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5.0 étoiles sur 5 Un livre passionant, 19 décembre 2009
Ce commentaire fait référence à cette édition : A Brief History Of Time: From Big Bang To Black Holes (Relié)
Ce livre même lu en anglais par un jeune de 14 ans comme moi avec un petit dico à portée de main est une vrai mine d'informations sans formules complexes . Vraiment un livre à lire pour savoir ce qui se passe dans l'espace !
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5.0 étoiles sur 5 Time is of the essence, 21 décembre 2005
Par 
FrKurt Messick "FrKurt Messick" (Bloomington, IN USA) - Voir tous mes commentaires
(TOP 1000 COMMENTATEURS)   
Ce commentaire fait référence à cette édition : A Brief History Of Time: From Big Bang To Black Holes (Broché)
The mark of a true educator, which Stephen Hawking certainly is, is that he would take time (very valuable time, in his case) away from research and contemplation of the great mysteries of the universe to write a piece that would serve to help explain to the greater number of less-scientifically-adept persons the fruits and implications of modern scientific research from the cutting edge of physics. Hawking is ranked in popular and scientific thinking on a par with Einstein, and has motor neuron disability that severely restricts his ability to move, even to type or write, so, when he takes time to write something for general consumption, it is probably going to be worthwhile. And indeed, this is.
'Someone told me that each equation I included in the book would halve sales. I therefore resolved not to have any equations at all. In the end, however, I did put in one equation, Einstein's famous equation. I hope that this will not scare off half of my potential readers.'
Hawking begins by exploring the large scale structure of the universe (time being part of the `fabric' of the universe, in spacetime), the connections of space and time as a relatively new concept in thinking of the universe, and the way the universe `acts' (cosmological dynamics). From there, he explores the universe at a very basic level, as elementary particles and forces of nature, introducing quarks.
'There are a number of different varieties of quarks: there are thought to be at least six "flavours", which we call up, down, strange, charmed, bottom and top. Each flavour comes in three "colours", red, green and blue. ...We now know that neither the atoms nor the protons and neutrons within them are indivisible. So the question is: What are the truly elementary particles, the basic building blocks from which everything is made?'
From this discussion Hawking proceeds to black holes (and the fact that they aren't so black and permanent as popular belief holds them to be), which circles back around to the origin and destiny of the universe (which relates back to the large-scale structure), which ultimately brings us to time. This is where things begin to get interesting.
'When one tried to unify gravity with quantum mechanics, one had to introduce the idea of "imaginary" time. Imaginary time is indistinguishable from directions in space. If one can go north, one can turn around and head south; equally, if one can go forward in imaginary time, one ought to be able to turn around and go backward.'
Hawking explains variations of the thermodynamic, psychological and cosmological laws that regulate the direction of time's arrow, which, despite the theoretical flexibility of time with regard to scientific principles, always apparently goes in one direction.
Finally, Hawking explores the most current topic in theoretical physics: unification theories, which may or may not be a wild goose on the loose. Hawking also explores what such a grand unified theory (also called sometimes the `theory of everything') would mean, and what it wouldn't mean. But Hawking assures us that the quest for understanding is worthwhile even it won't be the final word on everything.
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5.0 étoiles sur 5 Time is of the essence, 21 décembre 2005
Par 
FrKurt Messick "FrKurt Messick" (Bloomington, IN USA) - Voir tous mes commentaires
(TOP 1000 COMMENTATEURS)   
Ce commentaire fait référence à cette édition : A Brief History of Time: From the Big Bang to the Black Holes (Cassette)
The mark of a true educator, which Stephen Hawking certainly is, is that he would take time (very valuable time, in his case) away from research and contemplation of the great mysteries of the universe to write a piece that would serve to help explain to the greater number of less-scientifically-adept persons the fruits and implications of modern scientific research from the cutting edge of physics. Hawking is ranked in popular and scientific thinking on a par with Einstein, and has motor neuron disability that severely restricts his ability to move, even to type or write, so, when he takes time to write something for general consumption, it is probably going to be worthwhile. And indeed, this is.
'Someone told me that each equation I included in the book would halve sales. I therefore resolved not to have any equations at all. In the end, however, I did put in one equation, Einstein's famous equation. I hope that this will not scare off half of my potential readers.'
Hawking begins by exploring the large scale structure of the universe (time being part of the `fabric' of the universe, in spacetime), the connections of space and time as a relatively new concept in thinking of the universe, and the way the universe `acts' (cosmological dynamics). From there, he explores the universe at a very basic level, as elementary particles and forces of nature, introducing quarks.
'There are a number of different varieties of quarks: there are thought to be at least six "flavours", which we call up, down, strange, charmed, bottom and top. Each flavour comes in three "colours", red, green and blue. ...We now know that neither the atoms nor the protons and neutrons within them are indivisible. So the question is: What are the truly elementary particles, the basic building blocks from which everything is made?'
From this discussion Hawking proceeds to black holes (and the fact that they aren't so black and permanent as popular belief holds them to be), which circles back around to the origin and destiny of the universe (which relates back to the large-scale structure), which ultimately brings us to time. This is where things begin to get interesting.
'When one tried to unify gravity with quantum mechanics, one had to introduce the idea of "imaginary" time. Imaginary time is indistinguishable from directions in space. If one can go north, one can turn around and head south; equally, if one can go forward in imaginary time, one ought to be able to turn around and go backward.'
Hawking explains variations of the thermodynamic, psychological and cosmological laws that regulate the direction of time's arrow, which, despite the theoretical flexibility of time with regard to scientific principles, always apparently goes in one direction.
Finally, Hawking explores the most current topic in theoretical physics: unification theories, which may or may not be a wild goose on the loose. Hawking also explores what such a grand unified theory (also called sometimes the `theory of everything') would mean, and what it wouldn't mean. But Hawking assures us that the quest for understanding is worthwhile even it won't be the final word on everything.
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5.0 étoiles sur 5 It does what it says, 1 mars 2014
Achat vérifié(De quoi s'agit-il ?)
Ce commentaire fait référence à cette édition : A Brief History Of Time: From Big Bang To Black Holes (Broché)
No wonder this book was such a big hit when it was first released - the story it tells of Time and Space is facinating and it is told without recourse to heavy technicalities. It is an amazing piece of work and is just as relevant today as it was when first published. If you want to read about what space and the cosmos mean then this is the first stop, even for me it was enjoyable and still interesting to read the thoughts of a true genius.
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