Cosmos by Carl Sagan: Book Notes & Summary

In one of our team meetings at DCKAP, Vibha Nair referenced this book ‘Cosmos’ by Carl Sagan. I have not read any books of this genre and thought it was high time to read one.  Carl Sagan is a name you would have heard a lot. He was the Professor of Astronomy and Space Sciences at Cornell University. He is also the author of more than a dozen books , including Intelligent Life in the Universe, The Cosmic Connection, and the best selling science fiction novel ‘Contact’. This book was written in the 1980s. Let me tell you that it was not easy for me to read this one compared to a business book. It took quite a bit of time as I needed to digest the learnings. I am still not there, however glad I made a start in learning about Cosmos.

In the Introduction of the book there were quotes from other books. Some of it is obvious when you think about it. Here is one. ‘There will come a time when our descendants will be amazed that we did not know things that are so plain to them…) – when memory of us will be erased, quoted from -Seneca, Natural Questions , Book 7, first century. 

Here are my notes from the book. I have broken it down into chapters. Some of these notes are my thoughts and others are just excerpts from the book.

Chapter 1: The Shores of the Cosmic Ocean: 

As humans who live on earth, all of us have concerns. However our concerns are insignificant in the grand scheme of things. To give some context, the author writes that ‘The surface of the earth is the shore of a cosmic ocean’.  In one second a beam of light travels 186,000 miles (300,000 kms) or seven times around the earth. The distance light goes in a year is called the light year. The earth is a place we live in. However, by no means this is the only place. Cosmos is mostly empty space.  For example, if we are randomly inserted into the cosmos, the chances that we will find ourselves on or near a planet would be less than one in a billion trillion trillion. A galaxy is composed of gas, dust and stars (billions of stars). We are in the Milky Way Galaxy. The Milky Way has some 400 billion stars of all sorts. 

In this context , if you think about it, what is the likelihood that only one ordinary star ‘Sun’ is accompanied by an inhabited planet? The author writes that the Universe we live in is brimming over life. We just don’t know yet. We grew up in isolation and are slowly teaching ourselves the Cosmos. Are there our brothers and sisters in Cosmos? Are they very different from us? What is their form, biochemistry, neurology? There must be many such worlds scattered around space. 

‘Eratosthenes’:

The discovery that Earth is a little space or world was made sometime in the 3rd Century B.C at the Egyptian city of Alexandria. Here lived a man called ‘Eratosthenes’. One of his envious contemporaries called him Beta because he was second best in everything (Beta is the second letter of the Greek alphabet). However in almost everything ‘Eratosthenes’ was alpha. He was an astronomer, geographer, philosopher, poet, mathematician and more. The titles of the book he wrote range from Astronomy to On Freedom from Pain. He was also the Director (Chief Librarian) of the Great Library of Alexandria. 

‘Eratosthenes’ was a scientist. He is best known for being the first person known to calculate the circumference of the Earth. He asked himself how at the same moment a stick could cast a shadow in one place (Syene) and no shadow in another place (Alexandria). He asked, How can there be a shadow at Syene and no shadow at Alexandria?  The only possible answer that he saw was that the surface of the earth was curved. The sun is so far that its rays are parallel when they reach the earth. Sticks placed at different angles to the Sun’s race cast shadows of different lengths. The distance between Alexandria and Syene had to be about 7 degrees along the surface of the earth.  He also knew that the distance between Alexandria and Syene was approximately 800 kms (he hired a man to figure it out) . He also predicted that the circumference of earth would be 40,000 kms. This was a remarkable prediction 2200 years ago. He was the first person to accurately measure the size of the planet.  Our Universe is some 15 to 20 billion years old. 

The discovery of America by Christopher Colombus and the journeys the following centuries have completed the geographical exploration of earth. The earth now is thoroughly explored. But the interesting thing is that the technology that allowed us to explore the remotest parts of the earth also allows us now to venture into space and explore new worlds. Our ancient astronomers like ‘Eratosthenes’ were correct and they would have been excited seeing our discoveries which were very much in line with theirs. 

Alexandria: 

The city of Alexandria was founded by Alexander the Great and constructed by his former bodyguard.  His city was a world center of Culture , Commerce and Learning. Alexander’s monumental tomb and an enormous lighthouse , the Pharos is one of the seven wonders of the world.  However the great marvel was the library and its associated museum. This place was truly the first research institute in the world. The scholars in the library studied the entire cosmos. ‘Cosmos’ is a Greek word for the order of the Universe. It implies the deep interconnectedness of different things. In the library, scholars explored physics, literature, medicine, astronomy, geography, philosophy and more. 

In addition to ‘Eratosthenes’ there was an astronomer Hiparchus who mapped the constellations and estimated the brightness of the stars. Herophilus the physiologist firmly established that the brain rather than head is the seat of intelligence. Heron of Alexandria, inventor of gear trains and steam engines (and the author of Automata, the first book on robots). 

The Greek Kings of Egypt who succeeded Alexander were serious about learning. For centuries they supported research and maintained the library. The library contained half a million volumes of handwritten papyrus scroll. Only a small fraction survived. The library was destroyed seven centuries after its founding.  In one of the books in the library, an astronomer Aristarchus of Samos argued that Earth was one of the planets and the stars were far away. Each of these conclusions were correct and we appreciate this achievement of our classic civilization.

Chapter 2: One Voice in Cosmic Fugue

Ten thousand years ago there were no dairy cows. Creatures looked quite different and we controlled their breedings. We preferentially reproduced based on the properties we considered desirable. If humans can make new varieties of plants and animals, should nature also do so? This process is called Natural Selection. If artificial selection can make massive changes in a short span of time, what about natural selection working over a billion years? The beauty and diversity of the biological world we live in is the answer. Evolution is a fact and not just theory. Evolution through natural selection is the great discovery associated with the names of Charles Darwin and Alfred Russel Wallace. 

Origin of Species:

‘The environment selects those few mutations that enhance survival resulting in a series of slow transformations of one life form into another , the origin of new species’- Charles Darwin.

What happened on earth could be typical of how life evolves in other worlds. However life on earth is unique in all the Milky Way Galaxy.  Sex was invented some 2 billion years ago. Organisms are selected to engage in sex. The ones that find it uninteresting quickly become extinct. For most of the 4 billion years of the origin of life, the dominant organisms were blue green algae which covered and filled the oceans. 600 million years ago, new forms of life emerged in an event called the Cambrian explosion. Species now on the planet once did not exist. Species appear, live and flicker out. 10 million years ago , species who resembled human beings appeared and only a few million years ago the first true humans emerged. If we go far back, we have a common ancestor. In the future we may be able to assemble or produce whatever characteristics we desire in a human being.  Evolution works through mutation and selection. 

We humans look different from a tree. However trees and us are essentially the same. We both use nucleic acids for heredity. Both use proteins as enzymes to control the chemistry of our cells. All of us descended from a single and common instance of the origin of life in the early history of our planet. 

The smallest known free living organisms are the PPLO (pleuropneumonia like organisms). However the earth we live in today is not favorable for small organisms. (They have to work hard to make a living). There is still a lot to be understood about the origin of life. However we have been performing such experiments only for 70 years or so. Nature has had a 4 billion years head start. The diversity of living things on earth share an identical molecular biology. 

Chapter 3: – The Harmony of Worlds

There used to be a time when there was no television, before motion pictures and books – The greatest part of human existence was spent in this time , campfires, and on a moonless night, people watched the stars. We live in an in-between Universe where things change, but it was according to patterns or rules – which we called the Laws of Nature. (e.g. If a stick is thrown up in the air, it always falls down, sun rises in the east and sets in the west). Occasionally our ancestors would see a very bright star. They called it a falling star. There are different constellations in different seasons. There is an order and predictability about stars. The rising of the sun after its absence in the night was noted by people all around the world. People all over the world made an effort to study astronomy.The more predictably you knew the movement and position of the sun, moon and stars you would know when to hunt, when to sow, reap and gather the tribes.  There are more astrologers than astronomers. A good way to overthrow a regime is to predict its downfall. The notion of personal astrology developed in Alexandrian Egypt and spread to Greek and Roman worlds 2000 years ago.  We correlate astrology with stars. It can also be found in words such as disaster, (Greek Word for Bad Star). Astrology can be tested in the lives of twins. Though two babies were born almost at the same time we have seen where one of the twins dies (maybe struck by lightning) and other loves to a prosperous old age. The flags for a lot of countries have stars in them (United States) have 50 stars. We seek connection with the Cosmos. 

Modern popular astrology runs back to when Claudius Ptolemaeus (called Ptolemy) worked in the library of Alexandria. As an astronomer Ptolemy names the stars, listing their brightness. He gave good reasons for believing earth is a sphere. He believed that the earth is the center of the Universe and Sun, Moon, Planets and stars went around the earth. His model prevented the advancement of astronomy for a millennium. However in 1543 Nicholas Copernicus’ proposition was that the Sun and not the earth is at the center of the Universe and earth was just one of the planets. 

Johannes Kepler:

Kepler was born in December 1571 and lived until 15 November 1630. During Kepler’s time there were only six planets known (Mercury, Venus, Earth, Mars, Jupiter and Saturn). Kepler was a brilliant thinker, however a very poor classroom teacher. He was a German astronomer, mathematician, astrologer, and natural philosopher. He is best known for his laws of planetary motion. Kepler also collaborated with Tycho Brahe in Prague. His work also influenced Newton to discover the laws of gravitation. He is also described as the father of science fiction for his novel Somnium.

Kepler was one of the first to propose that planets were material objects made of imperfect stuff like the earth. He also found that Mars moves about the Sun not in a circle, but in an ellipse. Kepler’s first law of planetary motion – A planet moves in an ellipse with the Sun at one focus. 

When a planet is close to the sun, it traces out a large arc in the orbit but the area represented by the arc is not large as it is close to the sun. When the planet is far from the sun, it covers a much smaller arc in the same period of time. Kepler found that these two areas were precisely the same no matter how elliptical the orbit.  This was Kepler’s second law – Planets sweep out equal areas in equal times. 

Kepler’s Third Law of Planetary Motion – a law that related to motion of planets with respect to one and another. His third law states that the time that takes for a planet to complete one orbit is proportional to the cubes of their average distance from the sun. The more distant the planet, the more slowly it moves. Simple Formula (p^{2}=a^{3}. (P square = A cube). P represents the period of evolution of the planet and A is the distance of the planet from the sun measured in astronomical units. An astronomical unit is the distance of the earth from the Sun measured. Jupiter for example is 5 astronomical units from the Sun. a cube = 5 X 5 x5 = 125 – What number of times equals 125?  (11 is close enough) – It takes 11 years for Jupiter to go around the sun (A similar argument applies for every planet and asteroid and comet). 

Kepler said Astronomy was a part of physics. He could be considered as the first Astrophysicist.  When Galileo discovered the first astronomical telescope, Kepler called Lunar geography was becoming possible. The observational search for extraterrestrial life began in the same generation of the invention of the telescope. 

Kepler is a key figure in the 17th-century Scientific Revolution, best known for his laws of planetary motion, and his books Astronomia nova, Harmonice Mundi, and Epitome Astronomiae Copernicanae, influencing among others Isaac Newton, providing one of the foundations for his theory of universal gravitation.[6] The variety and impact of his work made Kepler one of the founders and fathers of modern astronomy, the scientific method, natural and modern science. He has been described as the “father of science fiction” for his novel Somnium.

Sir Isaac Newton:

During the Christmas Day of 1642, Sir. Isaac Newton was born , so tiny. He was quarrelsome, felt abandoned by his parents, and unsociable. He perhaps is the greatest scientific genius who ever lived.  At the Stourbridge Fair in 1663, at age 20, he purchased a book on Astrology out of curiosity to see what was in it. He could not understand and he started learning about trigonometry. He found a copy of Euclid’s Elements of Geometry and began to read. Two years later he invented differential calculus.

In 1666, at age 23, when Newton was an undergraduate at Cambridge University when an outbreak of plague forced him to spend a year in an isolated village of Woolsthorpe(where Newton was born). He spent his time wisely inventing differential and integral calculus , making fundamental discoveries on the nature of light and laying the foundation for universal gravitation. 

When Newton was asked how he made such great discoveries, he just replied ‘By Thinking about them’. According to his servant, Newton did not take any recreation. When he lectured hardly a few students went to hear him and even fewer understood him.

Sir Newton invented the Law of Inertia , the tendency of a moving object to move in a straight line , unless something influences it and moves it out of its path. The Moon would move in a straight line unless there was a force diverting it. This force Newton called Gravity. Newtonian gravity applies everywhere in the universe. Newton does not acknowledge the contributions of Johannes Kepler in his masterpiece ‘Principia’. However, In his 1686 letter to Edmund Halley he says of his law of gravitation ‘I can affirm that I gathered it from Kepler’s theorem about twenty years ago’. Newton was fiercely competitive, however modest.  Just before his death, Sir Isaac Newton wrote ‘I do not know what I may appear to the world; but to myself I seem to have been only like a boy, playing on the seashore, and diverting myself, in now and then finding a smoother pebble or prettier shell than the ordinary, while the great ocean of truth lay all undiscovered before me’.

Johann Bernoulli in 1696 independently of Newton had invented the differential calculus. 

Chapter 4 : Heaven and Hell

There is abundant evidence of major catastrophes. An event which may be unthinkable in 100 years may be inevitable in a hundred million. In the early morning of June 30, 1908 in Central Siberia a giant fireball was seen moving rapidly across the sky. An enormous explosion took place and it leveled some 2000 square kilometers of forests and burned thousands of trees in a flash. It produced an atmospheric shock wave that circled the earth twice. This was called the ‘Tunguska’ event. The reason, in 1908 a piece of comet hit the earth.

A comet is made mostly of ice – water (H2O) ice, with little methane (CH4) ice and some ammonia (NH3) ice. Striking the earth’s atmosphere will cause a great radiant fireball and blast wave which will burn down trees, forests and more.

On some nights we can see a shower of meteors , always on the same few days of every year. Meteors are the remnants of comets.  Newton before his invention of the reflecting telescope spent sleepless nights searching the sky for comets with his naked eye. Following Tycho and Kepler Newton conclude that comets seen from the earth do not move within our atmosphere. Regular cometary orbits led Edmund Haley to calculate that comets of 1531, 1607 and 1682 appeared in intervals of 76 years and predicted its return in 1758. The comet duly arrived and was named after him – ‘Comet Halley’ and has played an interesting role in human history. Modern planetary scientists argue that collision of a comet with a planet may make a significant contribution to the planetary atmosphere.

The earth is r=1 astronomical unit.  1 Astronomical Unit = 1,50,000,000 kilometers from the Sun. Earth’s orbital speed is about 30 km/second.  An impact of a small cometary fragment with earth as at Tunguska should occur once in 1000 years. An impact with a large comet like Halley’s Comet should occur only once in a billion years. A thousand earths can fit inside a jupiter. If a comet or an asteroid dropped into Jupiter, there would not be much impact. Between the orbits of Mars and Jupiter are countless asteroids , tiny terrestrial planets.Jupiter is made almost entirely of hydrogen.Venus has almost the same size, mass and density as of earth and for centuries has been considered as earth’s sister. The first person to see Venus through a telescope was Galielo in 1609. The atmosphere of Venus is composed of 96% carbon dioxide. The development of science on earth was driven by observations of the regularity of stars and planets.  Like Venus, the Earth also has the GreenHouse effect. The GreenHouse effect is the reason for high surface temperature. The global temperature of the earth will be below freezing point of water if not for the greenhouse effect.  We burn wood, coal and more and this causes the release of more CO2 to the atmosphere. We have to be careful. Even a one or two degree rise in the global temperature could have catastrophic consequences. We pollute the atmosphere with long term consequences largely unknown. 

The author also writes that most of Europe was once covered with ice. A few million years ago, the present City of Chicago was buried under 3 kilometers of frost.  Our lovely planet earth is the only home we know so far. Venus is too hot, Mars is too cold , but the earth is just right, a heaven for humans. 

Chapter 5 – Blues for a Red Planet

Why Mars? Mars is very earth-like. It is the nearest planet whose surface we can see.  Percival Lowell founded a major observatory where the most elaborate claims in the support of life on Mars were developed. The first two letters of the name Pluto are the initials of Percival Lowell. His vision of Mars gained acceptance. Because Mars is farther from the sun as compared to the earth, its temperatures are much lower.

Five Soviet spacecraft, Venera 8 – 12 have landed on earth and successfully returned data from the surface.  Large plants and animals did not colonize the earth until the last 10% of the earth’s history. Yet, for three billion years there were microorganisms everywhere on earth. To look for life on Mars we should look for Microbes. 

Wolf V. Vishniac was a key figure in the search for life on Mars. Vishniac was a professor of biology at the University of Rochester. He died while on a research trip to Antarctica in 1973.

The author shares that every now and then we read that the chemicals that constitute the human body costs 97 cents or 10 dollars. We are mostly made of water which costs almost nothing, the carbon is cost in the form of coal, calcium in our bones as chalk, nitrogen in our proteins as air, iron in our blood as nails. All we have is a mixture of atoms.

The surface area of Mars is as large as the land area of earth. The author writes that there will be a time when Mars is fully explored.  Terraforming is the concept of transforming the alien landscape into a place more suitable for human beings.

Chapter 6 – Travelers’ Tales

The author writes that the 15th through 17th centuries represent a major turning point in our history. Vessels from European nations dispersed to every ocean. Greed, Ambition, National Pride, scientific curiosity and many could be reasons for this.  Holland(Netherlands) was at the center of this during this time. Some expeditions journeyed from there to a place called New Holland (now called Australia). Seventeenth century Holland was home of the great Jewish Philosopher Spinoza whom Einstein admired. This was the time of Leeuwenhoek , the inventor of the microscope.  In the Dutch tradition of encouraging freedom of thought the University of Leiden offered a professorship to Italian Scientist Galielo. Never before or since then has Holland been the world power since then. Holland became the leading publisher and bookseller in Europe, translating works written from other languages. Dutch Republic was governed by the people. 

In Italy, Galileo who had announced other worlds was reprimanded,  however in Holland Christiaan Huygens who had similar thoughts was showered with honors. Leeuwenhoek and Huygens were the first people ever to see human sperm cells , which helped us understand human reproduction. Microscopes and Telescopes both developed in early 17th century Holland.  Huygens also invented the pendulum clock. 

Jupiter is a source of radio emission, and was discovered accidentally in the 1950s by Americans Bernard Burke and Kenneth Franklin while examining the sky with newly constructed radio telescopes. They were searching for radio sources beyond our solar system. These accidental discoveries are typical in the history of science. 

Chapter 7 – The backbone of Night

The author writes about his curiosity to learn about astronomy. Superstitions and Gods were created because we were not sure about some of the things that were happening around us. (e.g earthquakes, storms, epidemics and more). Humans eat animals and animals eat humans and we are all part of the same ecosystem. Earth is a planet and there could be a lot more planets like earth which we do not know. Science would have been discovered by one culture or the other. It so happens that sometimes one culture is first in the discovery. Ionia (present day Turkey) was the place where Science was born (between 600 and 400 B.C), approximately 2600 years ago. Some of the brilliant Ionian thinkers were sons of some of the sailors, farmers and weavers. The first Ionian scientist was Thales of Miletus. He had traveled to Egypt and was conversant with the knowledge of Babylonian. It is said that he predicted the solar eclipse.He learnt how to predict the height of the pyramid from the length of its shadow and the angle of the sun above the horizon, a method used today to determine the heights of the mountains of the moon.The continuity of intellectual effort is there from Thales to Euclid to Isaac Newton that created the modern Science and Technology. Thales attempted to understand the world without invoking the intervention of Gods. Thales lived in poverty, however because of his scientific skills, he could predict the harvest times and that made him rich. 

Anaximander of Miletus (ancient Greek City) was the first person in Greece to make a sundial , a map of the known world and a celestial globe that showed the constellations. He also concluded that human beings evolved from other animals. Democritus from the Ionian colony of Abdera in Northern Greece discovered the existence of atoms. He invented the word atom (Greek for unable to cut). When we cut an apple , the knife should pass through empty spaces between atoms. Anaximander and Democritus’ thoughts preceded Darwin’s great idea of evolution by natural selection. People were punished for having unusual ideas. 

Anaxagoras (who lived around 450 B.C) was the first person to state clearly that the Moon shines by reflected light and devised a theory for the phases of the moon. Pythagoras (6th century B.C) was very influential and the first person to conclude that earth was a sphere. He and his disciples discovered the  Pythagoras theorem. (The sum of the squares of the shorter sides of the right triangle equals the square of the longer side). He was the first person who used the word Cosmos (a well ordered harmonious universe). Artistarchus , born in Samos,  three centuries after Pythagoras was the first to hold that the Sun is at the center of the planetary system and not the earth. Near the center of the milky way, millions of stars will be visible to the naked eye compared to the paltry few thousand. 

Chapter 8 – Travels in Space and Time

Cosmos is very rich. The total number of stars in this universe is greater than all the grains of sand on all the beaches of planet earth. A constellation is an arbitrary group of stars. Few stars move out and some come in changing the constellation. All places on earth are the same distance from any star. Astronomically the US and Russia are at the same place. The average distance between the stars is a few light years  A light year being ten trillion kilometers. Stars are born, evolve and die (New ones are born). Nothing in physics prevents us from traveling at the speed of light. Interstellar space flight is possible and it is not an objective for a hundred years but for a thousand or ten thousand.  

Chapter 9 – Lives of the Stars

Atoms are mainly empty space. Matter is composed of nothing. As we know. Water is a molecule made of Hydrogen and Oxygen atoms. Air is made mostly of the atoms Nitrogen(N), Oxygen (O),Carbon(C) , Hydrogen (H1) and Argon (Ar). The earth is a mixture of atoms, mostly silicon, oxygen, aluminum, magnesium and iron. If we subtract one proton and three neutrons from mercury we make gold. Stars like the Sun are born in batches. The author writes that in billions of years from now, there will be the last perfect day on earth. The sun will slowly become red and disintended, ice caps will melt, flooding the coasts of the world. Eventually the oceans will boil and human beings will have evolved into something quite different. The origin and evolution of life is connected to the evolution of stars. Life on earth runs because of sunlight. Farming is made possible by sunlight. All of us are solar powered. Black Holes were first thought by an English Astronomer John Michell in 1783.  The Sun is an ordinary or mediocre star. We are at the beginning of our galaxy exploration. 

Chapter 10 – The Edge of Forever:

The author writes of the Big Bang which happened ten or twenty billion years ago which created the universe. He also writes on God. If God created the world, where was he before and after?  Sound is a succession of waves in air. The closer together the waves are, the higher the frequency and pitch, the farther apart the waves are, the lower the pitch.  The author writes that the Universe has been expanding since the Big Bang, the expansion may gradually slow , stop and reverse itself. The author imagines a strange country where everyone is flat. Everyone in flatland had width and length, no height.  We have no trace of up-down. 

Chapter 11: – The persistence of Memory

The author writes that Writing is perhaps the most important invention of this world. This ensured that history was documented. The information stored in our genes (most of it) is millions of years old, writing (in books) is thousands of years old and in our brains is only 10s of years old. We have 5 fingers because we descended from the devonian fish that had five bones in its fins… If they had 4 or 6, then 4 or 6 fingers would have been the norm. For 99.9% of history, Whales did not have any interference. However with the invention of steam ships , there was noise pollution and suddenly the ocean had to be shared. The dinosaurs did not survive the evolution and no one knows what wiped them out. In the 17th century we travelled from Brooklyn to Manhattan across the east river by Ferry. This changed in the 19th century. With technology a suspension bridge was built and later a tunnel under the river was built. This use and reconstruction of previous systems is very similar to the pattern of biological evolution.

Chapter 12: Encyclopedia Galactica: –

The author writes that we do not expect an advanced technical civilization on any other planet in our solar system. If one was behind us (say 1000 years), they would have no advanced technology and if they were ahead of us , they would be here by now. How do we communicate with other civilizations or other planets? This method is called radio astronomy. The largest radar observatory on the planet earth is the Arecibo facility which Cornell University operates for the National Science Foundation The Arecibo Observatory has been used to search for intelligent signals from civilizations in space , broadcast messages and more  Radio Waves travels at the speed of light. With a third or half a trillion stars in the milky way, would ours be the only inhabited planet? We define an advanced civilization as one capable of radio astronomy. The author writes that we are perhaps the first civilization to emerge in the history of the galaxy. 

Chapter 13: – Who Speaks on Earth?

The author writes that the exploration of the cosmos is a voyage of self discovery. The cosmos was discovered only yesterday. For a million years we thought that there were no other places other than earth.If our explorations are successful , it will be as important as colonization or the descent from the trees. The author also writes on the Alexandria Library and how Alexandria was the publishing capital of the planet. Books were expensive, each one of them was copied by hand. They encouraged and financed scientific research. Every major culture (China, India, West Africa) has made significant contributions to our global society and has had great thinkers.The impact of the war is measured by a war index M (Magnitude). M=3 , 10 to the power (10*10*10)=1000 – Only a 1000 people are killed. If the Magnitude is 5 or 6, hundred thousand people or 1 million people are killed. The higher the magnitude, the less likely that the war will happen soon again. The world population was one billion people around 1835 (M=9) and approximately 4.5 billion people now (M=9.7). The author talks about all of us being one world. Our loyalties slowly shifted from self to city to town to state to nation. Instead of investing in wars, we need to invest more on space exploration. One study suggests  that for every dollar spent on the planets, seven dollars are returned to the national economy. This is bound to have better results. The Darwian lesson is that there are no humans elsewhere. We are rare as well as an endangered species. The author writes that our loyalties are to the species and the planets. We speak for earth. 

My Take on the Book:

Thanks Carl Sagan for your excellent book. When I started reading, I was a little worried that I may not be able to complete it. I am glad that I finished reading your book and it offered me a lot of learning. Though I did not understand everything because of my limited ability, I am really glad that I started reading on the Cosmos. Thanks for being a starting point for me. Appreciate your writing.