The video masterfully translates abstract cosmological probabilities into a compelling narrative about the nature of existence. It successfully bridges the gap between rigorous mathematical necessity and the profound mystery of human identity.
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Infinite Versions of You Exist… Here’s HowAdded:
Tonight, we're going to talk about infinite versions of you. Not in a metaphorical sense, not in the way self-help books use that phrase to mean you have unlimited potential. In a literal, physical, mathematically grounded sense, multiple copies of you right now, experiencing different versions of this moment.
And the evidence that this might be true comes not from speculation but from physics.
Before we get into it, if this is the kind of question you genuinely want to sit with, take a second to like the video or subscribe. It helps this channel reach more people who want to think carefully about things that matter. Now, let's actually work through this.
Most people hear infinite versions of you exist and file it under philosophy or science fiction. something that sounds interesting at a party but doesn't really mean anything concrete.
That's a reasonable response because the claim sounds absurd and claims that sound absurd usually are. But this one comes wrapped in enough real physics that dismissing it requires understanding it first. And understanding it is genuinely worth your time.
By the end of tonight, you'll have a clear picture of the actual physical arguments, where they're solid, where they're uncertain, and what they imply about what you are.
Here's what most people don't realize.
The arguments for infinite copies of you aren't one argument.
There are at least three completely independent arguments coming from completely different areas of physics.
One comes from cosmology, the study of the large scale structure of the universe. One comes from inflationary theory, the physics of the universe's earliest moments.
And one comes from quantum mechanics, the most precisely tested physical theory ever developed. Each of these stands on its own. Each points toward the same conclusion through a completely different route.
That convergence is what makes the idea worth taking seriously rather than dismissing.
Let's start with the most straightforward version of the argument.
The one that doesn't require anything exotic, the one that follows from just two things we're fairly confident about.
First, the universe might be infinite.
Second, the number of possible arrangements of matter is finite.
That's it. That's the whole argument in its compressed form.
Let's unpack it properly. The observable universe is a sphere centered on us extending about 46 billion lightyear in all directions.
The diameter of that sphere is 92 billion lightyear.
To give that a human frame, light travels about 300,000 km every second.
fast enough to circle the Earth roughly 7.5 times per second.
In one year, light covers about 9.46 trillion km. Multiply that by 92 billion, and you have the diameter of what we can see. That's the bubble of space from which light has had time to reach us since the Big Bang. But here's the thing. The observable universe is not the universe. It's our observable universe. It's the part we can see given the finite age of the universe and the finite speed of light beyond the edge of that bubble. Space continues.
We just can't see it because the light from those regions hasn't had time to reach us.
And based on what we can measure, particularly the near perfect flatness of space geometry, there's strong reason to think the universe extends much further than our observational bubble.
Think about what that means for a moment. Every galaxy, every star, every planet we've ever observed or photographed or detected sits within this bubble.
The Hubble Space Telescope's deepest images showing thousands of galaxies in a patch of sky smaller than a period on this page are all within our observable region.
Everything we know about the cosmos, every data set, every measurement, every conclusion ever drawn from telescope observations refers to a region that is in a very specific sense local, a neighborhood, not the full city. The flatness of space is measured by looking at the cosmic microwave background, the faint afterglow of the big bang that fills every direction of the sky.
The plank satellite which operated from 2009 to 2013 from a point about 1.5 million km from Earth roughly four times the distance to the moon mapped that background to extraordinary precision.
What plank found is that space on the largest scales we can measure is geometrically flat to within about 0.4%.
Flat in the cosmological sense means that the angles of a cosmic triangle add up to 180°.
That parallel lines stay parallel. That the geometry of space follows Uklidian rules.
Why does flatness imply a large universe?
Think of a balloon. If you draw two parallel lines on a deflated balloon, they're not parallel. They curve. But if you inflate the balloon enormously, a small patch of its surface looks very nearly flat. The curvature is there, but at the scale of the small patch, it's undetectable.
If you could only measure a patch the size of your thumbnail on a balloon the size of the Earth, you'd conclude the surface was flat. Cosmologists measuring our observable region and finding it flat are in a similar position. We're measuring a patch. The full balloon might be enormous.
For space to appear this flat within our observable region, the total universe has to be at minimum about 250 times larger in radius than the observable portion.
That's just the minimum implied by the measurement precision. Think of it this way. If the observable universe were a single grain of sand, the minimum total universe would be larger than a pile of sand filling a living room. That's the floor. Many cosmological models, particularly those based on inflation, predict a total universe that's orders of magnitude larger. Still, some models predict the universe is effectively infinite. Truly, literally infinite. No edge, no boundary.
Space going on forever.
Now, here's where the mathematics gets interesting.
The observable universe contains a certain amount of matter, roughly 10 to the 80 atoms. That's a number so large it doesn't have an everyday name.
For comparison, if every atom in the observable universe were itself a universe containing the same number of atoms, you'd still have fewer total atoms than 10 to the 80 raised to the power of 80.
We're talking about a specific, countable, though unimaginably large amount of material.
And those atoms can only be arranged in a finite number of ways.
Not because we're running out of space to arrange them, but because quantum mechanics places fundamental limits on the number of distinguishable states a physical system can occupy.
Two configurations of matter that differ only by shifting an electron by one plank length aren't really distinct physical states.
The plank length is about 10us 35 m compared to the diameter of a proton which is about 10 -15 m. The plank length is 20 orders of magnitude smaller. If a proton were the size of the observable universe, the plank length would be roughly the size of a typical grain of sand.
Below that scale, states become indistinguishable.
This limits the number of truly different configurations.
The maximum number of distinct configurations of the matter in one observable universe-sized volume has been estimated at roughly 10 ^ of 10 to the 122.
The physicist Max Tegmark who works on these questions at MIT has done this calculation carefully. The number 10 to the 10 to the 122 is not 10 to the 122.
It's 10 raised to the number that itself equals 10 raised to 122. It's a number so incomprehensibly large that if you tried to write it out in full, the number of digits required would far exceed the number of atoms in the observable universe. But it's finite.
This is the key point and it's worth slowing down on.
The number of possible configurations of matter in a region the size of the observable universe is finite. not small, not manageable, incomprehensibly large, but finite. And if the total universe is infinite, then the universe contains an infinite number of observable universe-sized regions.
An infinite number of regions, each able to contain only a finite number of configurations.
The consequence follows by pure mathematics.
configurations must repeat.
In fact, every possible configuration occurs infinitely many times. This isn't a physical claim that could turn out to be wrong if we discover new physics.
It's a mathematical necessity.
Infinite divided by any finite number, no matter how large, gives infinity.
If there are infinite regions and finitely many configurations, each configuration occurs in infinitely many regions. That's not negotiable.
That's not a hypothesis. That's arithmetic.
Including the configuration that is you.
Let's be precise about what that means.
Your body, your brain, your exact arrangement of approximately 37 trillion cells. Each cell containing specific proteins in specific configurations.
Each protein made of specific atoms arranged in specific ways. All of this constitutes a particular physical configuration of matter.
It's an extraordinarily complex configuration, but it's still a configuration, still a finite state. And in an infinite universe, that state must be replicated.
Not once, an infinite number of times.
And not just you, as you are right now.
Every version of you that's physically possible within the laws of physics. You right now, you 5 minutes from now. You in a moment where you made a different decision this morning. you in a version where some past event in your life had a different outcome.
Every configuration of matter that corresponds to you from slightly different to dramatically different occurs infinitely many times somewhere in the infinite universe. Where are the nearest copies?
Tegmark has estimated the distance to the nearest exact copy of our observable universe.
Not an approximately similar region, an exact duplicate, atom for atom. His estimate puts the nearest exact copy at approximately 10 to the 28 m from here.
To picture how far that is, the observable universe is only about 8.8 * 10 26 m in diameter. The nearest copy is at a distance of 10^ the 10 to the 28 m.
The ratio of that distance to the diameter of the observable universe is a number with about 10 billion zer in it.
If you wrote that ratio on paper using the smallest possible handwriting, you'd need a paper wider than the observable universe to fit all the zeros. It's so far away that it might as well be in another universe.
But in an infinite universe, it exists.
This is the level one multiverse as Tegmark categorizes it. No exotic physics, no separate dimensions, no new laws of nature, just space extending infinitely with the consequence that everything that can happen does happen infinitely many times. Now let's think carefully about the regions between copies because the nearest exact copy is at 10^ the 10 28 m. But what about all the space between here and there? That space isn't empty of people. It's full of near copies regions where almost everything is identical to our observable universe. But some things differ. A star in a slightly different position. A planet that formed with slightly different composition. A version of Earth where a single mutation in a single organism 500 million years ago sent evolution down a slightly different path.
These near copies are far more common than exact copies because there are many more ways to be slightly different than there are ways to be exactly the same.
As you move outward from our observable universe into the space beyond, you're gradually moving through a landscape of configurations.
The configurations nearest to ours are abundant. Almost us regions where the differences are microscopic.
Regions where you exist and are almost exactly as you are now, but some small detail differs. Further out, the differences compound. Regions with different versions of your life.
different histories, different choices, different outcomes.
And then beyond the scale of a typical human life's difference, regions where you don't exist at all, where the circumstances that produced you were never assembled, where Earth formed differently or didn't form or formed, but life took a different path and never arrived at anything like you.
And then at the extreme distances, the exact copies, full duplicates, every atom in place. This spatial structure of the level one multiverse, the gradient from near copy to far copy to exact copy, is actually a more specific and interesting claim than the simple infinite copies exist summary. It tells us something about the texture of the infinite universe.
The universe is full of variations on themes. We're a theme and we're repeated with variations and without across an infinite space. Now, let's talk about whether the universe is actually infinite because everything in the level one argument depends on this and it's worth being honest about the uncertainty.
We don't know for certain that the universe is infinite. We know it's at least 250 times larger in radius than the observable portion from the flatness measurement.
Some inflationary models predict it's effectively infinite. But model predicts is different from we've confirmed.
There are alternatives.
The universe might be finite and wrap around on itself like the surface of a sphere in three dimensions.
In that case, the universe would be finite in volume and configurations wouldn't necessarily repeat.
But here's the honest state of the evidence.
The current data is fully consistent with an infinite universe.
The flatness measurement doesn't give us a lower bound of 250 times the observable universe because we know it wraps around at 251 times.
It gives us 250 as a minimum because we can't detect any curvature at the precision we've measured.
If the universe had significant curvature, we'd have seen signs of it.
We haven't. The simplest interpretation is that it's flat and therefore infinite or very nearly so. There's a philosophical principle in science called parimony, sometimes called Okam's razor. It says that among competing hypotheses that explain the same data, prefer the one that requires the fewest assumptions.
Applied here, a finite universe that happens to appear flat at every scale we can measure requires us to assume it happens to be very large but not infinite.
That very large but just this side of infinite is an awkward place to stop. An infinite universe by contrast requires no such special assumption.
The mathematics just runs to completion.
Parsimony favors the infinite.
If we accept the infinite universe picture, which is the standard cosmological model's default assumption, the level one multiverse is not a fringe idea. It's a direct consequence of mainstream cosmology.
And this is what makes the claim about infinite copies of you more than a philosophical curiosity.
It follows from things that serious cosmologists take seriously.
But the level one multiverse is just the beginning. Let's now move to a different physical mechanism that produces multiple universes. One that's somewhat more speculative but also more dramatic.
This is the idea that comes from inflation.
Inflation is the theory that in the very first moments after the big bang, perhaps starting at around 10 to the - 36 seconds, the universe underwent a period of extraordinarily rapid exponential expansion.
In an interval of time so short that writing it in decimal form would require a 1 after 35 zeros following a decimal point. the universe expanded by a factor of at least 10^ the 26.
Imagine a grain of rice.
If that grain of rice expanded by the same factor during inflation, it would become an object larger than the observable universe today.
The entire observable universe was before inflation smaller than a single proton.
Why do cosmologists think this happened?
Because without it, several features of the observable universe are deeply puzzling.
The cosmic microwave background is nearly perfectly uniform in every direction.
Regions of the sky so far apart that light couldn't have traveled between them in the entire age of the universe are at essentially the same temperature.
Without inflation, there's no mechanism for those regions to have equalized their temperatures. They were never in contact. Inflation solves this by saying they were in contact before inflation when the entire observable universe was compressed into a tiny region.
The uniformity is a relic of that pre-inflation contact. We have good evidence that inflation happened. Not proof but strong evidence. The cosmic microwave background shows specific patterns of temperature variation.
specific statistical signatures that inflationary models predicted and that have been confirmed with precision.
The Planck satellite mapped those signatures in detail. The match between inflation's predictions and what plank found is one of the more striking examples of a theoretical prediction being confirmed by observation in modern cosmology.
There's also the flatness problem. We've already noted that space is very flat.
Without inflation, this flatness requires the early universe to have been flat to extraordinary precision. One part in 10^ the 60 or more.
That level of initial flatness requires an explanation. Inflation provides one.
Whatever curvature the pre-inflationary universe had was stretched smooth by the rapid expansion. The same way the wrinkles on a balloon disappear as you inflate it.
But here's what happens when you think carefully about how inflation ends.
The field that drives inflation, the inflatant field, doesn't stop everywhere simultaneously.
Quantum fluctuations in the field cause it to end in some regions while continuing in others.
The regions where it ends become normal expanding universes like ours. The regions where it continues keep inflating and they inflate so fast that the volume grows faster than the regions converting to normal universes.
Inflation as a whole never ends. Locally it stops but globally it continues forever. This is called eternal inflation and it was proposed by Andre Linda at Stanford and Alan Guth at MIT in the 1980s refined over subsequent decades.
In eternal inflation, the universe as a whole is always inflating always seeding new pocket universes where inflation happens to end.
The result is an enormous constantly growing collection of pocket universes.
Each one beginning with a big bang-like event when inflation ends locally. Each potentially having different physical properties.
The picture is something like foam. The inflating background is the liquid. The pocket universes are bubbles forming in the liquid. But unlike ordinary foam where the bubbles can touch and merge, the inflating regions between pocket universes expand faster than the bubbles can approach each other. Each pocket universe is forever isolated from every other. They can never communicate, never exchange information, never interact in any way. Each bubble is causally sealed. Our universe in this picture is one bubble.
It began 13.8 billion years ago when inflation ended in our particular region. The big bang in this picture was not the beginning of everything.
It was the beginning of our bubble.
Beyond the inflating regions surrounding our bubble, other bubbles formed before and after ours. Some are probably still forming right now. We'll never see them.
We'll never detect them directly. But the physics of inflation, if correct, implies they're there. Why different physical properties?
Because the specific physical constants in each pocket universe depend on how the inflaten field settles when inflation ends. String theory, which is one of the leading attempts at a unified framework for physics, suggests that there might be around 10 to the 500 different stable configurations the inflatin field can settle into.
Each configuration corresponds to different values for fundamental constants, different strengths of gravity, different masses for electrons, different coupling constants for the nuclear forces.
10^ the 500 is not 500, it's a one followed by 500 zeros.
To put that in perspective, the number of atoms in the observable universe is roughly 10 to the 80.
The number of distinct stable configurations in string theory's landscape exceeds the number of atoms in the observable universe by a factor of 10 to the 420.
If each atom in the observable universe were a universe and each of those universes contained as many universes as there are atoms in ours, you'd still be nowhere near 10 to the 500.
It's a number that defeats all human intuition about large.
The string theory landscape is not just big. It's big in a way that makes big feel like the wrong word entirely.
In this picture, the level two multiverse, each pocket universe is a separate causally disconnected bubble, completely inaccessible to any other bubble.
The inflating regions between bubbles expand faster than light can cross them.
There's no way for information, matter, or signals of any kind to travel from one bubble universe to another. We can't see them. We can't reach them. We can only reason about them from the physics of inflation and string theory. And in this multiverse, copies of you exist not just in distant regions of the same universe, but in other universes entirely.
Universes with the same physical laws as ours, which would be required for the chemistry of life to work contain the same potential for complex organized matter.
In an infinite collection of universes, some fraction of them will have constants compatible with life. Some fraction of those will develop complex organisms.
Some fraction of those will have organisms that purely by the enormously large number of evolutionary pathways available arrive at configurations virtually identical to you. This is uncomfortable territory. Not because it's scary because it strains the concept of identity.
What does it mean to be you? If there are infinite other beings who are atom byat atom copies of you, who have your memories, who think your thoughts, who in every measurable physical way are you? We'll come back to this, but first let's talk about the third mechanism for infinite copies. The one that comes not from the large scale structure of the universe but from the smallest scale we know. Quantum mechanics.
Quantum mechanics is the most precisely tested theory in the history of science.
Its predictions match experimental results to better than one part in a billion. In some cases, the anomalous magnetic moment of the electron, a subtle quantum property, matches the theoretical prediction, to about 12 decimal places.
That's equivalent to predicting the distance from London to New York to within the width of a human hair. No other theory in any field of science has been verified to this degree of precision. Quantum mechanics works perfectly.
And at the heart of it sits something deeply strange.
Before you measure a quantum system, the system doesn't have definite properties.
Not just unknown properties, genuinely undefined ones.
An electron before you measure its spin isn't secretly spinning up or secretly spinning down.
It's in a superp position, a quantum state that contains both possibilities.
Simultaneously when you make the measurement you get a definite result either up or down. But what happened to the other possibility?
This question simple as it sounds is one of the most contested in physics.
It's been debated since quantum mechanics was formalized in the 1920s and it's still not settled.
Different physicists give different answers with complete conviction. The debate isn't because the question is unimportant.
It's because the answer has consequences for what we think reality is.
The founders of quantum mechanics disagreed sharply about this. Neil's Bor's Copenhagen interpretation which became the standard view taught in textbooks essentially says don't ask the wave function the mathematical object that describes the quantum state gives you probabilities when you measure you get one outcome with the appropriate probability the other possibilities vanish they were never real just probability amplitudes that collapsed on measurements Bore was deeply serious about this. He wasn't being evasive.
He genuinely believed that quantum mechanics was not describing a reality that existed independently of observation.
It was describing the relationship between physical systems and the observations we make of them. Reality in Bor's view is not something that exists prior to observation.
It comes into being through the act of measurement.
Einstein disagreed with Boore profoundly.
He believed that there was a physical reality independent of observation and that quantum mechanics was therefore incomplete.
It gave the right predictions but didn't tell the full story. His phrase, God does not play dice, was an expression of this conviction.
He thought the apparent randomness of quantum mechanics reflected our ignorance of some deeper deterministic theory, not genuine fundamental randomness.
The problem with the Copenhagen interpretation isn't that it's wrong about the predictions. It gets the predictions right. The problem is that it's philosophically incomplete.
It doesn't explain what counts as a measurement. It doesn't explain why the quantum realm is different from the classical realm. It doesn't say at what scale superp position stops and definite classical reality begins. It just says trust the math and don't ask too many questions.
That works for doing calculations.
It doesn't work for understanding what's actually happening.
In 1957, a Princeton graduate student named Hugh Everett III proposed a different answer. He called it the relative state formulation.
We now call it the many worlds interpretation.
And it's one of the most discussed, most debated ideas in the foundations of physics. Everett's idea was simple in principle.
When you measure an electron's spin and get up, what if the wave function doesn't collapse? What if all the possibilities continue to exist? What if the universe itself branches?
In one branch, the electron was measured as up. In another branch, it was measured as down. Both branches are equally real. Both contain observers who made the measurement and got a definite result. Both continue to evolve.
Neither knows about the other. This interpretation removes the collapse postulate from quantum mechanics entirely.
It keeps only the Schroinger equation, the equation that describes how quantum states evolve and takes it completely seriously.
The Schroinger equation is a wave equation. It describes how quantum amplitudes spread and interfere. The equation is perfectly deterministic.
It never says anything about collapse.
Collapse was always an addition. A patch applied to make the math give definite results consistent with our experience of definite outcomes. Everett said, "What if we don't need the patch? What if the equation is telling us something true and our experience of definite outcomes is what we'd expect from inside one branch of a larger quantum reality?
The mathematical consequence of taking the Schroinger equation literally without collapse is that every quantum measurement causes the universe to split into branches.
Every radioactive decay that either happens or doesn't, every photon that either reflects or transmits, every quantum event with multiple possible outcomes, creates new branches of reality, not metaphorical branches, physical branches, equally real branches of the universal wave function, each containing a version of every observer who is present for the event.
Now let's think about how many quantum events happen per second. This is where the scale becomes genuinely difficult to hold in your head. In 1 cm of air at normal conditions, there are roughly 27 billion billion molecules.
That's 2.7 * 10^ the 19 molecules in a space about the size of a sugar cube.
Each molecule is constantly vibrating, rotating, colliding.
Each collision involves quantum mechanical processes.
Each quantum process has multiple possible outcomes. The number of quantum branchings happening in a single sugar cube of air per second is estimated in the range of 10 to the 50 or larger. The sugar cube on your kitchen counter is branching the universe roughly 10 the 50 times every second.
If each branching produced a sound and each sound were a musical note, the sugar cube would be producing a symphony with more notes per second than the number of atoms in the entire solar system.
Your body is roughly 10,000 sugar cubes in volume. the Earth's atmosphere, the oceans, the solid rock of the planet, every atom in everything that exists.
The total number of quantum branchings happening in the universe per second is so large that no human analogy captures it. But every single one of those branchings creates a new version of reality, a new branch of the wave function, a new world. And in many of those branches, you exist in a slightly different state with a slightly different history, having experienced a slightly different moment because quantum events propagate upward.
The specific quantum fluctuations in the neurons firing right now as you process this information are quantum events.
They have multiple possible outcomes in the many worlds picture. You reading this are branching constantly.
This is the level three multiverse. Not separate regions of space. Not separate bubble universes.
Separate branches of the same quantum wave function. All coexisting.
All real in the physical sense that the mathematics describes them. none accessible to any other. The branching is irreversible in practice.
Once two branches have diverged enough, the interference effects that would allow them to reconnect become effectively impossible.
The branches decoheree.
They become causally isolated from each other. From within any branch, the other branches are not detectable. Not because they're hidden, because the physics of decoherence prevents the quantum correlations from being observed.
Decoherence is a real experimentally confirmed process, not just a theoretical patch.
When a quantum system interacts with a large environment, the quantum superposition spreads out into the environment.
The coherence between the different branches, the quantum interference that would allow you to observe superposition gets dissipated into the enormous complexity of the environment.
Think of it like sound in a large room.
A clear tone can maintain coherence, interfering constructively and destructively.
But add millions of reflecting surfaces and the sound becomes noise.
The coherence is lost to complexity.
Quantum decoherence works the same way.
The quantum superposition becomes noise in the environment irretrievably spread across so many degrees of freedom that recovering the original coherence is effectively impossible.
For microscopic systems in careful laboratory conditions, decoherence can be delayed. A single atom can be kept in superp position long enough to measure.
A small number of carefully isolated quantum bits can be kept coherent long enough to compute. But for macroscopic objects like cats and humans and planets, decoherence happens effectively instantaneously, far faster than any measurement could detect.
The time scale for decoherence of a macroscopic object like a grain of sand is something like 10 the minus 23 seconds shorter than the time light takes to cross a proton.
This is why you don't walk around feeling like you're in a super position.
Decoherence has already happened.
Your experience, your definite single valued experience of reality is the experience of a single branch. The branches that split off are no less real from the perspective of the physics, but they're causally disconnected from yours.
And within your branch, everything looks classical. Everything looks like there's one definite outcome. Because from within a branch, there is.
Now, let's slow down and address the obvious objection. How do we know Many Worlds is right? The honest answer is we don't with certainty.
Many worlds is a serious scientific hypothesis, but it's not the only interpretation of quantum mechanics.
The Copenhagen interpretation, as we mentioned, is still widely used.
There also pilot wave theories where particles have definite positions guided by an additional wave.
There are objective collapse theories where physical wave function collapse is a real process with a specific mechanism and there are relational interpretations where quantum states are always relative to an observer.
None of these interpretations changes the predictions of quantum mechanics.
They all give the same experimental results.
That's part of why the debate has continued for nearly a century without resolution. The interpretations differ in their metaphysics, in what they claim is real, not in what they predict we'll observe.
You can't currently design an experiment that discriminates between them because they're designed to agree on what we observe.
This situation is unusual in science.
Normally competing theories make different predictions and experiments decide between them.
The history of physics is full of these decisive moments.
Einstein's general relativity predicting the bending of starlight confirmed during the 1919 solar eclipse.
The Higs boson predicted by the standard model finally detected at the Large Hadron Collider in 2012.
In these cases, theory went ahead of experiment, made a specific prediction, and the experiment answered.
With quantum interpretations, the theories are constructed to make identical predictions. The experiment can't answer. The question sits in a different category.
What makes many worlds scientifically attractive is that it uses fewer assumptions.
It takes the Schroinger equation at face value. It doesn't add a collapse mechanism. It doesn't add hidden variables.
It doesn't introduce a special role for observers.
It's minimal in the sense of requiring no additions to the standard mathematical framework.
What it gives up is intuitiveness.
Accepting that the universe branches with every quantum event requires accepting a picture of reality that's very far from everyday experience.
Some physicists find many worlds completely compelling.
David Deutsch at Oxford who is one of the founders of quantum computing is a committed many worlder. Max Tegmark at MIT accepts it as the most natural interpretation.
Shan Carol at Johns Hopkins has written an entire book arguing for it. Other physicists, including many excellent ones, find it metaphysically extravagant and prefer alternatives.
The debate is genuine and ongoing.
A survey of physicists at a major conference found about 18% supported many worlds while about 42% supported some version of Copenhagen and the rest were distributed among other interpretations or agnostic not a majority for many worlds but not a fringe.
What we can say with confidence is this.
If Many Worlds is correct, the number of versions of you is not just very large.
It's incomprehensibly large, growing every fraction of every second, branching in ways that range from imperceptibly different to radically different. And every branch is occupied by a version of you who is convinced they're the only one. Let's now think about what these copies actually experience.
Because this is the part that makes the mathematics feel real. Imagine a quantum event in your brain. Not metaphorically.
Actually, neurons fire through the activity of ion channels. Ion channels open when specific molecules bind to specific receptors.
Those binding events are influenced by the exact positions and velocities of molecules.
Those positions and velocities at the relevant scales are subject to quantum uncertainty.
The exact moment a neurotransmitter binds to a receptor. The exact confirmation a protein takes when it folds. The exact location an ion finds itself when a channel opens. These are quantum events. They have multiple possible outcomes.
Some neuroscientists argue that the brain is too warm and wet for quantum effects to play a meaningful role in neural processing. Quantum coherence, they argue, is destroyed by thermal noise long before it can influence anything as large as a thought or a decision.
Roger Penrose and Stuart Hamarof have proposed a specific mechanism by which quantum effects in microtubules inside neurons might influence neural processing. Their orchestrated objective reduction hypothesis.
Most neuroscientists remain skeptical of this specific proposal, but the broader question of whether quantum effects play any role in cognition remains genuinely unsettled.
Even if quantum effects don't directly influence highle cognition, they don't need to for the many worlds argument to produce copies of you.
Quantum events at the molecular level in your brain are happening regardless.
In the many worlds picture, each one branches the universe. Even if the branching at the molecular level doesn't change your behavior, it produces a slightly different physical configuration.
and slightly different physical configurations accumulated over time can produce macroscopically different outcomes.
In the many worlds picture, each of those outcomes actually occurs in different branches.
So consider a decision you made today.
Anything. What time you woke up, what you had for breakfast, whether you responded to a specific message.
Each of those decisions was influenced by a neural process.
And each neural process was influenced by quantum events at some level of its physics.
In the vast majority of branches, you made the same choice you made here because quantum randomness mostly averages out at the scale of behavior.
But in some small fraction of branches, the fluctuations added up differently.
and you made a different choice. Those branches continue. The you in that branch has different subsequent experiences, makes different subsequent choices. Over time, the branches diverge. The you in each branch doesn't remember the other branches because decoherence has already made them inaccessible.
Each version of you experiences a single continuous internally consistent life.
Each version is convinced they're the original. None of them is wrong. Within their branch, they are the original.
Now, let's think about what this means for the question of identity.
Because this is where the philosophy gets genuinely difficult.
In everyday terms, you're you. You have a continuous memory that connects your current self to your past self. You have a body that persists through time with gradual replacement of cells but maintained continuity of structure. You have a sense of being a single unified subject of experience.
This is what we normally mean by personal identity and we normally take it for granted. The question of whether you're the same person you were 10 years ago feels almost silly. Of course you are. You remember being that person, but philosophers have long noticed that personal identity is more complicated than it first appears. Your cells are replaced almost entirely every 7 to 10 years.
The atoms making up your body right now are largely not the atoms that made up your body a decade ago.
If you're not the same atoms, what makes you the same person?
The continuity of pattern, most people answer. The arrangement persists even as the material changes like a wave that's the same wave even though it's made of different water at different moments.
But in the multiverse picture, which version is really you? The one sitting here? All the ones that share your past up to this exact moment and then diverge. The infinite copies in distant regions of the level one multiverse who have the same history up to some point and then different futures. The quantum branches that split off yesterday, the day before, a year ago. There's no obvious answer. And philosophers have struggled with this seriously.
The philosopher David Lewis developed what's called counterpart theory where each person in each possible world is a distinct individual. A counterpart but not strictly identical to the versions in other worlds.
When you ask what would have happened if I'd made a different choice, Lewis says you're not asking about yourself in another world. You're asking about your counterpart, a distinct person who resembles you closely but is not numerically identical to you. Derek Parit in his book Reasons and Persons pushed even further.
He argued through careful thought experiments involving vision cases where a person splits into two that personal identity is less important than we normally think. What matters, Parit argued, is psychological continuity, the persistence of memories, personality, and beliefs. And cases of fish and multiplication don't threaten any deep facts about persons because there are no deep facts about personal identity to threaten.
Identity in Parettit's view is not a deep metaphysical fact about the universe. It's a useful concept we employ when the usual conditions of continuity are met and an indeterminate one when they're not.
The discomfort with these ideas comes from an assumption we usually don't examine. The assumption that there's exactly one of us, that our uniqueness is guaranteed by some feature of the universe. The many worlds picture and the level one multiverse both challenge that assumption directly. We're not necessarily unique. We might be one occurrence of a particular physical pattern and physical patterns in the right conditions recur.
This is either deeply disconcerting or oddly liberating depending on how you hold it.
Some people find it disturbing to think that their decisions might be made differently by copies of themselves elsewhere.
Some find it comforting that no matter what choice they make, some version of them makes the other choice. Some find it philosophically clarifying to realize that the uniqueness they felt was always somewhat illusory. How you respond to it says something about your prior intuitions about selfhood. Let's now talk about a version of the infinite copies argument that's even more fundamental.
One that goes deeper than space or quantum mechanics.
This is the level four multiverse that Tegmark describes. And it's the strangest one. The level four multiverse is based on the observation that the laws of physics are mathematical.
Not just described by mathematics, actually mathematical in their structure.
The electron has a specific mass because of its specific place in the mathematical structure of the standard model.
The gravitational constant has the value it has because of the mathematical relationships in general relativity.
Every fundamental fact about physics traces back to mathematical relationships. This observation is not new.
The physicist Eugene Wakner wrote a famous paper in 1960 called the unreasonable effectiveness of mathematics in the natural sciences, noting that mathematical structures invented for purely abstract reasons with no physical application in mind repeatedly turned out to describe physical reality with extraordinary precision.
Non- uklitian geometry developed as a mathematical curiosity in the 19th century turned out to be exactly the right framework for Einstein's general relativity.
Complex numbers involving the square root of negative 1 which seem to have no physical reference are essential for quantum mechanics. Group theory, an abstract study of symmetry, describes the behavior of fundamental particles almost perfectly. The unreasonable effectiveness is a real phenomenon. And Tegmark's proposal is one way of explaining it. Tegmark's proposal is that all mathematically consistent structures exist, not just physically, exist in the same sense that our universe exists.
If a mathematical structure is self-consistent, if it doesn't contain contradictions, then there's no mathematical reason to think it's less real than ours.
Our universe is one mathematical structure among all possible ones.
We find ourselves in it not because it was specially created, but because beings like us can only exist in mathematical structures that permit complex, organized matter.
In this picture, there are universes with completely different laws of physics, not just different constants, different equations, different types of space, different numbers of dimensions, different fundamental symmetries. Some of those universes might support complexity.
Some might support something like life.
Some might support something like us in a very different physical substrate. The level four multiverse includes the level two and level one multiverses as subsets.
It's the most expansive claim and it's the most speculative.
The idea that mathematical existence implies physical existence is a philosophical claim, not a straightforwardly scientific one. But Tegmark argues it's actually more parimonious than assuming only one specific mathematical structure exists, which requires an explanation for why this one rather than any other.
Why should reality be limited to the mathematical structures we happen to find ourselves in? What principle would do the limiting? Tegmark argues there's no good answer and that the more natural position is that all consistent structures are equally real.
Whether you find this compelling or not depends partly on your philosophy of mathematics.
Plonists who believe mathematical objects exist independently of any physical instantiation might find it natural. Anti-realists who think mathematics is a human construction would find it question begging.
Most physicists who engage with it find it interesting and possibly insightful but hard to evaluate empirically.
Let's come back to something more grounded. Let's talk about what if anything distinguishes you from your copies.
This is a question that most discussions of the multiverse skip over too quickly.
In the level one multiverse, the copies are far enough away that they're causally isolated. They can never interact with you. From a physical standpoint, each copy is a separate physical system. But from a mathematical standpoint, they're essentially identical configurations of matter. If you care about the physical facts, you're the same as your copies. If you care about causal relationships, you're distinct because you're causally connected to different future events.
The U here is connected to what happens in this region going forward. The copy is connected to what happens in their region. The futures diverge. The pasts up to some point were identical. Think of it like two books printed from the same file. Every word on every page is identical, but each book has a separate physical existence.
It sits in a different location. It experiences different handling. Some pages might get dogeared differently.
Over time, the two books diverge physically even though they started identically.
You and your level one copy started identically and are already diverging because quantum events in your respective regions are already different. In the many worlds interpretation, the copies are branches of the same wave function. They share a past. The version of you in each branch has the same memories up to the branching event. After the branch, they diverge.
The divergence might be small and slow.
Most quantum branchings don't immediately produce macroscopically different worlds.
The quantum fluctuations in an individual neurons firing might not change what you have for dinner tonight.
But over enough time with enough branches diverging, the space of possible worlds includes radically different versions of your life.
There are versions of you where a quantum fluctuation in your brain at the right moment led to a slightly different choice last year which led to a chain of different interactions which compounded over months into a substantially different life trajectory.
In some branches far separated from this one. The differences are enormous. a different career, a different relationship, a different city, different children, different everything.
And in each of those branches, the version of you who lives that life has no memory of the alternatives, has no sense of being an alternative, is fully committed to the reality of their own experience.
This has a strange implication for regret.
Most people carry regrets about choices they didn't make, the path not taken, the opportunity not pursued, the relationship not started or not ended.
In the many worlds picture, those paths were taken by other versions of you.
Right now, in other branches, those versions are living those lives.
The path not taken here was taken there.
Whether this should affect how you feel about your own choices is genuinely unclear, but it changes the metaphysical status of regret.
What you're regretting is not that the other option doesn't exist anywhere. It exists in other branches. What you're regretting is that you here in this branch didn't take it.
Let's think about what this implies for the way you make decisions.
In a deterministic universe, without quantum mechanics, your choices would be predetermined.
The initial state of the universe plus the laws of physics would in principle determine every future state, including your every action. Free will in the traditional libertarian sense of being the uncaused first cause of your own choices would be elucery. This was Einstein's view of reality and it was deeply uncomfortable for him. Quantum mechanics introduces genuine randomness.
If many worlds is correct, that randomness plays out by the universe branching. When a quantum event in your brain could go either way, it goes both ways. In one branch, you chose left. In another, you chose right. But that's not quite what we mean by free will, either.
The branching is random. You didn't control which branch you ended up in.
The version of you that went left didn't choose to go left over right. It just found itself on the left branch. What this might actually tell us is that the traditional question of free will versus determinism is posed in a framework that doesn't fit the physics. The universe isn't deterministic, but it also isn't randomly undetermined. It's both.
The wave function evolves deterministically according to the Schroinger equation.
But which branch you subjectively experience is not determined by any prior cause. The meaning of this for human agency is still being worked out by philosophers who take the physics seriously.
But it suggests that the question did I really have a choice might have a genuinely complex answer.
Yes, in the sense that you were in a physical state that permitted multiple outcomes. No, in the sense that you didn't control which outcome you experienced.
Both in the sense that all outcomes occurred and all versions of you made all choices.
There's a perspective called compatibilism in philosophy that argues free will and determinism are compatible. that free will means something like acting from your own desires and reasons without external compulsion rather than being the uncaused cause of your actions.
In many worlds, a version of compatibilism might work. Within any branch, you act from reasons. Your choices reflect your values, your preferences, your deliberative process.
The fact that other branches exist with different outcomes doesn't undermine the fact that in this branch you deliberated and chose the choice was yours in the sense that it expressed who you are in this branch even if other branches have other versions of you expressing differently.
Now let's talk about something that complicates the infinite copy story. The question of consciousness.
Everything we've discussed so far treats you as a physical configuration of matter. A particular arrangement of atoms.
And in some sense, that's right. Your body, your brain, your entire physical state can be described in physical terms. And physical configurations.
In the right circumstances recur, but most people feel like there's something more to them than a physical configuration.
There's the experience of being them, the felt quality of their thoughts, the redness of red, the painfulness of pain, the sense that there is something it is like to be them. Philosophers call this phenomenal consciousness.
And it raises a question. Even if there's an exact physical copy of you somewhere in the level one multiverse, does that copy have your experience?
We don't know.
This is the hard problem of consciousness posed explicitly by the philosopher David Charmer's in the 1990s.
We don't have a physical theory that explains why specific physical processes give rise to specific experiences.
We know that certain brain states correlate with certain experiences.
Damage to the visual cortex impairs vision.
Stimulating certain brain regions produces specific sensations.
But the correlation between physical process and experience doesn't explain why there's experience at all.
Why isn't it all just information processing in the dark without any inner light? If experience is fully determined by physical configuration, then a physical copy of you would have exactly your experience, not just your memories, your felt inner life. If experience is somehow additional to physical configuration, then a physical copy might be a philosophical zombie behaving exactly like you, making the same claims about having experiences without actually having any inner life.
We don't have the tools to determine which of these is true. There are multiple philosophical positions on this. Physicalists hold that consciousness is fully determined by physical processes.
Exact physical copy means exact experiential copy. Dualists hold that mind and matter are fundamentally different kinds of thing and that physical facts don't fully determine mental facts.
Pans psychists hold that consciousness is a fundamental feature of reality present in some form even in simple physical systems and that complex consciousness in humans is built from simpler forms in the components.
and eliminativists hold that our folk psychological concepts of experience and consciousness are confused and that a properly scientific understanding would replace them with something else entirely.
The hard problem means we can't be certain that the infinite physical copies of you are also infinite experiential copies.
The physical argument for copies is solid, assuming the premise of an infinite universe.
The experiential argument requires a theory of consciousness we don't have.
This is not a reason to dismiss the physical argument.
The infinite copies are real in the physical sense regardless of what happens with consciousness.
But it is a reason to be careful about what you conclude.
The claim that infinite versions of you are having experiences right now, that infinite versions of you exist in a subjectively felt sense, requires the additional premise that physical configuration determines experience, which might be true, but is not proven.
Let's now address something practical.
What difference does it make? If you can never interact with your copies, if they're causally disconnected from you, if you'll never experience being them or being connected to them, then in what sense does it matter that they exist?
This is a fair question and different philosophers give different answers.
One answer is that it matters for epistemology, for how we think about probability and randomness.
In the many worlds picture, when you flip a coin, the universe branches. In one branch, the coin lands heads. In another, it lands tails. But both branches are real. So, what does it mean to say the probability of heads is 50%.
This is called the probability problem in many worlds, and it's a genuine technical issue that philosophers of physics are still working to resolve. If both outcomes occur, why should we talk about probabilities at all? The leading approach developed by David Deutsch and later refined by David Wallace argues that probability in many worlds is a rational preference structure.
A rational agent, not knowing which branch they'll find themselves in, should assign weights to outcomes based on the squared amplitudes of the wave function, which gives you the standard quantum probabilities.
This is the Bourne rule derived from decision theory rather than postulated as a fundamental axiom.
Another answer is that it matters for how we evaluate our lives.
If every choice you make is being made differently by copies of you in other branches, then in a sense, every possibility is being explored. No choice is the final word on who you are. The space of your possible lives is being fully explored somewhere. Whether this is comforting or disturbing probably depends on your temperament, but it's a different relationship to choice than the one most people operate with.
A third answer is that it matters for the foundations of physics.
If many worlds is correct, it resolves the measurement problem that has been a source of confusion in quantum mechanics since the beginning. It explains what happens during a quantum measurement without invoking collapse.
It makes quantum mechanics consistent with relativity in ways that collapse interpretations struggle with. If many worlds is actually the right picture of reality, that matters enormously for theoretical physics, even if it has no practical implications for daily life.
Let's now think about what a physicist would say about the most controversial version of this argument, the one about the level one multiverse.
Because some physicists find this the least exotic and most straightforwardly implied by current cosmology, while others find it deeply uncomfortable. The discomfort comes partly from the scientific community's tradition of requiring observational verification.
The copies in the level one multiverse are by definition beyond our observational horizon. We can never see them. We can never interact with them.
We can never collect data about them.
From one perspective, this makes the claim unfalsifiable.
And unfalsifiable claims make many scientists uncomfortable because unfalsifiability is often a sign that a claim has stepped outside the domain where science can help.
But this objection applies unevenly.
The alternative that the universe simply ends at the edge of our observable horizon also can't be tested. There's no observation we can make that would tell us space stops just beyond what we can see.
The hypothesis that space continues versus the hypothesis that it stops are equally unfalsifiable in their extremes.
The question is which picture is more natural which is more consistent with the physics we do understand which requires fewer arbitrary assumptions.
And on that score, the infinite universe wins. A finite universe that happens to end just beyond our observational horizon requires an explanation for why it ends there specifically.
An infinite universe requires no such explanation.
The copies in the level one multiverse are then not a new hypothesis.
They're an implication. You don't add them. You get them automatically if you accept the infinite universe, which is the simplest interpretation of the current data.
Now, let's take all three levels of the argument and think about what they collectively imply about uniqueness.
In the level one multiverse, every physically possible configuration of matter in an observable universe-sized volume occurs infinitely many times, including every version of your history, every version of your possible future.
You are not unique in the physical sense.
You're one occurrence of a configuration. In the level two multiverse, even our specific laws of physics are not unique.
Other bubble universes have different constants, different fields, different particles.
In those universes, entirely different forms of complexity might arise. We might be unique at the level of laws within our bubble, but not unique in the multiverse.
In the level three multiverse, every quantum possibility of your moment to moment experience plays out in some branch. You're not just one person.
You're a diverging tree of people, all sharing your past up to now. All branching in different directions from here. What's left that's unique?
Your specific causal history in this specific branch in this specific region of the level one multiverse.
The chain of causes that produced this particular version of you reading this particular moment, that chain is unique.
Even if the endpoint configuration has been repeated elsewhere, the path that led to it here is specific to here. And there's something in that specificity worth thinking about. Not as a constellation, as a fact. You are the result of a particular causal chain stretching back through the history of this specific region of spaceime. your great-grandparents lives, the specific quantum events in the synthesis of the specific gametes that became your parents, the specific immune responses that your ancestors had to specific diseases that allowed their survival.
The specific stellar evolution of the star that went supernova several billion years ago and scattered the iron that's in your blood.
the specific asteroid impact 66 million years ago that cleared the landscape for mammals to diversify.
All of that happened in this specific thread of history. In the other threads, even the ones with someone physically identical to you, that causal history is different. The historian in each of us, the part that cares about where things came from, can find something genuinely unique here. Even if the physicist finds the endpoint configuration duplicated, the journey to this configuration is in the observable universe unreped.
Let's now look at some of the numbers more carefully because getting a feel for the scales involved changes how you hold the idea. The number of distinct quantum states for a system the size of the observable universe is estimated at 10^ the 10 to the 1 22.
This is the beckonstein bound applied to the observable universe based on its entropy. The beckenstein bound was developed by physicist Jacob Beckinstein in the 1970s.
It relates the maximum information content of a physical region to the surface area of that region.
Specifically, the number of plank areas each about 2.6 * 10 to the -70 m that fit on the boundary of the region.
The observable universe has a surface area of roughly 10 to the 122 plank areas giving a maximum information content of about 10 to the 122 bits.
This means the total number of distinguishably different states the observable universe can occupy is at most 2 to the^ of 10 to the 122 which is roughly 10^ the 10 to the 122.
And in an infinite universe, every one of those states occurs, not once, infinitely, many times with exact copies occurring at intervals of roughly 10^ the 10 to the 1 22 m.
Within the many worlds picture, the number of branches created per second is harder to count because it depends on how you count branchings.
Each particle interaction creates a branching event.
In the observable universe, which contains roughly 10 to the 80 particles, each interacting many times per second, the total branch count grows at a rate that dwarfs any number with a name.
But each branch is a real physical configuration of matter, evolving according to the same laws.
What's interesting about this is the relationship between the level one and level three multiverses.
Tegmark points out that they actually contain the same amount of information.
Any state you might find yourself in within the level three multiverse is also a state that exists somewhere in the level one multiverse.
The quantum branches and the distant spatial copies are different ways of talking about the same set of possible physical histories.
At a deep mathematical level, they might not be two separate multiverses, but two descriptions of the same multiverse.
The level three adds no new states.
It just describes the level one states differently from within. looking at the branching structure of your experience rather than from outside looking at the spatial distribution of configurations.
Now let's think about some specific scenarios because abstract discussion of infinite copies can remain strangely distant from your life. Let's bring it closer. Right now you're at a specific moment in your experience. Let's call it this moment. Across the level three multiverse, branches of reality that shared your history up to five minutes ago have already diverged. Some of those branches contain a version of you who decided 5 minutes ago to stop watching this video. That version exists in a real physical branch right now doing something else entirely.
They have the same memories as you do of everything before 5 minutes ago. They remember beginning this video. They just didn't continue. Right now in their branch, they're in a completely different moment. Maybe they made a cup of coffee. Maybe they picked up a book.
Maybe they fell asleep. Their version of right now is nothing like yours. And they don't know you exist. Other branches diverged a year ago. A version of you that took a different job. A version that moved to a different city.
A version that had a conversation with someone differently and changed a relationship.
These versions share your memory of everything before that branching point.
After it, they've been living different lives. Right now, in those branches, they're doing something completely different.
They're not thinking about this video.
They might not have even known it existed. They're in a different moment entirely. But they exist. According to many worlds, they're as real as you are.
And here's the part most people don't sit with long enough. Those other versions of you right now are having experiences.
They're thinking thoughts. They feel what they feel. They're as convinced of their reality as you are of yours. The version of you who walked away from this video 5 minutes ago is somewhere right now in a branch of the universal wave function fully experiencing their life with no awareness that they're a branch.
They think they're the main trunk just as you do. And in the level one multiverse somewhere far beyond our observable horizon there is a region of space that has produced through 13.8 8 billion years of the same physics operating on the same initial conditions. A configuration of matter that is you with your exact neural state, your exact memories reading this exact script at this exact moment.
That version of you in that distant region is having an experience that in its physical details is identical to yours. What they'll do next might differ.
Quantum branching in their region has already separated their future from yours. But right now, in this moment, the physical state of their brain matches the physical state of yours.
Is that other one you? They'd say yes.
You'd say you're you and they're a copy.
There's no physical fact that decides between these answers. From outside both systems, they're both occurrences of the same configuration. from inside each is the original. The question of which one is really, you might not have an answer.
Not because we don't have enough information because the question assumes a uniqueness that the physics doesn't support.
Let's now talk about whether any of this could ever be tested. Because if it can't, we need to be honest about its status. The level one multiverse in principle could become detectable if the universe is large but finite and wraps around on itself. In that case, you might see the same patterns in the cosmic microwave background repeated in different parts of the sky as if you're looking at a room with mirrors on opposite walls.
Cosmologists have searched for these patterns, correlations in the temperature maps that would indicate repetition.
So far, no detection. But the current data puts the minimum size of the wraparound scale larger than the observable universe. So, there's nothing to have detected yet, even if the universe does wrap around.
Future more precise measurements of the cosmic microwave background might tighten the constraints or find a signal.
The level two multiverse has one potential testable implication. Bubble collisions.
If our bubble universe and a neighboring bubble happen to collide early in their histories, the collision might leave a circular imprint in the cosmic microwave background.
Cosmologists have searched for such imprints.
Several groups have looked carefully at the plank data. No confirmed detection.
This doesn't rule out the level two multiverse, but it doesn't confirm it either. The collision might not have happened or might have left a signal too subtle for current instruments or might be located at a position on the sky we haven't fully analyzed.
The level three multiverse is in some ways the most robustly connected to testable physics.
Many worlds is a full interpretation of quantum mechanics, not an addition to it.
It makes all the same predictions as standard quantum mechanics which means all the evidence for quantum mechanics is indirect evidence for many worlds but also for all other interpretations.
Distinguishing them experimentally requires finding a situation where they make different predictions.
Some physicists have proposed scenarios where the interpretations differ, but these are very speculative and not yet experimentally accessible.
David Deutsch has argued that quantum computers are evidence for many worlds.
The computational power of quantum computers depends in his view on computations occurring across many branches simultaneously.
When a quantum computer solves a problem that would take longer than the age of the universe for a classical computer, it must be doing the computation across an exponentially large number of parallel configurations.
Where do those parallel computations happen if not in parallel branches?
Critics argue you can describe quantum computing without invoking branches.
But Deutsche's point is that many worlds provides the most natural and honest description of what's happening. If the branches aren't real, what is performing the parallel computation? So the honest status of all of this is well motivated, physically grounded, not confirmed, not falsified. better than speculation. Not as certain as we'd like, which is actually the normal state of frontier physics.
The history of physics is full of ideas that spent decades in the well- motivated but unconfirmed category before either being confirmed or being ruled out.
The expanding universe was in that category in the 1920s.
The existence of atoms was in that category at the end of the 19th century.
Black holes were in that category for decades before the first strong evidence for them arrived. We don't dismiss ideas because they're unconfirmed.
We hold them with appropriate uncertainty and keep refining.
Let's now think about the practical implications, if any, for how you live.
Most people when they really sit with the many worlds idea find that it doesn't change how they make decisions.
You still feel the weight of your choices. You still care about what you do. The fact that another branch of you does things differently doesn't relieve this branch of you of the responsibility for this branch's choices. From within any branch, the choice is real. The consequences are real. The relationships are real. Consider what it would mean to use the multiverse as a justification for bad behavior.
I didn't need to be honest because in some branch I was honest is not a coherent ethical position. In this branch you were dishonest.
The people in this branch were affected by that. The version of you that was honest in another branch had no effect on this branch's people.
The ethics of your actions are determined by this branch's consequences.
The multiverse doesn't provide an escape hatch.
Some people find the many worlds picture depressing.
If every possible version of your life exists somewhere, does your particular version matter?
If there's a branch where you've made every good choice possible and a branch where you've made every bad choice possible and everything in between, what's the significance of this particular trajectory?
But this framing might be backwards.
The question, does my life matter given infinite copies? Assumes that mattering requires uniqueness.
That might be wrong. You're the only one having your experience in this branch.
Your relationships here are with real people in this branch. Your choices affect real outcomes in this branch.
The infinity of other branches doesn't dilute any of that.
The fact that there's another version of you having another experience somewhere doesn't make this experience less real or less valuable. There's an analogy here that comes from something mundane.
When you learn that other people in the world have similar joys and sorrows to yours, does your joy become less valuable?
When you discover that millions of people love the same piece of music you love? Does the music become less meaningful to you personally?
Universality of a pattern doesn't negate the particular value of a specific instance.
Your copy in a distant region of the level one multiverse experiences what to them is a fullrich real life and so do you. Neither cancels the other. Let's now think about something that rarely comes up in popular accounts of the multiverse.
The relationship between infinite copies and the problem of finetuning.
The fine-tuning problem is one of the most discussed puzzles in modern physics.
The constants of nature, the strength of gravity, the mass of the electron, the cosmological constant, appear to be tuned to values that allow for complex structure to form. Small changes in those values, even tiny changes, would produce a universe with no atoms, no stars, no planets, no life.
The cosmological constant, the number that describes the energy density of empty space, is fine-tuned to within one part in 10^ the 120.
If that number were even slightly larger, the universe would have expanded so fast after the big bang that gravity could never pull matter into clumps. No galaxies, no stars, no anything.
If it was slightly negative, the universe would have collapsed back on itself billions of years ago. That's fine-tuning to one part in a number with 120 zeros.
For perspective, if the cosmological constant were the position of a randomly thrown dart on a dart board the size of the observable universe, hitting the life permitting range would be like the dart landing on a single atom.
That level of precision cries out for explanation.
Why should the constants have these specific values?
One answer is that they don't have to.
In a multiverse with different constants in different regions, the anthropic principle applies. We find ourselves in a region with life permitting constants because only such regions contain beings who ask why the constants are life permitting. It's a selection effect, not design, not coincidence selection. The level two multiverse with its 10 to the 500 possible configurations from the string theory landscape provides exactly the variety needed for this anthropic selection.
If every possible set of constants exists in some pocket universe, and most sets don't support life, and the ones that do are rare, then beings will only ever find themselves in the rare ones.
Not because those are the only ones, but because those are the only ones that contain beings to find themselves.
We didn't win the cosmic lottery. There was no lottery. Every ticket was drawn.
And we're standing in the region where the ticket said life. The infinite copies of you in the level one multiverse all exist in regions with the same fundamental constants as ours because they're in the same bubble universe, the same pocket of the level two multiverse where inflation ended with the same configuration.
The copies in other bubble universes, if any exist, would be in universes with different laws. They might not be copies of you at all. They might be copies of something that we wouldn't recognize as related to us in any way. Or they might be copies of nothing because the constants in their universe don't permit complex chemistry.
This connection between fine-tuning and the multiverse is one reason many physicists take multiverse ideas seriously, not as confirmed facts, but as a potential resolution of a genuine puzzle.
If there's no multiverse, you need another explanation for the finetuning.
You need either incredible coincidence or a designer or a deeper theory that predicts these constants as necessary.
The multiverse offers a fourth option, abundance. All constants exist.
We observe the ones that support us.
The mystery of finetuning becomes as explainable as the fact that we live on a planet in the habitable zone of a stable star.
There are lots of planets. We live on one with the right conditions. Of course, we do. We couldn't live on the others.
Now, let's bring this all together and think about what the three levels of multiverse mean for the particular question we started with.
Infinite versions of you.
In the level one multiverse, across the infinite spatial extent of the universe, there are infinite copies of you existing simultaneously right now in regions causally disconnected from ours.
Some are very similar to you. Some have slightly different histories.
Some have dramatically different histories. All are right now experiencing their lives as completely as you're experiencing yours.
In the level three multiverse, if many worlds is correct, you're currently branching constantly.
The you who exists in each branch shares your history.
The branches diverge going forward. Some future versions of you will have very different lives from the life this branch is heading toward. And all those future versions exist in the level two multiverse. Even the specific laws of physics that govern you might not be unique.
Other bubble universes with different constants might contain complex organized matter that experiences something though not something recognizable to us.
What does all of this say about you?
About the specific you that you are?
It says you're a physical pattern. a pattern that has arisen in this region of spacetime through this specific causal history in this specific branch.
The pattern is complex. The specific configuration of your brain right now, the exact state of every neuron, every protein, every ion channel is unreed in any known region of spaceime.
It's replicated in distant unknown regions but not nearby. It branched from other quantum states in the past and will branch into others in the future.
But right now in this branch, in this region, this specific configuration is having this specific experience.
And that experience, the experience of understanding these ideas, of feeling whatever reaction you feel to them, of sitting with the strangeness of the claim that you might be one of infinite copies, is something that only this version of you is having.
Other branches of you are having other thoughts. Other copies in distant space are having the same thoughts or very similar ones.
But this experience in this branch in this moment is specific to this version of you. That doesn't make it more or less valuable than the other versions, but it makes it real. As real as anything is, which according to the physics we've been discussing, might be very real indeed.
Let's think about the history of how this idea developed. Because it's worth knowing that these ideas didn't spring fully formed from one person's mind.
They emerged from people working on different problems, often surprised by where the physics led them. Hugh Everett III proposed the many worlds interpretation in 1957 in his Princeton PhD thesis. He was 27 years old. It was almost completely ignored for about a decade. John Wheeler, his thesis adviser and one of the most influential physicists of the 20th century, found it initially compelling, but then distanced himself from it under pressure from Boore. Neil's Boore, who ever met in Copenhagen in 1959, was reportedly dismissive. The meeting was apparently deeply discouraging. Everett left academic physics shortly afterward and never returned. He worked for the Department of Defense doing operations research building early nuclear targeting models. He died in 1982 at the age of 51 reportedly from health problems linked in part to heavy drinking and smoking.
He never saw his ideas receive serious scientific attention. The many worlds interpretation was revived in the 1970s by the physicist Bryce Dwit who gave it the name many worlds and published articles popularizing the idea. Dwit student Neil Graham worked on the interpretation.
Over the following decades, it attracted growing attention, partly because physicists working on quantum cosmology found the Copenhagen interpretation impossible to apply to the universe as a whole.
You can't have the wave function of the universe collapse because there's nothing outside the universe to perform a measurement.
Cosmologists needed an interpretation that worked without collapse. Everett provided one.
By the 1990s and 2000s, many worlds was being taken seriously by a significant minority of physicists. Not a majority, but serious people working on serious problems.
And the development of quantum computing has given it new attention because the computational power of quantum computers is most naturally explained as Deutsch argues in terms of parallel computations across branches.
Everett's ideas dismissed by the physics community during his lifetime are now part of a serious ongoing scientific discussion.
The level one and level two multiverse ideas have a parallel history.
The implications of an infinite universe for the existence of copies was noted by various physicists and philosophers over the decades, but were crystallized and systematized most clearly by Tegmark in a series of papers starting in the late 1990s and his 2014 book, Our Mathematical Universe.
The eternal inflation picture which underlies level two was developed by Linda and Guth in the 1980s. The string theory landscape which gives level two its variety of physical constants was worked out in the early 2000s by Raphael buso and Joseph Pchinski and others.
What's notable about this history is that none of these ideas were introduced to produce the infinite copies result.
Everett wasn't trying to say there are infinite copies of you. He was trying to solve the measurement problem in quantum mechanics.
Guth and Lindy weren't trying to produce a multiverse.
They were trying to explain the flatness and horizon problems in cosmology.
Tegmark wasn't making a metaphysical claim for its own sake. He was working out the implications of mainstream cosmological assumptions.
The infinite copies of you emerge as a consequence of trying to do physics carefully. They're not the premise.
They're what you get when you follow the physics. This is worth emphasizing.
The multiverse is not something anyone invented to be exotic. It keeps appearing as a byproduct of trying to understand things that don't have anything to do with parallel selves.
Inflation was proposed to explain the flatness of space.
The string landscape emerged from attempts to unify physics. Many worlds emerged from trying to make sense of quantum mechanics without contradictions.
The copies come along for the ride.
Let's close by thinking about what this all means for the most basic question you might have. Are you special? The answer depends on what you mean by special. If you mean unique in the sense of having no physical copies anywhere, the physics suggests probably not.
If you mean the only version of your exact configuration in the observable universe, then yes, almost certainly the probability of a configuration as complex as yours appearing twice within the observable universe is effectively zero.
You're unique in the observable universe with overwhelming certainty.
The copies are in regions so far beyond our horizon that they might as well be in a different universe.
For all practical purposes of our lives, they are. If you mean the only conscious being in the universe having your experience, then possibly, but we don't know enough about consciousness to say.
The hard problem of consciousness leaves that genuinely open. But here's what is straightforwardly true. You are the result of a causal chain extending back 13.8 billion years.
The specific chain of events that produced you, this version, in this branch, in this region, has never been exactly replicated in any region of spaceime we can observe.
The quantum history of your particular corner of the universe is unique in our observable patch. The distant copies of you exist on the physics, but they don't diminish you. They're more like the same song being sung in different rooms. The song in each room is fully the song. The fact that it's being sung elsewhere doesn't make it less the song in this room. And every performance is real. And there's one more thing worth noticing.
We've spent this video talking about the physics of infinite copies.
But here you are, a configuration of matter that has become curious about itself.
That's asking whether there are other versions of itself that's capable of holding a concept like infinite copies of me and examining it from multiple angles.
The physics doesn't make that less interesting.
It makes it more interesting.
The universe in this branch in this region has organized itself into something that can understand the physics of branching that can trace the implications of quantum mechanics to the conclusion that reality might be far larger and stranger than it appears.
That can read the consequences of an infinite universe and understand what they mean for personal identity.
that can sit with the strangeness and not collapse under it.
That can notice its own strangeness.
Whether there are infinite copies of you doing the same thing right now in other branches and other regions is something we can't confirm, but it's something the physics tells us is a real possibility.
And the fact that we can even frame the question clearly, can trace the arguments, can understand what would have to be true for the copies to exist is something. It's at least something.
The universe is 13.8 billion years old.
It spent most of that time as hydrogen and helium gas and then stars and then heavier elements scattered by supernovi.
And then about 4.6 6 billion years ago in this region a new star formed and a small rocky planet formed with it. And on that planet chemistry organized itself into something that could replicate.
And over billions of years that replicating chemistry became more and more complex.
And eventually it became something that could ask questions about the universe it found itself in. And tonight, a version of that something is sitting with the possibility that it exists in infinite copies across an infinite universe and finding that the universe is stranger and larger and more interesting for it. That's where we are.
Right at the edge of what the physics tells us and what we can fully understand in exactly the right place to keep going. What comes next? If this raised questions for you is the deeper physics underneath all of it. The next video goes into quantum decoherence specifically. How branches become causally isolated, what the actual mechanism is, and why some physicists think many worlds is the most natural way to interpret the math, while others think it's an elegant mistake. The physics of how one version of you becomes the only version you experience is the next step of this story.
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