The Doomsday Argument

Series on the Anthropic Principle:
The Anthropic Principle
The Doomsday Argument

65 million years ago, dinosaurs roamed the earth. Then, all of a sudden, they were gone. Something happened, we think it was a meteor strike, that made the earth uninhabitable for them. 251 million years ago, a major volcanic eruption and the ensuing global climate change killed most of the life on the planet. In total, there were 5 major extinctions in Earth’s history.

Human stories are full of tales of the end of the world. In Norse mythology, there is Ragnarok. In the Bible, Armageddon. In modern times, we have the Terminator, Galactus, disaster movies. We have fears of climate change, asteroid strikes, nuclear war, and uncontrollable artificial intelligence. It’s clear we have a question deep within our psychology: is humanity about to end?

The astrophysicist Brandon Carter thought so 35 years ago. The argument went like this: assume human population continues to grow exponentially until some cataclysmic event reduces our numbers to near or total extinction. If the population doubles every 50 years, then by the Anthropic Principle, you had a 50% chance of living in the final 50 years of human civilization, and a 50% chance of dying sometime in the entirety of human history before then.

If this were the entire human population over all time, probability says we would expect to find ourselves in the spike on the right side.

This seems crazy, but it isn’t immediately obvious why. When I argued against it way back in the day, I was completely wrong. The first thing I said was that because you and I are you and I, we are not randomly selected from human history. This is nonsense. If we choose randomly from all humans who ever have or ever will live, you and I are among the possible choices. It’s a perfectly valid framework for asking questions, and that’s what the Anthropic Principle does.

The other bad argument I had against it was this: “Pick a point in history between the dawn of agriculture and the end of time, and the Doomsday Argument will give the same result: humanity is about to end.” This is true, but it is not a counter to the Doomsday Argument. The fallacy was that I switched from a random sampling of humans to a random sampling of time. And because population increases over time, a random sampling over time gives the earlier times undue weight.

So then what is the counter-argument? There are a few. The first one that jumps out to me is the fact that it is really hard to think of a scenario that will make humanity go totally extinct. Think of your favorite existential disaster: catastrophic global warming, nuclear annihilation, super-virus, supervolcano, autonomous weapons that decide they want to destroy all humans. If any of these were to wipe out the vast majority of the human species, it would be a terrible, tragic event unparalleled by anything in human history. However, we only need a small number to survive, and they will be able to repopulate the planet and restore civilization.

A big enough asteroid strike could make the Earth uninhabitable, but we have the technology to see asteroids that big years before they would hit us, sometimes decades, plenty of time to nudge them off-course. There are no supernova or gamma ray burst progenitors close enough to harm us with their explosions, nor alien civilizations close enough to invade. And the sun won’t get hot enough to turn Earth into another Venus for another few hundred million years.

What could cause humanity to go extinct? There is only one realistic example that I can think of: superintelligent AI that wants to exterminate humanity. How likely is this? Well, that deserves a discussion of its own. We can rest assured that there are many extremely intelligent people thinking about this topic, and working hard to foresee the possible risks and dangers of developing artificial intelligence. Of course, there is always a possibility that we will miss something, but the more we think about it and work on it, the more likely we are to spot the dangerous paths and go around them.

The other thing that could cause humanity to go extinct lies in the unknown unknowns. It may be that some technology will be invented that is extremely easy to make, and can wipe out humanity. This is sometimes called a “black ball technology.” If such a potential technology exists, then anyone with the right equipment, materials, and recipe would be able to destroy humanity, and given that there are billions of people on the Earth, we would be in serious trouble.

However, the very thing that makes us vulnerable to black ball technology also guards us against it: technological progress and expansion. Once we are able to leave our home planet and start new civilizations on other planets and moons and giant artificial space habitats, then we will be able to survive even something that destroys all life on Earth.

A second problem with the Doomsday Argument is that it assumes humanity will continue to grow exponentially, and then be cut down to a level so low it cannot recover. We already know this model is incorrect, because the rate of human population growth is slowing. If we apply the anthropic principle to another function, say, a linear increase, we find that we have a slightly more than 50% chance of living within the final third of human history. That final third could have a range of anywhere between 100,000 years and 150,000 years. And 50% means there is an equal probability of living outside of that time. So with linear growth, the Doomsday Argument doesn’t tell us much of anything at all!

Since the area under the curve is about equal in each section, we would be about equally likely to find ourselves in either of them.

The final problem with the Doomsday Argument is that it assumes the growth of civilization will stop with some catastrophic event. There are plenty of other models of human population that work perfectly fine with the anthropic principle. For instance, if it looks more like a bell curve, we would be more likely to find ourselves near the top. If it levels off, we would be equally likely to find ourselves anywhere along the level period. If it looks bumpy and wavy, we are more likely to find ourselves near one of the peaks. It’s very difficult to say what the human population curve will look like in the future, because every model carries with it plenty of assumptions.

There is one sense in which the Doomsday Argument seems to get things right. When we look out into the universe, we see a vision of a possible future where life, humanity’s descendants, and perhaps alien species, thrive and live around every star and in the spaces between. The number of people in such a multitude of societies astronomically outnumbers the number of humans who have ever lived. Therefore, regardless of what the population curve looks like, the odds of living on such a civilization’s planet of origin before it spreads out into the galaxy is astronomically small. It’s like winning the lottery, and the reward being another lottery ticket, which wins again, and is rewarded with a third lottery ticket, which wins yet again.

Yet here we are. And we have two options. One, we can look at the staggeringly improbable odds that we would find ourselves at this time in such a universe, and hang our heads in despair, declaring that these odds mean such a civilization is doomed never to happen. The other option is to accept that the future has not happened yet; it depends on what we do now. So since we have already won the cosmic lottery, let’s do our part to build the machine that generates our winning tickets. The world hasn’t ended yet, so as Samuel L. Jackson says, let us act as though it intends to spin on.

The Anthropic Principle – Toolbelt of Knowledge

Toolbelt of Knowledge: Concepts
Algorithms
Equivalence
Emergence
Math
The Anthropic Principle
Substrate-Independence
Significance

Today’s topic is something I’ve long struggled to wrap my head around. In fact, I’ve gotten it wrong in previous blog posts, and only recently have I come to really understand it. This topic is called the Anthropic Principle, and it’s a method for inferring knowledge about our surroundings by observing that we are there.

Suppose you wake up in a locked room. There is a note on the ground, telling you that you are in an experiment. There are a thousand rooms just like this one. Nine hundred ninety-nine of them have their doors painted red, and one has its door painted blue. You look up, and notice your door is blue.

Before the experiment began, the researchers flipped a coin. If it landed heads, a thousand people would be drugged and each put into one of the rooms. Nine hundred ninety nine would find themselves in rooms with red doors, and one in a room with a blue door. If the landed tails, only one person would be drugged and wake up in the room with the blue door.

The note says you must guess whether the coin landed heads or tails. If you get the answer right, you get a hundred dollars. Which do you bet, heads or tails?

On the surface, it seems like the odds are equal, 1:1. After all, a coin can either land heads or tails, and each possibility has one person behind a blue door. However, we’re ignoring part of the story, so let’s look at the probabilities of each possibility.

If the coin landed heads, you would only have a probability of 1/1000 of landing in the room with the blue door, and a 999/1000 chance of landing with a red door. If the coin landed tails, you would be in the room with a blue door, and have 0 chance of a red door.

Let’s put these together. The chances of you getting a red door, written as heads:tails, is .999:0. The chance of you landing at a blue door is .001:1. This means, if you wake up in a room with a blue door, it is a thousand times more likely the coin landed tails than it landed heads!

Wait a minute, you say. If the coin landed heads, someone would have to be with the blue door. How do you know that’s not you? The answer is, we don’t have absolute certainty. However, the fact remains we have a thousand to one odds against it, so the reasonable bet by far is to choose tails.

Now that we’ve gone through that example, let’s take a step back and remember the big picture of what we did. We were given a little bit of information, and based on the fact that we were there, deduced more information. That is the Anthropic Principle.

There are many applications of the Anthropic Principle, and we will talk about some of them in future posts. For now, let’s apply it to the situations most people turn to first: life on Earth and in the universe.

The history of science has shown us that we are not nearly as significant in the grand scheme of the universe as we might like to think. The sun and planets do not go around the Earth, the Earth goes around the sun. Neither the sun nor the Earth is a special feature of the cosmos; there are trillions of stars in each galaxy, and trillions of galaxies in the universe. A significant fraction of the stars are sun-like, and a significant fraction of stars have Earth-like planets. There is nothing special about the sun or the Earth.

This idea, that we aren’t special in the universe, is called the Mediocrity Principle (also known as the Copernican Principle). Because the Mediocrity Principle applies to so many things we know about, it is easy to assume it applies to things we don’t know about too. Perhaps, for instance, life like us exists all over the universe.

But in the realm of the unknown, the Anthropic Principle steps in and says, “not so fast.” We don’t live on a random planet, we live on a planet where the conditions were right for life to emerge, and continued to be right for life to evolve, until intelligent life appeared. Regardless of whether life is common or rare in the universe, this observation would be the same; we are in a place where the conditions are right and have been right for intelligent life. Thus, even if it turns out Earth is the only planet in the entire universe where intelligent life exists, we should not be surprised.

Just like there are people who want us to occupy a special place in the universe, there are people who want everything about us to be commonplace. Both of these beliefs are fallacious. We know our planet and our star are not special, but we don’t have nearly enough evidence to determine how common life is. Given only the information we have, there is roughly the same probability that there are a billion trillion civilizations in the universe as there is that we are the only one.

On a larger scale, the Anthropic Principle can be applied to the universe as a whole. The laws of physics, as we currently understand them, have a bunch of parameters that don’t seem to follow any pattern. However, it seems as though if any of them were slightly different, life could not exist at all.

Let’s apply the Anthropic Principle to this question. Assume we don’t know whether life exists or not. If the physical constants must be what they are, and every other combination is impossible, we would bet against life existing without hesitation. After all, the number of permutations that allow life are vastly dwarfed by the number of permutations where life is impossible. So if there is only one combination, it would be vastly more likely to be one where life is impossible.

However, if the physical constants could have been different, we have another story. It would mean they could be tuned to allow for life to exist, making a universe that allows life vastly more likely.

The fact that we are here, that we observe ourselves to exist, is evidence via the Anthropic Principle that the physical parameters of the universe could have been different. And we know this without even knowing how they were set!

So then, what are the possible explanations for why the parameters of the universe allow life to exist? It could be that there are many universes, each with their own physical constants, most of which don’t have life. It could be that the universe was created for life, either intentionally or unconsciously. See the Multiverses post for more discussion on these. And finally, it may be that if something is unobservable, it is the same as not existing. If this is true, then even if there is a multiverse, all universes have life, because if a universe cannot be observed, then it doesn’t exist. We’ll talk more about that in the next installment of the Consciousness series.

If the Anthropic Principle still confuses you, that’s okay. I’ve been thinking about science and philosophy for years, and I’ve only come to understand it a few months ago. Still, it’s worth spending the time to understand, because it opens up new paths by which to explore deep and interesting questions.

A Multitude of Multiverses

Long ago, we believed the Earth, the World, and the Universe were just about the same thing. The heavens were above, and the watery abyss below, and the Earth stood in the middle on its immovable foundations. In the more scholarly parts of the world, the Earth was known to be a sphere, but still thought to be the center of the Universe, with the sun, moon, and stars revolving around it. Since then, a series of world-changing scientific revolutions showed that the Earth revolves around the sun, the sun and all the visible stars are just a tiny section of the Milky Way galaxy, which is one of 50 in the Local Group, which is one of 100 galaxy clusters in the Virgo Supercluster. Yet the observable universe is so vast that 10 million superclusters fit inside it.

Click to enlarge.

The observable universe is as far as we have been able to see. However, there is no reason to believe reality ends there. Time and again, the Universe has been discovered to be bigger than we thought, so why should it be any different now? Perhaps if we could look far enough in space, back in time, through another dimension, or outside of the space-time continuum, we would find the whole of physical reality to be as much bigger than we think it to be now as our current picture is to the view that Earth is most of reality—many universes, or a multiverse.

How would a multiverse come to be, and how could we know about it? You might think that if something is outside of what is observable to us, then by definition we cannot observe it. However, most multiverse hypotheses are not theories themselves, but the logical conclusions of other theories, which make other, more testable predictions. It actually turns out to be very difficult to come up with a theory that encompasses the entire observable universe throughout space and time without getting a multiverse or two on the side.

Today, we will look at several possible reasons why multiverses might exist, including physical and philosophical. We will also examine the arguments for why this universe might be the only one.

Arguments for a multiverse:

Quantum Many Worlds
The multiverse that most people are familiar with from science fiction is the Many-Worlds interpretation of quantum physics. There have been many a Star Trek episode where a hole opens up in space in front of the Enterprise, and another Enterprise emerges, complete with all of the crew members, but everything is just a little bit different. It is a handy way to write a “what if” story, where in the other universe a key moment for the story played out differently.

Let’s look at the science behind the Many-Worlds hypothesis. Now the average person gets exposed to quantum physics either from science fiction or from modern mystics, both of whom use the word “quantum” as a substitute for “magic;” an empty term meant to convince people the speaker knows what they are talking about. Quantum physics is often described as strange and weird, the same adjectives that are used to describe consciousness, supernatural creatures, spooky coincidences, etc. But just because the same words are used does not mean they have anything to do with each other. Matter can be solid, liquid, gas, or plasma, but that does not mean all matter is made of earth, water, air, and fire. Quantum physics is a real science, the study of the basic building blocks of matter and energy at the scale of atoms and their parts. So let’s leave all of our preconceptions behind and take a look at the real weirdness of quantum physics.

Before quantum physics, the Universe was thought to be deterministic. There was a thought experiment called “Laplace’s Demon,” in which it was imagined that if there were a mind that knew the positions and velocities of every particle in the Universe with infinite precision, that mind would be able to use Isaac Newton’s laws of motion to predict everything that happened in the Universe until the end of time. Everything was thought to be determined ahead of time—not planned or fated, but flowing naturally by the laws of physics with no possibility of changing course.

The essence of the weirdness of quantum physics is that it throws determinism out the window. With classical physics, if you set up two experiments exactly the same, they give you exactly the same result every time. That’s determinism. But in a quantum experiment, you can set up two systems exactly the same, and they can give you different results. For instance, sodium-24 is an unstable atom that decays into magnesium-24, with a half-life of 15 hours. This means that if you have a bunch of sodium-24 atoms, then in 15 hours, roughly half of them will have turned into magnesium-24. This means that if you look at an individual sodium-24 atom, there is a 50% probability that it will decay within 15 minutes, and a 50% probability that it will not. This probability is baked into the fabric of reality, and does not depend on some internal clockwork of the nucleus. Rather than deterministic, quantum physics suggests that at the fundamental level, the Universe is probabilistic.

For myself, I am perfectly happy with accepting quantum physics as probabilistic, that reality itself has an element of chance that cannot be explained away. This view is known as the Copenhagen interpretation of quantum physics. But many people see this as ignoring the question, and insist that there must be some explanation that resonates with a deterministic intuition (or a consciousness-based reality intuition, but that is a topic for another time). One of the most popular explanations is what we have been waiting for, the Many-Worlds interpretation.

The Many-Worlds interpretation of quantum physics says that every time a particle does something that is probabilistic, a new universe branches off in which each possibility happens. If there is a 50% chance that a particle goes to the right and a 50% chance that it goes to the left, then there will be two universes, one in which the particle goes to the right, and one in which it goes to the left.

Schrodinger's Cat. The release of the poison is triggered by the radioactive decay of an atom, so according to the Many-Worlds hypothesis, there are two universes, one in which the cat is alive, and one in which the cat is dead.

The Many-Worlds hypothesis is often explained in terms of choices. It will be said that when you get up in the morning, there will be one universe in which you have cereal for breakfast, and one universe in which you have toast. But this is a misrepresentation. It is not merely choices that cause branching universes, but any time any particle does anything probabilistic. Few people pause to consider the massive implications of this. There are 10^27 atoms in your body alone. That is more than the number of stars in the observable universe. According to the Many-Worlds hypothesis, these atoms are creating branching universes all the time, sometimes at rates much shorter than seconds. The sheer number of universes that would exist under the Many-Worlds hypothesis is beyond comprehension, even for someone like me who spends a lot of time thinking about the size and scope of the universe.

I personally don’t subscribe to the Many-Worlds interpretation, because particles do not behave according to discrete probabilities, but probability densities. To explain what that means, I’ll take us back to the unstable sodium-24 atom. With a 50% chance it will decay within 15 hours and a 50% chance it will decay after 15 hours have passed, that means there will be two universes, right? Not so fast. If we change the time frame—say, 30 hours—then there is a 75% chance it will decay before, and 25% chance it will decay after. This would mean there are three universes in which the atom decays before 30 hours, and one universe in which it decays afterward. But we can change the time again, say 20 hours, 15 minutes, and 22 seconds, and run the probabilities again. In fact, we can set up our time windows to be arbitrarily small, each with its own infinitesimal probability. This would mean that for a single atom, an infinite number of universes would be created. In 50% of these infinite universes, the atom decays before 15 hours, in 25% of the universes, it decays after 30 hours, etc.

Following the Many-Worlds interpretation to its logical conclusion, we don’t end up with a set of discrete universes, but a continuous infinite-dimensional smear of universe-ness. This does not mean it is not true, but if the reason to consider the Many-Worlds interpretation was because the idea of probability being an inherent feature of reality was too weird, it fails, because the explanation it provides is even weirder.

Hubble Volumes
Now for something that is definitely true, but may or may not count as a multiverse depending on your definition. Far off in the depths of space, there are two distances that could be considered the edge of the universe. These distances are spheres that are centered around the Earth, or rather, centered around whoever is doing the observing no matter where in the universe they are. The first is the particle horizon, which is the distance light has had time to travel in the age of the universe. Our universe began 13.8 billion years ago, which means that from 13.8 billion light years away, light from the beginning of the universe is reaching us now. As time goes on, the particle horizon expands at the speed of light. This makes sense, because when the universe was a million years old, the particle horizon was a million light years in radius, and when the universe is a trillion years old, it will be a trillion light years in radius.

But there is another sphere which is important too. The universe is not just sitting still, but it is expanding. The farther away two points are from each other, the faster they are moving apart (assuming they aren’t held together by gravity or other forces). This means there is a distance from Earth at which space is moving away at the speed of light, which is called the cosmic event horizon. Because nothing can travel faster than light, nothing that passes across the cosmic event horizon can ever affect Earth or send signals that could affect Earth.

Whichever is smaller at any given time, the particle horizon or the cosmic event horizon, contains the observable universe. Right now, the cosmic event horizon is around 16 billion light years away, so we have a couple more billion years of new light reaching us before things start vanishing across it.

There isn’t one single observable universe. Rather, every point in space has an observable universe centered around it. Our observable universe is centered on Earth, 13.8 billion light years in all directions. But if we went to the Andromeda galaxy next door, its observable universe would be 13.8 billion light years in all directions centered on it. When talking about the observable universe centered on a point other than the Earth, it becomes confusing, so instead we will call it a Hubble volume, after Edwin Hubble who discovered the expansion of the universe. A galaxy on the edge of our Hubble volume would have its own Hubble volume centered on it, and we would be at the edge of its Hubble volume. Now imagine a galaxy on the opposite side of that Hubble volume. We now have two Hubble volumes that do not overlap. In a sense, we have two different universes. And since we have no indication that there is an end to space, there may be an infinite number of non-overlapping Hubble volume universes. If you interpret this as a multiverse, there is no question that a multiverse exists.

Inflation
During the first Planck-time moments of the big bang, our present cosmological paradigm says the universe expanded at insane speeds many times faster than light. This is called inflation. Within the inflation, a small volume crystallized into what we know as normal space, the parameters of physics freezing into place. This volume continued to expand to become our universe, including everything within our Hubble volume and far beyond.

It might be that elsewhere, far away from us during the inflation era, other universe seeds crystallized into universes with different physical parameters. It could even be that inflation happens forever in space and time, constantly birthing new universes in its infinite expanding alternative-space. Each of these bubbles within inflation would contain many Hubble volumes, and so each of them would be its own Hubble volume multiverse.

Theory of Everything
The universe as we know it had a beginning, the big bang. It might have been the beginning of time, or it may have been a transition from another kind of universe. Either way, when we try to calculate back in time to the earliest moments of the big bang, our current understanding of physics doesn’t work. That’s fine; after all, we have two theories, Quantum Field Theory and General Relativity, and they don’t fit together. Although in this era of the universe they respectively describe the extremely small and the extremely large, the instant of the big bang falls under both of their domains.

In order to understand the beginning of the universe, we need to bridge the gap between Quantum Field Theory and General Relativity. Right now we have two major contenders for such a Theory of Everything: String Theory and Loop Quantum Gravity, though neither of them have been tested. Both theories predict the existence of a multiverse, so if either of them is true, our universe is not alone.

But let’s consider the possibility that both String Theory and Loop Quantum Gravity are false, and some other Theory of Everything that we have not thought of yet is correct. Such a theory must be able to describe the beginning of the universe, either from Nothing or from another universe.  No matter what it is, whatever principle or substance caused our universe to come to be would logically cause a multitude of other universes to be created for the same reason. In fact, I think it would be quite difficult, if not impossible, to formulate a theory of how the universe began that did not leave us with a multiverse.

Metaphysics
If truly no physical law acts upon a State of Nothing, then Nothing cannot remain as it is, nor can there be any limit on what would come from it, because such a limit would count as a law of physics. If that is true, then everything that is logically and mathematically possible must exist, though in completely separate spacetime continua. These possible-made-real universes would range from those with the conditions for life like our own to emerge, to many kinds of universes where life is impossible, to universes that blink out of existence the moment they appear, to the really bizarre, like universes where a single particle corkscrews through space eternally, or where time loops back on itself and events repeat in an eternal cycle.

Arguments against a multiverse:

It is untestable
The most common criticism against the existence of any kind of multiverse is that it can never be tested. If these other universes are disconnected from ours, how could we possibly be able to measure them? It is a fair point, and reminds us to approach the topic with due skepticism, but it isn’t really an argument against a multiverse’s existence. Furthermore, there are some kinds of multiverses that we might, in fact, be able to detect. Gravitational wave detectors might be able to pick up signals from before the big bang, which would confirm that our universe was born from another universe. If String Theory is true, then we might be able to see signs that our 3-brane universe bumped into another 3-brane universe traveling through a fourth dimension. So while some types of multiverses really are untestable, like the physical existence of all things possible, there are some types of multiverses that we simply do not have the technology to test yet.

Strong Anthropic Principle
If our universe is the only one, then there are no other spacetime continua, no extra dimensions, and nothing at all, including space and time, before the big bang. However, in the laws of physics there are several physical constants, which describe the relative scales of things. For instance, the speed of light links space and time, the fine structure constant determines the strength of the electromagnetic force, and Planck’s constant sets the size of atoms. The number of possible combinations of physical constants that can support life is massively dwarfed by the number of combinations that prohibit life from existing. If there is only one universe, then it would be ridiculously unlikely for that one universe to be able to support life. This problem doesn’t have an official name, but I call it the Teleological Paradox, meaning the paradox of apparent design.

If there is a multiverse, then everything that can happen does happen, and the Teleological Paradox goes away. But if there is only one universe, there must be another resolution. One possibility is the Strong Anthropic Principle, the hypothesis that it is impossible for conscious, intelligent minds not to exist. If this is the case, then it is not correct to say the Universe came into being with the conditions for life, but rather the necessity of intelligent minds caused the Universe to come into being.

The Strong Anthropic Principle breaks causality as we know it. In all the rest of our experiences, causality goes from past to future. The Strong Anthropic Principle, on the other hand, says that future events (the existence of intelligent minds) cause the past (the beginning of the universe). The claim that intelligent minds must exist is also arbitrary; there is no more reason that intelligent minds necessarily exist than that elm trees necessarily exist, or that ringed planets necessarily exist. The only reason intelligent minds are chosen as the basis is to patch the Teleological Paradox. Furthermore, we might expect the Strong Anthropic Principle to make a much smaller universe, perhaps just a dwarf galaxy or star cluster, because the rest of the universe isn’t necessary for life. So although the Strong Anthropic Principle has no logical contradictions, it is a very weak explanation for why the universe can support life.

Intelligent Design

Another possible way for our universe to be the only one is if it was created intentionally so that we might exist by a personal God who exists independently of physical reality. But consider this: we have seen through our telescopes that the Universe is vast beyond comprehension. Remember, the universe is expanding, which means the farther something is from us, the faster it is moving away. Almost all of the trillions of galaxies scattered all over the observable universe will be pushed farther and farther away, until they cross the cosmic event horizon, which, remember, is the distance at which the expansion is faster than light. Once this happens, it will be physically impossible to reach them, or even see them anymore. If the Universe was created for us by an intelligent designer, we would either expect these galaxies to be reachable someday, or to not exist. If the goal was to create a universe where intelligent life would arise, it would be far easier to create a single galaxy, or even a single solar system, because that is all that is needed.

Perhaps God created all of those far-off galaxies to show his grand splendor, that the more technologically advanced we get, the greater we find the universe to be, and the more awe we feel for its creator. That makes sense, but let’s follow it through to its full implications. If God created multitudes of galaxies beyond the Virgo Supercluster to display his majesty, then why not for the same reason create a multitude of equally splendorous universes? I think that, even if the cause of the universe was that it was designed by a God, we still have good reason to believe there is a multiverse.

Instinctive Design
Finally, there is the option of some kind of unconscious mind, like the Force or a sleeping God, which created the universe with the right conditions for life out of instinct rather than intent. It may be that this kind of being would create one universe, since one is all that is needed for life. Being instinctive rather than intelligent, it might end up filling the universe with galaxies as a by-product. However, I would expect a universe created by such a being to be teeming with life on every planet, moon, and asteroid, and so far we have found no evidence of life from anywhere besides Earth.

Conclusion:

There are many physical and philosophical theories that hint toward the idea that our universe is not the only one, that there may be several universes, or an infinite number, all with different properties, dimensions, and contents. If this universe is the only one, we run into the Teleological Paradox, that the conditions being right for intelligent life to exist is too improbable to be coincidence. Each of the Teleological Paradox’s possible resolutions predict either that we would more likely find ourselves in a universe that looks quite different from this one, or that we have a multiverse anyway. There is no evidence that a multiverse exists, but with all the possibilities, I would not be surprised if one day we discover, in the depths of time and space or in the hearts of black holes, other universes lying hidden.

Life in the Universe – Probability and Perspective

Recommended Pre-Reading:
The Fermi Paradox

When we look up at the sky at night from a place without too much light, we can see thousands of stars. Telescopes and centuries of formal astronomy have shown us that there are billions of stars in our Milky Way galaxy, and billions of galaxies in the observable universe. Considering the mind-bogglingly high number of chances for civilizations to arise, and the incomprehensible amount of time that has passed since the big bang, it seems natural to ask why the sky is so silent. Where are all the aliens? This is famously called the Fermi Paradox. But is it actually a paradox? Do we really have good reason to believe there should be aliens everywhere?

Back in the days of Ancient Greece, Aristotle modeled the solar system—or rather the terrestrial system—with the Earth in the center, and the sun, moon, stars, and planets revolving around it in perfect circles. There is something in human nature that makes it easy to believe that the universe is centered around us. Aristotle’s model survived for over a thousand years into the middle ages, until a troublemaker by the name of Nicolaus Copernicus shook the world with the model we all know today, with the sun in the center and the Earth being a planet, just like all the other planets. Since then, the Copernican Principle has been the idea that there is nothing special about us. We don’t live at the center of the Universe, Earth is not a special planet, the sun is not a special star, and so on. We are an ordinary part of the Universe, just like everything else. Taking the Copernican Principle to its conclusion, it seems the cosmos should be positively teeming with civilizations’ phone calls, TV shows, and internet sites.

On the other hand, we must also consider the Anthropic Principle,* which basically says, “we should not be surprised to find ourselves in a place where intelligent life is possible.” For example, if you were to wake up in a room and find a letter which said, “There are a million rooms just like this one, and only one of them is occupied,” would you think to yourself, “what a miracle it is that I find myself in the only room out of a million that is occupied”? Of course not, because the fact that you are there is what makes it occupied. When applied to life in the Universe, the Anthropic Principle shows us that even if the chances of life arising around any particular star are a soul-crushing one in one septillion (1 in 1,000,000,000,000,000,000,000,000, or 0.000000000000000000000001) over 13 billion years, it is completely unsurprising that we find ourselves here on a planet that is perfectly suited for intelligent life. In fact, since we have no reason to believe the entire Universe ends anywhere near the edge of the observable universe, it doesn’t matter how infinitesimally small the odds are, there is really nothing interesting about the fact that we exist.

Taking the Copernican and Anthropic principles together, all we can really conclude is that we are probably normal as far as civilizations go. However, we still can make no reasonable guess as to how many civilizations should exist. There might be millions in our own galaxy that we are just on the brink of finding, or there might be no others in the entire observable universe. There are those who claim life should be everywhere, and those who claim Earth is unique. Who is right? We don’t know. What we do know is that neither has a good enough argument to win the debate, because there just isn’t enough data yet.

Click to view larger.

Speaking of data, we can turn this question into a scientific one with the Drake Equation, which says the number of civilizations in a given volume of space is equal to a bunch of stuff multiplied together. Those variables are the rate of formation of stars in that volume that could potentially host life, the fraction of habitable stars with solar systems, the average number of habitable planets per solar system, the fraction of habitable planets where life begins, and the fraction of planets with life that evolve civilizations. I have taken liberties and condensed some of the variables together to make it easier to explain, but that is the gist of it. We know the first three pretty well. Almost all stars have solar systems, and it is quite common for stars to have rocky or ocean planets in their habitable zones. However, Earth is the only planet we know of that has life, and we don’t know how it got started, so we have no idea what the last two variables are. They could be anything from so small that ours is the only planet in the Universe with even microbial life, to so large that we might stumble upon our neighbors’ interstellar radio network any day now.

Talking about the Fermi Paradox has always bothered me. Not because it is a paradox, but because everyone calls it a paradox and I don’t see why. A paradox requires a valid theoretical prediction that either leads to two apparently contradictory conclusions, or disagrees with observational evidence. But the assumption that life should be everywhere in the Universe is not valid, hence no paradox. Regardless, whether or not we are alone is still one of the deepest, most awe-inspiring questions a human being can ask.

*The Anthropic Principle should not be confused with the Strong Anthropic Principle or the Weak Anthropic Principle, both of which apply the Anthropic Principle to the Universe. The Weak AP assumes there is a multiverse, while the Strong AP assumes there is not.