Scientists have measured what appears to be a “negative” amount of time in a quantum physics experiment, according to a study published in Physical Review Letters.
The findings do not mean researchers have discovered time travel. Instead, scientists say the experiment reveals another unusual feature of quantum mechanics, the branch of physics that studies matter and energy at extremely small scales.
Researchers compared the strange effect to Odysseus’s journey in The Odyssey. In the ancient Greek story, Odysseus spends years stranded on the island of Calypso, yet somehow returns home sooner than expected. Scientists say quantum particles can behave in similarly puzzling ways.
Photons passed through rubidium atoms
The experiment used photons, the particles that make up light. Researchers fired single photons through a cloud of rubidium atoms under carefully controlled conditions.
The photons were tuned to a precise energy level that matched the atoms’ resonance frequency. This allowed the photons to temporarily transfer their energy into the atomic cloud before emerging again.
Most photons entering the cloud scattered in random directions and failed to pass through. But the few photons that successfully crossed the cloud produced an unexpected result.
Scientists have measured what appears to be “negative time” in a quantum physics experiment.
Researchers fired photons through a cloud of rubidium atoms and found the particles seemed to spend less than zero time inside it. pic.twitter.com/YnWfBeWyKq— Tom Marvolo Riddle (@tom_riddle2025) May 6, 2026
Using the photons’ average entry time, researchers calculated when they should emerge if they travelled normally at the speed of light. Instead, the photons appeared much earlier than expected. The measurements suggested the photons had spent a negative amount of time inside the atomic cloud.
Earlier studies questioned the effect
Physicists first observed the strange timing effect in experiments conducted in 1993. Many researchers later argued that the result was only an illusion caused by the front edge of the photon’s long light pulse passing through the cloud while the rest scattered away.
But physicist Aephraim Steinberg and his team wanted to test whether the effect could be measured directly inside the atomic cloud itself.
The challenge was that observing quantum systems too precisely changes their behavior, a phenomenon linked to the Quantum Zeno Effect. To avoid disturbing the photons, researchers used a technique known as weak measurement.
Weak measurements confirmed a negative time
Researchers passed a separate weak laser beam through the rubidium cloud and monitored tiny changes in the laser’s light. These changes revealed whether the atoms temporarily stored the photon’s energy.
Single measurements provided only rough information. But after millions of repeated experiments, researchers calculated the photons’ dwell time with high precision.
The results matched the earlier timing measurements. The weak measurements also showed a negative dwell time inside the atomic cloud.
Researchers say the findings suggest the effect is not simply a measurement illusion. Instead, it appears to be a real and measurable property of quantum systems.
Although the experiment does not break the laws of physics, scientists say it highlights how differently time can behave in the quantum world compared with ordinary human experience.
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