Dark Matter is hypothetical matter that is undetectable by its emitted radiation, but whose presence can be inferred from gravitational effects on visible matter.

Dark Energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe

--Mark Gonzalez GEOL 1403

The protons, neutrons and electrons that make up everything we can see - and that means with every telescopes we've got -- accounts for only about 4% of the mass and energy of the Universe. The rest is dark and mysterious. More specifically, about 70% of the Universe is what is known as dark energy; about 26% is so-called dark matter.

According to this timeline, the expansion of the

universe is accelerating.

While the growth of our universe is broadly accepted, the future of it is not. Respected scientists quarrel for both extremes. The universe may persist to expand forever, or it may ultimately slow down enough to collapse. Read about additional theories like the Big Crunch, Big Freeze Big Rip and Heat Death of the Universe theory.

While dark energy repels, dark matter attracts. And dark matter’s influence shows up even in individual galaxies, while dark energy acts only on the scale of the entire universe.

If the hypothetical dark energy continues to dominate the universe's energy balance, then the current expansion of space will continue to accelerate, exponentially. Structures which are not already gravitationally bound will ultimately fly apart.

SOURCES:

Images: • http://www.nasa.gov/images/content/56197main_dark_schematic-lg.jpg • http://dsc.discovery.com/space/top-10/gallery/dark-matter-energy-625x450.jpg • http://hetdex.org/images/dark_energy/cosmic_tug_of_war.jpg • http://chandra.harvard.edu/blog/files/images/blog_pie.jpg • http://www.mpa-garching.mpg.de/HIGHLIGHT/2002/fig0206_1.jpg • http://www.lsst.org/Science/images/Universe_fate.jpg • http://www.nikon.com/about/feelnikon/light/chap01/img/sec03_p02.jpg • http://www-news.uchicago.edu/releases/03/darkmatter0903.jpg Information: • Mark J Hadley(2007)"Classical Dark Matter • P. J. E. Peebles and Bharat Ratra (2003). "The cosmological constant and dark energy" (subscription required).

Reviews of Modern Physics 75: 559–606. doi:10.1103/RevModPhys.75.559. http://www.arxiv.org/abs/astro-ph/0207347.

• http://chandra.harvard.edu/blog/node/56 • http://science.howstuffworks.com/dark-matter5.htm • http://spacenews.uuuq.com/space-universe.html • http://hetdex.org/dark_energy/dark_matter.php • http://www.lsst.org/lsst/public/dark_energy