Researchers at the European X-Ray Free-Electron Laser Facility (European XFEL) near Hamburg, Germany, observed unexpected atomic vibrations in a molecule of iodopyridine cooled to near absolute zero, a finding published in 2025. The team, utilizing an intense laser pulse to break the chemical bonds of the 11-atom molecule, discovered that the resulting freed atoms continued to move in a correlated fashion, indicating residual vibrational energy despite the extreme cold.
The experiment wasn’t initially designed to detect these vibrations, according to Rebecca Boll, an experimental physicist at the facility. “It’s basically something that we found,” she said. The European XFEL, a 3.4 kilometer-long research facility, generates extremely intense X-ray flashes used to study atomic details of matter, including viruses and chemical reactions. It delivers approximately 27,000 X-ray flashes per second, with a brilliance exceeding conventional X-ray sources by a factor of a billion, according to DESY, the German Electron Synchrotron, which operates the facility.
The observed phenomenon relates to the concept of zero-point energy, a fundamental aspect of quantum mechanics. Quantum field theory posits that even in a vacuum, fields are not truly empty but contain inherent energy due to constant quantum fluctuations. This energy, known as zero-point energy, implies that a system never reaches absolute stillness, even at the lowest possible temperature. Hendrick Casimir predicted an effect of this energy in 1948, with definitive observation occurring in 1997, demonstrating a measurable force between uncharged plates due to fluctuations in the electromagnetic field.
Physicists grapple with the implications of infinite zero-point energy. While the concept initially raised doubts, they learned to manage the mathematical infinities by focusing on energy differences. However, the effect of this energy on gravity remains a significant puzzle. Wolfgang Pauli, as early as 1946, recognized that a substantial amount of zero-point energy should generate a powerful gravitational field, potentially destabilizing the universe. Sean Carroll, a physicist at Johns Hopkins University, explained, “All forms of energy gravitate,” meaning vacuum energy cannot be ignored in gravitational calculations.
The vacuum, in quantum physics, isn’t truly empty but is imbued with the potential for existence. Physicist Pierre Milonni described it as containing “electronness” even without the presence of electrons, representing all possible forms of matter, including those yet undiscovered. The zero-point energy of the vacuum, is a composite of every potential particle and interaction. The European XFEL’s ability to generate intense X-ray flashes allows researchers to probe these fundamental aspects of reality at unprecedented levels of detail.
The facility, a collaboration between multiple nations, began user experiments in September 2017. The recent iodopyridine experiment adds to a growing body of research exploring the nature of the quantum vacuum and its implications for our understanding of the universe.
