Want to stay on top of all the space news? Follow @universetoday on TwitterTo discuss the history of the Universe, we must first agree on which particular cosmological model we are going to base it upon. Since the Big Bang is currently the most widely accepted then we will draw parts of our story from it.
In this regard, we now focus our attention on a singularity, an infinitely hot and infinitely dense entity. That’s how the Universe was in the beginning – practically, nothing.
We are not exactly sure how long it stayed in this state. What we know is that it eventually underwent a rapid expansion and cooling. After about 380,000 years, the temperature was cool enough to allow the first atoms to come into being.
The most simple atoms were formed first: hydrogen, which only has one proton, neutron, and electron, and helium, with two protons, neutrons, and electrons. They all gathered up into clouds. These clouds are believed to have crowded together in certain regions, leaving other regions with very thin clouds or having none at all.
In this kind of distribution, it is expected that in places where the density was high, the temperature should have been higher by about a few millionths of a degree. This theory that the Universe was once composed of an uneven distribution of such clouds is consistent with the measurements of the so-called cosmic microwave background radiation (CMBR) we’re getting today.
This uneven distribution is also believed to be a prerequisite condition for the formation of planets and stars in the denser areas. We shall now proceed to see what happened in these areas.
As time went by, gravitational attraction brought everything in the denser clouds even closer together. As they were drawn closer, the density in their cores went up. This allowed the hydrogen atoms to fuse and form helium, and was accompanied by a release of great energy.
We can imagine that there were many of these kind of reactions in the core. The released energy subsequently produced more of the same fusions, and then more, and then even more … basically, what ensued was a chain reaction of gargantuan proportions. Many of these events throughout the young universe eventually evolved into the first stars.
When all that energy in the core was used up, the star collapsed, shooting up the temperature and pressure inside even more. This gave just the right conditions for helium to fuse and form heavier elements like carbon and oxygen. The process continued until many heavier elements were produced.
This pressure and temperature build-up was finally too much for the stars to contain, leading to their deaths through dramatic explosions. We still see some of these explosions today.
We end our brief history up to this point, i.e., the formation of stars. We shall talk about the formation of planets in another article.
You can read more about the history of the universe here in Universe Today. Click on these links:
There’s more about it at NASA:
Here are two episodes at Astronomy Cast that you might want to check out as well: