The matter in the Universe with which we are all familiar is Baryonic. Protons, neutrons and electrons; atoms and molecules; your body, your car, stars, galaxies and the rest all comprise Baryonic matter. However, this is only a small percentage of what makes up the Universe; only about 4.6% in fact. Dark matter makes up another 23% or so, with the remainder, over 72%, as dark energy. This section looks at the dark matter and dark energy in the Universe, as well as hypothetical "cosmic topological defects" that may exist, though none has been found. But then no one has actually found dark matter or dark energy yet! We just know (probably) that it must (probably) be there. To the right, I have included an image showing the difference between dark matter and dark energy.
Certainly there are high hopes that the Large Hadron Collider will find something interesting, like the Lightest Supersymmetric Particle or other light Weakly Interacting Massive Particles (WIMPs) that may be the elusive dark matter.
Yes; it is all conjecture. On the other hand, the motions of stars in galaxies, the relative motions of galaxies themselves and the increasing acceleration of the expansion of the Universe all point to SOMETHING going on. These are the BEST ideas around for now; but they may not be the RIGHT ones.
Astronomy & Cosmology -
Image courtesy: Dr Katherine Mack - @AstroKatie