In this blog post, we will reconsider whether the future of physics is truly over, considering the limitations of the Standard Model and the possibilities of superstring theory.
In 1900, British physicist William Thomson declared at the British Association for the Advancement of Science: “There is nothing new to be discovered in physics. The only task left for us is to improve the accuracy of our observations.” Until the end of the 19th century, physicists believed that the logical system of physics, or classical physics, had been completed and that the only task remaining was to improve the accuracy of observations and calculations. However, with the advancement of technology and science in the 20th century, physicists conducted various experiments related to elementary particles, and when they tried to explain the results of these experiments using Newton’s classical physics system, contradictions arose. This highlighted the need for a new mechanics.
Finally, in December 1900, Max Planck attempted to explain blackbody radiation and solved the problem of ultraviolet radiation by departing from the classical physics framework of continuous energy and instead thinking of energy as small packets with definite values. In 1905, Einstein pointed out that the atomic theory, which states that all matter has a minimum unit, and Maxwell’s electromagnetic theory, which describes radiation as waves, are compatible with each other. He also explained the photoelectric effect through the photon theory, which states that light energy is proportional to the integer multiples of its frequency, heralding the beginning of quantum mechanics.
Later, through de Broglie’s wave theory of matter and Niels Bohr’s model of the hydrogen atom, Schrödinger derived the Schrödinger equation from the wave function of classical mechanics. In 1927, Bohr, Schrödinger, and Heisenberg gathered in Copenhagen and announced the Copenhagen interpretation of the meaning of wave functions based on the principles of complementarity and uncertainty. Immediately after its announcement, this interpretation was met with numerous counterarguments and paradoxes from scientists, such as Einstein’s thought experiment using a photon box, Schrödinger’s cat, and the EPR paradox. However, it eventually succeeded in adequately explaining all of these, and remains the most widely accepted interpretation to this day.
Based on the Copenhagen interpretation of quantum mechanics, physicists studied various quantum theories (quantum field theory, quantum chromodynamics, etc.) and established a theoretical framework called the Standard Model, which deals with the particles that make up matter and the interactions between them. In addition, various elementary particles predicted to exist in this model have been confirmed through experiments using particle accelerators from the mid-1900s to the present, and with the discovery of the Higgs particle, the last remaining particle, in 2013, the Standard Model, a theory dealing with the elementary particles of nature and their interactions except for gravity, was completed. This is the greatest achievement of modern physics, which was created to overcome the limitations of classical physics, and has greatly helped to explain numerous phenomena in the microscopic world that could never be explained by classical physics.
Nevertheless, it seems that the day when humanity will be able to perfectly explain the world is still far away. The first reason for this is that even the Standard Model has many limitations.
First, the Standard Model cannot completely explain four of the five fundamental forces of nature: electromagnetism, weak force, strong force, and gravity. Unlike the weak force and electromagnetism, which can be expressed as a single force and integrated into the electromagnetic force under certain conditions such as high temperatures, the strong force is a completely separate interaction from the other forces within the Standard Model. Various theories to complement this have not yet been experimentally verified. Even the graviton, which is expected to be the particle that mediates gravity, has not been included in the Standard Model. Gravity is a force that we feel as closely as we do electromagnetic forces. Nevertheless, the fact that even the Standard Model, the most complete theory created by humankind to explain the world, which has been verified through experiments, cannot explain gravity means that humankind does not have a sufficient theoretical background to understand the physical phenomena of the microscopic world. In order to describe gravity in terms of quantum mechanics, quantum field theories of gravity and quantum gravity theories that introduce gravitons as mediators of gravity have been proposed, but all of them have been found to be impossible to renormalize. Humanity’s dream of perfectly explaining the universe has been blocked by the enormous wall of gravity, the first interaction to be discovered.
In addition, there are too many types of particles in the Standard Model, and there are as many as 20 constants. There are 18 types of quarks alone, with six flavors and three colors, and when electrons, muons, tau particles, and their corresponding neutrinos are added, there are a total of 24 types of fermions in nature. Furthermore, since all particles have their own antiparticles, there are 48 types of fermions, and the Standard Model includes a total of 61 particles, including photons, W+, W-, Z0, and gluons, which mediate interactions, and the Higgs particle, which gives mass to elementary particles. However, this is too many to be considered the fundamental particles that make up the world. Why do particles have such specific numbers and generations? Why do the 20 constants have their specific values? How are they related to each other? These questions cannot be answered theoretically and can only be answered through experimentation. The Standard Model cannot even explain why important constants have their specific values.
Another reason is that the various theories proposed to resolve the limitations of the Standard Model currently have their own problems, large and small, and it is impossible with current technology to conduct experiments to verify whether they are correct or incorrect. Among the theories proposed to date, the most promising candidate for a theory of everything (TOE) that could resolve the limitations of the Standard Model is superstring theory, which solves the problems of point particle theory by considering elementary particles as one-dimensional strings. However, American mathematician and theoretical physicist Peter Woit argues in his book *The Truth About Superstring Theory* that superstring theory has never made any specific experimental predictions, cannot explain any macroscopic phenomena, and is nothing more than a collection of unrealized hopes.
First, in order to discover and experimentally prove the particles predicted by superstring theory, an astronomical amount of energy equivalent to 100 billion to 10 trillion times the output of the LHC, the world’s largest particle accelerator, is required, and the size of a particle accelerator capable of producing such output would be about the size of the solar system, making it impossible to verify in reality and requiring various assumptions. In addition, there is a severe lack of background theory necessary for the advancement of superstring theory research, and even proper research has not yet begun. In extreme cases, it is even treated as pseudoscience.
The Standard Model is a theory created by humans that almost perfectly explains the interactions of all particles. Along with the theory of general relativity, it is considered one of the greatest achievements of human intelligence, and even today, it is the most accurate explanation of physical phenomena in the real world among theories that have been experimentally verified. However, even the Standard Model has the above problems and ultimately remains an incomplete theory, and even theories that attempt to compensate for the flaws of the Standard Model cannot be verified through experimentation at this point. Therefore, it seems that the day when humanity will be able to perfectly explain the world is still far off.
