Quantum physics studies matter and energy at the most fundamental level. Think of it as studying the most minor units of everything; the very small stuff(i.e. protons, neutrons). Quantum physics dives into the behavior of atoms and makes sense of them in the natural world. Sometimes, quantum mechanics(QM) and quantum physics are used interchangeably. However, quantum mechanics is used to emphasize the calculation part of the subject.
A major part of the quantum world is studying these small units(atoms, protons, neutrons, and molecules) in something called a wave function.
This is where things get a bit tricky; wave functions are not physically real. It is only a mathematical description used to identify the position and momentum of a particle. Mathematics allows physicists to predict where an electron or particle is. In quantum physics, we do not know every little detail(no pun intended). Rather, we are making very great predictions.
Quantum physics is different from the classical physics that Sir Isaac Newton created. One of the main components of QM is the difference in how the light was originally theorized. It was originally classified as a particle until the scientist Thomas Young came to the scene. Young created an experiment called the "Double Slit" Experiment in 1801. He took a light and shined it through two small slits. The expectation was for light particles to shine through the two slits and create two spots on a screen. However, a pattern across the whole screen appeared because the light was displaying wave-like characteristics rather than particle characteristics.
What Was Expected:
If we were to shoot tennis balls through the two slits we would expect those tennis balls to hit around the same spot every single time like in the photo shown below.
What Actually Happened:
Instead of tennis balls, Young shot a particle through the slits and did not get a pattern at two spots. He got patterns across the whole screen.
With this experiment, physicists can predict the behavior and position of a subatomic particle through its wave-like characteristics. Quantum physics is all about the study of small particles that behave like waves. We can take these theories and expand to theoretical physics and other mathematics that help us understand the universe.