Final answer:
The subject of this question is Physics, and it is referring to the concept of particles and their ability to pass through a barrier, known as tunneling. This phenomenon is essential in various fields, including solid-state physics, electronics, and quantum computing.
Step-by-step explanation:
The subject of this question is Physics.
Pool: Openings in barrier not allowing a ____ to pass through refers to the concept of particles and their ability to pass through a barrier. In physics, this concept is known as tunneling, where particles have a probability of passing through a barrier even if they do not have enough energy to overcome it based on classical physics principles.
For example, in quantum mechanics, electrons can tunnel through a potential energy barrier. This phenomenon is crucial in various fields, including solid-state physics, electronics, and quantum computing.