Table of Contents
Big Bang: Let There be Universe
13.7 Billions years ago, there was nothing. There was no space or time or stars or galaxies or solar systems or planets or life. Then suddenly an infinitely hot, dense, and small point appears from nothingness. The point was smaller than an atom. The point was smaller than a sub-atomic particle. The point was smaller than anything on the Universe. That point is called ‘Singularity’. The appearance of the Singularity was the instant when the Big Bang started and our Universe began its journey.
From this event began time, space, and everything else we can see and perceive. Even with their intelligence and knowledge, scientist could not properly explain or understand the state of the universe at that time. Frankly, it is impossible for humans to even imagine the state the universe at the time of Big Bang.
This time entire Universe was saturated with pure energy. There were no suns, stars, planets, satellites, animals, people, matter, atoms, or anything in it. Universe at this time was perfect and complete. No formation or structure has yet been created in it. There are no natural forces such as gravity, electromagnetic force, strong nuclear force, and weak nuclear force. All these natural forces were present in an unified state.
If we were to hypothetically assume that a human being were present in this new-born universe, what he would have experienced would be beyond the understanding of human kind. His or her speed would almost be equal to the speed of light. He or she would felt no friction, electromagnetism, or gravitational force. At this time the universe would look milky white and opaque. This time the imaginary man or woman could see nothing very far in this new universe.
Cosmic Inflation
Then tiny Universe started to expand very rapidly in a very short period of time. Now let’s define these words – “in a very short period of time” and “very rapidly”. Let’s understand how “short” this “short time” is and how “fast” this “speed” is. This short time is a tiny fraction of a second. How small is the fraction? Let one second be divided by one hundred. Then divide that number with one million. Then divide that number by one billion. Then divide it again by one billion. That is, one second must be divided by 1032 (1 followed by 32 zeros). Mathematically this number can be called one hundred nonillion.
During this time, the universe expanded approximately 1026 times in all direction. So, approximately in 10-32 seconds Universe expanded by magnitude of 1026. So, in this time Universe expanded faster than light. This phenomenon is called ‘Cosmic Inflation’. But the question will be, how can something go faster than light? We know that nothing in this universe can travel faster than light. Well, the rule is that nothing in this universe can travel faster than light through this universe. But the universe itself is an exception to the rule. So if the universe itself is expanding faster than light, it does not violate law of the speed of light.
The new universe continued to expand. It expanded from a microscopic state to the size of a glass marble. Then the universe expanded further. In a fraction of a second it expanded from size of a glass marble to the size of the Earth. Then in another fraction of a second it became equal to the size of the solar system. As the universe continued to increase in size, its temperature decreased. Although I am saying that the temperature began to decrease, but at this time the temperature of the universe was several million degrees Celsius – approximately 1020 to 1022 Celsius degrees.
Creation of Matter: Proton and Neutron
Quarks bounded by gluons within Proton and Neutron
After the Big Bang, the Universe needed to cool down a bit more for matter to be created. The raw material for the creation of the matter was the pure energy created after the Big Bang. As we know from the famous equation of Einstein – E = mc2 (E = energy, m = mass, c = speed of light) – energy can be transformed into matter and vice versa. In nuclear fusion and fission, the matter transforms into pure energy. However, in order to transform energy to matter, there has to be extreme temperature and density.
After the Big Bang, the temperature and the density were conducive for the energy to transform into matter. But before that, unified form of 4 fundamental forces of the nature got dissolved from each other and they became separate forces. At this time the temperature of Universe was around 1022 to 1020 which was higher even for the creation of matter.
Then the Universe cooled down a bit more. Once the Universe reached at around 1012 to 1014 degree Celsius, pure energy concentrated and the first first fundamental particle – Quark – appeared. Around this time Higgs Boson or Higgs Field came into existence however the temperature of the Universe was too high for Higgs Field to get activated.
The temperature was too high for any other particles to form and Universe was still in plasma form Quarks and gluons. Then when the temperature dipped below 1010 degree Celsius, first Hadrons – Proton and Neutron among them – were created. Protons were created by two up quarks and one down quark held together by gluons and Neutrons were created by two down quarks and one up quarks held by gluons.
Around the same time, as a result of Universe cooling down, Higgs Boson or Higgs Field got activated and elementary particles started interacting with the it. This interaction manifested as mass for the elementary particles. We will discuss more about Higgs Field in later portion of this article.
At the same point in time, similar particles with opposite charges (anti-matters) were created. The matter and anti-matter annihilated each other and created gamma rays. If this continued, everything would have been destroyed and there would have been nothing left in the Universe. But there was asymmetry in the number of matter and anti-matter in the young Universe. For 1 billion anti-matter particles, there were 1 billion and 1 matter particles.
It is important to remember, that all these above mentioned activities since the Big Bang took only 1 second to complete.
Creation of Matter: Electron and Nucleus
Strong Nuclear Force: Exchange of Meson between two nucleons
The next activity of the Universe was to create Lepton particles-electron among them. Along with Lepton particles, their anti-matter particles also came into existence. Electron’s anti-particle is called ‘Positron’. It is to note that even though the Positron has positive charge, it is not Proton which also has a positive charge and is a Hadron, made of three quarks.
Just like Hadron particles and anti-matter particles, Electron and its anti-matter – Positron – annihilate each other in cosmic battle, producing gamma rays. Due to slight asymmetry, some electron particle remains in the cosmos.
Several minutes after the Big Bang, when the temperature of the Universe was 105 to 107 degree Celsius, first nucleus of the matter to take shape. Proton and Neutron were bound together by ‘Strong Nuclear Force’. Even though the Neutrons are neutral charged, the all Protons have positive charge. By that virtue, the same charged Protons should repel each other and the Nucleus should not be stable. But the Nucleus stays stable due the ‘Strong Nuclear Force’ in which the ‘meson‘ particle gets exchanged between the Nucleon particles. This exchange manifest itself as the Strong Nuclear Force and bind the Nucleus together.
First Atoms of Matter
Till now, all the above mentioned incidents took place within several minutes after the Big Bang. In this time, the Universe was filled with plasma which was made of free electrons, nucleus of matter, and photon which was stuck in the plasma. The Universe was opaque at best. At this point in time, the temperature of the Universe was around 105 to 107 degree Celsius which was not conducive for the stable matter to form. This situation remained for several thousands of years.
The Universe had to cool down from several millions to few thousand degree Celsius for the first stable matter to come to existence. Around 370,000 years after the Big Bang, Universe cooled down enough for the matter to form. The temperature came down to 3000 to 4000 Kelvin and the free electrons were bounded to the nucleus of the matter and formed first stable atom of matter.
Due to this process, the plasma was cleared and the photons were no longer restricted within it. The Photons started to travel in the Universe freely. As a result, 370,000 to 380,000 years after the Big Bang, the Universe was not opaque anymore and it became transparent. We can still see this first light of the Big Bang in the form of Cosmic Microwave Background. After traveling for almost 14 billion years this light from the Big Bang has turned into microwave. Our analog T.V. antenna can catch this microwave in the form of static signal.
The Cosmic Microwave Background was discovered by two US scientist – Arno Penzias and Robert Wilson– in 1964. They were awarded with Nobel Prize for their discovery. Later, in 2001, NASA sent Wilkinson Microwave Anisotropy Probe (WMAP) to make a detailed map of Cosmic Microwave Background. To this date, Cosmic Microwave Background remains the strongest evidence of Big Bang.
Higgs Boson and Mass of Matter
Pictorial Depiction of Higgs Field
Higgs Boson was proposed in 1964 by three different teams of (total six individuals) scientists. They are Peter Higgs, C.R Hagen, Tom Kibble, Gerald Guralnik, Robert Brout, and Francois Englert. Working in three different teams, these scientists came with various mechanisms which would would explain how some elementary particles have mass while others don’t. At that point of time there were no evidence for it. In 2012, the Higgs Boson was finally discovered by Large Hadron Collider (LHC) at CERN in Switzerland. In 2013 Peter Higgs and Francois Englert received Nobel Prize for their contributions.
In popular culture Higgs Boson is referred as ‘God Particle’. Nobel Prize winner scientist Leon Lederman and write Dick Teresi in their book – ‘God Particle: If the Universe Is the Answer, What Is the Question?’ – have used this term and the popular media were quick to catch on it. Leon Lederman wrote the book in order to encourage more spending on big scientific projects and to outline the role of Higgs Boson (Not discovered at that time) to give mass to elementary particle and to shoulder the standard model of particle.
Just after the Big Bang, the sub-atomic particles (like electron, quarks) were created but these particles were virtually mass less. If they were to remain mass less, then they would not have created stable atom. As a result, the Universe would have been completely different and would probably not have harbored life. For example, photon is a mass less particle which goes around the Universe in almost light speed and as a result it does not feel time and its existence is instantaneous.
Higgs Boson is actually a quantum field which propagate through the Universe. It is a scalar field which does not have any spin or any charge. It appeared approximately 10-12 second after the Big Bang when the temperature dropped below 1015 degree Celsius.
Sub-atomic particles do have their intrinsic mass in the form of energy. However, only by interacting with Higgs Field, they attain the property of mass. For example, Proton has two up quarks and one down quarks which are bounded by gluon. These quarks have very negligible mass. However, when Proton interact with the Higgs Field, energy that bounded the quarks, manifests as mass of proton. The mass less particles such as photon does not interact with the Higgs Field and hence is mass less.
Cosmic Dark Ages
370,000 years after the Big Bang, electrons were bounded to the nucleus of the matter and the Universe became transparent as the photons were no longer bouncing off the free electrons and were able to travel freely through the Universe. The ‘Cosmic Microwave Background’ provides snapshot of this time.
The temperature of the Universe fell around 3500-3800 Degree Celsius. At this time, apart from the freed photons, there were no source of visible light in the Universe. No stars were born and no galaxies have been formed. At this time, Universe had lot of Hydrogen and Helium. The atoms of these elements were not emitting visible light instead they were emitting radio waves.
The Universe continued to expand and continued to cool. 10-20 millions years after the Big Bang, the temperature of the Universe fell to around -200 Degree Celsius. The photon particles released after the Big Bang were shifted to infrared wavelength.
At this time, there were no source of visible light and the Universe was mostly dark. Scientist calls this time period of the Universe – ‘Cosmic Dark Ages‘. Scientists estimates that this era have lasted for 300 Million to 1 Billion years after the Big Bang. As scientist depends on the visible light to study the Universe, studying the Dark Ages is difficult for them.
First Stars
The First Stars of the Universe were starting to form since 100 million years of the Big Bang. These stars are called Population 3 Stars. At this time, Universe was made of mostly Hydrogen and Helium and few traces of Lithium and even fewer traces of Beryllium. These population 3 stars were made mostly of Hydrogen. There were no traces of heavier elements in these stars as heavier elements were not created by Big Bang directly. Death of these first stars were the event which created the heavier elements in the Universe.
As these first stars were made mostly of Hydrogen, they were gigantic and extremely hot. They used to emit high volumes of x-ray and other highly energetic wavelength of lights. Hence, they would have looked dark blue in our eyes. Scientist estimates that these stars could be 100 to 1000 times heavier than the Sun.
As they are extremely heavy, the inward pressure in their core was also extremely high and in order to balance out this inward pressure, these stars needed to burn out their Hydrogen fast, a process through which heavier elements were formed at the core of these stars. Hence these stars have not lived long and at the end of their life they went supernova, spreading the heavier elements at their core to the depth of the Universe.
The newer stars including our Sun, planets, asteroids, comets, and moons were created from the elements forged at the core of these first stars. The elements responsible for the creation of intelligent life have also came from these stars. It is also hypothesized by the scientists that from the destruction of these stars massive black holes were created which in time, by gobbling up huge amounts of materials, have grown into supermassive black hole. These supermassive black holes, which can be seen at the center of every galaxy, may have shaped these galaxies and in turns shaped the Universe itself.
Limitation of Big Bang Theory
Of all the theories about the creation of the Universe, Big Bang is the most accepted theory in the scientific community as it has some concrete proof backing it up. But still, the Big Bang theory does have some limitations.
The Big Bang theory does not provide any explanation as to how the Big Bang happened. The theory has to accept the fact that the event of Big Bang happened and any explanation or expansion of the theory only begins after it except that fact. Some theorist believe that Big Bang could happen due to quantum fluctuation. Some scientist believe that our Big Bang is one of only several Big Bangs which happened throughout the cyclic creation and destruction of our Universe. We do not have any concrete answer of the question.
Big Bang theory also does not tell us whether anything, if at all, existed before the the start. World renowned scientist Stephen Hawking had stated that the question if anything existed before the Big Bang is meaningless as everything started with the Big Bang. However, there are some scientist who believe that our Universe could be one of many Universes that existed in the Multiverse. Some scientist believe that our Big Bang could be one of several Big Bangs which are happening in the vast multiverse where each Big Bang would branch out to a new Universe.
Big Bang theory also does not say from where all the energy, created after the Big Bang, came from. If nothing at existed before Big Bang, then all these energy, which later transformed into matter, came from nothing. However, the first law of thermodynamics tells that the energy can not be created or destroyed. The energy can only change its form.
Six Giant Ancient Galaxies as red blurry dots. Image taken by JWST
Recently James Webb Space Telescope (JWST) have taken pictures of 6 blurry red dots. As insignificant as it sounds, these blurry red dots could actually be giant ancient galaxies which could be as old as 13.3 Billion years. That means, if these are indeed giant ancient galaxies, they have formed roughly 500-700 Million years after the Big Bang. Early analysis suggests that these galaxies could be as large as our Milky-Way galaxy. According to our current understanding these galaxies should have been tiny. If further research do establish these findings as fact, scientists would have to change the current understanding of the birth of our Universe and its eventual evolution.
