Expanding universe

[[Image:Redshift.png|thumb|165px|The visible light spectrum of a distant group of galaxies (right), compared to the optical spectrum of the Sun (left). Note that the more distant light sources have shifted towards the red end of the spectrum.]]{{Astronomy}}
It is generally agreed by [[scientist]]s that the observable [[Universe]] is expanding<ref>http://archive.ncsa.uiuc.edu/Cyberia/Cosmos/ExpandUni.html</ref> and doing so at an increasingly [[Dark energy|rapid rate]]. This [[knowledge]] is based primarily on the observed [[red shift]] of distant galaxies. Objects with a higher red shift are moving away from us faster (see [[Doppler Effect]]). [[Edwin Hubble]], who first measured the distance to other galaxies, found that almost all galaxies display a red shift and are therefore receding from the [[Sun]],<ref>http://cosmology.berkeley.edu/Education/IUP/GlossaryF_J.htm</ref> and that galaxies further away display a greater red shift than ones nearby &mdash; indicating that the furthest away are receding faster. A common misinterpretation of this is that the Sun (or at least our own galaxy) is the centre of the [[universe]], but this isn't the case; ''everything'' is receding away from ''everything else'' &mdash; like spots drawn onto a balloon as it inflates. A few of the nearest galaxies, such as [[Andromeda Galaxy|Andromeda]]<ref>[http://en.wikipedia.org/wiki/Andromeda-Milky_Way_collision Andromeda-Milky Way collision]</ref>, and even some farther away as some galaxies in the nearby Virgo Cluster<ref>{{wpl|Messier 86}}. See also {{wpl|Messier 90}}.</ref> show a blueshift instead of a redshift, because either local variations (as happens with Andromeda) or perspective effects caused by the infall of a galaxy in a galactic cluster from behind (as those in Virgo) may be stronger than the overall expansion effect.

==The Big Bang==
{{Main|Big Bang}}
The expanding Universe is one of the pillars of the Big Bang [[theory]]. There is an inverse relationship (known as [[Hubble's law]]) between any galaxy's distance and the speed at which it recedes from us. Hubble's law is a linear function, implying that all galaxies (and therefore all visible matter) once occupied the same point.

==Objections==
[[Image:Redshift_blueshift.png|thumb|left|How red and blue shifting works]]
A [[Google]] search reveals numerous websites which purport to explain the observed red shift by invoking the interference of intergalactic gases like [[Molecule|molecular]] [[hydrogen]], and which use this to attack the Big Bang theory.<ref>http://www.newtonphysics.on.ca/hydrogen/index.html</ref> The problem with the intergalactic gas interference explanation is that the frequency-filtering effects of such interference &mdash; called ''interstellar reddening'' &mdash; are very different from a red shift. A red shift lengthens the apparent wavelength of all [[radiation]], including the absorption and emission lines that give each element their fingerprint; interstellar reddening merely reduces the intensity of shorter wavelengths of light, without causing any wavelength shift. The red shift is an observer-dependent phenomenon &mdash; observers at different locations will perceive different red shifts for the same object due to differing relative motion, though, if the expanding universe hypothesis is correct, the totality of observations from any point in the universe would point to the same conclusions we arrive at from [[Earth]].

Furthermore, Hubble's Law has been observed to hold [[Truth|true]] with a high degree of accuracy; given that [[matter]] likes to [[Gravity|clump together]], it's highly unlikely that intergalactic hydrogen is distributed evenly enough to produce these results. An isotropic expansion of space in all directions is by far the [[Occam's razor|simplest explanation]] for the observations.

==See also==
*[[Red shift]]
*[[Edwin Hubble]]
*[[Doppler Effect]]
*[[Dark energy]]

==External links==
*{{wpa|Hubble's law}}

==References==
{{reflist}}

[[Category:Science]]
[[Category:Cosmology]]

Categories: Science, Cosmology