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<front>
<journal-meta>
<journal-id journal-id-type="publisher-id">Front. Phys.</journal-id>
<journal-title>Frontiers in Physics</journal-title>
<abbrev-journal-title abbrev-type="pubmed">Front. Phys.</abbrev-journal-title>
<issn pub-type="epub">2296-424X</issn>
<publisher>
<publisher-name>Frontiers Media S.A.</publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="publisher-id">995977</article-id>
<article-id pub-id-type="doi">10.3389/fphy.2022.995977</article-id>
<article-categories>
<subj-group subj-group-type="heading">
<subject>Physics</subject>
<subj-group>
<subject>Hypothesis and Theory</subject>
</subj-group>
</subj-group>
</article-categories>
<title-group>
<article-title>Dark matter and dark energy denote the gravitation of the expanding universe</article-title>
<alt-title alt-title-type="left-running-head">Annila and Wikstr&#xf6;m</alt-title>
<alt-title alt-title-type="right-running-head">
<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.3389/fphy.2022.995977">10.3389/fphy.2022.995977</ext-link>
</alt-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname>Annila</surname>
<given-names>Arto</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<uri xlink:href="https://loop.frontiersin.org/people/255534/overview"/>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Wikstr&#xf6;m</surname>
<given-names>M&#xe5;rten</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<xref ref-type="corresp" rid="c001">&#x2a;</xref>
<uri xlink:href="https://loop.frontiersin.org/people/1217371/overview"/>
</contrib>
</contrib-group>
<aff id="aff1">
<sup>1</sup>
<institution>Department of Physics</institution>, <institution>University of Helsinki</institution>, <addr-line>Helsinki</addr-line>, <country>Finland</country>
</aff>
<aff id="aff2">
<sup>2</sup>
<institution>Institute of Biotechnology</institution>, <institution>University of Helsinki</institution>, <addr-line>Helsinki</addr-line>, <country>Finland</country>
</aff>
<author-notes>
<fn fn-type="edited-by">
<p>
<bold>Edited by:</bold> <ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/1685322/overview">Pavan Kumar Aluri</ext-link>, Indian Institute of Technology (BHU), India</p>
</fn>
<fn fn-type="edited-by">
<p>
<bold>Reviewed by:</bold> <ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/1896500/overview">Mohammad Atazadeh</ext-link>, Azarbaijan Shahid Madani University, Iran</p>
<p>
<ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/159134/overview">Christian Corda</ext-link>, International Institute for Applicable Mathematics and Information Sciences, India</p>
</fn>
<corresp id="c001">&#x2a;Correspondence: M&#xe5;rten Wikstr&#xf6;m, <email>marten.wikstrom@helsinki.fi</email>
</corresp>
<fn fn-type="other">
<p>This article was submitted to Cosmology, a section of the journal Frontiers in Physics</p>
</fn>
</author-notes>
<pub-date pub-type="epub">
<day>14</day>
<month>10</month>
<year>2022</year>
</pub-date>
<pub-date pub-type="collection">
<year>2022</year>
</pub-date>
<volume>10</volume>
<elocation-id>995977</elocation-id>
<history>
<date date-type="received">
<day>16</day>
<month>07</month>
<year>2022</year>
</date>
<date date-type="accepted">
<day>27</day>
<month>09</month>
<year>2022</year>
</date>
</history>
<permissions>
<copyright-statement>Copyright &#xa9; 2022 Annila and Wikstr&#xf6;m.</copyright-statement>
<copyright-year>2022</copyright-year>
<copyright-holder>Annila and Wikstr&#xf6;m</copyright-holder>
<license xlink:href="http://creativecommons.org/licenses/by/4.0/">
<p>This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.</p>
</license>
</permissions>
<abstract>
<p>We reason that it is the gravitation of all ordinary matter, extending from the dense distant past to the sparse present, rather than dark matter, that shows up in galaxy rotation and velocity dispersion. Likewise, we argue that it is this gradient in the gravitational energy due to the expansion, rather than dark energy, that explains Type 1a supernovae brightness vs. redshift data. Our conclusions follow from statistical mechanics, the thermodynamic theory based on the atomistic axiom that everything comprises quanta. In line with the Einstein field equations, the vacuum quanta embodying gravitation, geometrized as spacetime, equate in dynamic balance to the quanta embodying the substance of the stress&#x2013;energy tensor. In accordance with quantum field theory, the proposed ground-state field of paired light quanta complies with Bose&#x2013;Einstein statistics and assumes an excited state around a particle.</p>
</abstract>
<kwd-group>
<kwd>dark energy</kwd>
<kwd>dark matter</kwd>
<kwd>flatness problem</kwd>
<kwd>graviton</kwd>
<kwd>horizon problem</kwd>
<kwd>photon</kwd>
<kwd>quantum of action</kwd>
<kwd>vacuum</kwd>
</kwd-group>
</article-meta>
</front>
<body>
<sec id="s1">
<title>1 Introduction</title>
<p>Astronomical observations have revealed more gravitation than expected. Most notably, spiral galaxies rotate faster [<xref ref-type="bibr" rid="B1">1</xref>], galaxies in clusters move faster [<xref ref-type="bibr" rid="B2">2</xref>], and light rays passing by galaxies bend more than is accounted for by visible matter in the galaxies [<xref ref-type="bibr" rid="B3">3</xref>,<xref ref-type="bibr" rid="B4">4</xref>]. Consequently, the dark matter parameter was added to the 1980s concordance model to match calculations with data [<xref ref-type="bibr" rid="B5">5</xref>,<xref ref-type="bibr" rid="B6">6</xref>]. However, the composition of dark matter remains unknown.</p>
<p>In contrast, other astronomical observations have shown less gravitation than expected. Most importantly, distant supernovae, dimmer than projected from their redshifts, entail that the gravitation of all matter, luminous and dark, cannot hold back the universe from expanding at an accelerating rate [<xref ref-type="bibr" rid="B7">7</xref>]. Hence, the dark energy parameter was included in the concordance model at the turn of the millennium to square calculations with data. However, the quintessence of dark energy also remains enigmatic.</p>
<p>Despite disclosing such deviations from expectations, astronomical data display unexpected unity. The same patterns emerge at all scales of the evolving universe. For example, baryonic mass vs. orbital velocity and vs. velocity dispersion of galaxies follow a power law over 10 orders [<xref ref-type="bibr" rid="B8">8</xref>]. Likewise, the Type 1a supernovae luminosity vs. redshift follows a straight line over 10 orders of magnitude before deviating noticeably [<xref ref-type="bibr" rid="B9">9</xref>,<xref ref-type="bibr" rid="B10">10</xref>]. Also, cumulative curves of void size and galaxy mass follow power laws closely [<xref ref-type="bibr" rid="B11">11</xref>].</p>
<p>Moreover, the mass-to-light ratio for the main sequence stars is nearly scale-free over seven magnitudes in luminosity [<xref ref-type="bibr" rid="B12">12</xref>]. In other words, bands of the renowned Hertzsprung&#x2013;Russell diagram, luminosity vs. temperature, span straight lines across a log&#x2013;log plot [<xref ref-type="bibr" rid="B13">13</xref>]. The Tully&#x2013;Fisher relation, spiral galaxy mass vs. luminosity [<xref ref-type="bibr" rid="B14">14</xref>,<xref ref-type="bibr" rid="B15">15</xref>], covers several magnitudes in the same manner. So, the Faber&#x2013;Jackson relation, luminosity vs. central stellar velocity dispersion of elliptical galaxies, also extends as a straight line over many magnitudes [<xref ref-type="bibr" rid="B16">16</xref>&#x2013;<xref ref-type="bibr" rid="B18">18</xref>]. Also, the initial mass function for a group of stars decreases in a power law manner over three magnitudes [<xref ref-type="bibr" rid="B19">19</xref>]. Similarly, stellar velocities correlate with supermassive black hole mass in a galaxy bulge [<xref ref-type="bibr" rid="B20">20</xref>]. The cosmic ray flux vs. energy stretches 12 orders [<xref ref-type="bibr" rid="B21">21</xref>] and cosmic microwave background brightness vs. frequency stretches about four orders of magnitude.</p>
<p>For a long time, scale-free data have been thought to present a universal law [<xref ref-type="bibr" rid="B22">22</xref>&#x2013;<xref ref-type="bibr" rid="B26">26</xref>]; however, it was only recently related to thermodynamics [<xref ref-type="bibr" rid="B27">27</xref>&#x2013;<xref ref-type="bibr" rid="B30">30</xref>], which, in turn, derives from statistical mechanics of evolving systems [<xref ref-type="bibr" rid="B31">31</xref>&#x2013;<xref ref-type="bibr" rid="B34">34</xref>]. Hence, we draw insight from statistical mechanics into the cosmological-scale evolution and find dark matter and dark energy to be unnecessary hypotheses because the gravitation of all ordinary matter across the expanding universe accounts for the observations.</p>
<p>As derived below, our conclusions stem from the thermodynamic distributions of quanta embodying both matter and vacuum. In the dynamic balance, the energy of matter quanta equals the energy of vacuum quanta. The Einstein field equations express this balance locally and universally so that the stress&#x2013;energy tensor equates to the metric tensor of spacetime. However, this geometrization of gravitation leaves the substance of gravitation subject to speculations. Instead of matching the cosmological model with accumulating data by introducing unsubstantiated parameters, we derive a consistent theory from a universal axiom to make it falsifiable by all data.</p>
<p>To put our proposal in perspective, we stress that the dark matter and dark energy problems can be tackled in principle in the framework of extended gravity [<xref ref-type="bibr" rid="B35">35</xref>,<xref ref-type="bibr" rid="B36">36</xref>].</p>
</sec>
<sec id="s2">
<title>2 Distribution of quanta in matter</title>
<p>In their attempts to derive thermodynamics from a statistical theory, Boltzmann [<xref ref-type="bibr" rid="B37">37</xref>] and Gibbs [<xref ref-type="bibr" rid="B38">38</xref>] devised statistical mechanics and deduced macroscopic <italic>equilibrium</italic> properties from microscopic constituents such as atoms. However, the ubiquitous scale-free patterns emerge from <italic>non-equilibrium</italic> processes, heading toward thermodynamic balance. Therefore, we rederive the thermodynamic theory for evolving systems, most notably the expanding universe.</p>
<p>The thermodynamic balance between all matter and all space displays itself in <italic>Mc</italic>
<sup>2</sup> &#x3d; <italic>GM</italic>
<sup>2</sup>/<italic>R</italic>, equating the total energy of all mass, <italic>M</italic>, to the total gravitational potential of the universe within its radius, <italic>R</italic>, [<xref ref-type="bibr" rid="B39">39</xref>]. The balance implies exchange between matter and space. Newton had already inferred that matter and light are interconvertible [<xref ref-type="bibr" rid="B40">40</xref>]. Later, Einstein identified the sources of gravitation with density, flux of energy, and momentum and equated the corresponding stress&#x2013;energy tensor to metric tensors.</p>
<p>Presently, we know that annihilation produces photons and that pair production converts photons to particles. All known constituents of matter transform by emitting or absorbing quanta [<xref ref-type="bibr" rid="B41">41</xref>]; hence, we adopt the ancient atomistic axiom favored by Boltzmann, but in a modern form, where everything comprises quanta of actions [<xref ref-type="bibr" rid="B42">42</xref>&#x2013;<xref ref-type="bibr" rid="B44">44</xref>]. Explicitly, the quantum of light carrying energy, <italic>E</italic>, on its period, <italic>t</italic>, measures the universal invariant, Planck&#x2019;s constant, <italic>h</italic> &#x3d; <italic>Et</italic>, qualifying the photon as the fundamental constituent.</p>
<sec id="s2-1">
<title>2.1 Entropy</title>
<p>The all-inclusive axiom allows us to describe any system with a general energy-level diagram, where all entities comprise quanta (<xref ref-type="fig" rid="F1">Figure 1</xref>), and to derive the thermodynamics of dissipative systems constituting the evolving universe [<xref ref-type="bibr" rid="B31">31</xref>,<xref ref-type="bibr" rid="B33">33</xref>,<xref ref-type="bibr" rid="B45">45</xref>].</p>
<fig id="F1" position="float">
<label>FIGURE 1</label>
<caption>
<p>General energy-level diagram represents any system comprising quanta. Entities in numbers, <italic>N</italic>
<sub>
<italic>k</italic>
</sub>, of the same energy, <italic>G</italic>
<sub>
<italic>k</italic>
</sub>, relative to the average energy, <italic>k</italic>
<sub>
<italic>B</italic>
</sub>
<italic>T</italic>, are on the same level. While their mutual exchange (bow arrows) causes no change, the system evolves toward balance with its surroundings through transformations (horizontal arrows) where quanta with energy, &#x394;<italic>Q</italic>
<sub>
<italic>jk</italic>
</sub>, (wavy arrows) absorb into products, <italic>N</italic>
<sub>
<italic>j</italic>
</sub>, or emit from starting materials, <italic>N</italic>
<sub>
<italic>k</italic>
</sub>. The logarithm of the sigmoid, cumulative probability, <italic>P</italic>, (dashed line) is entropy, <italic>S</italic> &#x3d; <italic>k</italic>
<sub>
<italic>B</italic>
</sub> ln&#x2009;<italic>P</italic>. <bold>Inset:</bold> On the log&#x2013;log scale, <italic>S</italic> vs. potential energy, <italic>&#x3bc;</italic>, mostly follows a power law, i.e., a straight line.</p>
</caption>
<graphic xlink:href="fphy-10-995977-g001.tif"/>
</fig>
<p>The equation of state can be derived by considering what it takes for an entity, indexed with <italic>j</italic>, for example, a grain of dust, to exist. Its probability, <sub>1</sub>
<italic>P</italic>
<sub>
<italic>j</italic>
</sub> &#x3d; <italic>&#x3d5;</italic>
<sub>1</sub>
<italic>&#x3d5;</italic>
<sub>2</sub>
<italic>&#x3d5;</italic>
<sub>3</sub>&#x22ef; &#x3d; <italic>&#x220f;</italic>
<sub>
<italic>k</italic>
</sub>
<italic>&#x3d5;</italic>
<sub>
<italic>k</italic>
</sub>, is a product, <italic>&#x220f;</italic>
<sub>
<italic>k</italic>
</sub>, of the substrates, say atoms, indexed with <italic>k</italic>. If any <italic>k</italic>-substrate is missing, the product form ensures that <sub>1</sub>
<italic>P</italic>
<sub>
<italic>j</italic>
</sub> &#x3d; 0. The factor, density in energy [<xref ref-type="bibr" rid="B38">38</xref>], <italic>&#x3d5;</italic>
<sub>
<italic>k</italic>
</sub> &#x3d; <italic>N</italic>
<sub>
<italic>k</italic>
</sub> exp[( &#x2212; &#x394;<italic>G</italic>
<sub>
<italic>jk</italic>
</sub> &#x2b; <italic>i</italic>&#x394;<italic>Q</italic>
<sub>
<italic>jk</italic>
</sub>)/<italic>k</italic>
<sub>
<italic>B</italic>
</sub>
<italic>T</italic>], denotes the <italic>k</italic>-substrate in numbers, <italic>N</italic>
<sub>
<italic>k</italic>
</sub>, having an energy difference, &#x394;<italic>G</italic>
<sub>
<italic>jk</italic>
</sub> &#x3d; <italic>G</italic>
<sub>
<italic>j</italic>
</sub> &#x2212; <italic>G</italic>
<sub>
<italic>k</italic>
</sub>, with respect to the <italic>j</italic>-product. The energy, <italic>i</italic>&#x394;<italic>Q</italic>
<sub>
<italic>jk</italic>
</sub>, in the form of the vector potential, absorbed or emitted in the <italic>jk</italic>-transformation, is distinguished by the prefactor, <italic>i</italic>, from the scalar potential bound in matter, for example, to deal with decay that violates the presumed, stationary-state conservation of probability [<xref ref-type="bibr" rid="B46">46</xref>]. The self-similar exponential form, <italic>de</italic>
<sup>
<italic>x</italic>
</sup>/<italic>dt</italic> &#x3d; e<sup>
<italic>x</italic>
</sup>, applies for a statistical system, where a transformation perturbs the system&#x2019;s average energy, <italic>k</italic>
<sub>
<italic>B</italic>
</sub>
<italic>T</italic>, insignificantly [<xref ref-type="bibr" rid="B38">38</xref>].</p>
<p>The probability of a population, as a product, <inline-formula id="inf1">
<mml:math id="m1">
<mml:msub>
<mml:mrow>
<mml:mi>P</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mrow>
<mml:mo stretchy="false">(</mml:mo>
<mml:mrow>
<mml:mmultiscripts>
<mml:mrow>
<mml:mi>P</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
<mml:none/>
<mml:mprescripts/>
<mml:mrow>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:none/>
</mml:mmultiscripts>
</mml:mrow>
<mml:mo stretchy="false">)</mml:mo>
</mml:mrow>
<mml:mrow>
<mml:mo stretchy="false">(</mml:mo>
<mml:mrow>
<mml:mmultiscripts>
<mml:mrow>
<mml:mi>P</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
<mml:none/>
<mml:mprescripts/>
<mml:mrow>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:none/>
</mml:mmultiscripts>
</mml:mrow>
<mml:mo stretchy="false">)</mml:mo>
</mml:mrow>
<mml:mrow>
<mml:mo stretchy="false">(</mml:mo>
<mml:mrow>
<mml:mmultiscripts>
<mml:mrow>
<mml:mi>P</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
<mml:none/>
<mml:mprescripts/>
<mml:mrow>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:none/>
</mml:mmultiscripts>
</mml:mrow>
<mml:mo stretchy="false">)</mml:mo>
</mml:mrow>
<mml:mo>&#x22ef;</mml:mo>
<mml:mo>/</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi>N</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>!</mml:mo>
<mml:mo>&#x3d;</mml:mo>
<mml:msup>
<mml:mrow>
<mml:mrow>
<mml:mo stretchy="false">(</mml:mo>
<mml:mrow>
<mml:mmultiscripts>
<mml:mrow>
<mml:mi>P</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
<mml:none/>
<mml:mprescripts/>
<mml:mrow>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:none/>
</mml:mmultiscripts>
</mml:mrow>
<mml:mo stretchy="false">)</mml:mo>
</mml:mrow>
</mml:mrow>
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>N</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:msup>
<mml:mo>/</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi>N</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>!</mml:mo>
</mml:math>
</inline-formula>, enumerating <italic>N</italic>
<sub>
<italic>j</italic>
</sub> interchangeable entities, ensures that <italic>P</italic>
<sub>
<italic>j</italic>
</sub> &#x3d; 0 if one entity is missing entirely. Since the indistinguishable configurations, i.e., microstates, are not proper states differing by energy, <italic>P</italic>
<sub>
<italic>j</italic>
</sub> is divided by permutations, <italic>N</italic>
<sub>
<italic>j</italic>
</sub>!</p>
<p>The system&#x2019;s probability, <italic>P</italic>, is the product, <italic>&#x220f;</italic>
<sub>
<italic>j</italic>
</sub>, of all <italic>P</italic>
<sub>
<italic>j</italic>
</sub>,<disp-formula id="e1">
<mml:math id="m2">
<mml:mi>P</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:munder>
<mml:mrow>
<mml:mo>&#x220f;</mml:mo>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:munder>
<mml:msub>
<mml:mrow>
<mml:mi>P</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:munder>
<mml:mrow>
<mml:mo>&#x220f;</mml:mo>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:munder>
<mml:msup>
<mml:mrow>
<mml:mfenced open="(" close=")">
<mml:mrow>
<mml:munder>
<mml:mrow>
<mml:mo>&#x220f;</mml:mo>
</mml:mrow>
<mml:mrow>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:munder>
<mml:msub>
<mml:mrow>
<mml:mi>&#x3d5;</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>N</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:msup>
<mml:mo>/</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi>N</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>!</mml:mo>
<mml:mo>.</mml:mo>
</mml:math>
<label>(1)</label>
</disp-formula>
</p>
<p>The logarithm of <italic>P</italic> multiplied by <italic>k</italic>
<sub>
<italic>B</italic>
</sub> is entropy:<disp-formula id="e2">
<mml:math id="m3">
<mml:mi>S</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi>k</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>B</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2061;</mml:mo>
<mml:mi>ln</mml:mi>
<mml:mo>&#x2061;</mml:mo>
<mml:mi>P</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi>k</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>B</mml:mi>
</mml:mrow>
</mml:msub>
<mml:munder>
<mml:mrow>
<mml:mo>&#x2211;</mml:mo>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:munder>
<mml:mi>ln</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>P</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mrow>
<mml:mi>T</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:munder>
<mml:mrow>
<mml:mo>&#x2211;</mml:mo>
</mml:mrow>
<mml:mrow>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:munder>
<mml:msub>
<mml:mrow>
<mml:mi>N</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mfenced open="(" close=")">
<mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mi mathvariant="normal">&#x394;</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>&#x3bc;</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mi>i</mml:mi>
<mml:mi mathvariant="normal">&#x394;</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>Q</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi>k</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>B</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mi>T</mml:mi>
</mml:mrow>
</mml:mfenced>
<mml:mo>,</mml:mo>
</mml:math>
<label>(2)</label>
</disp-formula>where ln&#x2009;<italic>N</italic>
<sub>
<italic>j</italic>
</sub>! &#x2248; <italic>N</italic>
<sub>
<italic>j</italic>
</sub> ln&#x2009;<italic>N</italic>
<sub>
<italic>j</italic>
</sub> &#x2212; <italic>N</italic>
<sub>
<italic>j</italic>
</sub> approximates the factorial and &#x394;<italic>&#x3bc;</italic>
<sub>
<italic>jk</italic>
</sub> &#x3d; <italic>&#x3bc;</italic>
<sub>
<italic>j</italic>
</sub> &#x2212; <italic>&#x3bc;</italic>
<sub>
<italic>k</italic>
</sub> denotes the difference between the substrate potential, <italic>&#x3bc;</italic>
<sub>
<italic>k</italic>
</sub> &#x3d; <italic>k</italic>
<sub>
<italic>B</italic>
</sub>
<italic>T</italic>&#x2009;ln[<italic>N</italic>
<sub>
<italic>k</italic>
</sub> exp (<italic>G</italic>
<sub>
<italic>k</italic>
</sub>/<italic>k</italic>
<sub>
<italic>B</italic>
</sub>
<italic>T</italic>)], and the product potential, <italic>&#x3bc;</italic>
<sub>
<italic>j</italic>
</sub>. When multiplied with <italic>T</italic>, <italic>S</italic> equals the system&#x2019;s total energy, <italic>TS</italic>. It comprises the bound, <italic>&#x2211;N</italic>
<sub>
<italic>j</italic>
</sub>
<italic>k</italic>
<sub>
<italic>B</italic>
</sub>
<italic>T</italic>, and free, <italic>&#x2211;N</italic>
<sub>
<italic>j</italic>
</sub> ( &#x2212; &#x394;<italic>&#x3bc;</italic>
<sub>
<italic>jk</italic>
</sub> &#x2b; <italic>i</italic>&#x394;<italic>Q</italic>
<sub>
<italic>jk</italic>
</sub>), forms of energy.</p>
<p>As the system evolves with time, <italic>t</italic>, toward balance with its surroundings, free energy, &#x2212;&#x394;<italic>&#x3bc;</italic>
<sub>
<italic>jk</italic>
</sub> &#x2b; <italic>i</italic>&#x394;<italic>Q</italic>
<sub>
<italic>jk</italic>
</sub>, is consumed in dissipative transformations from <italic>N</italic>
<sub>
<italic>k</italic>
</sub> to <italic>N</italic>
<sub>
<italic>j</italic>
</sub>. For example, in stars, hydrogen is transformed into helium.</p>
<p>For a statistical system, the population changes can be approximated by continuous differentials, <italic>dN</italic>
<sub>
<italic>j</italic>
</sub>, to give the following:<disp-formula id="e3">
<mml:math id="m4">
<mml:mi>T</mml:mi>
<mml:mfrac>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:mi>S</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>T</mml:mi>
<mml:munder>
<mml:mrow>
<mml:mo>&#x2211;</mml:mo>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:munder>
<mml:mfrac>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:mi>S</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>N</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfrac>
<mml:mfrac>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>N</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mo>&#x3d;</mml:mo>
<mml:munder>
<mml:mrow>
<mml:mo>&#x2211;</mml:mo>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:munder>
<mml:mfrac>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>N</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mfenced open="(" close=")">
<mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mi mathvariant="normal">&#x394;</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>&#x3bc;</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mi>i</mml:mi>
<mml:mi mathvariant="normal">&#x394;</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>Q</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
<mml:mo>,</mml:mo>
</mml:math>
<label>(3)</label>
</disp-formula>where the variation in average energy, <italic>k</italic>
<sub>
<italic>B</italic>
</sub>
<italic>T</italic>, is contained in <italic>dS</italic>. Since entropy is a function of energy (<xref ref-type="disp-formula" rid="e2">Eq. 2</xref>), <italic>S</italic> attains at <italic>dS</italic>/<italic>dt</italic> &#x3d; 0 the steady-state maximum, <italic>S</italic> &#x3d; <italic>&#x2211;k</italic>
<sub>
<italic>B</italic>
</sub>
<italic>N</italic>
<sub>
<italic>j</italic>
</sub>, when free energy attains its minimum, &#x2212;&#x394;<italic>&#x3bc;</italic>
<sub>
<italic>jk</italic>
</sub> &#x2b; <italic>i</italic>&#x394;<italic>Q</italic>
<sub>
<italic>jk</italic>
</sub> &#x3d; 0.</p>
<p>Free energy drives the population changes<disp-formula id="e4">
<mml:math id="m5">
<mml:mfrac>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>N</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>k</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>B</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mi>T</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:munder>
<mml:mrow>
<mml:mo>&#x2211;</mml:mo>
</mml:mrow>
<mml:mrow>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:munder>
<mml:msub>
<mml:mrow>
<mml:mi>&#x3c3;</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mfenced open="(" close=")">
<mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mi mathvariant="normal">&#x394;</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>&#x3bc;</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mi>i</mml:mi>
<mml:mi mathvariant="normal">&#x394;</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>Q</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
<mml:mo>,</mml:mo>
</mml:math>
<label>(4)</label>
</disp-formula>through mechanistic factors, <italic>&#x3c3;</italic>
<sub>
<italic>jk</italic>
</sub> &#x3e; 0, facilitating <italic>jk</italic>-transformations [<xref ref-type="bibr" rid="B47">47</xref>]. For example, a high-density stellar core can be regarded as a mechanism enabling nuclear reactions.</p>
<p>Substituting <italic>dN</italic>
<sub>
<italic>j</italic>
</sub>/<italic>dt</italic> in <xref ref-type="disp-formula" rid="e3">Eq. 3</xref> with <xref ref-type="disp-formula" rid="e4">Eq. 4</xref> and squaring &#x2212;&#x394;<italic>&#x3bc;</italic>
<sub>
<italic>jk</italic>
</sub> &#x2b; <italic>i</italic>&#x394;<italic>Q</italic>
<sub>
<italic>jk</italic>
</sub> in the orthogonal <italic>jk</italic>-basis show <italic>dS</italic> &#x2265; 0. The fact that entropy cannot decrease follows from the conservation of quanta. If it were to be violated, the quanta emitted from matter would be lost into nowhere instead of being absorbed into the surrounding vacuum.</p>
</sec>
<sec id="s2-2">
<title>2.2 Continuum approximation</title>
<p>A continuous form of the equation of motion (<xref ref-type="disp-formula" rid="e3">Eq. 3</xref>) is useful for understanding the scale-free astronomical data. It is obtained by approximating the scalar, <italic>&#x3bc;</italic>
<sub>
<italic>j</italic>
</sub> &#x3d; (<italic>&#x2202;U</italic>/<italic>&#x2202;N</italic>
<sub>
<italic>j</italic>
</sub>), and vector, <italic>Q</italic>
<sub>
<italic>j</italic>
</sub> &#x3d; (<italic>&#x2202;Q</italic>/<italic>&#x2202;N</italic>
<sub>
<italic>j</italic>
</sub>), potentials by continuous scalar, <italic>U</italic>, and vector, <italic>Q</italic>, potentials:<disp-formula id="e5">
<mml:math id="m6">
<mml:mi>T</mml:mi>
<mml:mfrac>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>N</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mo>&#x3d;</mml:mo>
<mml:munder>
<mml:mrow>
<mml:mo>&#x2211;</mml:mo>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:munder>
<mml:mfrac>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>N</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mfenced open="(" close=")">
<mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mi>&#x2202;</mml:mi>
<mml:mi>U</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>&#x2202;</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>N</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfrac>
<mml:mo>&#x2b;</mml:mo>
<mml:mi>i</mml:mi>
<mml:mfrac>
<mml:mrow>
<mml:mi>&#x2202;</mml:mi>
<mml:mi>Q</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>&#x2202;</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>N</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfrac>
</mml:mrow>
</mml:mfenced>
<mml:mo>&#x3d;</mml:mo>
<mml:mfenced open="(" close=")">
<mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mi>&#x2202;</mml:mi>
<mml:mi>U</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>&#x2202;</mml:mi>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mo>&#x2b;</mml:mo>
<mml:mi>i</mml:mi>
<mml:mfrac>
<mml:mrow>
<mml:mi>&#x2202;</mml:mi>
<mml:mi>Q</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>&#x2202;</mml:mi>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfrac>
</mml:mrow>
</mml:mfenced>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mi>d</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mn>2</mml:mn>
<mml:mi>K</mml:mi>
<mml:mo>,</mml:mo>
</mml:math>
<label>(5)</label>
</disp-formula>where <italic>TdS</italic> equals the change in kinetic energy <italic>d</italic>2<italic>K</italic>. As mentioned previously, the prefactor, <italic>i</italic>, serves to distinguish dissipated energy from the concomitant change in scalar potential [<xref ref-type="bibr" rid="B46">46</xref>].</p>
<p>The integral form of <xref ref-type="disp-formula" rid="e5">Eq. 5</xref> with vanishing variation of the integrand <bold>p</bold>&#xb7;<bold>dx</bold> &#x3d; 2<italic>Kdt</italic> leads to Maupertuis&#x2019; principle of least action where quanta with momenta, <bold>p</bold>, propagate on geodesics, i.e., optimal paths, <bold>x</bold>, [<xref ref-type="bibr" rid="B48">48</xref>]. Unlike the Lagrangian, based on the conservation of energy, Maupertuis&#x2019; form is open for evolution. Mathematically speaking, the integration limit moves while integrating due to dissipation, <italic>&#x2202;Q</italic>/<italic>&#x2202;t</italic> &#x2260; 0. Thus, <xref ref-type="disp-formula" rid="e5">Eq. 5</xref> is non-integrable, yet not arbitrary, but bound by free energy. According to <xref ref-type="disp-formula" rid="e3">Eqs 3</xref>&#x2013;<xref ref-type="disp-formula" rid="e5">5</xref>, entropy does not only increase but also increase in the least time. Thus, bodies move along optimal, i.e., geodesics, rather than arbitrary paths. For example, a stone falls straight down.</p>
<p>Also multiplying Newton&#x2019;s second law, i.e., the change, <italic>d</italic>
<sub>
<italic>t</italic>
</sub>
<bold>p</bold>, in momentum, <bold>p</bold> &#x3d; <italic>m</italic>
<bold>v</bold>, with velocity, <bold>v</bold>, gives the equation of motion:<disp-formula id="e6">
<mml:math id="m7">
<mml:mtable class="align" columnalign="left">
<mml:mtr>
<mml:mtd columnalign="right">
<mml:mi mathvariant="bold">F</mml:mi>
</mml:mtd>
<mml:mtd columnalign="left">
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mi>d</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mi mathvariant="bold">p</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>m</mml:mi>
<mml:mi mathvariant="bold">a</mml:mi>
<mml:mo>&#x2b;</mml:mo>
<mml:mi mathvariant="bold">v</mml:mi>
<mml:mfrac>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mspace width="0.28em"/>
<mml:mspace width="0.28em"/>
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<mml:mo>&#x22c5;</mml:mo>
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<label>(6)</label>
</disp-formula>since kinetic energy, 2<italic>K</italic> &#x3d; <bold>v</bold> &#x22c5; <bold>p</bold> &#x3d; <italic>&#x2211;v</italic>
<sub>
<italic>j</italic>
</sub>
<italic>mv</italic>
<sub>
<italic>k</italic>
</sub>, vanishes for <italic>j</italic> &#x2260; <italic>k</italic> and <italic>d</italic>
<sub>
<italic>t</italic>
</sub>
<bold>v</bold> &#x22c5;<bold>p</bold> &#x3d; 0 for acceleration <bold>a</bold> &#x3d; <italic>d</italic>
<sub>
<italic>t</italic>
</sub>
<bold>v</bold> &#x22a5; <bold>v</bold>. The relativistic mass&#x2013;energy equivalence, <italic>E</italic> &#x3d; <italic>mc</italic>
<sup>2</sup>, derives from the total action, <italic>nh</italic> &#x3d; <italic>Et</italic> &#x3d; <italic>mc</italic>
<sup>2</sup>
<italic>t</italic> &#x3d; <italic>px</italic>, of a system with <italic>n</italic> quanta. Defined in dissipative terms, the change in mass, <italic>d</italic>
<sub>
<italic>t</italic>
</sub>
<italic>m</italic> &#x3d; <italic>d</italic>
<sub>
<italic>t</italic>
</sub>
<italic>E</italic>/<italic>c</italic>
<sup>2</sup> &#x3d; <italic>id</italic>
<sub>
<italic>t</italic>
</sub>
<italic>Q</italic>/<italic>v</italic>
<sup>2</sup>, denotes changes in geodesics, the quantized trajectories opening up for absorption of quanta from the surroundings or emission into the surroundings [<xref ref-type="bibr" rid="B49">49</xref>]. For example, in annihilation, quanta bound in matter transform into quanta of the vacuum.</p>
<p>When the system attains thermodynamic balance with its surroundings, <xref ref-type="disp-formula" rid="e5">Eqs. 5</xref> and <xref ref-type="disp-formula" rid="e6">6</xref> reduce to the integrable virial theorem, 2<italic>K</italic> &#x2b; <italic>U</italic> &#x3d; 0, relating the kinetic energy of a self-gravitating system, 2<italic>K</italic>, to the gravitational potential energy, <italic>U</italic>, of the system. The time invariance, corresponding to constant energy by Noether&#x2019;s theorem, 2<italic>Kt</italic> &#x3d; <italic>nh</italic>, means that the quanta orbit geodesics with characteristic periods, <italic>t</italic>, of the motional modes [<xref ref-type="bibr" rid="B42">42</xref>,<xref ref-type="bibr" rid="B50">50</xref>].</p>
</sec>
<sec id="s2-3">
<title>2.3 The universality in data</title>
<p>The ubiquitous, nearly lognormal, skewed distributions summing up in a power-law manner can be deduced from <xref ref-type="disp-formula" rid="e4">Eq. 4</xref> [<xref ref-type="bibr" rid="B32">32</xref>]. Initially, when there is a lot of free energy, e.g., for star formation, mechanisms, <italic>&#x2211;</italic>
<sub>
<italic>k</italic>
</sub>
<italic>&#x3c3;</italic>
<sub>
<italic>jk</italic>
</sub>, constrain the free energy consumption, <italic>d</italic>
<sub>
<italic>t</italic>
</sub> ( &#x2212; &#x394;<italic>&#x3bc;</italic>
<sub>
<italic>jk</italic>
</sub> &#x2b; <italic>i</italic>&#x394;<italic>Q</italic>
<sub>
<italic>jk</italic>
</sub>). Then, the change<disp-formula id="e7">
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<label>(7)</label>
</disp-formula>is approximately exponential. For example, the weak gravity of dilute gas curtails the initial star formation; however, soon, the increasing gravity of aggregating gas accelerates further aggregation. It should be noted that, in <xref ref-type="disp-formula" rid="e7">Eq. 7</xref>, the change reduces to <italic>d&#x3bc;</italic>
<sub>
<italic>j</italic>
</sub>/<italic>dN</italic>
<sub>
<italic>j</italic>
</sub> &#x3d; <italic>d</italic>(<italic>G</italic>
<sub>
<italic>j</italic>
</sub> &#x2b; <italic>k</italic>
<sub>
<italic>B</italic>
</sub>
<italic>T</italic>&#x2009;ln&#x2009;<italic>N</italic>
<sub>
<italic>j</italic>
</sub>)/<italic>dN</italic>
<sub>
<italic>j</italic>
</sub> &#x3d; <italic>k</italic>
<sub>
<italic>B</italic>
</sub>
<italic>T</italic>/<italic>N</italic>
<sub>
<italic>j</italic>
</sub> because <italic>&#x3bc;</italic>
<sub>
<italic>k</italic>
</sub>, <italic>Q</italic>
<sub>
<italic>j</italic>
</sub>, and <italic>Q</italic>
<sub>
<italic>k</italic>
</sub> do not depend explicitly but stoichiometrically on <italic>N</italic>
<sub>
<italic>j</italic>
</sub>. Conversely, the final phase dies out almost exponentially when the free energy has been nearly exhausted. For example, the star formation decreases as free gas is exhausted.</p>
<p>The bulk distribution between a process&#x2019;s initial and final phases follows a power law [<xref ref-type="bibr" rid="B32">32</xref>]. This becomes apparent using the atomistic axiom, <inline-formula id="inf2">
<mml:math id="m9">
<mml:msub>
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<mml:mi>N</mml:mi>
</mml:mrow>
<mml:mrow>
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</mml:mrow>
</mml:msub>
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</mml:mrow>
<mml:mrow>
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</mml:mrow>
</mml:msub>
<mml:msub>
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</mml:mrow>
<mml:mrow>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
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</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
<mml:msubsup>
<mml:mrow>
<mml:mi>N</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mrow>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msubsup>
</mml:math>
</inline-formula>. It should be noted that the <italic>j</italic>-entities, in numbers <italic>N</italic>
<sub>
<italic>j</italic>
</sub>, assemble from the elemental constituents, <italic>N</italic>
<sub>1</sub>, through various <italic>mn</italic>-transformations, amassed in <italic>&#x3b1;</italic>
<sub>
<italic>j</italic>
</sub> &#x3d; <italic>&#x220f;</italic>
<sub>
<italic>mn</italic>
</sub>exp[<italic>&#x2211;</italic>
<sub>
<italic>j</italic>
</sub>
<italic>N</italic>
<sub>
<italic>j</italic>
</sub>(&#x2212;&#x394;<italic>&#x3bc;</italic>
<sub>
<italic>mn</italic>
</sub> &#x2b; <italic>i</italic>&#x394;<italic>Q</italic>
<sub>
<italic>mn</italic>
</sub>)/<italic>k</italic>
<sub>
<italic>B</italic>
</sub>
<italic>T</italic>]. Thus, the change<disp-formula id="e8">
<mml:math id="m10">
<mml:mfrac>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:msub>
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</mml:mrow>
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<mml:mo>&#x2212;</mml:mo>
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<label>(8)</label>
</disp-formula>when integrated, follows a power law, ln&#x2009;<italic>N</italic>
<sub>
<italic>j</italic>
</sub> &#x3d; <italic>j</italic>&#x2009;ln&#x2009;<italic>N</italic>
<sub>1</sub> &#x2b; constant. The form is familiar from various self-organizing processes [<xref ref-type="bibr" rid="B51">51</xref>,<xref ref-type="bibr" rid="B52">52</xref>]. Also, Newton&#x2019;s second law (<xref ref-type="disp-formula" rid="e6">Eq. 6</xref>), when divided with momentum, <italic>p</italic>, and integrated, delivers the power law, <italic>d</italic>&#x2009;ln&#x2009;<italic>p</italic> &#x3d; <italic>d</italic>&#x2009;ln&#x2009;<italic>v</italic> &#x2b; <italic>d</italic>&#x2009;ln&#x2009;<italic>m</italic>. Thus, it is not surprising that power laws are ubiquitous, including gravitational phenomena.</p>
<p>When the system evolves gradually, the change in energy is small compared with the average energy, i.e., &#x7c;&#x2212;&#x394;<italic>&#x3bc;</italic>
<sub>
<italic>jk</italic>
</sub> &#x2b; <italic>i</italic>&#x394;<italic>Q</italic>
<sub>
<italic>jk</italic>
</sub>&#x7c;/<italic>k</italic>
<sub>
<italic>B</italic>
</sub>
<italic>T</italic> &#x226a; 1. As the variation, <italic>n</italic>, is small, i.e., <italic>n</italic> &#x226a; <italic>j</italic>, around the average factor, <italic>&#x3d5;</italic>
<sub>
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</sub>, the distribution of factors,<disp-formula id="e9">
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</disp-formula>can be given in terms, ln<italic>&#x3d5;</italic>
<sub>
<italic>j</italic>
</sub> &#x3d; <italic>j</italic>&#x2009;ln&#x2009;<italic>&#x3d5;</italic>
<sub>1</sub>, of the elemental factor, <italic>&#x3d5;</italic>
<sub>1</sub>. By the central limit theorem, data distribute around the typical form, <italic>j</italic>, in a skewed, approximately lognormal manner [<xref ref-type="bibr" rid="B23">23</xref>,<xref ref-type="bibr" rid="B53">53</xref>,<xref ref-type="bibr" rid="B54">54</xref>]. For example, all red giants look like red giants and not white dwarfs&#x2014;the red giant distribution peaks on the typical giant and the white dwarf distribution on the typical dwarf. Logarithmic spirals are also approximately lognormal distributions in polar coordinates, i.e., energetically optimal forms [<xref ref-type="bibr" rid="B32">32</xref>].</p>
<p>
<xref ref-type="disp-formula" rid="e7">Equations 7</xref>&#x2013;<xref ref-type="disp-formula" rid="e9">9</xref> show that the skewed distributions sum up along sigmoid curves [<xref ref-type="bibr" rid="B55">55</xref>]. Thus, data follow closely, but not precisely, the power law, deviating at low and high ends [<xref ref-type="bibr" rid="B56">56</xref>]. Moreover, many data display a series of power laws whose slope changes when a mechanism of transformations changes to another. For example, in the main sequence, the most massive stars are the most effective at releasing energy through nuclear reactions, whereas the stars with the lowest mass are the least effective. Likewise, the cosmic ray flux turns from one slope to another when one mechanism of dissipation changes to another [<xref ref-type="bibr" rid="B57">57</xref>,<xref ref-type="bibr" rid="B58">58</xref>].</p>
</sec>
</sec>
<sec id="s3">
<title>3 Distribution of quanta in the vacuum</title>
<p>Bose worked out the quantum statistics of photons that underlies Planck&#x2019;s law [<xref ref-type="bibr" rid="B59">59</xref>]. However, the vacuum structure that dictates the distribution was not explicitly spelt out. Therefore, we rederive the Bose&#x2013;Einstein distribution for the quanta that embody the vacuum.</p>
<p>To regard the vacuum as physical as matter is motivated because the vacuum holds the energy of all gravitation equal to the energy of all matter [<xref ref-type="bibr" rid="B39">39</xref>]. Moreover, similar to matter, voids also distribute in a power-law manner [<xref ref-type="bibr" rid="B11">11</xref>,<xref ref-type="bibr" rid="B60">60</xref>], suggesting thermodynamic balance between the two. Geometrically speaking, the Ricci curvature and metric tensor equate to the stress&#x2013;energy tensor in the Einstein field equations. Also, in quantum field theory, particles equate to the excitations of fields that permeate the vacuum.</p>
<p>While the readily detectable radiation accounts only for a tiny fraction <inline-formula id="inf3">
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<p>The correspondence between the speed of light, <italic>c</italic>, and the vacuum permittivity, <italic>&#x3f5;</italic>
<sub>
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</sub>, and permeability, <italic>&#x3bc;</italic>
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</sub>, by <italic>c</italic>
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<sub>
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</sub>
<italic>&#x3bc;</italic>
<sub>
<italic>o</italic>
</sub> [<xref ref-type="bibr" rid="B62">62</xref>], and the gravitation of the whole universe of mass, <italic>M</italic>, and radius, <italic>R</italic>, by <italic>c</italic>
<sup>2</sup> &#x3d; <italic>GM</italic>/<italic>R</italic> [<xref ref-type="bibr" rid="B39">39</xref>], suggests that the vacuum comprises quanta of light. Indeed, the Michelson&#x2013;Morley experiment did not rule out a light-embodying medium; it only rejected a light-carrying medium.</p>
<p>According to the atomistic axiom, two destructively interfering photons do not vanish into vacuum [<xref ref-type="bibr" rid="B63">63</xref>]. Instead, only their electromagnetic effects are negated. Thus, the vacuum comprising photons in such pairs is a transparent, relativistic substance without net electromagnetic force, yet with gravitational energy density.</p>
<sec id="s3-1">
<title>3.1 The radiation law</title>
<p>The background spectrum of free space can be derived from the atomistic axiom by considering how photons of energy, <italic>&#x25b;</italic>
<sub>
<italic>i</italic>
</sub>, relative to the average, <italic>k</italic>
<sub>
<italic>B</italic>
</sub>
<italic>T</italic>, distribute in numbers, <italic>n</italic>
<sub>
<italic>i</italic>
</sub>, among rays of paired photons (<xref ref-type="fig" rid="F2">Figure 2</xref>). The number of ways, in-phase and antiphase, the photons populate the numerous rays intersecting in degenerate directions, <italic>g</italic>
<sub>
<italic>i</italic>
</sub>, is the product of <italic>n</italic>
<sub>
<italic>i</italic>
</sub> combinations of the sets with <italic>n</italic>
<sub>
<italic>i</italic>
</sub> &#x2b; 2<italic>g</italic>
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</sub> &#x2212; 1 elements.<disp-formula id="e10">
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<label>(10)</label>
</disp-formula>
</p>
<fig id="F2" position="float">
<label>FIGURE 2</label>
<caption>
<p>Vacuum spectral density, <italic>u</italic>, sums up from numerous rays of photons (blue-red waves) with a spectrum of energies, <italic>&#x25b;</italic>
<sub>
<italic>i</italic>
</sub>, about the average energy, <italic>k</italic>
<sub>
<italic>B</italic>
</sub>
<italic>T</italic>. The paired photons cannot be seen as light but are sensed as inertia and gravitation through their coupling to matter [<xref ref-type="bibr" rid="B63">63</xref>]. In contrast, the odd quanta (blue or red), distributed in-phase or antiphase among the paired rays, are seen as light and manifest as electromagnetism. <bold>Inset:</bold> The cumulative spectral density vs. energy (dashed line) mostly follows a power law, i.e., a straight line on the log&#x2013;log plot.</p>
</caption>
<graphic xlink:href="fphy-10-995977-g002.tif"/>
</fig>
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</disp-formula>
</p>
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<mml:mo>,</mml:mo>
</mml:math>
<label>(12)</label>
</disp-formula>where quanta distribute according to the Bose&#x2013;Einstein distribution,<disp-formula id="e13">
<mml:math id="m16">
<mml:msub>
<mml:mrow>
<mml:mi>n</mml:mi>
</mml:mrow>
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</mml:mrow>
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<mml:mrow>
<mml:mn>2</mml:mn>
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</mml:mrow>
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</mml:mrow>
<mml:mrow>
<mml:mi>i</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>/</mml:mo>
<mml:msub>
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<mml:mi>k</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>B</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mi>T</mml:mi>
</mml:mrow>
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<mml:mo>&#x2212;</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
</mml:mfrac>
<mml:mo>,</mml:mo>
</mml:math>
<label>(13)</label>
</disp-formula>having two states for each photon, in-phase and antiphase, per locus in the paired ray (<xref ref-type="fig" rid="F2">Figure 2</xref>) [<xref ref-type="bibr" rid="B59">59</xref>]. Since the spectral density of the paired-photon vacuum has precisely the form of the black body spectrum, we consider that the void is basically as physical as matter comprising quanta.</p>
<p>In agreement with Planck&#x2019;s law of radiation, the photon pairs open up with increasing temperature and pair up with decreasing temperature. Moreover, the paired-photon vacuum responds to an accelerating charge by unpairing and radiating photons. Thus, the photons do not appear out of vacuum nor disappear into it but comprise the vacuum.</p>
<p>The proposed substance of space also complies with electromagnetism. Explicitly, the paired-photon vacuum, embodying the four-potential of the electric scalar potential, <italic>&#x3c6;</italic>, and magnetic vector potential, <bold>A</bold>, satisfies the Lorenz gauge[<xref ref-type="bibr" rid="B64">64</xref>],<disp-formula id="e14">
<mml:math id="m17">
<mml:mo>&#x2207;</mml:mo>
<mml:mi>&#x3c6;</mml:mi>
<mml:mo>&#x2b;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mi>&#x2202;</mml:mi>
<mml:mi mathvariant="bold">A</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>&#x2202;</mml:mi>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
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<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mrow>
<mml:mi>c</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mfrac>
<mml:mrow>
<mml:mi>&#x2202;</mml:mi>
<mml:mi>&#x3c6;</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>&#x2202;</mml:mi>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfrac>
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<mml:mi>c</mml:mi>
<mml:mo>&#x2207;</mml:mo>
<mml:mo>&#x22c5;</mml:mo>
<mml:mi mathvariant="bold">A</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>0</mml:mn>
<mml:mo>,</mml:mo>
</mml:math>
<label>(14)</label>
</disp-formula>as a seemingly continuous and indestructible substance whose wave nature gives rise to interference phenomena. For example, in the Aharonov&#x2013;Bohm experiment [<xref ref-type="bibr" rid="B65">65</xref>], a phase difference<disp-formula id="e15">
<mml:math id="m18">
<mml:mi mathvariant="normal">&#x394;</mml:mi>
<mml:mi>&#x3d5;</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi>&#x3d5;</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>1</mml:mn>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2212;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi>&#x3d5;</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mi>e</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>&#x210f;</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mo>&#x222b;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi mathvariant="bold">A</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>1</mml:mn>
</mml:mrow>
</mml:msub>
<mml:mo>&#x22c5;</mml:mo>
<mml:mi>d</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi mathvariant="bold">x</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>1</mml:mn>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2212;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mi>e</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>&#x210f;</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mo>&#x222b;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi mathvariant="bold">A</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msub>
<mml:mo>&#x22c5;</mml:mo>
<mml:mi>d</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi mathvariant="bold">x</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msub>
<mml:mo>,</mml:mo>
</mml:math>
<label>(15)</label>
</disp-formula>develops between waves when charges, <italic>e</italic>, traverse <bold>A</bold>
<sub>1</sub> and <bold>A</bold>
<sub>2</sub> along paths <bold>x</bold>
<sub>1</sub> and <bold>x</bold>
<sub>2</sub>, respectively</p>
<p>Gradients in the vacuum are fields [<xref ref-type="bibr" rid="B66">66</xref>&#x2013;<xref ref-type="bibr" rid="B68">68</xref>]. The electric field,<disp-formula id="e16">
<mml:math id="m19">
<mml:mi mathvariant="bold">E</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mo>&#x2212;</mml:mo>
<mml:mo>&#x2207;</mml:mo>
<mml:mi>&#x3c6;</mml:mi>
<mml:mo>&#x2212;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mi>&#x2202;</mml:mi>
<mml:mi mathvariant="bold">A</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>&#x2202;</mml:mi>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mo>,</mml:mo>
</mml:math>
<label>(16)</label>
</disp-formula>for example, around an electron is a gradient in the paired-photon rays, whose winding tallies the electron winding number, a topological quantum number [<xref ref-type="bibr" rid="B69">69</xref>]. Therefore, it takes the full 4<italic>&#x3c0;</italic>, rather than only 2<italic>&#x3c0;</italic>, rotation of the electron, e<sup>&#x2212;</sup>, to return the vacuum to its original state [<xref ref-type="bibr" rid="B70">70</xref>,<xref ref-type="bibr" rid="B71">71</xref>]. This <italic>SU</italic>(2)<sub>
<italic>L</italic>
</sub> symmetry is disclosed by monodromy of the vacuum around the electron, <italic>e</italic>
<sup>&#x2212;</sup> &#x3d; <italic>&#x222b;&#x3c1;dV</italic> &#x3d; &#x2212;<italic>&#x25b;</italic>
<sub>
<italic>o</italic>
</sub> <italic>&#x222b;</italic>&#x2207;&#x22c5;&#x2207;<italic>&#x3d5;dV</italic> &#x3d; &#x2212;<italic>&#x25b;</italic>
<sub>
<italic>o</italic>
</sub> <italic>&#x222b;</italic>&#x2207;<italic>&#x3d5;dS</italic>, enclosed in a volume, <italic>V</italic>, or, as by Gauss&#x2019; law, bordered by an area, <italic>S</italic>.</p>
<p>The vacuum polarization is similar to the polarization of a dielectric material; the paired-photon rays wind up, i.e., twist, to counteract introduced charges. Conversely, when charges neutralize, the unwinding of the paired-photon rays gives rise to a time-varying electric field, i.e., displacement current, <italic>J</italic>
<sub>
<italic>D</italic>
</sub> &#x3d; <italic>&#x25b;</italic>
<sub>
<italic>o</italic>
</sub>
<italic>&#x2202;</italic>
<sub>
<italic>t</italic>
</sub>
<bold>E</bold>.</p>
<p>The magnetic field<disp-formula id="e17">
<mml:math id="m20">
<mml:mi mathvariant="bold">B</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mo>&#x2207;</mml:mo>
<mml:mo>&#x2009;&#x2009;</mml:mo>
<mml:mo>&#xd7;</mml:mo>
<mml:mi mathvariant="bold">A</mml:mi>
<mml:mo>,</mml:mo>
</mml:math>
<label>(17)</label>
</disp-formula>is a vortex of the twists in the paired-photon rays, for example, encircling a line of moving charges (<xref ref-type="fig" rid="F3">Figure 3</xref>).</p>
<fig id="F3" position="float">
<label>FIGURE 3</label>
<caption>
<p>Electric potential diverges from a current-carrying wire (black, pointing straight at) as paired-photon rays (sketched as red and blue waves) whose winding matches the winding number of the charge density along the wire and decays inversely with distance, <italic>r</italic>. The magnetic field lines (thin concentric circles) correspond to the lines encircling the wire at a distance where the winding is the same.</p>
</caption>
<graphic xlink:href="fphy-10-995977-g003.tif"/>
</fig>
<p>The electromagnetic fields (<xref ref-type="disp-formula" rid="e16">Eqs. 16</xref> and <xref ref-type="disp-formula" rid="e17">17</xref>) give rise to the Lorentz force,<disp-formula id="e18">
<mml:math id="m21">
<mml:mi mathvariant="bold">F</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>q</mml:mi>
<mml:mfenced open="(" close=")">
<mml:mrow>
<mml:mi mathvariant="bold">E</mml:mi>
<mml:mo>&#x2b;</mml:mo>
<mml:mi mathvariant="bold">v</mml:mi>
<mml:mo>&#xd7;</mml:mo>
<mml:mi mathvariant="bold">B</mml:mi>
</mml:mrow>
</mml:mfenced>
<mml:mo>,</mml:mo>
</mml:math>
<label>(18)</label>
</disp-formula>experienced by a charge, <italic>q</italic>, moving with velocity, <bold>v</bold>. Thus, from the proposed perspective, it is not that charges themselves would attract or repel each other; instead, the charges move as they couple with the physical vacuum that is leveling off its gradients.</p>
<p>The proposed substance of space also complies with gravitation. The gradient in the gravitational four-potential of the scalar, <italic>&#x3d5;</italic>
<sub>
<italic>g</italic>
</sub>, and vector, <bold>A</bold>
<sub>
<italic>g</italic>
</sub>, components is the gravitational field [<xref ref-type="bibr" rid="B72">72</xref>&#x2013;<xref ref-type="bibr" rid="B76">76</xref>], i.e., acceleration.<disp-formula id="e19">
<mml:math id="m22">
<mml:msub>
<mml:mrow>
<mml:mi mathvariant="bold">E</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>g</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mo>&#x2212;</mml:mo>
<mml:mo>&#x2207;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi>&#x3d5;</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>g</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2212;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mi>&#x2202;</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi mathvariant="bold">A</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>g</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
<mml:mrow>
<mml:mi>&#x2202;</mml:mi>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mo>.</mml:mo>
</mml:math>
<label>(19)</label>
</disp-formula>
</p>
<p>For example, at a distance, <italic>r</italic>, from a body of mass, <italic>M</italic>
<sub>
<italic>o</italic>
</sub>, the density gradient of the paired-photon potential, <italic>&#x3d5;</italic> &#x3d; <italic>GM</italic>
<sub>
<italic>o</italic>
</sub>/<italic>r</italic>, tallies the geodesic curvature, the Euler characteristic, <italic>&#x3c7;</italic>, proportional to <italic>M</italic>
<sub>
<italic>o</italic>
</sub> (<xref ref-type="fig" rid="F4">Figure 4</xref>) [<xref ref-type="bibr" rid="B77">77</xref>]. The density gradient is observed as the bending of light rays, a gravitational time delay, and as a gravitational frequency shift, <inline-formula id="inf4">
<mml:math id="m23">
<mml:msub>
<mml:mrow>
<mml:mi>f</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>e</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>/</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi>f</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>o</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>&#x2b;</mml:mo>
<mml:mi>z</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:msup>
<mml:mrow>
<mml:mrow>
<mml:mo stretchy="false">(</mml:mo>
<mml:mrow>
<mml:mn>1</mml:mn>
<mml:mo>&#x2212;</mml:mo>
<mml:mi>G</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>M</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>o</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>/</mml:mo>
<mml:msup>
<mml:mrow>
<mml:mi>c</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
<mml:msub>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>e</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
<mml:mo stretchy="false">)</mml:mo>
</mml:mrow>
</mml:mrow>
<mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>/</mml:mo>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
</mml:math>
</inline-formula>, between emission, <italic>f</italic>
<sub>
<italic>e</italic>
</sub>, at the radius, <italic>r</italic>
<sub>
<italic>e</italic>
</sub>, and absorption, <italic>f</italic>
<sub>
<italic>o</italic>
</sub>, at the detection [<xref ref-type="bibr" rid="B73">73</xref>,<xref ref-type="bibr" rid="B78">78</xref>]. In turn, the leveling of a density gradient is detected as the Doppler shift of light emitted by the moving body coupled to the moving vacuum.</p>
<fig id="F4" position="float">
<label>FIGURE 4</label>
<caption>
<p>Gravitational potential of a body (black sphere) spreads out as paired-photon rays (sketched as red and blue waves) whose energy density decreases inversely with distance, <italic>r</italic>, observed as redshift. The paired-photon rays are dragged around a rotating body (counterclockwise).</p>
</caption>
<graphic xlink:href="fphy-10-995977-g004.tif"/>
</fig>
<p>Similar to <bold>B</bold> &#x3d; &#x2207; &#xd7; <bold>A</bold> (<xref ref-type="disp-formula" rid="e17">Eq. 17</xref>), the rotational field,<disp-formula id="e20">
<mml:math id="m24">
<mml:msub>
<mml:mrow>
<mml:mi mathvariant="bold">B</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>g</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mo>&#x2207;</mml:mo>
<mml:mo>&#x2009;&#x2009;</mml:mo>
<mml:mo>&#xd7;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi mathvariant="bold">A</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>g</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>.</mml:mo>
</mml:math>
<label>(20)</label>
</disp-formula>for example, at a distance, <italic>r</italic>, from a body with inertia, <italic>I</italic>, rotating with the angular velocity, <italic>&#x3c9;</italic>, revolves at the rate, &#x3a9; &#x3d; <italic>GI</italic>/<italic>c</italic>
<sup>2</sup>
<italic>r</italic>
<sup>3</sup>&#x2207; &#xd7; (<bold>
<italic>&#x3c9;</italic>
</bold>&#xd7;<bold>r</bold>) [<xref ref-type="bibr" rid="B79">79</xref>]. This vortex in the paired-photon density displays itself as frame-dragging precession [<xref ref-type="bibr" rid="B73">73</xref>] (<xref ref-type="fig" rid="F4">Figure 4</xref>) that was examined, for example, with Gravity Probe B [<xref ref-type="bibr" rid="B80">80</xref>,<xref ref-type="bibr" rid="B81">81</xref>].</p>
<p>Moreover, similar to Gauss&#x2019; law, the divergence of the density gradient in the vacuum potential relates to the mass density, <italic>&#x3c1;</italic>
<sub>
<italic>M</italic>
</sub> &#x3d; &#x2212;(1/4<italic>&#x3c0;G</italic>)&#x2207;<sup>2</sup>
<italic>&#x3d5;</italic>
<sub>
<italic>g</italic>
</sub>. Explicitly, &#x2207; &#x22c5; &#x2207;<italic>&#x3d5;</italic>
<sub>
<italic>g</italic>
</sub> &#x3d; &#x2207; &#x22c5; <bold>a</bold>
<sub>
<italic>R</italic>
</sub> &#x3d; <italic>&#x2202;</italic>
<sub>
<italic>t</italic>
</sub>
<italic>GM</italic>/<italic>R</italic>
<sup>2</sup>
<italic>c</italic> &#x3d; &#x2212;1/<italic>t</italic>
<sup>2</sup>, of the all-embracing gravitational potential, <italic>&#x3d5;</italic>
<sub>
<italic>g</italic>
</sub>, due to all mass, <italic>M</italic>, of the expanding universe of radius, <italic>R</italic> &#x3d; <italic>ct</italic>, relates inversely to the age, <italic>t</italic>, squared using the mass&#x2013;energy equivalence, <italic>Mc</italic>
<sup>2</sup> &#x3d; <italic>GM</italic>
<sup>2</sup>/<italic>R</italic>. In other words, the average mass density of the universe, <italic>&#x3c1;</italic>
<sub>
<italic>M</italic>
</sub> &#x3d; 1/4<italic>&#x3c0;Gt</italic>
<sup>2</sup>, decreasing with time, <italic>t</italic>, is the source of space embodied by the paired photons.</p>
<p>While all photons are bound to the universe they constitute, a paired photon is not a bound state because the vacuum&#x2019;s energy spectrum is continuous. Also, the difference in the photon phases may change continuously, for example, in response to a moving charge. Despite its dynamics, the paired-photon ground-state vacuum does not break apart easily because the electromagnetic force is huge, e.g., compared with gravity.</p>
<p>The vacuum moves toward thermodynamic balance so that gradients in the vacuum energy, e.g., electromagnetic and gravitational fields, decrease, which is seen as charges attracting or repelling, magnets reorienting, and bodies moving.</p>
<p>Since light cannot but propagate at the speed of light, <italic>c</italic>, in the relativistic medium comprising photons, the proposed physical vacuum makes sense of the classical experiments carried out by Arago [<xref ref-type="bibr" rid="B82">82</xref>], Fizeau [<xref ref-type="bibr" rid="B83">83</xref>], Michelson and Morley [<xref ref-type="bibr" rid="B84">84</xref>], Trouton and Noble [<xref ref-type="bibr" rid="B85">85</xref>], and Sagnac [<xref ref-type="bibr" rid="B86">86</xref>], and modern measurements named after Casimir [<xref ref-type="bibr" rid="B87">87</xref>] and Aharonov and Bohm [<xref ref-type="bibr" rid="B65">65</xref>,<xref ref-type="bibr" rid="B88">88</xref>]. Moreover, the dynamic Casimir effect yields photons out of the vacuum, showing two by two at a time [<xref ref-type="bibr" rid="B89">89</xref>].</p>
<p>In agreement with measurements [<xref ref-type="bibr" rid="B61">61</xref>] and theory [<xref ref-type="bibr" rid="B39">39</xref>], the vacuum and matter comprising quanta are in thermodynamic balance <italic>Mc</italic>
<sup>2</sup> &#x3d; <italic>GM</italic>
<sup>2</sup>/<italic>R</italic>, where the energy of all mass, <italic>M</italic>, in the universe of radius, <italic>R</italic> &#x3d; <italic>ct</italic>, and age, <italic>t</italic>, tallies with all gravitational energy. This is in line with general relativity. The vacuum quanta embodying the Ricci curvature tensor and metric tensor are in balance with the quanta bound in the sources of gravitation denoted by the stress&#x2013;energy tensor.</p>
<p>On the largest scale, gravitation is geometrized by the cosmological principle so that the metric, <italic>ds</italic>
<sup>2</sup> &#x3d; <italic>a</italic>(<italic>t</italic>)<sup>2</sup>
<italic>dx</italic>
<sup>2</sup> &#x2212; <italic>c</italic>
<sup>2</sup>
<italic>dt</italic>
<sup>2</sup>, sums up by Pythagoras&#x2019; theorem the infinitesimal distance, <italic>ds</italic>, from the spatial, <italic>dx</italic>, and temporal, <italic>dt</italic>, coordinates, which correspond to the photon wavelength and period. While the scale factor, <italic>a</italic>(<italic>t</italic>), parameterizes the expansion, the thermodynamic balance between all matter and space implies that the universe expands physically rather than [para]metrically. As the quanta of matter transform into the paired photons of the vacuum, the energy density decreases. Redshifts from distant sources document this density change from the past to the present [<xref ref-type="bibr" rid="B7">7</xref>,<xref ref-type="bibr" rid="B10">10</xref>]. In geometric terms, the curvature of spacetime not only corresponds to but also spacetime itself emerges from the stress&#x2013;energy tensor [<xref ref-type="bibr" rid="B90">90</xref>].</p>
<p>Also, consistent with quantum field theory, the physical vacuum comprising quanta of light, both paired and single, in balance with matter can be modeled with the mean-energy density photon wave function,<disp-formula id="e21">
<mml:math id="m25">
<mml:mi>&#x3c8;</mml:mi>
<mml:mfenced open="(" close=")">
<mml:mrow>
<mml:mi mathvariant="bold">r</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfenced>
<mml:mo>&#x3d;</mml:mo>
<mml:mo>&#x222b;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:msqrt>
<mml:mrow>
<mml:mi>E</mml:mi>
</mml:mrow>
</mml:msqrt>
<mml:mi>d</mml:mi>
<mml:mi mathvariant="bold">p</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:msup>
<mml:mrow>
<mml:mi>h</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>3</mml:mn>
<mml:mo>/</mml:mo>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
</mml:mrow>
</mml:mfrac>
<mml:mi>&#x3b3;</mml:mi>
<mml:mfenced open="(" close=")">
<mml:mrow>
<mml:mi mathvariant="bold">p</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfenced>
<mml:msup>
<mml:mrow>
<mml:mi>e</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi mathvariant="bold">p</mml:mi>
<mml:mo>&#x22c5;</mml:mo>
<mml:mi mathvariant="bold">r</mml:mi>
<mml:mo>/</mml:mo>
<mml:mi>h</mml:mi>
</mml:mrow>
</mml:msup>
<mml:mo>,</mml:mo>
</mml:math>
<label>(21)</label>
</disp-formula>as an integral over the photon probability amplitudes, <italic>&#x3b3;</italic>, of momentum, <bold>p</bold>, and energy, <italic>E</italic>, in the unit volume, <italic>h</italic>
<sup>3</sup>. The dependence on the position, <bold>r</bold>, is formal because the massless photon does not localize [<xref ref-type="bibr" rid="B91">91</xref>,<xref ref-type="bibr" rid="B92">92</xref>].</p>
<p>Accordingly, a particle perturbing the vacuum can be presented with a wave function. This wave packet of the vacuum wave functions follows the Schr&#xf6;dinger equation and disperses as the particle with mass couples to the vacuum. In other words, mass is the measure of the coupling, i.e., inertia. In contrast, a photon as part of the vacuum (Fig. 2) abides by the dispersionless wave equation. Without the physical vacuum, particles would not have mass just as without the Higgs field. While, in this sense, the proposed paired-photon boson resembles the Higgs boson, the massless photon does not decay, whereas the massive Higgs boson is short-lived.</p>
</sec>
<sec id="s3-2">
<title>3.2 The graviton</title>
<p>Assuming that the paired-photon strings or filaments form the fabric of space, their density gradients are gravitational fields [<xref ref-type="bibr" rid="B93">93</xref>&#x2013;<xref ref-type="bibr" rid="B97">97</xref>]. Since the substance of space seeks thermodynamic balance in the least time, the bodies move coupled to the moving vacuum along the least-time paths, i.e., geodesics. Conversely, orbits are closed at a stationary state of the vacuum, where the influxes and effluxes of quanta tally. Then, the kinetic energy, 2<italic>K</italic> &#x3d; <italic>mv</italic>
<sup>2</sup>, of an orbiter of mass, <italic>m</italic>, and velocity, <italic>v</italic>, balances gravitational potential energy, <italic>U</italic> &#x3d; <italic>GmM</italic>/<italic>r</italic>, at a distance, <italic>r</italic>, due to a central mass, <italic>M</italic>, as according to Kepler&#x2019;s third law.</p>
<p>The photon qualifies as the ground-state substance because it does not decay. In our judgment, the paired photon, a massless spin-2 particle, is indistinguishable from the theorized graviton, the carrier of gravitation [<xref ref-type="bibr" rid="B73">73</xref>]. Correspondingly, the photon, a massless spin-1 particle, is the carrier of electromagnetism. Moreover, gravitation and electromagnetism cannot but share the same 1/<italic>r</italic>-form when the photon-embodied vacuum mediates both forces [<xref ref-type="bibr" rid="B63">63</xref>], as was thought already early on [<xref ref-type="bibr" rid="B66">66</xref>].</p>
</sec>
</sec>
<sec id="s4">
<title>4 Dark matter</title>
<p>According to concordance cosmology, orbital velocities of stars and gas clouds in galaxies, radial velocities of galaxies in clusters, and gravitational lensing by galaxies imply the presence of large amounts of hypothetical dark matter. Dark matter exceeds ordinary matter five-fold when the standard &#x39b;CDM model is tuned to match the data.</p>
<p>In contrast, we argue that the excess gravitation attributed to dark matter, in fact, displays the aforementioned thermodynamic distribution of vacuum quanta across the expanding universe in balance with quanta bound in all ordinary matter. We motivate our conclusion empirically. Sky surveys show that galaxies and voids distribute in a power-law manner [<xref ref-type="bibr" rid="B11">11</xref>,<xref ref-type="bibr" rid="B60">60</xref>]. Newton&#x2019;s universal law of gravitation equates gravitational force to the distribution of matter [<xref ref-type="bibr" rid="B98">98</xref>], and the Einstein field equations equate the distribution of matter, in the broadest sense of energy, to the curvature of spacetime [<xref ref-type="bibr" rid="B99">99</xref>].</p>
<p>We arrive at our conclusion from the understanding that the universe is expanding. Thus, the distant early universe is dense, and the nearby present is sparse. In line with <xref ref-type="disp-formula" rid="e6">Eq. 6</xref>, as by the universal law of gravitation, this isotropic gradient in all mass, <italic>M</italic>, across the radius, <italic>R</italic> &#x2261; <italic>ct</italic>, about 13.8&#xa0;billion light years causes acceleration, <italic>a</italic>
<sub>
<italic>R</italic>
</sub> &#x3d; <italic>GM</italic>/<italic>R</italic>
<sup>2</sup> &#x3d; <italic>c</italic>/<italic>t</italic>, of the order of 10<sup>&#x2013;10</sup>&#xa0;m/s<sup>2</sup>. The universal density gradient due to the expansion is most discernible from gravitational redshifts of light originating from the most distant sources [<xref ref-type="bibr" rid="B7">7</xref>,<xref ref-type="bibr" rid="B78">78</xref>].</p>
<p>The universal gravitation builds up with distance, <italic>r</italic>, from numerous sources, i.e., galaxies, as their number &#x221d; <italic>r</italic>
<sup>2</sup> overpowers the 1/<italic>r</italic>-potential [<xref ref-type="bibr" rid="B100">100</xref>,<xref ref-type="bibr" rid="B101">101</xref>]. Quantitatively speaking, the vacuum energy density, <italic>&#x3c1;</italic> &#x3d; <italic>c</italic>
<sup>2</sup>/4<italic>&#x3c0;Gt</italic>
<sup>2</sup> &#x3d; <italic>GM</italic>
<sup>2</sup>/4<italic>&#x3c0;R</italic>
<sup>4</sup> &#x2248; 10<sup>&#x2013;9</sup>&#xa0;J/m<sup>3</sup>, gauged by WMAP [<xref ref-type="bibr" rid="B61">61</xref>], integrates to the gravitational potential, <italic>U</italic> &#x3d; <italic>GM</italic>
<sup>2</sup>/<italic>R</italic>, over all mass, <italic>M</italic>, equaling the total energy, <italic>Mc</italic>
<sup>2</sup>. This universal balance holds to an excellent approximation since, at any given moment, the dissipated energy is much smaller than the energy bound in matter, i.e., <italic>Q</italic> &#x226a; <italic>U</italic> (<xref ref-type="disp-formula" rid="e6">Eq. 6</xref>). Thus, we employ the virial theorem,<disp-formula id="e22">
<mml:math id="m26">
<mml:mn>2</mml:mn>
<mml:mi>K</mml:mi>
<mml:mo>&#x2b;</mml:mo>
<mml:mi>U</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>0</mml:mn>
<mml:mo>&#x21d4;</mml:mo>
<mml:mi>M</mml:mi>
<mml:msup>
<mml:mrow>
<mml:mi>c</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:msup>
<mml:mrow>
<mml:mi>M</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
</mml:mrow>
<mml:mrow>
<mml:mi>R</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mo>&#x21d4;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi>a</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>R</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>M</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:msup>
<mml:mrow>
<mml:mi>R</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
</mml:mrow>
</mml:mfrac>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:msup>
<mml:mrow>
<mml:mi>c</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
</mml:mrow>
<mml:mrow>
<mml:mi>R</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mi>c</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mo>&#x2261;</mml:mo>
<mml:mi>c</mml:mi>
<mml:mi>H</mml:mi>
<mml:mo>,</mml:mo>
</mml:math>
<label>(22)</label>
</disp-formula>to infer the acceleration, <italic>a</italic>
<sub>
<italic>R</italic>
</sub> &#x2248; 6.87 &#x22c5; 10<sup>&#x2013;10</sup>&#xa0;m/s<sup>2</sup>, of the expansion, happening per definition at the Hubble rate, <italic>H</italic> &#x2261; 1/<italic>t</italic>, decreasing <italic>d</italic>
<sub>
<italic>t</italic>
</sub>
<italic>H</italic> &#x3d; &#x2212;1/<italic>t</italic>
<sup>2</sup> as the universe ages with time, <italic>t</italic>. The rate of expansion is not free from the flow of time, assuming quanta of space emerge from quanta of matter because energy, <italic>E</italic>, and [period of] time, <italic>t</italic>, are physical properties of the quanta [<xref ref-type="bibr" rid="B49">49</xref>,<xref ref-type="bibr" rid="B50">50</xref>].</p>
<p>The density gradient across the cosmos from the beginning to the present manifests itself in the outward acceleration, <italic>a</italic>
<sub>
<italic>R</italic>
</sub>, known as the Hubble flow, as well as in the inward acceleration per orbital cycle, <italic>a</italic> &#x2248; <italic>a</italic>
<sub>
<italic>R</italic>
</sub>/2<italic>&#x3c0;</italic>, also deemed as modified gravity (<xref ref-type="fig" rid="F5">Figure 5</xref>) [<xref ref-type="bibr" rid="B102">102</xref>,<xref ref-type="bibr" rid="B103">103</xref>].</p>
<fig id="F5" position="float">
<label>FIGURE 5</label>
<caption>
<p>Within the radius, <italic>r</italic>
<sub>
<italic>o</italic>
</sub>, confining a local mass, <italic>M</italic>
<sub>
<italic>o</italic>
</sub>, the paired-photon graviton efflux from local processes exceeds the influx from distant sources. Thus, a body spirals inward until <italic>v</italic>
<sup>2</sup>/<italic>r</italic> balances the sum of the universal, <italic>a</italic>, and local, <italic>a</italic>
<sub>
<italic>o</italic>
</sub>, acceleration. Since the circumference, 2<italic>&#x3c0;r</italic>, shortens, graviton by graviton, as much as the distant space lengthens along with radius, <italic>r</italic>, the inward and outward acceleration relate as <italic>a</italic> &#x3d; <italic>a</italic>
<sub>
<italic>R</italic>
</sub>/2<italic>&#x3c0;</italic>. Beyond <italic>r</italic>
<sub>
<italic>o</italic>
</sub>, the graviton influx from numerous processes transforming matter into space exceeds the efflux. Thus, the body recedes at speed, <italic>u</italic> &#x3c; <italic>c</italic>. At <italic>R</italic>, enclosing all mass, <italic>M</italic>, the total graviton flux from all processes generates the expansion at the speed of light, <italic>c</italic>.</p>
</caption>
<graphic xlink:href="fphy-10-995977-g005.tif"/>
</fig>
<p>The outward and inward fluxes of quantized space (<xref ref-type="fig" rid="F2">Figures 2</xref>&#x2013;<xref ref-type="fig" rid="F5">5</xref>), originating from local and remote processes, balance each other at a distance of about 4&#xa0;million light years. This zero-velocity radius, <italic>r</italic>
<sub>
<italic>o</italic>
</sub> &#x3d; <italic>GM</italic>
<sub>
<italic>o</italic>
</sub>/<italic>c</italic>
<sup>2</sup>, relates to <italic>R</italic> &#x3d; <italic>GM</italic>/<italic>c</italic>
<sup>2</sup> as <italic>M</italic>
<sub>
<italic>o</italic>
</sub> of the local group relates to <italic>M</italic> of the universe (<xref ref-type="fig" rid="F5">Figure 5</xref>) [<xref ref-type="bibr" rid="B58">58</xref>,<xref ref-type="bibr" rid="B104">104</xref>,<xref ref-type="bibr" rid="B105">105</xref>]. Within <italic>r</italic>
<sub>
<italic>o</italic>
</sub>, the Milky Way, Andromeda, and other nearby galaxies approach one another because the efflux of space emerging from processes within the local group to the distant universe exceeds the influx therefrom (<xref ref-type="fig" rid="F5">Figure 5</xref>).</p>
<p>The thermodynamic balance between all matter and space free of matter (<xref ref-type="disp-formula" rid="e6">Eq. 6</xref>) [<xref ref-type="bibr" rid="B39">39</xref>] suggests that the cosmos is not ballooning through intrinsic metric expansion [<xref ref-type="bibr" rid="B106">106</xref>] without any cause. Instead of being a cosmic coincidence, the flatness, &#x39b; &#x2261; <italic>H</italic>
<sup>2</sup>/<italic>c</italic>
<sup>2</sup> &#x3d; 4<italic>&#x3c0;G&#x3c1;</italic>
<sub>
<italic>c</italic>
</sub>/<italic>c</italic>
<sup>4</sup>, follows from matter transforming into the physical space in stars, black holes, <italic>etc.</italic> These high-energy reactions, similar to annihilation, power the expansion by <italic>P</italic> &#x3d; <italic>Fc</italic> &#x3d; <italic>Ma</italic>
<sub>
<italic>R</italic>
</sub>
<italic>c</italic> &#x3d; <italic>c</italic>
<sup>5</sup>/<italic>G</italic>, generating pressure, <italic>p</italic> &#x3d; <italic>F</italic>/<italic>A</italic> &#x3d; <italic>c</italic>
<sup>4</sup>/4<italic>&#x3c0;R</italic>
<sup>2</sup>
<italic>G</italic> &#x3d; <italic>&#x3c1;</italic>
<sub>
<italic>c</italic>
</sub>, and dispersing distant galaxies apart with velocity asymptote, <italic>c</italic>
<sup>4</sup> &#x3d; <italic>a</italic>
<sub>
<italic>R</italic>
</sub>
<italic>GM</italic>.</p>
<p>In agreement with empirical evidence, it follows from the atomistic axiom that space emerges from matter. This old tenet [<xref ref-type="bibr" rid="B107">107</xref>,<xref ref-type="bibr" rid="B108">108</xref>] explains why the energy density, <italic>&#x3c1;</italic>, is precisely the critical <italic>&#x3c1;</italic>
<sub>
<italic>c</italic>
</sub>. There is neither a need nor room to adjust the cosmological constant, &#x39b; &#x2248; 1/<italic>R</italic>
<sup>2</sup>, to the observed flatness [<xref ref-type="bibr" rid="B109">109</xref>,<xref ref-type="bibr" rid="B110">110</xref>]. Since the scale-free data emerge from the least-time consumption of free energy [<xref ref-type="bibr" rid="B32">32</xref>], there is no point in modeling the expansion with scale-free cosmology [<xref ref-type="bibr" rid="B111">111</xref>].</p>
<p>Backed up by this reasoning, we focus on motions of the relativistic void, the paired-photon substance coupled to bodies, instead of assuming bodies themselves would attract one another.</p>
<sec id="s4-1">
<title>4.1 Galaxy rotation</title>
<p>To an excellent approximation, a spiral galaxy is a stationary system. At the dynamic steady state, integrated over its characteristic orbital period, <italic>t</italic>,<disp-formula id="e23">
<mml:math id="m27">
<mml:mo>&#x222b;</mml:mo>
<mml:mfenced open="(" close=")">
<mml:mrow>
<mml:mi mathvariant="bold">v</mml:mi>
<mml:mo>&#x22c5;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi>d</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mi mathvariant="bold">p</mml:mi>
<mml:mo>&#x2b;</mml:mo>
<mml:mi mathvariant="bold">v</mml:mi>
<mml:mo>&#x22c5;</mml:mo>
<mml:mo>&#x2207;</mml:mo>
<mml:mi>U</mml:mi>
</mml:mrow>
</mml:mfenced>
<mml:mi>d</mml:mi>
<mml:mi>t</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>0</mml:mn>
<mml:mo>,</mml:mo>
</mml:math>
<label>(23)</label>
</disp-formula>momentum, <bold>p</bold>, and acceleration, <bold>a</bold>, are orthogonal. The orbital velocity, <italic>v</italic>, at a distance, <italic>r</italic>, balances by <italic>v</italic>
<sup>2</sup>/<italic>r</italic> the galactic acceleration, <italic>a</italic>
<sub>
<italic>o</italic>
</sub> &#x3d; <italic>GM</italic>
<sub>
<italic>o</italic>
</sub>/<italic>r</italic>
<sup>2</sup>, due to the central mass, <italic>M</italic>
<sub>
<italic>o</italic>
</sub>, within the circumference, 2<italic>&#x3c0;r</italic>, and the universal acceleration, <italic>a</italic> &#x3d; <italic>GM</italic>/2<italic>&#x3c0;R</italic>
<sup>2</sup>, due to all mass, <italic>M</italic>, within the radius, <italic>R</italic>, of the expanding universe [<xref ref-type="bibr" rid="B112">112</xref>],<disp-formula id="e24">
<mml:math id="m28">
<mml:mfrac>
<mml:mrow>
<mml:msup>
<mml:mrow>
<mml:mi>v</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
</mml:mrow>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>a</mml:mi>
<mml:mo>&#x2b;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi>a</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>o</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi>a</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>o</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mfenced open="(" close=")">
<mml:mrow>
<mml:mn>1</mml:mn>
<mml:mo>&#x2b;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mi>a</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>a</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>o</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfrac>
</mml:mrow>
</mml:mfenced>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>M</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>o</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
<mml:mrow>
<mml:msup>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
</mml:mrow>
</mml:mfrac>
<mml:mfenced open="(" close=")">
<mml:mrow>
<mml:mn>1</mml:mn>
<mml:mo>&#x2b;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
<mml:mi>&#x3c0;</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mfrac>
<mml:mrow>
<mml:mi>M</mml:mi>
<mml:msup>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
</mml:mrow>
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>M</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>o</mml:mi>
</mml:mrow>
</mml:msub>
<mml:msup>
<mml:mrow>
<mml:mi>R</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
</mml:mrow>
</mml:mfrac>
</mml:mrow>
</mml:mfenced>
<mml:mo>,</mml:mo>
</mml:math>
<label>(24)</label>
</disp-formula>
</p>
<p>near the galactic center, <italic>a</italic> &#x226a; <italic>a</italic>
<sub>
<italic>o</italic>
</sub>. Therefore, the feeble universal acceleration is hardly detectable in motions of strongly bound bodies, such as stars in clusters [<xref ref-type="bibr" rid="B113">113</xref>].</p>
<p>Conversely, far away from the luminous edge, <italic>a</italic> &#x226b; <italic>a</italic>
<sub>
<italic>o</italic>
</sub>, where <italic>v</italic>
<sup>2</sup>
<italic>a</italic>
<sub>
<italic>o</italic>
</sub>/<italic>r</italic> &#x2248; <italic>aGM</italic>
<sub>
<italic>o</italic>
</sub>/<italic>r</italic>
<sup>2</sup>, <xref ref-type="disp-formula" rid="e24">Eq. 24</xref> limits to the Tully&#x2013;Fisher relation, <italic>v</italic>
<sup>4</sup> &#x3d; <italic>aGM</italic>
<sub>
<italic>o</italic>
</sub>, for example, orbital velocities of dwarf galaxy profile <xref ref-type="disp-formula" rid="e24">Eq. 24</xref> due to their low amounts of baryonic rather than high amounts of dark matter [<xref ref-type="bibr" rid="B114">114</xref>,<xref ref-type="bibr" rid="B115">115</xref>]. The flat tail of the orbital velocity curve signifies that distantly, the universal curvature, 1/<italic>R</italic>, dominates the curvature, 1/<italic>r</italic> &#x3d; <italic>a</italic>/<italic>v</italic>
<sup>2</sup>, of a bound geodesic. A closer match with a given observed rotation curve beyond the point-mass approximation (<xref ref-type="disp-formula" rid="e24">Eq. 24</xref>) would employ a detailed mass distribution, <italic>M</italic>
<sub>
<italic>o</italic>
</sub>(<italic>r</italic>), instead of an interpolation [<xref ref-type="bibr" rid="B116">116</xref>,<xref ref-type="bibr" rid="B117">117</xref>], from the dense galactic surroundings to the sparse universal voids.</p>
<p>Moreover, satellites of the Milky Way, Andromeda Galaxy, and other spirals can be understood to home in on the galactic plane [<xref ref-type="bibr" rid="B118">118</xref>] under the central force of the expansion because space, the substance of gravitation, zeros in on the free energy minimum of the least curvature. So, a galaxy punched by another realigns for the same reason as a poked top reorients. The substance of space also shapes bodies into spheroids.</p>
</sec>
<sec id="s4-2">
<title>4.2 Galaxy velocity dispersion</title>
<p>Just as stars in galaxies orbit around, galaxies also move about in clusters to balance the local gravity and the universal gravitation [<xref ref-type="bibr" rid="B16">16</xref>,<xref ref-type="bibr" rid="B119">119</xref>]. The Faber&#x2013;Jackson relation, ranging from tiny dwarf satellite galaxies through giant spiral galaxies to rich clusters of galaxies [<xref ref-type="bibr" rid="B120">120</xref>], even encompassing the whole expanding universe, displays the universal acceleration, <italic>a</italic>
<sub>
<italic>R</italic>
</sub> &#x3d; <italic>c</italic>
<sup>2</sup>/<italic>R</italic> &#x3d; <italic>u</italic>
<sup>2</sup>/<italic>r</italic> &#x3d; 2<italic>&#x3c0;a</italic> &#x3d; 2<italic>&#x3c0;v</italic>
<sup>2</sup>/<italic>r</italic>, in terms of speed of light, <italic>c</italic>, radial, <italic>u</italic>, and orbital, <italic>v</italic>, velocity. Since <italic>u</italic>
<sup>2</sup>/<italic>r</italic> &#x3d; 2<italic>&#x3c0;v</italic>
<sup>2</sup>/<italic>r</italic>, the mass vs. radial velocity line on a log&#x2013;log plot, relevant to galaxy velocity distribution, is offset by the factor <inline-formula id="inf5">
<mml:math id="m29">
<mml:msqrt>
<mml:mrow>
<mml:mn>2</mml:mn>
<mml:mi>&#x3c0;</mml:mi>
</mml:mrow>
</mml:msqrt>
<mml:mo>&#x2248;</mml:mo>
<mml:mn>2.5</mml:mn>
</mml:math>
</inline-formula> from the mass vs. orbital velocity line, relevant to galaxy rotational curve [<xref ref-type="bibr" rid="B8">8</xref>]. So, there is no need to extend MOND [<xref ref-type="bibr" rid="B121">121</xref>] or invoke the dark matter hypothesis to account for the velocity dispersion of galaxies in clusters.</p>
<p>While the universal acceleration due to the expansion shares the mathematical form (<xref ref-type="disp-formula" rid="e24">Eq. 24</xref>) of MOND [<xref ref-type="bibr" rid="B116">116</xref>], the thermodynamic tenet is intrinsically a relativistic formulation. The paired-photon void is a relativistic medium complying with the Bose&#x2013;Einstein statistics (<xref ref-type="disp-formula" rid="e13">Eq. 13</xref>).</p>
</sec>
<sec id="s4-3">
<title>4.3 Bending of light</title>
<p>According to concordance cosmology, gravitational lensing provides yet another evidence of dark matter. This belief is based on images of background galaxies lensed through foreground galaxy gravitation because the images are more distorted than expected from the lensing masses of visible, ordinary matter [<xref ref-type="bibr" rid="B122">122</xref>].</p>
<p>We follow Einstein, who stated early on that light going through a gravitational potential, such as through an optical medium, gets deflected and delayed [<xref ref-type="bibr" rid="B93">93</xref>]. The stronger the gravity, the more curved the geodesic, i.e., the least-time path. A local gravitational potential, <italic>GM</italic>
<sub>
<italic>o</italic>
</sub>/<italic>r</italic>, at a distance, <italic>r</italic>, from a mass, <italic>M</italic>
<sub>
<italic>o</italic>
</sub>, is part of the vacuum&#x2019;s total potential due to <italic>M</italic> within the universe of radius, <italic>R</italic>. Thus, near a celestial body of mass, <italic>M</italic>
<sub>
<italic>o</italic>
</sub>, the refractive index, <inline-formula id="inf6">
<mml:math id="m30">
<mml:msup>
<mml:mrow>
<mml:mi>n</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
<mml:mo>&#x3d;</mml:mo>
<mml:msup>
<mml:mrow>
<mml:mi>c</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
<mml:mo>/</mml:mo>
<mml:msup>
<mml:mrow>
<mml:mi>v</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
<mml:mo>&#x3d;</mml:mo>
<mml:msup>
<mml:mrow>
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<mml:mo stretchy="false">(</mml:mo>
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<mml:mo>/</mml:mo>
<mml:msup>
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</mml:mrow>
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</mml:mrow>
<mml:mrow>
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<mml:mn>1</mml:mn>
</mml:mrow>
</mml:msup>
<mml:mo>&#x2248;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>&#x2b;</mml:mo>
<mml:mi>G</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>M</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>o</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>/</mml:mo>
<mml:msup>
<mml:mrow>
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</mml:mrow>
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<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
<mml:mi>r</mml:mi>
</mml:math>
</inline-formula> [<xref ref-type="bibr" rid="B81">81</xref>,<xref ref-type="bibr" rid="B94">94</xref>,<xref ref-type="bibr" rid="B95">95</xref>].</p>
<p>According to <xref ref-type="disp-formula" rid="e22">Eq. 22</xref>, the space curving around a body, for example, the Sun, causes an angular acceleration, <italic>&#x3b1;</italic>. It integrates over time, <italic>t</italic>, to an angle of precession, <italic>&#x3c6;</italic>,<disp-formula id="e25">
<mml:math id="m31">
<mml:mtable class="align" columnalign="left">
<mml:mtr>
<mml:mtd columnalign="right">
<mml:mfrac>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:mi>L</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfrac>
</mml:mtd>
<mml:mtd columnalign="left">
<mml:mo>&#x3d;</mml:mo>
<mml:mi>I</mml:mi>
<mml:mi>&#x3b1;</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>I</mml:mi>
<mml:mfrac>
<mml:mrow>
<mml:mi>d</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>d</mml:mi>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mfrac>
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</mml:mrow>
<mml:mrow>
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</mml:mrow>
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<mml:msup>
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<mml:mrow>
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<mml:msup>
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<mml:mn>2</mml:mn>
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</mml:mrow>
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<mml:mrow>
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</mml:mrow>
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<mml:msup>
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<mml:mrow>
<mml:mn>2</mml:mn>
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</mml:msup>
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<mml:mi>m</mml:mi>
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<mml:mrow>
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</mml:mtd>
</mml:mtr>
<mml:mtr>
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<mml:mtd columnalign="left">
<mml:mspace width="1em"/>
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<mml:msup>
<mml:mrow>
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<mml:mrow>
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<mml:mi>&#x3c0;</mml:mi>
</mml:mrow>
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</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
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</mml:mrow>
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</mml:mrow>
<mml:mrow>
<mml:msup>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>3</mml:mn>
</mml:mrow>
</mml:msup>
</mml:mrow>
</mml:mfrac>
<mml:mi>d</mml:mi>
<mml:mi>t</mml:mi>
<mml:mi>d</mml:mi>
<mml:mi>t</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>2</mml:mn>
<mml:msup>
<mml:mrow>
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</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
<mml:mfrac>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>M</mml:mi>
</mml:mrow>
<mml:mrow>
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</mml:mrow>
<mml:mrow>
<mml:msup>
<mml:mrow>
<mml:mi>c</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
<mml:mi>r</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mo>,</mml:mo>
</mml:mtd>
</mml:mtr>
</mml:mtable>
</mml:math>
<label>(25)</label>
</disp-formula>where <italic>L</italic> is the angular momentum, <italic>G</italic> gravitational constant, <italic>r</italic> &#x3d; <italic>ct</italic> the distance to the center of the Sun of mass, <italic>M</italic>
<sub>&#x2299;</sub> &#x3d; 1.99 &#x22c5; 10<sup>30</sup>&#xa0;kg, and the mass, <italic>m</italic>, corresponds to light&#x2019;s energy, <italic>hf</italic>, per the speed of light squared, <italic>c</italic>
<sup>2</sup>. <xref ref-type="disp-formula" rid="e25">Eq. 25</xref> gives <italic>&#x3c6;</italic> &#x3d; 8.65<italic>&#x201d;</italic> for the ray that tangents the Sun&#x2019;s surface at <italic>r</italic>
<sub>&#x2299;</sub> &#x2248; 695,700&#xa0;km. Accordingly, it takes an excess time, &#x394;<italic>t</italic> &#x3d; 2<italic>r</italic>
<sub>&#x2299;</sub>
<italic>&#x3c6;</italic>/<italic>c</italic> &#x3d; 196&#xa0;<italic>&#x3bc;</italic>s, for the light to make a round trip along the geodetic line than along the night-sky straight line, in agreement with measurements [<xref ref-type="bibr" rid="B78">78</xref>].</p>
<p>The least-time principle reproduces bending and delay consistently with the same equation (<xref ref-type="disp-formula" rid="e25">Eq. 25</xref>), as the two phenomena are identical. In contrast, derivations from the Einstein field equations deliver the delay and bending in terms of different equations, which leads to a discrepancy. By <xref ref-type="disp-formula" rid="e25">Eq. 25</xref>, light passing a galaxy deflects 2<italic>&#x3c0;</italic>
<sup>2</sup>/4 &#x2248; 5 times more than by general relativity. So, there is neither a need nor room for dark matter to account for the galaxy image distortions due to gravitational lensing [<xref ref-type="bibr" rid="B78">78</xref>].</p>
<p>The amount of bending due to the Sun is determined by the difference between the line of sight to a star during an eclipse and the night-sky line 6&#xa0;months later. Although obvious, it is essential to note that the ray ends up at a different point on the ground when it has passed through the gravitational lens than when coming directly from the night sky. So, to trace the same ray, the telescope should be displaced by the distance corresponding to the change in direction.</p>
<p>It is easy to grasp the relation between the change in direction and the telescope&#x2019;s displacement. For example, looking at your finger with one eye and then switching to the other seems to shift it relative to the background. If the parallax is to be averted, the position of the eye, like the location of the telescope, has to be displaced to match the angle from which the object is seen. Unfortunately, as Eddington did not consider this, the bending appeared smaller than it was [<xref ref-type="bibr" rid="B78">78</xref>]. Thus, based on gravitational lensing, there are no compelling arguments to purport dark matter.</p>
<p>Since the gravitational time delay, &#x394;<italic>t</italic>, relates to the local mass, <italic>M</italic>
<sub>
<italic>o</italic>
</sub>, as the age of the universe, <italic>t</italic>, relates to the mass of the universe, <italic>M</italic>, i.e., &#x394;<italic>t</italic>/<italic>t</italic> &#x3d; (2<italic>&#x3c0;</italic>)<sup>2</sup>
<italic>M</italic>
<sub>
<italic>o</italic>
</sub>/<italic>M</italic> [<xref ref-type="bibr" rid="B123">123</xref>], &#x394;<italic>t</italic> between two images of a variable signal [<xref ref-type="bibr" rid="B124">124</xref>] can be used to determine the Hubble parameter, <italic>H</italic> &#x3d; 1/<italic>t</italic> &#x3d; (&#x394;<italic>&#x3b8;</italic>)2<italic>d</italic>
<sub>
<italic>l</italic>
</sub>
<italic>d</italic>
<sub>
<italic>s</italic>
</sub>/<italic>d</italic>
<sub>
<italic>ls</italic>
</sub>
<italic>R</italic>&#x394;<italic>t</italic>, from the image separation, &#x394;<italic>&#x3b8;</italic>, the observer&#x2013;source, <italic>d</italic>
<sub>
<italic>s</italic>
</sub>, observer&#x2013;lens, <italic>d</italic>
<sub>
<italic>l</italic>
</sub>, and lens&#x2013;source, <italic>d</italic>
<sub>
<italic>ls</italic>
</sub> distances [<xref ref-type="bibr" rid="B125">125</xref>]. However, as contemporary inconsistencies in <italic>H</italic> imply, interpretations of galaxy lensing, time delay data [<xref ref-type="bibr" rid="B126">126</xref>], cosmic background radiation, and Type 1a supernovae data are predicated on the amount of postulated dark matter [<xref ref-type="bibr" rid="B127">127</xref>]. Thus, the bending of light passing by the Sun, seemingly free of dark matter, provides the crucial experimental reference to judge the hypothesis.</p>
</sec>
</sec>
<sec id="s5">
<title>5 Dark energy</title>
<p>According to concordance cosmology, the universe is expanding at an accelerating rather than decelerating rate because distant Type Ia supernovae are slightly fainter, i.e., further away than projected from their redshifts. Dark energy is hypothesized to account for the difference between observations and calculations. When the &#x39b;CDM model is adjusted to match the data, the rate of expansion, the Hubble parameter, <italic>H</italic>, is mostly a function of dark energy, less of dark matter and even less of ordinary matter, and minimally of radiation and curvature of the universe.</p>
<p>However, we argue that the standard candle data attributed to dark energy, in fact, display the distribution of vacuum quanta in thermodynamic balance with matter quanta, extending from the early dense universe to the present sparse surroundings. We arrive at our conclusion by examining light&#x2019;s propagation from a supernova across the expanding universe as a physical process rather than modeling the supernovae data through metric expansion.</p>
<sec id="s5-1">
<title>5.1 The rate of expansion</title>
<p>Considering a photon emitted with the standard-candle energy, <italic>hf</italic>
<sub>
<italic>e</italic>
</sub>, the photon shifts red on its least-time path from the dense past to the sparse present to balance the decreasing universal gravitation. Otherwise, the photon would gain energy out of nothing [<xref ref-type="bibr" rid="B128">128</xref>] relative to the surrounding photon distribution, diluting, and cooling due to the expansion (<xref ref-type="disp-formula" rid="e13">Eq. 13</xref>).</p>
<p>The optical distance, <italic>D</italic>
<sub>
<italic>L</italic>
</sub>, to the supernova is deduced from the flux, <inline-formula id="inf7">
<mml:math id="m32">
<mml:mi>F</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>L</mml:mi>
<mml:mo>/</mml:mo>
<mml:mn>4</mml:mn>
<mml:mi>&#x3c0;</mml:mi>
<mml:msubsup>
<mml:mrow>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>L</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msubsup>
</mml:math>
</inline-formula>, i.e., the observed luminosity, <italic>L</italic> &#x3d; <italic>hf</italic>
<sub>
<italic>e</italic>
</sub>
<italic>f</italic>
<sub>
<italic>o</italic>
</sub>, that scales down as light spreads across an ever-larger area, <inline-formula id="inf8">
<mml:math id="m33">
<mml:mn>4</mml:mn>
<mml:mi>&#x3c0;</mml:mi>
<mml:msubsup>
<mml:mrow>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>L</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msubsup>
</mml:math>
</inline-formula>. For calibration, an explosion at a known distance, e.g., a nearby one without a marked shift in the observed frequency, i.e., <italic>f</italic>
<sub>
<italic>e</italic>
</sub>
<italic>&#x2245;f</italic>
<sub>
<italic>o</italic>
</sub>, serves as a reference flux, <italic>F</italic>
<sub>
<italic>r</italic>
</sub>, [<xref ref-type="bibr" rid="B78">78</xref>]. Thus,<disp-formula id="e26">
<mml:math id="m34">
<mml:mtable class="eqnarray">
<mml:mtr>
<mml:mtd columnalign="right">
<mml:mi>F</mml:mi>
</mml:mtd>
<mml:mtd columnalign="left">
<mml:mo>&#x3d;</mml:mo>
</mml:mtd>
<mml:mtd columnalign="left">
<mml:mfrac>
<mml:mrow>
<mml:mi>L</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>4</mml:mn>
<mml:mi>&#x3c0;</mml:mi>
<mml:msubsup>
<mml:mrow>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>L</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msubsup>
</mml:mrow>
</mml:mfrac>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi>F</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mfrac>
<mml:mrow>
<mml:mi>L</mml:mi>
<mml:mo>/</mml:mo>
<mml:mn>4</mml:mn>
<mml:mi>&#x3c0;</mml:mi>
<mml:msubsup>
<mml:mrow>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>L</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msubsup>
</mml:mrow>
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>L</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>/</mml:mo>
<mml:mn>4</mml:mn>
<mml:mi>&#x3c0;</mml:mi>
<mml:msubsup>
<mml:mrow>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msubsup>
</mml:mrow>
</mml:mfrac>
<mml:mo>&#x2245;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi>F</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mfrac>
<mml:mrow>
<mml:mi>h</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>f</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>e</mml:mi>
</mml:mrow>
</mml:msub>
<mml:msub>
<mml:mrow>
<mml:mi>f</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>o</mml:mi>
</mml:mrow>
</mml:msub>
<mml:msubsup>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msubsup>
</mml:mrow>
<mml:mrow>
<mml:mi>h</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>f</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>e</mml:mi>
</mml:mrow>
</mml:msub>
<mml:msub>
<mml:mrow>
<mml:mi>f</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>e</mml:mi>
</mml:mrow>
</mml:msub>
<mml:msubsup>
<mml:mrow>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>L</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msubsup>
</mml:mrow>
</mml:mfrac>
</mml:mtd>
</mml:mtr>
<mml:mtr>
<mml:mtd columnalign="right"/>
<mml:mtd columnalign="left">
<mml:mo>&#x3d;</mml:mo>
</mml:mtd>
<mml:mtd columnalign="left">
<mml:msub>
<mml:mrow>
<mml:mi>F</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mfrac>
<mml:mrow>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mrow>
<mml:mn>1</mml:mn>
<mml:mo>&#x2b;</mml:mo>
<mml:mi>z</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mfrac>
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msubsup>
</mml:mrow>
<mml:mrow>
<mml:msup>
<mml:mrow>
<mml:mi>R</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
</mml:mrow>
</mml:mfrac>
<mml:mfrac>
<mml:mrow>
<mml:msup>
<mml:mrow>
<mml:mfenced open="(" close=")">
<mml:mrow>
<mml:mn>1</mml:mn>
<mml:mo>&#x2b;</mml:mo>
<mml:mi>z</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
</mml:mrow>
<mml:mrow>
<mml:msup>
<mml:mrow>
<mml:mi>z</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
</mml:mrow>
</mml:mfrac>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi>F</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mfrac>
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msubsup>
</mml:mrow>
<mml:mrow>
<mml:msup>
<mml:mrow>
<mml:mi>R</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
</mml:mrow>
</mml:mfrac>
<mml:mfrac>
<mml:mrow>
<mml:mn>1</mml:mn>
<mml:mo>&#x2b;</mml:mo>
<mml:mi>z</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:msup>
<mml:mrow>
<mml:mi>z</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
</mml:mrow>
</mml:mfrac>
<mml:mo>,</mml:mo>
</mml:mtd>
</mml:mtr>
</mml:mtable>
</mml:math>
<label>(26)</label>
</disp-formula>where frequencies are in terms of the redshift, <italic>z</italic> &#x3d; (<italic>f</italic>
<sub>
<italic>e</italic>
</sub> &#x2212; <italic>f</italic>
<sub>
<italic>o</italic>
</sub>)/<italic>f</italic>
<sub>
<italic>o</italic>
</sub>, and the optical distance, <italic>D</italic>
<sub>
<italic>L</italic>
</sub> &#x3d; <italic>Rz</italic>/(1 &#x2b; <italic>z</italic>), relative to the radius of the universe, <italic>R</italic>.</p>
<p>On its way, light shifts to red due to the supernova&#x2019;s recession velocity and the expanding universe&#x2019;s decreasing gravitational energy density. More specifically, the gravitational frequency shift [<xref ref-type="bibr" rid="B73">73</xref>,<xref ref-type="bibr" rid="B129">129</xref>] is not the hypothetical tired light [<xref ref-type="bibr" rid="B130">130</xref>]. However, if the physical process is parametrized with the scale factor, as it is in standard cosmology, instead of using <xref ref-type="disp-formula" rid="e26">Eq. 26</xref>, the distance seems longer than it is. Then, the Type Ia supernova data give a false impression of the universe expanding at an accelerating rate [<xref ref-type="bibr" rid="B78">78</xref>].</p>
<p>Due to the same &#x39b;CDM parametrization, the angular size redshift relation is non-monotonous. When <italic>z</italic> &#x3e; 1.5, objects ever further away appear peculiarly, i.e., larger, contrary to empirical evidence [<xref ref-type="bibr" rid="B131">131</xref>]. In contrast, as quanta bound in matter transform into the vacuum quanta, the total energy density, <italic>&#x3c1;</italic> &#x3d; <italic>c</italic>
<sup>2</sup>/4<italic>&#x3c0;Gt</italic>
<sup>2</sup>, decreases with time, <italic>t</italic>, and the angular size, <italic>&#x3b8;</italic> &#x221d; 1/<italic>t</italic> [<xref ref-type="bibr" rid="B123">123</xref>].</p>
<p>On the logarithm scale, the brightness of a star (<xref ref-type="disp-formula" rid="e26">Eq. 26</xref>), the distance modulus,<disp-formula id="e27">
<mml:math id="m35">
<mml:mtable class="eqnarray">
<mml:mtr>
<mml:mtd columnalign="right">
<mml:mi>&#x3bc;</mml:mi>
</mml:mtd>
<mml:mtd columnalign="left">
<mml:mo>&#x3d;</mml:mo>
</mml:mtd>
<mml:mtd columnalign="left">
<mml:mo>&#x2212;</mml:mo>
<mml:mn>2.5</mml:mn>
<mml:mo>&#x2061;</mml:mo>
<mml:mi>log</mml:mi>
<mml:mfenced open="(" close=")">
<mml:mrow>
<mml:mfrac>
<mml:mrow>
<mml:mi>L</mml:mi>
<mml:mo>/</mml:mo>
<mml:mn>4</mml:mn>
<mml:mi>&#x3c0;</mml:mi>
<mml:msubsup>
<mml:mrow>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>L</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msubsup>
</mml:mrow>
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>L</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>/</mml:mo>
<mml:mn>4</mml:mn>
<mml:mi>&#x3c0;</mml:mi>
<mml:msubsup>
<mml:mrow>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msubsup>
</mml:mrow>
</mml:mfrac>
</mml:mrow>
</mml:mfenced>
<mml:mo>&#x2b;</mml:mo>
<mml:mi>K</mml:mi>
</mml:mtd>
</mml:mtr>
<mml:mtr>
<mml:mtd columnalign="right"/>
<mml:mtd columnalign="left">
<mml:mo>&#x3d;</mml:mo>
</mml:mtd>
<mml:mtd columnalign="left">
<mml:mo>&#x2212;</mml:mo>
<mml:mn>2.5</mml:mn>
<mml:mo>&#x2061;</mml:mo>
<mml:mi>log</mml:mi>
<mml:msup>
<mml:mrow>
<mml:mfenced open="(" close=")">
<mml:mrow>
<mml:mfrac>
<mml:mrow>
<mml:mi>R</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>r</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfrac>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>2.5</mml:mn>
<mml:mo>&#x2061;</mml:mo>
<mml:mi>log</mml:mi>
<mml:mfenced open="(" close=")">
<mml:mrow>
<mml:mfrac>
<mml:mrow>
<mml:msup>
<mml:mrow>
<mml:mi>z</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
</mml:mrow>
<mml:mrow>
<mml:mn>1</mml:mn>
<mml:mo>&#x2b;</mml:mo>
<mml:mi>z</mml:mi>
</mml:mrow>
</mml:mfrac>
</mml:mrow>
</mml:mfenced>
<mml:mo>&#x2b;</mml:mo>
<mml:mi>K</mml:mi>
<mml:mo>,</mml:mo>
</mml:mtd>
</mml:mtr>
</mml:mtable>
</mml:math>
<label>(27)</label>
</disp-formula>is a function of two terms, 5log(<italic>z</italic>) and &#x2212; 2.5log(1 &#x2b; <italic>z</italic>). So, <italic>&#x3bc;</italic>(<italic>z</italic>) does not follow a straight line but curves at <italic>z</italic> &#x2248; 1. The instrument factor, <italic>K</italic> &#x2248; 5log(1 &#x2b; <italic>z</italic>), corrects for sensitivity, i.e., the more light shifts to red, the less is detected [<xref ref-type="bibr" rid="B131">131</xref>,<xref ref-type="bibr" rid="B132">132</xref>].</p>
<p>The calculated moduli (<xref ref-type="disp-formula" rid="e27">Eq. 27</xref>) follow the measured ones closely (<xref ref-type="fig" rid="F6">Figure 6</xref>) [<xref ref-type="bibr" rid="B78">78</xref>], the difference mostly being within the scatter (<xref ref-type="fig" rid="F7">Figure 7</xref>). Thus, the least-time propagation of light explains the supernovae data. There is no room for purporting dark energy. In other words, the expansion rate does not increase. On the contrary, it decreases at the rate, &#x2212;<italic>d</italic>
<sub>
<italic>t</italic>
</sub>
<italic>H</italic> &#x3d; 1/<italic>t</italic>
<sup>2</sup> &#x3d; 4<italic>&#x3c0;G&#x3c1;</italic>
<sub>
<italic>M</italic>
</sub>, with decreasing density, <italic>&#x3c1;</italic>
<sub>
<italic>M</italic>
</sub>, as quanta in matter transform into quanta of space.</p>
<fig id="F6" position="float">
<label>FIGURE 6</label>
<caption>
<p>Curve calculated by the least-time principle (<xref ref-type="disp-formula" rid="e27">Eq. 27</xref>) (solid line) closely follows the brightness of Type Ia supernovae data, the distance modulus, <italic>&#x3bc;</italic>, vs. redshift, <italic>z</italic>, rather than the straight line of metric expansion without dark energy (dashed line) [<xref ref-type="bibr" rid="B7">7</xref>,<xref ref-type="bibr" rid="B9">9</xref>,<xref ref-type="bibr" rid="B10">10</xref>].</p>
</caption>
<graphic xlink:href="fphy-10-995977-g006.tif"/>
</fig>
<fig id="F7" position="float">
<label>FIGURE 7</label>
<caption>
<p>Difference, &#x394;<italic>&#x3bc;</italic> vs. <italic>z</italic>, between the measured supernova brightness vs. redshift and the values calculated by the least-time principle (<xref ref-type="disp-formula" rid="e27">Eq. 27</xref>).</p>
</caption>
<graphic xlink:href="fphy-10-995977-g007.tif"/>
</fig>
</sec>
<sec id="s5-2">
<title>5.2 The uniformity of the horizon</title>
<p>The uniformity of the cosmic microwave background temperature and the evenness of the distant galaxy distribution are customarily ascribed to a hypothetical inflationary scenario, a nascent exponential expansion [<xref ref-type="bibr" rid="B133">133</xref>].</p>
<p>However, by the thermodynamic theory, the correlation beyond causal connection follows naturally and necessarily from the least-time quest for balance (<xref ref-type="disp-formula" rid="e5">Eq. 5</xref>), namely, Newton&#x2019;s second law of motion states that the bigger a force, the faster the change in motion (<xref ref-type="disp-formula" rid="e6">Eq. 6</xref>), which means, for instance, that the higher the temperature difference, the faster the rate of cooling. Thus, there will be minute temperature differences in due course, regardless of how massive the differences were initially.</p>
<p>Although the early differences in temperature and density have by now nearly evened out, the process is still ongoing. A large difference in energy decreases rapidly and a small one evens out slowly. For example, the most massive stars shine the brightest and for the shortest time, well below 100&#xa0;million years; however, small stars glow over 100 billion years. Thus, there will be only small differences over time, as is observed. The derived distributions of quanta in matter (<xref ref-type="disp-formula" rid="e2">Eq. 2</xref>) and space (<xref ref-type="disp-formula" rid="e13">Eq. 13</xref>) imply that eventually, as <italic>T</italic> &#x2192; 0, everything will become even, regardless of how uneven the earliest universe was.</p>
</sec>
</sec>
<sec id="s6">
<title>6 Discussion</title>
<p>Massive amounts of astronomical data obtained through sky surveys have disclosed scale-free patterns. Observables distribute nearly in a power-law or lognormal manner and hence trail mostly straight lines on log&#x2013;log plots over many orders of magnitude.</p>
<p>This universality in data has long been suspected to reflect the unity of nature. However, the lead pointed out by Boltzmann and Gibbs has hardly been pursued beyond statistical mechanics of stationary-state systems. Yet, the same atomistic axiom also serves as the foundation for statistical mechanics of open, evolving systems. Assuming that all entities ultimately comprise the same basic constituents, motions of quanta from one state to another toward balance can be derived. This universal quest for thermodynamic balance between energy-dense matter and sparse space drives expansion and gives rise to the gradient of gravitational energy across the universe from the past to the present. As trivial as it might be, this universal gradient in the gravitation of all ordinary matter makes sense of galaxy rotation, velocity dispersion, and the Type 1a supernovae data without unsubstantiated hypotheses of dark matter and dark energy.</p>
<p>As is well known, when deriving general relativity from postulates, Einstein conformed to the tradition of theorizing, but departed by adding the cosmological constant. The mistake was insignificant in mistaking the universe as static but degrading the proper theory to an effective theory amenable for further fine-tuning rather than falsification [<xref ref-type="bibr" rid="B134">134</xref>].</p>
<p>Without question, the standard model of cosmology splendidly reproduces many local observations. Still, it falls short universally by assuming intrinsic metric expansion rather than recognizing that quanta in matter transform into quanta of space. Consequently, despite filling in the discrepancy between data and expectations, the dark matter hypothesis disregards the gravitation of all ordinary matter. Likewise, despite fulfilling galaxy rotation curves remarkably well [<xref ref-type="bibr" rid="B135">135</xref>], the modified Newtonian dynamics [<xref ref-type="bibr" rid="B136">136</xref>] misses identifing the universal acceleration with the gravitation of the expanding universe. Moreover, while fitting data, the dark energy model disregards the redshift due to the gravitational gradient of all ordinary matter across the universe.</p>
<p>So, despite a model matching data, its parameters need not relate to reality, whereas any data mismatching a theory founded on an axiom falsify that theory.</p>
</sec>
</body>
<back>
<sec sec-type="data-availability" id="s7">
<title>Data availability statement</title>
<p>The original contributions presented in the study are included in the article/Supplementary Material; further inquiries can be directed to the corresponding author.</p>
</sec>
<sec id="s8">
<title>Author contributions</title>
<p>All authors listed have made a substantial, direct, and intellectual contribution to the work and approved it for publication.</p>
</sec>
<ack>
<p>We thank Pekka Teerikorpi for comments and corrections.</p>
</ack>
<sec id="s9">
<title>Conflict of interest</title>
<p>The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.</p>
</sec>
<sec sec-type="disclaimer" id="s10">
<title>Publisher&#x2019;s note</title>
<p>All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors, and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.</p>
</sec>
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