Navigating the site: World views

Stephen W. Hawking A Brief History of Relativity, Time, and Brane New World (2001) "Toward the end of the nineteenth century, scientists believed they were close to a complete description of the universe."
Scientists before Einstein's work was confirmed by observations:
pp. 1921. Special relativity  Spacetime curvature  Time  General relativity  Strings  Universal expansion  Sun  Time travel?Einstein's significance  Comprehending time  Envisioning spacetime  Hidden existences  Hawking's views  Book's contents  Historical dates to know  vocabulary
Two competing views:Isaac Newton gave us the first mathematical model for time and space in his Principia Mathematica, published in 1687. . . .Time was separate from space and was considered to be a single line. . . . that was infinite in both directions. "Time itself was considered eternal." p. 32. "Einstein's theory of relativity, which agrees with a large number of experiments, shows that time and space are inextricably interconnected. p. 33. ". . . it spurred the greatest change in our perception of the universe in which we live since Euclid wrote," 300 BCE. "Einstein's general theory of relativity transformed space and time from a passive background in which events take place to active participants in the dynamics of the universe." Compare to page 35. spacetimeThe Universe in a NutshellContents
1 – A Brief History of Relativity, p. 3. 2 – The Shape of Time, p. 29. 3 – The Universe in a Nutshell, p. 67. 4 – Predicting the Future, p. 101. 5 – Protecting the Past, p. 131. 6 – Our Future? Star Trek or not? p. 155. 7 – Brane New World, p. 173.
Glossary, p. 202. Einstein's significance  Comprehending time  Envisioning spacetime  Hidden existences  Hawking's views  Book's contents  Historical dates to know  vocabularyUnseen dimensions hidden in reality.
"Spacetime may be similar: on human, atomic, or even nuclear physics length scales, it may appear four dimensional and nearly flat. On the other hand if we probe to very short distances using extremely high energy particles, we should see that spacetime was ten– or eleven–dimensional." pp. 178179. "If all the additional dimensions were very small, it would be difficult to observe them. However, there has recently been the suggestion that one or more of the extra dimensions might be comparatively large or even infinite. The idea has the great advantage that it might be testable by the next generation of particle accelerators or by sensitive shortrange measurements of the gravitational force.
p. 180. Einstein's significance  Comprehending time  Envisioning spacetime  Hidden existences  Hawking's views  Book's contents  Historical dates to know  vocabularyWhat is the origin of our current concepts of the material universe?
The Andromeda Galaxy, seen here, is actually moving away from our galaxy: the Milky Way in an expanding universe.
Special relativity  Curvature of spacetime  Time  General relativity  Universal expansion  Time travel?
supersymmetric string theory
"The reason general relativity broke down at the big bang was that it was not compatible with quantum theory, the other great conceptual revolution of the early twentieth century." Nutshell, p. 24.
"Our own sun contains about 2 percent of these heavier elements because it is a second or third generation star. It was formed some five thousand million years ago out of a cloud of rotating gas containing the debris of earlier supernovas." Hawking, The Theory of Everything, p. 103.
"...a small amount of the heavier elements collected together to form the bodies that now orbit the sun as planets like the Earth."
Hawking, The Theory of Everything. p. 126. "it is forbidden by the second law of thermodynamics. This says that disorder or entropy always increases with time. In other words, it is Murphy's Law–things get worse."
"The increase of disorder or entropy with time is one example of what is called an arrow of time, something that gives direction to time and distinguishes the past from the future." Special relativity  Curvature of spacetime  Time  General relativity  Universal expansion  Time travel?
Einstein's significance  Comprehending time  Envisioning spacetime  Hidden existences  Hawking's views  Book's contents  Historical dates to know  vocabulary"If one takes the positivist position, as I do, one cannot say what time actually is. All one can do is describe what has been found to be a very good mathematical model for time and say what predictions it makes." Hawking, Nutshell, p. 31. The inseparability of space and time; is called spacetime."One cannot curve space without involving time as well. Thus time has a shape. However, it appears to also have a one way direction. . . ." pp. 3335. By curving space and time, general relativity changes them from being passive background against which events take place to being active, dynamic participants in what happens." p. 35. "Our past is pear shaped." "If one follows our past light cone back in time (having originated in a single dense point), it will be bent back by matter in the early universe. The whole universe we observe is contained within a region whose boundary shrinks to zero at the big bang. This would be a singularity, a place where the density of matter would be infinite and classical general relativity would break down." p. 41. Three varieties of the arrows of time:
Hawking, Nutshell, p. 35, 138. & The Theory of Everything, p. 131 Time travel?
The Universe in a Nutshell : p. 153.Einstein's significance  Comprehending time  Envisioning spacetime  Hidden existences  Hawking's views  Book's contents  Historical dates to know  vocabularyChapter One A Brief History of Relativity "How Einstein laid the foundations of . . . general relativity and quantum theory." "Albert Einstein, the discoverer of the special and general theories of relativity . . . ." "Toward the end of the nineteenth century, scientists believed they were close to a complete description of the universe." The Universe in a Nutshell, p. 4.A 1920 photograph of Albert Einstein in his early forties. p. 5."By the century's end, discrepancies in the idea of an allpervading ether began to appear. It was expected that light would travel at a fixed speed through the ether but that if you were travelling through the ether in the same direction as the light, its speed would appear lower, and if you were travelling in the opposite direction of the light, its speed would appear higher." p. 6.Einstein abandoned this concept of the ether as "redundant." p. 7.
"This required abandoning the idea that there is a universal quantity called time that all clocks would measure." "This has been confirmed by a number of experiments, including one in which two accurate clocks were flown in opposite directions around the world. . . ." p. 9."Einstein's postulate that the laws of nature should appear the same to all freely moving observers was the foundation of the theory of relativity, so called because it implied that that only relative motion was important. Its beauty and simplicity convinced many thinkers, but there remained a lot of opposition." "Einstein had overthrown two of the absolutes of nineteenthcentury science:
"Many people found this an unsettling concept . . . .the unease continued. . . " " . . the theory of relativity is now completely accepted by the scientific community, and its predictions have been verified in countless applications." p. 11."a very important consequence of relativity is the relation between mass and energy.""Mass and energy are equivalent, as is summed up by Einstein's famous equation E = M C ^{2}. "To accelerate a particle to the speed of light would be impossible because it would take an infinite amount of energy." p. 12."Although the theory of relativity fit well with the laws that governed electricity and magnetism, it was not compatible with Newton's law of gravity. This law said that if one changed the distribution of matter in one region of space, the change in the gravitational field would be felt instantaneously everywhere else in the universe." p. 14."Einstein . . . realized that there is a close relationship between acceleration and a gravitational field."p.16."in 1912 Einstein . . . realizing that the equivalence would work if the geometry of spacetime was curved and not flat, . . . ."p.17.
p. 18.Einstein's significance
"General relativity completely changed the discussion of the origin and fate of the universe." p.22."So Einstein's theory does imply that time has a beginning, although he was never happy with the idea."
"a new picture of reality called quantum mechanics."
"excellent agreement with observations"
p. 26."The world has changed far more in the last hundred years than in any previous century. The reason has not been new political or economic doctrines but the vast developments in technology made possible by advances in basic science. Who better symbolizes those advances than Albert Einstein? p. 26." . . . but an equation is for eternity." NextEinstein's significance  Comprehending time  Envisioning spacetime  Hidden existences  Hawking's views  Book's contents  Historical dates to know  vocabulary"Einstein's general relativity gives time a shape. How this can be reconciled with quantum theory."
Einstein's significance  Comprehending time  Envisioning spacetime  Hidden existences  Hawking's views  Book's contents  Historical dates to know  vocabularyChapter Three The Universe in a Nutshell
"The Universe has multiple histories, each of which is determined . . . ."
p. 69."Although the universe seems to be much the same at each position in space, it is definitely changing in time. This was not realized until the early years of the twentieth century." p. 71."Something must have happened in the past to make the stars light up a finite time ago, which means that light from very distant stars has not had time to reach us yet. This would explain why the sky at night isn't glowing in every direction." p. 72."In 1923, Hubble (Edwin Hubble) discovered that many faint patches of light, called nebulae, were in fact other galaxies, vast collections of stars like our sun but at a great distance. In order for them to appear so small and faint, the distances had to be so great that light from them would have taken millions or even billions of years to reach us. This indicated that the beginning of the universe couldn't have been just a few thousand years ago.' pp. 7375."But the second thing Hubble discovered was even more remarkable . . . . To their great surprise , they found that nearly all galaxies are moving away. Moreover, the farther they are from us, the faster they are moving away." p. 75."The universe is expanding." p. 76."Roger Penrose and I were able to show that Einstein's general theory of relativity implied that the universe and time itself must have had a beginning in a tremendous explosion." p. 76." . . . no star could have been shining longer than ten to fifteen billion years, the time since the big bang." p. 79."While the theorems that Penrose and I proved showed the universe must have had a beginning, they didn't give much information about the nature of the beginning. . . . scrunched up [crushed] into a single point of infinite density." p. 79.Einstein's significance  Comprehending time  Envisioning spacetime  Hidden existences  Hawking's views  Book's contents  Historical dates to know  vocabularyChapter Four Predicting the Future How the loss of information in black holes may reduce our ability to predict the future. "In other words, if scientific determinism holds, we should in principle be able to predict the future. . . . Of course, in practice even something a simple as Newton's theory of gravity produces equations we can't solve exactly for more than two particles." "The trouble is that the sequence of events is not repeatable." p. 104."At first sight, determinism would also seem to be threatened by the uncertainty principle, which says we cannot measure accurately both the position and the velocity of a particle at the same time." p. 105."However good our computer is, if we put lousy data in, we will get lousy predictions out." p. 105."We now realize that the wave function is all that can be well defined. We cannot even suppose that the particle has a position and velocity that are known to God but are hidden from us." "Even God is bound by the uncertainty principle and cannot know the position and velocity. He can only know the wave function."p. 107."The situation was different in the general theory or relativity, in which spacetime was not flattened but curved, and distorted by the matter and energy in it." p. 109."Einstein himself never believed in black holes. . . . " pp. 111113.
•Kaku Einstein's significance  Comprehending time  Envisioning spacetime  Hidden existences  Hawking's views  Book's contents  Historical dates to know  vocabularyChapter Five Protecting the Past Is Time travel possible? "The Basis of all modern discussions of time travel is Einstein's general relativity." p. 135." . . . Einstein's equations made space and time dynamic by describing how they were curved and distorted by the matter and energy in the universe." "But there was now the possibility that spacetime could be warped so much that you could go off in a spaceship and come back before you set out." p.135."This book will not go into a . . . discussion of freewill. Instead it will concentrate on whether the laws of physics allow spacetime to be so warped that a macroscopic body. . . can return to its own past." pp. 136138.Einstein can't be quite right " . . .because we observe that matter is subject to uncertainty and quantum fluctuations." p. 138.Grandfather paradox: "The first is Einstein's general relativity, which assumes that the universe has a welldefined history without any uncertainty." "In this, we consider matter to behave according to quantum theory, with uncertainty and quantum fluctuations, but spacetime to be well defined and classical." p. 138."Finally, there is the full quantum theory of gravity, whatever that may be. In this theory, where not just matter but also time and space themselves are uncertain and fluctuate, it is not even clear of how to pose the question of whether time travel is possible." pp. 138139.
"This supports what I have called the Chronology Protection Conjecture: that the laws of physics conspire to prevent time travel by macroscopic objects." p. 153.
Chapter Six Our Future? Star Trek or not? How biological and electronic life will go on developing in complexity at an ever increasing rate "Clearly the present exponential growth cannot continue indefinitely." p. 159.
p. 171.Einstein's significance  Comprehending time  Envisioning spacetime  Hidden existences  Hawking's views  Book's contents  Historical dates to know  vocabularyDo we live on a brane or are we just holograms?
". . . we have already identified the Theory of Everything (T o E) as Mtheory. " . . .a network of apparently different theories that all seem to be approximations the same underlying fundamental theory in different limits." " . . . we are likely to find unexpected new phenomena whenever we extend the range of our observations to to smaller scales." p. 175.Russian, nested figurines fit neatly one inside the other."Each doll represents a theoretical understanding of nature down to a certain length scale." p.177."Mtheory is like a jigsaw. . . " ". . . the scales of classical physics, which is good from interstellar distances down to about a hundredth of a millimeter." ". . . but evidence began to emerge that matter is not smooth but grainy: it is made up of tiny building blocks called atoms . . . . but it was soon found that atoms consisted of electrons orbiting a nucleus made up of protons and neutrons. . . . Then we discovered that protons and neutrons are made of smaller particles called quarks." The limit to which tools can probe matter is measured by the Planck length [ "About 10^{–35} centimeters." ] . p. 176.
A four dimensional cube."Similarly spacetime may look four dimensional to us, but appear ten or elevendimensional when probed with very high energy particles." More about extra dimensionsp. 179."Matter and nongravitational forces like the electric force would be confined to the brane. This everything not involving gravity would behave as it would in four dimensions." "On the other hand, gravity in the form of curved space would permeate the whole bulk of the higher dimensional spacetime. pp. 180181."In this brane world, we would live on one brane but there would be another 'shadow' brane nearby. Because light would be confined to the branes and would not propagate through the space between, we could not see the shadow world. But we would feel the gravitational influence of matter on the shadow brane." p. 184."Gravity might be quite strong in the fundamental theory but the spreading of the gravitational force in extra dimensions would mean it would be weak at large distances on the brane on which we live." p. 199.
Einstein's significance  Comprehending time  Envisioning spacetime  Hidden existences  Hawking's views  Book's contents  Historical dates to know  vocabularySpecial relativity  Curvature of spacetime  Time  General relativity  Strings  Universal expansion  Time travel?TermsEinstein's significance  Comprehending time  Envisioning spacetime  Hidden existences  Hawking's views  Book's contents  Historical dates to know
"different oscillations of a string give rise to different masses and force charges." p. 52
What is an Angstrom, or the atomic diameter's extent? The dimensions in this model are deceptively wrong. Periodic Table of the Elements Earth – Sky magazineEinstein's significance  Comprehending time  Envisioning spacetime  Hidden existences  Hawking's views  Book's contents  Historical dates to knowEinstein the man  His relativistic insights  On Albert Einstein  The famous equation's meaning Ian Tattersall  Richard Feynman  Michio Kaku; Einstein's Cosmos  Jacob Bronowski  Stephen Hawking  Ernst Mayr Science Index  Analysis  Population Index  Global Warming Index  Nature Index  Brief on ideas 
