From Nothing to Everything: The Big Bang
“What was then in the dust particles, is still in you”
Before all this had happened, much smaller than a grain of sand or an atom, an incredibly hot and dense entity, for some unknown reason, expanded at an astonishing rate. Then this intensely hot and compact entity started expanding at an alarmingly rapid pace and exploded. As the universe grew larger, the radiation’s temperature dropped and within a second of the Big Bang, it had reduced to around ten billion degrees.
This was according to the Friedmann Model which says that as the universe expands, any matter or radiation in it gets cooler. In the early stages of the universe’s existence, the primary constituents were photons, electrons, and neutrinos, along with their respective antiparticles. A smaller number of protons and neutrons were also present. As the universe evolved, it continued to expand in size, a process that was accompanied by a decrease in temperature.
This expansion and cooling had a significant effect on the particles within the universe. In particular, it impacted the rate of creation and destruction of electron-antielectron pairs. These pairs were initially formed through high-energy particle collisions. However, as the universe expanded and cooled, the frequency of these high-energy collisions diminished. Consequently, the production rate of these electron-antielectron pairs started to fall.
At the same time, these pairs were being annihilated, a process that destroys both the electron and the antielectron and converts their mass into energy. As the universe continued to expand and cool, the rate of these annihilations remained high, while the creation rate fell. Thus, over time, the rate at which electron-antielectron pairs were being generated in collisions became lower than the rate at which they were being destroyed by annihilation.
However, neutrinos and antineutrinos, unlike other particles, didn’t annihilate each other due to their weak interaction with each other and other particles. Hence, they should still be present today. Their observation could validate our understanding of the universe’s extremely hot initial phase. But, unfortunately, their current energy levels are too low for direct observation.
Around a hundred seconds post the Big Bang, the temperature dropped to a billion degrees, matching the hottest stars’ temperature. At this temperature protons and neutrons would have started to combine to produce the nuclei of atoms of deuterium, which contain one proton and one neutron. These deuterium nuclei then merged with protons and neutrons to create helium nuclei, composed of two protons and two neutrons, as well as trace amounts of heavier elements like lithium and beryllium.
This immensely hot image of the universe was put forward by George Gamow. He along with his student Ralph Alpher and scientist Hans Bethe published a paper in 1948 and mentioned their name as Alpha, Beta, and Gamma. In this paper, they predicted that the radiation coming out of the very hot early stages of the universe might still exist but its temperature has been reduced to only a few degrees above absolute zero.
A few hours after the Big Bang, helium along with some other elements had stopped to form. This stage lasted for about 380,000 years. Eventually, the cosmos cooled enough for electrons to pair up with nuclei and make the first atoms. As time went on, the hydrogen and helium gas in the galaxies would break up into smaller clouds that would collapse under their gravity.
As they shrunk, atomic collisions within the clouds caused the gas temperature to rise until nuclear fusion reactions were triggered. These reactions turned hydrogen into more helium, and the heat increased the pressure, stopping the further shrinking of the clouds. They stayed stable as stars, like our Sun, converting hydrogen into helium and releasing energy as heat and light. But when the star ran out of fuel the central regions of the star would collapse to a very dense state, such as a neutron star or black hole.
The outer regions of the star may sometimes get blown off in a tremendous explosion called a supernova, which would outshine all the other stars in its galaxy. Some of the heavier elements produced near the end of the star’s life would be flung back into the gas in the galaxy and would provide some of the raw material for the next generation of stars.
Our sun contains about 2 percent of these heavier elements because it is a second or third-generation star, formed some five thousand million years ago out of a cloud of rotating gas containing the debris of earlier supernovas. Most of the gas in that cloud went to form the sun or got blown away, but a small amount of the heavier elements collected together to form the bodies that now orbit the sun as planets like the Earth.
The earth as a planet was a hot body initially, without any atmosphere. As time passed by the temperature started to change and was cooled, this brought up life on the earth that could flourish under those conditions and slowly animals were formed with the ability to reproduce. In this way, a process of evolution was started that led to the development of more and more complicated, self-reproducing organisms.
Simple life forms emerged that could survive by consuming various substances like hydrogen sulfide and releasing oxygen. This process gradually changed the composition of the atmosphere to what we have today and allowed the development of higher forms of life such as fish, reptiles, mammals, and ultimately YOU.
