![\"A](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2026\/06\/Cumrun-Vafa-BY-Hayward-Photography.webp\")
<\/p>\n
Cumrun Vafa, a physicist at Harvard University, thinks the mass of dark matter may vary over time.<\/p>\n
String theory posits the existence of six or seven extra dimensions in addition to our familiar three dimensions of space and one of time. All of these dimensions are thought to be as small as physically possible \u2014 close to the Planck scale (10-35 meters) \u2014 but the researchers proposed that the dark dimension could be significantly bigger than the others \u2014 on the order of a micron (10-6 meters).<\/p>\n
Gravitons, theoretical particles that impart the force of gravity, could leak into this enlarged dark dimension. If they did, they would pick up mass and become what are called dark gravitons. These massive gravitons would reside in the dark dimension, but their gravitational effects could be felt in other dimensions, allowing them to fulfill the role that is normally ascribed to dark matter.<\/p>\n
In this scenario, \u201cthere is a very natural coupling between dark energy and dark matter,\u201d said Georges Obied<\/a>, a physicist at the University of Chicago. Changes in the size of the dark dimension would affect both dark energy and dark matter.<\/p>\n In a July 2025 paper<\/a>, Obied and Vafa, along with Alek Bedroya of Princeton and David Wu of Harvard, found that the scenario proposed in 2019 was consistent with the DESI data. Their model predicts that the strength of dark energy and the mass of dark matter will decrease over time and that the rate at which dark energy changes will be proportional to its energy density. Because astrophysical measurements tell us that the energy density of dark energy is extraordinarily small, \u201cit won\u2019t change fast,\u201d Vafa said.<\/p>\n \u201cIt\u2019s not surprising that we didn\u2019t see it until now,\u201d\u00a0he said, because the rate of change is so tiny. \u201cWe had to wait the entire age of the universe to detect something that small.\u201d<\/p>\n If dark matter is coupled to dark energy, dark matter particles could interact with one another through a new, long-range force that is separate from gravity. The good news, Obied said, is that \u201cthere could be astrophysical ways of testing this.\u201d<\/p>\n Coincidentally, two physicists \u2014 Marc Kamionkowski<\/a>, now at Johns Hopkins University, and Michael Kesden, now at the University of Texas at Dallas \u2014 have already looked into one such test. In a paper<\/a> published in 2006, they imagined a sequence of events in which two galaxies come close to each other and the gravity of one galaxy tugs at the other. If dark matter has a stronger gravitational attraction to other dark matter than it does to ordinary matter, a special kind of \u201ctidal tail\u201d \u2014 an extended stream of stars, gas, and dust \u2014 would form behind one of the galaxies.<\/p>\n Kesden and Kamionkowski looked for this effect and didn\u2019t find it, which enabled them to set an upper bound on the possible strength of the extra attractive force. The upper bound was about 20 times bigger than the number Vafa\u2019s team proposed, so the predicted value fell well within the observational bound. \u201cIt is interesting that we are now finding connections between that fairly abstract work and observational and experimental work,\u201d Kamionkowski said.<\/p>\n The fact that a prediction based on calculations from string theory roughly agreed with the astrophysical evidence does not confirm the validity of these \u201cstringy\u201d models. But any correspondence between string theory and experiment is gratifying to Vafa, who has spent the past four decades trying to wrest the theory from the purely conceptual realm to the point of generating testable predictions.<\/p>\n Obied, one of Vafa\u2019s former Ph.D. students, is driven by the same goal. Understanding dark energy and dark matter and the relationship they may share is a daunting problem, he said. \u201cAnd I think it\u2019s very beneficial to come at this in different ways\u201d \u2014 be it from observational cosmology, from particle physics, or from string theory.<\/p>\n \u201cThis is how people should do science,\u201d Obied said. \u201cI mean, it\u2019s the job of theoretical physicists to explore everything that\u2019s possible, to get all the possibilities on the table. And eventually, the data will help us decide.\u201d<\/p>\n","protected":false},"excerpt":{"rendered":"According to the standard model of cosmology, that expansion rate should be the same no matter how you…\n","protected":false},"author":2,"featured_media":719580,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[49],"tags":[199,79],"class_list":["post-719579","post","type-post","status-publish","format-standard","has-post-thumbnail","category-physics","tag-physics","tag-science"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/719579","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/comments?post=719579"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/719579\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media\/719580"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media?parent=719579"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/categories?post=719579"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/tags?post=719579"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}