The Transformation of the Universe: From the Big Bang to a Cold Death
I really hope you enjoy this, even though it is very long for a blog. I would recommend reading until the end though, because I think the fate of the Universe is the most interesting part :)
THE START OF THE UNIVERSE- AKA THE BIG BANG
Before the Planck Epoch, the universe was just a singularity at the beginning of time. The Planck Epoch is known as the first instant after the Big Bang, and scientists currently don’t know what happened in this period.
The Inflation Epoch took place from 10^-36 seconds after the big bang, where the universe expanded radically, from billions of times smaller than a proton to something between the size of a marble or a football field. In this period, scientists believe that gravity split from the other forces of nature, followed by the strong nuclear force. This triggered the universe’s short but rapid expansion, and this theory helps explain why the universe is smooth and flat. At this point, an immense amount of mass-energy came into existence, together with an equal, negative amount of gravitational energy.
In this Epoch, which occurred 10^-32 seconds after the big bang, huge numbers of quark and antiquark pairs formed from energy, just to annihilate back into energy again when they met. Gluons, and some of the other more exotic particles, also appeared during this period. The universe was thought to be a ‘soup’ of elementary particles and antiparticles at this time.
During this time, starting 10^-12 seconds after the big bang, the electroweak force was separated into the weak force and the electromagnetic force. Only then did physical laws become what they are today. By 10^-6 seconds, the start of the Hadron Epoch, temperatures had dropped to 10^11K, and gluons could bind quarks together.
In the beginning of this period, vast amounts of quarks and antiquarks had combined to form particles called Hadrons, hence its name. Some types of Hadron particle include baryons (protons and neutrons), antibaryons, and mesons. The antibaryons and mesons, however, quickly decayed or were annihilated after they formed. The protons and neutrons formed during this epoch were done so through quark confinement, where ‘up’ quarks and ‘down’ quarks combine with gluons and make protons and neutrons.
This period in the transformation of the universe starts one second after its formation, when the universe was around 10^10 Kelvin. During the Lepton Epoch, leptons (electrons, neutrinos, and their antimatter particles) were very numerous. The electrons had annihilated with positrons by the end of the epoch.
During Big Bang Nucleosynthesis, collisions between protons and neutrons began forming helium-4 nuclei, and tiny amounts of other atomic nuclei, like helium-3, lithium, and deuterium. These reactions finished within twenty minutes, and by that time, 98% of the helium atoms today had formed.
Throughout the Photon Epoch, which lasted 380,000 years, the electrons, protons, and helium nuclei were constantly interacting with photons, which made the universe foggy.
The Recombination Epoch - 380,000 years after the Big Bang
When the temperature had dropped to around 4000 Kelvin, the protons and atomic nuclei had begun to capture electrons, which formed the first atoms. During this era, the Universe became transparent because electrons had stopped scattering photons after being bound up in atoms, and matter and radiation therefore became ‘decoupled’. The photons were released to travel through the Universe as radiation. The first free photons can actually still be detected as the cosmic microwave background radiation, or CMBR.
The Aftermath of the Big Bang
When the Universe was 400,000 years old, it was filled with photons of radiation streaming in all directions, and atoms of hydrogen and helium, neutrinos, and other dark matter. Astronomers try and look back into that time, and even though it was around 3,000 degrees celsius and filled with radiation, they see no light. This is because when the Universe expands, it stretches the wavelengths of radiation by 1,000x. We see the photons as cosmic microwave background radiation. Their wavelengths are now that of an object with a temperature of 3 Kelvin.
The first stars are thought to have formed roughly 180 million years after the Big Bang. They were all made of hydrogen and helium, because there weren’t really any other elements in the universe. Physicists think that nebulae that form stars would have condensed into larger clumps than those around today. The stars that formed these clumps would have been extremely hot and large, with masses between 100 and 1,000 times the mass of the sun. Although many of these stars only would have lasted a few million years before dying as supernovae, ultraviolet light from these stars may have actually triggered a key moment in the transformation of the Universe. Either the first stars, or radiation from quasars likely re-ionised hydrogen from a neutral gas to the ionised form seen today.
Astronomers are still trying to determine exactly when in time the very first stars ignited, and what types of galactic structures this could have caused. They have recently used instruments like the Spitzer Space Telescope and the Very Large Telescope to perform infrared studies and hopefully find early galaxies. Amazingly, they found very faint galaxies with very high red-shifts that existed as little as 400 million years after the Big Bang! One of these is GN-Z11, which is the most distant galaxy known.
Cosmic Chemical Enrichment
The first massive stars created and dispersed new chemical elements into space during the course of their lives and deaths. Elements like carbon, oxygen, silicon, and iron were all formed in the cores of these stars from nuclear fusion, and during the stars’ violent deaths, they formed elements like barium and lead.
Stars smaller than the first megastars, second- and third- generational stars, formed later from the interstellar medium. They created some of the heavier elements, then returned them to the interstellar medium through stellar winds and supernovae explosions.
Galactic mergers and the stripping of gas from galaxies led to even more mixing between the galaxies, and these processes even continue today.
This is really important, because without these new heavier elements, living organisms on rocky planets (like us) would not have formed.
The ‘Big Crunch’ theory of the end of the Universe is currently regarded as the least probable of the 4 theories to actually happen, even though it’s the most exciting. According to this theory, all matter and energy will collapse into an infinitely hot, dense singularity, kind of like the Big Bang in reverse. If this were to happen, it would be tens of billions of years from now, so there’s no need to worry about the incredibly painful death this would bring.
With this theory, the Universe would end with the strength of dark energy increasing so much that it would overcome all the fundamental forces and completely disintegrate the Universe. First, galaxies would be ripped apart, then even planetary systems like ours would be torn away from each other. We would have to say goodbye to any sunlight or warmth ever again and hello to a frozen death, but luckily this won’t happen until 20-30 billion years from now. Even if the theory is correct, we won’t be alive to experience it ourselves.
A Cold Death - The most probable theory
If the Universe were to end with a Cold Death, it would happen with galaxies eventually exhausting the gas that can form new stars, in about a trillion years, or 10^12 years. After this, in about 10^25 years or 10 trillion trillion years, most of the Universe’s matter will be in black holes and burnt-out white dwarfs that circle and fall into the supermassive black holes in the centres of galaxies. Then, in 10^32 years, protons will start to decay into photons, electrons, positrons, and neutrinos, and all matter that isn’t in black holes will fall apart. 10^67 years after that, black holes will start evaporating by emitting particles and radiation, and in about 10^100 years from now, even supermassive black holes can evaporate. The Universe will then be nothing more than a diffuse sea of photons and elemental particles.
Another version of The End which also leads to a Cold Death
In this theory, structures that are not bound by gravity will fly apart faster than the speed of light if the effects of dark energy continue the way they are now. (Whilst no matter can travel through space at greater than the speed of light, space itself can extend this speed limit). This theory also gets to the same Cold Death as the previous one, it just took a slightly different approach.
