This episode is brought to you by Brilliant. Our Universe is enormous and ancient, so we suspect it of being home to many alien races, and yet it may be but the tip of the iceberg. We may live in a Multiverse so vast as to dwarf our Universe, home to uncountable species. The Fermi Paradox is the big question of why, in a Universe so vast and ancient, we don’t see any other bigger and older civilizations, and it arose from our realization in the early 20th century of just how big and old the Universe really is. At about that same time, we began to contemplate how we might have parallel realities and alternate Universes, leaving even more potential to search for alien life. Our approach to the Search for Extraterrestrial Intelligence, or SETI, never really discusses Multiverse options, for the simple reason that almost everyone assumes we can find our first example of intelligent aliens in our own galaxy, and need not consider the whole wide Universe, let alone other Universes to find example number one. And yet, there are several reasons this assumption might be wrong, and that our first encounter with aliens may involve alternate realities. Even if it doesn’t, the topic of
interacting with and meeting aliens through the Multiverse is interesting in its own right. We’ll begin by quickly reviewing what a Multiverse is, or what it might be. For more details, you may want to check out our episodes Alternate Realities & Parallel Universes, and Infinite Improbability Issues, for more discussion of the science of how these work, as well as the Quantum Cheeseburger. Speaking of Cheeseburgers, our Fermi Paradox episodes tend to be on the longer side so you might want to grab a drink and snack before starting, and if you enjoy our episodes, don’t forget to like, share, and subscribe to the channel. So, what is a Multiverse? There are actually a ton of different ways you can have a Universe beyond our own, but the one most commonly discussed nowadays tends to be the Many Worlds Interpretation of Quantum Mechanics. This is the main alternative to the one presented by the Schrodinger’s Cat thought experiment, which is a popular example of the Copenhagen Interpretation of Quantum Mechanics, and I do want to emphasize that they are potentially alternative explanations of the same idea: either one is true, or the other is true, or neither is true, not both. To clarify, Schrodigner’s Cat is the example where a cat in a box has been poisoned
by a poison delivery device triggered by the decay of a particle, which is an example of a quantum event acting at the macroscopic scale, or the subatomic acting at the human level, or in this case the cat level. The Copenhagen interpretation says that the cat is both alive and dead until we open the box, at which point the cat is either one or the other when we observe it. But until that observation is made, both alive and dead are equally valid states for the cat. The Many Worlds Interpretation argues that the cat is alive in one reality and dead in another, and that opening the box to check just tells us which of those two Universes we’re in. Of course, this should be true for every event, so there’s a reality where the cat is alive, one where its dead, one where it never went into the box, one where it escaped the box and attacked Schrodinger, and one where it is alive in the box and a tree fell down on the other side of the planet, and one where it’s alive and the tree did not fall. The idea that all of these potential realities exist simultaneously leaves you with many worlds for every event, with one world for every possible state or every possible action. And
this isn’t just true of cats: there’d be countless Universes we could assemble from every state and configuration of every available particle. This number of Universes is so enormous that even just writing out that number on a piece of paper would take more sheets of paper than we have ever produced for every book ever written. Even if we were to limit every universe to a single unique address, like a Universe phone number, and store it on a digital medium so advanced you only needed one atom per bit of data, it would collapse under its own mass into a black hole.
In other words, it’s a lot of Universes. And mind you, that doesn’t even include the far more numerous options we have when we start contemplating different Universes. Ones identical to our own but where the Big Bang releases a few more atoms or a few less, or ten times as many, or where the speed of light was 3 billion meters per second, not 300 million, or 3, or 3.0001, or protons weighed just one millionth more than they do here, or a billionth, or a trillionth, and each of these have their own Multiverse that has an insanely huge number of possible combinations each atom can be in. And none of this contemplates an Infinite
Universe. All of these, each scenario we just considered, would still amount to a finite number, and so is still essentially meaningless on an infinite scale. When considering the Fermi Paradox, which is all about how strange it seems that we’re alone in our giant and ancient Universe, taking the Multiverse into account exacerbates that issue to the point of absurdity. In a Multiverse, every possible option which can exist, must exist. So at some point you might even have a Universe where intelligent life is literally emerging from nothing, what we call a Boltzmann Brain, with no need for evolution or even a habitable planet, simply because there is a finite chance of it happening. So what are the implications of all this? Well, if the Many Worlds Interpretation of Quantum Mechanics is right, then any alien that could ever exist inside physical laws must exist in our Universe’s Multiverse. In fact,
because of the potential variation in those laws, it might be that there are some possibilities we can’t even imagine. It would mean they exist in at least one of Earth’s various reflections too, since there should always be some version of Earth in which that organism could also have existed, including ones where it had not evolved but simply formed, like our Boltzmann Brain. I mention that particular point because if it’s possible to travel between Universes, then our chance of encountering aliens needs to consider that they need not travel very far in space to meet us. Indeed, this is a big conundrum a Multiverse raises for the Fermi Paradox. If travel between these alternate realities is possible, it would raise two very big concerns, one of which would be aliens on copies of your own world visiting, with the other being that a given species needs no motivation to colonize other planets.
Let’s address that second point first. If you consider the implications of having access to other universes, it soon becomes apparent that you wouldn’t really need to colonize space at all. While there are billions of galaxies out there, with billions of star systems to settle, that number of potential new homes is still miniscule compared to all the effectively-identical Earths, where the only difference is that humanity never arose. Perhaps that first critter that we think
of as the bridge between man and ape just didn’t occur yet, or died when it did, or its early tribe got eaten by predators a year before it would have divided to form another tribe, and so on. There would not be an infinite number of suchs worlds, but they would certainly outnumber the potentially habitable worlds in our current Universe. Indeed they would do so by a greater factor than the number of atoms in this Universe outnumber its stars. And that’s just the options where humanity could safely wander into those copies so close to our own we could hardly tell them apart, except for their having never been home to humanity.
Which is a pretty big exception, since there should be a near endless number of worlds identical to the here-and-now, including all our buildings and crops, and warehouses full of manufactured goods, except that all the people on it died yesterday, or five minutes ago. Fully colonized and terraformed worlds you could just step through a portal and inhabit certainly seem preferable to trying to terraform Mars, much less spending decades travelling through the depths of space to some other, more distant place. Now personally, I would think it a bit ghoulish and lazy to take over a corpse-reality where everyone had just died, rather than building fresh on some virgin world where mankind has never tread, even if it's just an Earth-clone where mankind never arose, or where the dinosaurs never died out. But I imagine that Corpse-Earths, near-identical to our present but with all the humans gone, would be a popular choice since they’re immediately ready to go. Presumably they would also be littered with novel bits of science, technology, and art that haven’t been produced by our civilization. I would still be worried about why they were uninhabited, though. It is true that there is
always a random chance everyone just spontaneously ceased to exist, but the probability of that is stupidly low compared to some more mundane cause of mass extinction, and thus virtually every world you would find that had our cities but not us is going to have an accompanying reason for that absence, like a super-plague, an alien invasion, or some neutron bombs going off. Unless you have some way to pick or sort them beyond looking at them, you will nearly always have a clear and present cause for an extinction event that might get the colonists we send there. Incidentally, the notion for random things appearing or disappearing in quantum mechanics is somewhat similar to the concepts we’re discussing, in that there is always a finite chance of a given particle or small group of particles undergoing some change of state that transmutes, teleports or changes them. There’s a very remote chance that a whole bunch of hydrogen atoms could fuse in exactly the right way to form a single molecule of chocolate. It’s a tiny chance, but it’s a finite
one, and thus it happening twice also has a finite chance, though significantly smaller. The same is true of it happening a quintillion times in exactly the same place, with all the appropriate textures, to form a perfect bar of chocolate. Although, those random particle interactions would still be spitting out other particles, or radiation. So someone spontaneously turning
into a big chocolate statue of themselves wrapped in gold foil ought to see the area heavily irradiated to the point of looking like a small nuclear bomb went off. However, nuclear detonation or fatal irradiation relies on those particles being absorbed by nearby matter. Since there is a finite chance any given gamma ray or alpha particle of radiation might be absorbed while traveling in any given medium for a given distance, there is a finite chance it will not be absorbed, thus not contributing to causing cancer or a thermonuclear shockwave. There is also a finite chance that nearly every particle of radiation produced in the event will travel vast distances before being absorbed or decaying too. Essentially there’s a finite chance a nuclear bomb could detonate and do no damage to the area at ground zero because none of the particles of energy produced randomly hit anything on their way out.
This is the craziness that one has to consider when dealing with a multiverse. There’s a finite chance you could be sitting on a nuclear bomb when it detonates and not die, and there’s a finite chance that bomb will instead turn into several thousand cheeseburgers. There’s also a chance that all the energy released in that transmutation, which ought to exceed even a normal nuclear detonation, won’t kill you, instead allowing you to enjoy one of those tasty Quantum Cheeseburgers. If this seems insane, it only gets worse.
Since there would be a near infinite number of uninhabited Earth-clones, there should also be a near infinite number of worlds where humanity - or something like it - would also exist. And a near-infinite number of such groups of humans who also want to colonize all those worlds. This is exactly what Isaac Asimov considers in his short Story “Living Space”. Humanity invents a way to peek at other empty versions of Earth and colonizes them, sort of. Most are just
colonized by a single family, as the worlds are so abundant everyone can have their own. In one case, they bump into a world where it wasn’t actually entirely uninhabited, but it turns out to simply be colonists from another reality who also saw it as empty. They then worry that there are a ton of these societies, and that each is probably only checking to see if the planet has a big and obvious civilization, so that likely many of the worlds they’ve colonized might also have other colonists in some small spot elsewhere on the planet. While they’re busy considering the issue of some of their colonists
eventually bumping into other colonists from other Earths, and speculating on the idea of alien life finding its way to their homeworld, a colonist enters to complain about weird red creatures with tentacles peering in through his windows on his home in one of the colonized realities. This raises the worrisome notion that someone might invade your reality, or that aliens in some reality might find Earth and invade all of its realities, or that something inhuman might evolve on a copy of Earth, and invade elsewhere. Truth be told, this isn’t actually as big a problem as one might initially think. First, it’s impossible to invade all possible realities, since there’s always a reality where an invasion did not occur. Second, the act of invading a world would subsequently create additional realities
where something goes wrong in an infinite number of ways, or where the invasion was called off, and so on. And lastly, the entire concept is that there is a Universe for any possible combination of the available particles, so if you can actually add or subtract mass or energy from one universe to another - in other words to travel there - then that alters the number of available Universes. Indeed you not only have a whole array of different Universes with one more or one less atom, or one quadrillion more or less, you have to have an additional reality for each moment and location in which a Universe could gain or lose mass from another one. The multiverse needs only interest us from a Fermi Paradox standpoint if such travel is possible, and since we can only detect or see things by sending a particle of light or some parallel, you can’t look at them or detect them or communicate with them unless you can exchange energy in some way. Even if you found a clever way to get around this by only exchanging information in a way that doesn’t move mass or energy, the simple act of sending the information is changing the state of something on both sides, which amounts to another new reality, or rather a whole new set of them for each possible combination of data you could send, and each place and time you might send or receive it, who sees it, and so on. If you find this all confusing, don’t feel bad, it really is. Essentially if travel is somehow possible, you should have at least one additional Universe for each possible travel scenario for each pair of Universes, or indeed for each possible combination of various Universes connecting to at least one other, multi-multi-verses as it were, and thus should never have to worry about running out of possible Universes to send colonists, in fact you are arguably getting infinite combinations splitting at infinitely small rates of time. I’m also not sure it would matter if two identical copies of me from different realities
happened to step onto the same place and time onto identical versions of Earth, but there should be a unique reality for each person stepping onto each possible planet, plus more for each combination of accompanying people and equipment. Perfectly identical repeat events, down to every atom at the exact right nanosecond, may represent two different universes anyway, but I’m not sure how you could tell or if it would matter. Now one thing that comes up in contemplating colonizing parallel universes in fiction is that they randomly jump to worlds and explore them, but if they like them they can dial the planet back up again. This is rather problematic though because assuming there was some unique identifier
for each reality, the equivalent of a phone number, that code would be so long that even stored digitally it would be impossible to work with. It is possible the code might be relative rather than absolute, how far and in what direction of your own reality it is, though I’m not sure you could do that, since there might be multiple pasts that result in a given reality, not just futures springing from it, and there’s still a lot of realities. Exactly how many realities there would be in a Multiverse is hard to pin down, but the approximate number typically kicked around for our Observable Universe is 10^10^77. To clarify that, that is a 10, followed by 10^77 zeros, or ten followed by a hundred thousand, billion, billion, billion, billion, billion, billion, billion, billion zeros. Which means any given reality phone number you are dialing has that many digits. Your typical book has
around a million digits in it, your typical modern harddrive, about a million times that, so if we used every harddrive on the planet, we might only need a billion, billion, billion, billion, billion, billion times that many to store a single Universe-code. In fact even trying to dial those numbers in as some stream of data in some period of time shorter than geological times ought to require passing data through a conduit with such speed and density that it ought to form a black hole. Which to be fair is not necessarily an issue, given that most notions for traveling to other Universes tends to involve modified black holes or wormholes to do it. It would be interesting if the method of making a gateway to another reality involved assembling a micro-blackhole gateway to it composed specifically of digits of its address sent in packets of energy. If any writers listening to this feel like incorporating that as a novel form of wormhole travel, feel free to steal the idea.
So it ought to be impossible to even keep a phone book of Universe addresses or dial them, but maybe we can come up with a way, and it's not that big a stretch compared to the stretch we already have to make to assume there’s an actual way to travel to these realities. It makes interstellar or intergalactic travel seem both vastly easier and vastly less desirable all at the same time. So what does this all say about the Fermi Paradox? Well that’s tricky since our conclusion would depend so much on the specifics. For example, if you can pretty much open up a portal to clones of our Earth, you can presumably also open portals to parallel realities where Earth is a few minutes or hours either ahead or behind in its current orbit, and listen for SETI-style radio signals without the noise of a planet in the way.
Or ones where Earth was Mars-Sized, or orbited a red sun, or both. The point being, you could rapidly flick through billions of possible Universes listening for loud radio signals in our area of space, while simultaneously looking at various weird combinations of stars and planets, until you get a pretty good idea of where life tends to pop up. If you have this capability, you ought to be able to get some useful answers about the Fermi Paradox rather quickly. This is often the case with the Fermi Paradox: if you actually possess a given technology which would influence it, you also get a pretty good idea of how relevant it is to the possible answer. As an example, if we invented a cluster of technologies that make it very easy to get into space, and build big spaceships with internal environments able to survive centuries of travel in interstellar space, then we’d know that other folks could have done it too, so Fermi Paradox Solutions which rely on interstellar colonization not being possible, or on species killing themselves off before they manage it, no longer look as plausible. Incidentally, those are examples of what we call Late Filters of the Fermi Paradox, and indeed those two in particular are usually considered the big Late Filters, a capacity and desire for interstellar travel, and successfully surviving long enough to do it.
On the other hand, travelling through a multiverse also undermines one of the critical assumptions behind the Dyson Dilemma, which looks at how we can assume there are no advanced civilizations in our galaxy if certain conditions hold true, three of which are that space colonization is possible, that growth is desirable, and that space colonization is the most attractive path for that growth. If they have an option available like colonizing the Multiverse by just stepping through a doorway, then that’s what they do. Even those who want to practice terraforming, or find non-Earthly conditions, are going to pick a version of Earth that suits their needs. There should be Multiverses where Earth has less gravity, or is bigger, or has a double planet instead of a Moon, that reality where Venus got bumped into Earth’s orbital plane by a collision and the two fell into a double planet lock. That version of Earth with Saturn-like Rings,
or that one where it recently had its surface ripped off to form a Moon, leaving exposed magma for you to easily mine for metals for return to your own world. So there’s just no reason to go out and colonize space. Not even to escape from entropy, since there should always be some other reality with less entropy or even the ability to run a heat engine through a gateway to lower entropy here and raise it there. On the other hand, you’d have virtually endless resources to build spaceships with, so you might still have folks doing it for the sake of exploration.
Now to address another big question: if such travel were possible, would aliens ever visit Earth? That is harder to say, but probably not, because they’d feel an overwhelming urge to explore space, the same as we would in their shoes. They ought to be focused on exploring copies of their own world, rather than visiting ours. We might also want to consider if we’re just talking about alternate histories or Universes with different physical laws, because if there are realities we can reach where the speed of light is faster, then those would be the ones you would expect folks to focus on exploring, or perhaps even using to travel around their own Universe. A popular approach to faster than light travel in
science fiction is to use some dimension or universe congruent to your own, where either travel is faster and easier or space is smaller, making for a shorter distance to travel. You pop in, travel, then pop back out to our Universe. Think of Hyperspace and its other analogies in various sci-fi settings. Such being the case, we might be in a type of Universe folks don’t bother traveling to or exploring much because it's harder to travel in and explore.
Or fatal, you might be able to extract energy from some place with different physical laws but by and large even a tiny change in physical constants should make you explode or implode. We also have to remember that in the context of a Multiverse, where every possible reality can exist, there must always be places where a given event does not occur, so there would always be ones in which no other aliens ever exist, or choose to visit if they do. Indeed, that’s another Isaac Asimov story, where people who can choose possible timelines pick one for humanity where humans are the only intelligent species to arise in the galaxy. You can never explore or colonize the entire Multiverse since it is by definition every possible scenario and that means there’s always a bit of it you haven’t explored, colonized, or conquered, and while you shouldn’t think of events spawning new universes, in this sense of them not having previously existed, conceptually if there’s a reality where the aliens decided to invade, there’s one where they did not too, there’s one where they visit on Tuesday and one where they visited last year and ten thousand years ago and never but there should always be an equal or greater number where they did not. How about that scenario where the aliens are from Earth, but just a different copy, one different enough we would call them alien not human? Same premise. If I’m jumping to another world, there’s a reality where I arrived at that given
time and place and its twin where I did not, and one for each scenario where I arrive at a given time and a given place, where I stepped out in Dallas, Texas on January first and another where I exited in London on March 2nd or Paris in 1903, and one for each of those option where you did, or where an alien did. But there would be vastly more where it did not happen. Just because there are a near infinite number of worlds where you or someone nearly identical to you is alive, doesn’t mean there are not vastly more where you’re not there. There should be worlds where intelligent races exist and travel to copies of their world different enough and inhabited so that it’s basically alien contact, but these ought to be a tiny minority of them. While it's hard to run the numbers, it ought to be very improbable
that you’d ever dial up an inhabited world. If you randomly dial places, then presumably very nearly all of them don’t even have anything resembling Earth there, but mostly because it's a dead lump or empty space. If we assumed some sort of congruity, like being more likely to dial up versions of Earth similar to our own, then for it to be inhabited by something human-smart but distinctly in-human ought to be unlikely, as that would imply some evolutionary divergence a long time back, not a minor change. Though it would depend on how that congruity happened, and while it strikes me as a fun thing to contemplate for a science fiction story, it would likely take us entirely into that realm, and away from even the remotely-possible science-fact. Multiverses and travel to them is at least in the realm of science, even if it’s near the fringe. Though I would emphasize that we don’t know such places exist nor have we any idea how we could travel to them if it's even possible. Again, the Many Worlds Interpretation is one of many,
Schrodinger’s Cat and the Copenhagen Interpretation being the other popular one, and they aren’t both true, it’s just a question of if either is, or if they’re both wrong. There’s zero evidence to suggest that Many Worlds is right, and the same is true of our other Multiverse concepts, and so far we’re not even sure how we might design an experiment or tool that could check. This a fascinating option though, and one that would have very unpredictable consequences for the Fermi Paradox. We only explored a handful today and, as mentioned, we explored some other related concepts in our episodes Alternate Realities & Parallel Universe, Infinite Improbability Issues, and Aloof Aliens, which considers options like alternate physics in more depth. I’d say that the key take-aways are that more or bigger Universes don’t necessarily exacerbate the Fermi Paradox, as it requires that they be able to reach us. And bigger means more numerous, but not
necessarily more dense. In a multiverse scenario, aliens would absolutely exist, and absolutely have visited Earth, but it doesn’t necessarily mean they came and visited our Earth, or that they exist in our area of the Universe, or Multiverse. It may even be that our universe is the case where nobody else is there, and nobody decides to visit, in which case we would never even know.
So we were talking about Multiverses and the Many Worlds Interpretation of Quantum Mechanics today and if Many Worlds is right, then on one of them there’s a version of you and I who both picked up and understood Quantum Mechanics with ease, but for most you probably found the topic as counter-intuitive as I did when first learning it and for that matter often still find it. When things get small, things get weird, and if you’re looking for a creative and interactive way to learn about the topic, there’s an excellent course on Quantum Objects over at Brilliant. Memorizing formulas and listening to lectures isn’t the best way to learn any topic, let alone Quantum, and our friends over at Brilliant understand that. Brilliant is a website and app built off the principle that you learn best while doing and solving in real-time. Jump right into solving problems and be coached bit-by-bit until, before you even realize it, you've learned a new subject in STEM. We have a ton of research telling us what
the best methods for learning are but it probably won't’ surprise you that the most critical part of learning is that you have to do it. You learn best while doing and solving in real-time, and Brilliant’s website and app are built around that principle. You won't need to memorize long messy formulas and endless facts — just pick a course you’re interested in, like Quantum or Computers or Quantum Computers, and get started. If you get stuck or make a mistake you can read the explanations to find out more and learn at your own pace. Brilliant has something for everybody — whether
you want to start at the basics of math, science, and computer science, or dive into cutting-edge topics like Cryptocurrency or Quantum Computing, and they do it all in a fun and interactive way. If you'd like to join me and a community of 8 million learners and educators today, click the link in the description down below or visit brilliant.org/IsaacArthur. So that will finish out April but May will be jammed packed, as we look at Biotechnology next week and how it will impact our civilization. Then we will move on to Alien Languages and how to decode them, and later in the month we’ll discuss Laser Pistols, Lightsabers, Arcologies, and Solar Flares and their impact on the Fermi Paradox. If you want alerts when those and other episodes come out, make sure to subscribe to the channel, and if you’d like to help support future episodes, you can donate to us on Patreon, or our website, IsaacArthur.net, which are linked in the episode description below,
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2021-05-04