Quantum Mechanics
At the end of the 19th century, it seemed that we had
the physics
of how things move all figured out. But then, with advancements in
technology, scientists begin to find that classical physics could not
explain the way the behavior of matter in certain situations. While
classical physics explained and predicted situations on the human scale
perfectly, when scientists performed experiements on a very tiny or
very massive scale or studied matter that was moving at really high
velocities, classical physics simply did not explain the empirical
results of each experiment.
Scientist Niels Bohr quickly began to
realize that minute sub-atomic particles such as atoms and photons
behave in totally different from what classical physics would predict.
In certain experiments, it was proved that atoms could cross from one
side of a solid piece of material to another. It was also discovered
that energy could convert into matter and vise versa. These discoveries
astounded common sense and reason. Bohr coined the term "quantum
mechanics" in 1924, and wrote about his findings, "Anyone who is not
shocked by quantum theory does not understand it." The wider group of
physicists around Bohr quickly accepted quantum mechanics because of
its ability to accurate predict how sub-atomic particles will behave
when Newtonian mechanics fails to describe the behavior of these
particles.
Now, quantum mechanics is an elemental branch of physics that describes
and predicts the way that matter and energy will behave on the smallest
and largest scales. Quantum mechanics is explains pretty much every
force of nature besides gravity.