How can we know something exists if it can't be seen?
What is Dark Matter?
Normal matter only makes up a mere 5 percent of the total composition of the universe. Where is the rest of it?
One missing component is dark matter, which makes up 27 percent of the universe. It is called “dark” because it doesn't interact with electromagnetic forces; dark matter cannot absorb, reflect, or emit any light. Dark matter is nearly impossible to observe and has only been hypothesized due to the effects it has on visible matter.
But what exactly makes up dark matter? To put it shortly, nobody knows.
Normal mass is composed of baryonic matter, like protons, neutrons, or electrons. Since dark matter doesn't interact normally like other matter does, some scientists propose that it is made of exotic particles, known as non-baryonic matter. One candidate is known as WIMPS, or weakly interacting massive particles. These particles can be up to a hundred times greater than the mass of a proton, but their weak interactions with normal matter particles can make them difficult to detect. Another strong candidate is neutralinos, a particle that is both heavier and slower than normal neutrinos. Similarly, there are also the hypothesized sterile neutrinos, a type of neutrino that can only interact with normal matter through gravity. However, neither of these candidates has been detected or observed well enough.
Dark matter was an idea that was proposed when scientists were observing spiral galaxies. It was expected that the material would move faster in the center of a galaxy compared to material on the outer edges. Instead, scientists found that objects, regardless of distance, moved at the same speed, which indicated that there were masses that could not be seen. Without this extra mass, clusters of galaxies would fly apart.
Then, What is Dark Energy?
Dark energy makes up the rest 68 percent of the universe. It is distributed within the vacuum of space and has a global effect across the universe, which means it acts everywhere evenly.
Dark energy was hypothesized as an explanation as to why the universe is expanding at an accelerating rate. Some expected that the universe would eventually run out of energy, and the rate of expansion would slow down; however, the rate was found to be speeding up.
Although they have different names, dark energy is unrelated to dark matter. Dark matter has attractive properties while dark energy has repulsive properties.
Like dark matter, more is unknown than is known about dark energy. Scientists understand that dark energy exists since it affects the universe’s expansion, but nothing is known further than that. Some assume that it is simply a property of space, while others might say that the current physics governing the universe isn't fully correct. Regardless, the mystery of dark energy continues.
Why is important?
Although we may never see dark energy or dark matter, understanding these phenomena is important to understanding the universe we live in. These mysteries can help us figure out if the universe will continue to expand forever, or if it will reach a point where expansion stops. Furthermore, it can also aid in explaining the formation and evolution of different galaxies or galaxy clusters, and why they don't behave as expected. Delving into the unknown of dark energy and dark matter will unlock many answers to our mysterious universe.
Thanks for reading!
Written by Kaylee Barrera
Sources
Dark Energy, Dark Matter | Science Mission Directorate. https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy. Accessed 3 Aug. 2021.
“Dark Matter.” CERN, https://home.cern/science/physics/dark-matter. Accessed 3 Aug. 2021.
Redd, Nola Taylor. “What Is Dark Matter?” Space.Com, 19 July 2019, https://www.space.com/20930-dark-matter.html.
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