What is Dark Matter? My Question and the beauty of uncertainty

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Every student at Quest must create a unique “Question” and create a proposal that will guide their learning and experiences they have during their final two years at Quest University. This is something that takes place during “Question Block,” a class that is dedicated to this effort. After many weeks of thought, constructive criticism, revision, and consultation, I am on the brink of completing the course, culminating into my Question: “What is dark matter?

This image is of the Bullet Cluster, one of the most compelling pieces of evidence for dark matter we currently have. The blue areas indicate where we have been able to detect dark matter concentrations using gravitational lensing, while the red is where the largest distribution of luminous matter lies. Image Credit: Nasa, ESA, CXC, M. Bradac (University of California, Santa Barbara), and S. Allen (Stanford University)
This image is of the Bullet Cluster, one of the most compelling pieces of evidence for dark matter we currently have. The blue areas indicate where we have been able to detect dark matter concentrations using gravitational lensing, while the red is where the largest distribution of luminous matter lies. Image Credit: Nasa, ESA, CXC, M. Bradac (University of California, Santa Barbara), and S. Allen (Stanford University)

Dark matter is a mysterious substance that composes 26% of the Universe’s energy density and 87% of its mass. We’ve had evidence of its existence since the 1930’s with the research efforts of Fritz Zwicky, and additional concrete evidence since the 1970’s has been compiled into our certainty that it is a large physical component of our universe. Notably, Vera Rubin showed that the observed tangential velocities of galaxies would be impossible if they weren’t accounted for by an additional “missing mass” with a distribution unique from that of luminous matter.

Vera Rubin, the principle contributor to evidence of dark matter via galaxy rotation. Source: American Institute of Physics, Emilio Segrè Visual Archives
Vera Rubin, the principle contributor to evidence of dark matter via galaxy rotation. Source: American Institute of Physics, Emilio Segrè Visual Archives

So we know that it exists. We know that it can account for the unnatural rotation of galaxies and the weird observations we have of the orbits of galaxy clusters, but we don’t know what it actually is. Finding out dark matter’s composition proves to be extremely difficult because it only weakly interacts with baryonic (normal) matter, the stuff that the Sun, Earth, cars, and pancakes are made out of. This means that currently we can only see its gravitational effects. It doesn’t interact with or emit light (other than the relativistic effects it has by bending its path through space), hence why we call it dark matter. As a result, a particle explanation for what it is proves rather difficult.

There is hope, however. CERN, the particle accelerator in Switzerland hopes to detect it directly through high-energy collisions. So far, through, nothing has turned up. Indirect detection is another possibility. This involves methods including the observation of hydrogen clouds in our Galaxy embedded within dark matter clusters. By measuring their motion and their contraction, we can gather information regarding the mass of each individual dark matter particle by using certain laws of thermodynamics. This is likely the direction my research while at Quest will head.

The Large Magellanic Cloud, one of the Milky Way's satellite galaxies. Clouds like this might be the key to understanding some of the properties of dark matter. Credit: C-141 KAO Imagery: Supernova 1987A (April 1987 - New Zealand Deployment) Large Magellanic Cloud; Photographer: C-141 Imagery; Date: Jun 23, 1987.
The Large Magellanic Cloud, one of the Milky Way’s satellite galaxies. Clouds like this might be the key to understanding some of the properties of dark matter. Credit: C-141 KAO Imagery: Supernova 1987A (April 1987 – New Zealand Deployment) Large Magellanic Cloud; Photographer: C-141 Imagery; Date: Jun 23, 1987.

This is not a question I expect to answer during my time at Quest. A good question never is. It’s going to require a lot of hard work and exploration well beyond my undergraduate education. It may be possible that an explanation doesn’t even arise during my lifetime and surprisingly, I’m more than okay with that. The fact that an unknown exists is the reason why science is worth doing. If that unknown exists for dark matter throughout my entire life, so be it. That just means I’ll always have something interesting to do.

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