Black Holes are a Thousand Times Weirder than You Think

In the depths of space, there are objects that undermine everything we feel we know about space and time. These objects are black holes.

A realistic depiction of what a black hole would look like up close, using the universe simulator Space Engine.

A black hole forms when an amount of matter is squeezed smaller than its Schwarzschild radius, the size at which its gravity is so strong that nothing, including light, can escape. When this happens, an event horizon forms at the S-radius, and the matter inside collapses to form a singularity. We’ll get a feel for what these mean as this post goes on.

The incredible amount an object must be compressed to form a black hole is staggering. In order to turn the sun into a black hole, we would have to crush it down to 6 kilometers across. That’s the total distance I walked every day to and from my university when I was in graduate school. If you were to compress the Earth into a black hole, it would be the size of a marble. If you didn’t have to worry about it tearing you apart, you could hold it in the palm of your hand.

Why do black holes look the way they do? Let’s start with a lone black hole in the cold depths of space. Since light can’t escape, it looks like a circle of blackness, and because the strength of their gravity is so great that they bend light around them, they distort the stars behind them like a lens.

From the YouTube video, “Colonizing Black Holes,” by Isaac Arthur

When a black hole is feeding on material around it, perhaps from a companion star or an object that came too close to it and was torn apart, it gets an accretion disk. Why does a disk form, rather than all the matter just falling in? There are two reasons working together. First, we have angular momentum. The matter isn’t falling straight into the black hole, but orbiting around it at insanely high speeds. Because of this, any stray matter that collides with the disk becomes part of the disk. Secondly, as the matter gets closer to the black hole, it crams together and can only go in so much at a time, like sand trickling through an hourglass.

An artist's impression of an accreting black hole. From Wikipedia

We can see an example of angular momentum creating a disk in the above artist’s rendition of a black hole accreting matter from a companion star. The star and black hole are revolving around each other, so the stream going from the star to the accretion disk curves in the forward direction, partially because of the star’s inertia, and partially because the black hole moves out of the way and the stream has to catch up.

With all that matter spiraling inward, feeding black holes build up quite the magnetic field. This magnetic field points outward from the poles, so instead of falling into the event horizon, some of the matter gets shot away at extreme speeds by these magnetic fields in two jets, as can be seen in the above picture.

As the matter in the disk crams together, it heats up due to friction, which causes the accretion disk to glow. The closer to the center, the hotter it gets, making it go from red on the outside to white on the inside. Because of how fast it is revolving, the light gets Doppler shifted, brighter and whiter on the side moving toward us, and dimmer and redder on the side moving away from us. This is heightened by the fact that the disk is spinning close to the speed of light.

A realistic depiction of a black hole up close, from the movie, Interstellar

You might notice that there is a halo around the event horizon. That’s an illusion, an image of the accretion disk on the back side of the black hole, which we can see both above and below it because of the light bending around the event horizon.

Up until 2015, we didn’t have direct observations of black holes. Now we do, first by gravitational waves with LIGO, and then a few years later by the Event Horizon Telescope, a composite telescope that uses advanced techniques to put together data from observatories all over the world, giving us an effective dish size as big as the entire Earth. Here is what that image, given artificial color, looks like.

The supermassive black hole at the center of galaxy M87.

The black circle in the center is the shadow, a blown-up view of the entire event horizon, front and back, because of the way light bends around it. If you could see it without any lensing effects, the event horizon would be a fraction of its size. There is a great YouTube video by Veritasium explaining this in more detail.

Black holes look cool, and a lot of interesting science goes into why the look like they do. But there’s more, oh so much more. So now it’s time to get to the good stuff: what black holes do to space and time. In order to discuss this, we have to be comfortable with space-time relativity, the principle that space and time are parts of the same thing, and this space-time can be curved and stretched. We talked about this in our discussion of faster-than-light travel and time travel, but here’s a little refresher.

When drawing space-time diagrams, we draw one dimension of space on the horizontal axis, and time on the vertical axis. An object sitting still will move straight up on the diagram, parallel to the time axis. An object moving will travel at a diagonal angle. We scale the plot so that light beams travel at 45-degree angles.

We choose a point to be the origin of the plot, which we call “here and now.” This could be you, it could be a space ship, a rock, or just a random point in space-time. From this point, we draw the light beams that go out into the future and come in from the past. If you imagine a third axis pointing out of the screen, these light beams circle around the time axis, making cones, which we call the past and future light cones. In reality, there is also a third dimension of space, making it a hypercone, but it is very hard to visualize four dimensions, so we talk about light cones.

From Wikipedia

No matter where you are or what the space-time curvature around you looks like, your light cone looks like this diagram. But someone else’s light cone at a different point in space could be distorted compared to your coordinate system. For instance, if we are in normal space far away from a black hole, then the light cone of something falling into a black hole curves to point toward the event horizon. And after an object has passed the event horizon, its entire light cone points toward the singularity. There is no direction it could go that would not end up at the singularity.

This is confusing, and not good for calculating. A much better and more intuitive way to understand black holes is with a Penrose diagram. To make a Penrose diagram, we use a math trick to change our coordinates so that we compress all of space-time into a diamond. The two bottom edges of the diamond are infinitely far back in time, and the top right is where time reaches future infinity. The top left is the event horizon of the black hole. On the other side of the event horizon, we join another half-diamond, representing the inside of the black hole.

In this diagram, lines of constant position and constant time are curved. Yet light always moves at 45-degree angles, making it easy to tell what observers in each region would see. Imagine two people, person A staying outside, person B falling in, sending signals to each other. To A outside, it would take an infinite amount of time for B to reach the event horizon, and A could keep receiving signals from B forever. However, in B’s reference frame, B passes the event horizon in a finite amount of time no problem. Then, a short time later, B reaches the singularity. Contrary to popular myth, B does not see the entire future of the universe, as we can see from the following diagram.

The paths of A and B exchanging light beams as they go. Everything moves upward, because that is the direction of time. As we can see, once B passes the event horizon, their light beams end at the singularity. B can receive signals from A, but there comes a point when A’s signals reach the singularity without reaching B first.

With a Penrose diagram, we can see a startling conclusion: inside the black hole, space and time have switched places! The singularity is no longer a point in space, but a moment in time, which all things inside the event horizon move inexorably toward. In addition, according to an observer outside the event horizon, everything that happens inside takes place after an infinite amount of time has passed!

Have a moment’s rest before we continue on. What, did you think that was as crazy as it gets? We haven’t even gotten to wormholes yet.

To get there, we first have to talk about spin. Everything floating in free space has a little bit of angular momentum, its outer parts rotating around its center of mass. Black holes are no different; the matter that forms and feeds them spirals in, contributing to their angular momentum. As a result, black holes have a property called spin. This spin prevents the matter from falling all the way to a single point, as the closer it gets the more centrifugal inertia it has to counteract the gravity. What this means is that the singularity is not a point, but a ring of zero thickness. If the spin is so high that the radius of the ring is larger than its Schwarzschild radius, then there is no event horizon, and it is called a naked singularity. Currently, no naked singularities are known to exist.

A simulation of what a naked singularity would look like from above.

If mass distorts space-time, do black holes pull space around them as they spin? Yes, they do. It’s called “frame dragging,” a name as cool as the phenomenon it describes. If we were to drop something directly toward a black hole near its plane of rotation, it would spiral around the black hole as it fell, due to the motion of space itself. There is a region near the event horizon called the ergosphere, where space is pulled so fast that an object has to travel faster than light in the opposite direction just to stay in the same place. The ergosphere is outside the event horizon, so in principle it is possible to send a ship or a probe into it and back out again. Now that would be a trip!

From Wikipedia

All right, now we’re ready to get to wormholes. Since black hole singularities are rings, it stands to reason that it’s possible to go through it. What happens? Well, you might think you just end up on the other side of the ring. After all, that’s what happens when you pass through any other kind of ring. But something weird happens. When you were a child, did you ever imagine you could go around a lamp post or a tree and find yourself somewhere else? That’s what happens when you pass through a ring singularity. Let’s look at the Penrose diagram:

With a path through the singularity, we can see that there is another side. When we get there, instead of the other side of the black hole, we find something called a white hole, an object with repulsive gravity and an event horizon nothing can get into. No one knows if white holes exist, and we don’t know of anything that has repulsive gravity. Thus, we have a one-way wormhole, with a black hole on one side nothing can get out of, and a white hole on the other side nothing can get into. What is on the other side? It could be a different place in the universe, maybe at a different time. Or, it could be another universe altogether, a space-time continuum completely separate from ours except for this one bridge.

We have never seen a white hole. This does not bode well for the possibility of their existence, since they would probably be extremely bright, launching out everything that fell into their black hole partner at relativistic speeds. Except, well, maybe we have. There is one thing that had a singularity and looks kind of what we’d expect a white hole to look like: the big bang. It’s common to think of the big bang as the beginning of everything, including time, but it might not be. Maybe it was the result of a black hole in another universe. This may seem like nothing more than sci-fi fancy, but there are a few high-profile physicists who take the possibility seriously.

So there we go, a glimpse into the depths of the weirdness of black holes. There is one more thing I’d like to say: we don’t actually know much about singularities. When we try to apply our best theories to them, General Relativity and Quantum Field Theory, we get unsolvable problems. In order to be able to model singularities, we need a theory of quantum gravity. Our two major contenders, String Theory and Quantum Loop Gravity, have both made predictions that turned out to be false. So the final tidbit of black hole weirdness I’ll leave you with is that there is still a feature about them, the singularity, that we know basically nothing about. I hope you sleep well tonight. See you next time.

Mathematics: The Language of the Universe

Nature of Reality:
Quasi-Realism
Representational Realism
Existence and Natures
Knowledge of Reality
The Language of Reality

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

In our discussions about the nature of reality, we have come to the view that reality is a thing unto itself, independent of perception, belief, or knowledge. Anything we perceive or think we know about reality is not reality itself, but only a representation we have constructed in our minds. A representation is true to the degree that its logic matches with the logic of the real thing it is describing. Today, we are going to talk about that logic, mathematics.

By WyrdWolf on Deviantart

A lot of people see math as something mysterious that they will never understand. But math is not supernatural. It is not hidden knowledge available only to an elite few. People who know math are not wizards or prophets, they are normal people just like you. I hope that after reading this discussion, you will be convinced that you can learn math too, if you so desire.

To start, let’s forget about numbers and just think about something physical, like air pressure. We know from centuries of experiments that, the pressure in a given volume is proportional to the number of molecules in the volume and the temperature. This may sound complicated, but all it means is if more air is added or the temperature is increased, the pressure increases.

Let’s look at the italicized statement. We have four physical quantities: pressure, volume, number of molecules, and temperature. Let’s shorten each of these to just their first letters: P, V, N, and T. “Is proportional to” means if you change what comes after it, then what comes before it changes by the same percentage. We can represent this by an equals sign and a constant, the letter k. Put this together, and we have,

It’s an equation! We have just done something marvelous; we have taken a fact about reality and written it as a mathematical statement. By doing this, we realize a profound truth: math is not just a tool to work with numbers and get answers to homework problems; it’s a language and a writing system. By becoming math-literate, we break into a higher level of understanding the universe.

Let’s try it again. This time we’ll start with an equation, and figure out what it means.

The first thing we need when trying to read this equation is what the letters mean. In normal languages, letters have mostly the same sounds wherever they appear. In math, it is not so; we must be told what each letter means every time. It is the organization, operations, and numbers that have consistent meaning. So here is what the letters in our new equation mean: capital T stands for temperature, small t stands for time, and k is a constant.

What operations does this equation have? The first thing we notice is d/d. This means, the rate at which the thing on top changes as the thing on the bottom changes. So for us, it would be the rate the temperature changes over time. Next, we notice a triangle before the T on the right. This triangle means the difference between two of what comes after it. So in our case, ΔT means the difference between the temperatures of two objects.

Putting all this together, we can read the equation. It says, “The rate at which temperature flows between two touching objects is proportional to the difference in temperature between the two objects.” This means if two touching objects have very different temperatures, heat will flow quickly between them, but if their temperatures are near each other, the heat will flow slowly.

There is one final piece to the equation, and that is the minus sign. This tells us that the temperatures are changing closer to one another, not running away to extremes. This makes sense. Cold things heat up when they touch hot things, and hot things cool down when they touch cold things. Heat always flows toward equilibrium.

The ability to read equations is only one small part of math. There is also geometry, group theory, set theory, vectors, tensors, and much more. All of these fields of study are called the same thing, math, so what do they all have in common? The answer is that mathematics is the set of all well-defined abstract ideas that follow the principle of non-contradiction. To create math, we must declare one or more axioms, statements that define an imaginary object.

Let’s take an example. "A circle is a shape where every point on its boundary is the same distance from its center." Based on this axiom, we can figure out all kinds of things about lines drawn through circles, intersecting circles, circles in curved space, and more. Everything in math is like this; we start with axioms, and then use logic on them to figure out all that we can about them.

Philosophers and scientists have often wondered at how well math is able to describe the universe. To some, it seems miraculous. However, based on everything we have talked about in the Nature of Reality series, I think it makes perfect sense. Here’s why:

1) A representation is true to the degree that its logic lines up with the logic of the part of reality it is meant to represent.
2) An idea is a representation.
3) Reality is well-defined and always follows the principle of non-contradiction.
4) Every idea that is well-defined and follows non-contradiction is mathematical.
Therefore, everything in reality can be truthfully represented by mathematical ideas.

If we accept the views of reality we have argued for on this blog, this is why Mathematics is the language of the universe.

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.

Why does Anything Exist?

We have talked a lot on this blog about the nature of reality, about how real things exist objectively, and have natures by the mere fact of their existence. But there is a question we have yet to touch upon, and that is why there is a reality in the first place. Why is there a Universe and people and furry critters and chocolate fondues, instead of nothing at all?

When we speak of “nothing,” there are three definitions we have to keep track of. The first refers to the lack of something expected, such as when a parent asks their child, “what are you doing,” and the child replies, “nothing.” We are not interested in this type of nothing today. The second type of nothing people think of is empty space. There is no air or other matter, just the void. Those who are thorough in their thinking will say that it does not count unless no light is passing through it either.

We, however, will go a step even beyond that. To get a true State of Nothing, we must eliminate even time and space. No matter, no energy, no particles, no space, and no time. When we ask, “why does anything exist rather than Nothing?” this is what we mean.

Figure 1: This is an empty rectangle. It is not Nothing.








Figure 2: This is not even an empty rectangle. It is Nothing.

One possible reason reality exists is because there is an eternal God who has the ability to will things into existence. With this kind of God, creatio ex nihilo, or “creation from nothing,” is possible. If you look carefully though, this does not answer the question, but shifts it to “why is there a God rather than nothing?” A common response to this is that God is exempt because he is eternal, whereas the Universe had a beginning. This is unsatisfactory on two accounts, the first being that the claim that something exists eternally does not, in fact, explain why it exists in the first place. Secondly, we don’t know for sure that the Universe is not eternal. Perhaps a parent universe gave birth to our universe, in which case the Greater Universe might have an infinite sequence of past events. There is also the issue that time behaves in ways not well-understood in extreme cases like the big bang, and future scientific discoveries might reveal that concepts like “beginning of time” and “past-eternal” are naive, like the belief that all matter is made of air, water, fire, and earth. Alternatively, it may be that God is ontologically necessary, that is, it is impossible for him not to exist. But the justifications for this claim, the Ontological Arguments, are circular in their logic.

Another common response to the question of why anything exists is to reverse it and ask, “why should we expect there to be Nothing rather than a Universe?” It is a fair question, but not an answer in itself, and we have to be careful not to use it as an excuse to stop thinking about the topic.

Two common philosophical ideas about Nothing are of interest to us. The first, is ex nihilo, nihil fit, which means, “from nothing, nothing comes,” or, “nothing comes from nothing.” It seems like common sense that if nothing exists, nothing can come from it. After all, we don’t see random things popping into existence out of nowhere. However, “out of nowhere” is an example of the first kind of “nothing” that we said at the beginning of the discussion that we were not talking about. It is different from out State of Nothing, because in our everyday experience the Universe is already there, and the Universe is not Nothing. Still, it may not seem a stretch to assume that nothing can come from a State of Nothing either.

The second philosophical idea about Nothing is that in order to be a true State of Nothing, not only must it have no matter or energy or space or time, but no laws of physics may apply to it either. In this view, a law of physics would count as something, and such a law would itself need an explanation as to why it exists.

Let’s take a look at what happens when we try to apply ex nihilo, nihil fit and “no laws of physics may apply” at the same time. As we talked about last time in the Nature of Reality series, a law of physics is a representation, often written as a mathematical equation, of a physical state’s nature. If Nothing’s nature is that nothing comes from it, we can write that as a mathematical equation, dQ = 0, where Q is a vector of all possible quantities that can change, and d represents any change that happens to those quantities. Translated into English, the equation means, “the change in anything that can be changed is zero,” or, “nothing changes.” Thus, if nothing comes from Nothing, then that in itself is a law of physics that applies to a State of Nothing.

What we have just shown is that the claims, “nothing comes from nothing,” and “no laws of physics apply to a State of Nothing” contradict each other. This means that at least one of them is not true. Either at least some law of physics applies to a State of Nothing, or a State of Nothing would be unstable, and instantly create something.

If we accept that at least some law of physics applies to a State of Nothing, we cannot yet answer why anything exists, because that law could easily be “nothing comes from nothing.” However, it could also be something like String Theory or some as yet unknown Theory of Everything, which would predict universes coming into existence. Either way, we run into the question of why that law of physics exists rather than Nothing. The only solution I can think of is that, since mathematics and logic are transcendentally true, there is something buried deep within their uncharted depths that makes the ultimate law of physics ontologically necessary.

On the other hand, if we accept that Nothing has no laws of physics that apply to it, then something must come from it. As there is no limitation on what pops into being from this state, we might expect not only to get the Universe from it, but an infinite number of universes, where everything that is logically possible happens. These universes would be completely separate spacetime continua, so we would never be able to observe them, and it does not make sense to think of them as being in any direction from us, or before our universe or after.

Ultimately, I cannot answer the question of why anything exists rather than Nothing. We can, however, propose some possibilities. Perhaps, emergent from pure logic and mathematics, there is a law of physics which, when acting upon a State of Nothing, causes a universe to be created. Perhaps Nothing is not bound by any law, and so from it all things that are logically and mathematically possible spring forth into existence, each in its own universe. Perhaps there is a middle-man, like a God or a Force or a cosmic automated factory that is brought into eternal being by pure logic, and from which universes are created. Or perhaps the Universe merely exists because it exists, and the State of Nothing is a meaningless construct. Regardless, the Universe does exist, so let’s get out there and make the most of it.