Nothingness that has the potential to be anything

A recent example was published in 2025 by researchers at the European X-ray and Free Electron Laser Facility near Hamburg, among other institutions. They cooled iodopyridine, an organic molecule made up of 11 atoms, to almost absolute zero, then hammered it with a laser pulse to break its atomic bonds. The team found that the motions of the liberated atoms were correlated, indicating that despite its cooled state, the iodopyridine molecule was vibrating. “This was not the main goal of the experiment initially,” said Rebecca Ball, an experimental physicist at the facility. “It’s basically something we found.”

Perhaps the best-known effect of zero-point energy in a field is that predicted by Hendrik Casimir in 1948, hinted at in 1958, and observed conclusively in 1997. Two plates of non-electrically charged matter—which Casimir envisioned as parallel metal sheets, although other shapes and materials would do so—exert a force on each other. The plates would act as a kind of guillotine for the electromagnetic field, cutting off long-wavelength oscillations in a way that would deflect zero-point energy, Casimir said. According to the most plausible explanation, the energy outside the plates is higher than the energy between the plates, a difference that pulls the plates together.

Quantum field theorists usually describe fields as a set of oscillators, each of which has its own zero point energy. There are an infinite number of oscillators in the field, so the field must contain an infinite amount of zero point energy. When physicists realized this in the 1930s and 1940s, they initially doubted the theory, but they soon came to terms with infinity. In physics – or most physics, anyway – the energy differences are what really matter, and with caution physicists can subtract an infinite number from the other to see what remains.

But this does not apply to gravity. As early as 1946, Wolfgang Pauli realized that an infinite or at least enormous amount of zero-point energy must create a gravitational field strong enough to blow up the universe. “All forms of energy are attracted,” said Sean Carroll, a physicist at Johns Hopkins University. “This includes vacuum energy, so you can’t ignore it.” Why this energy remains muted by gravity still mystifies physicists.

In quantum physics, the zero-point energy of a vacuum is more than just a constant challenge, more than the reason you can never empty a box. Instead of being something where nothing should be, it is nothing filled with the potential to be anything.

“The interesting thing about a vacuum is that every field, and therefore every particle, is represented in some way,” Meloni said. Even if there is not a single electron, the vacuum contains “electrons”. Zero point energy in a vacuum is the combined effect of every possible form of matter, including forms we have not yet discovered.

The original story is reprinted with permission from Quanta Magazine, an editorially independent magazine Simmons Foundation Its mission is to enhance public understanding of science by covering research developments and trends in mathematics, physical and life sciences.