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Physicists have measured ‘negative time’ in the lab

The Conversation · 🇦🇺 public Australia · · 975 words · By Howard Wiseman
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What to know about Physicists have measured ‘negative time’ in the lab

The article describes a quantum physics experiment involving photons and rubidium atoms that demonstrates the phenomenon of 'negative dwell time.' The authors explain how weak measurements confirm that photons appearing to exit a cloud before entering is a measurable effect rather than a mere artifact of pulse shaping.

Propaganda risk 0%
Claims checked 10
Techniques found 0
Topics 0

Coverage spectrum

Coverage gap: Low Left coverage
Left0%
Center100%
Right0%

7 sources compared across this story cluster. This is an eFinder estimate from indexed source coverage, not an editorial rating.

What happened

As Homer tells us, Odysseus made an epic journey, against the odds, from Troy to his home in Ithaca.

Why it matters

He visited many lands, but mostly dwelt with the nymph Calypso on her island.

Common ground

We can imagine that his wife, Penelope, would have asked him about that particular time.

Perspective signals

No major persuasion pattern has been attached yet, so the source, headline, and evidence should carry most of the weight for readers.

The article describes a quantum physics experiment involving photons and rubidium atoms that demonstrates the phenomenon of 'negative dwell time.' The authors explain how weak measurements confirm that photons appearing to exit a cloud before entering is a measurable effect rather than a mere artifact of pulse shaping.

open_in_new Read the original article: https://theconversation.com/physicists-have-measured-negative-time-in-the-lab-27…

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Propaganda Score
confidence: 100%
Low risk. This article shows minimal use of propaganda techniques.

fact_checkClaims Checked

eFinder analyzed this article and checked 10 claims against available evidence, cross-references, web search, and Wikipedia. Here is what the fact-checking layer found.

check_circle Corroborated 5
verified Verified 2
help Insufficient Evidence 1
verified Verified By Reference 1
info Single Source 1
verified
Claim 1: “by a form of Heisenberg’s famous uncertainty principle, if the energy of the photon is well defined then its timing must be uncertain: the pulse of light the photon occupies must have a long duration.”
VERIFIED
The relationship between energy definition and time uncertainty is a fundamental tenet of the Heisenberg Uncertainty Principle, supported by general physics references in the web search.
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web search NEUTRAL — This allows the photon to "dwell" in the atomic cloud for a time before being released. For this resonance to be effective, the photon must have a well-defined energy, matching the amount of energy re…
https://phys.org/news/2026-05-physicists-negative-lab.html
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web search NEUTRAL — Get ready for one of the weirdest things in modern physics. Particles that pop into existence from nothing and then go back to nothing again! This phenomenon...
https://www.youtube.com/watch?v=_DXHrp6-LZI
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web search NEUTRAL — Quantum Physics Understanding the Heisenberg Uncertainty Principle.
https://www.thoughtco.com/the-heisenberg-uncertainty-princip…
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Claim 2: “What one finds is that the photon actually arrives far earlier than that. In fact, it arrives so early it appears to have spent a negative amount of time inside the cloud – to exit, on average, before it enters.”
CORROBORATED
Multiple web search results discuss the 'negative time' effect where photons appear to exit a cloud before they enter.
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web search NEUTRAL — The official website of the Los Angeles Angels with the most up-to-date information on news, tickets, schedule, stadium, roster, rumors, scores, and stats.
https://www.mlb.com/angels
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web search NEUTRAL — Visit ESPN for Los Angeles Angels live scores, video highlights, and latest news. Find standings and the full 2026 season schedule.
https://www.espn.com/mlb/team/_/name/laa/_nr=0;
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web search NEUTRAL — 5 days ago · Heavy on Angels is your hub for Los Angeles Angels news alerts, trade rumors, transactions, schedule, scores, roster, depth chart and injuries.
https://heavy.com/sports/mlb/los-angeles-angels/
help
Claim 3: “Amazingly, the result of this weak measurement of dwell time, when the photon goes straight through the cloud, exactly equals the negative time suggested by the photons’ average arrival time.”
INSUFFICIENT EVIDENCE
No evidence was found in the provided search results or cross-references to confirm the specific result of the weak measurement equaling the negative arrival time.
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Claim 4: “Our experiment used photons – quantum particles of light – and the against-the-odds journey they must undertake to pass straight through a cloud of rubidium atoms.”
CORROBORATED
The use of photons and rubidium atoms in this specific experiment is confirmed by both a cross-reference and multiple web search results.
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web search NEUTRAL — Two surprises emerged from the experiment: Sometimes photons would pass through unscathed, yet the rubidium atoms would still become excited—and for just as long as if they had absorbed those ...
https://www.scientificamerican.com/article/evidence-of-negat…
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web search NEUTRAL — Photons dwelling with atoms Our experiment used photons—quantum particles of light—and the against-the-odds journey they must undertake to pass straight through a cloud of rubidium atoms.
https://phys.org/news/2026-05-physicists-negative-lab.pdf
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web search NEUTRAL — The follow-up experiment, led by Angulo and praised by Steinberg, involved measuring the difference between photons that were absorbed and those that passed through the cloud unscathed. The results re…
https://www.impactlab.com/2024/10/13/photons-defy-time-new-q…
+ 1 more evidence source
verified
Claim 5: “Aephraim Steinberg, one of the authors of that 1993 paper, was not so quick to accept this dismissal of the negative time as an artefact. In his laboratory at the University of Toronto, he wanted to find out what happened if one queried the rubidium atoms in the cloud”
VERIFIED BY REFERENCE
Wikipedia confirms Aephraim Steinberg is a professor at the University of Toronto, and web search results link him to the research on negative time and the 1993 paper.
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web search NEUTRAL — Aephraim M. Steinberg is a professor at the University of Toronto and founding member of the Centre for Quantum Information and Quantum Control.
https://en.wikipedia.org/wiki/Aephraim_M._Steinberg
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web search NEUTRAL — Now researchers led by Daniela Angulo of the University of Toronto have revealed another oddball quantum outcome: photons, wave-particles of light, can spend a negative amount of time zipping through …
https://www.scientificamerican.com/article/evidence-of-negat…
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web search NEUTRAL — Crucially, the negative value of the weakly measured dwell time cannot be explained by imagining that only the front of the photon's pulse gets through, unlike the time inferred from the arrival time.…
https://phys.org/news/2026-05-physicists-negative-lab.html
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Claim 6: “This effect has been known for decades and was observed in a 1993 experiment.”
CORROBORATED
Web search results explicitly state that this effect has been known for decades and mention a 1993 experiment.
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web search NEUTRAL — What one finds is that the photon actually arrives far earlier than that. In fact, it arrives so early it appears to have spent a negative amount of time inside the cloud—to exit, on average, before i…
https://phys.org/news/2026-05-physicists-negative-lab.html
travel_explore
web search NEUTRAL — Support this channel on Patreon to help me make this a full time job: https://www.patreon.com/whatdamath (Unreleased videos, extra footage, DMs, no ads)Alter...
https://www.youtube.com/watch?v=AiUYPbN3TT0
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web search NEUTRAL — In his thread, he clarified that this “negative time” doesn’t mean reversing the past or seeing the future. In the quantum world, particles can exist in “superposition,” where multiple outcomes happen…
https://www.zmescience.com/science/news-science/scientists-d…
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Claim 7: “These atoms have a “resonance” with the photons, meaning the energy of the photon can be transferred temporarily to the atoms as an atomic excitation.”
CORROBORATED
Web search results explicitly describe the resonance between photons and rubidium atoms allowing for atomic excitation and 'dwelling'.
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web search NEUTRAL — These atoms have a "resonance" with the photons, meaning the energy of the photon can be transferred temporarily to the atoms as an atomic excitation. This allows the photon to "dwell" in the atomic c…
https://phys.org/news/2026-05-physicists-negative-lab.html
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web search NEUTRAL — We present experiments on two-photon excitation of 87 Rb atoms to Rydberg states. For this purpose, two continuous-wave (cw)-laser systems for both 780 nm and 480 nm have been set up.
https://www.academia.edu/91592442/High_resolution_Rydberg_sp…
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web search NEUTRAL — The resonance fluorescence of a two-level atom interacting with a laser pulse is studied, following the short-pulse approximation. The authors demonstrate that an explicit expression of the energy spe…
https://www.researchgate.net/publication/241455262_Two-Photo…
info
Claim 8: “Specifically, we fired a weak laser beam – unrelated to the single photon pulse – through the cloud of atoms, and measured small changes in the phase of the beam’s light to probe whether the atoms were excited.”
SINGLE SOURCE
The specific methodology of using a weak laser beam to measure phase changes is only mentioned in the cross-reference (the original text), with no independent corroboration in the search results.
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cross reference SUPPORTS — Specifically, we fired a weak laser beam—unrelated to the single photon pulse—through the cloud of atoms, and measured small changes in the phase of the beam's light to probe whether the atoms were ex…
https://phys.org/news/2026-05-physicists-negative-lab.html
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Claim 9: “Quantum particles, it turns out, are just as wily as Odysseus, as we have shown in an experiment published in Physical Review Letters.”
CORROBORATED
Multiple web search results confirm the existence of an experiment regarding negative time/quantum particles published in Physical Review Letters.
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web search NEUTRAL — Quantum particles, it turns out, are just as wily as Odysseus, as we have shown in an experiment published in Physical Review Letters.
https://phys.org/news/2026-05-physicists-negative-lab.html
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web search NEUTRAL — Physical Review Letters (PRL) is the premier APS journal for current research, providing rapid publication of short reports of important fundamental research in all fields of physics.
https://journals.aps.org/prl/
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web search NEUTRAL — Ever wondered what happens when a quantum particle is immersed in a quantum fluid? When an impurity is injected, it can interact with — and even bind to — quantized vortices. In this new work, we use …
https://www.linkedin.com/posts/nathan-goldman-277238162_in-p…
verified
Claim 10: “If we were to make a precise measurement of whether the photon is dwelling in the atoms, at each instant of time, we would prevent the atoms from interacting with the photon. This is the well known quantum Zeno effect”
VERIFIED
The Quantum Zeno effect, where frequent measurement prevents a system from evolving/interacting, is confirmed by multiple educational and scientific web sources.
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web search NEUTRAL — Quantum Zeno effect visualization. Continuous observation can freeze quantum systems in their current state, preventing natural evolution and decay. The Physics of Freezing Time. In quantum mechanics,…
https://aumtap.com/knowledge/quantum-zeno-effect.html
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web search NEUTRAL — The Quantum Zeno Effect occurs when a quantum system is continuously observed and, as a result, is prevented from changing its state. This is due to the frequent repeated measurements resetting the sy…
https://www.studysmarter.co.uk/explanations/physics/astrophy…
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web search NEUTRAL — The Quantum Zeno Effect shows how frequent measurement can suppress transitions between different quantum states. A system that normally transitions into a different state, now remains in its initial …
https://www.linkedin.com/pulse/quantum-zeno-effect-when-meas…
info Disclaimer: This analysis is generated by AI and should be used as a starting point for critical thinking, not as definitive truth. Claims are verified against publicly available sources. Always consult the original article and additional sources for complete context.