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Dark Matter and Dark Energy: What We Currently Know
The expansion of the Universe, contrary to previous beliefs, is accelerating. The Hubble Space Telescope in the late 90s provided observations to reveal this information. The focus then turned to why. Why is the Universe expanding at a faster and faster rate than it was in the beginning? Are our theories incorrect? Or do we simply need to revisit other versions of our current theories? Is there something new in the Universe? In attempts to find an answer, several theories developed but dark matter and dark energy took center stage.
The idea of dark matter became popular because it offered a possible explanation to how gravity was playing a role in accelerating astral bodies. The concept of dark matter was first introduced by Zwicky in 1934 to explain the movement of galaxy clusters. We know that dark matter exists because observations reveal that approximately 26% of the Universe is made up of matter. However, only about 4% of that matter can readily be seen and is composed of atoms. Observations support that the remaining 22% of matter must be dark matter.
Despite knowing that dark matter exists and that it makes up about 22% of the Universe, we still know next to nothing about what dark matter actually is. Researchers have ruled out the possibilities that dark matter is dark clouds of normal matter, antimatter, or galaxy-sized black holes. What we know of these three possibilities does not apply to dark matter. Current thoughts are that dark matter may actually be normal matter, but is condensed into brown dwarfs, MACHOs (dense chunks of heavy elements), or made up of exotic particles such as axions and WIMPs. Although vast amounts of data have been collected and interpreted, the data is still inconclusive at this point.
Dark energy makes up the remaining 74% of the universe. This energy exists throughout space and is increasing the rate at which the Universe expands. No one knows why there is so much more dark energy than dark matter as the Universe ages. From what we can tell, there was less of it (or possibly even none at all) in the earlier stages of the Universe's evolution. Some believe this may simply be a matter of coincidence. Dark energy, according to current knowledge, remains a mystery.
One of the concerns regarding dark energy and the accelerated expansion of the Universe is that our current theories my be wrong or in need of adjustment. There is a possibility that Einstein's theory of gravity is incorrect, leaving us to have to start over on explaining how normal matter behaves in galaxies and galaxy clusters. However, none of the new proposals to date have proven anywhere near as accurate as Einstein's theory.
Another idea is that we simply need to revisit an earlier version of Einstein's theory. He suggested that empty space is not nothing. The earlier version included a concept called a "cosmological constant." Empty space possibly has an energy of its own and more space can come into existence. Rather than becoming diluted as space expands, new space comes into existence to accelerate the expansion. Other ideas include the quantum theory of matter explanation and Quintessence, but none to date have provided an answer we can readily justify with current data.
So What's Going On?
We know the Universe is expanding. We also know that the Universe is expanding at a faster rate than it was previously. We know that dark matter exists. Unfortunately, we do not know what the relationship between dark matter and dark energy is or if there even is one. We do not know exactly what dark matter is and we cannot explain dark energy with our current theories and suggested ideas. Although we have collected vast amounts of data in these areas, we do not have many answers. Our current explanations for the expansion of the Universe lies in dark matter and dark energy, but we know so little about them that we cannot guarantee future research will not lead us to a different conclusion. We have ruled out some possibilities, but far more data will be required to provided more detailed explanations.
Hub #18/30 for March Challenge
- Dark Energy, Dark Matter - NASA Science
What is dark energy? What is dark matter?
© 2012 Evylyn Rose