doi.org/10.1103/gjfq-k9dv
Credibility: 959
#Negative time
Scientists have managed to confirm, in an impressive experiment, that “negative time” is real
This means that, under certain quantum conditions, light can appear to exit a group of atoms before it even enters them.
And the most curious thing: it was the atoms themselves that “told” this to the researchers.
The phenomenon occurs when photons (the particles of light) pass through a cloud of rubidium atoms cooled to extremely low temperatures.
Normally, light is expected to take some time to pass through matter, as it interacts with the atoms.
However, in some cases, the photons transmit the information in such a special way that the peak of the light wave exits on the other side of the cloud before it has finished entering.
This results in a “negative group delay”.
To better understand this, physicists measured not only the arrival time of the light, but also how long the atoms remained in an excited state (that is, with their electrons in higher energy levels after interacting with the photon).
Using a technique called “weak measurement,” which allows observing the system without disturbing it much, they discovered something surprising: the average time the atoms spent excited could also be negative.
This confirms that it’s not just a mathematical illusion.
The atoms really “say” that they spent a negative amount of time in the excited state when the photon passes through the cloud.
In other words, it seems that the atom releases energy a little before the photon finishes interacting completely with it.
Important to note: this does not violate the laws of physics, such as causality or the speed of light.
There is no information traveling faster than light, nor is there real-time travel.
This is a subtle quantum effect related to the wave-like behavior of light and quantum superpositions, where “dwelling time” can assume negative values “”in statistical averages, but without allowing paradoxical effects in the macroscopic world.
The experiment, led by researchers such as Aephraim Steinberg of the University of Toronto, helps deepen our understanding of how light and matter interact at the quantum level.
Phenomena like this show that the microscopic world holds surprises that challenge our everyday intuition about time and the sequence of events, but which make perfect sense within the rules of quantum mechanics.
In short, negative time is not science fiction: it is an experimentally confirmed reality, revealed by the delicate dance between light and atoms.
Physicists Confirm, But It’s Simpler Than It Seems
Sabine Hossenfelder, a physicist and science communicator, calmly analyzed the article and explained what really happened. The experiment was conducted by Ephraim Steinberg’s group at the University of Toronto. They sent photons (light particles) through a material containing atoms. Under certain conditions, the photons interact with these atoms in a special way.
What the researchers measured was the time the atoms remained “excited” (i.e., absorbing energy) while interacting with the light. At some points, this excitation time appeared as a negative value. This sounds strange, but it doesn’t mean that time is running backward.
In fact, “negative time” here is a mathematical way of describing the delay or advance of the wave group of light as it passes through the material. When light travels through a medium, such as glass or atomic vapor, it can undergo a phenomenon called “group delay.” In specific situations, this delay can be interpreted as if part of the process had occurred in negative time.
It’s important to highlight: this has nothing to do with the real time we live in. It’s not possible to use this to go back in time, send messages to yesterday, or anything like that. It’s a statistical and mathematical property related to the phase of light waves and how photons interact collectively with atoms.
Scientists wanted to better understand where this delay that light undergoes comes from. They mapped the excitation time of atoms and discovered that, in some cases, the calculations resulted in negative values. This helps explain the quantum behavior of light, but it remains within what we already know about quantum mechanics. It’s not a revolutionary discovery that breaks the laws of physics, but rather an interesting refinement in understanding the interactions between light and matter.
Sabine humorously reinforces that, although the term “negative time” attracts media attention, it should not be understood literally. It is more of a descriptive tool used by physicists to account for complex quantum phenomena. The experiment confirms something that was theoretically already expected, but has now been observed more clearly in the laboratory.
Science continues to advance in understanding the quantum world, but without violating the basic rules of the universe as we know it. Negative time is real in the very specific context of this experiment – but, for our daily lives, the clock continues to move forward, as always.
This story serves as a reminder of how catchy headlines can exaggerate scientific discoveries. What matters is the careful explanation: another step in the fascinating study of light and matter.
Published in 05/22/2026 18h05
Text adapted by AI (Grok) and translated via Google API in the English version. Images from public image libraries or credits in the caption. Information about DOI, author and institution can be found in the body of the article.
Reference article:
Original study: