Changes

|accessdate=2012-10-14

|accessdate=2012-10-14

|url=http://www.youtube.com/watch?v=jWaOyy3WfWk

|url=http://www.youtube.com/watch?v=jWaOyy3WfWk

|quote=Michail S. Turner professor, Kavli institute for Cosmological Physics, University of Chicago:

|quote=Michail S. Turner professor, Kavli institute for Cosmological Physics, University of Chicago: His contributions include Coining the term dark energy ...and several key ideas that lead to dark matter theory of structure formation.}}</ref>  

His contributions include Coining the term dark energy ...and several key ideas that lead to dark matter theory of structure formation.}}</ref>  

== The problem ==

== The problem ==

Recall that <math>\beta</math> is a function of z, and r is sensitive to the mass-energy density fraction.

Recall that <math>\beta</math> is a function of z, and r is sensitive to the mass-energy density fraction.

Hartnett plotted the difference <math>M-M_B</math> against redshift for the supernovas studied most recently by Riess and Astier<ref name=Reiss/><ref name=Astier/>. He then adjusted the parameters <math>a</math> and <math>\Omega_m</math> to achieve the best statistical fit to the observations. He obtained these values:

Hartnett plotted the difference <math>M-M_B</math> against redshift for the supernovas studied most recently by Riess and Astier.<ref name=Reiss/><ref name=Astier/> He then adjusted the parameters <math>a</math> and <math>\Omega_m</math> to achieve the best statistical fit to the observations. He obtained these values:

<math>\,a = 0.2284</math>

<math>\,a = 0.2284</math>

[[Uniformitarianism|Uniformitarian]] cosmologists have three theories of what form this energy might take:

[[Uniformitarianism|Uniformitarian]] cosmologists have three theories of what form this energy might take:

# It is a fundamental property of the universe, as [[Albert Einstein]] originally suggested. Einstein's original idea was that this force, which he called a "cosmological constant," would exactly counterbalance [[gravity]] and thus keep all galaxies and other objects of similar size in the same place. Einstein initially discarded his own findings after [[Edwin Hubble]] showed that the universe was expanding. Some modern cosmologists suggest that Einstein might have been right after all.<ref name=Lloyd/><ref name=Preuss/><ref name=Williams/><ref name=nasa1/><ref name=Chaikin/>

# It is a fundamental property of the universe, as [[Albert Einstein]] originally suggested. Einstein's original idea was that this force, which he called a "cosmological constant," would exactly counterbalance [[gravity]] and thus keep all galaxies and other objects of similar size in the same place. Einstein initially discarded his own findings after [[Edwin Hubble]] showed that the universe was expanding. Some modern cosmologists suggest that Einstein might have been right after all.<ref name=Preuss/><ref name=Lloyd/><ref name=Chaikin/><ref name=Williams/><ref name=nasa1/>

# It is a previously unknown type of energy fluid or field, and perhaps even a fifth elemental force, in addition to the previously known four forces of gravity, the electromagnetic force, and the weak and strong nuclear forces. Some scientists name this new force "quintessence" (literally, fifth essence), a term that ancient Greek philosophers once coined for a fifth "element" of nature in addition to the four elements that they thought they knew (fire, [[atmosphere|air]], [[earth]], and [[water]]).<ref name=Preuss/><ref name=Williams/>

# It is a previously unknown type of energy fluid or field, and perhaps even a fifth elemental force, in addition to the previously known four forces of gravity, the electromagnetic force, and the weak and strong nuclear forces. Some scientists name this new force "quintessence" (literally, fifth essence), a term that ancient Greek philosophers once coined for a fifth "element" of nature in addition to the four elements that they thought they knew (fire, [[atmosphere|air]], [[earth]], and [[water]]).<ref name=Preuss/><ref name=Williams/>

# It is not a new property or force but a manifestation of an error of our understanding of an old one, namely gravity.<ref name=Preuss/><ref name=Williams/>

# It is not a new property or force but a manifestation of an error of our understanding of an old one, namely gravity.<ref name=Preuss/><ref name=Williams/>

NASA and the [[United States]] Department of Energy have also proposed a Joint Dark Energy Mission, essentially a new, very-high-resolution space telescope. Three different telescope designs are now under study.<ref name=jdem>Newman P and Tyler P. "[http://universe.nasa.gov/program/probes/jdem.html Beyond Einstein: The Joint Dark Energy Mission]." [[NASA]], n.d. Accessed July 26, 2008.</ref> Timothy Clifton, the proponent of the "void model" mentioned above, hopes that observations by JDEM might provide a reliable test of his model.<ref name=Clifton/>

NASA and the [[United States]] Department of Energy have also proposed a Joint Dark Energy Mission, essentially a new, very-high-resolution space telescope. Three different telescope designs are now under study.<ref name=jdem>Newman P and Tyler P. "[http://universe.nasa.gov/program/probes/jdem.html Beyond Einstein: The Joint Dark Energy Mission]." [[NASA]], n.d. Accessed July 26, 2008.</ref> Timothy Clifton, the proponent of the "void model" mentioned above, hopes that observations by JDEM might provide a reliable test of his model.<ref name=Clifton/>

==External Links==

==External links==

*[http://www.relativitycalculator.com/glossary.shtml Relativity Calculator - Glossary ]

*[http://www.relativitycalculator.com/glossary.shtml Relativity Calculator - Glossary ]

==References==

==References==

[[Category:Cosmology]]

[[Category:Cosmology]]

[[category:physics]]

[[Category:Physics]]