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Infinite Space Means Infinite Possibilities

The simplest idea of a multiverse almost follows naturally from what we know about the universe and its unimaginable size. If the universe is truly infinite, then everything must eventually repeat. This is what Tegmark calls a Level-1 multiverse, where regions of space beyond our cosmic horizon follow the same physical laws as our own universe.

You can imagine it like an infinite chessboard. There are only a limited number of possible positions for the pieces, but because the board is infinite, every possible arrangement appears infinitely often. The same applies to particles in an infinite universe. Atoms can only combine in a finite number of ways to form planets, stars or people.

It may be hard to picture, but considering infinity this means there are regions somewhere that are exactly like our observable universe. On top of that, there are infinitely many variations that differ to a greater or lesser degree. In some regions historical events unfold differently, in others we see entirely different technological developments or completely different cultures. Some versions of our Earth could be almost identical, while others only faintly resemble our world. And many regions are simply empty, barren or hostile to life, with no signs of civilization at all.

Since this theory arises directly from our current observations, cosmologists rely on the expansion of the universe and the distribution of matter. From this it follows logically that in an infinite space every possible arrangement must eventually repeat. It is therefore a theory that deserves serious scientific consideration.

However, since the universe continues to expand and light has only a finite speed, we will never be able to see or reach these twin universes. They will remain forever beyond our cosmic horizon.

How Cosmic Inflation Leads to Separate Universes in Bubbles

The theory of the inflationary bubble multiverse begins with the Big Bang, the moment our own universe came into existence.

In the very first fractions of a second, roughly between 10⁻³⁶ and 10⁻³² seconds after the Big Bang (meaning a 1 with 36 or 32 zeros after the decimal point), spacetime expanded extremely rapidly by a factor of 10²⁶ (meaning a 10 with 26 zeros). That was an expansion from a size far smaller than a proton to the size of an entire star system. Scientists call this process cosmic inflation.

During this early phase, there were no atoms or light, only fields, energy and quantum fluctuations. These fluctuations caused variations in matter density, which later gave rise to galaxies, stars and planets. Everything we know today as the universe started as a small, dense, hot point that spread out in all directions in a very short time.

And this expansion not only shaped our universe, it also suggests that multiple universes could have formed at the same time. In different regions of the expanding space, so-called bubble universes could have formed, each with its own initial conditions, physical properties and perhaps even its own laws of nature, a scenario known as Level 2 Multiverse in Tegmark's multiverse classification.

As the expansion continues, these bubbles move further and further apart, making direct contact practically impossible. Each bubble is a separate, expanding spacetime continuum with three spatial dimensions and one time dimension. They exist like isolated bubbles in the vast cosmic space, each self-contained, yet still part of a larger cosmic system.

Many physicists see this model as a logical consequence of inflation theory and consider it scientifically plausible, even though the existence of other bubbles has not yet been directly confirmed.

Every Quantum Choice Branches Into a New Reality

The Many-Worlds Interpretation of quantum mechanics is a theory that states every decision, every random outcome and every quantum event splits the universe into multiple parallel versions. Each of these versions is a separate universe where a particular outcome becomes reality. This means there is not just one possible future, but all possible futures exist simultaneously in parallel realities, which corresponds to Tegmark's Level-3 multiverse.

Although the Many-Worlds Interpretation initially sounds like science fiction, it is based on the phenomena of quantum mechanics, known for example through the Double-Slit Experiment. Originally, Thomas Young conducted the experiment in 1801 to demonstrate the wave nature of light. He discovered that light is not just a stream of particles, but spreads like waves and creates an interference pattern. In modern quantum physics, the experiment is applied with electrons and photons to illustrate the property of superposition, where multiple states exist simultaneously.

In this experiment, particles such as electrons or photons are sent through two slits. As long as no measurement is made, they behave as if they pass through both slits at the same time and occupy multiple states simultaneously, even though this seems impossible classically. Only when a measurement occurs does the superposition collapse and a single observable state appear. The interesting question is what a measurement actually means. According to the Copenhagen Interpretation, it is the observation that determines which state the system falls into.

The topic becomes easier to understand through Erwin Schrödinger's thought experiment, famously known as Schrödinger's cat. In this experiment, a cat is placed in a box containing a mechanism linked to a single radioactive atom. If the atom decays, a Geiger counter is triggered, which in turn activates a mechanism that releases poison and kills the cat. As long as the atom is not observed, it exists in a superposition of decayed and not decayed states according to the Copenhagen Interpretation of quantum mechanics, meaning the cat would also be simultaneously alive and dead.

Now we come to the crucial point. The idea that the cat is both alive and dead only arises if one assumes there is a single reality existing in an undefined intermediate state. From the perspective of the Many-Worlds Interpretation, this is not necessary. Instead of an undefined intermediate state, the universe splits at the moment of decay into two versions. In one, the atom remains undecayed and the cat lives, in the other it decays and the cat dies. Both states exist simultaneously, in parallel and independently.

This interpretation is one of several approaches to explaining quantum mechanics and is seen by a growing minority of physicists as an elegant solution without additional postulates. However, it is not the scientific consensus and exists alongside the still-dominant Copenhagen interpretation.

The concept of the Many-Worlds Interpretation is also the one often seen in movies and series. Unlike other multiverse theories, there is no spatial distance between the universes here. They exist simultaneously, coexist independently and each version represents its own reality. And if this theory is correct, the universe splits into infinitely many variations every fraction of a second, continuously. This means the most diverse branches of reality exist in parallel, some barely different, others completely divergent. In one universe the coin lands heads, in another tails. In one you call a taxi after drinking too much, in another you drive yourself anyway. In one you picked the wrong lottery numbers, in another you are already a millionaire. In this universe, you are reading this blog post, in another you may never have been born. Every possibility becomes reality in its own universe.

But even though it is fascinating and can feel comforting for many to know that everything could be different in other branches of the universe, we always follow only one thread. This raises the question of which direction our consciousness takes while countless new branches with alternative versions of ourselves constantly emerge. No one knows for sure. Some theories, like quantum immortality, suggest that in life-threatening situations, consciousness continues along the branch in which we survive. This does not mean one is invulnerable, only that in the hypothetical survival model, the version of consciousness that survives the event continues to exist.

The Mathematical Structure Underlying All Possible Realities

Mathematics is always logical, consistent and universally valid. If a mathematical structure is consistent, it works independently of space, time or physical conditions. Based on this, Max Tegmark came up with the idea of the Level-4 multiverse, the so-called ultimate multiverse (also known as the mathematical multiverse)

In this multiverse theory, there is no spatial distance between universes or quantum branches. It is not a place in space, but an abstract, higher-level reality. Each universe is a standalone reality based on a consistent mathematical structure. They do not exist in a multiverse landscape and are not physically overlapping, but embody all conceivable mathematical possibilities beyond space, time or physical locality.

This ultimate multiverse suggests that every conceivable universe that can be described by a consistent mathematical structure could be interpreted as a physical reality. Our universe would therefore not be determined solely by the equations of general relativity and quantum mechanics.

This means that not only do universes with different particles or forces exist, but also worlds with completely different dimensions, fundamental laws, forms of space and time or even other forms of logic. Every mathematical model that is internally consistent has the right to exist. Everything that is mathematically possible actually exists.

From a scientific perspective, however, the mathematical multiverse is a highly speculative idea. Since the postulated universes are, in principle, beyond empirical testing and have no directly observable consequences for our universe, this hypothesis is regarded by many as metaphysical rather than a testable scientific theory.

Multiple Universes Emerging From String Theory's Tiny Dimensions

String theory tries to answer the big open questions of physics. It assumes that the smallest building blocks of nature are not point-like particles but tiny vibrating strings. Depending on the vibration, a specific particle emerges, like an electron, photon or quark.

For the theory to work consistently, it requires more dimensions than we can perceive. Besides the three spatial dimensions and time as the fourth, string theory demands six additional dimensions, which are tightly curled up and therefore hidden from us. Just like Super Mario in the old Game Boy games could only jump left, right and up in his 2D world and could not perceive the third dimension, we lack the senses to detect the extra dimensions even though they really exist.

Within these tiny folds of the extra dimensions, the so-called Calabi‑Yau spaces, lie countless possibilities for how universes could be structured. Each type of folding changes fundamental properties like particle types, laws of nature or natural constants.

Our universe is just one of an estimated 10⁵⁰⁰ possible versions that could arise from the different mathematical foldings of the extra dimensions (10⁵⁰⁰ means a 1 followed by 500 zeros). In most of these universes, life could not develop because their laws of nature do not allow stable stars or atoms.

The string multiverse is not a collection of physically separated worlds but an abstract landscape of all possible solutions of string theory. Our universe is just one of countless points within it.

Scientifically, this multiverse theory is still considered speculative because there are no experimental data yet that can confirm or disprove it. The sheer number of possible universes also makes concrete predictions difficult, which is why it remains an open field of research.

Parallel Universes Floating on Higher Dimensional Branes

The brane multiverse is an extension of string theory. String theory is based on the idea that the smallest building blocks of nature are tiny vibrating strings and that, besides the three spatial dimensions and time as the fourth dimension, there are at least ten dimensions, of which we cannot directly perceive the extra ones.

In M-theory, an extended version of string theory, larger, multidimensional objects also appear alongside strings. These objects, called branes, form the foundation of the brane multiverse. Our universe could be such a three-dimensional brane, containing all known particles and forces except for gravity. Gravity, however, can spread freely into the higher dimensions.

You can imagine these branes as thin, flexible sheets floating in a vast space. Each brane is its own universe and countless such sheets could exist, moving in parallel. Some branes might touch or collide and such collisions could possibly trigger events like the Big Bang.

Like the pure string multiverse, the brane multiverse is not a collection of spatially separated worlds, but physical universes existing in a higher-dimensional space. So far, there is no way to directly test or observe branes, which is why the brane multiverse is still considered a speculative theoretical construct.

New Universes Born Inside the Core of Black Holes

Black holes are regions in space where gravity is so strong that not even light can escape. They form when very massive stars collapse. According to general relativity, everything that crosses a black hole's event horizon ends up in a singularity, a point where the density and curvature of spacetime theoretically become infinite. Many physicists, however, believe that a quantum theory of gravity could change this picture. One theory proposed by scientists like Nikodem Poplawski suggests that matter inside a black hole does not disappear into an infinite singularity but might instead undergo a "Big Bounce", a kind of rebound under extreme pressure. In this process, the matter could transform into a new expanding spacetime, creating a new universe.

In this model, each black hole would generate its own "baby universe", spatially and physically separate from our universe. Our universe itself could have originated from a black hole in a larger "mother universe". The laws of nature, particles and even the passage of time in these universes could vary depending on the conditions inside each black hole. Each universe would thus be completely independent.

Another theoretical approach is the holographic principle, which states that all information that falls into a black hole is not lost but stored on its two-dimensional event horizon. Some theories propose that this stored information could influence the physical properties of a new universe. That means if a new universe emerges from a black hole, the conditions and laws in that universe could partly be based on the information stored in the black hole of the previous universe.

The black hole multiverse and the holographic principle are, well, rather highly speculative theoretical concepts. They do offer some insights into quantum gravity and the structure of the cosmos, but they mostly remain in the realm of hypotheses and philosophical speculation.

Realities Crafted by Highly Advanced Simulations

The simulation hypothesis is based on the assumption that a technologically far superior civilization could create countless simulations. In this model, our universe could be a highly complex computer simulation, similar to today's video games, but on an unimaginably higher level of computing power. Everything we perceive, from matter to the laws of nature to time itself, could in this scenario be the result of calculations within a computer system.

Even though this may sound highly unlikely at first, we must not forget the progress humanity has made in the last hundred years. If we imagine how technology could develop over the coming thousands of years, it no longer seems entirely far-fetched. For this reason, scientific considerations also explore the question of whether our reality could be simulated.

According to philosophers like Nick Bostrom, there are three possible explanations. First, advanced civilizations may never reach the level to run many simulations. Second, they may reach that level but choose not to run them. Third, they may run many simulations, making it likely that most conscious beings live in simulated realities. This implies that the probability of living in the real base world could be very low.

A simulation multiverse would mean that not only our universe is simulated, but that there could be many such simulations. Each simulation could have different laws of nature, particles or initial conditions. Some universes could be very similar to our own reality, while others could be structured in completely different ways.

The simulation theory is, of course, a highly speculative scientific concept. Current science and technology cannot provide any evidence as to whether such a simulation exists or how it could be detected.

Multiple Multiverse Theories Could Be Possible

As you can see, there are many different theories about the multiverse. That does not mean only one of them can be true, because none of these ideas automatically rules out the others. Some describe different levels or mechanisms that could even complement each other. It is therefore conceivable that an infinite space like in Level-1 exists, where at the same time the effects of quantum physics according to Level-3 are taking place. Different physical constants like in Level-2 could also be embedded within it, along with ideas of new universes created through black holes, string theories or branes.

It is quite possible that our reality is a combination of several approaches. And in the end, the whole thing might even be running on a simulated computer, who knows.

Proving the Existence of the Multiverse

Many multiverse theories push the boundaries of our physics. They are logically conceivable and often mathematically describable, yet direct proof is and will likely always be extremely difficult. If other universes are truly completely separate from ours, we cannot simply observe them with a telescope or measure them through experiments.

All approaches therefore provide only indirect hints. Some physicists suspect that traces of collisions with other universes might be found in the cosmic background radiation. Others hope that one day properties of black holes or effects of quantum physics could offer possible windows into a larger reality. The only certainty is that even discovered hints would be hard to interpret clearly.

And even if the existence of a multiverse were proven, we could not visit it, since many theories assume that other universes are either unimaginably far from us or completely separate spacetime regions. Even models of a quantum multiverse, where all possible states exist simultaneously, offer no practical way to reach another universe, as these states only appear as probabilities within our own quantum framework. No known physical law thus allows for a transition or communication between these isolated realities.

But even without being able to travel to alternate worlds, I think it would be a huge achievement if we could prove the existence of other universes. Although this might initially raise more questions than answers, it could ultimately be liberating. We would no longer see ourselves as the crown of evolution in a unique universe created just for us. Perhaps humanity could finally break free from anthropocentric errors, beliefs and simple creation myths.

Closing Words

Next time you doubt whether to approach someone at the kiosk, whether you dare to start a new project, or if you are unsure about changing a job where you are just stagnating, remember this: In another universe, you take the step and succeed. The possibilities are endless. And in this universe, it is up to you which story unfolds.