What if aliens showed up today? Not just any run-of-the-mill group of aliens either. We are talking about a group of highly intelligent creatures that have cracked all the mysteries our universe holds. These alleged aliens would know everything about the nature of reality. If they were to try to explain these ideas, do you think humans would be able to understand them? Better yet, would our leading ideas in science line up with what the aliens have to say? With our present-day understanding of the universe, how close would we be?
Most physicists would tell you that we are on the right path, but we still have some progress to make. In humanity's relentless pursuit to understand our reality, we have come up with testable and astoundingly accurate theories that explain events happening in an unimaginably small scale and an infinitely expansive universe. However, the current mathematical frameworks explaining the colossal and the minuscule do not agree with each other. For the past century, leading physicists have placed their hopes in the ever so elusive unified field theory or theory of everything (TOE). But, should they?
In particle physics, a unified field theory, or grand unified theory, is an attempt to describe all fundamental forces and the relationships between elementary particles in terms of a single theoretical framework.
In the mid-19th century, James Clerk Maxwell formulated the first field theory in his theory of electromagnetism, which demonstrated the relationship between the forces of electricity and magnetism. Then, in the early 20th century, Albert Einstein developed general relativity, a field theory of gravitation. Later, Einstein and others attempted to construct a unified field theory that incorporated both electromagnetism and gravity as different aspects of a single fundamental field.
Some researchers say that a unified theory is chasing a unicorn. Nevertheless, a vocal majority, including Einstein, believe it is possible to bridge the gap between the electromagnetic force, the strong and the weak nuclear forces, and gravity.
As the Cosmologist and particle physicist John Barrow of the University of Cambridge in the UK wrote, "Finding a theory of everything is quite conceivable. The laws of nature are rather few, they're simple and symmetrical, and there are only four fundamental forces." However, we are getting ahead of ourselves. You may be asking what exactly is a theory of everything?
Why do we need a grand unified theory?
The universe and everything in it are held together by four fundamental forces; the electromagnetic force, the strong and the weak nuclear force, and the gravity. The first three forces form the standard model of particle physics, which is the world of quantum mechanics in a nutshell. You are probably familiar with some aspects of the quantum world, like quantum entanglement and the uncertainty principle. Gravity is the black sheep of this family of forces, walking around like an unruly child, making things very difficult for everyone.
The gravitational force explains the behavior of all things with mass or energy. In 1915, Albert Einstein proposed his general theory of relativity, which describes gravity not as a force, but as a consequence of the curvature of spacetime caused by the uneven distribution of mass.
However, things (mostly math) fall apart when both quantum mechanics and relativity are applied together. A theory of everything would bring everything together, mathematically, and hopefully in a beautifully unified theory. However, this is immensely difficult. Although our understanding of physics has expanded since Einstein's contributions (i.e., strong and weak nuclear forces).
As the famed physicist once said to a student, "I want to know how God created this world. I'm not interested in this or that phenomenon, in the spectrum of this or that element. I want to know his thoughts; the rest are just details." So how much closer are we to knowing the mind of God? Well, it depends on who you ask. There are multiple candidates for a theory of everything, each with their own peculiarities, but each of them is equally mind-boggling. For this article, we will focus on the core ideas of these theories. Let's begin.
String Theory: A vibrating multiverse
String theory is probably one of the strongest candidates on our list, as it is one of the most-explored potential theories of everything. You may have heard of it before in pop culture, or perhaps you have a friend who loves talking about it when drunk.
However, the world of string theory is a deep rabbit hole that can be a little brain-melting. String theory posits that particles are actually one-dimensional strings that vibrate at the very basic level.
According to String Theory, these strings vibrate at different levels determining particle types and properties, such as mass and charge. But, for this theory to work mathematically, extra spatial dimensions that cannot be experienced directly by humans need to be taken into the equation.
Though radical, the idea is an elegant approach to the conundrums mentioned above. However, there are multiple issues with string theory. We are going to focus on two big ones.
First and foremost, string theory is just that, "a theory," and theorists are having a hard time finding ways to properly test this idea, with some physicists going as far as to say that string theory is pseudoscience. This may change very soon. Leading physicists from institutions like Harvard University and Stony Brook University believe the key to constructing a TOE over string theory revolves around the concept of inflation.
Inflation is thought to have played a major role in the Big Bang's earliest moments, explaining why the universe looks the way it does, and why it went through a phase of extreme expansion. If string theory can eventually be made to explain inflation, it may be one step closer to becoming the grand unified theory that we have been looking for all these years. However, this leads to our next issue.
At the moment, there are too many variants to the theory. Physicists have taken a shot at unifying multiple string theory ideas, creating a more general framework dubbed M-theory. However, M-theory just opens the doors to 10^ 500 universes. Some believe that this could be proof that there are multiple universes, or that the theory is untestable. String theory appears to have a long way to go before the scientific community can embrace it.
Loop Quantum Gravity: A universe braided together
LQG or loop quantum gravity is currently one of string theory's biggest contesters for the title of "theory of everything". The general idea for loop quantum gravity is that space is not continuous but is broken up into tiny chunks or quantas: gravitational fields about 10^-35 meters across. These quantas of space are then connected by links to form the space that we experience. When these links get tangled into "braids" and "knots", they produce elementary particles. LQG has some bold claims, including describing how the universe may have formed after the collapse of a previous universe. Unlike string theory, LQG does not introduce extra dimensions and does not try to unify all forces. The theory could be used to explain some big real-world ideas and help clarify the beginning of our universe.
However, most versions of loop quantum gravity struggle to incorporate gravity, and in fact, some don't even attempt to. Instead, they make an effort to quantize the gravitational field while it is kept separate from the other forces
Quantum graphity: Things are getting a little radical
This is the point on the list where things begin to get a bit weird, moving beyond mainstream science to more fringe areas of science or full-on thought experiments. Fotini Markopoulou and her colleagues at the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada aim to throw many universal assumptions out the window on their quest to find a theory of everything. Dubbed Quantum Graphity, Markopoulou believes that when the universe formed in the Big Bang, space did not exist as we know it.
According to this theory, the universe as we know it was once an abstract network of "nodes" of space. Each node was connected to one other. However, soon after the Big Bang, the universe collapsed, creating the principles that govern our reality today.
Quantum Einstein gravity: Gravity to a point
One of the biggest issues with connecting gravity to the world of quantum mechanics is what happens to gravity on very small scales. Things get a little weird. The current models we have suggest that gravity is a very weak force. The same models would also have you believe that the closer two objects are to each other, the stronger the gravitational attraction between them. But this breaks down on the quantum level. Quantum Einstein gravity could be a potential explanation to this puzzle, and another candidate for a theory of everything. Proposed by Martin Reuter of the University of Mainz, Germany, this idea could open the doors to a quantum theory of gravity.
E8: One of the most beautiful theories in all of science
Garrett Lisi's paper "An Exceptionally Simple Theory of Everything" is controversial, elegant, and beautiful. According to the physicist's E8 theory, the 248-dimensional mathematical object above is the key to understanding the universe. The physicist and surfer's potential theory of everything can be summarized with an E8 Lie Group. Lisi created this structure by graphing the fundamental particles of a chart marking the electro-weak force, the hypercharge, and the charges in the Higgs field. After plotting all these particles on a 3D graph, this complex eight-dimensional mathematical pattern emerged with 248 points. Again, every single one of these dots are fundamental particles with different properties.
This is where things get interesting. There are a handful of particles on the diagram with specific properties that are "missing." This means that we can test and look for particles with these specific properties. Even more so, it is believed that these particles would correlate with gravity bridging our quantum and general relativity gap. Of course, this theory should be taken with a grain of salt, and even Lisi still believes the idea needs some work. However, he thinks it has a better chance of being a theory of everything than string theory. Shots fired.
Pseudoscience? Do we need a grand unified theory?
As you have probably noticed, a lot of these theories float on the fringes of science. Even our most promising candidate — string theory — still struggles with finding practical ways of being tested. A grand unifying theory is based on the assumption that nature has an elegant, symmetrical mathematical solution to the principles that govern our reality. However, science shows us time and time again, that this is rarely the case. In an article for Nautilus, Sabine Hossenfelder, a Research Fellow at the Frankfurt Institute for Advanced Studies, the researcher stated that "This whole idea of a theory of everything is based on an unscientific premise."
"This is simply not a good strategy to develop scientific theories, and no, it is most certainly not standard methodology. Indeed, the opposite is the case. Relying on beauty in theory development has historically worked badly."
At times, the theory of everything seems to be as elusive as a shiny Pokemon and as mythical as a unicorn. Do you think one of the theories above will explain the nature of reality? Or do we still have a long way to go? What other ideas or approaches should we consider?