1. A briefer History of Time. by Stephen Hawking
. Comment:- The Universe in a nutshell. Foreword:- Richard Feynman has said “ We are lucky to live in an age in which we are discovering the fundamental laws of nature”.....Our goal in writing this book is to share some of the excitement. Chapter 1. Thinking about the universe. The nearest star other than the sun is ‘Alpha (Proxima) Centauri’ which is about 4 light years away. Fastest space ship would take 10,000 years to reach it. Did the universe have a beginning, and if so what happened before then? What is the nature of time?....Can we go back in time? Chapter 2. Our evolving picture of the universe. Discusses the findings and views of great astronomers from Ancient Greece to Sir Isaac Newton. “ We had given up not only the idea that the Earth is the centre of the universe but even the idea that our sun. The change in worldview represented a profound transition in human thought; the beginning of our modern scientific understanding of the universe. Chapter 3. The nature of a scientific theory. Any physical theory is always provisional. You can never prove it…...You can disprove a theory by finding a single observation that disagree with the predictions of the theory. Today scientists describe the universe in terms of two basic theories.
Chapter 4. Newton’s Universe. This chapter explains the laws of Newton. ...Both Aristotle and Newton believed in absolute time….In the 20th C . physicists realised that they had to change their ideas about space and time. .. They discovered that ..time between events ,like the distance depends on the observer. They also discovered that time was not completely separate and independent of space. ...although our common sense notions work well when dealing with things such as apples or planets, ….they don’t work at all for things moving at or near the speed of light. Chapter 5. Relativity. The fact that light travels at a finite speed was first discovered by Ole Christensen Roemer in 1676. His value was 140,000. Miles / second while the modern value is 186,000. Miles /sec. In 1865 Maxwell’s equations predicted that there could be waves in the electromagnetic field. The speed of these was that of the speed of light. In 1887 Michelson and Morley found that the speed of light does not change with the speed of the earth.In 1905 Einstein’s theory of relativity threw some light on this. Chapter 6. Curved space. Chapter 7. The expanding Universe. What force could be responsible for this? We are not sure yet. We now have a good idea of its behaviour. Chapter 8. The big bang , black holes and the evolution of the universe. When the universe began the density of the universe and the curvature of space time would have been infinite. The theory of general relativity predicts that there is a point in the universe where the theory fails. Such a point is what mathematicians call a ‘singularity.’ When a theory predicts a singularity it is a sign to modify the theory. Chapter 9 Quantum Gravity. Quantum mecanics introduces an element of unpredictability. Einstein objected to this strongly. Thogh he was awarded the Nobel Prize for the contribution to quantum theory.” God does not play dice”. Chapter 10. Worm holes and time travel. "There was a young lady of wight Who traveled much faster than light She departed one day In a relative way And arrived on the previous night." According to Feynman time travel into the past. in a way occur on single particles. The possibility of time travel remains open. Chapter 11. The Forces of nature and the unification of physics. In quantum mechanics , the forces are supposed to be carried out by particles. matter particle, such as an e- emits a force carrying particle. the recoil from this emission changes the velocity of the natter particle.the force carrying particle then collides with another matter particle. Each force is transmitted by its own type of force carrying particle. If the mass of f particle is high it will be difficult to exchange them over large distances. 1.gravitational force..... particle = 'graviton' every particle feels this .... weakest of four.....always attractive....exerts over very long distances. 2.electromagnetic force- particle = photon. interacts with electrons and quarks not with neutrinos. this 10 40 times stronger than gravity. there is repulsion as well as attraction. 3. weak nuclear force responsible for radioactivity. ih 1967 Abdus salam and Weinberg proposed theories that unified this interaction with the electromagnetic force. 4.Strong nuclear force .... paticle= gluon binds protons and neutrons together. 2. Storm in a tea cup- The physics of everyday life. By Helen Czerski. Laws of physics have been explained in a very simple way without using technical terms. Chapter 1.Popcorn and rockets :- Gas laws Pop corn bursts due to steam pressure building up inside the grain due to heat. ( For this to occur the seed cover has to be watertight Sperm whales never breathe from their lungs when they make deep dives In 1650 Otto von Guericke performed the ‘Magdeburg sphere’ experiment. His experiment inspired Robert Boyle and Robert Hooke to carry out experiments on gas pressure. Chapter 2. What goes up must come down:- Gravity. How does a seed know gravity for the root to grow down and the shoot to grow up Inside the seed there are specialized cells called ‘statocytes.’ inside each one there are specialised starch grains that are more dense than the rest of t cell.and they settle towards t bottom.of t cells.protein networks can sense where they are and so the seed and later y plant knows which way is up Fresh eggs sink in and lie flat in cold water, a week old egg but stand up on the pointy end , if the egg floats it has been around for some time. T blue region of a candle flame =1,400 c. yellow= 1000 c
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