Quantum tunneling is a remarkable phenomenon in quantum mechanics where particles, such as electrons, can penetrate energy barriers that would be insurmountable according to classical physics.
Classical physics suggests that particles must have enough energy to overcome a barrier or potential well. However, in the quantum world, particles exhibit wave-like behavior and have a probability of tunneling through these barriers even when their energy is lower than the barrier's height.
Quantum tunneling has practical applications in various fields, including semiconductor devices like transistors and tunnel diodes, as well as nuclear fusion processes in stars. It also challenges our classical intuitions about the behavior of matter and energy at the quantum level.