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The Great Filter

A doomsday discovery

Thus far, astronomical observation has not shown evidence of extraterrestrial civilizations. This leads us to the famous question: Where is everybody?

This apparent lack of life outside Earth seems to be at odds with the data we have found so far. Originally, it was unknown how likely a star is to have planets. Now, it looks like planets are common. Similarly, experiments in chemistry suggest that organic compounds self-assemble under relatively mild conditions. Furthermore, there are seasonal methane shifts in the Martian atmosphere, similarly to Earth, where it is a byproduct of bacteria. Finally, there’s evidence of an ocean under Europa’s crust, and hydrothermal vents in the ocean of Enceladus. This means that at least 3 planets/moons other than Earth in our own solar system are prime candidates for life. If life is found on any of them, it will mean that bacterial life is likely to be extremely common.

Even if life is common, maybe the jump from simple bacteria to complex life never happened before? Why haven’t we found anything? Many people have tried to explain this apparent paradox, with varying success. The event that makes our galaxy seemingly lifeless is called “The Great Filter” - if abiogenesis or complex life is rare, then perhaps we are extremely lucky to exist.

There is also the possibility that we have not yet encountered the great filter. In this situation, technological civilizations might develop fairly frequently in our galaxy, but they all encounter something that keeps them silent: either they kill themselves, or perhaps they all hide. But even then, it is hard to believe that everyone would behave identically. Shouldn’t the great filter be triggered by something all technological civilizations have in common?

A Thought Experiment

In order for a civilization to send out radio waves, they must have developed science. There is no way to send radio waves without first discovering that electricity flowing through wires creates magnetic fields!

So let’s suppose that the very thing which is a prerequisite for technological development also starts the doomsday clock: science.

All around Earth, scientists are probing the limits of our understanding of physics - what if somewhere in extreme conditions there is an undiscovered quirk in the laws of nature? Perhaps something weird happens deep within stars, but we ourselves cannot see it until we accidentally recreate the necessary conditions in a lab?

I call such a quirk the “Doomsday Discovery”. There are two ways I see such a discovery destroying life of Earth:

  • The act of discovery itself could destroy the planet. For example, something is triggered in a fusion experiment which generates orders of magnitude more energy than predicted by theory.
  • Even if we survive discovery, it could turn out so easy to weaponize, that anyone with access to a hardware store and a grudge could sterilize the planet.

What is worse, since we will relatively soon be technologically capable of creating a self-sustaining colony on Mars, if this “Doomsday Discovery” is real, it means that we must either be on the verge of discovering it, or it sterilizes our entire solar system when triggered: perhaps it would make our sun go supernova.

This quirk in nature would need to have several properties:

  • It would require conditions unlikely to happen by chance, since it probably hadn’t happened on Earth at least since life appeared 3.8 billion years ago.
  • Be extremely high energy or destructive - enough to wipe a planet or solar system of civilization.
  • Be simple enough that technological species stumble upon it before they manage to create self-sustaining colonies away from the blast radius.
  • Be invisible or misclassified in astronomical observations, otherwise some species might get tipped off!

Although it wasn’t labeled as such, a discovery that fits some of these criteria was already shown in Science Fiction.

SciFi Candidate: Ender’s Game

In “Ender’s Game” (spoiler alert), the military had a weapon called the Molecular Disruption Device, which worked through a chain reaction, and had the effect of scrambling up molecules it comes in contact with. This device was used to rid an entire planet of life:

There is one issue here… How was this invented? What would have happened if the chain reaction was discovered in a lab on the surface of Earth? What if we are on the verge of accidentally stumbling on something similar in a lab somewhere?

Astronomical Candidates?

The next question that needs to be asked, is whether astronomical observations show high energy events coming from stars in our galaxy. If the doomsday experiment is the great filter, then depending on the mechanism of destruction, we might be able to observe random stars in our galaxy briefly flash a bit brighter than expected, as civilization after civilization makes its last discovery.

What about FRBs?

Fast Radio Bursts are quick, extremely high energy blasts of radio waves, which come from random directions (ie: do not seem to come from our galaxy). Their causes are unknown at this time, but they are thought to come from extreme events. Suppose for a moment that these bursts are the outcome of experiments of technological civilizations in our universe. What can we conclude?

If these are the effects of our doomsday experiment, then technological life is very rare indeed - only 16 were detected from the entire universe in all of 2010. It would suggest that we might be alone in our galaxy.

I would expect astronomical evidence of a doomsday experiment to be much mess pronounced than FRBs: a small, brief increase in the detected energy output of a star would be most likely given technological development of civilizations at the point when this experiment must happen.

Why not?

The above thought experiment proposes a cute possible explanation for the lack of visible large-scale civilizations, assuming that technological life is actually common in the universe. While it was fun to think about, it is also important to see where it falls short.

The “Doomsday Experiment” has a very simple weakness. It requires civilizations to do something that very rarely happens by itself on planets, and it requires that they do it at a specific point in their technological development: before they expand to other planets or stars. This means that given current technological progress, we should have the ability to perform this “Doomsday Experiment” within the next few centuries.

Here’s the thing: Every quirk of physics that we have explored so far happens countless times all around us in space. Our greatest particle accelerators are no match for the power of cosmic rays that daily pummel the earth. There is even evidence there there was a natural fission reactor on earth - and that’s just Earth! Extreme conditions exist all over our solar system, and yet we are supposed to do something that didn’t happen in our entire solar system for at least the last couple million years?

I could imagine us doing some intense physics if we had our entire sun’s energy output, but at that point we would have been able to at least send von-neumann probes to adjacent stars! Remember, the doomsday discovery would need to happen before we have a chance of escape.

It is for this reason that given current observations, the most likely conclusion is that either the great filter is already behind us, or life is rare enough, and space travel hard enough that it will take us more time to make contact - after all, we’ve only been listening to small patches of sky for the last 50 years!

In astronomical timescales, we’ve barely started the search.