What is Dark Energy?

In April 1990, when the Hubble Space Telescope (HST) was launched into orbit, scientists had high hopes that the telescope would help them map out the visible universe; however, few were really prepared for the Hubble revelations about the unseen world of dark matter and energy. Making up more than 72% of the physical universe, dark energy is a cosmological mystery that intrigues the general public and baffles scientists.

By Definition- What is Dark Energy?

Seeming more like a creation of science fiction than science fact, dark energy is more than the opposite of dark matter. Dark energy, considered a property of space, is the energy or force which acts upon objects that causes them to repel at an accelerated rate. Some theorize that this energy is a type of anti-gravity.

The Discovery of Dark Energy

Using the HST, scientists were analyzing images of the Bullet Cluster. In this area of space, supernovae were being studied because there were indications that cosmic matter was being emitted with little or no radiation. These discoveries of dark matter lead to another realization. As scientists studied the stars, they noticed that their ideas of the expanding universe implied that the rate of expansion would be slower over time, but their findings revealed the opposite. Something else, not explained wholly by Einstein's theory of gravitation, had to be facilitating the universe's expansion. This something, scientist named dark energy.

What is Known?

Before Einstein's theories of relativity and Newton's laws of motion and gravity, and before Aristotle's concept of the elements and the world, scientists have tried to unravel the mystery of our visible universe. From what modern physicists and astronomers can determine, dark energy has existed most of the history of the universe. It stands as a repulsive force that emanates from what we consider empty space. Dark energy, like its cosmic cohort dark matter, does not interact with light and serves as a dark void. As a property of space, dark energy is made up of particles with varying energies.

Concepts of Matter and Energy

Everything in the universe is made up of matter and energy. Matter is made up of atoms and molecules which define our physical world. Energy, whether kinetic or potential, is the ability to cause change. Popular forms of energy include light, electromagnetic and heat. Matter and energy are linked through Einstein's famous equation, E=Mc2. However, the concept of dark matter and energy warps this accepted interpretation of the interaction between matter and energy. Some scientists are proposing that dark energy and matter are simply two aspects of a single unknown force..

Gravity As We Know It

As dark energy is seen as a type of anti-gravity, astrophysicists are now considering the impact of dark energy on the manifestations of gravity. Gravity is one of the four fundamental interactions of nature. As a force, it causes objects to attract one another. On Earth, it draws objects to the ground and in space it impacts orbits of planets and paths of comets. However, dark energy seems to repel objects as opposed to attracting them. In our microverse, the same manifestations occur with atoms of like or opposite charges, but on the larger scale, dark energy seems to be the more powerful opposite of gravity.

Theories in Conflict

Nobel Laureate Alfred Einstein, who transformed the world's view of the universe, offered the earliest model for dark energy. He modified the general theory of relativity and proposed a cosmological constant. In his theory, the cosmological constant was needed to balance the force of gravity in order to form a static universe. While abandoned in that past, scientists are reintroducing the cosmological constant, because it use has aided scientist in reproducing the effects of dark energy. The use of Einstein's cosmological constant, however, does not explain dark matter.

Another possible theory is linked to the Chaplygin gas models, which was the work of Russian Physicist, Sergey Chaplygin in the 1930s. Fundamentally a gas dynamics model, this theory explains expansion and dark energy evolution, but does not adequately explain galaxy formation.

Many other scientists including Vanderbilt University's Robert J. Scherrer and Harvard's Nima Arkani-Hamed are tackling the question of dark energy and matter. Scherer's theories draws upon ideas that the universe is filled with an invisible fluid that exerts pressure on ordinary matter, which in turn changes the way that the universe expands. Scherer's theory offers insight on how stars and galaxies formed. Similar to Scherrer's theory, Nima Arkani-Hamed proposes low mass particle decay and an invisible and omnipresent fluid that they call a ghost condensate.

Making up the bulk of the known universe, dark energy will continue to challenge our concepts of gravity, the universe, matter and energy. While scientists grapple with this cosmological mystery and marvel, they will continue to look to the stars for explanations of this unusual constituent of space.