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Scientists at the University of Toronto<\/a> found light doing something similar with atoms, except they measured the part where it got really weird.<\/p>\n Experiment that shouldn\u2019t work<\/p>\n Light usually slows down when passing through materials. That\u2019s normal physics<\/a>. <\/p>\n But with very short light pulses<\/a> and the right conditions, the peak of a light wave can exit a material before it seemingly should. <\/p>\n Scientists have seen this for years but dismissed it as a reshaping effect, not actual negative time. The Toronto researchers weren\u2019t satisfied with that explanation. <\/p>\n They cooled rubidium atoms<\/a> to near absolute zero and shot incredibly weak light pulses through them \u2013 so weak that they could track individual photons.<\/p>\n Aephraim Steinberg<\/a>, a University of Toronto professor specializing in experimental quantum physics, led the work with researcher Daniela Angulo<\/a>. <\/p>\n They used two laser beams. One carried the signal they wanted to study. The other acted like a heartbeat monitor for the atoms.<\/p>\n \u201cThis is tough stuff, even for us to talk about with other physicists. We get misunderstood all the time,\u201d said Steinberg.<\/p>\n Measuring negative time<\/p>\n Here\u2019s where things get strange. When a photon<\/a> passed through and excited the atoms, the probe beam detected tiny changes. <\/p>\n These changes told them exactly how long the atoms remained excited. The answer? Sometimes it was negative.<\/p>\n \u201cThat time turned out to be negative,\u201d Steinberg explained.<\/p>\n The team discovered that when light pulses experienced what physicists call negative group delay<\/a> \u2013 when the pulse peak exits early \u2013 the atoms showed corresponding negative excitation times. <\/p>\n The two measurements matched perfectly, proving this wasn\u2019t just a visual trick but a real physical phenomenon.<\/p>\n How negative time actually works<\/p>\n Before you start planning trips to yesterday, understand what\u2019s really happening. The speed of light remains unchanged.<\/p>\n \u201cWe don\u2019t want to say anything traveled backward in time,\u201d Steinberg said. \u201cThat\u2019s a misinterpretation.\u201d<\/p>\n Light pulses contain many frequencies mixed together, like a chord in music. When these frequencies hit resonant atoms<\/a>, each gets shifted slightly differently. <\/p>\n Mix them back together, and the peak can end up ahead of where you\u2019d expect. No single part breaks the speed of light \u2013 the wave just reshapes itself through quantum interference<\/a>.<\/p>\n The atoms essentially record this reshaping. When the pulse peak shifts forward, the atoms\u2019 response shifts too, creating a measurable negative interaction time. It\u2019s quantum mechanics<\/a> at its strangest, but it follows all the rules.<\/p>\n Why scientists care<\/p>\n This experiment settles a long debate. Some physicists argued negative group delay was just mathematical sleight of hand. Others suspected it represented something physically real.<\/p>\n Their setup required extraordinary precision. They trapped rubidium-85 atoms in a tiny cloud, sending shaped signal pulses through it, while a probe beam traveled in the opposite direction. <\/p>\n The signal matched a specific atomic transition in rubidium. The probe stayed slightly detuned to monitor without being absorbed.<\/p>\n By correlating probe changes with single-photon detections<\/a>, they isolated effects from individual photons. <\/p>\n Tests across different pulse durations and cloud densities confirmed their predictions every time. Where theory predicted negative delays, they measured negative times.<\/p>\n This discovery matters for quantum technology. Future quantum computers<\/a> and networks need precise control of photon-atom interactions. <\/p>\n Understanding these timing effects, even negative ones, helps engineers build better quantum systems.<\/p>\n The work also pushes quantum mechanics into new territory. At quantum scales, particles behave in probabilistic ways that defy everyday intuition. <\/p>\n What happens next<\/p>\n This experiment shows that time measurements can get equally weird, though causality never breaks.<\/p>\n Steinberg acknowledged controversy around their findings, but noted that no scientist has challenged the experimental results.<\/p>\n \u201cWe\u2019ve made our choice about what we think is a fruitful way to describe the results,\u201d he said.<\/p>\n As for practical uses, Steinberg remains realistic. <\/p>\n \u201cI\u2019ll be honest, I don\u2019t currently have a path from what we\u2019ve been looking at toward applications,\u201d he admitted. \u201cWe\u2019re going to keep thinking about it, but I don\u2019t want to get people\u2019s hopes up.\u201d<\/p>\n The discovery opens new paths for exploring quantum effects. Sometimes the strangest findings lead to unexpected breakthroughs. <\/p>\n We now know negative time isn\u2019t just theoretical \u2013 it\u2019s measurable, real, and perfectly consistent with physics. It is not the kind that lets you change the past.<\/p>\n The full study was published in the journal arXiv<\/a>.<\/p>\n \u2014\u2013<\/p>\n Like what you read? Subscribe to our newsletter<\/a> for engaging articles, exclusive content, and the latest updates.<\/p>\n Check us out on EarthSnap<\/a>, a free app brought to you by Eric Ralls<\/a> and Earth.com.<\/p>\n \u2014\u2013<\/p>\n","protected":false},"excerpt":{"rendered":"Scientists just measured something that sounds impossible. When light passes through atoms, it can spend what appears to…\n","protected":false},"author":3,"featured_media":157358,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[25],"tags":[492,159,67,132,68],"class_list":{"0":"post-157357","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-physics","8":"tag-physics","9":"tag-science","10":"tag-united-states","11":"tag-unitedstates","12":"tag-us"},"share_on_mastodon":{"url":"https:\/\/pubeurope.com\/@us\/115053248382901451","error":""},"_links":{"self":[{"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/posts\/157357","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/comments?post=157357"}],"version-history":[{"count":0,"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/posts\/157357\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/media\/157358"}],"wp:attachment":[{"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/media?parent=157357"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/categories?post=157357"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/tags?post=157357"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}