Quantum mechanics 

Quantum mechanics can be thought of roughly as the study of physics on very small length scales, although there are also certain macroscopic systems it directly applies to. The descriptor “quantum” arises because, in contrast with classical mechanics, certain quantities take on only discrete values. However, some quantities still take on continuous values, In quantum mechanics, particles have wavelike properties, and a particular wave equation, the Schrodinger equation, governs how these waves behave.

The Schrodinger equation is different in a few ways from the other wave equations we’ve seen in this book. But these differences won’t keep us from applying all of our usual strategies for solving a wave equation and dealing with the resulting solutions.

In some respect, quantum mechanics is just another example of a system governed by a wave equation. However, although it is fairly straightforward to deal with the actual waves, there are many things about quantum mechanics that are a combination of subtle, perplexing, and bizarre. To name a few: the measurement problem, hidden variables along with Bell’s theorem, and wave-particle duality. 

Even though there are many things that are highly confusing about quantum mechanics, the nice thing is that it’s relatively easy to apply quantum mechanics to a physical system to figure out how it behaves.