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Length scale - Wikipedia
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href="https://el.wikipedia.org/wiki/%CE%9A%CE%BB%CE%AF%CE%BC%CE%B1%CE%BA%CE%B1_%CE%BC%CE%AE%CE%BA%CE%BF%CF%85%CF%82" title="Κλίμακα μήκους – Greek" lang="el" hreflang="el" data-title="Κλίμακα μήκους" data-language-autonym="Ελληνικά" data-language-local-name="Greek" class="interlanguage-link-target"><span>Ελληνικά</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Escalas_de_longitud" title="Escalas de longitud – Spanish" lang="es" hreflang="es" data-title="Escalas de longitud" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Scala_di_lunghezza" title="Scala di lunghezza – Italian" lang="it" hreflang="it" data-title="Scala di lunghezza" data-language-autonym="Italiano" data-language-local-name="Italian" 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#36c;background-color:#fbfbfb;box-sizing:border-box}.mw-parser-output .ambox+link+.ambox,.mw-parser-output .ambox+link+style+.ambox,.mw-parser-output .ambox+link+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+style+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+link+.ambox{margin-top:-1px}html body.mediawiki .mw-parser-output .ambox.mbox-small-left{margin:4px 1em 4px 0;overflow:hidden;width:238px;border-collapse:collapse;font-size:88%;line-height:1.25em}.mw-parser-output .ambox-speedy{border-left:10px solid #b32424;background-color:#fee7e6}.mw-parser-output .ambox-delete{border-left:10px solid #b32424}.mw-parser-output .ambox-content{border-left:10px solid #f28500}.mw-parser-output .ambox-style{border-left:10px solid #fc3}.mw-parser-output .ambox-move{border-left:10px solid #9932cc}.mw-parser-output .ambox-protection{border-left:10px solid #a2a9b1}.mw-parser-output .ambox .mbox-text{border:none;padding:0.25em 0.5em;width:100%}.mw-parser-output .ambox .mbox-image{border:none;padding:2px 0 2px 0.5em;text-align:center}.mw-parser-output .ambox .mbox-imageright{border:none;padding:2px 0.5em 2px 0;text-align:center}.mw-parser-output .ambox .mbox-empty-cell{border:none;padding:0;width:1px}.mw-parser-output .ambox .mbox-image-div{width:52px}@media(min-width:720px){.mw-parser-output .ambox{margin:0 10%}}@media print{body.ns-0 .mw-parser-output .ambox{display:none!important}}</style><table class="box-Unreferenced plainlinks metadata ambox ambox-content ambox-Unreferenced" role="presentation"><tbody><tr><td class="mbox-image"><div class="mbox-image-div"><span typeof="mw:File"><a href="/wiki/File:Question_book-new.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png" decoding="async" width="50" height="39" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/75px-Question_book-new.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/100px-Question_book-new.svg.png 2x" data-file-width="512" data-file-height="399" /></a></span></div></td><td class="mbox-text"><div class="mbox-text-span">This article <b>does not <a href="/wiki/Wikipedia:Citing_sources" title="Wikipedia:Citing sources">cite</a> any <a href="/wiki/Wikipedia:Verifiability" title="Wikipedia:Verifiability">sources</a></b>.<span class="hide-when-compact"> Please help <a href="/wiki/Special:EditPage/Length_scale" title="Special:EditPage/Length scale">improve this article</a> by <a href="/wiki/Help:Referencing_for_beginners" title="Help:Referencing for beginners">adding citations to reliable sources</a>. Unsourced material may be challenged and <a href="/wiki/Wikipedia:Verifiability#Burden_of_evidence" title="Wikipedia:Verifiability">removed</a>.<br /><small><span class="plainlinks"><i>Find sources:</i> <a rel="nofollow" class="external text" href="https://www.google.com/search?as_eq=wikipedia&q=%22Length+scale%22">"Length scale"</a> – <a rel="nofollow" class="external text" href="https://www.google.com/search?tbm=nws&q=%22Length+scale%22+-wikipedia&tbs=ar:1">news</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.google.com/search?&q=%22Length+scale%22&tbs=bkt:s&tbm=bks">newspapers</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.google.com/search?tbs=bks:1&q=%22Length+scale%22+-wikipedia">books</a> <b>·</b> <a rel="nofollow" class="external text" href="https://scholar.google.com/scholar?q=%22Length+scale%22">scholar</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.jstor.org/action/doBasicSearch?Query=%22Length+scale%22&acc=on&wc=on">JSTOR</a></span></small></span> <span class="date-container"><i>(<span class="date">September 2020</span>)</i></span><span class="hide-when-compact"><i> (<small><a href="/wiki/Help:Maintenance_template_removal" title="Help:Maintenance template removal">Learn how and when to remove this message</a></small>)</i></span></div></td></tr></tbody></table> <p>In <a href="/wiki/Physics" title="Physics">physics</a>, <b>length scale</b> is a particular <a href="/wiki/Length" title="Length">length</a> or <a href="/wiki/Distance" title="Distance">distance</a> determined with the precision of at most a few <a href="/wiki/Orders_of_magnitude" class="mw-redirect" title="Orders of magnitude">orders of magnitude</a>. The concept of length scale is particularly important because physical phenomena of different length scales cannot affect each other<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="This claim needs references to reliable sources. (March 2016)">citation needed</span></a></i>]</sup><sup class="noprint Inline-Template" style="margin-left:0.1em; white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Please_clarify" title="Wikipedia:Please clarify"><span title="The text near this tag may need clarification or removal of jargon. (May 2016)">clarification needed</span></a></i>]</sup> and are said to <a href="/wiki/Coupling_(physics)" title="Coupling (physics)">decouple</a>. The decoupling of different length scales makes it possible to have a self-consistent theory that only describes the relevant length scales for a given problem. <a href="/wiki/Scientific_reductionism" class="mw-redirect" title="Scientific reductionism">Scientific reductionism</a> says that the physical laws on the shortest length scales can be used to derive the effective description at larger length scales. The idea that one can derive descriptions of physics at different length scales from one another can be quantified with the <a href="/wiki/Renormalization_group" title="Renormalization group">renormalization group</a>. </p><p>In <a href="/wiki/Quantum_mechanics" title="Quantum mechanics">quantum mechanics</a> the length scale of a given phenomenon is related to its <a href="/wiki/De_Broglie_wavelength" class="mw-redirect" title="De Broglie wavelength">de Broglie wavelength</a> <span class="nowrap"><i>ℓ</i> = <i>ħ</i>/<i>p</i></span>, where <i>ħ</i> is the <a href="/wiki/Reduced_Planck_constant" class="mw-redirect" title="Reduced Planck constant">reduced Planck constant</a> and <i>p</i> is the momentum that is being probed. In <a href="/wiki/Relativistic_mechanics" title="Relativistic mechanics">relativistic mechanics</a> time and length scales are related by the <a href="/wiki/Speed_of_light" title="Speed of light">speed of light</a>. In <a href="/wiki/Relativistic_quantum_mechanics" title="Relativistic quantum mechanics">relativistic quantum mechanics</a> or <a href="/wiki/Relativistic_quantum_field_theory" class="mw-redirect" title="Relativistic quantum field theory">relativistic quantum field theory</a>, length scales are related to momentum, time and energy scales through the Planck constant and the speed of light. Often in <a href="/wiki/High_energy_physics" class="mw-redirect" title="High energy physics">high energy physics</a> <a href="/wiki/Natural_units" title="Natural units">natural units</a> are used where length, time, energy and momentum scales are described in the same units (usually with units of energy such as <a href="/wiki/GeV" class="mw-redirect" title="GeV">GeV</a>). </p><p>Length scales are usually the operative scale (or at least one of the scales) in <a href="/wiki/Dimensional_analysis" title="Dimensional analysis">dimensional analysis</a>. For instance, in <a href="/wiki/Scattering_theory" class="mw-redirect" title="Scattering theory">scattering theory</a>, the most common quantity to calculate is a <a href="/wiki/Cross_section_(physics)" title="Cross section (physics)">cross section</a> which has units of length squared and is measured in <a href="/wiki/Barn_(unit)" title="Barn (unit)">barns</a>. The cross section of a given process is usually the square of the length scale. </p> <div class="mw-heading mw-heading2"><h2 id="Examples">Examples</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Length_scale&action=edit&section=1" title="Edit section: Examples"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li>The atomic length scale is <span class="nowrap">ℓ<sub>a</sub> ~ <span class="nowrap"><span data-sort-value="6990100000000000000♠"></span>10<sup>−10</sup> m</span></span> and is given by the size of hydrogen atom (<i>i.e.</i>, the <a href="/wiki/Bohr_radius" title="Bohr radius">Bohr radius</a>, approximately <span class="nowrap"><span data-sort-value="6989530000000000000♠"></span>53 <a href="/wiki/Picometre" title="Picometre">pm</a></span>).</li> <li>The length scale for the <a href="/wiki/Strong_interaction" title="Strong interaction">strong interactions</a> (or the one derived from <a href="/wiki/Quantum_chromodynamics" title="Quantum chromodynamics">QCD</a> through <a href="/wiki/Dimensional_transmutation" title="Dimensional transmutation">dimensional transmutation</a>) is around <span class="nowrap">ℓ<sub>s</sub> ~ <span class="nowrap"><span data-sort-value="6985100000000000000♠"></span>10<sup>−15</sup> m</span></span>, and the "radii" of strongly interacting particles (such as the <a href="/wiki/Proton" title="Proton">proton</a>) are roughly comparable. This length scale is determined by the range of the <a href="/wiki/Yukawa_potential" title="Yukawa potential">Yukawa potential</a>. The lifetimes of strongly interacting particles, such as the <a href="/wiki/Rho_meson" title="Rho meson">rho meson</a>, are given by this length scale divided by the speed of light: <span class="nowrap"><span data-sort-value="6977099999999999999♠"></span>10<sup>−23</sup> s</span>. The masses of strongly interacting particles are several times the associated energy scale (<span class="nowrap"><span data-sort-value="7002500000000000000♠"></span>500 MeV/<i>c</i><sup>2</sup></span> to <span class="nowrap"><span data-sort-value="7003300000000000000♠"></span>3000 MeV/<i>c</i><sup>2</sup></span>).</li> <li>The <a href="/wiki/Electroweak" class="mw-redirect" title="Electroweak">electroweak</a> length scale is shorter, roughly <span class="nowrap">ℓ<sub>w</sub> ~ <span class="nowrap"><span data-sort-value="6982100000000000000♠"></span>10<sup>−18</sup> m</span></span> and is set by the rest mass of the <a href="/wiki/W_and_Z_bosons" title="W and Z bosons">weak vector bosons</a>, which is roughly <span class="nowrap"><span data-sort-value="7002100000000000000♠"></span>100 GeV/<i>c</i><sup>2</sup></span>. This length scale would be the distance where a Yukawa force is mediated by the weak vector bosons. The magnitude of weak length scale was initially inferred by the <a href="/wiki/Fermi%27s_interaction" title="Fermi's interaction">Fermi constant</a> measured by <a href="/wiki/Neutron" title="Neutron">neutron</a> and <a href="/wiki/Muon" title="Muon">muon</a> decay.</li> <li>The <a href="/wiki/Planck_length" class="mw-redirect" title="Planck length">Planck length</a> (Planck scale) is much shorter yet – about <span class="nowrap">ℓ<sub>P</sub> ~ <span class="nowrap"><span data-sort-value="6965100000000000000♠"></span>10<sup>−35</sup> m</span></span>, and is derived from the <a href="/wiki/Newtonian_constant_of_gravitation" class="mw-redirect" title="Newtonian constant of gravitation">Newtonian constant of gravitation</a>.</li> <li>The <a href="/wiki/Mesoscopic_scale" class="mw-redirect" title="Mesoscopic scale">mesoscopic scale</a> is the length at which quantum mechanical behaviours in liquids or solid can be described by <a href="/wiki/Macroscopic" class="mw-redirect" title="Macroscopic">macroscopic</a> concepts.</li></ul> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Length_scale&action=edit&section=2" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Orders_of_magnitude_(length)" title="Orders of magnitude (length)">Orders of magnitude (length)</a></li> <li><a href="/wiki/Extragalactic_distance_scale" class="mw-redirect" title="Extragalactic distance scale">Extragalactic distance scale</a></li> <li><a href="/wiki/Scale_height" title="Scale height">Scale height</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Length_scale&action=edit&section=3" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist"> </div> <!-- NewPP limit report Parsed by mw‐api‐ext.codfw.main‐69ddb88cc‐x4bhc Cached time: 20250210050714 Cache expiry: 2592000 Reduced expiry: false Complications: [vary‐revision‐sha1] CPU time usage: 0.182 seconds Real time usage: 0.241 seconds Preprocessor visited node count: 787/1000000 Post‐expand include size: 17124/2097152 bytes Template argument size: 2413/2097152 bytes Highest expansion depth: 12/100 Expensive parser function count: 3/500 Unstrip recursion depth: 0/20 Unstrip post‐expand size: 2594/5000000 bytes Lua time usage: 0.103/10.000 seconds Lua memory usage: 3930933/52428800 bytes Number of Wikibase entities loaded: 0/400 --> <!-- Transclusion expansion time report (%,ms,calls,template) 100.00% 210.759 1 -total 35.51% 74.843 1 Template:References_needed 32.39% 68.259 1 Template:Ambox 25.46% 53.664 1 Template:Short_description 18.64% 39.283 9 Template:Val 16.88% 35.569 5 Template:Nowrap 15.25% 32.143 2 Template:Pagetype 9.25% 19.504 1 Template:Citation_needed 7.60% 16.007 1 Template:Fix 6.73% 14.190 1 Template:Find_sources_mainspace --> <!-- Saved in parser cache with key enwiki:pcache:697181:|#|:idhash:canonical and timestamp 20250210050714 and revision id 1220243920. 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