In this blog post, we explore the reasons why the Copenhagen interpretation has garnered significant support over time among the various interpretations of quantum mechanics, despite its complexity.
Quantum mechanics is the science applied to microscopic particles like atoms and molecules. It forms the foundation of semiconductors, including transistors, and has profoundly influenced numerous scientific and technological fields, such as molecular biology. Furthermore, through its interpretations, it has impacted philosophy and art, including subjectivism and positivism. However, another reason quantum mechanics is famous is its complexity. Even Niels Bohr, who made a crucial contribution to the establishment of quantum mechanics by revealing that electrons orbiting atomic nuclei possess quantized physical quantities, said this: “If you aren’t dizzy after reading quantum mechanics, you haven’t understood it!” That’s how complex quantum mechanics is. So, why is quantum mechanics so complex?
The primary reason quantum mechanics became complex is its divergence from classical mechanics. In classical mechanics, the meaning of equations was clear, allowing precise descriptions of motion or the state of an object through those equations. However, in quantum mechanics, it was unclear what the wave function—the solution to the Schrödinger equation—physically signified. Quantum mechanics revealed that the wave nature of microscopic particles cannot be ignored, and the Schrödinger equation is the wave equation describing this wave nature. In quantum mechanics, the wave function relates to the probability of finding matter at a specific location in space at a specific time, but it itself has no inherent physical meaning.
Interpretations of quantum mechanics diverged depending on how this intrinsically meaningless wave function was interpreted, leading to ongoing debates. The most famous interpretation is the Copenhagen interpretation. This interpretation was advocated by Niels Bohr, Werner Heisenberg, Max Born, and others. In the Copenhagen interpretation, the square of the absolute value of the wave function is viewed as the probability density function, representing the probability that a microscopic particle is at a specific location. This means the particle’s position cannot be determined with certainty; before observation, the particle is superimposed across multiple locations.
Scientists accustomed to classical mechanics opposed representing a particle’s position as a probability, leading to the emergence of alternative interpretations of quantum mechanics. For example, the Everett interpretation posits that particles are not superimposed; rather, distinct worlds exist, and selecting one state creates a corresponding universe. Another example is the ensemble interpretation, which statistically interprets quantum physics’ probability, stating that an ensemble of particles exists at that location, each with an expected value.
We have described the three main interpretations of quantum mechanics above. All of these interpretations can be complex and difficult to understand. However, as Max Born said, that is natural. So why has the Copenhagen interpretation been adopted by the most scientists?
Is it because the proponents of the Copenhagen interpretation made significant contributions to quantum mechanics research at the time? While that might seem plausible, it isn’t necessarily the case, as evidenced by Albert Einstein—who proved light behaves as particles rather than waves—advocating for a hidden variable theory that extended the ensemble interpretation. The hidden variable theory posits that more variables exist to describe a particle’s state, but because humans are unaware of these variables, particles are described probabilistically. Albert Einstein believed that knowing these variables would allow quantum mechanics to be described as precisely as classical mechanics.
Niels Bohr’s persuasive approach played a crucial role in the Copenhagen interpretation gaining widespread acceptance. Influenced by positivism, Niels Bohr believed scientific theories need not provide philosophical explanations. He avoided philosophical debates with scientists, insisting on explanations based solely on experiments. He argued the Copenhagen interpretation was the correct theory because it could explain experimental results and predict outcomes of new experiments.
Does this mean only the Copenhagen interpretation can account for experimental results? Not necessarily. However, Niels Bohr’s approach to explanation meant less time was spent on interpreting quantum mechanics. If a theory could explain experimental results and predict the outcomes of new experiments, it came to be considered the correct theory. Many interpretations of quantum mechanics emerged thereafter.
As various interpretations of quantum mechanics appeared, support for the Copenhagen interpretation ceased to be overwhelming. According to British science writer John Gribbin, while the Copenhagen interpretation still received the most support among scientists after the 1980s, its support rate declined. This can also be seen as a shift in scientific and technological trends. The Everett interpretation mentioned earlier was philosophically a non-mainstream interpretation. However, it gained renewed attention when David Deutsch applied the Everett interpretation to his quantum computer theory.
This blog post has examined the history of interpretations of quantum mechanics. Specifically, we explored why interpretations of quantum mechanics have diversified and the consequences of this. Quantum mechanics is applied to all fields related to molecules and atoms, and understanding it is essential for such applications. Knowing about the interpretations of quantum mechanics is also important. While the Copenhagen interpretation currently enjoys the widest support, the emergence of quantum computers has brought renewed attention to the Everett interpretation, leading to a decline in support for the Copenhagen interpretation. Given this situation, it is important to understand multiple interpretations of quantum mechanics rather than relying on just one.
