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<title>Universal wavefunction</title>

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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Universal wavefunction</span></span>

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<p>The <b>universal wavefunction</b> or the <b>wavefunction of the universe</b> is the <a href="Wavefunction" class="mw-redirect" title="Wavefunction">wavefunction</a> or <a href="Quantum_state" title="Quantum state">quantum state</a> of the entire <a href="Universe" title="Universe">universe</a>.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> It is regarded as the basic physical entity<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> in the <a href="Many-worlds_interpretation" title="Many-worlds interpretation">many-worlds interpretation</a> of <a href="Quantum_mechanics" title="Quantum mechanics">quantum mechanics</a>,<sup id="cite_ref-everett57_3-0" class="reference"><a href="#cite_note-everett57-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> and finds applications in <a href="Quantum_cosmology" title="Quantum cosmology">quantum cosmology</a>. It evolves deterministically according to a wave equation.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup>

</p><p>The concept of universal wavefunction was introduced by <a href="Hugh_Everett" class="mw-redirect" title="Hugh Everett">Hugh Everett</a> in his 1956 PhD thesis draft <i>The Theory of the Universal Wave Function</i>.<sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> It later received investigation from <a href="James_Hartle" title="James Hartle">James Hartle</a> and <a href="Stephen_Hawking" title="Stephen Hawking">Stephen Hawking</a><sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> who derived the <a href="Hartle%E2%80%93Hawking_state" title="Hartle–Hawking state">Hartle–Hawking solution</a> to the <a href="Wheeler%E2%80%93DeWitt_equation" title="Wheeler–DeWitt equation">Wheeler–DeWitt equation</a> to explain the initial conditions of the <a href="Big_Bang" title="Big Bang">Big Bang</a> cosmology.

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<div class="mw-heading mw-heading2"><h2 id="Role_of_observers">Role of observers</h2></div>

<p><a href="Hugh_Everett" class="mw-redirect" title="Hugh Everett">Hugh Everett</a>'s universal wavefunction supports the idea that observed and observer are all mixed together:

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</style><blockquote class="templatequote"><p>If we try to limit the applicability so as to exclude the measuring apparatus, or in general systems of macroscopic size, we are faced with the difficulty of sharply defining the region of validity. For what <b>n</b> might a group of <b>n</b> particles be construed as forming a measuring device so that the quantum description fails? And to draw the line at human or animal observers, i.e., to assume that all mechanical apparata obey the usual laws, but that they are not valid for living observers, does violence to the so-called principle of <a href="Psychophysical_parallelism" title="Psychophysical parallelism">psycho-physical parallelism</a>.<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup></p></blockquote>

<p><a href="Eugene_Wigner" title="Eugene Wigner">Eugene Wigner</a> and <a href="John_Archibald_Wheeler" title="John Archibald Wheeler">John Archibald Wheeler</a> take issue with this stance. Wigner wrote:

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<blockquote class="templatequote"><p>The state vector of my mind, even if it were completely known, would not give its impressions. A translation from state vector to impressions would be necessary; without such a translation the state vector would be meaningless.<sup id="cite_ref-t895_11-0" class="reference"><a href="#cite_note-t895-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup></p></blockquote>

<p>Wheeler wrote:

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<blockquote class="templatequote"><p>One is led to recognize that a wave function 'encompassing the whole universe' is an idealization, formalistically perhaps a convenient idealization, but an idealization so strained that it can be used only in part in any forecast of correlations that makes physical sense. For making sense it seems essential most of all to 'leave the observer out of the wave function'.<sup id="cite_ref-v766_12-0" class="reference"><a href="#cite_note-v766-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup></p></blockquote>

<ul><li><a href="Heisenberg_cut" title="Heisenberg cut">Heisenberg cut</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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<li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text">Everett [1956]1973, "Theory of the Universal Wavefunction", introduction, pg 8–9</span>

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<li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text">Everett 1957, section 3, 2nd paragraph, 1st sentence.</span>

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<li id="cite_note-everett57-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-everett57_3-0">^</a></b></span> <span class="reference-text"><a href="Hugh_Everett" class="mw-redirect" title="Hugh Everett">Hugh Everett</a>, Relative State Formulation of Quantum Mechanics, <i>Reviews of Modern Physics</i> vol 29, (1957) pp 454–462. An abridged summary of <i>The Theory of the Universal Wavefunction</i></span>

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<li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"><a href="John_Archibald_Wheeler" title="John Archibald Wheeler">John Archibald Wheeler</a>, Assessment of Everett's "Relative State Formulation of Quantum Theory", <i>Reviews of Modern Physics</i>, vol 29, (1957) pp 463–465</span>

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<li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text"><a href="Bryce_Seligman_DeWitt" class="mw-redirect" title="Bryce Seligman DeWitt">Bryce Seligman DeWitt</a>,

Quantum Mechanics and Reality, <i>Physics Today</i>,23(9) pp 30–40 (1970) also April 1971 letters followup</span>

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<li id="cite_note-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-6">^</a></b></span> <span class="reference-text"><a href="Bryce_Seligman_DeWitt" class="mw-redirect" title="Bryce Seligman DeWitt">Bryce Seligman DeWitt</a>, The Many-Universes Interpretation of Quantum Mechanics, <i>Proceedings of the International School of Physics "Enrico Fermi" Coursu IL: Foundations of Quantum Mechanics</i>, <a href="Academic_Press" title="Academic Press">Academic Press</a> (1972)</span>

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<li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text">Everett [1956]1973, "Theory of the Universal Wavefunction", chapter 6 (e)</span>

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<li id="cite_note-8"><span class="mw-cite-backlink"><b><a href="#cite_ref-8">^</a></b></span> <span class="reference-text"><a href="Bryce_Seligman_DeWitt" class="mw-redirect" title="Bryce Seligman DeWitt">Bryce Seligman DeWitt</a>, R. Neill Graham, eds, <i>The Many-Worlds Interpretation of Quantum Mechanics</i>, Princeton Series in Physics, <a href="Princeton_University_Press" title="Princeton University Press">Princeton University Press</a> (1973), <style data-mw-deduplicate="TemplateStyles:r1238218222">

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</style><a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>0-691-08131-X</bdi> Contains the reprint of Everett's thesis: <i>The Theory of the Universal Wave Function</i>, pp 3–140.</span>

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<li id="cite_note-9"><span class="mw-cite-backlink"><b><a href="#cite_ref-9">^</a></b></span> <span class="reference-text"><a href="Stephen_Hawking" title="Stephen Hawking">Stephen W Hawking</a>, <a href="James_Hartle" title="James Hartle">James B Hartle</a> "The Wave Function of the Universe," <i>Physical Review D</i>, vol 28, (1983) pp 2960–2975</span>

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<li id="cite_note-10"><span class="mw-cite-backlink"><b><a href="#cite_ref-10">^</a></b></span> <span class="reference-text">Everett [1956]1973, "Theory of the Universal Wavefunction", introduction, pg 6</span>

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<li id="cite_note-t895-11"><span class="mw-cite-backlink"><b><a href="#cite_ref-t895_11-0">^</a></b></span> <span class="reference-text"><cite id="CITEREFWigner1973" class="citation book cs1">Wigner, E. P. (1973). "Epistemological Perspective on Quantum Theory". <i>Philosophical Reflections and Syntheses</i>. Berlin, Heidelberg: Springer Berlin Heidelberg. pp. <span class="nowrap">55–</span>71. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1007%2F978-3-642-78374-6_5">10.1007/978-3-642-78374-6_5</a>. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-3-540-63372-3</bdi>.</cite></span>

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<li id="cite_note-v766-12"><span class="mw-cite-backlink"><b><a href="#cite_ref-v766_12-0">^</a></b></span> <span class="reference-text"><cite id="CITEREFWheeler1977" class="citation book cs1">Wheeler, John Archibald (1977). "Include the Observer in the Wave Function?". <i>Quantum Mechanics, A Half Century Later</i>. Dordrecht: Springer Netherlands. p. 1–18. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1007%2F978-94-010-1196-9_1">10.1007/978-94-010-1196-9_1</a>. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-94-010-1198-3</bdi>.</cite></span>

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