Quantum Superposition Challenges Us to Confront Profound Realities

Physicists observe that students often exhibit a “digging expression” when first introduced to quantum superposition, as noted by Marcelo Gleiser. Having taught quantum mechanics for several decades, he notes the consistent surprise among students as they grapple with the complexities of atomic and particle behavior.

The term “clear” often adds confusion in this field. Since the inception of superposition, its true implications have been debated for centuries. What is universally acknowledged is that this concept challenges our understanding of what constitutes “reality.”

A foundational aspect to grasp is the Schrödinger equation. Formulated by Erwin Schrödinger in the 1920s, it serves as a cornerstone of quantum theory, outlining the probabilities of finding particles in specific states upon measurement. Notably, quantum mechanics focuses on predicting potential outcomes rather than clarifying the exact activities of particles pre-measurement.

The Schrödinger equation articulates all conceivable positions a particle may occupy before measurement, utilizing mathematical constructs known as wave functions. This establishes one mathematical interpretation of superposition, defined as the combination of various potential quantum states.

It is well-established that particles can indeed exist in superposition. For instance, in a double-slit experiment, a solitary photon (a light particle) is directed toward a barrier with two narrow openings. When a detector is active, the photon seems to “choose” one slit and strikes a specific point on the screen. In contrast, without the detector, an “interference pattern” is observed, indicating that the particles act like waves, traversing through both slits simultaneously and interacting with themselves.

However, the true significance of being “in a superposition” remains elusive. Generally, two perspectives exist. Some view wave functions merely as mathematical constructs rather than reflections of reality—this aligns with Gleiser’s stance at Dartmouth University, New Hampshire. He asserts, “In quantum mechanics, we argue that wave functions must constitute a part of physical reality,” asserting that equating mathematical constructs with truth has become almost cult-like.

Gleiser endorses an interpretation known as quantum Bayesianism (or QBism), which posits that the theory addresses our understanding rather than reality itself. Consequently, during quantum state measurements, what shifts is merely our information about reality, not reality itself.

Conversely, some scholars, like Simon Saunders, a philosopher from Oxford University, argue against this view, asserting that wave functions represent an authentic state of existence. He suggests that particles in superposition physically occupy multiple locations simultaneously. “It’s an extended object,” he clarifies. “It’s delocalized.” Within this framework, our experience of particle reality may deviate from actual reality. For example, electrons orbiting atoms appear as a cloud of probability until measured.

Critics of this interpretation often question the fate of alternate possibilities once measurement constrains a particle to a single location. Saunders concedes to the radical notion that this may suggest the existence of a branching infinite multiverse.

Ultimately, a resolution to this question isn’t imminent. Meanwhile, researchers have successfully extended superposition beyond individual particles to larger molecules and even 16-microgram crystals. This suggests that reality is much stranger than it appears.