A pot of water sits on the stove. When the water boils, it suddenly turns into steam: that's a phase transition. In the first moments after the Big Bang, the Universe underwent something similar, but it wasn't liquid and gas that changed, but fundamental fields. This violent process should have created ripples in the fabric of space — gravitational waves that still wander through the cosmos as a background hum.

Future space-based detectors LISA and DECIGO are trying to catch this hum. But hearing the noise isn't enough: you need to understand what kind of "melody" it's playing. The authors modeled the signal from such a transition as a broken line with a bump: a peak at a certain frequency and two kinks at the edges. For LISA, the peak was set at a very low frequency (one three-hundredth of a hertz (a wave would stretch over hours), and for DECIGO) at one hertz (one oscillation per second). Then they checked how accurately the instruments could recover the parameters of this broken line.

The result was instructive. Both detectors will accurately determine where the peak is and how high it is. But the slope of the lines before and after the peak, as well as the exact location of the kink: these are much more elusive parameters. For DECIGO, if the interfering signal from stellar binaries is not completely removed, the error in determining the slope will grow by a factor of 1.5. It's like trying to discern the timbre of a violin when a whole orchestra is playing nearby. So it's important not only to detect the very fact of the early Universe's "boiling," but also to be able to clean the recording from extraneous noise.