In 1900 physics was turned upside down, when Max Planck presented the hypothesis to the Physical Society of Berlin that physical quantities cannot take on arbitrary values on the atomic level, but only occur in certain portions, in so-called quanta. And thereby opening up the door to a completely new world of the microcosm, the quantum world, whose paradoxical effects continue to fascinate people til day and which forms the basis of almost all modern technologies.
Without quantum physics there would be no modern computers, we would not understand how nuclear fusion works inside the sun, and not even the atoms would be stable, and the universe would collapse to a point. Without quantum physics, the world would be boring.
Quantum physics is such a crazy and yet so beautiful theory. It makes assumptions that are completely contrary to common sense. It destroys a classical, deterministic view of the world that everything can be predicted exactly, and replaces absolute predictions with probabilities for various possible events. Bodies behave like particles, but move like a wave. Their location and momentum can no longer be measured simultaneously with arbitrary accuracy. And suddenly they can even move through walls, which is classically not possible.
No one really understands why quantum physics is the way it is, not even physicists. “If you are not shocked by quantum theory, you have not understood it,” is a quote attributed to Niels Bohr, one of the early founders of quantum theory. Quantum physics is not intuitive, in a sense that it does not relate to our everyday experience. Perhaps we simply have to accept that nature behaves differently on very small length scales than we are used to in our macroscopically large world.
The point is, however, that quantum physics with its bizarre assumptions works exceptionally well and its predictions have been tested in experiments more thoroughly than any other theory.