If intelligent life should be common, why don’t we see any?
Astronomer Frank Drake tried to create an equation that would predict the probability of intelligent life existing beyond Earth, known as the “Drake Equation.”
The Drake equation is expressed as: N = R\* \* fp \* ne \* fl \* fi \* fc \* L.
- N = the number of civilizations in our galaxy with which communication might be possible.
- R\* = the average rate of star formation in our galaxy.
- fp = the fraction of those stars with planets.
- ne = the average number of planets that can potentially support life per star with planets.
- fl = the fraction of planets that develop life.
- fi = the fraction of life-bearing planets on which intelligent life emerges.
- fc = the fraction of civilizations that develop a technology that releases detectable signals into space.
- L = the average length of time for which such civilizations release detectable signals.
Disposing of the Drake Equation is pretty simple. While it has the benefit of appealing to our belief that math is authoritative, it fails to tell us anything useful because we have no idea what numbers we should put in for any of the variables. We don’t even know how many stars have planets, no less habitable planets. I assume that planets are extremely common–it makes sense given how stars form–but as for “habitable planets” we have no idea. We aren’t even sure what a “habitable planet” is, since we only have an N of one to study.
In other words, the Drake Equation is useless for our purposes, which leaves us with the Fermi Paradox, which seems to me to be worth thinking about.
Why HAVEN’T we seen evidence of intelligent life elsewhere in the universe?
Obviously we don’t know, but I think it is unsurprising that we haven’t for some very basic reasons–both because the chances of intelligent life on any one planet might be high while the chances that intelligent life develops on two relatively close planets at the same time are likely to be very low.
Human beings have only been putting out detectible signs of intelligent life on our planet for a little more than a century, and we grossly overestimate how detectible those signs would be from any appreciable distance.
Consider radio and TV broadcasts. We have been sending out such broadcasts for over a century, so any planet within a 100 light years might have detected them, right?
Probably not. If you are as old as I am, you probably put tin foil on your TV antenna trying in vain to bring in a fuzzy signal so you could watch that Star Trek rerun in black and white. When I lived in Tucson our TV had trouble deciphering a signal from a few tens of miles away–it was already snowy or worse. That’s because the intensity of the signal diminishes by the “inverse square law,” where the intensity of a signal (or light) reduces at a rate of 1/r². What this means is that if you double your distance from a radio or light signal the intensity you can measure is 1/4th of what it was.
So imagine picking up a radio or TV signal from 10 or 100 light years away. It’s not going to happen, especially with how “noisy” space is with signals.
Then there is the issue of whether somebody is there to listen at that time. Let’s say there is a habitable planet 5 light years away, and intelligent life develops there. Given that it took billions of years for intelligent life to develop here, it’s reasonable to assume the same might be true elsewhere.
How likely is that there would be overlap in time? And even if you assume very long lifespans for civilizations–a questionable assumption–“long” is a relative term. If human civilization lasts a million years, that is an eyeblink compared to the lifespan of planets.
Then there is the question of density. Intelligent civilizations may be “common,” but only at a galactic scale. In other words, galactically speaking there may be many civilizations–hundreds or thousands even–but the density would still likely be low. The galaxy is HUGE–it’s why we use the term “astronomical” to mean really big.
To give you an idea of just how big even a solar system is, it can take light up to 7 hours just to reach Pluto from the Sun. And Pluto is in our solar system. If civilizations are scattered around the galaxy separated by hundreds of light years, they are functionally alone, even if they overlap temporally–which to me seems unlikely.
Even if we–as I hope we do–find a way to travel faster than light–and it would have to be MUCH faster than light to make interstellar travel practical–we might even land on a planet that once had intelligent life and never see any evidence it was there unless it died out quite recently in the lifespan of the planet.
For that matter, it could even be that there have been prior civilizations on Earth–non-human, presumably–and all the evidence has been wiped out due to the ravages of time.
It’s even remotely possible that human civilizations have risen and fallen, leaving behind little to no evidence that we could discover. I have no reason to believe that has happened, but I would not be gobsmacked if it had.
Given all the variables, it strikes me as utterly unsurprising that we have yet to discover evidence of other intelligent life in the universe. Not because I think there is none–I share Fermi’s belief that intelligent life is pretty common in the universe, and it would be a crying shame if it wasn’t. The universe is a wondrous creation.
But life at the same time, nearly the same place, and detectible using ordinary means? That would be extraordinary.
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