The Dark Forest Hypothesis: The Terrifying Reason Why We Should Stop Broadcasting Earth’s Location
One of the many possible solutions to the Fermi Paradox, the dark forest hypothesis suggests that we haven’t heard from aliens because they’re all cowering in fear. Maybe we should be too.
Where Is Everybody!?
In the summer of 1950, famous Italian physicist Enrico Fermi sat at lunch in the Los Alamos National Laboratory, the top-secret laboratory responsible for designing nuclear weapons during World War 2, and unexpectedly asked his colleagues “Where is Everybody!?” Although it initially drew laughs, everyone at the table understood that Fermi’s question was profound and unsettling. For some, it’s terrifying. It became known as the Fermi Paradox, and it refers to the idea that according to our understanding of the universe, we should already have evidence of alien civilizations.
There’s a lot of ways to crunch the numbers, but the most famous equation for calculating the likelihood of us detecting advanced alien civilizations in our galaxy is the Drake Equation. Formulated by Frank Drake in 1961, this equation uses 7 variables, all of which fluctuate depending on our evolving knowledge of the cosmos.
- R∗ = the rate at which stars are formed in the Milky Way
- fp = how many of these stars have planets
- ne =how many of these planets could support life
- fl = how many of these planets actually developed life
- fi = how much of this life became intelligent civilizations
- fc = how much of these civilizations developed the ability to release detectable signals
- L = how long these advanced civilizations broadcasted their signals
The exact values on these 7 variables are impossible to nail down, but we have a pretty good idea of what some of them should be. For example, we estimate R∗ to be between 1.5–3 stars created in our galaxy per year; that fp is around 1 planet per star on average; that ne is at least 10% of these planets have conditions favorable to life. The other values, though, are highly debated, but even with conservative estimates, the chances of other technologically advanced civilizations existing and us detecting them are pretty good.
If this is true, then where are they?
Possible Solutions to the Fermi Paradox
There’s a lot of ways to interpret and answer Fermi’s question. Some of the solutions are easy to understand, others can get fairly weird, others mind-bending.
One such solution to the paradox is that we don’t have accurate values for the variables in the Drake equation. Maybe our estimates are too high and life is exceedingly rare, in that we might be alone in the galaxy, possibly the universe. For example, we assume abiogenesis, the ability for life to emerge from organic molecules, is possible on other planets than Earth. Maybe it’s not possible. Maybe even simple life is anomaly. Or maybe life does exist, yet for it to evolve to the point that they can communicate across the cosmos is so rare that we are the only ones to do it.
Another possible solution is that aliens are broadcasting their signals, but we just don’t know how to detect them. Maybe using the electromagnetic spectrum to broadcast is outdated to them and they’ve moved on to communicating with neutrinos, gravity waves, or something we aren’t aware of. If this is true, then the sky might be full of alien signals, but we aren’t technologically advanced enough to recognize them as such. Maybe aliens and their signals are extradimensional, possibly in dimensions we could never possibly have access to.
A more disturbing idea is that advanced civilizations don’t last that long. Many of us seem to believe that humanity’s survival and continue technological advancement is inevitable, as if part of a larger plan. But what if it’s not? What if it’s only a matter of time before we are destroyed by a gamma ray burst, black hole, collision with other universes, meteor collisions, etc.? Maybe the universe is for more hostile to life than it seems. Or maybe advanced civilizations are prone to self-destruction, either through war, mismanagement of resources, disease, or whatever else you can imagine.
There’re a lot of possible solutions to Fermi’s paradox, but perhaps the most terrifying is that the galaxy and the universe are crowded and everyone has learned to keep quiet.
Like Hunters in a Dark Forest
The Dark Forest is the 2nd book in The Three-Body Problem trilogy written by acclaimed Chinese writer Liu Cixin. Although he didn’t create the Dark Forest hypothesis, it features prominently in the plot. He described like this:
The universe is a dark forest. Every civilization is an armed hunter stalking through the trees like a ghost, gently pushing aside branches that block the path and trying to tread without sound. Even breathing is done with care. The hunter has to be careful, because everywhere in the forest are stealthy hunters like him. If he finds other life—another hunter, an angel or a demon, a delicate infant or a tottering old man, a fairy or a demigod—there’s only one thing he can do: open fire and eliminate them. In this forest, hell is other people. An eternal threat that any life that exposes its own existence will be swiftly wiped out. This is the picture of cosmic civilization. It’s the explanation for the Fermi Paradox.
Liu Cixin, The Dark Forest
In other words, the only logical step once another civilization is discovered is to eliminate it immediately. The logic starts with 2 axioms:
- Survival is paramount for every civilization
- Every civilization will naturally advance and grow, but the universe has only finite resources.
With these 2 axioms in mind, it’s clear that civilizations are either going to be hostile to each other or learn to cooperate. Here on Earth, the intention to be either friendly or hostile can be easily communicated. If country A wants to enter into a treaty with country B, they merely send an ambassador, make a phone call, etc. Across the vastness of the universe, though, communication is limited to the speed of light. If Civilization A is 1000 light-years away from Civilization B, then it would take 1000 years to send a message and another 1000 to reply. So, Civilization A and Civilization B can only guess at what the other’s intentions are.
Let’s look at this in terms of game theory. If Civilization A detects a signal from Civilization B, they have 2 choices: be hostile or be friendly. If they choose to be hostile, then Civilization B is destroyed and Civilization A lives on. However, if Civilization A chooses to be friendly, then Civilization B has a chance to respond with the same 2 options: be hostile or be friendly. If B chooses to hostile, then A dies and B lives on. If B chooses to be friendly, then both A and B live on. So imagine you’re Civilization A, and you have the option of striking first. Why would you wait to see what Civilization B does? It’s not worth the risk to wait.
Therefore, if you’re a hunter in a dark forest, your only chance of survival is to assume every other hunter has made the same calculations and will eliminate you, meaning you must strike first. If this is the case in the universe, then it’s possible that other advanced civilizations learned that they shouldn’t so haphazardly broadcast their location, which explains why the cosmos is so quiet. They’re all terrified of being detected and eliminated because it makes good sense to do so.
It Might Be Too Late
Humans have been broadcasting radio signals capable of breaking through Earth’s ionosphere, the layer of the atmosphere filled with free electrons that can effectively block electromagnetic radiation, since 1962. It was then that the Soviet Union broadcasted the Morse message, which consisted of 3 Russian words: “mir” meaning both peace and world, “Lenin,” and “USSR.” This was the first message intended for communicating with alien civilizations.
One of the more famous broadcasts was the “Wow! Reply” in 2012. In 1977, Ohio State researchers detected an unusually strong signal coming from the constellation Sagittarius. In the margin of the print out, an astronomer named Jerry R. Ehman circled the signal and wrote “Wow!” To this date, this is considered the strongest candidate for the first alien signal ever detected. As response, we sent about 10,000 Twitter messages curated by National Geographic to Hipparcos 34511, 33277, and 43587, known star systems in the region.
There have been dozens of other messages sent to targeted areas that we believe have a chance of supporting life. All of these messages could feasibly be detected by life on 1 or more of the many star systems near Earth. Just within 12 light-years, there’re over 20 stars, many which are likely to contain planets, some of which might contain an advanced, yet quiet civilization.
To make matters worse, these messages could potentially continue on indefinitely. Although their strength is declining over time, they could theoretically be detected, meaning it might be too late because we’ve already broadcasted our location. It could just be a matter of time before our signals traverse the vast distances of the galaxy and the universe and the aliens respond with our complete destruction.
Because it’s the only logical move in the dark forest.
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It is possible for aliens to detect our radio signals, but we have to broadcast properly.
Set up a broadcaster that radiates 1 gigawatt into one spherical quadrant (1/8 of a sphere).
At a distance of one light year, the flux will be 6.64E-25 watts/square foot.
A receiving antenna of 2G square foot will gather 1.33E-15 watts.
Researchers report receiving signals of -118 dBm (1.58E-15 watts).
So we could detect that signal, using super cold quantum detectors, an antenna of 2 billion square feet, on light year from earth, in the correct quadrant.
Alien technology is at least 100 times more sensitive than ours, so they can detect our signals at a distance of 10 light years when they set up their antenna in the right quadrant.
Of course, we can help them by broadcasting 8 gigawatts into a sphere.
And as has been done, we can send collimated beams into 1/1000 of a sphere, with a flux of 1.33E-12 watts in a 2G square foot antenna at one light year, or 1.33E-14 watts at ten light years.
Aliens could detect that, should they have nothing better to do.
Feel free to test my numbers; they suffer from haste and lack of review.