{"id":472697,"date":"2026-02-13T16:21:09","date_gmt":"2026-02-13T16:21:09","guid":{"rendered":"https:\/\/www.newsbeep.com\/ca\/472697\/"},"modified":"2026-02-13T16:21:09","modified_gmt":"2026-02-13T16:21:09","slug":"controversy-that-has-divided-quantum-physics-since-1927-is-settled","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/ca\/472697\/","title":{"rendered":"Controversy that has divided quantum physics since 1927 is settled"},"content":{"rendered":"

A single trapped atom has been used to carry out Einstein\u2019s proposed test of the double-slit experiment, a challenge he believed could expose a flaw in quantum<\/a> mechanics by measuring its recoil<\/p>\n

The laboratory result was decisive: any attempt to track a particle\u2019s path destroys the interference pattern, confirming Niels Bohr\u2019s claim that wave-like and particle-like behavior cannot be observed at the same time.<\/p>\n

Atoms, slits, and recoils
\n
\n \"EarthSnap\"\/
\n<\/a><\/p>\n

Inside a modern experiment that released photons, the smallest units of light, one at a time instead of as a beam, a movable barrier actually recoiled each time a photon struck it.<\/p>\n

By controlling that recoil<\/a>, Jian-Wei Pan at the University of Science and Technology of China (USTC<\/a>) turned an old argument into data.<\/p>\n

Pan\u2019s team tuned how sharply the barrier\u2019s kick could be read, and the famous fringes faded on cue.<\/p>\n

Once the kick became informative enough, the pattern lost contrast, demonstrating Bohr\u2019s claim that gaining path information eliminates interference<\/a>.<\/p>\n

Einstein\u2019s movable slit<\/p>\n

Back in 1927 Brussels, Einstein sketched a slit<\/a> mounted on springs, so a passing photon would jolt it.<\/p>\n

Measuring the slit\u2019s recoil would reveal which route the photon took, even as the two-slit screen showed interference.<\/p>\n

A December 1926 letter<\/a> captured his stance on randomness, and it fueled the experiment he carried to Brussels.<\/p>\n

\u201cI am at all events convinced that He does not play dice,\u201d wrote Albert Einstein, rejecting the idea that nature is governed by irreducible randomness.<\/p>\n

Bohr\u2019s strict limit<\/p>\n

Bohr answered that the recoil measurement would not stay gentle, because the slit had to be movable.<\/p>\n

Any tighter readout of that kick would scramble another property, a rule later called complementarity<\/a>, wave and particle views cannot fully coexist.<\/p>\n

Instead of blaming clumsy tools, Bohr treated the tradeoff as baked into nature, not a temporary engineering problem.<\/p>\n

His reply turned Einstein\u2019s plan into a prediction in which clearer path clues would steadily erase the interference pattern.<\/p>\n

An atom as slit<\/p>\n

Recreating the movable slit required something far lighter than a metal plate, yet steady enough to control.<\/p>\n

A rubidium atom<\/a> filled the role when the USTC team held it in an optical tweezer, a laser trap that grips tiny objects.<\/p>\n

Cooling the atom close to its lowest motion kept its recoil honest, instead of being drowned out by random jitters.<\/p>\n

With that ultralight target, the experiment finally matched Einstein\u2019s premise, where the slit itself behaved like a quantum object.<\/p>\n

Tuning the atom\u2019s recoil<\/p>\n

Changing the trap\u2019s depth let the researchers decide how free the atom was to move during each hit.<\/p>\n

In a deeper trap, confinement rose and the atom gained more momentum uncertainty, the spread of possible push values.<\/p>\n

Loosening the trap did the opposite and made the recoil easier to read, because the atom started calmer.<\/p>\n

Such tuning gave the team a clean dial between vague recoil and sharp recoil, without swapping materials or geometry.<\/p>\n

Where interference goes<\/p>\n

On the detector screen, bright and dark stripes appeared when the photon had no clear path record.<\/p>\n

As recoil information sharpened, the stripes lost visibility, the contrast between bright and dark bands, until they nearly washed out.<\/p>\n

\u201cBy varying the trap depth of the optical tweezer, we dynamically tune the atom\u2019s intrinsic momentum uncertainty, thus enabling the observation of a gradual shift in the visibility of single-photon interference,\u201d wrote Pan.<\/p>\n

The smooth fade showed the old debate was never about opinion, but about what information a measurement creates.<\/p>\n

Entanglement sets visibility<\/p>\n

Behind that fading pattern sat a link between the photon and the moving slit, not just a blurry disturbance.<\/p>\n

When the photon kicked the atom, quantum entanglement, a shared state where outcomes stay connected, linked their motion.<\/p>\n

Stronger entanglement carried clearer path clues in the atom\u2019s motion, and reduced the overlap needed for interference.<\/p>\n

At the point where the atom became a trustworthy recorder, the experiment forced a choice between paths and stripes.<\/p>\n

Noise versus limits<\/p>\n

Even with careful tuning, not every loss of fringes came from quantum rules, because atoms can heat up.<\/p>\n

Random heating adds classical noise, extra jitter from ordinary motion, and can blur a pattern for the wrong reason.<\/p>\n

By measuring how heating changed the atom\u2019s motion, the team separated that blur from the recoil effect they wanted.<\/p>\n

The separation revealed a quantum-to-classical transition, where quantum behavior gave way to everyday statistics, once ordinary noise took over.<\/p>\n

Why an atom\u2019s recoil matters<\/p>\n

Beyond settling a 98-year argument, the setup gives researchers a controlled way to study what measurement does.<\/p>\n

Future runs at USTC can map the joint state directly and track decoherence, the gradual loss of quantum links to surroundings.<\/p>\n

Scaling the slit\u2019s mass upward should reveal when recoil becomes negligible, and when entanglement fades into plain noise.<\/p>\n

Such results could guide designs for quantum sensors and networks, where extra information often comes at a real cost.<\/p>\n

This single-atom remake turned a philosophical clash into a tunable system that shows how knowledge reshapes outcomes.<\/p>\n

As teams push the same control to heavier objects, the boundary between quantum and everyday physics should become easier to pin down.<\/p>\n

The study is published in 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":"A single trapped atom has been used to carry out Einstein\u2019s proposed test of the double-slit experiment, a…\n","protected":false},"author":2,"featured_media":472698,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[24],"tags":[49,48,314,66],"class_list":{"0":"post-472697","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-physics","8":"tag-ca","9":"tag-canada","10":"tag-physics","11":"tag-science"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/472697","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/comments?post=472697"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/472697\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media\/472698"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media?parent=472697"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/categories?post=472697"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/tags?post=472697"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}