The idea that there could be other versions of our world, where different choices led to different lives, has fascinated people for centuries. Today, parallel worlds appear in movies, comics, novels and series, but they are also discussed seriously by physicists and philosophers. What does science actually say about the multiverse, and why does the idea capture our imagination so strongly?
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What is a multiverse?
A multiverse is the idea that our universe might be one of many. These other universes, often called parallel worlds or alternate realities, could have different histories, different versions of us or even different laws of physics.
It's important to be clear from the start: there is currently no direct evidence that other universes exist. The ideas below are scientific hypotheses, interpretations or consequences of theories, not confirmed facts. Some physicists find them compelling; others are skeptical.
Scientific ideas about the multiverse
A universe beyond what we can see
The observable universe has a limit, defined by how far light has been able to travel since the beginning of the universe, about 13.8 billion years ago. Because space has expanded, the edge of the observable universe is now much farther away than 13.8 billion light-years. Many cosmologists think space continues beyond that horizon, possibly infinitely. If space is infinite and matter is distributed in similar ways everywhere, some scientists argue that regions very similar to ours could exist far away. This is sometimes called a "level one" multiverse.
Cosmic inflation and bubble universes
Inflation is a widely studied theory proposing that the early universe expanded extremely rapidly in a fraction of a second. Some versions of the theory, known as eternal inflation, suggest that inflation could continue in some regions while stopping in others, creating separate "bubble universes." Each bubble could have different properties.
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The many-worlds interpretation
Quantum mechanics describes the behavior of particles at very small scales, where outcomes are described by probabilities. In 1957, physicist Hugh Everett proposed an interpretation in which every possible outcome of a quantum event actually happens, each in a separate branch of reality. In this view, the universe constantly splits into countless versions. The many-worlds interpretation is one of several ways physicists interpret quantum mechanics, and it remains debated.
String theory and the landscape
String theory, an attempt to unify all the forces of nature, suggests the existence of extra dimensions. Some interpretations imply an enormous "landscape" of possible universes with different physical constants. String theory itself has not yet been confirmed by experiments.
Fine-tuning
Some scientists point out that certain physical constants seem precisely suited to allow stars, planets and life. One possible explanation, debated among physicists and philosophers, is that many universes exist with different constants, and we naturally find ourselves in one where life is possible. This reasoning is related to the "anthropic principle."
Why it is so hard to test
Other universes, if they exist, may be completely inaccessible to us: we may never be able to observe, travel to or communicate with them. That makes it difficult to design experiments to confirm or rule them out. Some researchers have proposed looking for indirect signs, such as patterns in the cosmic microwave background left by collisions between bubble universes, but no convincing evidence has been found.
For this reason, the multiverse is controversial. Some scientists see it as a natural consequence of well-supported theories; others argue that ideas that can't be tested should be treated with great caution.
Philosophical questions
Parallel worlds raise deep questions:
- Identity: if there are other versions of you, which one is "you"?
- Choice and responsibility: if every possibility happens somewhere, do our choices still matter? Most philosophers argue they do, since we experience only one path.
- Probability: what does it mean for something to be likely if every outcome occurs?
- Reality: what counts as "real" if it can never be observed?
Parallel worlds in fiction
Fiction has explored parallel worlds for a long time:
- Literature: stories about alternate histories imagine how the world would be if key events had gone differently.
- Comics and superhero movies: stories like the "Spider-Verse" films and the Doctor Strange movies show alternate versions of familiar characters.
- Award-winning films: "Everything Everywhere All at Once," which explores a multiverse, won the Academy Award for Best Picture in 2023.
- Television: many series use alternate realities to ask "what if?" questions about history, family and personal choices.
These stories often use the multiverse to explore regret, second chances and the meaning of ordinary life.
Why the idea fascinates us
Parallel worlds invite us to imagine who we might have become with different choices: another career, another city, another partner. They connect science, philosophy and storytelling, and they offer a way to think about chance, possibility and identity. For many people, the idea is less about physics and more about reflecting on the path they are actually living.
Common misconceptions
- "Scientists have proven the multiverse": they have not; it remains hypothetical.
- "We can travel to parallel worlds": there is no known way to do so.
- "Quantum physics means anything is possible": quantum mechanics follows precise rules and predictions.
- "Every multiverse idea is the same": there are several very different proposals.
Frequently asked questions
Do parallel universes exist?
There is no direct evidence. They appear in some scientific hypotheses and interpretations but remain unproven.
What is the many-worlds interpretation?
An interpretation of quantum mechanics, proposed by Hugh Everett in 1957, in which every possible outcome of a quantum event happens in a separate branch of reality.
What is eternal inflation?
A version of inflation theory suggesting that the universe could continuously create separate "bubble universes."
Can we travel to a parallel world?
No. There is no known way to reach or communicate with other universes, if they exist.
Why do so many movies use the multiverse?
It allows stories to show alternate versions of characters and explore "what if" situations creatively.
Why is the multiverse controversial among scientists?
Because other universes may be impossible to observe, making the idea very difficult to test.
Conclusion
Parallel worlds sit at the meeting point of science and imagination. Physicists debate whether a multiverse could exist and how it might ever be tested, while philosophers explore what it would mean for identity and choice. Meanwhile, fiction keeps using the idea to help us reflect on our own lives. For now, the multiverse remains one of the most fascinating open questions in science.