In quantum tunneling, a particle is not actually borrowing energy from any external source. Instead, it is exploiting the inherent probabilistic nature of quantum mechanics to pass through a barrier that would normally be classically impassable.
According to quantum mechanics, particles such as electrons do not have definite positions or energies until they are measured. Instead, they exist in a state of superposition, meaning they can simultaneously exist in multiple states or locations. When a particle encounters a potential energy barrier, there is a finite probability that it can "tunnel" through the barrier and appear on the other side, even though it does not have enough energy to overcome the barrier classically.
The key to understanding quantum tunneling lies in the Heisenberg uncertainty principle, which states that there is an inherent uncertainty in the measurement of a particle's position and momentum simultaneously. This uncertainty allows particles to have a non-zero probability of being found in regions where their energy is lower than the barrier's potential energy.
In essence, the particle's energy remains constant throughout the tunneling process. It does not "borrow" energy from elsewhere but rather exploits its quantum wave nature to manifest on the other side of the barrier, even though classically it would be considered impossible due to insufficient energy.
It's important to note that the concept of quantum tunneling is a fundamental aspect of quantum mechanics, and it has been experimentally observed and verified in various contexts, such as in scanning tunneling microscopy and the tunneling effect in semiconductor devices.