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September 3, 2025<\/p>\n
4 min read<\/p>\n
What\u2019s the Smallest Particle in the Universe?<\/p>\n
The answer to this supposedly simple particle physics question isn\u2019t so simple<\/p>\n
By Gayoung Lee edited by Lee Billings<\/span><\/p>\n An artist’s concept of multiple types of subatomic particles.<\/p>\n Mark Garlick\/Science Photo Library<\/p>\n Forget about turtles; for all practical purposes, it\u2019s really particles all the way down.<\/p>\n Whether as the protons and neutrons that help form chemical elements, the photons that we perceive as light or even the flows of electrons that power our smartphones, subatomic particles constitute essentially everything any of us will ever experience. Ironically, however, because they\u2019re so minuscule, the particles underpinning our everyday reality tend to escape our notice\u2014and our comprehension.<\/p>\n Consider the seemingly simple matter of their size, the very thing that makes them so alien. We\u2019re typically taught to imagine any and all particles as tiny, colorful spheres, as if they were solid things that we could lay a ruler alongside to determine their dimensions like we\u2019d do for any other physical object in the world. But subatomic particles don\u2019t actually look like that at all. And while, for the largest particles, there are ways to measure \u201csize\u201d in a very general sense, for those that are smaller and ostensibly more \u201cfundamental,\u201d the concept of size itself is so slippery that it becomes almost meaningless.<\/p>\n If you’re enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.<\/p>\n Still, if Google queries are any guide, people really do want to know \u201cWhat\u2019s the smallest particle in the universe?\u201d Never mind that the better question might be \u201cIs there any point in asking?\u201d<\/p>\n \u201cThere\u2019s a lot of meanings for \u2018small,\u2019\u201d says Janet Conrad, a particle physicist at the Massachusetts Institute of Technology. \u201cLike, I could say a cotton ball is \u2018small\u2019 because it\u2019s very light. Or I could say a tiny metal ball is \u2018small\u2019 because its radius is very small, but it would weigh a lot more than the cotton ball.\u201d<\/p>\n Conrad\u2019s point is that there\u2019s a categorical difference between a particle that\u2019s \u201csmallest\u201d in mass and a particle that\u2019s \u201csmallest\u201d in diameter. There\u2019s another important categorical difference to account for as well, a functional distinction between two different classes of particles: fermions, or \u201cmatter\u201d particles such as protons or electrons that comprise everything in the universe, and bosons, or \u201ccarrier\u201d particles such as photons that deliver forces between fermions.<\/p>\n And most fundamentally, there is the matter of so-called fundamental particles, which are set apart from seemingly nonfundamental ones. Whether it\u2019s a fermion or a boson, physicists consider a particle \u201cfundamental\u201d if it cannot be broken down any further with any currently available technology. In that sense, some relatively well-known particles, such as protons, are not fundamental particles; if you hit a proton with a certain amount of force, it\u2019ll burst into quarks, which are considered to be fundamental.<\/p>\n So in terms of physical size, you\u2019d probably think that fundamental particles would be \u201csmaller\u201d than nonfundamental ones. But that\u2019s where things get really tricky, says Juan Pedro Ochoa-Ricoux, a particle physicist at the University of California, Irvine. According to the Standard Model of particle physics, which incorporates all known particles and forces besides gravity to make ludicrously accurate physical predictions, all fundamental particles have no size whatsoever. That is, asking whether one is bigger or smaller than another is a nonsensical question, akin to wondering what\u2019s north of \u201cup\u201d or trying to divide by zero.<\/p>\n \u201c[Fundamental particles] are Euclidean points,\u201d Ochoa-Ricoux explains. \u201cThey\u2019re not even one-dimensional. We think of them as [zero-dimensional] points [that] don\u2019t have a determined position. And so, rather than thinking of electrons as little balls going around an atomic nucleus, in reality, we should think of them as a cloud [of probabilities].\u201d<\/p>\n All fundamental particles seem to be this way, showing no signs of deeper internal structure, Conrad adds. \u201cWe keep testing to see if there\u2019s any spatial extent associated with them,\u201d she says, \u201cbut we don\u2019t see any evidence that there\u2019s something inside of these particles.\u201d<\/p>\n Physicists like to circumvent this uncertainty, Ochoa-Ricoux says, by doing some reverse calculations using Albert Einstein\u2019s famous equation E = mc2, which quantifies the equivalence between energy and mass. Specifically, such calculations usually involve the electron volt (eV), a unit of energy for which 1 eV represents the charge of one electron. Using Einstein\u2019s equation to convert this value to mass reveals that the electron effectively weighs about 0.51 mega-electron-volts per speed of light squared (0.51 MeV\/c2)\u2014that is, about 9.109 \u00d7 10\u201331 kilogram. In comparison, the \u201clightest\u201d quark, the up quark, is more than four times heavier, weighing in at about 2.14 MeV\/c2.<\/p>\n As small as these values are, they\u2019re still much bigger than \u201czero,\u201d which is the mass inferred for certain other particles. These so-called massless particles are arguably the best candidates for the \u201csmallest,\u201d too.<\/p>\n Strictly speaking of bosons, or force-carrying particles, the clear winner of the competition for \u201cuniverse\u2019s smallest particle\u201d would be the massless photon. (Gluons\u2014bosons that bind together quarks\u2014are also thought to be massless but are much harder to study because they\u2019re typically trapped inside protons and neutrons.) If we\u2019re talking about fermions, the particles that are the building blocks of matter\u2014a reasonable guess for the universe\u2019s smallest particle would be the neutrino. This is a \u201cguess\u201d because we don\u2019t really know the exact mass of a neutrino for certain, although we\u2019re sure it\u2019s not zero. To put the neutrino\u2019s mass into perspective, it probably weighs about 0.45 eV\/c2\u2014less than one millionth the mass of an electron!<\/p>\n But again, as Ochoa-Ricoux and Conrad each independently emphasize, this is just one approach experts tend to use when considering a particle\u2019s size. As with many kinds of scientific inquiry, the answer you get intimately depends on how exactly you\u2019re asking the question.<\/p>\n","protected":false},"excerpt":{"rendered":" September 3, 2025 4 min read What\u2019s the Smallest Particle in the Universe? The answer to this supposedly simple particle physics question isn\u2019t so simple By Gayoung Lee edited by Lee Billings An artist’s concept of multiple types of subatomic particles. Mark Garlick\/Science Photo Library Forget about turtles; for all practical purposes, it\u2019s really particles<\/p>\n","protected":false},"author":1,"featured_media":19139,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[58],"tags":[11549,10168,1179,264],"class_list":{"0":"post-19138","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-science","8":"tag-particle","9":"tag-smallest","10":"tag-universe","11":"tag-whats"},"_links":{"self":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/posts\/19138","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=19138"}],"version-history":[{"count":0,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/posts\/19138\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/media\/19139"}],"wp:attachment":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=19138"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=19138"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=19138"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}On supporting science journalism<\/h2>\n
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