[Music throughout] Immediately after the universe was born, it was too tiny
and too hot for protons, electrons and even photons to exist.
Within a second, it had expanded and cooled enough for
protons and neutrons, collectively called baryons, to form.
Almost instantly, there was a rapid burst of sound waves triggered by tiny
variations in this particle soup. Scientists call these waves
Baryon Acoustic Oscillations. The pressure waves traveled outward
for 400,000 years until the universe thinned and cooled enough
for light to travel through it. The universe became transparent
and the waves froze in place. Over
time, the denser regions formed by the waves encouraged more star and galaxy formation
than other areas. The imprint of those waves expanded
with the universe, slowly accelerating due to dark energy.
Today, with our “snapshot” of the universe, there is a
slight tendency for galaxies to be separated from each other by a
distance related to that expanding-ring radius.
Although difficult to see, it is
detectable as a slight bump through careful surveys of many galaxies.
[Music]