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width: 0.3em;"></span> <a href="/nlab/show/HomePage" accesskey="H" title="Home page">Home Page</a> | <a href="/nlab/all_pages" accesskey="A" title="List of all pages">All Pages</a> | <a href="/nlab/latest_revisions" accesskey="U" title="Latest edits and page creations">Latest Revisions</a> | <a href="https://nforum.ncatlab.org/discussion/6075/#Item_1" title="Discuss this page in its dedicated thread on the nForum" style="color: black">Discuss this page</a> | <form accept-charset="utf-8" action="/nlab/search" id="navigationSearchForm" method="get"> <fieldset class="search"><input type="text" id="searchField" name="query" value="Search" style="display:inline-block; float: left;" onfocus="this.value == 'Search' ? this.value = '' : true" onblur="this.value == '' ? this.value = 'Search' : true" /></fieldset> </form> <span id='navEnd'></span> </div> <div id="revision"> <html xmlns="http://www.w3.org/1999/xhtml" xmlns:svg="http://www.w3.org/2000/svg" xml:lang="en" lang="en"> <head><meta http-equiv="Content-type" content="application/xhtml+xml;charset=utf-8" /><title>Contents</title></head> <body> <h1 id="contents">Contents</h1> <div class='maruku_toc'> <ul> <li><a href='#idea'>Idea</a></li> <li><a href='#properties'>Properties</a></li> <li><a href='#related_concepts'>Related concepts</a></li> <li><a href='#references'>References</a></li> <ul> <li><a href='#general'>General</a></li> <li><a href='#in_physics'>In physics</a></li> </ul> </ul> </div> <h2 id="idea">Idea</h2> <p>The analog of <a class="existingWikiWord" href="/nlab/show/complex+analytic+space">complex analytic space</a> with the <a class="existingWikiWord" href="/nlab/show/complex+numbers">complex numbers</a> replaced by the <a class="existingWikiWord" href="/nlab/show/real+numbers">real numbers</a>.</p> <h2 id="properties">Properties</h2> <p>Whitney: every <a class="existingWikiWord" href="/nlab/show/paracompact+topological+space">paracompact</a> <a class="existingWikiWord" href="/nlab/show/smooth+manifold">smooth manifold</a> admits a real analytic structure.</p> <p>Use the <a class="existingWikiWord" href="/nlab/show/Whitney+embedding+theorem">Whitney embedding theorem</a> to realize the smooth manifold as the <a class="existingWikiWord" href="/nlab/show/zero+locus">zero locus</a> of non-degenerate <a class="existingWikiWord" href="/nlab/show/smooth+functions">smooth functions</a>, then use the <span class="newWikiWord">Weierstrass approximation theorem<a href="/nlab/new/Weierstrass+approximation+theorem">?</a></span> to replace these by <a class="existingWikiWord" href="/nlab/show/polynomials">polynomials</a>. The resulting zero locus gives the desired real-analytic version of the manifold.</p> <p>(<a href="http://www.math.niu.edu/~rusin/known-math/95/real.anal">from here</a>):</p> <p>One can also use Whitney’s methods to show that two diffeomorphic real analytic manifolds are real-analytic equivalent provided that they both admit embeddings in Euclidean space, equivalently provided that global, real-valued, real analytic functions distinguish points. This preliminary result also holds true for any other category of functions and manifolds, or Nash category, with an implicit and inverse function theorem and a few other features. For example, it’s true for Nash manifolds. The hard part is then showing that every real analytic manifold does indeed embed in Euclidean space. This is the Morrey-Grauert theorem. Grauert’s proof, the more sophisticated one, takes as its starting point a complex analytic manifold which is a tubular neighborhood of the real analytic manifold. It then applies some hard stuff in several complex variables to prove the existence of many global, complex analytic functions on the complex manifold.</p> <h2 id="related_concepts">Related concepts</h2> <ul> <li><a class="existingWikiWord" href="/nlab/show/GAGA">GAGA</a></li> </ul> <h2 id="references">References</h2> <h3 id="general">General</h3> <ul> <li id="Huisman02"><a class="existingWikiWord" href="/nlab/show/Johannes+Huisman">Johannes Huisman</a>, <em>The exponential sequence in real algebraic geometry and Harnack’s Inequality for proper reduced real schemes</em>, Communications in Algebra, Volume 30, Issue 10, 2002 (<a href="http://pageperso.univ-brest.fr/~huisman/rech/publications/exphi.pdf">pdf</a>)</li> </ul> <h3 id="in_physics">In physics</h3> <p>Generalization of the <a class="existingWikiWord" href="/nlab/show/time+tube+theorem">time tube theorem</a> to <a class="existingWikiWord" href="/nlab/show/AQFT+on+curved+spacetimes">AQFT on curved</a> but <a class="existingWikiWord" href="/nlab/show/real+analytic+space">real analytic</a> <a class="existingWikiWord" href="/nlab/show/spacetimes">spacetimes</a>:</p> <ul> <li> <p><a class="existingWikiWord" href="/nlab/show/Alexander+Strohmaier">Alexander Strohmaier</a>, <em>On the Local Structure of the Klein–Gordon Field on Curved Spacetimes</em>, Letters in Mathematical Physics <strong>54</strong> (2000) 249–261 [<a href="https://doi.org/10.1023/A:1010927625112">doi:10.1023/A:1010927625112</a>, <a href="https://arxiv.org/abs/math-ph/0008043">arXiv:math-ph/0008043</a>]</p> </li> <li> <p><a class="existingWikiWord" href="/nlab/show/Alexander+Strohmaier">Alexander Strohmaier</a>, <a class="existingWikiWord" href="/nlab/show/Edward+Witten">Edward Witten</a>, <em>Analytic states in quantum field theory on curved spacetimes</em> [<a href="https://arxiv.org/abs/2302.02709">arXiv:2302.02709</a>]</p> </li> <li> <p><a class="existingWikiWord" href="/nlab/show/Alexander+Strohmaier">Alexander Strohmaier</a>, <a class="existingWikiWord" href="/nlab/show/Edward+Witten">Edward Witten</a>, <em>The Timelike Tube Theorem in Curved Spacetime</em> [<a href="https://arxiv.org/abs/2303.16380">arXiv:2303.16380</a>]</p> </li> </ul> </body></html> </div> <div class="revisedby"> <p> Last revised on March 30, 2023 at 07:38:54. See the <a href="/nlab/history/real+analytic+space" style="color: #005c19">history</a> of this page for a list of all contributions to it. </p> </div> <div class="navigation navfoot"> <a href="/nlab/edit/real+analytic+space" accesskey="E" class="navlink" id="edit" rel="nofollow">Edit</a><a href="https://nforum.ncatlab.org/discussion/6075/#Item_1">Discuss</a><span class="backintime"><a href="/nlab/revision/real+analytic+space/3" accesskey="B" class="navlinkbackintime" id="to_previous_revision" rel="nofollow">Previous revision</a></span><a href="/nlab/show/diff/real+analytic+space" accesskey="C" class="navlink" id="see_changes" rel="nofollow">Changes from previous revision</a><a href="/nlab/history/real+analytic+space" accesskey="S" class="navlink" id="history" rel="nofollow">History (3 revisions)</a> <a href="/nlab/show/real+analytic+space/cite" style="color: black">Cite</a> <a href="/nlab/print/real+analytic+space" accesskey="p" id="view_print" rel="nofollow">Print</a> <a href="/nlab/source/real+analytic+space" id="view_source" rel="nofollow">Source</a> </div> </div>  </div>  </body> </html>