former post-doc of mine) remarked: I have sold more books on physics than Madonna file:///C|/WINDOWS/Desktop/blahh/Stephen Hawking - A brief history of. Chapter 1 - Our Picture of the Universe Chapter 2 - Space and Time Stephen Hawking -A Brief History Of nvilnephtalyca.gq former post-doc of mine) remarked: I have sold more books on physics than Madonna has on sex. ALSO BY STEPHEN HAWKING this book. In the years since A Brief History of Time was published A Briefer The Art of Photography. Pages··
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former post-doc of mine) remarked: I have sold more books on file:///C|/ WINDOWS/Desktop/blahh/Stephen Hawking - A brief history of time/A. Stephen Hawking, one of the most brilliant theoretical physicists in history, wrote the modern classic A Brief History of Time to help non-scientists "It's one of a very few books in this category that continues to fascinate despite the fact that. PDF | The continuing interest in the book of S. Hawking "A Brief History of Time" makes a philosophical evaluation of the content highly desirable. As will be.
In , astronomer Edwin Hubble discovered that galaxies are moving away from each other. 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. Today, scientists use two partial theories, Einstein's general theory of relativity and quantum mechanics , to describe the workings of the universe.
Scientists are still looking for a complete unified theory that would describe everything in the universe. Hawking believes that the discovery of a complete unified theory may not aid the survival of our species, and may not even affect our life-style, but that humanity's deepest desire for knowledge is justification enough for our continuing quest,and that our goal is nothing less than a complete description of the universe we live in.
So 'rest' can't be the standard position. Moreover, Galileo Galilei also disproves Aristotle theory that heavier body falls more quickly than the lighter one just because of its mass.
He experimentally proves it by sliding objects of different weights, and even concludes that both these object would fall at same rate and would reach the bottom at the same time, unless external force acts on them. Aristotle and Newton believed in absolute time. They believed that if an event is measured using two different clocks at different state of motion, they'll have to agree on the same time, if clocks used are synchronized, which by now we know it isn't.
He observed that Io appeared sometimes quicker and sometimes later when it revolves around Jupiter, because the distance between Earth and Jupiter changes every time because of their orbital motion around the sun. The actual propagation of light was published by James Clerk Maxwell who told that light travels with a fixed speed.
Later, many argued that light must travel through a hypothetical fluid called aether , which was disproved by the Michelson—Morley experiment. The Special Theory of Relativity is based on this, that light travels with a finite speed no matter what the speed of the observer is. Moreover, the speed of light is assumed to be the ultimate speed.
A new way of defining a metre using speed of light is also developed.
The new 4-dimensions is also described, how different the path is seen when one changes reference from 3D to 4D or 3D to 2D. General Theory of Relativity explains about how path of light ray is affected by ' gravity ' which according to Einstein is a mere illusion in contrast to Newton's views.
It is space-time curvature where light moves in a straight path in 4D which is seen as a curve in 3D. These straight line paths are Geodesics. Twin paradox , a part theory of Relativity which explains that two twins can age differently if they move at relatively different speeds or even at different places where spacetime curvature is different.
Special relativity is based upon arenas of space and time where events take place whereas General Relativity is dynamic where force could change spacetime curvature, which gives rise to the expanding universe. Hawking and Roger Penrose worked upon this and later proved using general Relativity that if the Universe had a beginning then it also must have an end.
The picture shows the Universe expanding over time. In this chapter, Hawking first describes how physicists and astronomers calculated the relative distance of stars from the Earth.
A Briefer History of Time
In the 18th century, Sir William Herschel confirmed the positions and distances of many stars in the night sky. In , Edwin Hubble discovered a method to measure the distance using brightness of the stars.
The luminosity , brightness and distance are related by a simple mathematical formula. Using all these, he fairly calculated distances of nine different galaxies. We live in a spiral galaxy just like other galaxies containing vast numbers of stars.
The stars are very far away from us, so we only observe their one characteristic feature, their light. When this light is passed through a prism, it gives rise to a spectrum. Every star has its own spectrum and since each element has its own unique spectra, we can know a star's composition. We use thermal spectra of the stars to know their temperature. In , when scientists were examining spectra of different stars, they found that some of the characteristic lines of the star spectrum was shifted towards the red end of the spectrum.
The implications of this phenomenon was given by the Doppler effect , and it was clear that some stars were moving away from us. It was assumed that since some stars are red shifted, some stars would also be blue shifted.
When found, none of them were blue shifted. Hubble found that the amount of redshift is directly proportional to relative distance.
So, it was clear that the Universe is expanding. Despite this the concept of a static universe persisted until the 20th century. Einstein was so sure of a static universe that he developed ' Cosmological Constant ' and introduced 'anti-gravity' forces to persist with the earlier claim. Moreover, many astronomers also tried to avoid the face value of General Relativity and stuck with their static universe except one Russian physicist Alexander Friedmann.
Friedmann made two very simple assumptions: the universe is identical in every direction, i.
Homogenity and that this would be true wherever we look from, i. His results showed that the Universe is non-static. His assumptions were later proved when two physicists at Bell's laboratory, Arno Penzias and Robert Wilson found extra microwave radiation noise not only from the one particular part of the sky but from everywhere and by nearly the same amount. Then, Friedmann's first assumption was proved as true.
At around the same time, Robert H. Dicke and Jim Peebles were also working on microwave radiation. They argued that they should be able to see the glow of the early universe as microwave radiations.
Wilson and Penzias had already done this, so they were awarded with the Noble Prize in In addition, our place in the Universe is not exceptional, so we should see the universe as the same from any other part of space, which proves Friedmann's second assumption. His work remained largely unknown until similar models were made by Howard Robertson and Arthur Walker.
Friedmann's model gave rise to three different types of model of the universe. First, the universe would expand for a given amount of time and if the expansion rate is less than the density of the universe leading to gravitational attraction , it would ultimately lead to the collapse of the universe at a later stage.
Secondly, the universe would expand and at sometime if the expansion rate and the density of the universe become equal, it would expand slowly and stop at infinite time, leading to a somewhat static universe. Thirdly, the universe would continue to expand forever if the density of the universe is less than the critical amount required to balance the expansion rate of the universe. The first model depicts the space of universe to be curved inwards, a somewhat earth-like structure.
In the second model, the space would lead to a flat structure, and the third model results in negative curvature, or saddle shaped.
Even if we calculate, the current expansion rate is more than the critical density of the universe including the dark matter and all the stellar masses. The first model included the beginning of the universe as a big-bang from a space of infinite density and zero volume known as ' singularity ', a point where General Theory of Relativity Friedmann's solutions are based in it also breaks down. This concept of the beginning of time was against many religious beliefs, so a new theory was introduced.
A Brief History of Time - Stephen Hawking
Its predictions also matched with the current Universe structure. But the fact that radiowave sources near us are far fewer than from the distant universe and there were numerous more radio sources than at present, resulted in failure of this theory and everybody finally supported the Big Bang theory. Roger Penrose used light cones and General Relativity to prove that a collapsing star could result in a region of zero size and infinite density and curvature called a Black Hole.
Hawking and Penrose proved together that the universe should have arisen from a singularity, which Hawking himself disproved once Quantum effects are taken into account. Chapter 4: The Uncertainty Principle[ edit ] The uncertainty principle says that the speed and the position of a particle cannot be found at the same time. To find where a particle is, scientists shine light at the particle. If a high frequency light is used, the light can find the position more accurately but the particle's speed will be unknown because the light will change the speed of the particle.
If a lower frequency light is used, the light can find the speed more accurately but the particle's position will be unknown. 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. Some theories say that light acts like particles even though it really is made of waves; one theory that says this is Planck's quantum hypothesis.
A different theory also says that light waves also act like particles; a theory that says this is Heisenberg's uncertainty principle. Light interference causes many colors to appear. Light waves have crests and troughs. The highest point of a wave is the crest, and the lowest part of the wave is a trough.
Sometimes more than one of these waves can interfere with each other - the crests and the troughs line up.
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This is called light interference. When light waves interfere with each other, this can make many colors. An example of this is the colors in soap bubbles. Chapter 5: Elementary Particles and Forces of Nature[ edit ] Quarks and other elementary particles are the topic of this chapter.
Quarks are very small things that make up everything we see matter. There are six different "flavors" of quarks: the up quark, down quark, strange quark, charmed quark, bottom quark, and top quark. Quarks also have three "colors": red, green, and blue. There are also anti-quarks, which are the opposite of the regular quarks. In total, there are 18 different types of regular quarks, and 18 different types of anti quarks. Quarks are known as the "building blocks of matter" because they are the smallest thing that make up all the matter in the universe.
A particle of spin 1 needs to be turned around all the way to look the same again, like this arrow. All particles for example, the quarks have something called spin. The spin of a particle shows us what a particle looks like from different directions. For example, a particle of spin 0 looks the same from every direction.
A particle of spin 1 looks different in every direction, unless the particle is spun completely around degrees. Hawking's example of a particle of spin 1 is an arrow. A particle of spin two needs to be turned around halfway or degrees to look the same. The example given in the book is of a double-headed arrow.
All of these particles follow the Pauli exclusion principle. Pauli's exclusion principle says that particles cannot be in the same place or have the same speed. If Pauli's exclusion principle did not exist, then everything in the universe would look the same, like a roughly uniform and dense "soup".
This is a proton. It is made up of three quarks. All the quarks are different colors because of confinement. Particles with a spin of 0, 1, or 2 move force from one particle to another.
Some examples of these particles are virtual gravitons and virtual photons. Virtual gravitons have a spin of 2 and they represent the force of gravity. This means that when gravity affects two things, gravitons move to and from the two things.
Virtual photons have a spin of 1 and represent electromagnetic forces or the force that holds atoms together. Besides the force of gravity and the electromagnetic forces, there are weak and strong nuclear forces. Weak nuclear forces are the forces that cause radioactivity , or when matter emits energy. Strong nuclear forces are the forces that keep the quarks in a neutron and a proton together, and keeps the protons and neutrons together in an atom.
The particle that carries the strong nuclear force is thought to be a gluon. The gluon is a particle with a spin of 1. The gluon holds together quarks to form protons and neutrons.
However, the gluon only holds together quarks that are three different colors. This makes the end product have no color. This is called confinement. Some scientists have tried to make a theory that combines the electromagnetic force, the weak nuclear force, and the strong nuclear force. This theory is called a grand unified theory or a GUT.
This theory tries to explain these forces in one big unified way or theory. Chapter 6: Black Holes[ edit ] A picture of a black hole and how it changes light around it. Black holes are talked about in this chapter. Black holes are stars that have collapsed into one very small point. This small point is called a singularity.
Black holes suck things into their center because they have very strong gravity. Some of the things it can suck in are light and stars. Only very large stars, called super-giants, are big enough to become a black hole. The star must be one and a half times the mass of the sun or larger to turn into a black hole.
This number is called the Chandrasekhar limit. If the mass of a star is less than the Chandrasekhar limit, it will not turn into a black hole; instead, it will turn into a different, smaller type of star. Obviously he is entitled to think as he wishes about the ultimate questions, but his assertion that his hypothesis of a finite world without beginning or end would leave no place for God seems beside the point. The classic divide has not changed: some folks look around and say stuff just is, and other folks say there's a power behind the stuff that has at least as much going for it as we do.
That argument hasn't changed with his theories. At one point in the book he claims that the late John Paul II told gathered scientists that they mustn't inquire into the Big Bang because that was God's territory. I would wager with anyone reading this comment that such an assertion is just plain false.
JPII was a flawed mortal, to be sure, but he was no dope; it certainly sounds to me like someone hearing what he thinks the pope would say. And the Galileo jokes are pretty dumb -- does anyone think that JPII, who apologized for the embarrassing Galileo fiasco, would go after this guy?
It must be all that influence the Vatican has had in Britain over the last years that has him scared. Other philosophical complaints involve his use of entropy he defines it first within closed systems and then uses it to explain why the "thermodynamic arrow of time" and the "personal arrow of time" must run in the same direction -- leaping from a box of molecules to the entire universe!
His opinions may be very rich, deep, though-provoking, but how would I or most general readers know? You can't really evaluate a judgment unless you know something in the field. And so that is why I ultimately cannot recommend this book: if you know physics inside and out, you might find his opinions interesting.Augustine believed it was created at a specific time.
This claim or theory was not acknowledged nor accepted until the arrival of Galileo Galilei in the 17th century. In fact, gravity messed things up. Applegate The Purrfect Sleepover: Imagine this, without any evidence, years ago Aristotle wrote — The planet is round and probably we are not alone in this vast space. Mirror Earth: Applegate The Particle at the End of the Universe: Flesh and Machines:
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