First Atom and First Light
By Ritik Balyan
Cosmofluencer (Season 03)
You have studied in school that every object in the universe is made up of atoms which consist of protons and neutrons in the nucleus and electrons around that nucleus.
Protons and neutrons are further made of quarks and gluons. You may wonder about two key questions: how many atoms in the observable universe and, where do they come from.
A rough estimate tells us that the observable universe contains 10^78 atoms which means one followed by seventy-eight zeros, but the answer to the second question is not that simple.
Let’s begin this journey to find the answer to our second question which is far more important than the first one and see how the universe we see today is due to some kind of luck.
You have probably heard that the universe is expanding at an accelerated rate, if we go back in time then it must be converging into something — a point or anything you may guess.
However, the universe doesn’t behave according to our guesses but rather through its laws, some of which we study as Physics through the language of Mathematics.
And that fits with our guess of the converging universe up to the very beginning of time to an infinitesimal point called the singularity.
At this point of infinite density, all the matter and energy of the present universe were contained. Note that singularity is a mathematical concept, we are not very concrete about its existence at the very beginning, it is our best assumption.
We can predict the behavior of the universe at the beginning of the time but not as back at t = 0 sec because our theories are incomplete.
The best we can predict is one Planck time, the shortest time we can measure about 10^ -43 seconds. This is the smallest unit of time that can theoretically exist according to quantum mechanics.
We have no idea what comes before this, we need a quantum theory of gravity to explain before 10^ -43 seconds, also called the Planck era, as the singularity is infinitesimal so we need quantum mechanical laws of gravity at that scale.
In the Planck era, we expect there was a point at which all the four fundamental forces, i.e. gravity, weak nuclear, strong nuclear, and electromagnetic force, united to form one grand unified force.
To build a timeline for our theory, we started before the Planck era and set the clock at t = 0. Keep in mind this is not the absolute beginning, but we start here because we don’t want to get into the singularity. There might have been something before which is unknown to us.
After the Planck era, rapid inflation started from about 10^ -36 seconds to 10^ -12 seconds in which the universe grew exponentially faster, faster than the speed of light.
Note that information cannot travel faster than the speed of light in space but the space itself can expand faster than the speed of light.
The process of cosmic inflation destroys the information of what came before it due to causality hence we don’t know much about the period of rapid inflation, we can only speculate.
The theory of the standard model of cosmology is only well understood at about 10 ^ -12 sec because, at this moment, the universe has energies that are approximately replicated in our particle accelerators.
In the Planck era, gravity separated from the unified force, later the strong force, and around the time of inflation, the electromagnetic and weak forces still united as the Electroweak force. At this point, the universe probably consists of quarks and gluons existing together in the quark-gluon plasma along with some other fundamental particles that were massless because the Higgs field had not gained a non-zero potential that allows fundamental particles to gain mass by interacting with it.
As time ticks slightly forward to 10^ -11 sec, the temperature of the universe drops further to about 10^ 15 Kelvin. This low temperature and energy lead to separating the electroweak force into electromagnetic and weak force which further leads to the Higgs field gaining a non-zero potential.
This means that the fundamental particles now interact with the Higgs Field, it’s a field that permeates the universe, interacting with particles and giving them mass.
At this point, t = 10^ -11 sec, we have all the building blocks for atoms but the universe is still too hot, 10^ 15 Kelvin, for the quarks to combine to form hadrons (protons and neutrons). The universe keeps expanding and cooling, as the temperature drops to 10^ 12 Kelvin at 10^ -5 sec, the quark plasma turns into a Hadron gas consisting of protons, neutrons, and some mesons which are combination of quark-antiquark pairs that eventually decay into photons and electrons. This marks an important step in the formation of matter in the early universe.
As the universe cooled down, annihilation started. It is a process in which particles and antiparticles collide and disappear, releasing energy.
Due to the temperature drop, quark – antiquark pairs began to annihilate, creating lighter particle and antiparticle pairs ending up as the lightest particles – neutrinos and photons.
We expected an equal number of particles and antiparticles to be created, but this did not happen, slightly more particles were created than the antiparticles, 10 billion particles for 1 antiparticle.
We don’t know the reason behind this asymmetry, but we do know one thing: if the symmetry existed then there would be equal number of particles and antiparticles in pairs which then be annihilated into photons and neutrons in the form of energy then there would be no quarks as all the quark – antiquark pairs got annihilated then the protons and neutrons couldn’t be formed which means no nucleus, no atom and no matter.
Also, then there would be no galaxy and stars, only photons and neutrons which would make it impossible for any life to be formed on earth as there also would not be elements which make us. That’s why we are kind of lucky to have the universe today.
As the particle – antiparticle symmetry broke, some quarks and electrons survived the annihilation which formed protons, neutrons, and electrons which eventually lead to the creation of the first atoms and the universe as we know of today.