The early universe underwent a rapid expansion — inflation. In a tiny fraction of a second, minuscule quantum jitters were stretched to galactic scales and became the seeds of all large-scale structure.
Clocks in the Universe are tricky things. Usually, in calculations of the birth of the world, a special scalar field plays the role of a clock — something like an invisible fluid filling all of space. It ticks, and physicists watch how the world changes relative to that ticking. But these clocks are man-made, introduced for convenience.
The authors of the new work took a different path.