physical phenomena as 'law of nature'

19th century technology was able to show that Kepler’s laws were only an approximation for planetary movement. In reality, gravitational forces associated with all of the different celestial bodies (not just the un, as idealized by Kepler) led to the planets following a slightly different (though still elliptical) path than Kepler predicted. These actual observed trajectories are much more complex than can be explained solely through Kepler’s laws. On top of this, Kepler’s laws do not explain the causal nature of the movement of celestial bodies — they only provide an empirical framework to accurately predict and analyze their approximate motions. However, these kinds of “universal” laws are still important to scientific knowledge because they give us a framework to analyze the causes behind natural phenomena.

To begin talking about universal laws and their importance, we need to define what a universal law really is, since it is not clear how (if a universal law is not an exact representation of what occurs in nature) they can be referred to as “universal.” I define a universal law to be a general mathematical formula or statement that can accurately describe patterns in nature. Universal laws also necessarily attempt to explain a truth about nature. However, universal laws also make assumptions about other factors being static, because it is impossible to account for every possible variable that affects the phenomenon. The “universality” comes from the law being applicable to all scenarios within the given scope.

In order to see how universal laws provide us a framework to develop the causes of natural phenomena, I will show how two of Kepler’s laws led directly to the derivations of causal explanations for planetary movement. Kepler’s first law states that planets trace an elliptical path around the Sun: the ellipse is defined by placing the Sun at the first focus, and reflecting the Sun about the vertical axis as the second focus. This discovery was a shock to scientists at the time, who were fascinated with elegant mathematical symmetries. The assumption that all natural movement was symmetric and stable implied that celestial orbits acted in uniform circular motion at a constant speed. However, Kepler’s discovery directly opposed this belief, and allowed scientists to move towards providing more rigorous, empirical evidence for the causes behind natural phenomena. Kepler’s second law states that bodies move faster as they get closer to the Sun, and slower when they are farther out. This law similarly served to push scientists away from providing a divine explanation for their scientific reasoning, since the planets did not move at a constant velocity throughout their orbits. Further, it gave Newton, whose Law of Gravitation dealt with the causes of planetary motion, a reason to account for this change in speed and thus Kepler’s laws directly contributed to the discovery of a cause for this motion. In order to formally derive this cause, Newton had to develop his three laws of motion which fundamentally altered the way we think about all objects and their forces and movement, and revolutionized the (extremely scientifically important) field of classical mechanics.

Nancy Cartwright provides a convincing argument as to why universal scientific laws may be problematic in her How the Laws of Physics Lie. She explains that scientific laws contain a lot of idealizations, which implies that we should not treat them as direct representations of nature or natural processes. When a universal law gives us an idealized result, we often forget that the real world will likely give us a different answer. If we take these universal laws as the natural truth, we may not explore why the real world is different from the idealized version that the model gives us, and thus may not ever delve into the causes behind the disparities, and these causes may actually be extremely scientifically useful. For example, Newton’s law of gravitation is idealized to be in a vacuum, and in a vacuum, both a feather and a bowling ball will fall at the same rate. However, due to air resistance these items will not fall at the same time in the real world. If we only look at the universal model, this may cause issues: we may not research the scientific discoveries associated with air resistance, such as fluid dynamics and the importance of considering all forces that apply to an object, which are both extremely scientifically important understandings. I agree with this argument, which is why we need to make a conscious effort to treat these universal laws as approximations that may not always be perfectly accurate. We need to explore the situations where the universal law and the real world give us different results, and make tweaks to the law as needed.