Science and knowledge
Dr. Sohail Zuberi
Thanks to all of us.
When the universe began, there was neither space nor time. Free from space and time. It is impossible to imagine that the vast universe that we see around us, with trillions of galaxies and billions of stars in each galaxy, was focused on a single point. And then the universe began with a big bang. Contrary to the name, the Big Bang does not mean that the universe began with a loud explosion. The term implies that the universe began to expand very rapidly and is still expanding.
How was the universe created?
Why was it born?
What were the motivations behind its inception?
It is still a mystery.
The first second of the universe is the most important in the life of the universe. What happened in those early moments essentially determined what kind of universe it would be and what the laws of nature would be by which this universe and all the matter and energy in it would continue to travel. will Here we first present the evolution of the universe in this critical second based on current theories.
The earliest moments of the universe spanned from the time of the Big Bang to the present, which is a trillionth of a trillionth of a billionth of a second. That's an incredibly short time. This is the era when energy and its associated fluctuations, dominated. The important thing is that we know nothing about these very early moments of the universe. What happened during this period cannot be fully understood until the two major theories, quantum mechanics and the theory of relativity, (which have been the subject of this series of articles) are combined into a unified theory. This era is called the Planck era, named after Max Planck, the founder of modern quantum mechanics.
At the end of the Planck era, the universe was trillions of times smaller than the size of an electron. Remember that the size of an electron is one trillionth of a millimeter. It was the time when all the forces of nature, gravity, electric and magnetic forces, the nuclear force that binds the nucleus together, and the weak force that allows particles to escape from the nucleus, all converged. They were all part of the same force.
The most important event associated with the birth of the universe occurred at the end of the Planck period, an incredible expansion of the universe in a very short period of time. This was the time when the universe consisted only of energy and no particles of any kind existed. At that time the energy density was very high. At that time the temperature and pressure were incredibly high, just like steam in a pressure cooker. As a result of this pressure, the universe expanded very rapidly over a very short period of time. During this period, known as the period of inflation, the volume of the universe increased by 10^78 (i.e. 78 after one) times.
In this early period, the universe was extremely hot with immense energy. This energy was creating pairs of massive particles and their antiparticles like electrons and positrons. A positron is the antiparticle of an electron. These particles exist for a short time and then combine with each other and convert back into energy. This exchange of energy and particles continued during this period of incredibly high temperatures.
This is the period when something happened that resulted in particles like electrons completely dominating the antiparticles like positrons, thus breaking the equality of numbers of electrons and positrons. It gave birth to the universe we see today. If, for each particle, there was a corresponding antiparticle, they would be merging into energy, and there would be no stars, no planets, no humans, no trees, no oceans.
At the end of a billionth of a second, the universe had cooled to about a thousand trillion degrees Celsius and had expanded to a size larger than the solar system during that time.
All the forces of nature were separated from each other. Now the nature of gravity began to look very different from the electric and magnetic forces.
As time went on, the universe cooled. By the end of the first second, it had cooled enough that smaller particles, such as electrons, protons, and neutrons, could exist. As we will mention later, such particles, with energy in the form of photons, will cause further evolution. As the universe cooled by about a billion degrees, it expanded by about ten light-years.
Obviously the expansion of several light years in just one second means that the rate of expansion was much faster than the speed of light.
After the period of initial inflation, the rate of expansion slowed considerably. For example, the universe was about the size of our galaxy, the Milky Way, about three years into its existence.
When the universe was a second old, it was too hot to form a stable nucleus consisting of protons and neutrons. At that time, the universe was like an ocean of particles like electrons, protons and neutrons.
After a few minutes the temperature dropped to 1 billion degrees. At this temperature, protons and neutrons combine to form deuterium nuclei. Deuterium is a form of hydrogen whose nucleus consists of one proton and one neutron. Deuterium nuclei, through a process called nucleosynthesis, combine to form helium nuclei, which contain two protons and two neutrons.
After the first three minutes, no new elements could be formed for millions of years. The universe consisted only of hydrogen and helium nuclei and energy.
The universe was still too hot for electrons, protons and neutrons to combine to form atoms.
For about 380,000 years, electrons, positively charged nuclei of light elements, and photons dominated the universe. At the end of this period, the temperature was 3000 degrees. This is approximately the moment when the electrons are able to combine with the hydrogen nuclei to form hydrogen atoms. Light (or photons) could now travel long distances. The universe was no longer a blur. An atomic age had now begun, paving the way for the formation of hydrogen, then helium, and then heavier atoms, such as oxygen, carbon, iron, and other elements.
This was the time when hydrogen and helium atoms were scattered all over the universe and moving in different directions. It took a long time for the gravitational force to pull the hydrogen and helium clouds together to form a star. The first stars formed about 180 million years after the Big Bang. Nuclear fusion began in the stars' cores, giving the stars light and heat. It took another 200 million years for the first galaxies to form. Over billions of years, stars, galaxies, and clusters of galaxies evolve into other cosmic bodies such as pulsars, neutron stars, and black holes.
The process of forming galaxies is still going on. Galaxies can merge together under the influence of gravity. For example, our galaxy, the Milky Way, is about 2.5 million light-years away from the nearest galaxy, the Andromeda Galaxy. Despite such a great distance, the two galaxies are pulling each other due to gravity and are approaching each other at a speed of about 100 kilometers per second. At this rate, it can be estimated that these two galaxies will collide after five billion years.
This seems quite surprising. How can gravity be strong enough to attract a galaxy so far away? But the total mass of galaxies can be much larger. The Milky Way contains three hundred billion stars, and the Andromeda Galaxy has about a trillion stars. The distance between the two is only 25 times the size of the Milky Way. Thus, the presence of gravity between the two galaxies becomes possible.
Our Sun was born about 9 billion years after the Big Bang. The planetary system, including the Earth, also came into being at the same time. Since the universe is now believed to be 13.8 billion years old, the age of our Sun can be deduced to be approximately 4.8 billion years.
Earth was born 4.6 billion years ago. For the first 700 million years, Earth was too hot to support any form of life. Temperatures gradually cooled and the Earth was able to support life about 4 billion years ago. The oldest rocks with fossil evidence of life on Earth are about 3.5 billion years old, 10 billion years after the creation of the universe.
The beginning of life on Earth, from our perspective, was a defining event in the history of the universe. Imagine if, for all those billions of years, there were no terrestrial beings to observe or make use of the universe.
It is still a mystery how life originated on our planet, Earth. It is a mystery how those scattered atoms could somehow come together to form life from these elements.
How did all the basic building blocks of life, such as DNA, RNA, amino acids, and sugars, come together to create life?
It is still a scientific mystery how life evolved from elements that had no signs of life.
There are many theories about the beginning of life on Earth, but there is no consensus. One plausible theory is that life began as a 'soup'. After the birth of the Earth, it was possible for oceans to form, full of chemicals that contained the life-giving elements that were important for the creation of life. They accidentally created, at some point, the simplest form of life, a living cell. This is a hypothesis, the exact way life started is still hidden from scientists.
And then how did the human evolve from this cell? The whole story of this long journey is not yet known. But it can be hoped that in the coming years we will know the answer to this question.
Many more questions come to mind with the Big Bang model of the universe.
The first question is, what was there before the Big Bang? Some cosmologists argue that this is a meaningless question because both space and time came into being as a result of the Big Bang. So there was no time before the Big Bang. But then what does it mean to say that the universe was born 13.8 billion years ago? What was happening 14 billion years ago, 200 million years before the Big Bang? At this point, it seems more a metaphysical question than a science question.
Then the question is, what triggered the Big Bang? Again, current theories are unable to answer this fundamental question.
Another question is, if the universe is expanding, what is it expanding into? When a balloon expands, its two-dimensional surface expands into a third dimension. Our universe is three dimensional. Is three-dimensional space expanding into a dimension we cannot imagine? Scientists answer that the universe is not expanding in a vacuum, but is expanding throughout space. This is something that seems very difficult to understand.
Then how is it that the diameter of the universe, born 14 billion years ago, is more than one trillion light years, when according to the known laws of physics, anything that can reach light Can't go faster than that? The answer is that speed limits apply to material objects. This does not apply to space expansion.
A question comes to mind, why is there three dimensional space and one dimensional time in the universe? When was it decided that our universe must be four-dimensional: three dimensions for space and one for time?
One of the biggest mysteries of the universe is that about 95% of the universe is hidden from our view. This huge part of the universe consists of dark matter and dark energy. How did we arrive at this surprising conclusion?