What was it like at the beginning of the Big Bang? | by Ethan Siegel | Starts With A Bang! | Nov, 2023

This timeline of the Universe shows how, from a Planck-scale region of space that possessed an inflationary state, the properties of the hot Big Bang were set up beforehand. Once the Big Bang occurs, our Universe becomes filled with a primordial particle soup, which evolves into the atoms, stars, galaxies, and large-scale structure we’re familiar with today. (Credit: Ben Gibson/NASA/Pablo Carlos Budassi/Big Think)

Some 13.8 billion years ago, the Universe became hot, dense, and filled with high-energy quanta all at once. Here’s what it was like.

Looking out at our Universe today, we not only see a huge variety of stars and galaxies both nearby and far away, we also see a curious relationship: the farther away a distant galaxy is, the faster it appears to move away from us. This continues as far as we’ve ever looked, and remains true on average for all galaxies: the farther away they are, the greater their observed redshift (corresponding to recession) is. In cosmic terms, the Universe is expanding, with all the galaxies and clusters of galaxies getting more distant from one another over time. In the past, therefore, the Universe was hotter, denser, and everything in it was closer together.

Imagine what this means if the Universe is, and has always been, expanding: not just for the future, but for our cosmic past as well. If we extrapolate back as far as possible, we’d come to a time:

  • before the first galaxies formed,
  • before the first stars ignited,
  • before neutral atoms,
  • or atomic nuclei,
  • or even stable matter,

could exist. The earliest moment at which we can describe our Universe at hot, dense, and uniformly full-of-stuff is known as the Big Bang. Here’s the story of how it first began.

Nearby, the stars and galaxies we see look very much like our own. But as we look farther away, we see the Universe as it was in the distant past: less structured, hotter, younger, and less evolved. If you look farther and farther away, you also look farther and farther into the past. The earlier you go, the hotter and denser, as well as less-evolved, the Universe turns out to be. The earliest signals can even, potentially, tell us about what happened in, and even just prior to, the first moments of the hot Big Bang. (Credit: NASA/ESA/STScI/A. Feild)

Some of you are going to read that last sentence and be confused. You might ask, “isn’t the Big Bang the birth of time and space?” And this is a view that many modern cosmologists can be sympathetic to, as at one point in the history of cosmology, that’s how the Big Bang was originally conceived. Take something that’s expanding and of a certain size and age today, and you can go back to a time where it was arbitrarily small and dense. When you get down to a single point, where all the matter and energy in the Universe comes together at once, that event corresponds to what we know as a singularity: a point from…

Source link

Back to top button