Imagine someone asking you to draw a triangle with four sides, or to think of a number less than 10 but greater than 1 billion.
Although such requirements are not complex, they are absurd and therefore difficult to comply with.
The path to quantum physics is similar.
Quantum physics is a world of four-sided triangles and numbers that don't follow the usual rules.
Parallel universes and contradictions lurk everywhere, and things don't need to care about space or time.

---From the "Preface"

This strange phenomenon was called the "ultraviolet catastrophe" by physicist Paul Ehrenfest, and has since become famous as it is referred to in many physics books.
(…)UV radiation breakdown is the result of a misconception about how light energy works.
No one could have predicted that by gradually correcting this misconception, humanity would eventually enter the path of a quantum revolution.
Even the person who came up with the answer to the UV-induced breakdown problem wasn't trying to do something that revolutionary.
I just wanted to make a cheap light bulb.
---From "Chapter 1_Blooming with Confidence"

Before 1926, there were only a few loosely connected threads to quantum theory.
But Schrödinger brought those strands together and wove them together.
He showed that wave-particle duality is connected with the energy levels of electron shells, and explained all chemical phenomena related to the shape of atomic orbitals with it, and showed that particles can be predicted using probability.
---From "Chapter 4: Taming the Freak"

I think by now you've probably noticed that it won't be long before all the theories of quantum mechanics are proven wrong.
To those who don't know much about science, this situation may seem unsettling, as if scientists are constantly in a state of uncertainty (anyone like Heisenberg-style puns?), but in fact, this whole situation is normal.
---From "Chapter 5_The situation becomes even stranger"

Toy Story is about quantum mechanics.
When Andy, the toy's owner, observes, Woody acts like an ordinary toy, but when Andy is not looking, he comes to life and moves.
Andy never sees the toys as alive, and treats them as just ordinary toys.
But if Andy observes his toys carefully, he will notice that they are placed in slightly different positions each time.

The particles are similar.
When we don't see a particle, it seems to behave quite differently than when we do.
Although the Schrödinger equation can be used to infer what the final outcome of a particle will be, it is impossible to accurately predict what will happen every time.

---From "Chapter 7_The World is a Mirage"

They are all put into boxes and sent to opposite ends of the solar system.
When you open the box at one end and find a red cat, you can simultaneously find out what is inside the other box.
While we could use the analogy that the information about the 'green cat' traveled across the universe to reach us, there is no need for anything to actually move between the two boxes, so there is no violation of relativity here.
From a quantum perspective, cats do not pre-determine their properties, but rather exchange randomly determined state information at the moment of measurement via telepathy at faster than the speed of light.
On the other hand, from Einstein's perspective, the cat's characteristics are always fixed.
It's just that you can't determine the cat's characteristics before measuring them.
---From "Chapter 8_Quantum Must Disappear"

The question that always arises when trying to understand quantum mechanics is whether there is a better interpretation than the Copenhagen interpretation, which simply dismisses it as "just what happens."
Most physics textbooks teach the Copenhagen interpretation.
Because Bohr was a giant in the academic world, and for decades his interpretation was the only one.
But today, the Copenhagen interpretation is no longer the only one.
While it is clear that classical concepts will eventually have to be abandoned, there are still some incomprehensible parts in any interpretation of quantum mechanics.
As the Copenhagen interpretation of the past passed its sanctuary, approaches to replace it developed in a variety of ways, much like the Scandinavian table setting.
---From "Chapter 10: Proving I'm Batman with Quantum Mechanics"

Feynman diagrams are elegant.
But beautiful pictures alone don't win you a Nobel Prize.
However, the Feynman diagram is better than my illustration in that it is not just a sketch drawn from imagination.
Anyway, Feynman diagrams are surprisingly powerful in prediction.
(…) The coupling constant of the two sheets they calculated was 0.00729735256.
The experimentally measured value is 0.00729735257.
There is a 10-digit difference between the theoretical and experimental values.
Feynman described this accuracy as having an error in measuring the distance from New York to Los Angeles smaller than the width of a human hair.
Until now, there has been no prediction this accurate in science.
---From "Chapter 12_Straight Lines and Wavy Lines"

We don't know everything about the world, and incredibly exciting questions still remain, but quantum field theory is guiding humanity in the right direction.
In this new realm, we are still taking our first steps.
It's true.
But I no longer feel ahead with my eyes closed.
Every event in history is the result of particles interacting with fields, and today we have a framework that can explain all of those phenomena.
Except for one problem.
Quantum field theory cannot yet handle this.
gravitation.
---From "Chapter 15_The Problem Caused by G"

---From "Chapter 15_The Problem Caused by G"