{"id":777,"date":"2021-01-01T01:49:14","date_gmt":"2021-01-01T01:49:14","guid":{"rendered":"https:\/\/kohette.com\/wpthemes\/narratium\/?p=715"},"modified":"2023-05-02T14:54:20","modified_gmt":"2023-05-02T14:54:20","slug":"physicists-nail-down-the-magic-number-that-shapes-the-universe","status":"publish","type":"post","link":"https:\/\/kcsnowbourne.webstead.nl\/?p=777","title":{"rendered":"Physicists Nail Down the \u2018Magic Number\u2019 That Shapes the Universe."},"content":{"rendered":"\n
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The fine-structure constant was introduced in 1916<\/strong> to quantify the tiny gap between two lines in the spectrum of colors emitted by certain atoms. The closely spaced frequencies are seen here through a Fabry-P\u00e9rot interferometer.<\/strong><\/p>\n<\/div>\n\n\n\n

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As fundamental constants go, the speed of light, c<\/em>, enjoys all the fame, yet c<\/em>\u2019s numerical value says nothing about nature; it differs depending on whether it\u2019s measured in meters per second or miles per hour. The fine-structure constant, by contrast, has no dimensions or units. It\u2019s a pure number that shapes the universe to an astonishing degree \u2014 \u201ca magic number that comes to us with no understanding,\u201d as Richard Feynman described it. Paul Dirac considered the origin of the number \u201cthe most fundamental unsolved problem of physics.\u201d<\/p>\n<\/div>\n<\/div>\n\n\n\n

Numerically, the fine-structure constant, denoted by the Greek letter \u03b1 (alpha), comes very close to the ratio 1\/137. It commonly appears in formulas governing light and matter. \u201cIt\u2019s like in architecture, there\u2019s the golden ratio,\u201d said Eric Cornell<\/a>, a Nobel Prize-winning physicist at the University of Colorado, Boulder and the National Institute of Standards and Technology. \u201cIn the physics of low-energy matter \u2014 atoms, molecules, chemistry, biology \u2014 there\u2019s always a ratio\u201d of bigger things to smaller things, he said. \u201cThose ratios tend to be powers of the fine-structure constant.\u201d<\/p>\n\n\n\n

The constant is everywhere because it characterizes the strength of the electromagnetic force affecting charged particles such as electrons and protons. \u201cIn our everyday world, everything is either gravity or electromagnetism. And that\u2019s why alpha is so important,\u201d said Holger M\u00fcller<\/a>, a physicist at the University of California, Berkeley. Because 1\/137 is small, electromagnetism is weak; as a consequence, charged particles form airy atoms whose electrons orbit at a distance and easily hop away, enabling chemical bonds. On the other hand, the constant is also just big enough: Physicists have argued that if it were something like 1\/138, stars would not be able to create carbon, and life as we know it wouldn\u2019t exist.<\/p>\n\n\n\n

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Physicists have more or less given up on a century-old obsession over where alpha\u2019s particular value comes from; they now acknowledge that the fundamental constants could be random, decided in cosmic dice rolls during the universe\u2019s birth. But a new goal has taken over.<\/strong><\/h2>\n\n\n\n
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Look at this image caption. Look<\/strong>.<\/figcaption><\/figure><\/div>\n\n\n\n
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Physicists want to measure the fine-structure constant as precisely as possible. Because it\u2019s so ubiquitous, measuring it precisely allows them to test their theory of the interrelationships between elementary particles \u2014 the majestic set of equations known as the Standard Model of particle physics<\/a>. Any discrepancy between ultra-precise measurements of related quantities could point to novel particles or effects not accounted for by the standard equations. Cornell calls these kinds of precision measurements a third way of experimentally discovering the fundamental workings of the universe, along with particle colliders and telescopes.<\/p>\n<\/div>\n\n\n\n

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With a margin of error of just 81 parts per trillion, the new measurement is nearly three times more precise than the previous best measurement<\/a> in 2018 by M\u00fcller\u2019s group at Berkeley, the main competition. (Guellati-Kh\u00e9lifa made the most precise measurement before M\u00fcller\u2019s in 2011.) M\u00fcller said of his rival\u2019s new measurement of alpha, \u201cA factor of three is a big deal. Let\u2019s not be shy about calling this a big accomplishment.\u201d<\/p>\n<\/div>\n<\/div>\n\n\n\n

Guellati-Kh\u00e9lifa<\/strong> has been improving her experiment for the past 22 years. She gauges the fine-structure constant by measuring how strongly rubidium atoms recoil when they absorb a photon. (M\u00fcller does the same with cesium atoms.) The recoil velocity reveals how heavy rubidium atoms are \u2014 the hardest factor to gauge in a simple formula for the fine-structure constant. \u201cIt\u2019s always the least accurate measurement that\u2019s the bottleneck, so any improvement in that leads to an improvement in the fine-structure constant,\u201d M\u00fcller explained.<\/p>\n\n\n\n

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Look this nice<\/em><\/strong> Image Caption<\/span><\/strong>!<\/figcaption><\/figure>\n\n\n\n

The Paris experimenters begin by cooling the rubidium atoms almost to absolute zero, then dropping them in a vacuum chamber. As the cloud of atoms falls, the researchers use laser pulses to put the atoms in a quantum superposition of two states \u2014 kicked by a photon and not kicked. The two possible versions of each atom travel on separate trajectories until more laser pulses bring the halves of the superposition back together. The more an atom recoils when kicked by light, the more out of phase it is with the unkicked version of itself. The researchers measure this difference to reveal the atoms\u2019 recoil velocity. \u201cFrom the recoil velocity, we extract the mass of the atom, and the mass of the atom is directly involved in the determination of the fine-structure constant,\u201d Guellati-Kh\u00e9lifa said.<\/p>\n\n\n\n

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In such precise experiments, every detail matters. Table 1 of the new paper is an \u201cerror budget\u201d listing 16 sources of error and uncertainty that affect the final measurement. These include gravity and the Coriolis force created by Earth\u2019s rotation \u2014 both painstakingly quantified and compensated for. Much of the error budget comes from foibles of the laser, which the researchers have spent years perfecting.<\/p>\n\n\n\n
I love building shiny nice machines. And I love applying them to something important.<\/strong><\/p>Americo Clever<\/cite><\/blockquote>\n\n\n\n
For Guellati-Kh\u00e9lifa, the hardest part is knowing when to stop and publish. She and her team stopped the week of February 17, 2020, just as the coronavirus was gaining a foothold in France. Asked whether deciding to publish is like an artist deciding that a painting is finished, Guellati-Kh\u00e9lifa said, \u201cExactly. Exactly. Exactly<\/strong>.\u201d<\/p>\n\n\n\n
Surprisingly, her new measurement differs from M\u00fcller\u2019s 2018 result in the tenth digit, a bigger discrepancy than the margin of error of either measurement. This means \u2014 barring some fundamental difference between rubidium and cesium \u2014 that one or both of the measurements has an unaccounted-for error. The Paris group\u2019s measurement is the more precise, so it takes precedence for now, but both groups will improve their setups and try again.<\/p>\n\n\n\n
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Though the two measurements differ, they closely match the value of alpha inferred from precise measurements of the electron\u2019s g<\/em>-factor, a constant related to its magnetic moment, or the torque that the electron experiences in a magnetic field. \u201cYou can connect the fine-structure constant to the g<\/em>-factor with a hell of a lot of math,\u201d said Cornell. \u201cIf there are any physical effects missing from the equations [of the Standard Model], we would be getting the answer wrong.\u201d<\/p>\n\n\n\n
Instead, the measurements match beautifully, largely ruling out some proposals for new particles<\/a>. The agreement between the best g<\/em>-factor measurements and M\u00fcller\u2019s 2018 measurement was hailed as the Standard Model\u2019s greatest triumph. Guellati-Kh\u00e9lifa\u2019s new result is an even better match. \u201cIt\u2019s the most precise agreement between theory and experiment,\u201d she said.<\/p>\n\n\n\n
And yet she and M\u00fcller have both set about making further improvements. The Berkeley team has switched … <\/p>\n\n\n\n
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Keep reading this article in Quanta Magazine<\/a><\/div>\n<\/div>\n\n\n\n
<\/p>\n","protected":false},"excerpt":{"rendered":"
The fine-structure constant was introduced in 1916 to quantify the tiny gap between two lines in the spectrum of colors emitted by certain atoms. The closely spaced frequencies are seen here through a Fabry-P\u00e9rot interferometer. As fundamental constants go, the speed of light, c, enjoys all the fame, yet c\u2019s numerical value says nothing about nature; it […]<\/p>\n","protected":false},"author":1,"featured_media":598,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8,11,13],"tags":[],"class_list":["post-777","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-nature","category-science","category-technology"],"_links":{"self":[{"href":"https:\/\/kcsnowbourne.webstead.nl\/index.php?rest_route=\/wp\/v2\/posts\/777","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/kcsnowbourne.webstead.nl\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/kcsnowbourne.webstead.nl\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/kcsnowbourne.webstead.nl\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/kcsnowbourne.webstead.nl\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=777"}],"version-history":[{"count":1,"href":"https:\/\/kcsnowbourne.webstead.nl\/index.php?rest_route=\/wp\/v2\/posts\/777\/revisions"}],"predecessor-version":[{"id":778,"href":"https:\/\/kcsnowbourne.webstead.nl\/index.php?rest_route=\/wp\/v2\/posts\/777\/revisions\/778"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/kcsnowbourne.webstead.nl\/index.php?rest_route=\/wp\/v2\/media\/598"}],"wp:attachment":[{"href":"https:\/\/kcsnowbourne.webstead.nl\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=777"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/kcsnowbourne.webstead.nl\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=777"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/kcsnowbourne.webstead.nl\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=777"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}