A joke from The Big Bang Theory

Spherical Chicken in a Vacuum

The chickens on the farm are sick. The farmer called in biologists, chemists, and physicists to find out what was wrong with the chickens. The biologist examined the chicken and finally said that he did not know what disease the chicken had. The chemist did some experiments and measurements, but in the end he couldn't find any reason. The physicist stood there and looked at the chicken for a while, without even touching the chicken. Then, he took out his notebook and started writing. Finally, after some terrible calculations, the physicist said, "It's done, but it only applies to spherical chickens in a vacuum."

American TV series "Life" "The Big Bang" once told a joke that many viewers didn't understand. It is said that a farmer found that his chickens had problems and could not lay eggs, and asked a physicist for help. The physicist did some calculations and announced that I had found a solution! But this solution only works for spherical chickens in vacuum farms. The joke is that physicists use an oversimplified model to simulate the real world.

A more effective model would presumably consider the impact of airborne viruses on chickens with egg-laying organs on farms where air is present. But no matter what model you use, you have to use a model. Any calculations in any scientific study are made against the model chosen by the scientist, not against the "real world" itself.

Sometimes a simplified model is good enough. For example, if we want to calculate the orbit of celestial bodies, all stars and planets can be simplified into particles without volume. Sometimes you have to simplify. For example, if you want to simulate global climate, you probably need to consider the impact of ocean current movements and the Arctic and Antarctic glaciers. Then should you consider cloud changes? Should we consider the impact of sunspots? Should we consider the impact of plant distribution? Should we consider the impact of the Icelandic volcanic eruption, the Himalayas, Lake Baikal, the Three Gorges Dam and the Spring Festival travel rush in China? It is impossible to consider them all under limited computing power. But the complexity of the world is not the essential reason why we must use models.

The essential reason we must use models is that our observations of the world are subjective. Hawking and Leonard Mlodinow told a story about goldfish in the book "The Grand Design". They said that the Italian city of Monza banned keeping goldfish in curved bowl-shaped fish tanks because looking out of the curved fish tank would see a distorted reality. , this is "too cruel" to goldfish. In this regard, Hawking raised a Zhuangzi-style question: How do we know that the reality we see is not distorted? Goldfish can still summarize a set of physical laws for the world outside their tank. Maybe because the coordinate system is curved, the physical laws summarized by Goldfish will be a little more complicated than what we summarized, but simplicity is just a matter of personal taste, and the physics of Goldfish is equally correct.

From this perspective, all physical laws, and even all scientific theories, are nothing more than subjective models. Ptolemaic theory said that the earth was stationary and the sun revolved around the earth; Copernicus' theory said that the sun was stationary and the earth revolved around the sun - both models can actually be used, but one is more useful than the other. a little.

The revolution in physics is actually the replacement of one model with another. We can interpret force as a fluctuating field, or the curvature of space, or a bunch of particles passing back and forth, or we can interpret various particles as the vibration of strings. When physicists invented these models, they were not thinking about philosophical questions such as "What is the real force? Does superstring theory fit my world view?" They were thinking about using whatever model worked. What model.