The next few days are national celebrations. Canada Day on the first and US Independence on the fourth. No fireworks, but rather I'll pick up on something from a recent post and mention a real beginning - the beginning of structure in the Universe.
About 380,000 years after the beginning the hot dense plasma that filled the universe had cooled to the point where electrons combined with protons and the universe started to become transparent. It was a thermal glow - sort of an orangish color. We can see and map this surface. It's the most ancient time we can directly see. It's so far back in time and the universe has expanded so much, that the light has been redshifted into the microwave region.
By the mid 90s observation techniques had become good enough to map structure in the CMB (Cosmic Microwave Background). It looks sort of splotchy. The colors are arbitrary, here the reddish ones represent denser regions. In reality the blotches are very nearly the same.. the temperature difference between the reddest reds and the bluest blues is about one part in one hundred thousand.
The denser regions attracted more mass than the less dense regions and kept growing in mass. Ultimately they became enormous clusters of galaxies. There's a weblike structure, defined by gravity and density that spreads through parts of the universe. It's like clusters of galaxies are tiny dew drops on a huge spider webs. The splotchy picture allows us to measure this structure. Think of the vertical axis as some measure of density and the horizontal axis the angular area of the sky. There's a peak around 1° - a region about twice the apparent width of the Moon. It corresponds to the size of these enormous clusters of galaxies. There's finer structure, of course, but the measurements are more difficult.
A bit on the plot - there are a large number of measurements using three different instruments. The red curve is the best fit to the experimental data. The grey region is the best theoretical prediction so far. Each of the points has an error bar.. notice that many are so good they're almost invisible!
These slight differences in temperature and density, along with the fact that hydrogen and helium were made in the first two minutes of the universe, are one of the reasons why you're here. And another thing to celebrate. Carl Sagan noted we're all stardust. But about 62 percent of your atoms are hydrogen that were forged in the first two minutes of the Universe. Most of your atoms are primordial - as old as the Universe itself! Much of you is Hot Big Bang dust!
And on that spiderwebish cosmic web of galaxies -- here's a computer simulation from the Virgo Consortium. The small bright blobs are clusters of millions of galaxies. There are huge voids with very little.
Oddly enough the period from two minutes after the beginning until the surface of first scattering about 380,000 years later isn't terribly exciting. But the first two minutes represent the most jaw dropping physics I know.
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