The story of the beginning of our Universe is probably one of the hardest biographies one could work on.
It requires the work of several generations of philosophers, cosmologists, mathematicians, physicists, and astronomers to find out what actually happened at the beginning of the Universe.
It was only now that astronomers realized that we don’t merely look at the stars and the galaxies far away while gazing at the night sky, but also back into the past as light takes a significant amount of time to reach our eyes from such large distances.
With advanced telescopes, we’re now able to see much farther away and back in time than we ever had, which helped us attempt to unfold the origins of the cosmos.
Infant Universe
And it begins…the existence of something enigmatic, without which our existence wouldn’t have been possible. It is the birth of space and time.
It is theorized that before the birth of something magnificent, a lot of phenomenal changes occur and that is what happened during the birth of this huge mysterious void.
It started with a bang, but not an explosion at all.
The Big Bang was not an explosion in space, as the name suggests, instead, it was as quoted by researchers, a “sudden appearance of space and time everywhere in the Universe”.
According to the Big Bang theory, the Universe was initially very hot, immensely dense, and even smaller than a grain (a billionth the size of a nucleus of an atom), a baby space-time, a violent one in fact.
The sudden catalysis of this massive event remains a mystery and has kept scientists pondering for ages.
One theory suggests that the process involved was inflation, in which the space was suddenly mobilized and expanded more rapidly than anything.
The inflationary expansion concluded when this energy was transformed into more familiar forms of matter and energy.
The earliest time frame–the first picosecond (10−12s) of the Big Bang–included massive events like the following:
Planck epoch (and it begins): 0 to 10−43 seconds
This would have been the best time for students to live probably, since the laws of physics do not hold at this point.
It is the closest current physics can get us to the Big Bang and almost nothing is known about this period, although they would have, at unusually high temperatures, the Big Bang occurred at this stage.
WIMPS (weakly interacting massive particles) or dark matter and dark energy (terms that I’m going to throw more light on further) are suspected to be the parental guides to the maturity of the Universe.
Slight occurrences of quantum variances can be seen as a disruption to the smoothness of the infant Universe.
These tiny ripples are believed to be the basis of large-scale structures that formed much later.[1]
The Grand Unification Epoch: 10−43 to 10−36 seconds
While still a small baby, the Universe cools down to 1032 kelvins, it’s high time for the fundamental forces to take birth now, initially, gravity separates and begins operating on the Universe.
The remnant forces, stabilize into the electronuclear force, also known as the Grand Unified Force (GUT).
The temperature given here is expressed as 2.725 K(1 + z), where ‘z’ represents the redshift and 2.725 kelvins represents the current temperature of the cosmic microwave background.
Inflationary Epoch: 10−36 seconds
The Universe now cools down to 1028 kelvins, due to this, strong nuclear force can be differentiated from electroweak forces sparking yet another wave of expansion.
10−33 seconds
Space is now expanding extremely rapidly, by a factor of the order of 1026, over a time order of 10−33 to 10−32 seconds, as a result, the Universe is again subjected to supercooling from about 1027 to 1022 kelvins.
This was also a very strange period in the Universe as energy existed in its purest form, space was so dense that even light couldn’t have existed, and nor did matter.
10−32 seconds
Cosmic inflation ends finally! the familiar elementary particles, (such as quarks, leptons, and bosons), now form a broth of hot ionized gas called quark–gluon which is popularly known as quark-gluon soup.
This was not a thick soup of energy, and by the end of this epoch, the temperature of the Universe came down to 1022 kelvins.[2])
Electroweak Epoch: 10-32 to 10-12 seconds
In this epoch, the weak nuclear or strong force separates from the electromagnetic forces resulting in the functioning of all four fundamental forces of nature.
Now since all forces are functioning, the Universe had the foundation required to manifest the energy within itself in the form of matter along with Bosons such as W, Z, and Higgs bosons and photons which emerged as the force carriers. But the Universe is still too hot for the matter to exist.
Quark Epoch: 10-12 to 10-3 seconds
After 10-12s, the temperature cools down enough to coalesce into hadrons forming the first elementary particles.
But it gave rise to an equal amount of matter and anti-matter which would annihilate each other and nothing lasted for more than a moment, during this epoch, the Universe cooled down to 1015 K.
Nucleosynthesis Epoch: 10-3 seconds to 3 minutes
During 10-3s to 3 minutes of the Big Bang, something bizarre happens.
For some reason yet not understood, the population of matter surpasses the population of antimatter and the annihilation of matter-antimatter stops.
This allows the Universe to cool off enough to synthesize nucleons such as protons and neutrons and we have some first nuclei, hydrogen and Helium.
The universe is still not cool enough so that electrons can bind to the nucleus and form an atom.
Most of the research, that has brought a certain conclusion, that these events may have occurred, comes from the cosmic microwave background.
This contains the afterglow of light and radiation, left over from the Big Bang, this memoir of the Big Bang is visible to microwave detectors, which allows scientists to solve the puzzle regarding the early Universe.[3]
Nuclei Soup Epoch
I am not sure what to call this period as for the next 380,000 years nothing significant happened in the Universe.
The temperature cooled down to 4000K, the matter remained in the form of Photon-Nuclei soup.
Temperature was not yet enough to allow the formation of atoms but at the end of this epoch, the Universe expanded enough to be transparent which results in the redshift of the remnant radiation enough so that the energy falls below the visible spectrum.
It can still be observed to date in the form of Cosmic Microwave Background Radiation (CMBR).
We can’t see CMBR from our eyes because it has further redshifted to Microwave (radiation with a wavelength of around 2mm), because of the expansion of the Universe which is continuing and still accelerating today.
CMBR is the single most important evidence of all of these events which begin after the Big Bang and an important subject of study in Cosmology as they show us the ripples in the early Universe.
If we simulate those ripples and let them evolve on a computer simulation, we’ll see the large-scale structure of the Universe as it is today.
The Dark Ages of the Universe
About 300,000-500,000 years after the Big Bang, recombination occurred when the first atoms were created, hydrogen and helium, and the temperature fell to around 60-100K.
There was almost no source of light and the Universe was filled with hydrogen and helium gas so it was all dark for several hundreds of thousands of years.[4]
You may think that it must be the most boring as there was almost nothing to see.
However, recent research has shed light on this period, revealing that it was a time of significant change and evolution, with the formation of the first stars also taking place during that time.
The universe couldn’t have remained a gas chamber for all of its eternity, the gravitational potential was at its work coagulating the masses of gas and starting fusion reaction within its core giving birth to the first stars.
This process can be understood with the perturbation theory which says that a small perturbation in the uniformly distributed gas mass is enough to let it evolve into clumped masses forming first stars.
But any radiation emitted by those first stars was mostly scattered and absorbed by the fog of neutral hydrogen permeated throughout the Universe.
So, light from those stars might never reach us ever, such stars are also called Population III stars.
The Cosmic Dawn
It was time for the Universe to wake up again out of the Dark age, the formation of first stars marked the dawn of the cosmos as we are all familiar with.
A cosmos surrounded by colorful galaxies, nebulae, and stars, the giant nuclear reactors spew energy and new heavier elements like carbon, oxygen, silicon, and metals.
All of these elements which become crucial for life today.
Reionization Epoch
As the population of stars increased and they started forming clusters and galaxies among themselves, the Universe was brought out of the Darkness.
Radiation emitted by stars ionized the gas around them, forming a bubble of ionized gas encompassing stars and galaxies.
This allowed the light to travel across the Universe without any hindrance and the modern Universe as we know it started to emerge. In this period the ionization of neutral hydrogen and helium in the Universe takes place.
This epoch lasted for about a billion years after the Big Bang and at the end of this epoch, almost all of the gasses either clumped into the stars forming heavier elements or becoming completely ionized in the vicinity of the Universe.
The oldest observed galaxies and stars belong to this epoch only, for example, the oldest galaxy known to us is GN-z11 which was discovered by the Hubble Telescope back in 2015. The galaxy is said to have come around 400 million years after the Big Bang.
Gravity kept working by drawing the matter towards each other forming galaxies which yet came together to form galaxy clusters.
The galaxy where we live, the Milky Way galaxy is estimated to formed around 8.8 billion years ago.
During this time the expansion of the Universe was also slowed down and at this moment you may think that everything that could’ve happened, has happened.
But not yet, the behavior of the Universe is about to change gradually for the third time, the Dark energy-dominated era.[5]
Dark Energy Dominated Era
The universe was originally in radiation radiation-dominated era for around 47,000 years after the Big Bang during which the Universe expanded rapidly.
After that, matter took charge and dominated the Universe for around 9.8 billion years when the expansion of the Universe decelerated.
But since after, the expansion of the Universe is yet again accelerating and we’re currently living in this era, this is a peculiar observation made by cosmologists and its cause is still unknown.
Currently, most cosmologists and astronomers claim that this is caused by some Dark Energy.
The first direct evidence for dark energy came from observations of distant supernovae in 1998, which showed that the expansion of the Universe was accelerating rather than slowing down as expected.
In the late 1990s, astronomers sought to determine whether the Universe was open, closed, or flat—by studying the rate of its expansion.
They focused on Type Ia supernovae, treated as standard candles for distance measurements, surprisingly, observations revealed that the Universe’s expansion is accelerating, contrary to expectations.
Along with the dark matter which accounts for 27% percent of the Universe and the dark energy which accounts for another 68% of the Universe, all that we can see and observe is just the 5% of the entirety.
Even though it was discovered at the end of the 20th century, a hint of it was already given to Albert Einstein in 1915 when he came up with general relativity where he introduced cosmological constants into his equation to maintain a static Universe.
In 1920 when Edwin Hubble discovered the expansion of the Universe, Einstein took down the constant can and called it the biggest blunder of his career.
Later when it was discovered that the expansion of the Universe was increasing, the constant was reintroduced as it accounted for the dark energy which is nothing but the energy density of the space itself affecting the geometry and dynamics of the Universe.[6]
What Would Be Fate of the Universe
After all this, the only question that remains is how it’ll end up, of course, there is no one simple answer as different cosmologists have come up with different theories about the fate of the Universe depending on its overall shape, density, and the amount of dark energy that exists.
Here are some of the most popular theories –
Big Freeze
This theory suggests that the Universe will continue to expand at an ever-increasing speed, causing galaxies, stars, and planets to be pulled farther and farther from one another.
In the very distant future, everything will be so far away that the light from distant stars and galaxies can never reach us.
Eventually, planets, stars, and galaxies would be pulled so far apart that the stars would lose access to raw materials needed for nuclear fusion, and the Universe would become a cold, dark, and lifeless place
Big Crunch
This theory suggests that the Universe will eventually stop expanding and start contracting, leading to a “Big Crunch” where everything in the Universe is compressed into a single point.
This would result in a massive explosion, leading to the creation of a new Universe.
It somehow suggests the oscillatory behavior of the Universe such that it repeats the cycle of creation and destruction.
Big Rip
This theory suggests that the expansion of the Universe will continue to accelerate until it reaches a point where it rips apart everything in the Universe, including atoms and subatomic particles.
This would result in the Universe being torn apart into its fundamental components, the big rip rather paints the bit unsettling portrayal of the Universe succumbing to the overwhelming force of dark energy.
The Heat Death
This theory suggests that the Universe will continue to expand and cool until it reaches a state of maximum entropy, where everything is evenly distributed and there is no more energy left to be expended.
This would result in a Universe that is cold, dark, and lifeless.[7]
Even if we’re talking about the fate of the Universe, it doesn’t imply we know its history precisely.
In order to test the likelihood of any of the theories being true, we may require the lifetime of humanity to last till eternity of the Universe, which is again unlikely.
References
- Trevor Jepsen, ‘Plank Epoch,’ The First Second of The Universe, 2016, http://ffden-2.phys.uaf.edu/webproj/211_fall_2016/Trevor_Jepsen/trevor_jepsen/title_page.html[↩]
- Trevor Jepsen, ‘Inflationary_Epoch,’ The First Second of The Universe, 2016, http://ffden-2.phys.uaf.edu/webproj/211_fall_2016/Trevor_Jepsen/trevor_jepsen/title_page.html (Accessed 2 March 2024[↩]
- Barbara Ryden, ‘Nucleosynthesis & the Early Universe’, Introduction to Cosmology, 13 January 2006, p[208][↩]
- Barbara Ryden, “The Physics of Recombination”, Introduction to cosmology, 13 January 2006, p[194][↩]
- U.S. National Science Foundation, ‘First Stars and First Light: The Epoch of Reionization,’ https://www.nsf.gov/news/special_reports/astronomy/epoch_reionization.pdf[↩]
- Harvard & Smithsonian, ‘Dark Energy and Dark Matter’, Center for Astrophysics, 8 May 2023, www.cfa.harvard.edu/research/topic/dark-energy-and-dark-matter[↩]
- Woollaston-Webber, Victoria, ‘Big Freeze, Big Rip or Big Crunch: How Will the Universe End?‘, Wired UK, 10 October 2016, https://www.wired.co.uk/article/how-will-Universe-end[↩]
