In the twenties of the last century, astronomer Edwin Hubble observed the speed of the galaxies away and realized that the more they do so, the faster their speed, establishing the Hubble Law that indicates an expansion of the universe at constant speed ( as if it were a balloon when inflating).
However, in 1998 astronomers Saul Perlmutter and Brian Schmidt along with Adam Riess (in 2011 they won the Nobel Prize in Physics for their discoveries) making observations of light from a type of supernovae allowed to deduce a non-constant expansion, and provided evidence of a type of energy that was called dark.
Dark energy is an enigmatic phenomenon that sounds similar to dark matter but is different, perhaps its only similarity is the lack of certainty of what could be. “We do know that it is not matter,” said Eduard de la Cruz Burelo, a researcher at the Physics Department of Cinvestav.
The force of gravity is attractive, while the accelerated expansion resembles a repulsive force and this is identified as dark energy. For Nora Bretón Báez, researcher at the Physics Department of Cinvestav, “we do not really know if it’s an energy or an effect of the geometry of the universe, maybe we just do not have the right model of it or maybe our law of gravitation fails to long distances”.
It was called energy because an expansion means repulsive force, the only example of this is the electrical case, where you can have loads of different sign, then the force can be attractive or repulsive.
In gravitation, all forces are attractive because the mass can not be negative, it means that any particle attracts and here it is the opposite, it is a kind of repulsion that accelerates. It is not matter and it is called energy because it can be modeled as an extra energy in Einstein’s equations for gravitation.
“From the experimental point of view we know nothing; It is present since the big explosion, it affects gravitationally and it is something to take into account when describing the behavior of the cosmic background radiation, “said Eduard De la Cruz.
From the beginning there was a component of dark energy and that shows it as a fundamental phenomenon not yet understood. It is known of its existence because the light of the observed supernovae arrives more tenuously than expected if the expansion of the universe occurred at a constant speed.
Broadly speaking there are three possibilities to explain it: that it is a material or substantial medium, modeled by scalar fields with different properties; that its origin is the geometry of spacetime (a geometry of the hyperbolic type would have that effect); or that Einstein’s relativity is only a valid approximation at the solar system scale and for great distances there is another more precise theory.
Its study is something relatively new and although it can not be said what the cause, the calculations indicate that it represents about 74 percent of the universe, for that reason its scientific interest, “does not mean that we have not advanced, it can already be said that it was from the beginning; we have learned many things but we have not yet come to say what it is, “assured De la Cruz Burelo.
Determine what produces the accelerated expansion of the universe would allow to know better than what this done; if it is a material medium or if the existing theories of physics are correct at any scale and distance in space. In addition, the ideas to detect and prove it, with their experiments and innovative technologies could generate applications for the benefit of the human being; but it is still difficult to predict whether or not it will have applications.
Some researchers have thought that when it is discovered it could be used as an energy source if it could be “collected”, but that will be very complicated. This type of research is what is called basic science, which aims to study nature and discover phenomena simply to learn.
The dark energy is responsible for the accelerated expansion of the universe but not constantly and causes the galaxies to separate more and more and accelerated, it was given the name dark because it is an unknown.
Phenomena that can not be explained in the context of current theories such as dark energy can lead to redefining the vision of nature, as happened with the theories of Newton or Einstein, said Eduard de la Cruz Burelo.
Culled From: http://avanceyperspectiva.cinvestav.mx/Publicaciones/ArtMID/4126/ArticleID/1570/Energ237a-oscura-un-fen243meno-enigm225tico-para-la-f237sica-moderna