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The most wonderful thing about science is its simplicity, its complexity. For scientists, there is no happiest moment than "snooping" into a complex matter to the simple laws behind them, and a few parameters or formulas of "just the right heat" look almost flawless. But the great scientists of history have all looked for the simplest theories based on facts.
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On October 5, 2021, the big words "Complex Systems" appeared on the official website of the Nobel Prize in Physics, which is the second time that complex scientific research has won the Nobel Prize, and has also pushed the seemingly unfamiliar scientific term "complex system" to the center of public opinion. Complexity science strives to find the simplest rules of interpretation for some particular complex phenomenon — in fact, it's a philosophy that most scientists practice all their lives. Why have scientists been pursuing simplification of theory?
Occam Razor Principle
Scientists' preference for simplicity can be traced all the way back to the Middle Ages. William of Occam's "do not add substance unless necessary" in response to the tedious metaphysical controversies of the time. Later generations derived this principle and applied it to the construction of scientific theories, calling it "Occam's Razor Principle". This principle holds that of several valid explanations of the same phenomenon, we should believe in the simplest one. The various redundant assumptions added to this should be "shaved off" by a razor.
So, if you pass by a house and hear cries and meows, you should assume that the family has dogs and cats, not that they have dogs, cats, and a rabbit that can't bark. Of course, rabbits may also be the family's pets, but available observations do not support this more complex hypothesis. Occam's Razor Principle suggests that we keep the model simple until the newly observed phenomena are not sufficient to explain with existing models. For example, if you see a pair of long ears from the window of this house, it is necessary to add rabbits to your hypothesis.
In the centuries after Occam's Razor Principle was proposed, great scientists forged modern science with this principle. The mathematician Claudius Ptolemy used a Byzantine complex theory to give a model of the motion of planets centered on the Earth. Copernicus, opposed to Ptolemy's "geocentric theory" and proposed the "heliocentric theory", describing the motion phenomena of the planets with fewer and simpler equations of motion. In fact, compared with the "geocentric theory", the biggest advantage of Copernicus's "heliocentric theory" is "simplicity".
Ptolemy said of the center of the earth. Image source: Wikipedia
Many advances in modern science involve a series of simplifications, either by unifying completely different phenomena before or by eliminating superfluous entities. Perhaps the greatest example of this is provided by Newton, who unified the motions of the earth and the sky using only three laws of motion and a formula of gravitation. Then in the late 19th century, Ludwig Boltzmann extended Newton's laws to the microscopic realm, reducing thermal phenomena to the motion of atoms, and thus thermal phenomena followed Newtonian mechanics. Later, Einstein unified space and time into a single entity, space-time, achieving the most important simplification in physics. Charles Darwin and Alfred Russel Wallace unified the entire natural world under one law, natural selection, in which Wallace mentioned: "The theory itself should be extremely simple." "These scientists all see their job as removing unnecessary complexity and providing the simplest solution to observed phenomena."
Why choose Simple?
Why is the simpler theory, the more likely it is to advance science? Bayesian inference, a statistical method named after the British statistician Thomas Bayes, may explain this. Using this set of statistical methods, we can update the degree of belief in an explanation, theory, or model based on information known at different stages.
Imagine you have a friend who has two dice. One is a simple 6-sided cube, the other has 60 faces and can roll out 60 different numbers. Suppose your friend secretly rolls a dice and then tells you the number of points you get, say 5, can you guess which dice she is more likely to roll? Just as both geocentric and heliocentric theories can explain astronomical data, both 6-sided dice and 60-sided dice have the potential to roll out points 5. But are they equal probability? The answer to Bayesian inference is no, which weights the optional model based on the likelihood of generating data. The probability of a 6-sided dice rolling 5 is 1/6, while the probability of a 60-sided dice rolling 5 is only 1/60. Well, comparing the probabilities, the number 5 from a 6-sided dice is 10 times more likely than a 60-sided dice.
This is also true of the fact that simplicity is favored by scientists. Simple models have fewer parameters to adjust and a smaller range of phenomena that they can effectively explain. If they happen to fit the observed phenomenon, then it is likely that they reveal the objective laws behind the phenomenon. Once models become more complex and have more parameters to adjust, they can effectively explain the scope of phenomena: for any set of observational data, these complex theories can make the theories match the data by delicately mediating parameters. Such complex theories seem to explain more phenomena, but they are also farther away from the objective laws behind the phenomena.
Shave our universe?
In May 1965, radio astronomers Arno Penzias and Robert Wilson "listened" to sounds from the universe with the Holmdel Horn Antenna, a huge, horn-like device. They tried to calibrate the antenna to reduce noise, but when they aimed the antenna at a dark region outside the galaxy with only a few stars, they didn't get the silence they expected, and instead they accidentally "listened" to a hissing sound—a hissing sound that filled the entire sky.
The fortuitous discovery supported the "hot explosion" model of the universe— the universe was initially very small, hot and dense, then gradually cooled and expanded outward. The hiss they "hear" is the afterglow of the Big Bang — the remnants of matter being diluted in the vast expanse of space after cooling, known in astronomy as the "cosmic microwave background." Scientists have reduced the original form of the universe to a very dense point, singularity, similar to the physics of thinking of an object as a particle, which is consistent with one of the basic characteristics of the model of physics: simplicity.
However, scientists don't always think of "simple" theories from the start. When Einstein tried to incorporate gravity into the theory of relativity, he initially used a very large number of parameters in the model, trying to integrate all the known information into the model. However, a decade of struggling with complex equations ended in failure, and Einstein eventually embraced Occam's razor, changing his equations as simple and elegant as possible, and the final theories were repeatedly verified by observations.
So are our other existing physical theories simple enough? Why are there as many as 17 kinds of particles in the Standard Model of particle physics? If the universe is simple, why are trillions of massless, electrically neutral neutrinos passing through our bodies every second? Will neutrinos be unnecessary entities that need to be "shaved off"? Another inevitable entity may be mysterious dark matter, and we have not observed any direct evidence of the existence of dark matter, will this be another physical model that will prove to be fictional in the future?
In fact, neutrinos and dark matter are proposed precisely because we observe new phenomena that cannot be explained by old simple theories. Physicists in the 1920s were puzzled by the phenomenon of energy conservation during the decay of β, so they proposed that there was a new particle that took some of the energy out of the reaction, and neutrinos were discovered. After incorporating this new phenomenon into known information, the hypothesis of the presence of neutrinos remains the simplest that can explain known physical phenomena.
The same is true of dark matter. In the 1970s, astronomers discovered that the edges of a large number of galaxies were rotating at a greater rate than the theory of gravity predicted. So astronomers speculated that there might be matter we can't see, and that it envelops the galaxy, providing additional gravity to keep the galaxy's rotation speed at a high level. Dark matter was added to the particle physics model precisely to explain new phenomena that the old theory of gravity could not explain.
Of course, there is no end to science, and the current Standard Model is not the ultimate answer to our universe. Future scientific exploration, on the one hand, will find more phenomena that cannot be explained by existing theories, prompting us to adjust the theory step by step and add some "necessary" entities; on the other hand, based on the phenomena that have been observed so far, scientists can still try to build simpler models.
For example, for the phenomenon that elicits dark matter, some scientists argue that there is no need to add a particle that does not now have any observational evidence, but to modify the existing theory of gravity to explain. Thus, while the revised theory of gravity is more complex than the original, it is simpler to explain new phenomena than to introduce dark matter. This is still consistent with the Occam Razor principle. Before the dust settles, scientists will make more efforts from these two aspects to find the relatively correct law of nature. In the process, we can still witness the guiding role of Occam's razor principle.
Original link:
https://aeon.co/essays/why-is-simplicity-so-unreasonably-effective-at-scientific-explanation
Simple: The Ultimate Answer to the Universe?
Source: Global Science
Edit: Garrett