Remove every clock from existence. No ticking sounds, no swinging pendulums, no caesium atoms keeping count of the seconds. Now pose a question that has perplexed physicists for nearly a century: how would you know if anything was occurring at all? In some of our most profound theories of reality, this is not a thought exercise. It is the real scenario.<\/p>\n
This disconcerting chasm between mathematical equations and lived experience is known as the problem of time, a concept that for decades has been largely confined to chalk dust and theoretical musings.<\/p>\n
At the University of Birmingham, Giovanni Barontini has brought it into a lab environment. He cooled about 24,000 rubidium atoms to mere billionths of a degree above absolute zero until they coalesced into a single radiant quantum blob, and then he separated that blob into two with a barrier of laser light. One side was observable. The other he purposely chose to ignore. The clever aspect, it appears, lies in the choice of what to overlook.<\/p>\n
Why engage in all of this? Because certain physics theories, with the Wheeler-DeWitt equation being the most notable, depict the universe as a singular frozen quantum state devoid of any inherent time.<\/p>\n
In that model, the cosmos merely exists<\/em>, whole and unchanged, like a film reel laid flat on a table rather than moving through a projector. And yet here we are, aging, reminiscing, observing coffee grow cold. The challenge lies in reclaiming the flowing river of time we collectively perceive from equations that, to be honest, don\u2019t reference it.<\/p>\n Barontini suggests letting one part of his miniature universe measure time for the other. \u201cIn some universe theories, particularly quantum gravity, time doesn\u2019t show up as an inherent component. Yet in daily life, time progresses from past to future \u2013 why is this the case when the fundamental laws of physics apply equally in both directions?\u201d he states.<\/p>\n This is where things become peculiar and rather beautiful. The observable half of the atomic cloud, referred to as the \u201cbright\u201d sector, does not remain still. It expands until it reaches a peak, then contracts and collapses back, completing a cosmic life cycle in approximately a tenth of a second: a miniature Big Bang succeeded by an equally miniature Big Crunch, repeatedly. Atoms migrate across the laser divide into the concealed \u201cdark\u201d sector and return, and it is this very movement, this dispersal and regrouping of particles, that Barontini employs as his timekeeping method. He dubs the resulting quantity entropic time. When the distribution of atoms shifts, time progresses. When there is no spread, time simply halts. No external second hand is necessary.<\/p>\n Moreover, this mechanism genuinely acts like time should. It flows in a singular direction, providing a clear arrow from past to future. It organizes the occurrences of each expansion and collapse in the correct order.<\/p>\n It even accelerates and decelerates depending on the rate at which entropy moves between the two sectors, a characteristic no standard clock possesses, and a somewhat disorienting concept to consider. If the laser barrier is raised sufficiently, entropy exchange diminishes to nearly nothing; the tiny universe approaches what Barontini, using an old cosmological term, refers to as a \u201cheat death,\u201d a static state where entropic time comes to a complete stop. Time does not conclude with a bang in this scenario. It merely runs out of items to measure.<\/p>\n The simplified description of the bright sector, it turns out, closely resembles the so-called minisuperspace models that quantum cosmologists have been developing for years, simplified toy universes with just a few moving elements. Barontini advanced the idea further and formulated a version of the Schr\u00f6dinger equation, which is the core engine of quantum mechanics, not based on laboratory time but on his entropic time, and demonstrated through simulation that it replicated the actual behavior of the atoms. Ordinary, purely reversible quantum mechanics, it turns out, is simply the special scenario that occurs when no entropy is being exchanged at all.<\/p>\n This does not imply that we have resolved what time actually is, and Barontini does not make such a claim. It is but a single isolated atom cloud, an analogue, a substitute, not the true fabric of spacetime.<\/p>\n Nonetheless, \u201cThis study offers the first controlled experimental evidence that \u2018time\u2019 can be articulated by changes within a system rather than relying on the external \u2018ticking clock\u2019 we commonly associate with time,\u201d he remarks, noting that this method could effectively describe dynamics in the same way as conventional time.<\/p>\n","protected":false},"excerpt":{"rendered":" Remove every clock from existence. No ticking sounds, no swinging pendulums, no caesium atoms keeping count of the seconds. Now pose a question that has perplexed physicists for nearly a century: how would you know if anything was occurring at all? In some of our most profound theories of reality, this is not a thought […]<\/p>\n","protected":false},"author":1,"featured_media":373078,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"Default","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[179],"class_list":["post-373077","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized","tag-source-scienceblog-com"],"_links":{"self":[{"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/posts\/373077","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=373077"}],"version-history":[{"count":0,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/posts\/373077\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/media\/373078"}],"wp:attachment":[{"href":"https:\/\/wolfscientific.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=373077"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=373077"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=373077"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}A Cosmic Event in a Container<\/h2>\n
From Theoretical Model to Laboratory<\/h2>\n