Quantum mechanics has driven some of the biggest scientific advances of the past century, but a new survey shows that physicists remain deeply divided over what the theory actually means. Nature conducted the largest ever survey of researchers in the field, gathering over one thousand responses from physicists around the world. The result is a picture of fundamental disagreement.
At the center of the debate is the wavefunction, the mathematical object used in quantum theory to describe a system’s state. Is it real, just a tool, or a reflection of personal belief about measurement outcomes? Researchers were nearly evenly split. About 36 percent said the wavefunction is something real, while 47 percent said it is just a useful mathematical tool. Another 8 percent said it represents subjective beliefs.
The community is also divided on whether there is a clear boundary between the quantum and classical worlds. Nearly half said yes, nearly half said no, and 10 percent were unsure. Many participants raised concerns with how the questions were framed and more than one hundred respondents wrote in their own interpretations.
The most widely supported interpretation of quantum mechanics remains the Copenhagen interpretation, favored by 36 percent of respondents. This interpretation suggests that particles do not have definite properties until they are measured and that the wavefunction collapse is an essential part of observation. Still, only 24 percent of all participants believed their favored interpretation was correct. Others said it was simply adequate or useful depending on the situation.
Some critics argue that the popularity of the Copenhagen view is more historical than philosophical. They say the dominance of this interpretation has allowed physicists to avoid addressing the deeper conceptual puzzles that quantum theory raises. Among researchers who specialize in quantum foundations and philosophy, only 20 percent chose Copenhagen. A much larger group from these fields preferred alternatives such as the many worlds interpretation, Bohmian mechanics, and newer epistemic approaches.
The many worlds interpretation, supported by 15 percent of respondents, claims that all possible outcomes of quantum measurements happen in separate, non-interacting branches of the universe. Bohmian mechanics, chosen by 7 percent, posits hidden variables and deterministic paths guided by pilot waves. Around 4 percent supported spontaneous collapse theories, which modify quantum equations to trigger collapses on their own without the need for observers.
A growing share of physicists support epistemic views. These suggest that quantum theory does not describe the world itself but rather our knowledge about it. This category gained more followers compared to past surveys and includes interpretations like QBism and relational quantum mechanics.
Despite a century of experimental success, quantum mechanics continues to provoke disagreement not only about how the world behaves at the smallest scales but about what kind of world it is describing in the first place.