The question of whether quantum objects could be described by a classical theory has long been a topic of debate. In 1985, a test was proposed to measure this: the “Leggett-Garg inequality.” This test determines if a theory can explain the world without resorting to the strange superposition states of quantum theory. A recent experiment at TU Wien has confirmed that quantum theory reigns supreme, as the Leggett-Garg inequality is violated. The study has been published in the esteemed journal Physical Review Letters.

Exploring Macroscopic Realism

In everyday life, we assume that objects have certain properties independent of observation. This concept, known as “realism,” extends to macroscopic objects and is termed “macroscopic realism.” However, quantum theory challenges this notion by allowing for multiple states until a measurement is made, collapsing the superposition state.

The Leggett-Garg Inequality

In 1985, physicists Leggett and Garg introduced a formula to test macroscopic realism: the Leggett-Garg Inequality. Unlike Bell’s inequality, which focuses on quantum entanglement, the Leggett-Garg Inequality examines the state of a single object at different points in time. By testing statistical correlations, the experiment demonstrates that quantum properties can manifest in macroscopic objects.

Neutron Beams: Bridging Quantum and Macroscopic Realms

Neutron beams, used in experiments at TU Wien, offer a unique opportunity to explore quantum behavior in macroscopic objects. Neutron interferometers split and recombine beams, showcasing quantum properties on a centimeter scale. The team’s results confirm that neutrons exhibit behavior inconsistent with classical theories, highlighting the enigmatic nature of quantum physics.

“Our experiment confirms that nature is truly as bizarre as quantum theory suggests,” says Stephan Sponar. “Classical theories cannot explain the reality we observe. Quantum physics is essential to understanding the complexities of our universe.”