Schrödinger’s cat equation unifies Einstein’s theory of relativity and quantum mechanics

The relationship between quantum mechanics and classical physics has baffled scientists for decades. In the quantum world, particles can exist in multiple states at once—a phenomenon known as superposition. Yet, this strange behavior seems to vanish at larger scales, leaving planets, stars, and entire galaxies bound by classical laws.

This contrast raises a fundamental question: if the universe is inherently quantum, why doesn’t it behave that way on a macroscopic level? Understanding this transition is one of the biggest challenges in modern physics. The answer could reshape how we view reality itself.

At the core of this mystery is a deeper puzzle—how quantum mechanics reconciles with classical frameworks like general relativity. Physicists have proposed many theories, but none fully explain why the universe follows classical rules while remaining rooted in quantum principles.

Seeking a breakthrough, Matteo Carlesso and his colleagues at the University of Trieste have explored new ways to modify the Schrödinger equation, the foundation of quantum theory.

Their approach introduces small adjustments to this equation, potentially offering insights into how quantum superpositions dissolve at larger scales. By refining the mathematical description of quantum behavior, they hope to bridge the gap between the microscopic and macroscopic worlds.

The quantum measurement problem complicates matters further. In standard quantum theory, a particle exists in multiple states until a measurement forces it into a single, definite state. But what exactly counts as a measurement? John Bell famously asked, “What exactly qualifies some physical systems to play the role of measurer?” This question remains unresolved, adding to the uncertainty surrounding quantum-to-classical transitions.

Schrödinger’s famous cat paradox illustrates the issue. The cat, trapped in a box with a quantum-triggered poison, exists in a limbo—both alive and dead—until someone opens the box and observes it. While this thought experiment highlights the strangeness of quantum mechanics, it also underscores the difficulty of applying quantum principles to large systems like the universe itself.

Clues about the universe’s classical behavior appear in the Cosmic Microwave Background (CMB), the faint radiation left over from the Big Bang. This ancient signal has quantum origins, yet its large-scale properties align with classical predictions. Physicists rely on inflationary cosmology to explain this, but a key question remains: what mechanism transformed an initially quantum universe into the classical one we observe today?

Carlesso’s team addresses this transition through models of spontaneous wavefunction collapse. These models modify the Schrödinger equation by introducing nonlinear and stochastic terms, which cause the collapse of quantum superpositions without requiring external observers or environments.

This mechanism becomes increasingly effective as systems grow larger, providing a natural explanation for why macroscopic systems exhibit classical behavior.

“The question is whether the Universe, lacking an external environment, can be in a superposition,” Carlesso explains. Observations suggest otherwise, showing adherence to classical laws. To resolve this, the researchers propose self-induced collapse mechanisms where systems interact with themselves, causing spontaneous localization into definite states.

“Without external influence, any system spontaneously collapses into a specific state,” Carlesso clarifies. This approach removes the distinction between measured systems and measuring devices, treating all entities equally under the collapse mechanism.

In their study, the researchers focus on the quantumness of space-time rather than matter fields. At the universe’s earliest stages, it might have existed in a superposition of different geometries. Through the proposed collapse mechanism, the universe transitioned into a single, classical geometry, enabling the observable classical dynamics that align with general relativity.

The researchers restrict their analysis to a flat, maximally symmetric, homogeneous, and isotropic Friedmann-Lemaître-Robertson-Walker (FLRW) universe. This model adheres to the cosmological principle, describing a universe where space-time is foliated into hypersurfaces connected by a time-like direction.

By incorporating spontaneous collapse models, Carlesso’s team bridges the gap between a quantum cosmological model in its infancy and a classical universe observable today.

“Our model describes a quantum universe that eventually collapses, becoming effectively classical,” Carlesso elaborates. This explanation does not predict deviations from classical cosmology after the CMB photon emission but provides a robust framework for understanding earlier stages of the universe.

Despite its theoretical elegance, testing the predictions of spontaneous collapse models poses significant challenges. These models suggest subtle deviations from conventional quantum mechanics at the level of atoms and molecules. However, such deviations are incredibly small, requiring highly sensitive experimental setups.

Carlesso and his colleagues are actively collaborating with experimental physicists to devise innovative methods for testing their model. These efforts aim to validate or refute the theory, pushing the boundaries of quantum mechanics and cosmology. If successful, these experiments could offer new insights into the fundamental workings of the universe and its transition from quantum chaos to classical order.

This groundbreaking study offers a fresh perspective on the quantum-to-classical transition, a pivotal issue in modern physics. By modifying the Schrödinger equation and introducing the concept of self-induced collapse, Carlesso’s team has paved the way for a deeper understanding of the universe’s evolution.

While challenges remain in experimental verification, their work represents a significant step toward reconciling the quantum and classical worlds.

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