题目内容
All that we really need to plot out the future of our universe are a few good measurements. This does not mean that we can sit down today and outline the future course of the universe with anything like certainty. There are still too many things we don't know about the way the universe is put together. But we do know exacdy what information we need to fill in our knowledge, and we have a pretty good idea of how to go about getting it. Perhaps the best way to think of our present situation is to imagine a train coming into a switchyard(调车场). All of the switches(转辙器) are set before the train arrives, so that its path is completely determined. Some switches we can see, others we cannot. There is no ambiguity if we can see the setting of a switch; we can say with confidence that some possible futures will not materialize and others will. At the unseen switches, however, there is no such certainty. We know the train will take one of the tracks leading out, but we have no idea which one. The unseen switches are the true decision points in the future, and what happens when we arrive at them determines the entire subsequent course of events.
When we think about the future of the universe, we can see our "track" many billions of years into the future, but after that there are decision points to be dealt with and possible fates to consider. The goal of science is to reduce the ambiguity at the decision points and find the true road that will be followed.
According to the passage, it is difficult to be certain about the distant future of the universe because we______.
查看答案
搜索结果不匹配？点我反馈
更多问题
听力原文：M: Say, Rason, what are you watching？
W: An old Japanese film. I wonder if I'm going to spend all my next year there. I'd better start familiarizing myself with the culture.
M: You mean you are accepted into the program？
W: Yes.
M: That's wonderful. You must be excited.
W: Excited and nervous. You know I owe a lot to Professor Mercheno. He wrote a letter of recommendation for me and he bought me a set of practice tapes and a book which goes with them. Just so I can work on my basic conversation skills.
M: How much Japanese can you understand？
W: Not a lot at present. But I signed up for intensive Japanese this semester.
M: I wish I were as talented as you are in foreign languages. I'd like to study abroad.
W: Than why don't you？ The university has lots of over- seas programs that don't require mastery of a foreign language. The tuition is about the same. You just have to be the kind of person who is receptive to new ways of looking at things and willing to adjust to a different kind of life style.
M: I had assumed that all programs required you to know a foreign language. I might check into this.
W: You won't regret it.
What is the woman doing when the man interrupts her？
In 1970, a young German schoolmaster had an idea which changed this state of affairs. He decided to turn his little schoolhouse into a dormitory or hostel for the summer holidays. Anyone who brought his sleeping bag and cooking equipment along could stay there for a very small quantity of money. The idea was a success. A few years later, the schoolhouse was much too small to hold the many young people who wanted to stay there. As a result, a dormitory was set up in an old castle nearby. This was the first Youth Hostel.
Today, young students and workers of every country can meet in the hostel and get to know each other. When young people arrive at the hostel, they have only to show their card of membership in a hostel organization in their own country. This card will permit him to use the facilities of hostels all over the world for very low prices.
Often, at the evening meal, a group of boys and girls from various parts of the country or the world will happen to meet at the same hostel. They may put their food together and prepare a dinner with many kinds of dishes. Sometimes a program will be organized after the meal with dances, songs, or short talks followed by a question period. One can learn a lot of things about other places, just by meeting people who come from those places. For this reason, a few weeks spent "hostelling" can be just as useful a part of one's education as classes in school.
The author says children in the city seldom went to the woods and fields because
Migration is big, dangerous, compelling. It is 60 million Europeans leaving home from the 16th to the 20th centuries. It is some 15 million Hindus, Sikhs, and Muslims swept up in a tumultuous shuffle of citizens between India and Pakistan after the partition of the subcontinent in 1947.
Migration is the dynamic undertow of population change: everyone's solution, everyone's conflict. As the century turns, migration, with its inevitable economic and political turmoil, has been called "one of the greatest challenges of the coming century."
But it is much more than that. It is, as it has always been, the great adventure of human life. Migration helped create humans, drove us to conquer the planet, shaped our societies, and promises to reshape them again.
"You have a history book written in your genes," said Spencer Wells. The book he's trying to read goes back to long before even the first word was written, and it is a story of migration.
Wells, a tall, blond geneticist at Stanford University, spent the summer of 1998 exploring remote parts of Transcaucasia and Central Asia with three colleagues in a Land Rover, looking for drops of blood. In the blood, donated by the people he met, he will search for the story that genetic markers can tell of the long paths human life has taken across the Earth.
Genetic studies are the latest technique in a long effort of modern humans to find out where they have come from. But however the paths are traced, the basic story is simple: people have been moving since they were people. If early humans hadn't moved and intermingled as much as they did, they probably would have continued to evolve into different species. From beginnings in Africa, most researchers agree, groups of hunter- gatherers spread out, driven to the ends of the Earth.
To demographer Kingsley Davis, two things made migration happen. First, human beings, with their tools and language, could adapt to different conditions without having to wait for evolution to make them suitable for a new niche. Second, as populations grew, cultures began to differ, and inequalities developed between groups. The first factor gave us the keys to the door of any room on the planet; the other gave us reasons to use them.
Over the centuries, as agriculture spread across the planet, people moved toward places where metal was found and worked and to centres of commerce that then became cities. Those places were, in turn, invaded and overrun by people later generations called barbarians.
In between these storm surges were steadier but similarly profound tides in which people moved out to colonize or were captured and brought in as slaves. For a while the population of Athens, that city of legendary enlightenment, was as much as 35 percent slaves.
"What strikes me is how important migration is as a cause and effect in the great world events," Mark Miller, co-author of The Age of Migration and a professor of political science at the University of Delaware, told me recently.
It is difficult to think of any great events that did not involve migration. Religions spawned pilgrims or settlers; wars drove refugees before them and made new land available for the conquerors; political upheavals displaced thousands or millions; economic innovations drew workers and entrepreneurs like magnets; environmental disasters like famine Or disease pushed their bedraggled survivors anywhere they could replant hope.
"It's part of our nature, this movement," Miller said. "It's just a fact of the human con
A great many cancers can be cured but only if______ before they have begun spread or "colonize" in other parts of the body.
微信支付 
支付宝支付