Sunday, June 28, 2020

Biology vs. Physics

This is the fifth post in the series on things to learn. See the intro or the last post on learning physics.

The natural sciences are divided into two branches: the physical sciences (primarily physics and its derivatives) and the life sciences (a.k.a biology). Biology is different than physics in many ways, which affect how one learns it:
  • Less Math - Math is fundamental to all of physics but it's more incidental in biology. This can make biology easier to learn for many people.
  • More complexity - As challenging as physics is, it's ultimately about simple concepts. But biology is about life, which is complicated.
    • Textbooks filled with terminology and small details can make learning biology more tedious. However I think there may be a way to focus more on the overall concepts involved than on the exact terminology and details. When learning for general curiosity, you don't need to know every exact term, you can just learn the terms that will be repeated enough to be worth learning. (See XKCD's thing explainer for an exaggerated example of explaining concepts with less terminology.)
  • Unknown frontier - Physics has already solved most areas that a layman would be interested in. The current frontier of physics deals with problems that would be hard a non-physicist to relate to, and it would take years of learning to understand them. Meanwhile biology is filled with unsolved questions in every area from neuroscience to nutrition to genetics to diseases, and one encounters these issues right away. 
    • Update: this point is debatable since there are unsolved questions in physics that a layman would be interested in.
  • Practical - If you're not an engineer you're unlikely to use knowledge of physics for anything practical. But biology topics like nutrition and disease are relevant to living longer and healthier lives.
There are other ways that physics and biology differ:

Inherent or accidental?
It seems that many parts of physics could be intuited based on other principles and couldn't be any other way:
  • Falling objects - Galileo argued against the Aristotelian idea of motion (that heavier objects fall faster) not only with experiments but by pointing out the logical paradoxes that would result.
  • Inverse-square law - While one could imagine forces decreasing in other ratios, decreasing in proportion to r2 seems the most logical since a force radiating out from a point will spread out according to the formula for a sphere's surface (4πr2).
  • Relativity - While most people wouldn't intuitively think of Special Relativity, it seems Einstein was able to recognize that it was the "only way" possible. He was able to derive this based on a deep understanding of the implication's of Maxwell's equations, and he may not even have been aware of the Michelson-Morley experiments.
Questions in physics are still resolved through experiments, but maybe this is to demonstrate the truth to those who don't have the right intuitions of the way nature "needs" to be. When Einstein was asked what if the experiments had disproven his theory of General Relativity, he said "then I would have felt sorry for the dear Lord. The theory is correct." While physics cannot just be pure deduction like mathematics, it's the closest one can get. The eventual goal of physics is to find the theory of everything from which everything else is derived.

Biology however deals with the complex messiness of life, and there's many ways to be a living thing. Scientists can may make predictions based on the data they have, but they can't derive how systems "must" be. Living things are "accidental" in the Aristotelean sense of having traits that they happen to have but could lack.

Ancient and medieval physics used teleological explanations as Aristotle emphasized the "final cause" (or purpose) as one of the "four causes" to explain the way things are, and argued against Democritus who rejected it. Modern physics, starting with Francis Bacon, returned to the physics of Democritus and dropped "purpose" from consideration. Since Isaac Newton, the motion of heavenly and earthly bodies is explained with simple physical laws, without reference to any goal or "natural place" of matter. 

Unlike rocks or stars, living things act with purpose. Even a simple bacterium seeks food, evades predators and maintains its internal state. While scientists no longer use theological explanations to explain why organs and organelles have certain functions and designs, these elements still exist and are worthy of explanation. Some use the term teleonomy to distinguish modern explanations of biological purpose from earlier ones.

In short physics is about mathematical explanations for "simple" things from atoms to galaxies, while biology is about the complexity of life, with all its purpose. 

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