The very first moment of the universe's existence is like a taut string suddenly struck. It vibrated, and those oscillations froze into galaxies and voids. But physicists suspect there were other vibrations — fast, local, almost like a drumroll against a slow melody.

These are oscillons — clumps of energy that could have appeared during inflation (the rapid expansion of the universe). They resemble bubbles in boiling water: they form, live for a while, and collapse. The authors of a new study examined how such bubbles arise in a particular version of the inflationary potential (the mathematical description of the field that drove expansion). Using Floquet analysis (a method that identifies instability zones), they found conditions under which oscillons actually form and numerically calculated their shape. It turned out that these objects can live quite long — from a thousand to tens of thousands of characteristic periods.

When an oscillon disappears, it shakes spacetime, generating gravitational waves. This process is called the "poltergeist mechanism"—an invisible force leaves a real trace. The calculated spectrum showed a peak at a frequency of about 2.5×10¹⁰ Hz (25 billion oscillations per second) with an amplitude a billion times weaker than the cosmic microwave background. For comparison, this is 250 times higher than the frequency of a typical microwave oven, but instead of heating food, the wave stretches and compresses space itself.

Such a signal does not violate constraints from primordial nucleosynthesis (the formation of the first nuclei), but if the model parameters are slightly shifted, the signal could become too strong. This provides a tool for testing hypotheses about the early universe. By catching such ripples, we could hear the echo of that very first strike on the string.