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	<entry>
		<id>https://en.formulasearchengine.com/w/index.php?title=Devil%27s_curve&amp;diff=17550</id>
		<title>Devil&#039;s curve</title>
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		<summary type="html">&lt;p&gt;95.146.224.76: &lt;/p&gt;
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A [[quantum field theory]] of [[General Relativity]] provides [[Operator (mathematics)|operators]] that measure the [[geometry]] of [[space time]]. The volume operator &amp;lt;math&amp;gt;V(R)&amp;lt;/math&amp;gt; of a region &amp;lt;math&amp;gt;R&amp;lt;/math&amp;gt; is defined as the operator that yields the expectation value of a volume measurement of the region &amp;lt;math&amp;gt;R&amp;lt;/math&amp;gt;, given a state &amp;lt;math&amp;gt;\psi&amp;lt;/math&amp;gt; of quantum General Relativity. I.e.&amp;lt;math&amp;gt;\lang \psi, V(R) \psi \rang&amp;lt;/math&amp;gt; is the expectation value for the volume of &amp;lt;math&amp;gt;R&amp;lt;/math&amp;gt;. [[Loop Quantum Gravity]], for example, provides volume operators, area operators and length operators for regions, surfaces and path respectively. &lt;br /&gt;
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==Sources==&lt;br /&gt;
*[[Carlo Rovelli]] and [[Lee Smolin]], [http://arxiv.org/abs/gr-qc/9411005 &amp;quot;Discreteness of Area and Volume in Quantum Gravity&amp;quot;, Nuclear Physics B 442, 593 (1995)].&lt;br /&gt;
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*[[Abhay Ashtekar]] and [[Jerzy Lewandowski]], [http://www.arxiv.org/abs/gr-qc/9711031 &#039;&#039;Quantum Theory of Geometry II: Volume operators&#039;&#039;] &lt;br /&gt;
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[[Category:Quantum field theory]]&lt;/div&gt;</summary>
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