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Biology 103
2003 Second Paper
On Serendip

Dark Energy: The Mystery of This Millennium

Melissa Teicher

Billions of years ago, the universe was nothing but an infinitesimally small particle. Then, in less time than the blink of an eye, the universe expanded and increased in size by a factor of 1050. Expansion eventually began to slow down, allowing galaxies, star clusters, and so on, to form. Theoretically, expansion should still be slowing down; but to the contrary, expansion is in fact accelerating (10). Some scientists theorize that an unknown force, called Dark Energy, may be the cause of this accelerated expansion, while others disagree.

For some time, exploding stars, or supernovas, were used as a "cosmic measuring stick" (4). That is, scientists used these supernovas to calculate the age of the universe. In 1998, two groups of astronomers surveyed supernovas in very distant galaxies. These supernovas were much dimmer than expected to be, and calculations proved that the stars were over ten billion light years away, much farther away than they should be had the universe been expanding at a slowing rate, or even a constant rate, as previously theorized (5). This discovery proved that the cosmos are not expanding at a slowing or a constant rate, but instead they are expanding at an accelerated rate (4). Since this discovery, scientists have been trying to uncover what it is that accounts for this accelerated expansion.

Scientists have calculated the density of the cosmos, and they have also calculated the total mass of all visible galaxies. However, the galaxies make up less than one-third of the density needed to satisfy the current calculations of the early universe (2). Simple logic tells us that there must be something else in the universe, with some kind of mass, which accounts for over two-thirds of the density of the cosmos. The new theory incorporates a different force called Dark Energy. At first, scientists did not know how Dark Energy works or what it is physically made up of. Some proposed ideas of Dark Energy are: a cosmic field associated with inflation, a low-energy field called "quintessence," and the cosmological constant, or a negative pressure, as suggested by Albert Einstein (7).

In July of 2003, scientists confirmed that Dark Energy exists, but they still cannot truly explain it (6). They do know that Dark Energy is different from every other kind of energy found. Some say it is a negative gravity (1), while others say that it does not necessarily act opposite to gravity, but, instead, it acts more like a negative pressure (5). Scientists do know for sure that Dark Energy moves space apart, causing the rate of expansion of the universe to increase (3). Physically, Dark Energy is invisible and of an unknown form, but accounts for 65 percent to 75 percent of the makeup of the early universe. However, scientists have no way of measuring Dark Energy with the current technology, as it affects only the universe over very large distances, as opposed to gravity which affects the universe over both large and small distances (2).

Einstein's Theory of Relativity allowed for the existence of a force such as Dark Energy. He spoke of a "cosmological constant" that left open the possibility that even empty space has energy. Also, according to his theory, this energy must have some kind of mass since energy equals mass multiplied by the speed of light squared, or E=mc2 (3). While most of Einstein's theory makes sense, some say the amount of Dark Energy decreases with time, as opposed to remaining constant. It is quite possible that Dark Energy is controlling the expansion of the cosmos, so understanding the nature of Dark Energy is vital to the prediction of the fate of the universe. In order to do so, scientists must create more advanced technology to measure density, pressure, changes with time, and so on, in galaxies billions and billions of light years away (3).

There are also those scientists who do not believe in the theory of Dark Energy. Some physicists claim that they can explain the expansion of the universe without having to factor Dark Energy into the equations. These scientists say that gravity is, in fact, the force causing the cosmos to expand. They have added a term to Einstein's equations in his theory of relativity to support their ideas, which will not affect the early universe, but will instead affect the universe after billions of years (1).

Of course, there are many other theories involving and excluding Dark Energy. For example, an additional theory is that gravity slowed the expansion of the universe after the "Big Bang" until the universe was half of its current age. Then, an opposing force, Dark Energy, consumed gravity and it began pushing the galaxies away at an accelerated speed. Others say that Dark Energy conceals other dimensions that scientists have yet to find; we know of a first, second and third dimension, but where are the forth, fifth, sixth, and so on, dimensions hiding (4)? Some even say that in order for Dark Energy to be real, space must be flat as opposed to curved (8).

Scientists say that Dark Energy could also be responsible for the end of our universe. Some other theories of the end include the "Big Crunch" and the "Big Chill" which deal with either an abundance of gravity or a lack of gravity. However, a new theory, called the "Big Rip," says that if dark energy continues to accelerate, it will eventually rip apart stars, solar systems, galaxies, and even atoms. This theory was created by a group of scientists from Dartmouth College, who say that the universe has twenty million years left of existence (9).

In short, scientists are very uncertain as to nature of Dark Energy, and every group of scientists that studies the force has formulated their own respective theories. Which theory is correct? Is Dark Energy just an excuse for our miscalculations of the density of the cosmos? Could empty space really just be empty space? Will the universe indefinitely continue to expand, leaving the Earth and the human species alone for eternity? Perhaps scientists will never have the ability to answer these questions. However, what they know for sure, as scientist Michael Turner of University of Chicago says, is, "This is very weird stuff" (4).


1)Accelerating Universe Theory Dispels Dark Energy
2)Universe Mostly Made of Dark Energy
3)Beyond Einstein
4)Dark Energy Quickens Universe Expansion
5)Dark Energy: Astronomers Still Clueless
6)Dark Energy Confirmed
7)Dark Energy Fills the Cosmos
8)Direct Evidence Found for Dark Energy
9)Dark Energy May Rip Apart Universe
10)Decoding the Mystery of Dark Energy

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