The foundations of the universe

Observing dark matter in distant galaxies

Image credit: NASA/ESA

How dark matter could potentially be at the nexus of our understanding of the Universe

TThe Universe is a vast, mindboggling collection of everything we know and don’t know yet. To understand the Universe, we need to look deeper. We can ask ourselves many philosophical questions about why the Universe is the way it is - Why does the Universe behave as it does today? Where did all of the matter we know come from? How did humans affect this timeline?. If we delve into the depths of these questions, where do we end, and what is our final answer?

As we dive into these little questions, a reality emerges. Particles smaller than atoms themselves, the subatomic particles, are the building blocks of the complex Universe we know today. They have existed for as long as we know - since the beginning of the timeline of our Universe. All of the matter we see today is made of these subatomic particles. All of these subatomic particles are only a small percentage of the Universe. All that is remaining is just void! One question remains unanswered, though: What is the remaining black, void-like part of the Universe made of? Is it really a void? Could it be that this will define the Universe? This void of blackness is filled with what particle physicists like to call dark matter, an unknown substance that some scientists think could help generalize and understand the Universe as a whole.

Before we understand dark matter, we need to understand the fundamental subatomic particles and their behavior. Dr. Can Kilic, a particle physicist working at the University of Texas at Austin, has worked in the field of collider physics at various particle accelerators. His research on the Standard Model of Particle Physics provides us with some insights. The Standard Model is an organized collection of the fundamental particles we know. To understand the basics of particle physics, there are a couple of key ideas that we need to wrap our heads around. First is the Standard Model, and the second is quantum field theory.

“Quantum field theory tells us basically the general rules, or what particles are, how they interact with each other, and how they exchange energy,” Dr. Kilic said. “Basically, it comes down to a set of rigid rules, which are pretty mathematical, but the intuitive way to think about it is … there are a bunch of particles [in space], there are [strict]

“Thinking is not the same as proving. Right now, there is no [definitive] evidence.”

rules for who can exchange energy with whom, and that forms a quantum field theory. So, the Standard Model is a quantum field theory. Quantum field theory describes all possible worlds, and the Standard Model describes the one that we happen to live in, with the particles that we know and the forces that we are aware of.” Realm” in Avengers: Endgame, which Ant-Man, Doctor Strange, and The Wasp accessed only through shrinking to a very tiny scale. There were no other ways to get there. One could consider the Standard Model as the set of rules that predict what happens in this Quantum Realm!

There are many things that the Standard Model can describe, Dr. Kilic explained. All of the particles we know exist, and the fundamental forces, except gravity, are described by the Standard Model. These include the electromagnetic force (transmitting electric/magnetic waves), the weak nuclear force (responsible for particle decay), and the strong nuclear force (holds atomic nuclei together). These three forces are transferred through the bosons (nicknamed the “force carriers” in our Universe) of the Standard Model. There are four bosons: the photons, the W and Z bosons, and the gluons. There is also one remaining boson, the Higgs boson, which gives other particles mass.

Remember the Quantum Realm? Well, as The Wasp learned, getting out of the realm was a matter of its own! Likewise, in the real world, we see that gravity (a fundamental force) is not included in the Standard Model, as it does not fit nicely with other force equations. There is a separate understanding required for gravity. Scientists do not know how to represent gravity using mathematical equations. Gravity is always present; it is dynamic and changing with space and time. However, quantum mechanics is rigid in space and time. Dr. Kilic explained that trying to mathematically represent gravity in quantum mechanics often resulted in inexplicable infinites in the

equations. String theory, he noted, was a promising method of explaining gravity using quantum mechanics to a certain extent. It may not give particle physicists a full mathematical understanding of gravity but promises to combine all forces into a single, unified theory.

Jacques Distler, a professor of physics at the University of Texas at Austin, has worked extensively on string theory. Dr. Distler generalizes string theory to higher-dimensional theories. He said we only see four dimensions: the x, y, z dimensions in space and the time dimension. However, there is a possibility of dimensions beyond these four (thus the name “higher dimensional theories”) that are curled up behind each other in a manner that does not allow us to observe them with the energies given to us.

“One analogy … is an ant crawling on a … very thin drinking straw,” Dr. Distler said. “So that is really two-dimensional, but if you’re large compared to the diameter of the straw, then you really only see the one dimension along the length of the straw and not the circular direction orthogonal to that.”

Using this concept of the possibility of multiple dimensions, Dr. Distler introduced string theory as a framework for other theories in nature. “Solutions” to string theory are a certain amount of dimensions curled up in a complex manner. He explained that understanding solutions individually could help us derive and understand results we could not have reached with ordinary quantum field theories. Scientists have even observed far-away places in the Universe that obey predictions by string theory. However, it does not give us a complete view of gravity because gravity is a classical concept understood at a macroscopic level. However, quantum theory, like string theory, is understood at a very microscopic level. This is the reason gravity is not a part of the Standard Model.

With all the basics of the Standard

Data from the Chandra X-Ray Observatory tests String Theory

Image credit: NASA/CXC/Cambridge Univ./C.S. Reynolds

The Linac4 particle accelerator

Image credit and copyright: CERN

Model and quantum mechanics, we can now take a step into the research of dark matter. Dr. Don Lincoln, a particle physicist at the Fermi National Accelerator Facility, is experienced in researching particles at accelerators around the world. These particle accelerators collide different particles at very high energies, enough to simulate the early Big Bang in a tiny microscopic area. The results of the collisions are observed, and new research is built upon it.

As Dr. Lincoln explained, dark matter cannot be easily observed like other particles. We do not even know if it exists in the Universe, but the thought of dark matter arises from observations about galaxies deep in space. We observe some galaxies (not all) to rotate faster on the outside than predicted, which could indicate there is some quantity of invisible mass we have not detected. This invisible mass is known as dark matter.

“People are going back to the drawing boards and saying, well, let’s take another look at the idea that gravity is messed up, or inertia is messed up,” Dr. Lincoln said. “Right now, it’s an open question. We simply do not know if dark matter is real or not. All I can tell you is that most astronomers think that it is. But thinking is not the same as proving. Right now, there is no [definitive] evidence.”

We can only experience or deduce that something like dark matter exists but cannot see or detect through our current tools or technologies. This brings memories of the scene from Star Trek: Enterprise. T’Pol detects a higher concentration of particles, yet all that is visible is just stars filling the black universe. Captain Archer sends two charges at what seems to be a void. A few moments later, the charges explode, and a brilliant “dark matter nebula” is revealed. In a similar manner, we can see the effects of dark matter through galaxy rotation but do not know what the root cause is.

Dark matter, as seen through these observations, only seems to interact with gravity. We have no clue what particles it is made of, if it exists, or if there is something we do not understand about the Universe yet. This brings back the point of how hard it is to observe dark matter because particle accelerators work with quantum particles, not classical objects. Dark matter, as a result, could be at the crux of our understanding of the Universe. It is a twist between dimensions and particles that scientists have yet to uncover.