"The most incomprehensible thing about the universe is that it is at all comprehensible."- ALBERT EINSTEIN
Look up at the mesmerizing night sky; what do you see? Billions of points of light dancing across the night sky, meteorites hurtling down to earth at incredible speed, large milky white band extending from North to South, planets moving haphazardly in the way they like, moon shining due to the reflection of sunlight by its surface, nebula where stars are being forged, alien system of billions of stars and dust called galaxies and large number of stars that have their own planetary systems are few extraordinary sights that a observer here on earth can enjoy. Looking at all these varieties of things one question that has been troubling me since my childhood comes in my mind; where all these things came from? How it all was created? Who are we? What are we doing here? Where are we going? And the most important of all; Can we understand this universe?
Well it’s not only me asking these questions. Humanity have the history of nearly 2,00,000 years here on earth and from its very beginning some intelligent persons were asking these questions and the explanation they came up with varied largely depending on their culture, religion, belief and social environment where they were born. After 2,00,000 years science at its frontier have altered the scenario in the way these questions are answered.
Religious cosmology is a way of explaining the origin of the universe, its evolution and death in terms of mythology that are themselves defined for the ease of humans. The Rig Veda of Hindu religion questions the origin of the cosmos in: “What was concealed? And where? And in whose protection?…Who really knows? Who can declare it? Whence was it born, and whence came this creation? The devas were born later than this world's creation, so who knows from where it came into existence? None can know from where creation has arisen, and whether he has or has not produced it. He who surveys it in the highest heavens, he alone knows-or perhaps does not know.” It now offers a simple explanation to all these questions; Brahma (the creator) created this world in the form of egg (that’s why universe is called “brahmanda”); this egg expanded and ultimately gave rise to everything-you, me, plants, animals, land, ocean, Earth, planets, solar system, stars, galaxies and the whole universe itself. Clearly this explanation is unsatisfactory. It says nothing about the detailed process of formation of the large structure of the universe, how stars were formed, how earth formed, why there are so many stars in the universe? So this explanation doesn’t seem satisfactory.And another thing that troubles me is that these answers were not given on the basis of observation. How can we explain the real world without observing it? It is like asking some blind person how the stars look at night. I believe we need some extraordinary logic and observations of the real world to describe the origin, evolution and death of the cosmos which are based upon some real facts and have solid proof which are observation based but logically consistent and Science is one and only the gift for humanity that has got all these powers within it.
After 2,00,000 years on Earth humanity have developed a tool for measuring and explaining this universe in some remarkable way which our ancestors even had not imagined of. Science which is based upon the observations of the real world combined with logic to give consistency in what we think and what goes in the real world have come up with an extraordinary explanation to some of the above questions.
Nearly 13.7 billion years ago there was nothing-nothing at all not even space and time and so there was no outside and no events. All there was, was inside and this inside is not ordinary. With its temperature sworing up to 10^28 K * and density can’t be counted by numbers everything was in the form of pure energy, a chaotic system of immense energy and power where the usual laws of physics do not work at all. Imagine compressing our Earth into the size of a soccer ball. What will happen is that all the things we see around us, mountains, hills, plants, tracks everything would have to lie within that soccer ball. Even our wildest imagination can’t grasp what will happen then. Due to the compression the particles of earth would come close to each other and start bouncing off thereby raising the temperature to some thousands of degrees and its density; incredible. Take one spoonful matter of this compressed earth; you’ll find its weight equivalent to a cargo ship full of load (thousands of tons). This is the compressed earth; a system full of chaos and uncertainties. Earth hurtling through space at the speed of 1,00,000 miles/hr relative to the center of Milky way is a planet orbiting a medium sized yellow star Sun somewhere in a system of billion of stars what we called Milky-Way galaxy. Our Milky way is one among billion of galaxies that make up the universe, so Earth is nothing more than a speck of sand in this extraordinarily large universe, so imagine what could have happened when all of the entire universe was compressed down into a single point, no larger than an atom….Incredible! Here every physical parameter that describe our world like density, mass, force etc was infinite, so you can’t apply the usual laws of physics and see what happens, even law of conservation of matter and energy is not applicable here- this is called a singularity, a place of infiniteness and this is the place where we came from.
Suddenly something happened; that tiny point suddenly exploded throwing all of its energy in the space that was itself created at this moment, so space came into existence and then time and obviously energy. The reason of this explosion is however unknown till this day. Whatever be the cause the universe was born with all of its incredible energy pouring down onto the space much like water spreading out in a plane plastic plate. Now the universe began to grow larger and larger by each passing second, so the temperature of the universe began to drop with its expansion. After about 10^-36 seconds some mysterious force (negative energy) began to act on the baby cosmos that began to drive the whole universe wildly like a drunkard accelerating his car wildly. This period is called “inflation” and was discovered by American theoretical physicist Alan Guth in 19780 in order to solve the flatness problem of Big Bang theory. The universe expanded from the size of an atom to golf ball size in trillionth of a second, amazingly this rapid expansion of the baby universe took place for only 10^-4 seconds. The universe is inflating rapidly now, in less than a hundredth of a second the universe was as big as our solar system. All the energy of the cosmos is now expanding in all direction getting cooler and cooler by each passing moment.
While the universe was cooling down, the pure energy of the cosmos began to form subatomic particles and their antiparticle- the first stuff there ever was. When a particle and antiparticle (say electron and positron) comes in contact to each other they both destroy themselves thereby releasing the pure energy. There were large number of particles and antiparticles in this baby universe which were moving randomly in all directions along with the expanding universe, so they used to come in contact with each other and destroy themselves thereby releasing pure energy (in physics we term this process as “annihilation”). If one could see this process from outside then it would like a battle between particle and antiparticle. Everywhere in the entire universe, flashes of light were seen. We would never be here to talk about all these things if there was a complete symmetry between particle and antiparticle (if there were equal number of particle and antiparticle) in the early universe. Luckily there was little more matter than antimatter, so after all this processes of annihilation, little (one out of billion) matter survived which would make up the universe as we see today. So it is clear that we are made up of smoke from the big bang.
Over the next 4 lakh years since the Big bang the universe was ultra thick fog of gas (mostly hydrogen), so light couldn’t travel from one place to another. Clearly the universe was completely dark because at this time the universe was totally opaque and this era is rightly called “Dark Age”. After 4 lakh years the fog finally cleared and suddenly there was light, the universe was lit up and became visible. Today we can see this light coming from all direction at all times from every part of the sky. Everywhere in the universe, this light can still be found. In physics we call it “Cosmic Microwave Background Radiation” or simply CMB and was accidently discovered by Robert Wilson and Arno Penzias while working at Bell Laboratory in 1964. They were awarded Nobel Prize in physics for their discovery in 1978. Let’s return to early universe now! All there is now in the universe is a fog of hydrogen gas and other subatomic particles distributed almost equally in all parts of space. Think about it! If the matter in the early universe would have spread out equally in all parts of space then gravity would attract each and every particle equally in all directions, so the net force on each particle would be zero. If this was what continued the universe would be a very boring place because there would be nothing more than a cloud of dense hydrogen gas everywhere in the universe which would stay motionless at all times. I mean there would be no stars, galaxies, planets, earth and nothing at all, only a dense fog of hydrogen gas. Luckily there was little imperfection in the early universe; in some parts of the cosmos there was little bit more matter than in other parts, so gravity now begins to pull the matter more in one direction than in other, so clump of matter began to form in the universe. As time passes by this small clump would grow larger and larger because it attracts more and more nearby matter towards it. In doing so the temperature of the clump began to rise and after millions of years the core temperature is hot enough (over 10 million degrees) to allow hydrogen to fuse into helium, the same process that powers an atom bomb. At such a high temperature and pressure atom of hydrogen gas will fuse to from an atom of helium thereby releasing huge amount of heat and light energy that light up the whole cosmos. This is what powers the sun and other stars till this day. The first star turned on; it was 100 times more massive than our sun and burned deep blue. Now everywhere in the universe stars were turning on one after another. These stars being much more massive than our own sun lived a very short life (a few million of years) and destroy itself into the cataclysmic explosion called “supernova” , the core of the star compressed on itself due to gravity until a massive black hole was formed. Other stars and matter formed a cluster around this massive black hole which after billion years of evolution would form the first galaxies. This is how everything got going.
You may ask “Isn’t it a fancy story? You tell that this happened and then after this happened. But how do u know that this all happened?”. Believe me it is the achievement that science have got due to the hard labor of the greatest minds in the human history for nearly 2 thousand years. Big Bang is not the theory proposed by some individual over a night, it’s the story of 2 thousand year of humanity’s search for ultimate reality, it’s the greatest endeavourer of human mind. Nothing can be more complex and bigger than the universe, so the study of this vast universe also must be great. That’s why I would like to say Cosmology is the greatest science of all.
Time was passing by, with each passing second the universe was evolving rapidly- stars were forming everywhere, black holes were produced, planetary systems like our own were born, life may have been evolved in various forms, stars and black holes were shaping the first galaxies, galaxies were joining the group to form galactic cluster and the whole other processes that would ultimately (after 13.7 billion years) give rise to our beautiful universe as we see it today. Somewhere in one small corner of this vast lonely cosmos a galaxy with all of its majestic spiral arm turning slowly around it emerged out of dust cocoons much like a baby silk worm emerging out from a cocoon; our Milk Way galaxy. It is our home among hundreds of billions of galaxies that make up our visible universe, it is the place of great wonder because somewhere in the depth of one of the spiral arm lives a species who has just figured out how remarkable place the universe really is; us. About 5 billion years ago this small place (our solar system) was filled with dust and gas called solar nebula which was at least 5 times greater than our solar system. This system of dust and gas was in a perfect equilibrium because gravity was acting in all directions so there was no net force in any particle, that’s why it remained stationary without much interesting things going on there. Suddenly within the periphery of this giant nebula a massive star ends its life by going out in a bang, a very huge bang indeed. This star threw all the elements (carbon, oxygen, iron, gold and all the elements of periodic table except hydrogen) that were synthesized at its core in its whole lifetime in all directions, some part of which got mingled with our solar nebula, today from which we all are made up of. Even the atoms in your eyelashes came from the heart (core) of this ancient forgotten exploding star. This massive shockwave disturbed the original equilibrium of the solar nebula so gravity got its teeth to sink. Gravity slowly began to pull more and more matter together like whirlpool of water. Material slowly began gathered in the center and the temperature began to rise (when something is compressed its temperature begins to rise). This process of heating continued for millions of years until the core temperature reached to 15 million degrees Celsius. At this temperature three atoms of hydrogen combines to from an atom of helium (nuclear fusion) thereby releasing huge amount of energy in the space. For the first time our sun ignited, some 4 billion years ago. Planets were forming out dust cocoons in the periphery of the sun. About 15 crore kilometers away from the center of nebula a small planet was taking its shape, out of dust cocoons a planet begins to appear. With its temperature sowring upto thousands of degrees everything in this little young planet was totally molten, large rocks (some as large as Mars) were striking this planet each second which altered the shape of this young planet drastically. One Mars sized big rock was heading towards this young planet with enough energy to alter its story forever. There was a huge collision between them and the materials were blown into the space. This material after rotating Earth for millions of years condensed into one small rocky world; Our Moon. This was how the moon that we see at night was born. And that young planet after billion of years cooled down and became our most lovely thing today; Our beloved home planet, Earth. Life evolved here out of a single cell and due to evolution of billions of years we Human arrived at the scene. This is our story of genesis.
Today when we look out in the universe with powerful telescopes like the one Hubble Space Telescope* we see this sort of process of star formation everywhere in the universe. Large pillar of dusty hydrogen gas stands light year across where stars and planets are formed and amazingly this process is going right in front of our eyes, all you need is to look up at night sky and gaze for hours and hours. This process of star formation doesn’t seem to occur in isolation. I mean there are no places in the universe where one single star is condensing out of dust and gas instead we find that thousands of stars are condensing out at once in the same place. Our solar system is not the special place because there are billions of stars like our sun in our Milky Way galaxy alone. I can’t say exactly how many because no one have ever counted them. So it seems obvious for me to believe that our solar system was formed along with other many stars in the primordial solar nebula, so we must have at least thousands of sibling stars. Another reason to prove this fact is that in the universe stars are rarely found in isolation, they generally love to stay in pair (what we call Binary Star) or in a group of thousands and even millions of stars (what we call Globular Star Cluster) . Of course I can’t explain you where the rest of our siblings have gone but it can be a good research topic to research upon. Our siblings have been lost in this vast chaotic darkness of deep space and we do not know how to recognize them. One method I can suggest to recognize them is to calculate the lifetime of all nearby stars and study those stars in detail which have the same life time as our sun at this moment (it is about 4.5 billion years). Who knows what will happen next?
Sun is in the mid time of its life and burning its hydrogen fuel at a steady rate just slow enough to allow we like civilization to grow and tell this story. But sun is getting brighter and brighter by about .05% every ten years. This may not sound much but over the course of billions of years sun’s temperature would reach up to twice the current temperature i.e. 30 million degrees. In such a condition every life on Earth will be eradicated away and what remains is the lonely planet Earth hanging in space. Sun will grow it’s our layer bigger and bigger after about 5 billon years and become a red giant star. By then it would have already swallowed all of our inner planets; Mercury, Venus, Earth and probably Mars too. Finally sun uses up all of its hydrogen, so there will be no fuel to keep sun burning. Our sun will slowly fade away in the everlasting darkness of space until there will be no light at all to lit our solar system, this stage of sun is called white dwarf. Outer planets Jupiter, Saturn, Uranus and Neptune will fly away in space and get lost in the immensity of this immense universe. If someone will look towards our solar system (perhaps we like civilization) there would be no trace left for them to figure out there ever was star like sun and in one of its planet we like intelligent animal was evolved. We came from space and end in space and this sort of process of life and death would continue in this ever evolving cosmos forever. What a remarkable realization! I think we have got the partial answer of the question “Who are we and what is our destiny?” which have perplexed our ancestors for thousands of year.
The universe would not end with the end of solar system, it will continue to exist at least 30 billion years from now and who knows it may never end too. The universe is expanding and right at this very moment its speed of expansion is increasing i.e. the whole universe is accelerating. It is supposed that a mysterious form of energy called dark energy which pervades all of space and can’t be detected (that’s why it is called dark energy) is driving the universe rapidly. If this continues and if the universe do not have enough mass (to be more accurate it is density rather than mass) to halt this expansion the universe would end its life in complete darkness. Stars would have used up all their fuel and there would be nothing to burn in the entire universe. Galaxies would have move so much apart that no civilization living in one galaxy would ever realize that there are other billion of galaxies like theirs in the universe. A galaxy would be their entire universe. So the universe is now completely dark and the dark energy would tear all the atoms and split it into its constituents (proton, neutron and electron), nothing would exist then. This theory of cosmic death is called “Big Rip”. Look how elegant the universe is; Big Bang combined all the protons, neutrons and electrons into an atom and Big Rip tore all the atoms back into its constituents. Fantastic law of nature at work!
However if the universe have enough mass to halt this expansion then the universe would begin to collapse down into a single point once again, gravity would attract each and every piece of matter and even space and time into a single point so that once gain there is no outside and no events just like in the first moment of Big Bang. This theory is called “Big Crunch”.
Personally I believe in the eternal universe; a universe with no beginning and no end. It may sound strange to you because up to now all I described is the birth and death of the universe as described by science and now I am saying that the universe is eternal. Wait a moment! Let me explain you why? What if our universe is not a unique one? I mean what if there are billion of the universes like our own? I am not trying to bother you here. Think in this way! When the entire universe have been crushed down to a single point at the moment of Big Crunch, I believe another Big Bang would happen and creates a new universe probably with the new laws of physics that are different than in our universe, so this would be a very strange universe for us where the law of gravitation would not exist and even if it existed it would be in a whole new form. May be in this universe force of gravity would decrease not by the square of the distance but may be by cube or 4th power of the distance. I am not sure exactly what will happen but I am trying to illustrate you that this new universe would be a very strange place for us. Maybe we like civilization would grow in that universe and ask about the origin of their universe and discover that their universe was born from Big Bang just like we are doing at this moment. And I think it would be logical to think that this process of formation and death of the universes is not new, it would have continued for several time (may be infinite number of times too), so there were many universes born out of Big Bang and end in Big Crunch before our universe ever existed. It’s the continual creation and destruction of the universes that have been running forever and will do so forever. So isn’t it eternal? Although Big Bang is the origin of our universe but it’s not the origin of everything. For me Big Bang is not the origin of the universe but it’s the point of discontinuity where the information about the earlier universe is lost.
This is the story of everything; from the birth of the our universe to the formation of stars, black holes, galaxies and our own solar system within it and how it will all end. So it is the right time to be alive by things and make the sense of the world around us because we know much more about our universe and our place within it than in all of our human history. So awake now!!
[The writer is second year student of B.Sc. Physics St. X's College, Maitighar, Kathmandu and Active Member of Astronomical Society (NASO), Kathmandu, Nepal]