A Brief History of Time Summary

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Theoretical Physics, a modern topic of science with an extremely deterring sound and famous for being beyond complex, is a subject which cannot be explained with ease. Stephen Hawking, the most famous living scientist today, wrote A Brief History of Time in 1988, updated in 1996, in order to take upon this daunting task of explaining basic theoretical physics to a population who had previously barely studied any science. Within A Brief History of Time, Hawking touches upon seven topics in-depth while easily explaining them in a simple manner: our picture of the universe, space and time, the expanding universe, the uncertainty principle, elementary particles and the forces of nature, black holes, and the origin and fate of the universe.

The first chapter, our picture of the universe, Hawking gives a small amount of background information pertaining to how the current picture was developed. Aristotle, one of the first scientists to live on in infamy, believed the Earth was round; however, he also believed in a geocentric solar system. Ptolemy, agreeing with Aristotle’s ideas, created a planetary model describing the position of the bodies in our solar system. In 1609 though, Nicholas Copernicus dared to challenge the long believed Aristotelian model and formulated the idea of a heliocentric solar system. Galileo Galilei and Johannes Kepler not long afterwards discovered evidence using the moons of other planets in the solar system that would help prove Copernicus’s ideas to be true and also expanding upon them. Isaac Newton, maybe the most important name in all of physics, published a book in 1687, Philosophiae Naturalis Principia Mathematica, in which he first presents the ideas of universal gravitation and his famous three laws of motion.

Within the second chapter Hawking delves into the topic of space and time focusing upon the main points of absolute rest and position, the theory of relativity, as well as light. With Newton’s laws of gravity, it was impossible for objects to be at absolute rest when moving at speeds close to the speed of light. In 1676, Ole Christensen Roemer discovered the speed of light; however, it was calculated at a finite speed which disagreed with Newton’s Laws. Thus, the ether was created. Albert Einstein proposed though that the ether was not needed, for objects do not have to be at absolute rest as long as there was no absolute time. Thus, the theory of relativity was developed. In his discussion of light, Hawking cites that light is described by a cone. The top of the cone represents the future path of light, the bottom half of the cone represents the past path of the light, while the central vertex represents the actual light.

In the third chapter, Hawking takes upon the continuous and accelerated expansion of the universe. In order to prove this, he uses the “Doppler shift” which is almost identical to the Doppler Effect. In sound, the Doppler Effect creates an increasingly louder sound as the event approaches us, and then as the event moves away the sound begins to dull. In light the same basis applies, but with a color shift. Blue shifting and red shifting are the opposite effects of the “Doppler shift”. When objects are moving away from us, their light is shifted in the red direction on the electromagnetic spectrum. Inversely, as objects approach us; their light is shifted in the blue direction. Hawking uses this to prove the expansion of the universe, for many stars found by Edwin Hubble, of whom the Hubble telescope is named after, are observed to be red shifted. Thus, Hawking cites the universe began with The Big Bang.

Chapter four is completely devoted to the uncertainty principle. According to the uncertainty principle the speed and the position of a particle cannot be known at the same time. This is due to the fact that if one calculates the speed of the particle, the particle’s position would have changed too much to be determined. If the position of the particle is...
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