Cosmology

Download A Brief History of Time: From the Big Bang to Black Holes by Stephen W. Hawking, Ron Miller, Carl Sagan PDF

By Stephen W. Hawking, Ron Miller, Carl Sagan

ISBN-10: 055305340X

ISBN-13: 9780553053401

Stephen Hawking, probably the most extraordinary theoretical physicists in heritage, wrote the trendy vintage a short heritage of Time to aid nonscientists comprehend the questions being requested via scientists at the present time: the place did the universe come from? How and why did it commence? Will it come to an finish, and if that is so, how? Hawking makes an attempt to bare those questions (and the place we are searching for solutions) utilizing not less than technical jargon. one of the issues gracefully coated are gravity, black holes, the large Bang, the character of time, and physicists' look for a grand unifying thought. this is often deep technology; those techniques are so giant (or so tiny) as to reason vertigo whereas analyzing, and one can not help yet wonder at Hawking's skill to synthesize this hard topic for individuals no longer used to brooding about such things as trade dimensions. the adventure is unquestionably worthy taking, for, as Hawking says, the gift of realizing the universe could be a glimpse of "the brain of God."

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Additional info for A Brief History of Time: From the Big Bang to Black Holes

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However, when an electron changes from one allowed orbit to another one nearer to the nucleus, energy is released and a real photon is emitted – which can be observed as visible light by the human eye, if it has the right wave-length, or by a photon detector such as photographic film. Equally, if a real photon collides with an atom, it may move an electron from an orbit nearer the nucleus to one farther away. This uses up the energy of the photon, so it is absorbed. The third category is called the weak nuclear force, which is responsible for radioactivity and which acts on all matter particles of spin-½, but not on particles of spin 0, 1, or 2, such as photons and gravitons.

So the best answer we can give to our question depends on how high a particle energy we have at our disposal, because this determines on how small a length scale we can look. These particle energies are usually measured in units called electron volts. (In Thomson’s experiments with electrons, we saw that he used an electric field to accelerate the electrons. ) In the nineteenth century, when the only particle energies that people knew how to use were the low energies of a few electron volts generated by chemical reactions such as burning, it was thought that atoms were the smallest unit.

The obvious way to do this is to shine light on the particle. Some of the waves of light will be scattered by the particle and this will indicate its position. However, one will not be able to determine the position of the particle more accurately than the distance between the wave crests of light, so one needs to use light of a short wavelength in order to measure the position of the particle precisely. Now, by Planck’s quantum hypothesis, one cannot use an arbitrarily small amount of light; one has to use at least one quantum.

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