The world is the most difficult physics book to understand. This sentence is often quoted in novels because it describes many theories and concepts in physics. These theories and concepts are very difficult for ordinary people to understand. Physics was a very esoteric subject. It studied the laws and phenomena of nature, including force, energy, matter, motion, and so on. Many physicists spent a long time trying to understand the theories and concepts in physics. Therefore, this sentence expressed the difficulty of understanding physics and also expressed the hardships of the characters in the novel to explore physics.