In quantum mechanics, the phenomenon of particle tunneling is a well-established concept that has been experimentally verified in various contexts. While the observation of macroscopic objects, such as a sand grain tunneling through a sheet of paper, is challenging due to the technical difficulties involved, there is empirical evidence and indirect confirmation of tunneling at the macroscopic scale through several experiments and phenomena. Here are a few examples:
Scanning Tunneling Microscopy (STM): Scanning tunneling microscopy is a technique that allows researchers to image surfaces at the atomic scale. It relies on the principle of electron tunneling, where a fine metallic tip is brought in proximity to a surface, and a small bias voltage is applied between them. The current resulting from the tunneling of electrons between the tip and the surface provides direct evidence of the tunneling phenomenon.
Superconductivity: Superconductors are materials that can carry electric current with zero resistance below a certain critical temperature. One of the key phenomena in superconductors is the expulsion of magnetic fields, known as the Meissner effect. This effect can be understood through the concept of macroscopic quantum tunneling of magnetic flux, where magnetic fields are expelled from the superconductor by tunneling through a region of zero resistance.
Alpha Decay: In nuclear physics, alpha decay is a type of radioactive decay where an atomic nucleus emits an alpha particle (consisting of two protons and two neutrons). This process can be seen as the quantum tunneling of the alpha particle through the potential barrier created by the nuclear forces. The empirical observation of alpha decay in various isotopes provides strong evidence for the existence of quantum tunneling at the macroscopic level.
While direct observations of macroscopic objects tunneling through barriers are challenging, these and other phenomena provide indirect empirical evidence for the existence of tunneling at the macroscopic scale. Additionally, the quantum mechanical framework has been exceptionally successful in describing and predicting a wide range of phenomena, including those at both microscopic and macroscopic scales.