Does an Infinity of Versions of Ourselves Really Exist?
Did another version of you make the opposite choice, live a different life, or follow another future? Between many worlds, the multiverse, extra dimensions, and spacetime, physics allows dizzying ideas — but not exactly the ones science fiction has taught us.
There may be a version of you who never started reading this article.
Another who opened it thirty seconds later. One who lives in a different city. One who made, several years ago, a tiny decision that gradually transformed their entire life. Perhaps even a version of you who will die tomorrow and another who will live to a hundred.
It’s an almost obscenely fascinating idea.
The problem is that the sentence “there exists an infinity of mes in other dimensions” mixes several concepts that, physically, have almost nothing to do with each other.
Extra dimensions, parallel universes, the cosmological multiverse, the many-worlds interpretation, and four-dimensional spacetime are not different ways of saying the same thing.
And above all: we do not know today whether other versions of us really exist.
But certain serious theories at least oblige us to take this possibility much more seriously than one might think.
A Dimension Is Not Another Universe
Let’s start by killing an extremely widespread confusion.
When a movie speaks of a character who “travels to another dimension,” it usually means another world.
In physics, that’s not what the word dimension means.
A dimension is, roughly, an independent direction needed to locate something.
Our everyday experience has three spatial dimensions:
-
left ↔ right;
-
forward ↔ backward;
-
up ↔ down.
To this, relativity adds time in a single structure: spacetime.
We therefore describe our relativistic universe using four coordinates: three of space and one of time.
Certain physical theories do indeed envisage additional spatial dimensions. They could be extremely small, compactified, or otherwise invisible at our scale. CERN is notably searching for phenomena likely to reveal their existence indirectly. But no extra dimension has been established experimentally.
And even if they existed, that would absolutely not mean that a version of you lives there with a different haircut and a different career.
To get to the “other yous,” you have to go elsewhere.
The Real Concept That Resembles This Idea: Many Worlds
In 1957, the physicist Hugh Everett III published a strange formulation of quantum mechanics.
To understand what he proposes, let’s take a simplified example.
Imagine a photon sent toward a device where two outcomes are possible:
A or B.
Quantum mechanics does not simply describe the photon as quietly hiding an answer A or B that we are unaware of. Its state can be a superposition of the different possibilities.
The real problem arrives when we perform a measurement.
In a traditional presentation of quantum mechanics, one roughly says:
before measurement: A and B are present in the quantum state;
after measurement: only one outcome is observed.
One then introduces what is called the collapse of the wave function.
Everett proposes a radically different solution:
what if this collapse never happened?
The wave function would simply continue to evolve according to the quantum equations.
After the experiment, there would no longer be:
A or B
but a structure containing:
observer having measured A
and
observer having measured B.
This is the starting point of what is called today the many-worlds interpretation, or Many-Worlds Interpretation.
Everett himself spoke rather of a formulation of “relative states”; the popular image of universes literally splitting was developed and popularized later, notably by Bryce DeWitt.
And this is where our story becomes seriously weird.
After the Split, There Would Be Two “You”
Imagine a quantum experiment giving two possible outcomes.
Before:
toi
│
│
expérience
/ \
/ \
résultat A résultat B
│ │
toi-A toi-B
In an Everettian reading, the two outcomes would not be two abstract possibilities of which only one becomes real.
Both would be present in the global quantum reality.
In one branch, you observe A.
In the other, a version of you observes B.
And neither considers itself a copy.
Each possesses all your memories up to the experiment. Each remembers having been “you.” Each looks around and observes a single, perfectly normal outcome.
The Stanford Encyclopedia of Philosophy precisely summarizes this strange consequence: a present observer can correspond, in the future, to multiple continuators located in different branches.
In other words, the question:
“Which of these people will I be?”
itself becomes problematic.
Before the split, they share your history.
After, there no longer exists a unique future allowing one to designate only one of them as the real you.
But Your Choice Between Pizza and Burger Doesn’t Magically Create Two Universes
This is where popular versions of this idea often go wrong.
One hears:
“At every decision, the universe splits. In one universe you chose A, in the other you chose B.”
This is not really what the physics says.
Quantum mechanics grants no special cosmic power to our decisions.
The Universe doesn’t wait for you to hesitate in front of two buttons to say: very well, let’s create two realities.
Quantum interactions occur constantly, everywhere.
Your body, the air, photons, the molecules of a table, stars, and practically everything around us interact with their environment.
The fundamental phenomenon allowing different quantum components to become practically independent is called decoherence. It explains why quantum superpositions can give rise to macroscopic structures that no longer seem to interfere with each other.
A human decision could obviously depend, directly or indirectly, on different physical events.
But it is not your will that causes the branching.
Consciousness is not sitting at the center of the Universe with a “create a timeline” button.
So Does Another You Exist Today?
If a certain version of the many-worlds interpretation is correct: something quite close to this idea could indeed be true.
There could exist branches containing continuators of people who once shared exactly the same past.
But the word “copy” is misleading.
Suppose that yesterday two branches diverged.
Today:
même histoire
│
│
hier à 18 h
/ \
/ \
A B
│ │
version A version B
From the divergence onward, these two people no longer accumulate the same experiences.
They gradually become two different individuals.
The older the divergence, the more speaking of the “same me” loses its meaning.
A branch that diverged three seconds ago could contain someone almost impossible to distinguish from you.
A branch that diverged before your birth could contain no you at all.
Your parents might never have met.
A slightly different fertilization could have produced another person.
Human history itself could be profoundly different.
Many worlds therefore do not mean:
every universe necessarily contains the same cast with different scenarios.
Some branches can become radically foreign to our own.
And Does an Infinity of “You” Exist?
This is even more delicate.
Saying “Many Worlds = an infinity of copies of me” goes much too far.
In modern formulations linked to decoherence, a “world” is not even necessarily a fundamental entity possessing perfectly defined boundaries. Branches can be understood as emergent and approximately independent structures within the global quantum state.
There is therefore not necessarily a cosmic counter displaying:
Universes currently existing: 8,719,392,188,593,421…
Depending on how one defines branches and the level of description adopted, asking exactly how many worlds exist may not have a well-defined answer.
There may be an enormous number.
Some mathematical models can lead to extremely vast sets.
But going from there to:
“an exact infinity of versions of me exists”
is a claim that current physics does not allow to be presented as a fact.
The Cosmological Multiverse Is Yet Another Story
There is, however, a second route to multiple universes.
This time, it comes not from the interpretation of quantum measurement but from cosmology.
Certain models of cosmic inflation lead to what is called eternal inflation.
In these scenarios, inflation — a phase of extremely rapid expansion of the primordial Universe — would stop in certain regions while continuing elsewhere.
This could continuously produce sorts of regions or bubble universes separated from each other.
Alan Guth, one of the principal architects of inflation theory, showed how certain models can lead to an endless production of such regions.
This too is regularly called a multiverse.
But be careful: this is not the same multiverse as Everett’s.
In one:
quantum branches describe different outcomes.
In the other:
separated cosmological regions can appear in a much vaster inflationary spacetime.
The word multiverse is convenient, but it gives the misleading impression that there is a single grand theory of parallel universes.
That is not the case.
The Even More Troubling Scenario: A Universe So Large It Eventually Repeats Itself
One can push the reasoning further.
Suppose — and every word counts here — that space is truly infinite.
Suppose also that a given region can only possess a finite number of distinct accessible physical configurations.
With enough regions, some configurations should eventually repeat.
And in a truly infinite universe, this opens a dizzying possibility: somewhere incredibly far away could exist a region resembling ours almost exactly.
Potentially down to containing someone resembling you exactly.
But this conclusion depends on strong cosmological hypotheses. It is not an observation.
We have discovered no Earth number 2 at an absurd distance with your double on it.
One must maintain this intellectual boundary. A possible consequence of a model is not an observed thing.
Can Your Past Also Be Different?
This is an important subtlety.
Many worlds are often represented like this:
passé ───────── présent
├──── futur A
├──── futur B
├──── futur C
└──── futur D
From your current point of view, you possess memories and traces corresponding to a certain history.
In a standard representation of branches, your current world therefore has a determined past, then multiple future continuations can appear.
The Stanford Encyclopedia precisely underscores this asymmetry: a world considered now goes back to a particular past history but can have a multitude of future continuations.
Yet, if we look at the global quantum state, other present branches can obviously contain different histories from ours because they diverged earlier.
Therefore:
in the many-worlds scenario, there can exist present versions of reality whose past differs from ours.
But it is not as if your own past changed retroactively.
You do not wake up tomorrow in a branch where Napoleon won Waterloo while mysteriously retaining the memories of our history.
Branches possess their own coherent chains of events and traces.
There Is Yet Another Strange Idea: Perhaps Your Future “Already” Exists
And we still haven’t finished.
Relativity destroyed an extremely deep intuition: the idea that there exists a universal “now,” common to the entire Universe.
Two observers moving differently may not agree on the simultaneity of very distant events.
This structure inspired a conception called the block universe, or block universe.
In this representation, all of spacetime is a four-dimensional structure.
Your birth, this precise moment where you read this sentence, and the subsequent events of your life correspond to different places on your line in spacetime.
Certain philosophical interpretations of relativity, called eternalism, consider past, present, and future as equally real, even if we subjectively experience a present that seems to advance. The exact interpretation of what relativity imposes metaphysically remains debated.
But be careful once again:
the block universe is not the multiverse.
It does not claim that there exist ten thousand versions of your life.
It poses a different question: that of whether the events we call “past” and “future” all form part of a single spacetime structure.
Which is perhaps even more unsettling.
Can One Visit Another Branch?
This is where science fiction usually takes back control.
If two versions of you exist, why couldn’t you meet the other?
Because decoherence is not a door.
In the modern many-worlds interpretation, macroscopic branches become dynamically independent to an extraordinary degree.
It is therefore not enough to invent a sufficiently fast machine and “change frequency.”
One would need to be able to reverse entanglement with a gigantic number of environmental degrees of freedom and recreate a coherent interference between macroscopically distinct states.
On controlled quantum systems, producing and recombining superpositions is perfectly real: this is precisely what interference experiments demonstrate.
At the scale of a human and their entire environment, we are in another technological universe.
Current experiments do not allow directly testing an interference between two macroscopic “worlds,” and no known realistic experiment today allows definitively deciding between the many-worlds interpretation and other no-collapse interpretations that reproduce the same observable predictions.
So no: known physics gives us no means of contacting our other self.
The Most Important Point: None of This Is Established as “Reality”
This is probably the most important boundary of this entire article.
Quantum mechanics works extraordinarily well.
We observe superpositions.
We observe interference.
We observe entanglement.
We understand and measure decoherence.
What remains debated is what the quantum formalism actually tells us about the nature of reality.
Everett’s interpretation is a serious solution to the problem.
It has defenders among physicists and philosophers of physics.
It also has opponents.
And no observation has today shown:
“We have detected another universe containing a second version of someone.”
That would be transforming a fascinating scientific interpretation into a belief.
I find the idea much more beautiful when one precisely refuses to cheat with it.
Physics doesn’t need us to invent additional certainties for it.
Perhaps You Are Not a Person with a Future
There is a rather troubling way of turning this whole story around.
Our intuition tells us:
I am a person.
I have a past.
There exist several possible futures.
Only one will end up becoming real.
But if Everett is right, this last sentence could be false.
There might not exist a future waiting to be selected.
Several continuations could exist.
And the one that “you” experience would not necessarily be the winner of a competition between possible futures.
It would simply be the history lived by one of your continuators.
Today, we do not know if nature really works this way.
We do not know if other branches must be considered as worlds.
We do not know if the Universe is infinite.
We do not know if the inflationary multiverse really exists.
And we have never observed another version of ourselves.
But the most fascinating thing is precisely not that an exotic physics has demonstrated the existence of an infinity of doubles.
It is that some of our best theories seriously allow us to envision a reality in which our history may be only one trajectory among an immensity of others.
Science fiction usually begins by inventing parallel worlds.
Physics, on the other hand, has achieved something much more disturbing:
it has given us good reasons to wonder if the word “reality” has ever been as singular as we thought.