Welcome to the Dark Side...Of Physics!
By: Shaila Murthy
Dark energy. What is it? Unfortunately, we don't really know. We know that it makes up about 68% of the universe, however we have not yet figured out what it truly is.
If we don't know what it is, how do we know it exists? Well, we know it must exist because the universe is expanding. When we think about it, the universe's expansion should technically be slowing due to gravitational forces between objects, and yet it isn't. This means that there must be a different dominant force in the expansion of the universe, one that can overpower the force of gravity. This energy was dubbed "dark energy", due to how it is not visible like other energy forms are.
Dark energy. What is it? Unfortunately, we don't really know. We know that it makes up about 68% of the universe, however we have not yet figured out what it truly is.
If we don't know what it is, how do we know it exists? Well, we know it must exist because the universe is expanding. When we think about it, the universe's expansion should technically be slowing due to gravitational forces between objects, and yet it isn't. This means that there must be a different dominant force in the expansion of the universe, one that can overpower the force of gravity. This energy was dubbed "dark energy", due to how it is not visible like other energy forms are.
A diagram showing the expansion of the universe since its birth. The shallower the curve, the faster the rate of expansion, showing that roughly 7.5 billion years ago the universe's expansion sped up.
There are four potential explanations for dark energy. The first is that it is a property of space. This would make dark energy a "cosmological constant", meaning that as space expands it would not be diluted but rather more of it would be produced. However, no one knows why this constant exists, and especially not why it would have the exactly perfect value to to cause the acceleration of expansion.
The second theory is that it is "quintessence", named after the fifth element of Greek philosophers. This "quintessence" would be a new kind of dynamical energy fluid that permeates all of space but has the opposite effect on expansion to normal matter and energy. This could be the answer, however we still do not know what this theoretical quintessence is.
The third explanation is based upon quantum mechanics, or the "physics of the very small". In quantum mechanics, energy and matter can appear out of nothingness for a miniscule period of time. Theoretically, dark energy could be created from these types of particles continually forming and disappearing. Unfortunately, when physicists tried to calculate this theory they got an answer that was 10120 times too large, meaning this is probably not the explanation.
The fourth theory is simply that Einstein's theory of gravity is incorrect. This could explain why the universe is expanding, however it would also affect the ways matter interacts and behaves, opening up a whole new door to the unknown.
So, we don't really know much about dark energy except that it exists. What about dark matter? We know a bit more about it, and that it makes up about 27% of the universe... but what is it?
Dark matter is-as the name suggests-dark, meaning that it is not in the same form of the stars and planets we are able to see. We also know that it is not dark clouds of normal matter, as their absorption of radiation does not match up. In addition, dark matter cannot be antimatter, because they do not emit the unique gamma rays that antimatter produces. Finally, we know it is not large black holes since they do not produce enough lensing events. So, as we can see here, we know more about what dark matter is not than we do what it actually is. However, we do certainly have a few theories.
Dark matter could still be made up of baryonic matter, provided it is all tied up in brown dwarfs (substellar objects that occupy the mass range between the heaviest gas giants and the lightest stars) or small, dense chunks of heavy elements. The most popular theory, however, is that dark matter is not baryonic but is instead made up of exotic particles like axions or WIMPS (Weakly Interacting Mass Particles).
Basically, we don't know much about dark energy and matter, but we do know it exists. With enough data and experimentation, we may eventually be able to properly understand what it is that our universe is truly made up of.
Sources:
1.) "Dark Energy, Dark Matter." Science Beta. NASA, n.d. Web. 23 May 2018.
2.) Panek, Richard. "Dark Energy: The Biggest Mystery in the Universe." Smithsonian.com. Smithsonian Institution, April 2010. Web. 23 may 2018.
3.) "What is Dark Energy?" Hubblesite. Space Telescope Science Institute, n.d. Web. 23 May 2018.
A diagram of potential futures based upon theories on dark energy.
The third explanation is based upon quantum mechanics, or the "physics of the very small". In quantum mechanics, energy and matter can appear out of nothingness for a miniscule period of time. Theoretically, dark energy could be created from these types of particles continually forming and disappearing. Unfortunately, when physicists tried to calculate this theory they got an answer that was 10120 times too large, meaning this is probably not the explanation.
The fourth theory is simply that Einstein's theory of gravity is incorrect. This could explain why the universe is expanding, however it would also affect the ways matter interacts and behaves, opening up a whole new door to the unknown.
So, we don't really know much about dark energy except that it exists. What about dark matter? We know a bit more about it, and that it makes up about 27% of the universe... but what is it?
Dark matter is-as the name suggests-dark, meaning that it is not in the same form of the stars and planets we are able to see. We also know that it is not dark clouds of normal matter, as their absorption of radiation does not match up. In addition, dark matter cannot be antimatter, because they do not emit the unique gamma rays that antimatter produces. Finally, we know it is not large black holes since they do not produce enough lensing events. So, as we can see here, we know more about what dark matter is not than we do what it actually is. However, we do certainly have a few theories.
An x-ray image showing dark matter (blue coloring represents dark matter).
Dark matter could still be made up of baryonic matter, provided it is all tied up in brown dwarfs (substellar objects that occupy the mass range between the heaviest gas giants and the lightest stars) or small, dense chunks of heavy elements. The most popular theory, however, is that dark matter is not baryonic but is instead made up of exotic particles like axions or WIMPS (Weakly Interacting Mass Particles).
A diagram displaying relative sizes of brown dwarves to other spacial bodies.
Basically, we don't know much about dark energy and matter, but we do know it exists. With enough data and experimentation, we may eventually be able to properly understand what it is that our universe is truly made up of.
Sources:
1.) "Dark Energy, Dark Matter." Science Beta. NASA, n.d. Web. 23 May 2018.
2.) Panek, Richard. "Dark Energy: The Biggest Mystery in the Universe." Smithsonian.com. Smithsonian Institution, April 2010. Web. 23 may 2018.
3.) "What is Dark Energy?" Hubblesite. Space Telescope Science Institute, n.d. Web. 23 May 2018.
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