Editing Space (section)

== Physics ==
{{Classical mechanics|cTopic=Fundamental concepts}}
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Space is one of the few [[fundamental quantity|fundamental quantities]] in [[physics]], meaning that it cannot be defined via other quantities because nothing more fundamental is known at the present. On the other hand, it can be related to other fundamental quantities. Thus, similar to other fundamental quantities (like time and [[mass]]), space can be explored via [[measurement]] and experiment.

Today, our [[three-dimensional space]] is viewed as embedded in a four-dimensional [[spacetime]], called [[Minkowski space]] (see [[special relativity]]). The idea behind spacetime is that time is [[hyperbolic-orthogonal]] to each of the three spatial dimensions.

=== Relativity ===
{{main|Theory of relativity}}
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Before [[Albert Einstein]]'s work on relativistic physics, time and space were viewed as independent dimensions. Einstein's discoveries showed that due to relativity of motion our space and time can be mathematically combined into one object–[[spacetime]]. It turns out that distances in [[Spacetime#Space-like interval|space]] or in [[Spacetime#Time-like interval|time]] separately are not invariant with respect to Lorentz coordinate transformations, but distances in Minkowski space along [[spacetime interval]]s are—which justifies the name.

In addition, time and space dimensions should not be viewed as exactly equivalent in Minkowski space. One can freely move in space but not in time. Thus, time and space coordinates are treated differently both in [[special relativity]] (where time is sometimes considered an [[imaginary number|imaginary]] coordinate) and in [[general relativity]] (where different signs are assigned to time and space components of [[spacetime]] [[metric tensor|metric]]).

Furthermore, in [[Einstein's general theory of relativity]], it is postulated that spacetime is geometrically distorted – ''curved'' – near to gravitationally significant masses.<ref>Wheeler, John A. ''A Journey into Gravity and Spacetime''. Chapters 8 and 9, [[Scientific American]], {{ISBN|0-7167-6034-7}}</ref>

One consequence of this postulate, which follows from the equations of general relativity, is the prediction of moving ripples of spacetime, called [[gravitational wave]]s. While indirect evidence for these waves has been found (in the motions of the [[Hulse–Taylor binary]] system, for example) experiments attempting to directly measure these waves are ongoing at the [[LIGO]] and [[Virgo interferometer|Virgo]] collaborations. LIGO scientists reported the [[first observation of gravitational waves|first such direct observation of gravitational waves]] on 14 September 2015.<ref>{{cite news|last1=Castelvecchi|first1=Davide|last2=Witze|first2=Alexandra|title=Einstein's gravitational waves found at last|url=http://www.nature.com/news/einstein-s-gravitational-waves-found-at-last-1.19361|access-date=12 January 2018|work=Nature News|date=11 February 2016|archive-url=https://web.archive.org/web/20160216095503/http://www.nature.com/news/einstein-s-gravitational-waves-found-at-last-1.19361|archive-date=16 February 2016|url-status=live}}</ref><ref name="PRL">{{cite journal |collaboration=LIGO Scientific Collaboration and Virgo Collaboration |last1=Abbott |first1=Benjamin P. |title=Observation of Gravitational Waves from a Binary Black Hole Merger |journal=[[Phys. Rev. Lett.]] |volume=116 |issue=6 |pages=061102 |year=2016 |doi=10.1103/PhysRevLett.116.061102 |arxiv=1602.03837 |bibcode=2016PhRvL.116f1102A |pmid=26918975|s2cid=124959784}}
*{{cite web |title=Observation of Gravitational Waves from a Binary Black Hole Merger |website=LIGO Scientific Collaboration |url=https://www.ligo.caltech.edu/system/media_files/binaries/301/original/detection-science-summary.pdf}}</ref>

=== Cosmology ===
{{main|Shape of the universe}}
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Relativity theory leads to the [[cosmology|cosmological]] question of what shape the universe is, and where space came from. It appears that space was created in the [[Big Bang]], 13.8&nbsp;billion years ago<ref>
{{cite web
|title = Cosmic Detectives
|url = http://www.esa.int/Our_Activities/Space_Science/Cosmic_detectives
|publisher = The European Space Agency (ESA)
|date = 2 April 2013
|access-date = 26 April 2013
|archive-url = https://web.archive.org/web/20130405083228/http://www.esa.int/Our_Activities/Space_Science/Cosmic_detectives
|archive-date = 5 April 2013
|url-status=live
|df = dmy-all
}}
</ref> and has been expanding ever since. The overall shape of space is not known, but space is known to be expanding very rapidly due to the [[Inflation (cosmology)|cosmic inflation]].