Dark Matter: The Extended Definition

The Andromeda Galaxy: Scientists believe dark matter must exist to explain how stars and galaxies form. (Image dailymail.co.uk)

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It is extremely difficult to try and explain to someone that something can be real although it has never been directly, yet, indirectly viewed. Like a person who believes in a higher entity through religion, and basing their opinions off The Bible or the Quran – a story told from thousands and thousands of years ago, over a period of thousands and thousands of years. Religious persons have not had the honor of meeting their “God”, and yet, still have the ability to believe in such power. In this paper, I am going to try and illustrate, as well as attempt to prove to you that dark matter is real. To do so, I will be providing definitions as to what matter – mainly the differences - and dark matter are, in much the same way that the Bible or Quran may show to certain individuals, that a God is real. As well as how matter is viewed and perceived in our everyday lives, and how dark matter can be known – yet, unknown at the same time. I will also be using analogies to both, illustrate and give a better understanding of how we can know that dark matter is an authentic property, and not just some made up idea within our minds.

Everything around us consist of matter. Atoms and molecules are all composed of matter and contributes to the entirety of all things that has mass and takes up space. Sometimes relating to light and electromagnetic radiation, matter consist of four basic states here on Earth: solids, liquids, gasses, and plasmas (States).

Image - Chem4kids.com

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We sleep on a solid bed, in solid clothes, and brush our teeth with a solid toothbrush – at least, I hope most of us do. To have a solid, the molecules and atoms within that object have to be tightly condensed, leaving little to no room, or space in-between other molecules. By doing so, these molecules and atoms have very little room to move or sprawl out. Basically sitting in a suspended or static state, in turn, keeps them – in a sense, from changing shape. This in turn gives us a solid object of matter for which we can hold, sit, lay on, and/or wear. When we take a shower or a bath, we use a liquid known as water. The molecules and atoms within a liquid are a little less condensed, giving them the room to move around, and at a greater speed. This action causes a fluid type state which gives these molecules and property the ability to take the form to which it is inserted to; a bowel, container, and/or cup. When we drink a glass of something, anything, its base is usually made of water. If you take that same water and add heat, you get steam. That steam is in the form of a gas. The molecules within that water have become even more spaced, and lets them move throughout this space a lot more quickly than when in a liquid state. Now plasma on the other hand, is an “electrically neutral medium of unbound positive and negative particles (i.e. the overall charge of a plasma is roughly zero)” (Plasma). You must take in to account though, this does not mean that the particles are “free” - in essence, when they move, “they generate electric currents with magnetic fields, and as a result, they are affected by each other’s fields” (Plasma). Outside of dark matter, plasma is the second most abundant form of matter in the universe and can be easily seen here on Earth by looking at lightning or neon signs (Plasma).

Dark matter on the other hand, is a hypothetical form of matter invisible to electromagnetic radiation, postulated to account for gravitational forces observed in the universe (Trefil). Dark matter emits little or no detectable radiation. Gravitational forces observed on many astronomical objects suggest that there is a significant presence of such matter in the universe, accounting for approximately 21 to 26 percent of the total mass of the universe (Trefil).

The components of our universe. Dark energy comprises 69% of the mass energy density of the universe, dark matter comprises 25%, and “ordinary” atomic matter makes up 5%. Three types of neutrinos make up at least 0.1%, the cosmic background radiation make. (Image Science/AAAS)

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Its exact nature is not well understood, but it may be largely composed of varieties of subatomic particles that have not yet been discovered, and may be the mass that makes up black holes and stars too dim to observe, also known as, missing mass (Gayle). As the name implies, dark matter does not interact with light or other electromagnetic radiation, thus it cannot be seen (Gayle).

Since dark matter is an invisible force and we have yet to detect it in any form directly, we use indirect methods to observe it. One way of detecting its presence is by looking at the behavior, or, the rotation of galaxies:

. . . like leaves on a stream, the hydrogen [in the galaxy] is moving as if it were still caught up in the general flow of the galaxy. The most direct conclusion that can be drawn from this is that most galaxies are surrounded by a huge halo of material that doesn't emit detectable amounts of radiation but that does exert a gravitational force. When you put in the numbers, you find that typically at least 90 percent of a galaxy like our own Milky Way is made up of this dark matter. - Trefil, James

A collage of galaxy clusters with dark matter maps in blue and x-ray visible in pink

(Image: NASA/ESA)

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Another way of looking at how dark matter could exist without having viewable observations of such an extraordinary force is by thinking of, let’s say, the motor under your car’s hood. You know your car is working because it starts and you are able to drive it. In much the same way, dark matter may be invisible, but because of the way galaxies are formed and how visible matter interacts in the darkness of space, we can hypothesis that there is an unseen force which plays a factor in the way our universe works. And as Matthew Craig and Sara Schultz have mentioned, another way to think about dark matter is, like attempting to hang a picture on your wall. You first want to find the studs that are not visible to you directly, however, you know they are there because they are the structures that are holding up your office or room within your house. Those studs are hidden behind a layer of plywood and paint, which takes a stud finder, or some knocking along the wall, therefore locating their exact whereabouts. In much the same way, scientist are aware that dark matter is in an abundance throughout the cosmos - it’s the sole factor that can explain, outside of gravity, why the galaxies are held to tightly together.

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Works Cited

Craig, Matthew, and Sara Shultz. "Invisible Galaxies: The Story of Dark Matter." Astrosociety.org. N.p., 2007. Web. 23 Feb. 2016.

Dictionary.com. Dictionary.com, n.d. Web. 23 Feb. 2016.

Gayle, Damien. "Shedding Some Light on Dark Matter: The $2bn Experiment in Space That May Be about to Turn the World of Physics on Its Head." Mail Online. Associated Newspapers, 19 Feb. 2013. Web. 23 Feb. 2016.

"Plasma." Wikipedia. Wikimedia Foundation, n.d. Web. 23 Feb. 2016.

"States of Matter." Chem4Kids.com: Matter:. N.p., n.d. Web. 23 Feb. 2016.

Trefil, James. "What Is Dark Matter?" Academic Search Complete [EBSCO]. EBSCO, June 1997. Web. 23 Feb. 2016.

Zandonella, Catharine. "The Dark Side of Cosmology." The Dark Side of Cosmology. N.p., 6 Mar. 2015. Web. 23 Feb. 2016.