In the infant universe, right after the Big Bang, space was expanding rapidly, and the vacuum resembled a superheated liquid. When 'boiling' began, bubbles of true vacuum emerged. Expanding at the speed of light, they triggered gravitational waves — tremors of space itself that have reached us.

The problem is that old calculations of these waves depended on the choice of coordinates, like a shadow cast by a lamp. The authors applied a mathematical trick from neutrino physics — the Nielsen identity — and got rid of this ambiguity. Now, within the Standard Model of elementary particles, the birth of bubbles is described uniformly.

This method will allow a more accurate reconstruction of the cosmic boiling signal and, perhaps, let us hear the echo of creation.