(PDF) Jayant V. Narlikar, Fred Hoyle - Introduction to cosmology (1993, Cambridge University Press) | Akshay SB - Academia.edu
Introduction to Cosmology J.V. Narlikar pdf free
If you are interested in learning about the origin, structure, evolution, and fate of the universe, you might want to read Introduction to Cosmology by J.V. Narlikar. This is a comprehensive and accessible textbook that covers all the major topics and concepts in cosmology. It is written by J.V. Narlikar, a renowned Indian physicist and cosmologist who has made significant contributions to the field.
IntroductionToCosmologyJVNarlikarPdfFree
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In this article, we will give you an overview of what cosmology is and why it is important, a brief history of cosmology from ancient times to modern era, a summary of the main features and predictions of the standard model of cosmology (the Big Bang theory) and some of its alternative or complementary theories, a discussion of the main components and properties of the universe (such as dark matter, dark energy, cosmic microwave background, etc.) and how they are observed and modeled by scientists, a speculation on what might happen to the universe in the future and what are the prospects for further research and exploration, and finally a guide on how to get a free pdf copy of Introduction to Cosmology by J.V. Narlikar online.
What is cosmology and why is it important?
Cosmology is the scientific study of the origin, structure, evolution, and fate of the universe as a whole. It is one of the oldest branches of science, dating back to ancient civilizations that observed and speculated about the nature and meaning of the sky, stars, planets, sun, moon, and other celestial phenomena. It is also one of the most fascinating and challenging branches of science, dealing with some of the most fundamental and profound questions that humans can ask, such as:
How did the universe begin and what was it like before?
How did the universe evolve and what are the laws and forces that govern it?
What is the universe made of and what are its main components and properties?
How big, old, and diverse is the universe and what are its different regions and structures?
How do we observe and measure the universe and what are the limitations and uncertainties of our knowledge?
What will happen to the universe in the future and what are the possible scenarios and outcomes?
What is the purpose and meaning of the universe and what is our place and role in it?
Cosmology is important because it helps us understand our cosmic origins and context, expand our horizons and perspectives, test our theories and models of physics and mathematics, discover new phenomena and possibilities, and inspire our curiosity and imagination.
The history of cosmology
The history of cosmology can be divided into four main periods:
The ancient period
This period spans from the earliest recorded civilizations (such as the Babylonians, Egyptians, Indians, Chinese, Greeks, etc.) to the Middle Ages (around the 15th century). During this period, cosmology was mostly based on observation, mythology, religion, philosophy, and speculation. Different cultures developed different cosmological views and models, ranging from flat earths to spherical earths, from geocentric to heliocentric systems, from finite to infinite universes, from static to dynamic universes, from cyclical to linear histories, etc. Some of the most influential figures of this period include Pythagoras, Plato, Aristotle, Ptolemy, Copernicus, etc.
The classical period
This period spans from the Renaissance (around the 16th century) to the early 20th century. During this period, cosmology became more scientific, empirical, mathematical, and experimental. The development of new instruments (such as telescopes) and methods (such as calculus) enabled more accurate and detailed observations and measurements of the sky, stars, planets, comets, etc. The discovery of new phenomena (such as the phases of Venus, the moons of Jupiter, the rings of Saturn, etc.) and the formulation of new laws (such as Kepler's laws of planetary motion, Newton's law of universal gravitation, etc.) challenged and revised the old cosmological views and models. Some of the most influential figures of this period include Galileo, Kepler, Newton, Herschel, Laplace, etc.
The modern period
This period spans from the early 20th century to the present day. During this period, cosmology became more relativistic, quantum-mechanical, statistical, and cosmological. The development of new theories (such as general relativity, quantum mechanics, thermodynamics, etc.) and new observations (such as redshifts, Cepheid variables, supernovae, etc.) led to the emergence and establishment of the standard model of cosmology (the Big Bang theory) and its main features and predictions (such as expansion, Hubble's law, cosmic microwave background, nucleosynthesis, etc.). The discovery of new components (such as dark matter, dark energy, black holes, etc.) and new structures (such as galaxies, clusters, superclusters, etc.) revealed the complexity and diversity of the universe. Some of the most influential figures of this period include Einstein, Hubble, Gamow, Penzias, Wilson, etc.
The future period
This period spans from the present day to the unknown future. During this period, cosmology will face new challenges and opportunities. The development of new technologies (such as gravitational waves detectors, quantum computers, space telescopes, etc.) and new methods (such as machine learning, big data analysis, simulations, etc.) will enable more precise and comprehensive observations and measurements of the universe. The exploration of new frontiers (such as multiverse theories, quantum gravity theories, string theories, etc.) and new possibilities (such as time travel, wormholes, parallel universes, etc.) will expand our theoretical and conceptual understanding of the universe. The resolution of open questions and problems (such as dark energy problem, dark matter problem, singularity problem, The Big Bang theory
The Big Bang theory is the standard model of cosmology that describes how the universe began and evolved. According to this theory, the universe started from a very small, hot, and dense point (called a singularity) about 13.8 billion years ago. Then, it underwent a rapid expansion (called inflation) that stretched it to a much larger size and cooled it down. During this expansion, the basic elements of matter (such as protons, neutrons, and electrons) were formed from pure energy. As the universe continued to expand and cool, these elements combined to form atoms (mostly hydrogen and helium), which then formed clouds of gas that eventually collapsed to form stars and galaxies. The Big Bang theory also predicts that the universe is still expanding today and that it will continue to do so in the future.
The Big Bang theory is supported by several lines of observational evidence, such as:
The redshift of distant galaxies: This means that the light from these galaxies is shifted to longer wavelengths (red end of the spectrum) because they are moving away from us due to the expansion of the universe.
The cosmic microwave background (CMB): This is the faint radiation that fills the entire sky and that is a remnant of the intense heat and light that existed shortly after the Big Bang.
The abundance of light elements: This means that the relative amounts of hydrogen, helium, and other light elements in the universe agree with the predictions of how they were produced during the early stages of the Big Bang.
The Big Bang theory is not a complete or final explanation of the origin and evolution of the universe. It still has some limitations and uncertainties, such as:
The singularity problem: This means that we do not know what caused or what happened before the initial singularity, or if such a concept even makes sense in physics.
The horizon problem: This means that we do not know why different regions of the universe that are too far apart to have ever been in contact have the same temperature and density.
The flatness problem: This means that we do not know why the geometry of the universe is so close to being flat (neither curved nor open), which requires a very precise initial condition.
These problems have led some cosmologists to propose alternative or complementary theories to the Big Bang, such as:
The steady state theory: This is an older theory that suggests that the universe has always existed and has always been expanding at a constant rate, with new matter being continuously created to fill the gaps.
The inflation theory: This is an extension of the Big Bang theory that suggests that the universe underwent a brief period of extremely rapid expansion during its first fraction of a second, which solved some of the problems mentioned above.
The multiverse theory: This is a collection of theories that suggest that our universe is not unique or isolated, but rather one of many possible universes that exist in parallel or in different dimensions.
The structure and evolution of the universe
The structure and evolution of the universe refer to how the universe is organized and how it changes over time. The universe is composed of various types of matter and energy that interact with each other through different forces. The universe also has different regions and structures that vary in size, shape, density, temperature, and composition. The universe is dynamic and constantly evolving, as matter and energy move, transform, and interact with each other.
The main components of the universe are:
Ordinary matter: This is the type of matter that we are familiar with, made of atoms and molecules. It includes stars, planets, gas, dust, and living beings. Ordinary matter accounts for only about 5% of the total mass-energy of the universe.
Dark matter: This is a mysterious type of matter that does not emit or reflect any light or radiation, but exerts a gravitational influence on other matter. It is inferred from its effects on the motion and distribution of galaxies and clusters. Dark matter accounts for about 27% of the total mass-energy of the universe.
Dark energy: This is a mysterious form of energy that causes the expansion of the universe to accelerate. It is inferred from its effects on the distance and brightness of distant supernovae. Dark energy accounts for about 68% of the total mass-energy of the universe.
Radiation: This is a form of energy that travels in waves or particles, such as light, heat, radio waves, X-rays, gamma rays, etc. Radiation accounts for a very small fraction of the total mass-energy of the universe.
The main structures of the universe are:
Galaxies: These are large collections of stars, gas, dust, and dark matter that are held together by gravity. There are billions of galaxies in the observable universe, with different shapes, sizes, and ages. Some galaxies are isolated, while others form groups or clusters.
Stars: These are massive balls of plasma that produce light and heat by nuclear fusion in their cores. There are trillions of stars in the observable universe, with different colors, sizes, temperatures, and lifetimes. Some stars are single, while others form binary or multiple systems.
Planets: These are solid or gaseous bodies that orbit around stars or other objects. There are thousands of planets in the observable universe, with different sizes, compositions, atmospheres, and climates. Some planets have moons or rings around them.
Asteroids, comets, and meteoroids: These are small rocky or icy bodies that orbit around stars or other objects. They vary in size from a few meters to hundreds of kilometers. Some of them collide with planets or moons, causing craters or impacts.
The main regions of the universe are:
The observable universe: This is the region of space that we can see or detect with our current instruments and methods. It has a radius of about 46 billion light-years (the distance that light travels in one year), which means that it contains information from up to 46 billion years ago (the age of the oldest light we can see).
The unobservable universe: This is the region of space that we cannot see or detect with our current instruments and methods. It may be larger or infinite than the observable universe, but we do not know for sure.
The multiverse: This is a hypothetical concept that suggests that our universe may not be unique or isolated, but rather one of many possible universes that exist in parallel or in different dimensions. There is no direct evidence for this concept, but some theories predict its existence.
The future of cosmology
The future of cosmology is bright and exciting, as new discoveries and technologies will enable us to explore and understand the universe better than ever before. Some of the possible scenarios and outcomes for the fate of the universe and the prospects for further research and exploration are:
The Big Crunch: This is a scenario in which the expansion of the universe eventually reverses and the universe collapses back into a singularity. This could happen if the density of matter and energy in the universe is high enough to overcome the dark energy that drives the expansion. This scenario is unlikely, given the current observations that suggest that the expansion is accelerating.
The Big Rip: This is a scenario in which the expansion of the universe becomes so fast and violent that it tears apart everything in it, from galaxies to atoms. This could happen if the dark energy that drives the expansion is increasing over time and becomes dominant over other forms of energy. This scenario is possible, but not very probable, given the current observations that suggest that the dark energy is constant over time.
The Big Freeze: This is a scenario in which the expansion of the universe continues forever, leading to a cold, dark, and empty cosmos. This could happen if the density of matter and energy in the universe is low enough to allow the dark energy to dominate over other forms of energy. This scenario is likely, given the current observations that support this trend.
The Big Bounce: This is a scenario in which the universe undergoes a cyclic process of expansion and contraction, with each cycle ending with a big crunch and beginning with a big bang. This could happen if there are some physical mechanisms or laws that prevent the singularity from forming or that trigger a new inflation after each collapse. This scenario is speculative, as there is no direct evidence or theoretical framework for it.
The future of cosmology also depends on the development of new instruments and methods that will allow us to observe and measure the universe more precisely and comprehensively. Some of these include:
Gravitational waves: These are ripples in space-time caused by massive objects accelerating or colliding with each other, such as black holes or neutron stars. They can provide information about events and phenomena that are otherwise invisible or inaccessible to electromagnetic radiation, such as the early stages of the big bang or the interiors of black holes.
Quantum computers: These are devices that use quantum mechanics to perform computations that are impossible or impractical for classical computers. They can help solve some of the most complex and challenging problems in cosmology, such as simulating the evolution of the universe or testing quantum gravity theories.
Space telescopes: These are telescopes that operate in space, outside of Earth's atmosphere and interference. They can observe and detect electromagnetic radiation across a wide range of wavelengths, from radio waves to gamma rays, and reveal new aspects and details of the universe.
How to get a free pdf copy of Introduction to Cosmology by J.V. Narlikar?
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The legal and ethical issues
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The best sources and websites
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The Internet Archive: This is a non-profit digital library that provides free access to millions of books, documents, audio files, video files, and web pages. You can find a free pdf copy of Introduction to Cosmology by J.V. Narlikar at https://archive.org/details/introductiontoco0000narl.
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Conclusion
In this article, we have given you an overview of what cosmology is and why it is important, a brief history of cosmology from ancient times to modern era, a summary of the main features and predictions of the standard model of cosmology (the Big Bang theory) and some of its alternative or complementary theories