1. ”According to this theory [strong anthropic principle], there are either many different universes or many different regions of a single universe, each with its own initial configuration and, perhaps, with its own set of laws of science. In most of these universes the conditions would not be right for the development of complicated organisms; only in the few universes that are like ours would intelligent beings develop and ask the question: "Why is the universe the way we see it?" The answer is then simple: If it had been different, we would not be here!”
2. “Any physical theory is always provisional, in the sense that it is only a hypothesis: you can never prove it. No matter how many times the results of experiments agree with some theory, you can never be sure that the next time the result will not contradict the theory. On the other hand, you can disprove a theory by finding even a single observation that disagrees with the predictions of the theory... Each time new experiments are observed to agree with the predictions the theory survives, and our confidence in it is increased; but if ever a new observation is found to disagree, we have to abandon or modify the theory.”
3. “Disorder increases with time because we measure time in the direction in which disorder increases.”
4. “Even if there is only one possible unified theory, it is just a set of rules and equations. What is it that breathes fire into the equations and makes a universe for them to describe? The usual approach of science of constructing a mathematical model cannot answer the questions of why there should be a universe for the model to describe. Why does the universe go to all the bother of existing?”
5. “God not only plays dice. He also sometimes throws the dice where they cannot be seen.”
6. “Hamlet may have meant that although we human beings are very limited physically, our minds are free to explore the whole universe, and to go boldly where even “Star Trek” fears to tread – bad dreams permitting.”
7. “... if there were a complete set of laws, that would infringe God's freedom to change his mind and intervene in the world. It's a bit like the old paradox: Can God make a stone so heavy that he can't lift it? But the idea that God might want to change his mind is an example of the fallacy, pointed out by St. Augustine, of imagining God as a being existing in time: time is a property only of the universe that God created. Presumably, he knew what he intended when he set it up!”
8. “... if we do discover a complete theory, it should in time be understandable in broad principle by everyone, not just a few scientists. Then we shall all, philosophers, scientists, and just ordinary people, be able to take part in the discussion of the question of why it is that we and the universe exist. If we find the answer to that, it would be the ultimate triumph of human reason - for then we would know the mind of God.”
9. ”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. This means that there can be no important difference between the forward and backward directions of imaginary time. On the other hand, when one looks at "real" time, there's a very big difference between the forward and backward directions, as we all know. Where does this difference between the past and the future come from? Why do we remember the past but not the future?”
10. “Is the universe actually infinite or just very large? And is it everlasting or long-lived? How could our finite minds comprehend an infinite universe? Isn´t it presumptuous of us even to make the attempt? Do we risk the fate of Prometeus, who in classical mythology stole fire from Zeus for human beings to use, and was punished for his temerity by being chained to a rock where an eagle picked at his liver?”
11. "I think computer viruses should count as life. I think it says something about human nature that the only form of life we have created so far is purely destructive. We've created life in our own image."
12. "It is said that there's no such thing as a free lunch. But the universe is the ultimate free lunch."
13. “It matters if you just don't give up.”
14. "My goal is simple. It is complete understanding of the universe, why it as it is and why it exists at all."
15. “Physics is the most fundamental of the sciences. In that sense, it is the most poetic."
16. “Someone told me that each equation I included in the book [A Brief History of Time ] would halve its sales.”
17. “Some people have blamed the atom bomb on Einstein because he discovered the relationship between mass and energy, but that is like blaming Newton for causing airplanes to crash because he discovered gravity.”
18. “So what is real and what is imaginary? Is the distinction only in our minds?”
19. "Space and time are now dynamic quantities: when a body moves, or a force acts, it affects the curvature of space and time--and in turn the structure of space-time affects the way in which bodies move and forces act. Space and time not only affect but also are affected by everything that happens in the universe."
20. "The conclusion of this lecture is that rapid space-travel, or travel back in time, can't be ruled out, according to our present understanding. They would cause great logical problems, so let's hope there's a Chronology Protection Law, to prevent people going back, and killing our parents. But science fiction fans need not lose heart. There's hope in string theory."
21. ”The discovery of a complete unified theory, therefore, may not aid the survival of our species. It may not even affect our life-style. But ever since the dawn of civilization, people have not been content to see events as unconnected and inexplicable. They have craved an understanding of the underlying order in the world. Today we still yearn to know why we are here and where we came from. Humanity's deepest desire for knowledge is justification enough for our continuing quest. And our goal is nothing less than a complete description of the universe we live in.”
22. ”The progress of the human race in understanding the universe has established a small corner of order in an increasingly disordered universe. If you remember every word in this book, your memory will have recorded about two million pieces of information: the order in your brain will have increased by about two million units. However, while you have been reading this book, you will have converted at least a thousand calories or ordered energy, in the form of food, into disordered energy, in the form of heat that you lose to the air around you by convection and sweat. This will increase the disorder of the universe by about twenty million million million million units - or about ten million million million times the increase in order in your brain - and that's if you remember everything in this book.”
23. “The universe has multiple histories, each one determined by a tiny nut.”
24. “The usual approach of science of constructing a mathematical model cannot answer the questions of why there should be a universe for the model to describe. Why does the universe go to all the bother of existing?”
25. “The whole history of science has been the gradual realization that events do not happen in an arbitrary manner, but that they reflect a certain underlying order, which may or may not be divinely inspired.”
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 techonology made possible by advances in basic science. Who better symbolizes those advances than Albert Einstein?”
27. “To confine our attention to terrestrial matters would be to limit the human spirit.”
28. “Today scientists describe the universe in terms of two basic partial theories - the general theory of relativity and quantum mechanics... The general theory of relativity describes the force of gravity and the large-scale structure of the universe, that is, the structure on scales from only a few miles to as large as a million million million million (1 with twenty-four zeros after it) miles, the size of the observable universe. Quantum mechanics, on the other hands, deals with phenomena on extremely small scales, such as a millionth of a millionth of an inch. Unfortunately, however, these two theories are known to be inconsistent with each other - they cannot both be correct.”
29. “We are just an advanced breed of monkeys on a minor planet of a very average star. But we can understand the Universe. That makes us something very special.”
30. “We now know that every particle has an antiparticle, with which it can annihilate. There could be whole antiworlds and antipeople made out of antiparticles. However, if you meet your antiself, don't shake hands! You would both vanish in a great flash of light.”
31. "We see the universe the way it is because we exist."
32. “What is time? Is it an ever rolling stream that bears all our dreams away, as the old hymn says? Or is it a railroad track? Maybe it has loops and branches, so you can keep going forward and yet return to an earlier station on the line.”
33. “Why does the universe go to all the bother of existing? Is the unified theory so compelling that it brings about its own existence?”
