Quantum tunneling is an important phenomenon that explains many phenomena such as alpha decay and the workings of certain diodes. It goes against the intuition of classical physics because in quantum mechanics, particles do not have a definite position, but are described by wave functions. When passing the barrier, the wave function decays within the barrier, but is not equal to zero. This means that the particle has a certain probability of crossing the barrier to reach the other side, and also a certain probability of reflecting back. As the barrier length decreases, the probability of the particle passing through increases and the probability of reflection decreases. Although the probability of a single particle passing is small, at least some of the large number of particles will pass. Quantum tunneling plays an important role in quantum mechanics and, contrary to classical physics, makes possible some seemingly impossible phenomena.