I often hear a lot of very flowery definitions of Physics, such as “The Application of the Scientific Method to Natural Law” or “The Investigation of the Laws of the Universe”. However, much of this appears to make Physics seem much more all-encompassing than it truly is. For example, a Physicist does not concern himself with questions of purely abstract philosophy. What is beauty? Perhaps he may have an opinion, but an objective answer evidently eludes him. Arguably, such an answer could never come from within Physics itself purely due to the nature of the question. If we were to take any of the above answers from above, though, it should be logically true that we can build on the foundations which Physics has given us to find an answer. This is obvious nonsense.

I would like to propose a much simpler and - in my opinion - more accurate definition of Physics:

Physics (noun) - The Study of Rates of Change

Ethan Marshall (2023)

That’s it! Think about it: what is there in Physics which does not involve a rate of change? One of the core principles of Physics is time, a “substance” which does not really exist but which is made to exist through our perceptions of rates of change around us. Physics was shook most severely to its core by the discovery that time may pass at different rates for different observers by Einstein and some of the most important principles of Physics (time invariance or independence, for instance) rely entirely upon rates of change. Even fields of Physics in which no change occurs (such as statics) are simply defined by the rate of change being zero!

I think the perfect quote to illustrate this point is the following:

Since Newton, mankind has come to realize that the laws of Physics are always expressed in the language of differential equations.

Steven Strogatz

Of course, the language of differential equations is that of rates of change. I rest my case.