As physicists ambitiously search for the most fundamental particles, we get closer and closer to understanding the science of all matter. According to Columbia University physics professor Brian Greene, “the ultimate theory would provide an unshakable pillar of coherence forever assuring us that the universe is a comprehensible place.” But is such a thing even possible?
While preparing for an evening lecture, 19th-century Danish physicist Hans Christian Ørsted watched his compass needle change direction when it was close to an electrical battery. Understanding how electricity affected magnetism led to the discovery of electromagnetism, a force that unified electricity and magnetism. Physicists began to wonder if they could unify all the forces this way, and perhaps, create a theory of everything.
The universe has been expanding from a hot dense state of matter for about 13 billion years. Throughout time, everything that makes up atoms came about from interactions between light and quarks, particles that compose protons and neutrons. The force that made this happen was separated into fundamental forces along the way. And we’ve come a long way in trying to unify those forces.
These four fundamental forces are electromagnetism, gravity and strong and weak nuclear force. Most people are familiar with electromagnetism, the force between electrically charged particles, and gravity, the force between mass (but also energy). The latter two affect quarks and similar particles that comprise subatomic particles.
In the second half of the 20th century, physicists subsequently discovered relationships unifying electromagnetism with the nuclear forces. But their relationship to the gravitational force remains a mystery. In addition, our theories of quantum mechanics and general relativity are incompatible with one another. Our Standard Model of particle physics explains these unified forces, but to understand what everything is made of, we need to unify all the four forces to obtain a theory of everything and resolve these differences. So what’s the issue?
On a large scale, theories are riddled with randomness, uncertainty and inaccuracy. We can always cast off events as outliers and limitations. For physicists, we can’t simultaneously know the position and momentum of a particle. Theoretical physicist Lawrence Krauss writes in his article “The Trouble with Theories of Everything,” that “there is an inherent uncertainty in energy and momenta that can never be reduced.”
The ways physicists describe the universe have limits. Some scientists, such as Greene, argue replacing point-particle material with microscopic physical processes of strings (known as string theory) would explain everything. The same way the strings on a guitar vibrate to create chords and melodies, strings would create matter and forces. But string theory’s main issue is it doesn’t have empirical (or observable) evidence. Simply put, it works on paper, but not in practice.
What if there is no theory of everything? As 20th century American physicist Richard Feynman speculated, it is possible there is no theory that applies everywhere all the time. Even if we don’t know everything, we do know some things. While scientists continue to debate, mother nature will work while we watch in wonder.