<p>The Weak Equivalence Principle is the founding pillar of General Relativity, and as such, it should be verified as precisely as possible. The <i>Microscope</i> experiment tested it in low Earth orbit, finding that Pt and Ti test masses fall toward Earth with the same acceleration to about 1 part in <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10569_2024_10233_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="29" /> </InlineMediaObject> <EquationSource Format="TEX">\(10^{15}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mn>10</mn> <mn>15</mn> </msup> </math></EquationSource> </InlineEquation>, an improvement of about two orders of magnitude over ground tests. Space missions, even if small, are expensive and hard to replicate; yet, the essence of physics is repeatability. This work is an assessment of the <i>Microscope</i> results based on the laws of physics and knowledge from previous experiments, focusing on the limiting thermal noise and the treatment of acceleration outliers. Thermal noise reveals anomalies that we explain by stray sub-<InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10569_2024_10233_Article_IEq2.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="25" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mu {\textrm{V}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>μ</mi> <mtext>V</mtext> </mrow> </math></EquationSource> </InlineEquation> potentials caused by patch charges, giving rise to an unstable zero. The measurements were affected by numerous acceleration spikes occurring at the synodic frequencies relative to the Earth (the signal frequency) and the Sun, which we interpret as evidence of a thermal origin. In <i>Microscope</i> authors’ analysis, the spikes were removed and the resulting gaps replaced with artificial data (up to <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10569_2024_10233_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="31" /> </InlineMediaObject> <EquationSource Format="TEX">\(35\%\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>35</mn> <mo>%</mo> </mrow> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10569_2024_10233_Article_IEq4.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="31" /> </InlineMediaObject> <EquationSource Format="TEX">\(40\%\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>40</mn> <mo>%</mo> </mrow> </math></EquationSource> </InlineEquation> of the sessions data), which retain memory of the gaps and may simulate or cancel an effect (signal or systematic). An alternative approach based exclusively on real measured data would avoid any ambiguity. The lessons of <i>Microscope</i> are crucial to any future improved mission.</p>

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On the first test of the Weak Equivalence Principle in low Earth orbit

  • Anna M. Nobili,
  • Alberto Anselmi

摘要

The Weak Equivalence Principle is the founding pillar of General Relativity, and as such, it should be verified as precisely as possible. The Microscope experiment tested it in low Earth orbit, finding that Pt and Ti test masses fall toward Earth with the same acceleration to about 1 part in \(10^{15}\) 10 15 , an improvement of about two orders of magnitude over ground tests. Space missions, even if small, are expensive and hard to replicate; yet, the essence of physics is repeatability. This work is an assessment of the Microscope results based on the laws of physics and knowledge from previous experiments, focusing on the limiting thermal noise and the treatment of acceleration outliers. Thermal noise reveals anomalies that we explain by stray sub- \(\mu {\textrm{V}}\) μ V potentials caused by patch charges, giving rise to an unstable zero. The measurements were affected by numerous acceleration spikes occurring at the synodic frequencies relative to the Earth (the signal frequency) and the Sun, which we interpret as evidence of a thermal origin. In Microscope authors’ analysis, the spikes were removed and the resulting gaps replaced with artificial data (up to \(35\%\) 35 % , \(40\%\) 40 % of the sessions data), which retain memory of the gaps and may simulate or cancel an effect (signal or systematic). An alternative approach based exclusively on real measured data would avoid any ambiguity. The lessons of Microscope are crucial to any future improved mission.