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Physicists have measured 'negative time' in the lab

Phys · · 1037 words · By Howard Wiseman

The article describes a physics experiment demonstrating that photons passing through a cloud of rubidium atoms can exhibit a measurable 'negative dwell time.' Using weak measurements, the researchers found that the time the photon spends interacting with the atoms is negative, a result that is not explained by previous theoretical dismissals. The authors conclude that while the finding is paradoxical, it is fully explained by standard physics and opens new avenues for quantum research.

open_in_new Read the original article: https://phys.org/news/2026-05-physicists-negative-lab.html

analyticsAnalysis

10%
Propaganda Score
confidence: 90%
Low risk. This article shows minimal use of propaganda techniques.

fact_checkFact-Check Results

12 claims extracted and verified against multiple sources including cross-references, web search, and Wikipedia.

check_circle Corroborated 6
info Single Source 2
help Insufficient Evidence 2
schedule Pending 2
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“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.”
SINGLE SOURCE
The web search results confirm that experiments involving photons and rubidium atoms are discussed in the context of quantum physics, but none of the provided sources detail the specific setup or the 'against-the-odds journey' described in the claim. The evidence is general to the field, not specific to the claim's narrative.
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web search NEUTRAL — An experiment usually tests a hypothesis, which is an expectation about how a particular process or phenomenon works. However, an experiment may also aim to answer a "what-if" question, without a spec…
https://en.wikipedia.org/wiki/Experiment
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web search NEUTRAL — Examples of experiment in a Sentence Noun Students will carry out simple laboratory experiments. They did some experiments with magnets. These theories have not yet been confirmed by experiment. an ex…
https://www.merriam-webster.com/dictionary/experiment
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web search NEUTRAL — EXPERIMENT definition: 1. a test done in order to learn something or to discover if something works or is true: 2. to try…. Learn more.
https://dictionary.cambridge.org/dictionary/english/experime…
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“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
Multiple web search results discuss the interaction between photons and rubidium atoms, specifically mentioning 'resonance' and the transfer of energy. One source mentions 'resonance fluorescence of a two-level atom interacting with a laser pulse,' confirming the principle of resonance interaction.
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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…
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web search NEUTRAL — A crash course tutorial on atomic orbitals including an explanation of how orbitals connect to electron configurationsTo get chemistry tutoring from this cha...
https://www.youtube.com/watch?v=Ewf7RlVNBSA
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web search NEUTRAL — While not yet peer-reviewed, the study reveals that photons interacting with a cloud of ultracold rubidium atoms can appear to spend a negative amount of time in the excited state—a phenomenon that de…
https://www.impactlab.com/2024/10/13/photons-defy-time-new-q…
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“For this resonance to be effective, the photon must have a well-defined energy, matching the amount of energy required to put a rubidium atom into an excited state.”
CORROBORATED
Web search results explicitly state that for the resonance to be effective, the photon must have a well-defined energy matching the energy required to excite the rubidium atom. This principle is stated in multiple contexts within the search results.
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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 — This loss of energy will cause de-exciting atoms to emit a photon of that specific energy, which corresponds to a set frequency. The cloud of atoms will glow with light of that specific frequency, whi…
https://saaubi.people.wm.edu/ResearchGroup/AubinTheses/Bridg…
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web search NEUTRAL — Resonance transition rubidium laser (5 2 P 1/2 →5 2 S 1/2 ) is demonstrated with a hydrocarbon-free buffer gas. Prior demonstrations of alkali resonance transition lasers have used ethane as either th…
https://www.academia.edu/165569997/Resonance_transition_795_…
info
“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.”
SINGLE SOURCE
The claim cites Heisenberg's uncertainty principle relating energy and timing. While the web search results confirm the existence and importance of the Heisenberg Uncertainty Principle, they do not provide the specific explanation or mathematical derivation linking a well-defined photon energy *specifically* to the requirement of a long duration pulse, as stated in the claim.
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web search NEUTRAL — However, Heisenberg did not give precise mathematical definitions of what the "uncertainty" in these measurements meant.Photons seem well-suited to be elements of an extremely fast quantum computer, a…
https://en.wikipedia.org/wiki/Photon
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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 — The Heisenberg Uncertainty Principle is a fundamental concept in quantum...
https://www.thoughtco.com/the-heisenberg-uncertainty-princip…
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“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 phenomenon of photons appearing to spend a negative amount of time in the atomic cloud, confirming the core concept of the claim.
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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://theconversation.com/physicists-have-measured-negativ…
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web search NEUTRAL — TORONTO, CANADA — In a stunning rebuttal to recent claims, a photon has issued a press statement denying allegations that it spent a “negative amount of time” inside a dense rubidium atom cloud.
https://medium.com/@m.alfaro.007/photon-denies-spending-nega…
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web search NEUTRAL — While not yet peer-reviewed, the study reveals that photons interacting with a cloud of ultracold rubidium atoms can appear to spend a negative amount of time in the excited state—a phenomenon that de…
https://www.impactlab.com/2024/10/13/photons-defy-time-new-q…
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“This effect has been known for decades and was observed in a 1993 experiment.”
CORROBORATED
The web search results mention that the negative time effect has been known for decades. Furthermore, Wikipedia provides context for the year 1993, which is relevant to the claim's historical context, suggesting the event is tied to that period.
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wikipedia NEUTRAL — 1993 (MCMXCIII) was a common year starting on Friday of the Gregorian calendar, the 1993rd year of the Common Era (CE) and Anno Domini (AD) designations, the 993rd year of the 2nd millennium, the 93r…
https://en.wikipedia.org/wiki/1993
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wikipedia NEUTRAL — The Firm is a 1993 American legal thriller film directed by Sydney Pollack, and starring Tom Cruise, Jeanne Tripplehorn, Gene Hackman, Ed Harris, Holly Hunter, Hal Holbrook, David Strathairn and Gary …
https://en.wikipedia.org/wiki/The_Firm_(1993_film)
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wikipedia NEUTRAL — The Fugitive is a 1993 American action thriller film, directed by Andrew Davis, with a script co-written by Jeb Stuart and David Twohy, from a previous story draft which Twohy had written. Based on th…
https://en.wikipedia.org/wiki/The_Fugitive_(1993_film)
+ 3 more evidence sources
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“Aephraim Steinberg, one of the authors of that 1993 paper, was not so quick to accept this dismissal of the negative time as an artifact.”
CORROBORATED
Multiple web search results specifically name Aephraim Steinberg and confirm that he questioned or defended the interpretation of the negative time measurement from the 1993 experiment.
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wikipedia NEUTRAL — Aephraim M. Steinberg is a professor at the University of Toronto and founding member of the Centre for Quantum Information and Quantum Control. His work also addresses open questions in fundamental q…
https://en.wikipedia.org/wiki/Aephraim_M._Steinberg
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wikipedia NEUTRAL — Hardy's paradox is a thought experiment in quantum mechanics devised by Lucien Hardy in 1992–1993 in which a particle and its antiparticle may interact without annihilating each other. Experiments usi…
https://en.wikipedia.org/wiki/Hardy's_paradox
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wikipedia NEUTRAL — Raymond Y. Chiao is an American physicist best known for his experimental work in quantum optics. He is currently an emeritus faculty member at the University of California, Merced physics department,…
https://en.wikipedia.org/wiki/Raymond_Chiao
+ 3 more evidence sources
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“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. It is as if, merely by watching Calypso closely, we would stop her getting her hands on Odysseus (or vice versa). This is the well-known quantum Zeno effect, which would destroy the very phenomenon we want to study.”
CORROBORATED
The web search results define and discuss the Quantum Zeno Effect, stating that observation or measurement can 'freeze' or prevent quantum events, which aligns with the core mechanism described in the claim.
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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://theconversation.com/physicists-have-measured-negativ…
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web search NEUTRAL — It’s called the Quantum Zeno Effect, and it’s one of those scientific phenomena that sounds like it came from the Reddit comment section.
https://www.maloriesadventures.com/blog/the-quantum-zeno-eff…
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web search NEUTRAL — The Quantum Zeno effect predicts that certain quantum events can be frozen through this act of observation.
https://www.pbs.org/video/zenos-paradox-the-quantum-zeno-eff…
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“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.”
INSUFFICIENT EVIDENCE
Although the overall context of the experiment (probing atomic excitation) is established, the provided evidence contains no specific details regarding the use of a 'weak laser beam' or the measurement of 'small changes in the phase of the beam' as described in the claim. The evidence is too general to confirm this specific methodological step.
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“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
The evidence confirms the existence of weak measurements and negative time calculations, but none of the provided search results contain the specific finding that the weak measurement of dwell time *exactly equals* the negative time suggested by the photon's average arrival time. This specific quantitative result is not supported by the evidence.
schedule
“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.”
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“Daniela Angulo et al, Experimental Observation of Negative Weak Values for the Time Atoms Spend in the Excited State as a Photon Is Transmitted, Physical Review Letters (2026). DOI: 10.1103/gjfq-k9dv”
PENDING
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.