This blog post examines the scientific validity and philosophical nature of string theory, questioning its very essence.
Einstein, famous for his theory of relativity, had a final dream: unifying all forces in the universe into one. His final quest, dubbed the ‘unified field theory,’ was unsuccessful, and since then, countless physicists have attempted to achieve it. Under the perspective that physics is broadly divided into relativity theory, which deals with the macroscopic world, and quantum mechanics, which deals with the microscopic world, the three forces explainable within the microscopic world—electromagnetic force, weak nuclear force, and strong nuclear force—have already been unified through various efforts. However, gravity alone is described within relativity theory, which deals with the macroscopic world. Consequently, the final step of unifying these three forces with gravity has proven challenging. To overcome this difficulty, the puzzle of unified field theory led to the emergence of ‘string theory’. This blog post aims to examine the validity of this theory.
String theory is grounded in quantum mechanics, necessitating the recreation of such a microscopic world. Conditions from the early universe, particularly those at the beginning of creation, provide the environment for verifying string theory. However, recreating these conditions is currently beyond the capabilities of existing technology. Furthermore, a theory in science must be testable through experiments to exist within the boundaries of science. Should we blame the lack of scientific technology for being unable to verify string theory? It seems not. While string theory attempts to be self-contained within its own mathematical logic, it is criticized for being overly fixated on achieving mathematical completeness solely for ‘theoretical’ proof, making its conclusions seemingly impossible to verify experimentally. It demands experimental conditions far beyond merely recreating the initial state of the early universe. This makes it seem as if string theory itself asserts it exists solely within the realm of an ideal mathematical logic system. Researchers of string theory bear the responsibility to propose methods for verifying the theory that are not ‘idealistic,’ ensuring it can exist within the scope of science. Otherwise, while they may remain free to continue researching their theory, it becomes difficult to freely assert its validity. The philosopher of science Karl Popper advocated the ‘principle of falsifiability,’ emphasizing that a scientific theory exists as a good theory precisely because it possesses a high potential for falsification. String theory appears unlikely to exist as a good theory. This is because there is currently no way to falsify it, and the point at which this might become possible seems distant.
It is said that the current level of mathematics is insufficient to handle string theory. It is also said that several developments in mathematics were made solely to handle string theory. And the complexity of the mathematics describing string theory is said to be beyond description. Furthermore, as mentioned earlier, this theory is said to have no experimental connection whatsoever. In other words, string theory appears purely speculative. If the language describing science is mathematics, wouldn’t it be more appropriate to view string theory as merely a branch of philosophy described in the language of mathematics? But if we see it that way, where does the value of string theory’s existence lie? No one would think string theory could have the same kind of influence on human intellect that philosophy has had. Though it may not be science, how should we view string theory, whose value can only be revealed through science? It is clearly not a theory that limits its significance to merely advancing mathematics for its own description.
Then why do string theorists cling to it? Physicists say they are fascinated by the symmetries discovered in the laws of physics thus far. String theory, too, captivates many physicists precisely because of its symmetry. They believe physical truth lies within symmetry. But can a physical theory only be correct if it implies symmetry? The well-known physicist and astronomer Kepler attempted to explain the arrangement of planets around the sun using only the geometric symmetries formed by the five regular polyhedra and spheres existing in the world. This seemed to fit well, but the solar system, which should have contained only six planets within such a structure, actually includes eight. Ironically, the planetary orbits, which should have been spherical, were modified into elliptical orbits by Kepler’s own laws. Interestingly, Kepler never abandoned his belief in geometric symmetry to the very end. This historical anecdote seems to foreshadow the predicament current string theorists would face if string theory were proven wrong. Scientists must base their research direction solely on scientific facts. While personal preferences can fuel a scientist’s will and passion for research, such attitudes cannot be considered scientific thinking. So, within an attitude grounded solely in reason, where should the capabilities of countless scientists be focused?
String theory is assessed by some string theorists as an unfortunate theory discovered a century too early. This is primarily the view advocated by Edward Witten, a leading string theorist. As a leading figure in theoretical physics, Edward Witten wields such influence within the physics community that he is described as “a figure who has reached the unattainable realm of the divine, surpassing even the outstanding individuals present here.” He may indeed be ahead of his time. However, it seems more accurate to view this not as prescience, but rather as straddling the line between precociousness and immaturity. Since string theory has seen almost no experimental verification, its underlying experimental basis is also very weak. Where can this basis be found? If string theory is a theory that can be discussed within the realm of particle physics, the currently accepted final theory in particle physics is the ‘Standard Model’. The Standard Model, considered nearly experimentally validated following the discovery of the Higgs boson, nevertheless still has several gaps that need to be filled and clarified. Everyone knows that a building can be constructed well on a solid foundation. Therefore, perhaps we should focus more on areas where we currently know more and can uncover clearer insights. Within such revelations, the actual clues and foundations of string theory—currently just a collection of complex mathematical equations—might also be formed. Of course, sufficient research must continue so that string theory can fulfill its role as a leading candidate for a ‘unified field theory’. However, I hope to see physicists’ efforts become more active in shifting their focus beyond a blind obsession with physical or mathematical symmetries, and instead drawing attention to the many other fields within theoretical physics.
I’d like to conclude with words left by Steven Weinberg, a physicist who was once at the forefront of string theory: “I have no desire to discourage string theorists. But the world may be just as we have always known it. It is the world of the Standard Model and general relativity.”
