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A Briefer History of Time Will Meldon Yuska, Biology 3 By Steven Hawking Chapter 1-Thinking about the universe At the beginning of the chapter, the book tells a brief story about a scientist who lectured a group of people about what the universe truly is a vast collection of starts that orbit around the sun. At the end of his lecture, an old woman stood up and said that what he said was rubbish and that the world was really a flat disk supported on the back of turtle on top of an infinite tower of turtles. Although most people would pass this off as ridiculous, they really don’t know a whole lot more than the woman who thinks were all supported on the backs of an infinite stack of turtles. Someday we may know much more than we do now and things with make sense and be reasonable, or they will be as absurd as the turtle theory. Chapter 2-Our evolving picture of the universe Although as late as the time of Christopher Columbus, the theory that the earth was flat was widely accepted as fact but theories that the world was in fact round have existed since 430 B.C. in the times of Aristotle. His arguments were that if the world was completely flat, then it would not eclipse the moon so completely and that you saw the masts and sails of a ship on the horizon before you saw the rest of the ship. He also noted that all the stars moved as one but the planets moved independently leading Ptolemy to create his model of the universe. His model of the universe consisted of 8 rotating spheres that contained all heavenly bodies with the earth in the center of it all. Later, Copernicus’ theory that the earth revolved around the sun was conceived in part due to the discovery that other planets had moons of their own. Along with Galileo Kepler’s discovery discovery that the planetary orbits were elliptical rather than perfect circles helped to disprove Ptolemy’s theory. But until Newton, the elliptical orbits theory could not be explained. Chapter 3-The Nature of Scientific Theory Chapter threes primary focus is on the pursuit for the ultimate theory that will explain all aspects of the universe. But problems arise in that we always break our theories into smaller parts which give inaccurate results due to the fact that all things in the universe are dependent on each other. One major problem is unifying the theories of General Relativity and quantum mechanics. The problem is that the two theories are inconsistent with each other meaning at least one if not both are wrong in some way or another. Another possibility is that the ultimate theory governs everything and even says what will or will not happen, the problem there is that if this is true, the theory itself has already decided whether we find it or not. The only theory that can really help us is Darwin’s theory of natural selection. Although science has helped us survive in the past, there is a possibility that it will be our destruction in the future. Chapter 4-Newtons Universe The chapter starts with a brief overview of Aristotle’s believe that heavy things fall faster than light things which was disproved by Galileo and then explained by Newton. Newton’s theories said that all bodies are attracted to each other and although larger bodies have more gravitational attraction, they require more force to move which cancels out mass difference and explains why heavy items fall just as fast as light ones. Another major difference in the beliefs of Aristotle and Newton are that Aristotle believed the earth was at rest while Newton realized that everything is moving from someone’s perspective. One thing that they did agree on was that time was absolute which has been disproved by 20th century physicists. Chapter 5-Relativity The concept that travels light travels at a finite speed was first introduced by de Roemer in 1676 when he noticed that Jupiter’s eclipse happened at irregular intervals that happen more often when Jupiter is close and less often when Jupiter is far away. This was confirmed by Maxwell with his discovery of the electromagnetic spectrum and electromagnetic fields however this did not correspond with the lack of a definite form of rest. To reconcile the theories, the idea of ether was formulated. Ether was a substance found everywhere including the vacuums of empty space and no matter what perspective you had; you would measure the speed of light in relation to the ether. Michelson and Morley decided to test this theory. They realized that the earth was hurtling though ether very fast so their lab must be too. They decided to measure the speed of light when going at right angles to ether and when going with the ether and to their surprise, the speeds were exactly the same. With ether disproven, Einstein came up with the theory of relativity which forces us to abandon the idea that time and space are definite and separate. To prove that you could not go faster than light, E=MC² which says that as you increase speed, you increase mass and at the speed of light you would have a infinite mass which would require an infinite amount of energy to move. The problem with Einstein’s theory is that according to Newton’s laws, gravity moves at an infinite speed, which conflicts with the general theory of relativity. Chapter 6-Curved Space Einstein’s general theory of relativity suggests that space-time follows a curved path because of gravity. Things like the earth don’t follow curved paths because gravity makes them but because of the geodesic which is the nearest thing to a straight path in curved space-time. Because of this, light can be bent by large masses with larger gravitational pulls. Another part of the general theory of relativity suggests that time runs more slowly near a massive body like the earth. This also means that uniform acceleration and uniform gravitational fields cannot be differentiated and thus, time is unique to everyone and everything as does the universe which gives it a finite life. Chapter 7-The Expanding Universe Because of the vast distance of space, methods like parallaxes and luminosity cannot be used to classify and measure star distances. Instead, scientists were forced to put the light emitted by the stars through prisms dispersing it. By looking at what areas of the spectrum are weaker, they can determine various things about a star. What scientists noticed was that al the stars spectrums were on the red side of the spectrum, meaning that they were slowly moving away from us according to the functioning of the doplar effect. Before then, all other physicists though the universe was static but Friedmann said that it couldn’t be static. With further discoveries like dark matter, scientists have begun to figure out how the universe behaves. Friedmann put forth three behaviors that the universe could follow. One involved the universe expanding slowly then collapsing on itself. The second involves the universe rapidly expanding forever. And the third has the universe expanding and then eventually slowing down but never quite stopping. Currently, none of these match observations. Chapter 8-The Big Bang, Black Wholes, And the Evolving Universe At the beginning of the universe, the distance between everything was zero and the temperature was infinite. After the big bang and rapid expansion of the universe, particles began to lose energy and stick together and eventually succumb to things like strong force and electromagnetic force. The particles not destroyed by their antiparticles counterparts formed mostly hydrogen and some other heavy metals. For the next million years, the universe would have continued to expand uneventfully but eventually, gravitational attraction would have caused some sections of the universe to collapse. Collapsed galleys would begin to rotate slowly and then as they began to flatten out, they would start spinning faster and faster till the section restabilized. This spinning would create spiral galaxies. As time goes on, the helium and hydrogen clouds in the galaxy would break apart and collapse forming stars which burn hydrogen into helium. After it runs out of fuel, the star would collapse and become hotter and more dense and its gravitational force would be too great for even light to get past, forming a black whole on the surface of which, time has stopped. When this happens to massive stars, it gives of massive amounts of radiation in super novas. This is why life would not evolve in areas where super novas were common. Chapter 9-Quantum Gravity Marquis de Laplace formulated that the universe was completely deterministic. What was later proven was that determining the exact position of particles and at the same time measuring speed accurately was impossible which led to the belief that nothing is certain. Another aspect of quantum theory is that particles and waves can reinforce and cancel each other out. What this led to was the discovery that orbiting electrons behave similar to waves and takes every possible path they can when going to a destination. This also means that nothing is certain. Although the chance of something happening may be so unlikely you couldn’t get it to happen by chance in the entire life of the universe, there is still a possibility it could happen. All this helps lead to the quantum theory of gravity and the probability that the universe is endless and boundaries. Chapter 10-Wormholes and Time Travel To travel in time, one must go nearly the speed of light. When returning from your trip, time will have gone faster on earth than it did for you. This means that traveling forward in time is not only possible; it’s just a matter of engineering before we can do it. But as for going back in time, it’s slightly more complicated. The first possibilities that people could travel back in time were formulated by Gödel. His mathematic solution to Einstein’s equation allowed time travel but his universe rotated and didn’t not expand, ours does. To go back in time, one must go faster than the speed of light, which is supposed to be impossible. But it still is theoretically possible through the use of a wormhole. A wormhole is a straight tunnel in curved space that would shorten distances enormously. One particularly damning piece of evidence that goes against traveling back in time is the fact that no one has ever come from the future and told us about it and other paradoxes that no one has come back and messed everything up for us yet. Chapter 11-Forces of Nature and the Unification of Physics The quest to find the complete theory for everything in the universe is known as the Unification of Physics. Although we have made great strides in science in recent years, the unified theory is still a very difficult thing to achieve. We now know more about particles than we did before and we also know more about their forces. The four forces are Gravitational, electromagnetic, weak force and strong force. With the knowledge of these forces, attempts have been made to unify strong, weak and electromagnetic forces in the Grand Unified theory which isn’t all that grand nor is it unified. Yet it is still progress towards the unified theory. The problem when adding gravity is that because of the uncertainty principles, empty space has particles but cant be included into the formula because their energy cannot be calculated. Even by canceling out infinities and other factors, the answers still have a very high chance of coming out wrong and giving you bad info, which is where string theory comes into play. These so called strings are particles with only the dimension of length and have lengths running along them. String theory required the existence of ten or 26 dimensions which were discovered to probably be very very small dimensions that were really curvy. With the creation of the anthropothic principle, it explains that we are 3 dimensional because living creatures would not be able to live as well if we were 2 dimensional and on an atomic scale, electrons would spiral away from their orbits and leave their atoms. All of this leads to the realization that there could be a unified theory or it could just be infinite overlapping ones. Chapter 12-Conclusion As time progresses, we learn more and more about our universe. We learned that certain regularities exist making it so that spirits aren’t the ones controlling things. We learn more and more about what we can’t see. Why the universe exists, how it began and what it will do are always going to be asked but until later, we won’t know what the answers are. Some answers could be found through divine beings or we could still be on the right track. Even so, the ultimate quest still is and always will be to find the ultimate unified theory. The sciences used in this book are Relativity, which deals with things on an enormous scale, and Quantum physics, which deals with things on an atomic scale. The book “A Briefer History of Time” by Steven hawking primarily focuses on the complex nature of the universe we live in. From things on the size of atoms and smaller to things larger than could be comprehended by a human being, the science of how it works is all described in the book. One of the most focused on scientific aspects of this book is Newtonian physics. Although his other theories are very important in the real world, the one most used that nothing is at rest. Everything is moving from someone’s perspective. This is very important to the book because one of the most discussed topics is light speed and if nothing is at rest, than speed is undeterminable. Another very important science used in the book is the theory of relativity. Relativity was conceived by Einstein and it helps prove that you cannot go faster than light. This affects time travel because the only way to go back in time is to go faster than light, which is impossible. Einstein and his theories play a major roll in quantum physics and without them; this book would have had huge amounts of loose ends. Some of the other Subjects discussed in the book are string theory, wormholes, black holes and that our universe is expanding. Mathematical equations are used to solve all these theories and the digits used are often incredibly largest or incredibly small. The primary of the books focus however, is on the acquisition of the ultimate unified theory that explains and predicts everything. So far we have unveiled vast amounts of information and partial theories of how the universe works but were have yet to find the unified theory. A Although some points in the book make it impossible to ever find it, the ultimate goal of science and this book is to someday uncover it.