Science is my favourite realm of study. Although physics is the branch that I am most comfortable with, I find science as a whole very fascinating. It seems to me that science can be broken down into five categories: physics, chemistry, biology, psychology and sociology – in that order.
How do these five pillars relate to one another? What is their connection? Consider the following simple organizational chart.
A Scientific Road Map
The scientific road map shown above is organized in terms of causality and complexity.
Although my physics students would disagree, physics is the simplest science, as there are only a few key relationships to consider. There are only four kinds of forces that affect the way in which matter interacts in the universe. Conversely, there exist hundreds of known elements and millions of known chemicals, each with their own unique properties. Chemistry is indeed more complex than physics. Bring the chemistry to life, and you have biology. The most baffling aspect of biology is the brain of an organism, which is the least understood organ in the human body by far. The only thing more complicated than psychology would be how many psyches interact: sociology.
Let us now follow this chart in the reverse sequence. Why do people act the way they do? This is the root question in sociology. Well, the answer may be found in the study of psychology. What controls our psyche? It is most certainly biological. Biology is simply chemistry, and the way in which chemicals interact is governed by the laws of physics.
The neat thing about the scientific road map is that it is chronological from left to right. What arrived first in the universe after the big bang? For the first 5 billion years, the laws of physics were sufficient to describe everything in the universe. After all, there were only two elements in existence (hydrogen and helium undergoing fusion within stars). When stars burn out, they release many new elements, and the study of chemistry becomes necessary. Perhaps 10 billion years after the big bang, life begins to emerge, and biology is born. Evolution then runs its course, such that biological complexity increases from bacteria to organism. Once organisms become sentient, the study of psychology pops up. Finally, when groups of sentient beings begin to interact in large groups, the branch of sociology comes into existence.
It makes sense that the complexity of the universe should grow with time. This is what the second law of thermodynamics predicts: entropy (chaos) can never decrease with time.
One final conclusion I take from this picture, which comes as no surprise, is that physics governs everything. If you continuously ask “Why?” for any problem within the scientific realm, you will eventually arrive in physics territory. Physics is where the why ends. In truth, physics is the how, and the rest of science from chemistry on down is the what. Physics is the king of the scientific jungle, sitting atop the scientific food chain.
This is what Rutherford meant when he said, “Physics is everything – the rest is stamp collecting.”