Stephan Hawking - A Brief History Of Time : #1 Our Picture Of The Universe - Simple Explained

Overview

Through the lines of the book author describe about most fundamental questions of physics and cosmology, such as the nature of time, the origins of the universe, and the ultimate fate of the universe. These theories got improved with new scientists with time. Author clearly mentions that these all are just theories and there is no clear evidence that these are definitely true. These theories grow complex with new scientists and are difficult to understand because of lack of keen observation and lack of brief knowledge about space and existence of universe.

 

Moreover, the book also discusses some of the most important discoveries in cosmology, such as the Big Bang theory, the expanding universe, black holes, and the search for a unified theory of physics. Hawking presents these concepts in a way that is accessible to the layperson, using analogies and examples to help readers grasp the complex ideas.

Finally, ends with an idea that we require a theory that connects quantum mechanics and gravitation theories (mainly The Theory of Relativity) called 'The Theory Of Everything.'

About The Author

Stephen Hawking - famous physicist who made important contributions to our understanding of the universe. He was known for his work on black holes, which are incredibly dense objects in space. He also wrote other popular science books, including "A Brief History of Time," which helped bring complex scientific ideas to a wider audience. Hawking was suffering with a rare motor neuron disease at a young age, which gradually left him paralyzed and unable to speak. However, he continued to work and communicate using a speech-generating device. Despite his physical challenges, he became a well-respected and admired figure in the scientific community and beyond.

#1 OUR PICTURE OF THE UNIVERSE

Bertrand Russell - the first person who gave the true reality of universe by describing how the earth orbits around the sun and how the sun, in turn, orbits around the center of a vast collection of stars called our galaxy - many revolted it.

340 B.C. - Greek philosopher - Aristotle - in his book On the Heavens - gave two good arguments for believing that the earth was a round sphere rather than a flat plate:

1. Lunar eclipse was caused by the earth coming between the sun and the moon. The earth’s shadow on the moon was always round, which could be true only if the earth was spherical.
2. North Star appeared lower in the sky when viewed in the south than it did in more northern regions. If earth was flat, then it must appear in same position from everywhere.

• Aristotle even quoted an estimate that the distance around the earth was 400,000 stadia. Which was twice the current distance.

Even Greeks gave a simple argument:

    

       3.Why ships appear to move downwards when they reach too far.

Ptolemy - 2nd century A.D. - developed complete cosmological model:

•  The earth stood at the center, surrounded by eight spheres that carried the moon, the sun, the stars, and the five planets known at the time, Mercury, Venus, Mars, Jupiter, and Saturn 
• The outermost sphere carried the so-called fixed stars, which always stay in the same positions relative to each other, but which rotate together across the sky.
• What lay beyond the last sphere was never made very clear, but it certainly was not part of mankind’s observable universe.
• It was adopted by the Christian church as the picture of the universe that was in accordance with Scripture, for it had the great advantage that it left lots of room outside the sphere of fixed stars for heaven and hell.

Nicholas Copernicus - 1514 - Polish priest - gave model - sun was stationary at the center and that the earth and the planets moved in circular orbits around the sun.

Johannes Kepler - modified Copernicus’s theory - suggesting that the planets moved not in circles but in ellipses and some satellites moved around planets.

Sir Isaac Newton - Philosophiae Naturalis Principia Mathematica - theory of how bodies move in space and time, developed the complicated mathematics needed to analyze those motions.

•  Law of universal gravitation - each body in the universe was attracted toward every other body by a force that was stronger the more massive the bodies and the closer they were to each other.

• However, it eventually means that every object must collapse to a single point due to attraction of gravity.
• Newton argued, this would only happen if there were only finite number of stars in finite space. On the other hand, if there were infinite number of stars and space had no boundary. Then, there would be no central point for collapse to take place.

Till 20th Century no one proposed the idea of expanding universe. Due to people’s tendency to believe in eternal truths, as well as the comfort they found in the thought that even though they may grow old and die, the universe is eternal and unchanging.

People who suggested that universe can't be static they attempted to modify the theory that gravitational force repulsive at very large distances.

The problem still continued and had many flaws.

Heinrich Olbers - 1823 - wrote about theory on infinite static universe (endless, but not expanding or contracting) - it also created a difficulty.

• if universe was endless then everywhere would be stars as far as we see.
• so if stars were turn on forever then whole universe would light up as surface of star due to absorption of light by intervening matter. (which is not true cause light travels in vacuum space so there is no inverting matter + light behaves as electromagnetic waves in vacuum space)
• as the above case is not true. Then stars must have lightened up in past and not glow from forever.

People who believed that universe had a beginning were more accused to divine faith. However, Aristotle and others believed that the human race and the world around it had existed, and would exist, forever. Moreover, mentioned human civilization how much they get evolve but they were set to beginning of civilization by natural disasters. Due to divine faith.

Edwin Hubble - 1929 - observed - distant galaxies are moving rapidly away from us - so these must be closer in past - so it also contradicted Newton theory that gravity must attract objects - gave a solution - by saying that universe is expanding (brief explanation in chapter 3) - suggested that Big Bang was cause of start of universe.

Newton theory make accurate predictions about distance, orbits, length etc. but fails to explain why mercury orbits behave in such irregular way and not follow newton theories completely.

Einstein theory is much better than of Newton theory and explains much wider sections and answers the question about mercury orbit.

However, Newton theories are still widely used for practical purposes because - difference between its predictions and those of general relativity is very small - when questions are limited to small sections + simpler to work with than Einstein’s! In an all, Einstein theories are more accurate.

Stephan says: eventual goal of science is to provide a single theory that describes the whole universe.

                        Approach most scientists actually follow is to separate the problem into two parts:

• there are the laws that tell us how the universe changes with time. (how universe follows laws)
• there is the question of the initial state of the universe (how universe formed)

                           If these questions are answered effectively the theory describing everything can be devised easily.

• Partial theories (all theories given by famous persons) describes and predicts a certain limited class of observations, neglecting the effects of other quantities, or representing them by simple sets of numbers. (eg. limitations of newton theories as discussed above)
• If everything in the universe depends on everything else in a fundamental way, it might be impossible to get close to a full solution by investigating parts of the problem in isolation. (as if a ball falls down it is cause by a force applied, force might be caused by a person, force is applied due to neural impulse from his brain....etc..etc . So everything depends on each other. Hence, finding the first cause becomes impossible.)

Today scientists describe the universe in terms of two basic partial theories—the general theory of relativity and quantum mechanics.

• General theory of relativity - force of gravity and the large-scale structure of the universe
• Quantum mechanics - extremely small scales, such as a millionth of a millionth of an inch.
• —they cannot both be correct as there laws are very different and sometimes opposite.
• imagine you require two different laws to study same material but for different level of observation.
• One of the major endeavors in physics today, and the major theme of this book, is the search for a new theory that will incorporate them both—a quantum theory of gravity.

Darwin’s principle of natural selection - natural selection explains how genetic traits of a species may change over time. This may lead to speciation, the formation of a distinct new species.

And our goal is nothing less than a complete description of the universe we live in. OR Theory Of Everything