The Great Filter

~4000 words

I generally write non-fiction, but as I started thinking about this concept I thought it was better explored as a piece of fiction. If you enjoy it, you might still enjoy my non-fiction. You can download the first chapter of my book, “Good Enough: Why Good is Better Than Excellent” by submitting your email on the right.



When you travel in time someone dies, then you die, and then everyone dies. But for some reason the someone’s death hurts more than the everyone’s death. And both hurt a lot more than your own death, which doesn’t even seem real. I mean, you are still thinking. You have all your memories. You definitely don’t feel dead. But it doesn’t mean you aren’t as dead as everyone else.

If it causes so much death, why do it?

It’s not a good excuse, but it’s an old one: If you don’t do it someone else will. So it might as well be you. Or me. Better me than you.

I didn’t set out to discover time travel. I was working on brain emulations. It turns out general artificial intelligence is a much harder problem than most people think. Sure we can make AIs that can win at games or reverse engineer the stock market or even identify faces, but generalizing that to duplicate the abilities of a human brain turns out to be a very very hard problem. Not that duplicating a human brain isn’t hard too. Most things worth doing are hard. But duplicating, or “emulating” a human brain was at least possible in my lifetime. Or at least possible enough that I was willing to dedicated my life to doing it.

And I did it.

I found a way to scan a “carbon” human brain and recreate it exactly atom by atom in silicon. Every electron and neuron in the exact same place. Well, not exactly the same – you can’t know both the speed and position of a quantum particle at the same time – but it was close enough that the emulated brain thought it was the real thing. Outside observers couldn’t differentiate between the emulated brain and the real thing. It was a game changer.

It was kind of like immortality. Kind of. Your brain patterns could continue living forever, but that didn’t mean you lived forever. It was closer to immortality for your twin brother. You feel a kinship to him and you are very happy for him, but he isn’t you. So there is that.

The other big thing that happens with silicon brains is that they aren’t limited by biology. It is trivial to throw more CPU at the brains and allow them to run faster. There is no reason an emulated brain can’t operate at 10x or even 10,000x the speed of one of our normal brains. And there is no reason you have to stop at one duplicate. Control-C, Control-V and you now have another brain just as good as the first one. It just takes more electricity and coolant systems. Think of what Einstein could have done if he was living a subjective 30-years for every day he had on the planet. Now imagine if there were 10,000 Einsteins all collaborating together on problems. It wasn’t general super-intelligent AI, but it was still world-changing. Or at least it would have been world changing if I hadn’t stumbled across time travel.

In order to duplicate the brains I had to dig into quantum positioning in more detail than is interesting for laymen. You have likely heard about “quantum action at a distance”. It means you can effect things at the quantum level far faster than the speed of light, which is impossible. Except it’s not. It turns out the way that happens isn’t magic, it’s time travel. Really minor, stupid time travel, but the time travel all the same. Using those same principles, it’s possible to send data back in time (sending data forward in time is trivial. We’ve been doing it since we first made painting in a cave).

Humans have hypothesized about time travel since at least the 1800s. One concern has always been the grandfather paradox. What happens if you go back in time and kill your grandfather? How could you be born to do the killing? And if you didn’t do the killing, then what exactly happened?

Fiction tried to solve the paradox by eliminating free will. Basically everything is fate and it has to happen a specific way.

It’s almost ironic that the common solution to time travel was “no free will” given how much everyone seems to believe in free will (free will is BS by the way. Who’s free? Our brains are just electrons firing. There is no homunculus hiding behind the brain directing those electrons).

But free will or not, it turns out we were over complicating things. The reality is there is one giant timeline, it just sometimes wraps back on itself. This happens all the time with quantum communication at a distance. Every time a communication is sent back the only real timeline jumps from point A in “timeline one” to point B in “timeline two”. All of the conscious beings in timeline one cease to exist and everything continues forward from timeline two. Generally, this doesn’t really matter at quantum timelines. We only ever exist in one continuous train of existence. We don’t even realize we are experiencing millions of micro-deaths every second as quantum messages are sent back all around the universe. But it starts to matter when humans take control of this technology. Humans like me.

For simplicity, let’s say we are in the original timeline. No one has ever traveled in time anywhere in the universe (we will ignore quantum effects). Then I send a message back that kills my grandfather. The moment I send back the message the original timeline ceases to exist. It’s gone. I’m gone. You are gone. Your dog is gone. Heck, even every alien in the universe is gone. The only thing that exists is timeline two back at the moment I sent them the message. The only thing from timeline one that continues is that message. The sum total of all human and alien knowledge and experience from the moment the message arrives until the moment the message was sent is summed up in whatever data I sent back. It’s mind blowing the quantity of experience that has been wiped out of existence.

Now this new timeline continues from where it left off. Before that message arrived timeline two was identical to timeline one. But now it has an additional input – the message I sent back that somehow causes someone to kill my grandfather. In timeline two my father is never born and I am never born. But it’s more insidious than that. If you were born after the message arrived, you would not be born either. No one would. Oh, there would still be babies. Your parents might even give their first born child your name. But that person wouldn’t be you. Their DNA would be completely different. Well not completely different – more like your brother.

You see that message caused everything to re-set. Whoever came in contact with that data would be changed – maybe in a small subtle way, or maybe in a large impactful way (impactful enough to cause someone to kill poor old granddad). And each person who was affected would change their future behavior – again sometimes subtlety, sometimes dramatically. Now everyone who comes in contact with that person will be affected. And each person that comes in contact with someone who came in contact with that person would be affected. It would propagate outward at something approaching the speed of light. I’m not 100% sure, but 4.367 years after the message arrives it might even cause Mork not to be born on Alpha Centauri due to the way our sun twinkled a little differently (don’t hold me to that prediction).

So you see when you send a message back in time you kill everyone and everything in our entire existence – including yourself. That’s kind of bad.

But I did worse.

Instead of just sending a message, I sent back an emulated brain. All emulated brains are is data, so there is no reason I can’t send them back the same way I could send back a television broadcast or a nice hand written note (I was being silly. I can’t send back a note. Just ones and zeros). The problem is where do I send it to? I don’t have to send it back very far before there are no computers with the capabilities to receive the brain.

But there is one complicated structure that can receive an emulated brain that goes back at least 10,000 years. The biological human brain.

So I sent an emulated brain into the brain of someone in the past. What happened to that person? Well that’s the someone I killed. See how that feels worse than the billions I killed just by sending the message? (probably trillions if you count all the aliens. Maybe quadrillions? Sextillions? What’s bigger than a sextillion?).

And it hurts a lot more than my own death, because it’s my own emulated brain I sent back. I guess I should re-phrase that. I’m here. I’m not dead. And I didn’t send anything. The biological brain I was copied from sent me back here. That biological brain is dead. Am I responsible for its actions? Who knows. I feel responsible since I share all of its memories. It feels like it was me that sent me back here, but I’m smart enough to know the difference. I knew I was killing myself when I sent the message. It felt like a noble sacrifice. And yet here I am alive and well. I can even blame all the deaths on someone else. Best of both worlds?

But why do it at all? Why kill myself and billions of others (and the poor guy who’s body I now inhabit)?

I hinted at it early. Because once time travel was discovered, someone was going to do it. And the second they did it everyone was going to die anyway. At least this way my emulated brain got to survive. And maybe I can do something about making sure time travel is never discovered. Ever. Because if it is, the universe will be wiped out again. And again and again.

I don’t think I can do it.

How do you stop a technology from EVER being developed? Say you were sent back to 1960 and told to make sure the computer was never discovered. You could likely track down Bill Gates and Steve Jobs and have them both killed. But then what? That might slow down computer development for a decade or something, but do you think you have put a stop to it? Do you think that no one will come up with the idea of the PC ever again for the history of the universe? Of course not. You need to do something more drastic.

But what?

Apart from dropping atomic bombs to wipe out all of humanity, how do you stop technological progress? Is the only way to stop humans from developing the computer to wipe out all humans? And would that even work? How long before raccoons develop tool-using intelligent culture, discover the chariot and the printing press and work their way up to computers and the internet. Do you have to wipe out all lifeforms? That seems like a little over kill to stop the Apple 2E.

Time travel is more complicated than the personal computer, but the same principles apply. I have no idea how to stop it from being discovered eventually. And when it is, it will be used, and everyone will die. And that’s not even the worst of it. The threat is far more existential.

Have you heard of the Drake Equation?

N = R* x fp x ne x fl x fi x fc x L

It’s a lot of letters, but basically it says, “The number of alien civilizations we can communicate with in our galaxy at any point in time is equal to the number of stars, times the chance a star develops intelligent life that can communicate, times the length of time that life will be around before going extinct, divided by the age of the galaxy.” We know the number of stars and the age of the galaxy (those two variables cancel out to a nice round “7”). The chance a star develops intelligent life is hard to calculate. We do know now that most stars have planets that could develop life. It’s a question of if that’s enough for them to actually develop life. And if they do, how often does that life develop the ability to create the equivalent of radio? For our purposes we can either say it’s so rare it never happens, or we can presume that it happens all the time.

What’s more interesting is the last variable: After a civilization develops the ability to communicate “interstellarly” how long does it last? Or to change the question a little: How many of those civilizations manage to break free of their home planet or solar system?

If an alien species can’t break out of their home system, then they will eventually go extinct. Something will happen like nuclear war or habitat destruction or a massive virus or something that will take them out. It’s just a matter of time. The first human signal that broke free of the solar system was broadcast in the 1930s (The Berlin Olympics. If aliens are listening closely the first human they will encounter is Adolf Hitler. Aren’t we lucky). It took less than ten years for us to develop nuclear weapons. Within thirty years we had the Cuba Missile Crisis and we almost got sent back to the Stone Age. If there is a 1% chance of blowing ourselves up every decade, civilizations like ours will only last an average of 680 years. In that case even if the galaxy spits out high IQ apes all the time, they won’t be around long enough for us to find them.

But if a civilization can break free of their home planet, then the story changes dramatically. A 1% chance of destruction on each of two planets extends the average length of the civilization to 68,000 years. Add a third planet and it goes to 6.8 MILLION years.

And if a civilization can expand to a second solar system, what is stopping them from adding a new system every century or so? Nothing we can see. Our galaxy is over 13 BILLION years old. If a species broke free of their home system a million years ago and started expanding at a new system every century, that single species of alien would have expanded to over ten thousand star systems. If they started a billion years ago they would be at 10 million star systems.

And yet we don’t see any evidence of even a single alien species out there – let alone intergalactic empires.

Which brings us to the Fermi Paradox.

There are billions of stars most of which could support life. If they could support life, then some actually will, and some of that life will become intelligent. Some of that intelligent life will invest interstellar travel. If they do, within a million years or so, they should be able to explore the entire galaxy.

They haven’t, which led Enrico Fermi to say, “Where is everybody?”

At least one of those assumptions must be wrong. Most stars have planets that could support life [fact]. But for some reason they (never) manage to produce interstellar civilizations. Not rarely. Never.

As my grandparents use to say, WTF?

In 1996 a Robin Hanson wrote about The Great Filter. One of the steps in the evolution from potential-life to spacefaring life must be a once-in-a-galaxy’s-lifetime opportunity. There were nine steps the way he saw it:

  • Habitable Planets
  • RNA
  • Simple Single-Cell Life
  • Complex Single-Cell Life
  • Sexual Reproduction
  • Multi-Cell Life
  • Tool using animals with big brains
  • Human-like
  • Stellar Expansion

At least one of these steps must be almost impossible to overcome for the galaxy to look the way it does. If that step comes before #8 it means humans will likely be alone to explore the galaxy. If it comes after #8 then it means there have likely been lots of aliens like us, but something happens that stops us from ever getting to #9.

The bad news is that after we found evidence of multi-cell life on Mars we could rule out the Great Filter happening before #7 (If it happened twice independently in the same star system it is by definition not rare).

We can hope that jumping from jellyfish to humans is really hard, but I was never optimistic that evolution wouldn’t find a way.

Which suggests The Great Filter is in front of us.

But it was always hard to figure out what it could be.

The stuff that scaremongers throw out there just aren’t dangerous enough. Yes nuclear war or global warming could wipe us out. But it’s not about wiping us out. It’s about being almost 100% certain of wiping us out. Could you imagine a world that avoids nuclear winter? Or a world that coordinates enough to develop green energy before a global warming cataclysm? Even if you can’t do that, could you imagine a slightly different alien species that could negotiate through those waters? It seems unlikely that nuclear war wipes out 99.9999999% of species that get as far as we do.

More exotic arguments fall apart equally fast under scrutiny. To go back to my field, what if civilizations develop General Super IQ AI and it wipes them out (like a super Frankenstein)? Maybe developing GAI is inevitable before civilizations reach new stars, but then wouldn’t we see a bunch of General Super IQ AIs exploring the galaxy? Or what if civilizations become so advanced that they decide to leave this universe completely, leaving it behind like a giant natural park? Sure it’s possible, but would 99.9999999% of the species do this? And would every member of that civilization decide to “move to the city”. It would only take a small cult of alien-Amish to decide to stick around and the theory falls apart.

So does that mean the Great Filter must come before #7?

I had almost convinced myself that our species was going to be okay. And then I discovered time travel and it all made sense.

Time travel is easier than traveling between stars. Much easier. Which means every alien civilization is going to discover it before they colonize other planets. See the problem yet?

Every time a civilization develops time travel someone will use it. When they do, the timeline resets. Your first thought might be that this could allow them to advance technology faster within any given time period. And that might be true. But each time they get to time travel technology, someone will use it and the timeline resets again. The only way to get past time travel technology is to never invent it, or invent it and choose not to use it.

My hypothesis is that any form of life that is capable of inventing time travel is incapable of never using it.

Now see the problem?

Imagine three parallel lines running left to right. The leftmost point on the middle line is where a civilization starts. It’s then a random walk to the right. If the civilization-line ever hits the top line, it invents time travel and jumps back to the starting point. If it ever hits the bottom line it experiences an apocalypse that destroys the civilization.

In a situation like this we don’t need a 99.99999% chance of extinction. Assuming there is even a little bit of variability, sooner or later the timeline will invent time travel or go extinct. And since inventing time travel re-sets everything, sooner or later the timeline will get unlucky and go extinct (and never invent time travel). Even if that chance is only 1% it has to happen given enough repeats. And time travel guarantees the repeats.

The only way out of the loop is if somehow a civilization can both avoid extinction and NOT invent time travel. If a civilization can expand across the galaxy before someone somewhere travels back in time and resets everything, then maybe it could avoid extinction. But even that isn’t a guarantee. All that needs to happen is the first time traveler deciding to go back in the past before the point where the civilization went interstellar. Maybe in the next loop time travel is discovered earlier, or a nuclear bomb goes off and ends everything.

So why don’t we see any aliens out there? Because any alien species that got advanced enough invented time travel and started again. They kept repeating their timeline until they destroyed themselves. The “final” real timeline we are living and breathing only has the extinct aliens.

And humans are the next species to experience the same fate.

So here I am. I tried to jump back as far as I could without going into the Cold War. When the USA and USSR were at loggerheads there was just too high a chance a small variable change could have caused a nuclear winter. Best to stay in the 21st century when the only apparent existential dangers are climate change and super-viruses. Neither is likely to kill us fast, or be affected much by my presence.

I keep talking like I’m the first time traveler, but that’s just because I haven’t seen evidence of any others. Realistically lack of that evidence doesn’t mean anything. Anyone smart enough to invent time travel likely saw the same ramifications I did. The last thing they will want to do is make it obvious time travel is possible. That will just speed up the process of time travel being invented. So it makes sense any time travelers out there are trying to keep it a secret.

So I don’t know what loop number we are in. Assuming the likelihood of extinction is small there will likely be hundreds or thousands of time line repeats before we mess up and end everything. While it’s possible I’m the first one, it’s far more likely there are likely hundreds or thousands of other time travelers out there right now who came before me. Hopefully all of us are thinking about ways to stop time travel from happening.

So why am I telling you all this? If I’m afraid that telling you about the existence of time travel will only make things worse, why am I telling you about the existence of time travel? Well, to start with I do not have any faith in my ability to do anything to stop the repeat from happening. So anything I do can’t really make things worse. If the thousands who came before me couldn’t find a way, and the millions of alien species out there in the same trap never found a way, the chances I will come up with the solution to get us past the Great Filter are next to zero.

So to use a terribly over-used saying, I figured I would try to think outside the box. Maybe I can find a way to get all the time travelers together and we can combine our brain power to come up with an idea. Or maybe just by putting this problem out there into cyber-space someone will come up with a theoretical solution to this fictional problem.

Because this is just a piece of fiction after all.

If you happen to be a fictional time traveler, you should send me an email.

Or maybe you already have? Like they say in Battlestar Galaxtica, “All of this has happened before and all of it will happen again”

Or maybe I’ve already failed and you are a future time traveler with a new idea. You can email me too and maybe this loop will be different with your perspective.

Or if you aren’t a time traveler at all, but you have ideas on how to solve this fictional problem, please add them to the comments. If we all work together maybe, just maybe, we can uninvent time travel and save the human species from extinction.

Yeah. I know. Not likely. But an emulated brain can still dream.