The making of the universe
Modern life owes a lot to the scientific knowledge humanity has acquired in recent centuries. The capital of wisdom steadily accumulated and widely circulated since the invention of the printing press has been employed in several fields of research, from studies about the earth to life beyond the blue planet. There seems to be little doubt surrounding the contention that science, a method of learning about the world through experimentation and observation, has revolutionised the pace of change since it was adopted by scholars as the modus operandi for general enquiry.
Take, for instance, penicillin, the first antibiotic, discovered by Alexander Fleming in 1928. This drug is thought to have transformed the field of medicine. Without the discovery, claim medical researchers, humans would not be able to treat deadly diseases like bacterial meningitis, bacterial endocarditis and pneumococcal pneumonia, and fatalities in war, especially the two world wars of the twentieth century, would be much higher. In addition to health, stunning breakthroughs in information technology, transportation, industrial productivity, energy and environment, among other areas, have been taking place at breathtaking speed, largely thanks to the extensive employment of the scientific method to test puzzling phenomenon.
Since science has no boundaries, it encourages subject experts to investigate even the grandest of questions. This has allowed scientists to employ the same method used in discovering penicillin to look at the sky and question the very existence of the universe. Over the past few decades, cosmologists (scientists who study the origin, structure and dynamics of the universe), have made tremendous leaps in understanding how the universe has evolved to come to its present state. With the help of particle accelerators, astronomical observations and theoretical speculations, earthlings now have a coherent picture of what happened at the beginning of everything.
The most successful scientific effort to explain the making of the cosmos to date is the big bang theory, which the reader can explore in detail in this explainer. (There exist alternatives to the big bang theory, like the oscillating universe theory, which proposes never-ending cycles of the universe’s beginning (big bangs) and ending (big crunches), and the multiverse theory, which claims that our universe is a part of an ocean of universes, each of them having unique laws of physics).
Proposed by the Belgian astronomer Georges Lemaitre in 1927, the big bang theory argues that our universe came into existence from a very small, very hot and very dense point around 13.7 billion years ago. Expanding on that hypothesis, astronomers would later profess that the universe started expanding within the first second after it came into existence, and continues to do so today, which is causing a continuous drop in its temperatures. The cooling universe has led to the formation of protons and neutrons, created the first atoms, and spurred the formation of stars, galaxies and the solar system.
The Big Bang
Something out of nothing
Time Zero | 0 seconds
There had been nothing before this instant—no space and no time. Then, out of nothing, popped up the universe as an infinitesimally small, infinitely dense and infinitely hot point—the singularity. What caused this event— the big bang—is still unclear, but we do know that both space and time came into existence at this very time. Everything —the plants, animals, planets, stars, the space between them, and even human beings—all came from this singularity. As there was no time before the big bang, it is meaningless to ask what happened before it.
The Singularity Epoch
Searching for a theory of everything
After the explosion | 10-43 seconds
This time period is termed the Singularity Epoch (also called the Planck Era). Present-day understanding of the laws of physics is not applicable here. To be honest, there is no physical theory (at least presently) which can predict what happened during this small time period. Physicists are still actively working on a ‘theory of everything’ to understand the singularity epoch. The entire fundamental forces of nature —gravity, strong nuclear force, weak nuclear force and electromagnetic force—were unified as a single force during the Planck Era.
At the end of this time span, the gravitational force separated from the combination of other forces. The residual three forces were still mixed up as a single grand unified force. Physicists now have a theory—Grand Unified Theory—which can describe the grand unified force, and the laws of physics, as known today, become applicable from this point onward. At this instant, the universe had a very high temperature, and its size was much smaller than a proton.
Dramatic inflation lowers temperatures
Soup of basic particles | 10-35 seconds
Cosmologists believe that our universe went through an episode of dramatic expansion after the big bang. The incident, which they call ‘inflation’, increased the volume of the universe enormously in a very short time. Later on, the expansion rate slowed down. The expansion resulted in a continuous fall in the temperature of the universe.
The expansion of the universe is still continuing, according to scientists. In 1929, when American astronomer Edwin Hubble proved the expansion—he had observed that distant galaxies are moving away from us at a fast rate— to the scientific community for the first time, the big bang theory received great appreciation.
It was also around this time that the grand unified force was further separated into strong and electroweak forces. The temperature at this moment was still very high, which means no proton or neutrons could be formed yet. The universe was a soup of basic particles like quarks, photons and leptons.
Formation of Protons
Annihilation of anti-matter makes matter abundant
The electroweak force had divided itself into electromagnetic and weak nuclear forces a few milliseconds after the big bang (Pakistani Nobel Laureate Abdus Salam played a huge part in deciphering this process).
Now, all the four fundamental forces of nature were split up, as we observe them today. The continuous expansion of early universe had lowered the temperature enough to allow quarks to merge and form protons and neutrons. Anti-matter particles, like anti-protons and anti-neutrons, were also created at this point, but their interaction with matter particles resulted in the annihilation of the both. Somehow, matter particles was slightly more in number than the anti-matter particles, which is responsible of abundance of matter in the universe.
Here Come the Nuclei
Free electrons make for an opaque universe
Start-stop nucleosynthesis | 200 seconds
About 200 seconds after the big bang, the temperature of the universe fell, and the protons and neutrons could combine to from nuclei (core) of low-mass atoms, like hydrogen, helium and lithium—so called Big Bang Nucleosynthesis.
Astronomers can determine the abundance of elements in different regions of the universe by studying the spectrum of electromagnetic light coming from them. They have found out that no matter where one one looks in the universe, the percentage of elements remains roughly the same: hydrogen is around 74 per cent and helium is around 26 per cent. (All heavy elements make a tiny proportion in the universe). Such uniform distribution of elements was a mystery until the big bang theory accurately outlined the physics which makes this possible.
In less than 20 minutes after the big bang, the formation of low-mass nuclei stopped, because the temperatures had dropped below the minimum levels required to support nucleosynthesis. The universe did have light particles (photos) at this time, but due to the compactness of the universe, light could not travel much before it was scattered by interacting with free electrons present at the time. For this reason, early universe remained opaque until a few hundred thousand years after being born.
First Light Pops Up
A dark age follows the recombination processes
Atoms come into existence | 380,000 years
The universe had cooled down enough 380,000 years after the big bang, which allowed the electrons to affix around nuclei and form neutral atoms, a process termed as ‘recombination’. Free electrons in this time period were rapidly depleting, and hydrogen atoms were coming into existence, which do not interact with photons much. These photons gave birth to the first light of the universe—cosmic microwave background—which we can observe even today.
This existence of this light was predicted by physicists in 1948. It was detected accidently, though, in 1965, when two astronomers were working on a radio antenna. On detecting the signal, the duo initially thought it was ‘noise’ and tried to eliminate all of its nearby possible sources. When the ‘noise’ remained, they conducted further investigation into the sources behind it, which revealed it was cosmic microwave background, coming from the early universe.
After the emission of the first light, our universe went through an episode of darkness, known as the Dark Age, until the time first stars came into existence.
Early Stars are Born
Clumps of gas collapse under the influence of gravity
Temperatures allow for fusion reactions | 4 million years
Over time, under the influence of gravity, the hydrogen gas present in the early universe began to accumulate as giant dense clouds. These clumps of gas collapsed, due to their gravity, which raised their temperatures high enough to support fusion reactions between hydrogen atoms. This marks the formation of first stars in the universe which lit up the universe.
After the birth of the first stars, there appeared dense regions in the universe where star formation was active. These regions produced huge number of stars, gravitationally bound with each other, to become what are called galaxies. Soon around this time, the Milky Way galaxy, where the Sun resides, would be formed. The galaxies tended to form, with the support of gravity, giant systems called as galaxy clusters, and these clusters formed superclusters.
Nature of dark energy still unknown
Mysterious force wins over gravity | 9 billion years
In the first few billion years, the expansion of our universe was slowing down, thanks to the gravitational force. But, more recently, the universe has started undergoing an accelerated expansion. Cosmologists believe that this has occurred because a mysterious anti-gravity force has won over the gravity. This force is called Dark Energy, and its nature is not known yet.
Formation of Solar System
Exploding stars give birth to the sun and the planets around it
Break it down to build it back up | 9.1 billion years
The Sun and the planets around it formed when a huge, slowly rotating, cloud of gas and dust collapsed under its own gravity. This cloud had come from debris thrown out by exploding stars, present before the birth of the sun. The continuous collapse of the cloud not only increased its rotation speed, but it also escalated its temperature. At some point, the temperature rose enough in the centre of the cloud to initiate the fusion process, which stopped further collapse of the cloud.
As the Sun was being manufactured, the outer regions of the cloud transformed to become a disk of gas and rocks. The matter in the disk collided and merged into each other to form the planets including the Earth.
Complex life gradually populates the earth
Origins of living things puzzle experts | 10 billion years
The origin of life is still very much a mystery. Some scientists believe that life originated due to a complex chain of chemical reactions that happened in earth’s atmosphere, while many others are of a point of view that a meteorite must have brought living cells on the planet. Whatever be the origin of life, scientists are sure that it happened around 3.5 billion years ago, as this is the age of oldest rocks which have fossil evidence of life in them.
Later on, biologists believe, life evolved through a number of stages to reach its present form. In the beginning, only simple, unicellular organisms were present. It was much later that multi-cellular organisms turned up. After this, more complex life forms started to emerge, spreading across the globe.
Intelligent life has emerged on earth in the past few hundred thousand years. Homo sapiens are exploring the farthest reaches of the universe. On a grander scale, the universe is uniform in every direction. Most of the matter exists in the form of thin filaments and sheets with vast stretches of empty space—void—present between them.
Billions of galaxies are present in the universe and each of these galaxies host billions of stars. Hundreds of planets have been found orbiting their stars in our Milky Way. You just happen to be reading this explainer on one of these planets—the earth!