A brief history of the universe pdf

A brief history of the universe pdf was first published in 1988. Hawking wrote the book for nonspecialist readers with no prior knowledge of scientific theories.

10 million copies in 20 years. Mitton was doubtful about all the equations in the draft manuscript, which he felt would put off the buyers in airport bookshops that Hawking wished to reach. With some difficulty, he persuaded Hawking to drop all but one equation. The book does employ a number of complex models, diagrams, and other illustrations to detail some of the concepts it explores.

In the 1996 edition of the book and subsequent editions, Hawking discusses the possibility of time travel and wormholes and explores the possibility of having a universe without a quantum singularity at the beginning of time. A picture of Ptolemy’s earth-centric model about the location of the planets, stars, and sun. Aristotle’s thinking in more detail. Today, it is known that the opposite is true: the earth goes around the sun. The Aristotelian and Ptolemaic ideas about the position of the stars and sun were disproved in 1609. Newton’s model also meant that stars, like the sun, were not fixed but, rather, faraway moving objects. Nevertheless, Newton believed that the universe was made up of an infinite number of stars which were more or less static.

The origin of the universe represented another great topic of study and debate over the centuries. Augustine also believed that time was a concept that was born with the creation of the universe. Consequently, there was a time, between ten and twenty billion years ago, when they were all together in one singular extremely dense place. This discovery brought the concept of the beginning of the universe within the province of science. Scientists are still looking for a complete unified theory that would describe everything in the universe.

Hawking believes that the search for such a universal theory, even though motivated by the essential human need for logic, order and understanding, might affect the survival of the human species. Before Galileo and Newton, it was assumed that Aristotle was right in saying that objects are essentially at rest until a force acts to set them in motion. According to the Aristotelian tradition, events stay in the same place over a period of time. Newton’s laws proved that to be false, positing that each object in the universe is moving relative to others, and that it is impossible to assign an absolute resting position.

Both Aristotle and Newton believed in absolute time, a concept independent of space. But this belief does not work for objects moving at or near the speed of light. Ole Christensen Roemer, who observed that the time it took light to come from Jupiter’s moons varied depending on their distance from the earth. The speed of light was found to be very fast but finite. However, scientists found a problem when they tried to say that light always traveled at the same speed.

But the assumption of ether did not properly explain the speed of light in many other phenomena. The top of the light cone tells where the light from the event will travel, the bottom tells where the light was in the past, and the center is the event itself. Besides light cones, Hawking also talks about how light can bend. After talking about light, Hawking talks about time in Einstein’s theory of relativity. Einstein’s theory makes is that time will go by slower when something is near huge masses. However, when something is farther away from the mass, time will go by faster. The Big Bang is shown here.

The universe is getting bigger over time. The Doppler shift happens when something moves toward or away from another object. Red shifting happens when something is moving away from us. Red-shift is linked to the belief that the universe is expanding as the wavelength of the light is increasing, almost as if stretched as planets and galaxies move away from us, which shares similarities to that of the doppler effect, involving sound waves. Blue shifting happens when something is moving toward us, the opposite process of red-shift, in which the wavelength decreases and frequency increases, shifting the light towards the blue end of the spectrum. Hawking uses the Doppler shift to explain that the universe is getting bigger. To find where a particle is, scientists shine light at the particle.

The uncertainty principle disproved the idea of a theory that was deterministic, or something that would predict everything in the future. Here is a picture of a light wave. How light behaves is also talked more about in this chapter. Light interference causes many colors to appear. The highest point of a wave is the crest, and the lowest part of the wave is a trough. When light waves interfere with each other, this can make many colors. An example of this is the colors in soap bubbles.