Summary in seconds:
Light seems simple: it helps us see, powers our technology, and fills our world with color. But under extreme conditions, light can behave in ways that sound more like science fiction than science fact. At temperatures close to absolute zero1, researchers have discovered that photons can merge into a strange new state of matter—flowing together like a ghostly liquid.
Light is one of the most familiar phenomena in our daily lives, yet its true nature remains one of the deepest puzzles in physics. At its core, light is an electromagnetic wave that requires no medium to travel—it can move freely through the vacuum of space. But light is also a duality: sometimes it behaves as a wave, spreading and interfering, and at other times it behaves like a particle, carried by discrete packets of energy known as photons. This wave–particle duality lies at the heart of modern physics, and it becomes especially fascinating when we ask: What happens to light at absolute zero?
Absolute Zero and the Strange World of Quantum States
Absolute zero (0 Kelvin, or –273.15°C) represents the lowest possible temperature in the universe. At this extreme, particles lose nearly all kinetic energy and enter a state of near-complete stillness. While scientists have never quite reached absolute zero, they have come close enough to study extraordinary states of matter that emerge only in this frozen realm.
One such state is the Bose-Einstein condensate (BEC), first predicted in 1924 by Albert Einstein2 and Satyendra Nath Bose3. In a BEC, individual particles lose their separate identities and merge into a single quantum state, behaving collectively as if they were one “super-particle.” 4 Originally created in the laboratory with ultra-cold gases in 1995, this state was long thought impossible for light itself. After all, photons are massless and tend to disappear when cooled.
Can Light Condense?
Surprisingly, researchers have shown that photons can form a Bose-Einstein condensate. In 2010, physicists at the University of Bonn—including Jan Klärs, Julian Schmitt, Frank Vewinger, and Martin Weitz—achieved a remarkable breakthrough: they managed to trap light in a tiny mirrored cavity filled with dye molecules. Each time a photon bounced between the mirrors, it exchanged energy with the dye molecules, gradually cooling while still remaining confined. To the astonishment of many, the photons condensed—not at absolute zero, but at room temperature.
This new state of matter has been described as a “super-photon” 5: countless light particles behaving as a single, coherent quantum wave. The experiment not only overturned the assumption that light could never condense, but also demonstrated the unique way photons straddle the line between particles and waves.
Light as a Liquid – and Beyond
What does this mean for light at absolute zero? Theoretically, if photons can condense into a BEC at room temperature under the right conditions, then approaching absolute zero would only deepen this quantum fluid-like behavior. In such a state, light would no longer simply shine or scatter—it would flow, almost like a liquid, with particles locked in step as one.
Recent theoretical work, such as that by Alex Kruchkov6 at École Polytechnique Fédérale de Lausanne7 (EPFL), has even suggested that photons could be condensed and controlled in one dimension, offering new tools for quantum technologies. Such control over light holds enormous promise for fields like quantum computing8, where information could be processed and transmitted with unprecedented efficiency.
Why It Matters
The condensation of light into a Bose-Einstein state reveals a profound truth: even the most familiar parts of our world can behave in radically different ways when pushed to extreme limits. By chilling light to act like matter, physicists are uncovering new ways to bend its behavior, opening doors to revolutionary applications—from next-generation lasers to quantum computers.
So, can light become a liquid at absolute zero? In a sense, yes. Under the right conditions, photons can merge into a single quantum entity, behaving less like beams of energy and more like a flowing, unified fluid. It is a reminder that the universe still holds surprises, even in something as everyday as the light that reaches our eyes.
Notes:
1. Absolute Zero – The lowest possible temperature (0 Kelvin or –273.15 °C), where all classical motion of particles theoretically stops.
2. Einstein, Albert – German-born theoretical physicist who developed the theory of relativity and contributed foundational work to quantum mechanics.
3. Bose, Satyendra Nath – Indian physicist who pioneered quantum statistics, co-developing the Bose–Einstein statistics that describe bosons.
4. Super Particle – A hypothetical particle formed when many particles occupy the same quantum state, as in a Bose–Einstein condensate.
5. Super Photon – A collective state of light where many photons act together as if they were one particle, often studied in quantum optics and condensates.
6. Kruchkov, Alex – A physicist known for theoretical work on Bose–Einstein condensation of light and quantum many-body systems.
7. École Polytechnique Fédérale de Lausanne (EPFL) – A leading Swiss university specializing in science, engineering, and technology research.
8. Quantum Computing – An emerging field of computation that uses quantum bits (qubits) to perform calculations far faster than classical computers for certain tasks.
Sources
* “Light.” Wikipedia, December 4, 2023.
https://en.wikipedia.org/wiki/Light
* Kruchkov, Alex. “One-dimensional Bose-Einstein Condensation of Photons in a Microtube.” Physical Review A, April 11, 2016
https://journals.aps.org/pra/abstract/10.1103/PhysRevA.93.043817
* Moskowitz, Clara. “Einstein’s ‘Biggest Blunder’ Turns Out to be Right.” Space.com, November, 2024.
https://www.space.com/9593-einstein-biggest-blunder-turns.html
* Duan, Daniel. “Liquid Light Observed at Room Temperature for the First Time.” Labroots, June 26, 2025.