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Three researchers have now worked out exactly how it could. They solved for the amount of information a sender in the future could push back to a receiver in the past \u2013 not through a perfect channel, but a noisy one.<\/p>\n
An Interstellar problem<\/p>\n
The paper models its scenario on the film. A father stranded behind a black hole signals his young daughter, who lives in his past. The film treats it as poetry; the team treats it as math.<\/p>\n
Kaiyuan Ji, a quantum information researcher at Cornell University (Cornell<\/a>), posed the question carefully with collaborators at the Massachusetts Institute of Technology (MIT<\/a>). <\/p>\n If such a channel existed, even a noisy one, how many bits could reliably pass through it?<\/p>\n The backward-time channel they study can be simulated using quantum experiments \u2013 a way of modeling time travel without bending spacetime<\/a> at all. <\/p>\n The idea has been around for years, and an early test used entangled photons in a real lab.<\/p>\n Escaping the grandfather paradox<\/p>\n If a message can run backward in time, the worry is always the same. Grandfather paradoxes. Inconsistent histories. <\/p>\n Receivers who alter what their senders eventually transmit \u2013 the whole reason physicists treat backward signaling with deep suspicion.<\/p>\n The approach handles this in a strict way. Only self-consistent histories survive. <\/p>\n Anything that would erase its own cause gets filtered out automatically \u2013 the same way quantum teleportation<\/a> only works when a specific random result happens to come up.<\/p>\n That leaves a narrow window where a causal loop is allowed, provided it closes on itself cleanly. <\/p>\n The daughter decodes a message, then parks a record in long-term storage. Years later, the father retrieves it and consults it before writing his signal.<\/p>\n The mechanics of time communication<\/p>\n Until this paper, no one had a clean number for how much information could survive that loop when the channel was noisy.<\/p>\n Earlier work showed that an idealized backward channel could do remarkable things, but practical noise spoils most of those tricks.<\/p>\n The team\u2019s strategy is elegant. In the past, the daughter stores half of a linked quantum pair in long-term storage.<\/p>\n Years later, the father retrieves it. He performs a measurement connecting it to his message, then pushes the result into the channel.<\/p>\n The structure runs in reverse from what any sender expects: the receiver comes first, leaving a hint. The sender comes later, picks up that hint, and uses it to make the loop click into place.<\/p>\n The authors call this scheme amplified probabilistic teleportation. The amplification is what\u2019s new: the loop itself boosts the odds that the message arrives intact, far above what a single teleportation step could ever achieve.<\/p>\n How much information survives?<\/p>\n At the heart of the paper is a precise formula for how many bits the backward channel can carry.<\/p>\n Two quantities feed into it \u2013 how well the channel preserves information at its best and how badly it corrupts it at its worst.<\/p>\n The upshot is clear: noisier channels carry less information, and the formula reveals exactly how much less. Plugging in a specific noise profile produces an exact number, not a vague bound or a wave at infinity.<\/p>\n Researchers can now apply the formula to a realistic noisy channel \u2013 one that loses photons<\/a> or scrambles bits \u2013 and read off a precise limit on backward bandwidth.<\/p>\n Earlier work handled only the perfectly clean case, which was always a fantasy.<\/p>\n What this means for black holes<\/p>\n The paper ends with a striking link. Some models of black holes<\/a> describe their evaporation using the same mathematical structures the team analyzed. <\/p>\n One famous proposal connects a black hole\u2019s final state to quantum teleportation.<\/p>\n If that picture is correct, the team\u2019s math maps directly onto information escaping a collapsing black hole. Their capacity formula sets a limit on how much information could come back out.<\/p>\n That speaks to the long-running information paradox \u2013 the puzzle of whether a black hole destroys the data it swallows. <\/p>\n The debate has dragged on for nearly 50 years. A precise capacity bound offers a new way to approach the problem.<\/p>\n Seth Lloyd, a physicist at MIT and a co-author of the work, has pursued this line of research for years. His earlier paper on black-hole escape set the stage. The new analysis strengthens those arguments.<\/p>\n Moving time travel into science<\/p>\n Before this paper, no one knew how much usable information could survive a noisy backward-in-time channel. Now there is an exact formula derived from first principles. That represents a significant advance in understanding.<\/p>\n The practical consequences may sound distant. Real backward-in-time channels remain beyond the reach of current laboratories.<\/p>\n Even so, the same mathematics applies to ordinary quantum computing<\/a>, certain black-hole models, and a class of quantum experiments that physicists already run today.<\/p>\n What began as a thought experiment inspired by a science-fiction film now has a precise mathematical limit attached to it.<\/p>\n Theorists can use it to test alternative models of how black holes leak information. Experimentalists can compare their laboratory setups against the calculated limit.<\/p>\n The time travel math is settled. The harder physics is just beginning. The question now is whether nature permits any real version of the loop, and physicists have a much sharper tool with which to investigate it.<\/p>\n The study is published in the journal Physical Review Letters<\/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":"The scene from Interstellar is iconic: a father stranded in the future, tapping messages to his daughter, who…\n","protected":false},"author":2,"featured_media":672721,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[49],"tags":[199,79],"class_list":["post-672720","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\/672720","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=672720"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/672720\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media\/672721"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media?parent=672720"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/categories?post=672720"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/tags?post=672720"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}