A hundred years ago this week, at the height of the quantum revolution, Austrian physicist Erwin Schr\u00f6dinger submitted a manuscript for publication. Its centerpiece was an innocuous-looking equation that would alter science\u2019s entire conception of reality.<\/p>\n
Even now the Schr\u00f6dinger equation remains physicists\u2019 foremost window into the quantum realm. It tells scientists how that strange world works; that is, how quantum objects interact with their surroundings. But in doing so, it sets the mysteries of quantum mechanics\u2014many of which elude understanding to this day\u2014in stark mathematical relief.<\/p>\n
A full century after Schr\u00f6dinger penned his famous equation, scientists and philosophers are still seeking to define\u2014and expand\u2014its hazy boundaries. It does a great job describing the quantum systems that physicists study in their labs. But should the physicists themselves really be left out of the equation?<\/p>\n
Sign up for Today in Science, a free daily newsletter from Scientific American and join a community of science-loving readers.<\/a><\/p>\n As nonsensical as this question may seem, attempts to answer it are already offering new and surprising lessons about the quantum world. Inserting the observer into the Schr\u00f6dinger equation, it seems, allows transformative new perspectives on century-old questions.<\/p>\n \u201cWe’ve been trying to do physics as though it\u2019s just there,\u201d says Anne-Catherine de la Hamette, a physicist at the Swiss Federal Institute of Technology Zurich. \u201cAnd we forgot to ask, \u2018Well, who is actually measuring stuff?\u2019\u201d<\/p>\n An Insider\u2019s Perspective<\/p>\n Before Schr\u00f6dinger\u2019s 1926 breakthrough, the quantum revolution was in full swing but had mainly produced a hodgepodge of confounding truths. A particle could apparently be located in two places at once. Solid objects would sometimes act like ethereal waves of probability. Measuring an electron\u2019s spin on Earth could tell you instantaneously the spin of its entangled partner on Mars.<\/p>\n The Schr\u00f6dinger equation gave physicists a handle on this weird world. It determines the wave function, a mathematical object\u2014technically, a complex-valued function of probability amplitudes\u2014that captures all of a quantum system\u2019s myriad possibilities. If you have an electron\u2019s wave function, you can calculate how likely you are to find it in one place versus another.<\/p>\n The equation says how the wave function evolves over time but only while the system is left unobserved. The moment you check on, say, the position of an electron, its wave function \u201ccollapses,\u201d instantly snapping from a cloudlike distribution of possible places the particle might be to a narrow peak where it actually was. Experts still aren\u2019t sure how the act of measuring disrupts the quantum system, but it\u2019s unavoidable\u2014the \u201cmeasurement problem<\/a>\u201d remains the central mystery of quantum mechanics. The field of quantum reference frames, however, approaches it from a new direction.<\/p>\n \u201cIt\u2019s really about describing a quantum system from the inside,\u201d says Philipp H\u00f6hn, a physicist at the Okinawa Institute of Science and Technology in Japan.<\/p>\n Entangled Perspectives<\/p>\n To \u201cobserve\u201d a quantum system requires a measurement device, like a clock. But even clocks, in theory, are governed by quantum mechanics. \u201cBecause the clock is quantum, it\u2019s subject to the uncertainty principle,\u201d says Joshua Kirklin, a physicist at the Perimeter Institute for Theoretical Physics in Ontario, referring to Werner Heisenberg\u2019s realization in 1927 that certain properties of quantum systems can never be known with total certainty. \u201cThat means that the time that you measure is fuzzy.\u201d<\/p>\n Quantum reference frames account for this. They update the wave function in the Schr\u00f6dinger equation so that it describes both the system and the \u201cclock\u201d a scientist is using to measure it, complete with the fuzziness of that measurement.<\/p>\n And once devices like clocks are included in the quantum system, physicists are able to ask what two observers using different \u201cquantum clocks\u201d will then see.<\/p>\n This small change leads to surprising results. In 2019 physicists used it to show<\/a> that the phenomenon of quantum entanglement isn\u2019t an objective fact\u2014it actually depends on the circumstances of the observer. \u201cThings that don\u2019t look entangled in one frame can look entangled in another,\u201d de la Hamette says. The same is true for the phenomenon of superposition<\/a>, where a quantum object is described by a combination of distinct possibilities at once.<\/p>\n Uncertain Spacetime<\/p>\n Einstein\u2019s general theory of relativity, with its mind-bending revelations about the subjectivity of space and time, has long had issues meshing with quantum mechanics. Yet there are hints that quantum reference frames might offer a new approach here as well.<\/p>\n Take black holes. Their gravity warps space and time around them so much that no information from their confines can escape back out to the wider universe. But they also have a temperature and an entropy\u2014emergent physical quantities that usually arise from the quantum mechanical depths. Reconciling these seemingly contradictory properties using the same math is one of modern physics\u2019 great challenges<\/a>.<\/p>\n But in a 2023 paper, a team of physicists, including the great theoretician Edward Witten, added an observer with a quantum clock to their treatment of a black hole<\/a> and were surprised to find the gnarly math became simpler. Entropies that seemed infinite, impossible to calculate, suddenly became tractable. \u201cIf you take quantum reference frames into account, you find those infinities are made finite,\u201d Kirklin says.<\/p>\n And, if this new perspective can help break the impasse over black holes, what other long-standing puzzles might it help physicists solve?<\/p>\n New Century, New Outlook<\/p>\n Invigorated by this success, quantum reference frame enthusiasts gathered last year at a conference in Okinawa, the first of its kind, to discuss what would come next. \u201cIt seems to be becoming a community,\u201d Kirklin says. \u201cIt\u2019s really accelerated recently.\u201d<\/p>\n Much of the focus remains on quantum gravity. Relativity is all about relating different frames of reference, so making these \u201cquantum\u201d could be a path to resolving the many paradoxes that spring from Einstein\u2019s theory. \u201cSpace and time, which normally we use as this background stage on which physics is happening, that itself becomes uncertain,\u201d says de la Hamette. \u201cHow do we then describe anything?\u201d<\/p>\n But physicists aren\u2019t stopping there. They hope to pierce the quantum world\u2019s deepest secrets. They\u2019ve begun discussing \u201cWigner\u2019s friend<\/a>,\u201d a thought experiment related to the measurement problem and its more famous cousin, Schr\u00f6dinger\u2019s cat<\/a>. Perhaps this new lens on these old quandaries will continue to bring physicists closer to the biggest question of all: What happens to a quantum system at the moment of observation?<\/p>\n \u201cThe lesson may be,\u201d de la Hamette says, \u201cthat we should not have forgotten the observer.\u201d<\/p>\n","protected":false},"excerpt":{"rendered":"A hundred years ago this week, at the height of the quantum revolution, Austrian physicist Erwin Schr\u00f6dinger submitted…\n","protected":false},"author":2,"featured_media":266117,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[24],"tags":[139251,85,46,139252,370,139,16545,139249,139250,113900,141,139253],"class_list":{"0":"post-266116","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-physics","8":"tag-erwin-schrodinger","9":"tag-il","10":"tag-israel","11":"tag-physicists","12":"tag-physics","13":"tag-quantum","14":"tag-quantum-entanglement","15":"tag-quantum-objects","16":"tag-quantum-revolution","17":"tag-schrodinger-equation","18":"tag-science","19":"tag-wave-function"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts\/266116","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/comments?post=266116"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts\/266116\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/media\/266117"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/media?parent=266116"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/categories?post=266116"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/tags?post=266116"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}