With light, there is no way to see what was happening in the universe prior to the release of the Cosmic Microwave Background (CMB). Prior to that moment, the universe was opaque and completely hidden to our telescopes. If you asked me if we could ever observationally know anything about the universe’s first 400,000 years, I would have sighed and said I don’t think so; that time is hidden except for the echoes it left imprinted on the CMB.

What I hadn’t counted on was gravitational wave science advancing the way it has, with people not just using detectors like LIGO and Virgo to measure black hole mergers, but also teams using the timing of pulsars to detect the background perturbations in space caused by events that occurred early in the universe, before that CMB was released. Through gravitational waves, we can now imagine testing theories about what happened in the earliest moments of this universe. 

Researchers at the universities of Gottingen and Auckland created a simulation to look at the evolving structure of the universe in its first seconds. They were able to see a complex network of structures similar in form to today’s large-scale structure of the universe, only much, much smaller. According to Ph.D. student and lead author of this study, Benedikt Eggemeier: The formation of such structures, as well as their movements and interactions, must have generated a background noise of gravitational waves. With the help of our simulations, we can calculate the strength of this gravitational wave signal, which might be measurable in the future.

This is my favorite kind of theory paper. It is one that makes concrete predictions that can one day (maybe) be observed. What gets me about this work is the scale they were working at. The early universe was tiny. As Jens Neimeyer explains it: The physical space represented by our simulation would fit into a single proton a million times over. It is probably the largest simulation of the smallest area of the Universe that has been carried out so far. 

Here is to hoping we one day learn how to record early gravitational waves with the same detail as the CMB.

More Information

University of Göttingen press release

“Formation of inflaton halos after inflation,” Benedikt Eggemeier, Jens C. Niemeyer, and Richard Easther, 2021 March 22, Physical Review D