Why a physicist thinks we probably live in a quantum multiverse

What if every coin flip split the world in two, with one version of you seeing heads and another seeing tails? That sounds like science fiction, but according to physicist Philipp Strasberg, it follows from taking quantum mechanics at face value. In an essay for Scientific American titled Why We Probably Live in a Quantum Multiverse, he argues that this idea, known as the many-worlds interpretation, deserves much more serious attention. It is his argument, and it remains a contested view among physicists.

Two rules that do not fit together

Quantum mechanics is one of the most successful theories in science, but it runs on what Strasberg describes as two rules that contradict each other. According to the summary I could confirm, one rule says that a quantum system evolves smoothly and predictably. The other says that when you measure it, you get a single definite result. These two rules sit uneasily side by side, and physicists have argued about the tension for about a century.

I could not open the Scientific American essay itself, so the description of its argument here follows the summary provided to me rather than a direct reading. Where possible I have checked the surrounding science against Strasberg’s published research.

How many worlds tries to fix it

The many-worlds interpretation, first proposed by Hugh Everett in 1957, removes the second rule. It says every possible outcome of a quantum event actually happens, each in its own branch of reality. You do not get one result and lose the others. Instead, the world branches, and each version of the observer sees one outcome. In that picture, a coin flip that depends on a quantum event could create two copies of you.

What the research behind the essay shows

Strasberg is a physicist at the Autonomous University of Barcelona. With Teresa Reinhard and Joseph Schindler, he published a study in Physical Review X in 2024 that used numerical simulations of a quantum system with many energy levels. According to coverage in Spektrum der Wissenschaft, the team found that when a quantum system gets larger, a nearly identical, stable, classical-looking structure emerges, whatever the starting conditions. The effect appears quickly, so even a small collection of atoms or photons can behave in an everyday, classical way.

That matters because one common objection to many worlds asks why branches look like the stable, ordinary world we know. Strasberg’s work suggests that classical-looking branches can arise naturally. ScienceAlert’s report adds that this may explain why we do not perceive the multiverse directly.

Experiments are raising the stakes

The summary I received says that experiments showing quantum behavior in ever-larger molecules are making physicists take the idea more seriously. That fits a broader trend, because researchers keep pushing quantum effects into bigger objects, but I could not verify the specific experiments or molecule sizes in the essay.

Why this is still contested

Many worlds is one interpretation among several. Other approaches, such as the Copenhagen interpretation, treat the measurement result as a basic rule and do not require branching universes. Many worlds is also very hard to test, since the other branches are not something we can visit.

Strasberg himself admits that big questions remain, especially about probability. If every outcome happens, what does it mean to say one outcome is more likely than another? Physicists still debate how to answer that. The ScienceAlert report also notes that the 2024 results do not account for general relativity, and that how far quantum randomness can affect something as large as us is still unresolved.

So the honest conclusion is modest. Strasberg makes a strong case for why we might live in a quantum multiverse, but it remains an argument, not an established fact.

Sources

• Philipp Strasberg, Why We Probably Live in a Quantum Multiverse, Scientific American (opinion essay; could not be opened for this post)
• Spektrum der Wissenschaft: Unser Universum koennte Teil eines Quanten-Multiversums sein (on the 2024 Physical Review X study)
• ScienceAlert: New theory solves paradox of Schrodinger’s cat by claiming we’re in a multiverse