A fundamental string plucked at the moment of the Big Bang doesn't just hum a single note — waves run along it, and occasionally tiny loops peel off. These loops, like tuning forks, begin to ring at their own frequency, producing a very high-pitched sound. On a cosmic scale, this 'sound' is a ripple in the fabric of spacetime, known as gravitational waves.
For a long time, it was thought that hearing this high-pitched ring was nearly impossible: the early universe was too 'hot' and viscous, and the loops quickly lost energy before they could really sound off. But the authors of the new work have shown that even under such conditions, the loops leave a noticeable trace. They derived simple formulas that allow for quick calculation of this trace across a wide range of string properties. It turns out that the characteristic peak at high frequencies, like a sharp spike on a spectrometer screen, should be discernible in many scenarios, not just rare exceptions.
This discovery is important for future experiments. If the high-frequency peak exists, it could be captured by new detectors currently being designed. Such a signal would be direct proof that in the first moments of the universe's life, space was not smooth but riddled with fine 'wrinkles'. And then we could hear the very sound of the cosmos's birth.
as written by the authors arXiv:2605.22944
We derive analytical approximations to describe the ultra-high-frequency secondary peak of the stochastic gravitational wave background generated by cosmic strings that is sourced by loops created in the friction-dominated era. We show that these approximations provide a very good description of the contribution of the friction-era loops over the relevant frequency range and for a broad range of cosmic string parameters, thus enabling a fast and accurate characterization of this signature. We also use these approximations to uncover the full parameter range in which this ultra-high-frequency peak should be distinguishable on the stochastic gravitational wave background spectrum and show that it should be present in a broader range of high-energy physics scenarios than originally reported in~\cite{Mukovnikov:2024zed}.
A cosmic string as thick as a proton would weigh as much as a mountain range if it were a kilometer long.
In Arthur C. Clarke's novel 'The Fountains of Paradise', engineers use a cosmic string as the basis for a space elevator.