String Theory Explained
The Big Bang Theory will surely go down as one of the most successful sitcoms ever. It ran for twelve years and won many prestigious prizes. The science in the show, although perhaps not fully accurate, is not pure nonsense (Townsend, 2011). The ramblings, concerning quantum mechanics and String Theory, of one of the show's main characters, Sheldon Cooper, are not too inaccurate. Something else in which The Big Bang Theory has surely succeeded is in communicating scientific concepts to a wide audience. Although the number of people that can confidently explain String Theory is rather small, even in scientific communities, because of The Big Bang Theory, many people at least know of its existence. The Big Bang Theory has proven so successful, that big media outlets, including the Guardian, have written about how the TV show has increased students’ interest in hard sciences (Townsend, 2011). In 2016, Li and his team published this conclusion based on real statistics in an actual scientific article (Li, 2016). This string theory could be the theory of everything, a single theory that explains everything in physics, and thus, the nature of the universe. It would therefore combine all the realms of physics, including Einstein's General Relativity, and the infamous quantum mechanics, which will be described in this article too.
The laws of physics have allowed scientists to make incredibly accurate descriptions and estimations about real systems. Newtonian physics, which relies on the physical laws proposed by Newton in the late 17th Century, is amazingly accurate at describing the motions of vehicles, or even planets (Encyclopedia.com, n.d.). By publishing his results and his theories, Newton was one of the drivers of the Scientific Revolution (Schuster, 1990). In recent centuries, knowledge of physics has expanded, leading scientists to believe that they were close to the full understanding of the nature of the universe. When quantum mechanics, the study of physics the size of about an electron and smaller, was proposed by Max Planck, however, everything changed (Labmate Online, 2016). It turned out that the world of the subatomic particle, the really small things, is strange, to put it mildly. The quantum world functions immensely differently from the world that we observe every single day. At the foundation of the current understanding of quantum mechanics lies Heisenberg’s Uncertainty Principle (Busch et al., 2007). This mind-boggling equation shows that a particle’s position nor its speed can be known with perfect accuracy. These uncertainties, when multiplied, can never exceed a certain natural constant. In other words, the more accurately a particle's speed, or rather its momentum, is known, the less accurately its position is known. Consequently, scientists can never be absolutely accurate concerning the position of a particle. The fact that this principle itself is so difficult to comprehend makes all the theories and ideas relying on this key concept even more complex. For this reason, quantum mechanics is thought of as one of the most difficult scientific realms to understand. Richard Feynman, one of the Nobel Laureates heavily involved in developing the current understanding of the quantum world, famously said “I think I can safely say that nobody really understands quantum mechanics” (Caroll, 2019). Quantum physics is a complex realm of science and is mentioned repeatedly in The Big Bang Theory, alongside Einstein's Theory of Relativity and String Theory.
As particle physics too gained significantly more interest and technology, the science of the really small became clearer. The last century has seen a true revolution in terms of physics. Quantum mechanics, particle physics, and astrophysics have had brilliant minds working on them. One of the greatest minds, Albert Einstein, has made incredible contributions to the world of quantum mechanics as well as astrophysics. Another pioneering scientist, Stephen Hawking, has inspired thousands of physicists and other scientists about the wonders of stars and most notably, black holes. And now, after the past 100 years of accepting new theories and rejecting old theories, physicists know more about the universe than ever before. Nonetheless, experts still struggle with explaining the extremities. The very heavy things, most notably black holes, still have significant inexplicable features and paradoxes. Interestingly, one of the largest questions surrounding black holes, the information paradox, seems to be one step closer to being answered, since a publication at the end of last month (Crane, 2023).
One of the larger unanswered questions in science considers the nature of the universe. Scientists would like to see a single theory that explains the universe, a “theory of everything”. Currently, the two “big theories” are the theory of relativity and quantum theory. These explain, or try to, anyway, the really large and small things, respectively. A unification of these two, termed the “theory of everything” is the holy grail in physics, and has been for the past century (Paulson et al., 2015). Many brilliant minds, including Einstein, have tried unifying these two realms of physics, though have not come up with a single theory. At the same time, physicists have identified four fundamental forces, that practically govern everything that goes on in the universe. These four forces are the weak force, the strong force, the electromagnetic force and the gravitational force (Pultarova, 2022). Within an atom, the strong force governs the makeup of subatomic particles. In other words, the quarks that make up protons and neutrons are held together by the strong force, allowing the existence of these protons and neutrons. In very simple terms, the weak force governs the interaction between these subatomic particles (Webb, n.d.). These two forces cannot be seen in everyday life, though they are fundamental with respect to the build-up of matter. In other words, were these forces not to exist, neither would atoms, molecules, nor anything that humans see. The electromagnetic force describes how charged particles, including protons and electrons, interact with each other (Rehm & Biggs, 2021). This force describes many events in real life, including electricity and magnetism. With some very smart tricks, brilliant minds have been able to unify the first three into a single theory, and now know the physical cause of these forces. That is, physicists have identified which incredibly small particles “cause” and are subjected to the weak force, the strong force and the electromagnetic force. This is not yet known for the gravitational force. Neither is it known how this force could be incorporated into a unifying theory (Pultarova, 2022).
Scientists used to think the fundamental particles, i.e., the things that could not be broken down further, were atomic particles. Neutrons and protons famously make up nuclei, which were therefore thought not to be able to be broken down further. However, when scientists collided these small particles with each other at enormous velocity, they did break down further. Breaking down these particles is the goal of particle accelerators, including the Large Hadron Collider (LHC) in Geneva (Rehm & Biggs, 2021). These particles, quarks, were so small that they are not visible in any perceivable way. Because scientists cannot see these particles, their nature is not known. Scientists, therefore, came up with a model, a simplified version of reality that is the foundation of many physicists' theorems. The model used for a particle is a point-particle. These particles are infinitesimally small in size (in other words, they actually have no size) with a particular mass and sometimes a certain electric charge. Although we know that particles are not actually 'points', models based on this theory are incredibly accurate at predicting the features of the particles (Resende & Lopes Resende, n.d.).
The combination of quantum theory and particle physics has shown that all the fundamental forces are carried by specific particles. Gravity, however, is not carried by a particle. Although this sounds rather complicated, in short, we just do now know what causes gravity. Purely theoretically, without any physical proof yet, physicists came up with a new particle, the graviton, and studied formulas from the realm of quantum physics to unify the four fundamental forces (Blokhintsev & Gal’perin, 1934). This did not work, so scientists started to think about their assumptions, and which ones could be wrong. They considered that rather than so-called 'point-particles', particles could instead be a string (Resende & Lopes Resende, n.d.). In other words, every piece of matter in the universe consists of strings that are incredibly small, but able to build different things, comparable to how a single string of a guitar can produce different sounds. The way this string vibrates is different per particle (Johansson & Matsubara, 2011). Thus, the way in which the string of an electron vibrates is fundamentally different to how the strings of a gluon vibrate. Upon the foundation of String Theory, there was a wave of interest and investment in the area. String Theory was seen as a possible theory of everything, able to unify all the fundamental forces. It could do this by building a new particle that causes gravity in matter. One large issue remained, however. In the universe that we observe, which has three geometrical dimensions (x, y and z) and a temporal dimension (time), the math does not work out. Instead of these four dimensions, String Theory requires a world of 10 dimensions to actually work (Johansson & Matsubara, 2011). Although this sounds ridiculous at first instance, the math is so elegant that scientists do not want to consider string theory as a faulty hypothesis just yet. Instead, the idea of a universe consisting of many more dimensions than just four has gained some serious attention. Some physicists strongly believe that this is a possibility, to say the least.
The theory that the universe could consist of many more dimensions than we notice in our everyday life, is possible because these dimensions are incredibly small. So small, that living individuals cannot interact with these dimensions. Instead, these dimensions are compactified, similar to the wire in the image above (Johansson & Matsubara, 2011). Ants are able to walk along the length of the wire. Humans, on the other hand, because they are so large, cannot interact with the cable's second and third dimensions (width and height) in the same way. The theory argues that perhaps there are six more dimensions in the universe that are so small and “compactified” that they cannot be perceived or studied.
One of the big issues with string theory is that it has not been proven yet, and it is becoming less and less likely that it ever will be. The strings themselves would not be able to be observed, given their estimated size of about 10^-35 m (Muñoz-Andrade, 2008). In comparison to the scale animals like us interact with every day (one meter), this difference is incredible and hard to comprehend. The factor difference between these two scales is larger than the difference of one meter compared to the size of the entire universe (Gordon & Tillman, 2022). More importantly, Heisenberg’s Uncertainty Principle shows that however sophisticated technology becomes, this scale can simply never be observed. Similarly, the predictions that follow from String Theory cannot be observed, in part because of the interactions with these very small dimensions. Interestingly, there are many variants of String Theory, and no scientist is sure of which is the correct one. Until a new Albert Einstein or Stephen Hawking comes up with a brilliant insight, physicists will not be any nearer to a theory of everything than they are now (Siegel, 2020). Decades after the first proposal of String Theory, it has not been shown to be the holy grail of physics. That does not mean, however, that string theory is completely useless. For example, its ideas have helped to better understand black holes (Feldman, 2022).
String theory was thought to be a revolutionary theory of everything decades ago. Since then, scientists have moved away from the theory, as they believe its progress is no longer significant. The truth is, nowadays, no one knows for sure whether String Theory is the answer to the question about what the nature of the universe actually is. Even if String Theory proves not to be revolutionary, it will always have the title of the theory that made Sheldon Cooper of The Big Bang Theory a famous physicist, sharing a stage with Albert Einstein and Stephen Hawking.
Bibliographical References
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