In the Dark: 95 Percent of the Universe Remains Unexplained


Madison Donahue-Wolfe
Staff Writer
Illustration by Hector Lizarraga, Staff Illustrator

Humans, along with everything on Earth and everything we have ever discovered in space, constitute less than 5 percent of the universe. This type of matter, also known as “ordinary matter,” is minuscule when compared to dark matter, which, when combined with dark energy, forms the remaining 95 percent of the universe. Interestingly, the dark matter that composes the majority of the universe remains a mystery to astrophysicists and cosmologists alike.

Dark matter is hypothesized to account for a large part of the unexplained mass that appears to be missing from the universe. Since dark matter neither absorbs nor emits light, it cannot be observed through telescopes. The only way dark matter can be observed is through its gravitational effects on visible matter and radiation. Recently, the Planck space observatory, operated by the European Space Agency, released a map of the cosmic radiation of the universe, and it is through this map that the current figures for the composition of the universe are gleaned. According to the spacecraft’s findings, the universe is comprised of 4.9 percent ordinary matter, 26.8 percent dark matter, and 68.3 percent dark energy.

An attempt to understand dark matter was made at the Argonne National Laboratory in Illinois, where several supercomputers ran simulations modeling the intricate physics of mass in an expanding universe. This project, called the Hardware/Hybrid Accelerated Cosmology Code (HACC), tracks roughly 1.1 trillion particles as they expand and bind together. The goal was to better understand patterns of matter and, by doing this, be able to detect the dark matter that makes up a majority of the universe.

This project required some of the most powerful supercomputers on Earth. According to The Verge, the simulation used an astounding processing power of over 25 petaflops, a speed only one other supercomputer in the world could manage. This amount of processing power allowed the simulation to track trillions of mass particles as they combine to form larger structures. These initial mass distributions are dominated by dark matter, and from this dark matter, ordinary matter forms into galaxies and stars.

Although this simulation provided some idea of the mass distributions by which dark matter forms, scientists still debate what dark matter actually is. Clear ideas exist on what dark matter is not, however. It is not in the form of dark clouds of normal matter, which is made up of particles called baryons. Baryonic clouds would be detectable by the radiation passing through them, and since dark matter does not absorb any light or radiation, this is not a possible explanation. It is also not antimatter, which emits unique gamma rays when it annihilates with ordinary matter.

The most common view among cosmologists is that dark matter is comprised of WIMPS (Weakly Interactive Massive Particles). WIMPS are subatomic particles not made up of ordinary matter. As such, these particles can pass through matter without a trace, hence the name “Weakly Interactive.” WIMPS only interact with ordinary matter via gravity and the weak nuclear force. They also do not emit any form of light or radiation, which make them a reasonable candidate for the substance that composes dark matter.

There is still much to learn about the universe, and, as 85 percent of it remains unobserved, it is clear that discoveries will continue on centuries past our lifetime. The project conducted at Argonne National Laboratory is another step toward discovering and understanding the mysterious dark matter that makes up nearly the entirety of the universe.