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101 " If there are beings alive on Alpha Centauri today, they remain blissfully ignorant of the rise of Donald Trump. It "
― Stephen Hawking , Brief Answers to the Big Questions
102 " can one have atoms in which the nucleus is a tiny primordial black hole, formed in the early universe? "
103 " if there were such a God, I would like to ask however did he think of anything as complicated as M-theory in eleven dimensions. "
104 " Cuando te enfrentas a la posibilidad de una muerte temprana, te das cuenta de que hay muchas cosas que quieres hacer antes de que tu vida termine. "
105 " Somewhat surprisingly, this includes a form of electronic personhood, to ensure the rights and responsibilities for the most capable and advanced AI. "
106 " There is a history of the universe in which England win the World Cup again, though maybe the probability is low. "
107 " This process is known as inflation, something that was good for the universe in contrast to inflation of prices that too often plagues us. "
108 " We were told that you can never get something for nothing. But now, after a lifetime of work, I think that actually you can get a whole universe for free. "
109 " At some point during our 13.8 billion years of cosmic history, something beautiful happened. This information processing got so intelligent that life forms became conscious. Our universe has now awoken, becoming aware of itself. "
110 " People have searched for mini black holes of this mass, but have so far not found any. This is a pity because, if they had, I would have got a Nobel Prize. "
111 " People have always wanted answers to the big questions. Where did we come from? How did the universe begin? What is the meaning and design behind it all? Is there anyone out there? The creation accounts of the past now seem less relevant and credible. They have been replaced by a variety of what can only be called superstitions, ranging from New Age to Star Trek. But real science can be far stranger than science fiction, and much more satisfying. "
112 " I think this is an important subject for research, but one has to be careful not to be labelled a crank. If one made a research grant application to work on time travel it would be dismissed immediately. No government agency could afford to be seen to be spending public money on anything as way out as time travel. Instead one has to use technical terms like closed time-like curves, which are code for time travel. "
113 " So what does this mean in our quest to find out if there is a God? It means that if the universe adds up to nothing, then you don't need a God to create it. The universe is the ultimate free lunch. "
114 " Given the nature of the observations we can make now, all we can do is assign a probability to a particular history of the universe. Thus the universe must have many possible histories, each with its own probability. There is a history of the universe in which England win the World Cup again, though maybe the probability is low. This idea that the universe has multiple histories may sound like science fiction, but it is now accepted as science fact. It is due to Richard Feynman, who worked at the eminently respectable California Institute of Technology and played the bongo drums in a strip joint up the road. Feynman’s approach to understanding how things works is to assign to each possible history a particular probability, and then use this idea to make predictions. It works spectacularly well to predict the future. So we presume it works to retrodict the past too. "
115 " One way or another, I regard it as almost inevitable that either a nuclear confrontation or environmental catastrophe will cripple the Earth at some point in the next 1,000 years "
116 " How do we know that we are not just characters in a computer-generated soap opera? "
117 " In conclusion, rapid space travel and 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 their parents. "
118 " Scientists are now working to combine Einstein’s general theory of relativity and Feynman’s idea of multiple histories into a complete unified theory that will describe everything that happens in the universe. This unified theory will enable us to calculate how the universe will evolve, if we know its state at one time. But the unified theory will not in itself tell us how the universe began, or what its initial state was. For that, we need something extra. We require what are known as boundary conditions, things that tell us what happens at the frontiers of the universe, the edges of space and time. But if the frontier of the universe was just at a normal point of space and time we could go past it and claim the territory beyond as part of the universe. On the other hand, if the boundary of the universe was at a jagged edge where space or time were scrunched up, and the density was infinite, it would be very difficult to define meaningful boundary conditions. So it is not clear what boundary conditions are needed. It seems there is no logical basis for picking one set of boundary conditions over another. "
119 " However, Jim Hartle of the University of California, Santa Barbara, and I realised there was a third possibility. Maybe the universe has no boundary in space and time. At first sight, this seems to be in direct contradiction to the geometrical theorems that I mentioned earlier. These showed that the universe must have had a beginning, a boundary in time. However, in order to make Feynman’s techniques mathematically well defined, the mathematicians developed a concept called imaginary time. It isn’t anything to do with the real time that we experience. It is a mathematical trick to make the calculations work and it replaces the real time we experience. Our idea was to say that there was no boundary in imaginary time. That did away with trying to invent boundary conditions. We called this the no-boundary proposal. "
120 " If the boundary condition of the universe is that it has no boundary in imaginary time, it won’t have just a single history. There are many histories in imaginary time and each of them will determine a history in real time. Thus we have a superabundance of histories for the universe. What picks out the particular history, or set of histories that we live in, from the set of all possible histories of the universe? "