Why String Theory Deserves More Skepticism

String theory seeks to unify the theories of general relativity and quantum mechanics, but it currently lacks experimental evidence.

Reading Time: 3 minutes

Cover Image
By Yile Tong

The million-dollar question in theoretical physics is an elusive one. With Albert Einstein’s theory of gravity on one hand and quantum mechanics on the other, physicists have long struggled to unite the two. Einstein’s general relativity describes gravity as the warping of spacetime by massive objects, which has proved consistent with experimental results. General relativity correctly predicted the existence of black holes, gravitational lensing, the distortion of light around massive objects, and gravitational waves—waves in space caused by massive objects—and has shaped our understanding of physics for over a century.

However, physicists have reason to believe that general relativity may not be the full story. The issue arises with quantum physics. The quantum revolution in the early 20th century completely transformed our understanding of the subatomic world by revealing that subatomic particles exist as probability waves until disturbed by observation.

General relativity and quantum physics model the natural world at completely different scales and thus have fundamental differences. For instance, general relativity considers events like energy transfer to be continuous, while quantum mechanics considers them to be discrete. Though they both have withstood the rigorous tests of experimental physicists, the two theories are incompatible in certain extreme cases that scientists can not yet examine, such as in the centers of black holes or at the instant of the Big Bang. That's where string theory comes in, or at least awkwardly tries to. String theory first arose in the late 1960s to explain the strong nuclear force but was later revised to be a theory of quantum gravity, which attempts to unify general relativity and quantum mechanics.

Of the many proposed unified models of physics, string theory is undoubtedly the most popular. String theory, or superstring theory, proposes that the fundamental particles of the standard model of physics (quarks, gluons, etc.) are actually strings vibrating at different frequencies. Under superstring theory, gravity is thought to be the result of a particle, the graviton, which is again just a string. String theorists hold it as a possible unified theory of quantum gravity because it may unite general relativity and quantum mechanics.

Unfortunately, experimental results have yet to confirm superstring theory—rather, the experiments that have been conducted only invalidate it. For instance, superstring theory requires something called “supersymmetry,” which is where the theory gets part of its name from. Supersymmetry proposes the existence of a partner particle for all particles in the standard model of physics. Scientists have yet to uncover any evidence indicating the existence of these partner particles.

Superstring theory also requires the existence of at least nine dimensions of space. The proposed existence of these dimensions lacks evidence, but string theorists speculate that these other dimensions are so compact that modern experiments lack the energy to detect them. Furthermore, superstring theory clashes with the modern understanding of the cosmological constant, which deals with the energy density of space. It requires the cosmological constant to be negative, but Nobel Prize-winning experimental evidence demonstrated that the cosmological constant is in fact a positive value. This causes the universe to expand at an accelerating rate, whereas a negative cosmological constant would result in decelerating expansion. The contradictions between string theory and scientific observations undermine its validity.

Modern string theory is basically pseudoscience. When new experiments disprove its predictions, string theorists try to put another bandage on the already-dead theory. These impromptu explanations that are currently unfalsifiable prevent the theory from being totally discredited. This is a serious problem because high-energy physics, the sub-branch of physics encompassing topics like string theory, has fierce competition for research funding. It is already impossible for many physicists to find research positions and funding for work that produces meaningful results, so more funding for string theory comes at the cost of genuine progress in physics. But for now, string theory remains a thorn in the foot of physics academia, yet a source of hope for those who pursue it so religiously.