In the very earliest moments of the big bang, the universe experienced a period of rapid expansion known as inflation. That event planted the seeds that would eventually become galaxies and clusters. And now, a recent set of simulations is able to show us how that connection worked.
When our universe was less than a second old, it grew more than a trillion, trillion times in size in less than a trillionth of a trillionth of a microsecond. That landmark event, known as inflation, is largely a mystery to modern physics. Besides being pretty sure that it happened, we don’t know what triggered it, what made it last as long as it did, or how it ended.
But the effects of inflation can be seen all the way to the present day, more than 13 billion years later. That’s because inflation turned microscopic quantum fluctuations into something a little larger. Over time, those tiny little differences in density grew and grew, eventually becoming the starting points for stars, galaxies, and the largest structures in the universe.
So by mapping the arrangement of galaxies in the universe, we can see the fingerprint of inflation. But connecting modern-day maps to that early epoch is a challenging task, because of the incredible amount of time and all the complicated physics (unrelated to inflation itself) that have intervened in that time. Most importantly, the gravitational interactions between galaxies has disguised a lot of the original imprint of inflation.
To solve this, scientists used the ATERUI II supercomputer at the National Astronomical Observatory of Japan (NAOJ) to perform a series of complex computer simulations. These simulations attempted to reconstruct the process of inflation by, essentially, “rewinding” the evolution of galaxies.
If you know how galaxies move over time, then you can use that knowledge to guess as to where they were in the past. This process erases some of the interactions that have obscured the effects of primordial inflation.
The researchers created 4,000 simulated universes and compared them to galaxy surveys. They could then pick out the model of inflation that best explained the data. This method isn’t perfect, of course, but it is powerful.
“We found that this method is very effective,” said team leader Masato Shirasaki, an assistant professor at NAOJ and the Institute of Statistical Mathematics. “Using this method, we can verify of the inflation theories with roughly one tenth the amount of data. This method can shorten the required observing time in upcoming galaxy survey missions such as SuMIRe by NAOJ’s Subaru Telescope.”
“Besides being pretty sure that it happened, we don’t know what triggered it, what made it last as long as it did, or how it ended.”
I’m becoming pretty sure we have a handle on all that since 2018, albeit Planck’s results may not be robust. Flat space seems to be expected to be robust and has turned out so though, so expansion would be spontaneous (adiabatic free process of average zero energy space). The preferred inflation theory would have it last indefinitely and end locally by fluctuating out into a natural exit, but is a _very_ slight preference -albeit starting to bite into “not knowing”.
It will be interesting to see how it turns out. For one thing, matter-andtimatter asymmetry seems a deeper mystery now since inflation and the resulting universe may be so nice behaved. (With both electroweak and QCD breakings looking like smooth crossovers AFAIU.)