Joy of Discovery (in history of quantum mechanics)

Science can help us fulfill a deep human need, because it is one way to search for answers when, inspired by our curiosity, we ask questions about what, how, and why. Most of us want to know the truth, so an intrinsically appealing goal is the design of scientific theories that are true because they correctly describe what is happening now and what has happened in the past.
And the process of science is fun.
In our search for truth in nature, we are motivated by curiosity about how things work, a desire to solve mysteries. One fascinating mystery story is the discovery of quantum mechanics, an elegantly simple theory that is strange, beautiful, and successful. A brief outline of the story will help you understand why, after decades of uncertainty and mental struggle, a pioneer who began the adventure "eagerly listens to the solution of a riddle" and "rejoices over the beauties" of the elegant solution.

The history of quantum ideas began in 1900 when, in an effort to explain the observations of light emitted from glowing objects, Max Planck proposed a new idea. He found that the observations could be explained if emitted light has quantized energies, if the energy can have some values but not others. This quantization of energy is analogous to the quantization of height when you walk up stairsteps, in contrast with the continuously variable heights on a smooth ramp.
In 1905, Albert Einstein explained the puzzling observations in photoelectric experiments by proposing that light (previously thought to be just a wave) also behaves like a particle.* Another aspect of wave-particle duality was recognized in 1923, when Louis De Broglie creatively extended the creative idea of Einstein by proposing that electrons (previously thought to be just particles) also behave like waves. {* In 1921, Einstein won the Nobel Prize in Physics "for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect," not for his Theory of Relativity, which he called a Theory of Invariance. }
How strange is the concept of wave-particle duality? Nobel Prize winner Richard Feynman says, "The difficulty is psychological and exists in the perpetual torment that results from your saying to yourself, ‘But how can it be like that?’ which is a reflection of uncontrolled but utterly vain desire to see it in terms of something familiar. ... Nobody knows how it can be like that. ... I think I can safely say that nobody understands quantum mechanics."
But don't give up hope. If you just accept the fact that "yes it is like that, strange as it seems," then you can understand a simple analogy that is the key to the beauty and success of quantum mechanics:
If electrons are waves, and an electron-wave in an atom is analogous to a sound-wave in a bugle, this explains the quantization of electron energies in an atom. Because a wave can vibrate only in specific ways, a sound-wave in a bugle can have only specific quantized musical pitches, and an electron-wave in an atom can have only specific quantized energy levels, as proposed by Max Planck in 1900. The mathematical wave equation for an electron-wave in an atom was written in 1926 by Erwin Schrodinger.

You can see the joy of scientific discovery in letters between two scientists who played key roles at the beginning and end of this grand adventure. Max Planck, who found the first piece of the puzzle, writes to Erwin Schrodinger and describes his pleasure in seeing the elegantly simple wave equation: "I am reading your paper in the way a curious child eagerly listens to the solution of a riddle with which he has struggled for a long time, and I rejoice over the beauties that my eye discovers." Erwin Schrodinger replies by agreeing that "everything resolves itself with unbelievable simplicity and unbelievable beauty, everything turns out exactly as one would wish, in a perfectly straightforward manner, all by itself and without forcing." They struggled with a problem, solved it, and were thrilled. It's fun to think and learn!

But this is not the end of the story. There were more puzzles to solve, and scientists — including those in the outline above, plus Niels Bohr, Werner Heisenberg, and others — had a powerful new tool they could use in many ways. They soon discovered, for example, that wave equations could explain the structure of the periodic table. This was exciting because scientists now had two independent confirmations for periodic patterns, with support for the same theory coming from two very different directions, from experimental observations of chemistry (in the 1880s) and from theoretical mathematics of waves (in the 1920s) that explained the periodic patterns. Today, scientists are still exploring the mysteries and applications of quantum mechanics, which has served as a powerful unifying theory for a wide range of domains.

Are the joys of science only for the special few, for geniuses like Planck and Einstein, de Broglie and Schrodinger? No, you can also understand and enjoy science, because the thinking used in science is not strange and mysterious, it's the same thinking you use in daily life. A companion page about The Logic of Scientific Method explains how — in scientific logic, as in daily life — you use reality checks to decide whether "the way you think the world is" matches "the way the way the world really is."