From the concept of the atom as proposed by ancient Greek philosophers to the superstring theory of modern physics, this course explores how and why the smallest unit of matter and the four forces of nature vary.
The ancient Greeks believed that all matter was made up of microscopic, indivisible building blocks called “atoms.” They thought that the vast and diverse material world was formed by a few types of atoms combining in various combinations. They came to this conclusion through a variety of philosophical ideas and observations of nature, which was highly innovative thinking at the time. Ancient Greek philosophers, notably Democritus and Leucippus, sought a deeper understanding of the nature of matter and developed the concept of the atom. This atomism remains an important concept that is the foundation of modern science. Although the idea of the smallest unit has changed over time, the ancient Greeks’ view of matter is still accepted as truth.
In the 19th century, scientists discovered microscopic elements thought to be the smallest unit of matter and gave them the name “atom,” inherited from the Greeks. They believed that the atom was immutable and the basic unit of all matter, but it was not the smallest unit of matter. By the 1930s, it was realized that an atom is a complex of electrons circling around a nucleus made up of protons and neutrons. For a while afterward, physicists thought that protons, neutrons, and electrons were the smallest unit the Greeks had in mind: the atom. But in 1968, experiments at Stanford’s Linear Accelerator Center shockingly revealed that even protons and neutrons are not the smallest unit of matter. Protons and neutrons are made up of a combination of two particles named “down quarks” and “up quarks”. Physicists have since invented more powerful instruments and discovered several new particles.
Why are there so many different types of particles in nature, and why is there no apparent regularity between their values (masses)? These questions have long been a big mystery to physicists. The question becomes even more puzzling when you consider the forces that act between particles. There are four forces between particles: the gravitational, electromagnetic, strong, and weak forces*, all of which vary in magnitude and nature. Why do these four forces exist? This is a question that scientists have continually explored in their efforts to understand the fundamental principles of nature.
One candidate for a theory that might answer these questions is superstring theory. The basic idea behind superstring theory is that all matter is made up of vibrating strings. According to superstring theory, the way that the smallest unit of matter, the string, vibrates determines the form it takes, and thus the particles that conventional physicists have discovered are all “different faces of a vibrating string”. And this idea applies to the four forces as well. For example, heavy particles have violent vibrations of the string that makes them up, while light particles have relatively smooth vibrations of the string.
Previously, physicists had thought that the different particles thought to be the smallest units of matter had their own unique shapes and properties, but superstring theory turns this idea on its head. As the smallest unit of matter, strings are all the same. According to the theory, a string is a one-dimensional object that vibrates at a very small scale, and its mode of vibration determines the particle’s properties. If this is true, then the universe, with its countless strings vibrating in different ways, is a giant stage on which a grand “cosmic symphony” is being played. The players in this cosmic symphony are the fundamental laws of nature, and we are constantly trying to understand the music.
The discovery of superstring theory has opened up new possibilities for physicists, providing important clues to understanding the fundamental principles of the universe. The theory also has the potential to provide a unified explanation for many unsolved problems. For example, in the problem of unifying general relativity and quantum mechanics, and in the problem of describing the initial conditions of the universe, superstring theory could be a powerful tool. Although the theory is currently not fully verified, its potential is enormous. Scientists are continuing to study superstring theory, and new discoveries and breakthroughs are expected.
As a result, we will gain a deeper understanding of the fundamental principles of nature through such research, which will contribute greatly to the advancement of human knowledge and technology. In the end, the search for the smallest unit of matter, dreamed of by ancient Greek philosophers, remains an ongoing mystery at the forefront of modern science. We will continue to work tirelessly to solve this mystery, and with each new discovery, we will reveal the secrets of the universe one by one.
