What Is Dark Energy?

    

        In 1929, Hubble  American astronomer Edwin  studied  exploding determined  a  number  of  stars, or supernova, and  that the  universe was  expanding. The notion galaxies were moving ours was a radical idea.  that distant  awav trom  It seemed obvious to astronomers  that gravity-the mutual attraction between all matter-would   affect  the   expansion process. But how? Would the pull of gravity completely halt the expansion of  the universe? Could the universe stop  expanding and then reverse itself back  toward  us?  Or  would  the  universe  eventually escape the gravitational effect  and continue to expand? The universe may  be  expanding,  reasoned  the  scientific community, but its expansion was surely slowed by the forceful effects of gravity.

        Fast forward nearly 70 years to a time when two teams of astrophysicists-one led by Saul Perlmutter at the Lawrence Berkeley National Laboratory and the other by Brian Schmidt at Australian National   University-began   studying supernovas  to  calculate  the  assumed deceleration  of  expansion.  To  their astonishment,   they   discovered   that supernovas as far as 7 billion light-years away were not brighter than expected but rather dimmer, meaning they were more distant than the teams had calculated them to be. The universe isn't slowing down, they concluded. It's speeding up.

        

   The discovery turned the scientific world on its head: If gravity isn't the most dominant force in the universe, what is? In 1998, American theoretical cosmologist Michael S. Turner dubbed the mysterious new something "dark energy." Yet even with a name, we know little about dark energy.

      

  Theorists have come up with several explanations for dark energy. The leading theory claims that dark energy is a property of space. Albert Einstein claimed it is possible for more space to come into existence and that "empty space" can have its own energy. "As more space comes into existence," reports NASA, "more of this energy-of-space would appear. As a result, this form of energy would cause the universe to expand faster and faster."   

   

     NASA reports that scientists have been able to theorize how much dark energy there is out there because we know how it affects the expansion of the universe. Roughly 69 percent of the universe is dark energy. Dark matter accounts for about 27 percent,  leaving  the  rest-all  normal matter, everywhere-adding up to less than 5 percent of the universe.   

      

   Another explanation posits that dark energy is a new type of energy field or energy fluid that fills space but affects the expansion of the universe differendy than matter and normal energy. Scientists have labeled this energy "quintessence," but we still don't know what it interacts with or why it even exists.