Why Every Physicist Secretly Believes in Parallel Universes? | Truth By Lisa Randall

Added: 2026-05-09

[00:00:00]Scientists have mathematically proven there are infinite copies of you making every decision you never made. Hugh Ever III published this conclusion in his 1957 doctoral thesis at Princeton. And the physics community has never been able to disprove it, only quietly accept it, then look away and hope nobody asks too many questions. By the end of this video, you're going to understand three things that most people who call themselves science fans have never been told. First, you will understand why the mathematics of quantum mechanics does not merely suggest parallel universes.

[00:00:27]It demands them. Second, you will see why the most decorated physicists alive today privately believe in the many worlds interpretation but almost never say so in public and why that silence itself is one of the most revealing things in modern science. And third, you will understand something about your own existence, your own consciousness, your own sense of being a singular you that will be very difficult to unthink. Stay with me cuz the last part changes everything. I want you to do something right now. Look at your hand. Go ahead.

[00:00:54]Really look at it. It feels completely solid, completely real, completely certain. There is no ambiguity in it.

[00:01:01]You can feel its weight. You can feel the temperature of the air around it. It is without question one thing in one place at one time. Now, here is what quantum physics actually says about that hand. Every single atom inside it, every proton, every electron, every quark is made of particles that, according to the most tested and verified scientific theory in human history, do not have a fixed position until something measures them. Before measurement, they exist in what physicists call superposition. That is not a metaphor. That is not philosophy. Superposition means a particle is genuinely, mathematically, physically in multiple states simultaneously. It is not that we do not know which state it is in. It is that it has not chosen yet. Your hand feels like one thing. Quantum mechanics says the particles building it are smeared across a landscape of probabilities. So, here's the question that this entire video is built to answer. When you observe that particle, when the universe forces it to choose, where do all those other states actually go? Because if they simply vanish, then physics has a problem. And if they do not vanish, then you have a much bigger one. To understand why parallel universes are not science fiction, but scientific necessity, we need to go back to the beginning. Not the beginning of the universe, the beginning of the problem. It is 1925.

[00:02:10]Verer Heisenberg, a 23-year-old German physicist working in Guttingan, is trying to build a mathematical framework that explains why atoms behave so strangely. Classical physics, Newton's physics, the physics of billiard balls and planets and falling apples, works perfectly at the scale of everyday objects. But at the scale of the atom, it falls apart completely. Electrons do not orbit the nucleus like planets orbit a star. They appear in places they should not be able to reach. They seem to know when they are being watched.

[00:02:36]They refuse to obey the rules.

[00:02:38]Heisenberg's solution was matrix mechanics, a system of equations that described not the position of a particle, but the probability of finding it in any given position. The electron does not have a location. It has a probability cloud, a smear of likelihood, and the mathematics worked perfectly. Every experimental result matched. The predictions were extraordinary in their precision. Then Irvin Schroinger, who deeply disliked Heisenberg's approach and wanted something more intuitive, independently derived the same predictions using what he called wave mechanics. His famous equation, the Schroinger equation, describes how the quantum state of a particle evolves over time. And it is beautiful. It is smooth. It is deterministic. If you know the wave function at one moment, you can calculate it perfectly at any future moment. There is just one problem. The Schroinger equation never stops. It keeps evolving. It keeps branching. It describes a particle as existing in superposition indefinitely, all possible states simultaneously. And it has no mechanism, none whatsoever, for the particle to ever choose just one state.

[00:03:37]But particles do choose. We watch them choose. Every single experiment confirms it. You fire an electron at a detector screen and it lands in one spot. Not everywhere, one spot. The superp position collapses. The probability cloud vanishes. One outcome survives.

[00:03:52]This is called wave function collapse.

[00:03:54]And it is the single most contested, most debated, most philosophically explosive concept in all of modern physics. Because the Schroinger equation, the equation that describes everything perfectly up until the moment of measurement, simply does not contain it. Wave function collapse is not in the math, it has to be inserted by hand by assumption, by a rule that says when you observe a quantum system, the wave function collapses, one outcome is selected and the rest disappear. This set of assumptions is called the Copenhagen interpretation. It was assembled primarily by Neils Boore and Verer Heisenberg in the late 1920s and for nearly 30 years it was the only game in town. You wanted to do quantum mechanics. You accepted Copenhagen. You accepted that observation causes collapse. You accepted that the other outcomes simply cease to exist. You did not ask where they went. Bor's famous answer to that question was essentially do not ask. The job of physics is to predict measurement outcomes, not to describe what happens between measurements. Most physicists accepted this. They had to. The predictions were too good to argue with. But one person could not stop asking. His name was Hugh Everett III. He was a graduate student at Princeton in the mid 1950s and he had a question that would not leave him alone. The question was this. If the Schroinger equation is universally true and every experiment suggested it was, then why does it stop applying the moment we observe something? Who gave observation that power? What is so special about a human eye or a detector or a measuring device that it causes the laws of physics to suddenly switch modes? Everett thought this was incoherent. He thought the Copenhagen interpretation was not a physical explanation but a philosophical patch, a way of avoiding a difficult answer by simply refusing to look at it. So he looked at it. His proposal laid out in his 1957 doctoral thesis titled relative state formulation of quantum mechanics was radical in its simplicity. He said, "What if the Schroinger equation never stops? What if it applies universally always to everything, including the observer? What if wave function collapse is not something that actually happens, but something that appears to happen from inside one branch of a larger reality? Here is what that means in practice. You fire an electron at a detector. In standard quantum mechanics, the electron exists in superp position.

[00:05:58]It might go left, it might go right, and then when you observe it, it picks one and the other vanishes. In Everett's framework, the electron does not pick.

[00:06:06]The universe branches. In one branch, the electron goes left and you observe it going left. In another branch, the electron goes right and you observe it going right. Both branches are equally real. Both versions of you exist. The wave function never collapses. It simply becomes too large and complex for any single branch to perceive the others.

[00:06:23]This is the many worlds interpretation.

[00:06:25]And the crucial essential often misunderstood point is this. Everett did not add anything to quantum mechanics.

[00:06:30]He did not insert a new force, a new particle, a new equation. He simply took the Schroinger equation seriously, completely seriously, more seriously than anyone had before. The parallel universes are not an assumption. They are what the math produces when you refuse to add the extra assumption of collapse. The physics community's reaction was not kind. Boore dismissed it. The Copenhagen establishment ignored it. Everett's thesis was significantly reduced in length under pressure before publication, stripping out much of his original argument. He left academic physics shortly after, went to work in defense research, and reportedly drank heavily for the rest of his life. He died in 1982, largely unrecognized. But the idea did not die with him. In the decades that followed, a quiet revolution began. Physicists who were uncomfortable with Copenhagen who found the collapse postulate philosophically unsatisfying and physically unjustifiable began taking Everett seriously. Bryce Dowit, an American physicist, was one of the first to openly advocate for the many worlds interpretation in the 1960s and 1970s.

[00:07:27]He coined the term many worlds itself and argued that the branching was not metaphorical but literal. He wrote that every quantum transition taking place on every star in every galaxy in every remote corner of the universe is splitting our local world on earth into myriads of copies of itself. David Deutsch at Oxford went further in 1985.

[00:07:44]He published a paper arguing that the many worlds interpretation was not merely one possible interpretation but the only one consistent with quantum mechanics taken as a complete physical theory. He later argued that the existence of quantum computers which exploit superp position to perform calculations across what appears to be multiple simultaneous states is direct experimental evidence of parallel computation happening across parallel branches of reality. Max Tegmark at MIT conducted a survey of physicists at a major quantum foundations conference in 1997 and found that the many worlds interpretation was the most popular single interpretation among the attendees beating Copenhagen for the first time. He has since written extensively arguing that the multiverse is not a hypothesis but a prediction, a necessary consequence of applying quantum mechanics without arbitrary additional assumptions. Shan Carroll, a theoretical physicist at Johns Hopkins and one of the most publicly visible physicists in the world, published a full-length treatment in 2019 called something deeply hidden in which he argues not only that the many worlds interpretation is correct, but that it is obviously correct that the resistance to it is primarily psychological and sociological rather than scientific. And Steven Weinberg, Nobel laurate, one of the architects of the standard model of particle physics, one of the most decorated theoretical physicists of the 20th century, spent years examining the many worlds interpretation, looking for a flaw. He found the probability structure uncomfortable. He wrote about his discomfort honestly, but he could not find a way to eliminate it. In one of his final papers before his death in 2021, he wrote that he had reluctantly concluded there was no satisfactory alternative. So why don't physicists say this publicly? Why don't science communicators lead with it? Why does the many worlds interpretation still feel fringe when the people closest to the physics find it the most mathematically honest position? There are two reasons.

[00:09:23]The first is the probability problem. In Everett's framework, all branches happen, but we experience some outcomes as more likely than others. A radioactive atom has a 10% chance of decaying in the next second. In many worlds, both happen. It decays in one branch. It does not in another. But if both happen, why do we consistently experience the decay as rare rather than common? Everett's framework needs to explain why we find ourselves in branches with frequencies that match the Bourne rule, the quantum probability formula, rather than in branches where anything goes. This problem called the probability problem or the preferred basis problem has been worked on extensively by David Deutsch and David Wallace who argue it can be solved using decision theory. Not everyone agrees, but it is a technical problem, not a conceptual reputation. The second reason is simpler. It is deeply profoundly strange. Accepting many worlds means accepting that every quantum event, every radioactive decay, every photon absorption, every electron interaction splits the universe into branches. Given the number of quantum events happening every second across the observable universe, the number of branches is not merely large. It is incomprehensibly, staggeringly beyond all human intuition vast. Most people, including physicists, find this viscerally uncomfortable. Not because the math fails, because the conclusion is so enormous that the human mind resists it. But discomfort is not a scientific argument. The math does not care whether we find the answer comfortable. The Schroinger equation does not pause to check whether its implications are emotionally acceptable.

[00:10:47]It evolves. It branches. It produces from its own internal logic a reality far larger and stranger than the one we thought we were living in. And that is not science fiction. That is what happens when you take the most successful physical theory in human history completely seriously. Now step back from the equations. step back from the experiments and the Nobel laureates and the doctoral thesis because if ever it is right, if the many world's interpretation is not just mathematically consistent but physically real, then what does that mean for you?

[00:11:14]Not for physics, for you. Let's start with choice. Right now, you are watching this video. At some point in the last few seconds, your attention may have flickered. You may have considered stopping. Maybe you thought about checking your phone or skipping ahead or closing the tab. You didn't. Or maybe you almost did. Either way, something in your brain made a decision. A cascade of electrochemical signals, each one governed by quantum processes at the molecular level, produced a choice. In the Copenhagen interpretation, the quantum events underlying that decision collapsed into one outcome. One you, one choice. In the many worlds interpretation, every quantum branch that contributed to that decision produced a universe. In one, you stayed.

[00:11:52]In another, you left. Both versions of you are equally real. Both are continuing right now in parallel, diverging from this moment forward, never able to communicate with each other, never aware of each other's existence, each one convinced it is the only one. This is not a thought experiment. This is what the mathematics of quantum mechanics produces when you do not add artificial constraints to stop it. Now, think about what that means for identity. We have a very strong intuition that we are singular, that there is one me moving through time, accumulating experiences, making choices, building a life. That intuition is the foundation of everything we call personal responsibility, personal growth, personal meaning. But in a many worlds universe, the entity you call me is not singular. It is a branch point.

[00:12:34]Every moment of decision, every quantum event in your nervous system, every photon that enters your eye and triggers a neural cascade, each one is a fork in an infinite tree. The you that exists right now is not the original. There is no original. There is only an everexpanding family of versions. Each one convinced of its own uniqueness.

[00:12:51]Each one the product of a slightly different sequence of quantum outcomes.

[00:12:55]Each one living a life that feels entirely real because it is entirely real. Now think about what that means for death. One of the most disturbing implications of the many worlds interpretation and physicists do not like to talk about this is what it suggests about mortality. In most branches of the quantum multiverse, versions of you will die at various points. Accidents, illness, age. In those branches, that version ends. But in the branches where you survive, and quantum mechanics guarantees there will always be some, you continue. The you that continues will always find itself in a branch where it survived because a version that does not survive cannot observe anything. This idea is sometimes called quantum immortality. It is deeply speculative. Most physicists find it uncomfortable to the point of dismissal.

[00:13:37]But it follows logically from the same framework that produces the rest of many worlds. If the Schroinger equation never stops, if all branches are real, then death is not a universal ending. It is a branching event. In the branches where you died, there is no observer left to notice. In the branches where you didn't, there is. The philosopher Derek Parett spent much of his career arguing that personal identity across time is far less solid than we assume. That the U of tomorrow is not strictly the same entity as the U of today, merely a continuation with strong psychological connections. Quantum mechanics taken seriously makes Parfett's argument look conservative. Because in a many worlds universe, the question, which version of me is the real one, has no answer. They are all real. They are all you. And none of them will ever know about the others.

[00:14:20]Think about every major decision of your life. The relationship you chose or didn't choose. The path you took or didn't take. The moment you acted or didn't act in the many worlds framework, every other version of that decision produced a universe. Those versions are living those outcomes right now. Not as ghosts, not as simulations. As fully real, fully conscious beings who remember the same childhood you remember and made a different call at the fork.

[00:14:41]And here's the thought that is hardest to hold. Those versions of you do not feel like alternatives. They feel like the only version just like you do. So the question that quantum physics is really asking underneath all the equations and the wave functions and the Nobel lectures is not whether parallel universes exist. The math has already answered that. The question is whether the you that is watching this right now is a person or a perspective. Whether you are the universe's only observer of your own life or simply one branch of an infinite tree that does not know its own size. So let's return to the three things I promised you at the beginning.

[00:15:11]I promised you would understand why the mathematics of quantum mechanics demands parallel universes rather than merely suggesting them. And now you do. The Schroinger equation is universal, continuous, and branching. Wave function collapse is not in the math. It is an assumption added by hand to make the theory comfortable. Remove the assumption and the branches remain.

[00:15:30]Remove the assumption and many worlds is not a theory. It is what the equation already says. I promised you would understand why physicists privately believe this and publicly stay quiet.

[00:15:39]Now you understand that, too. It is not because the science is weak. It is because the conclusion is so vast, so strange, so resistant to human intuition that saying it plainly in a lecture hall or a press conference feels like inviting ridicule. It is easier to say there are several interpretations and move on than to say the most mathematically honest reading of our best theory says reality is infinitely larger than anyone imagined. Weineberg could not refute it. Deutsch built his career on it. Teagmark calls it a prediction, not a hypothesis. Carol calls it obvious. The silence of the physics community on this is not skepticism. It is the particular discomfort of people who have seen something too large to talk about comfortably. And I promised you something about your own existence.

[00:16:17]Something difficult to unthink. I hope I delivered it because if the many worlds interpretation is correct and no one has found a way to prove it is not, then you are not a single story. You are a branching library. Every version of you that could exist does exist right now in a universe that feels exactly as real as this one. That version of you who made the other choice is not a fantasy. They are a fact. A quantum fact buried in the same mathematics that makes your phone work and your MRI scan possible. The question I want to leave you with is this. If every version of you is equally real, which one is responsible for the life you are living? And that question leads somewhere even stranger. Because the same quantum mechanics that creates the parallel branches also raises a possibility that physicists are even more reluctant to discuss. If observation is what determines reality, if the act of measurement is what makes the universe concrete, then what was the universe before anything existed to observe it? That question and the deeply unsettling answer physics is quietly moving toward is what we are covering next. If you believe reality is stranger than it looks, subscribe. We post one proof every week, not speculation, not philosophy dressed as science, real experiments, real physicists, real peer-reviewed results that quietly dismantle the version of reality most people never thought to question. This channel exists for the people who cannot stop asking why. If that is you, you are already home. And drop your answer in the comments right now because I genuinely want to know. If every version of you exists in a parallel universe, making every choice you never made, living every life you didn't choose, which version of you is the real one? We read every single comment. Everyone.