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3 internautes sur 4 ont trouvé ce commentaire utile :
5.0étoiles sur 5
A Briefer (and more brilliant) History of Time, Mai 27 2007
Summary of the Novel:
Hawking and Mlodinow have put together an in-depth look at the field of physics that is simple enough to be accessible by the general public. This summary will give an explanation of the general themes of discussion present throughout the novel. Scientific research does not occur within a vacuum, the consequences of these new theories must also be examined. Hawking and Mlodinow have condensed some of the most complex and important ideas of the 21st century into a simple and easy to understand format. They begin by discussing the history of physics and the way the world has viewed this branch of science.
Scientific discoveries have been made since before recorded history. The Greeks are probably some of the earliest contributors to what would be deemed "modern physics". Hawking and Mlodinow study the field of astronomy in particular, noting the accomplishments of Greeks like Aristotle and Ptolemy but also those of others like Copernicus, Kepler and Galileo. Sir Isaac Newton is also analyzed and his theories (like gravity) are discussed. It is important to note that not all of these great thinkers were correct in their views. Ptolemy, for instance, created a very flawed model, which showed that the Earth was the center of the universe.
Hawking and Mlodinow explain that this does not devalue their contributions. In fact, Chapter Three explains that imperfect and partial theories are the norm in physical studies since the creation of a single theory is exceptionally difficult. The two main theories that govern the universe are "general relativity" and "quantum mechanics". Other important theories are discussed as well, like Newton's Laws and special relativity. The behavior of light becomes especially important. The fact that is both a wave and particle, that it has a constant speed, and that it can be used to measure objects is very relevant. Multiple scientists have developed these concepts and others over many years and it is stressed that they are continuing to change today.
Hawking and Mlodinow then begin a discussion about the properties of the universe that we have come to discover. They explain that space is curved, much like the surface of the Earth itself. They go on to talk about the effects of gravitational fields and acceleration (two forces which they explain are really the same thing as long as the acceleration is uniform). They say that both light and time (thought to be completely weightless) can be bent and warped by very powerful gravitational fields or very extreme acceleration.
By examining the changing positions of objects in the far reaches of space we have come to accept that our universe is expanding. Using the Doppler Effect we have measured the increase to be between 5-10% every billion years. The authors chronicle the history of these achievements and the methods used to determine that our universe is growing and changing all the time.
Questions about physics always return to the initial state of the object one is trying to analyze. The changes that have taken place can only be described in relation to what the original model showed. Chapter Eight condenses what we know about the "Big Bang" and black holes in space and time. The matter in the universe (and anti-matter) was formed at the "Big Bang" and it is apparent that the expansion of the universe will continue. We also have run into a very serious problem with calculating the initially state of the universe because of Heisenberg's Uncertainty Principle. We measure quantum properties using waves of light. However, the light itself disturbs the speed of the particle and so we cannot measure the exact position and velocity of a particle at the same time.
Hawking and Mlodinow then delve into one of the most intriguing avenues of modern science, the possibility of time travel. They discuss most of the popular theories about this issue. These include time paradoxes as well as the ability to travel across great distances without time passing. They argue that wormholes (a passage through space-time) are possible due to the curved state of the universe described earlier. By traveling through, instead of along, the curved surface at high speed a person might be able to arrive previous to when they left (travel back in time).
The final section of the novel addresses the quest for a unified theory of physics by combining the four forces that act on matter. Gravity, electromagnetism, weak and strong nuclear forces control the movements of all objects in the universe from sub-atomic particles to the pull of galaxies on one another. The theory studied most closely is the evolution of String Theory as an answer to unifying these forces. Whether such a theory exists is even disputed, but this only goes to show us that science is constantly evolving and that we must continue to search for answers to the questions posed by the world around us.
Recommendation:
This book goes a long way towards translating complex experiments and theories into language that can be understood by the general public. It discusses topics that are of interest, not just to scientists, but to the common person as well. It is written in such a way that it is engaging without losing its scientific validity. "A Brief History of Time" was a landmark novel and its counterpart continues that tradition. Despite its relative simplicity, it deals with concepts that will take some time and thought to wrap your head around. But the discoveries are exciting and their potential to revolutionize the world is very real. It is astounding to think of our universe the way that the authors must. In essence, it is a brilliant look at existence itself from any perspective.
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5.0étoiles sur 5
Really interesting, Oct. 5 2008
Throughout school I learned about the major scientific advancements, but none of that schooling really explained things the way this book did. Stephen Hawking really explained the basic discoveries in a way that is simple and easy to understand.
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1 internautes sur 2 ont trouvé ce commentaire utile :
5.0étoiles sur 5
A Rather Long review of A Briefer History of Time, Nov. 23 2006
How big is the universe? Did it have a beginning and will it have an end? What was Gods role in creating the universe?
My dictionary defines the universe as the totality of all matter and energy that exists in the vastness of space, whether known to human beings or not. Thats pretty big, so in this book review Ill limit my discussion to that part of the universe that we humans can observe and Ill refer to it as the known universe. Perhaps only God can comprehend the universe beyond the confines of our known one.
Our known universe is a wonderful and astonishing place to live! In A Briefer History of Time, Stephen Hawking points out that we can see about five thousand stars with our naked eyes. But thats only about .0001 percent of all the stars in just our own galaxy, the Milky Way. The Milky Way itself is but one of more that a hundred billion galaxies that can be seen with modern telescopesand each galaxy contains on average some one hundred billion stars. You do the math.
Not surprisingly, A Briefer History of Time is a briefer version of Stephen Hawkings worldwide bestseller, A Brief History of Time. I think of it as the version for the rest of us. Ive always wished I could get my brain around Einsteins general theory of relativity and concepts such as space-time, curved space, and worm holes. This book offers people like me, born with only average intelligence, the simplest explanations of these concepts that I have come across. And all with no mathematics!
Hawking has done a masterful job organizing the material he presents. He starts by asking the BIG QUESTIONS. He then leads the reader quite gently through a broad history of the scientific discoveries leading up to the first half of the last century--the golden age of astrophysics. Of special interest to me was Chapter 3 The Nature of a Scientific Theory, where he explains that all the laws of physics are really only theories, since they can never be fully tested in the entire universe.
Did you know that Newtons simple and elegant Law of Gravity has been replaced with Einsteins relativity equations? Newtonian gravity describes the motion of the solar system almost perfectly, but not quite. Relativity describes it perfectly. Without relativity, your GPS would be about 1000 times less accurate.
Understanding relativity is tough; the universe becomes four dimensional rather than three dimensional, with time being the fourth dimension. Hawking describes this beautifully, along with some of its more bizarre implications, such as how time passes at different rates for different observers. Yep, time is not linear. Thats why physicists refer to it as space-time.
So far, relativity has been confirmed by every scientific observation. Hawking shows how this has led to the accepted expanding soap-bubble model of the universe. Its truly fascinating stuff. In Chapter 8 he describes black holes, worm holes, anti-matter and other exotic aspects of cosmology. He even explains how time travel via worm holes is theoretically possible!
Our known universe is pretty big, but it is made up of very small stuff--sub atomic particles. The study of these particles and how they interact is called quantum mechanics.
Hawking goes on to describe how there are four fundamental forces in nature; what we call gravity, the well-known electromagnetic force, the weak nuclear force that binds electrons to the nucleus in an atom, and the strong nuclear force that holds the sub-atomic particles in the nucleus of an atom together. Relativity equations explain only the first three. So far, theoretical physicists have not been able to come up with a theory that unifies the strong nuclear force with the other three. As Hawking points out, the effort to do so has been the focus of theoretical physics for the last fifty years.
In Hawkings concluding remarks, he offers his insights into what the future may be like once a Unified Theory of the Universe is finally discovered.
In our lifetime, scientific discovery has accelerated to the point where ordinary people havent got the time or mental capacity to take it all in. For me, A Briefer History of Time helped fill in some of the broad and exciting facts.
The intertwined histories of scientific discovery and religion are the story of our trying to comprehend our universe. Just as faith and study are the cornerstones of a religious explanation of the universe, logic and study are fundamental to a scientific understanding of it. As Hawking points out, science and religion are not at odds. In fact quite the opposite; a better understanding of modern science may bring open-minded Christians to a more profound belief in their God.
I highly recommend this book.
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de Stephen Hawking
