1 . When it comes to black holes, we are caught between a rock and a hard place. In the 1970s, Stephen Hawking showed that all black holes give off thermal radiation(热辐射)and eventually evaporate(蒸发). In doing so, they seemed to be destroying information contained in the matter that fell into them, therefore going against a rule of quantum mechanics(量子力学): information cannot be created or destroyed.
Some argued that the outgoing “Hawking radiation” preserved the information. However, if this were the case, then given certain assumptions, the event horizon(视界)—— the black hole’s boundary of no return—— would become intensely energetic, forming a firewall. But such firewalls go against the theory of general relativity, which says that space-time near the event horizon should be smooth. The black hole firewall paradox was thus born.
Now, Sean Carroll at the California Institute of Technology and his colleagues have shown that the paradox disappears when the evolution of black holes is understood in the context of the many-worlds interpretation of quantum mechanics.
The quantum state of the universe is described by something called the global wave function(全局波函数). According to traditional quantum mechanics, whenever there are many possible outcomes for physical process, this wave function ”collapses“ to represent one outcome. But in the many-worlds Interpretation, the wave function doesn’t collapse-rather, it branches, with one branch for each outcome. The branches evolve independently of each other, as separate worlds.
In this way of thinking, the formation of a black hole and its evaporation due to Hawking radiation lead to multiple branches of the wave function. An observer monitoring a black hole also splits into multiple observers, one in each branch.
The new work shows that from the perspective of an observer in a given branch, space-time behaves as described by general relativity and the black hole has no firewall.
But does that imply loss of information? No, says team member Aidan Chatwin-Davies, also of Caltech. That is because the principle of preservation of information applies to the global wave function and not to its individual branches, he says. Information is preserved across all branches of the global wave function, but not necessarily in any one branch. Given this case, a black hole that doesn’t lose information and yet has a smooth, uneventful event horizon without a fire wall isn’t a contradiction.
Yasunori Nomura at the University of California at Berkeleyy has independently arrived at some similar conclusions in his work. He agrees that the many-worlds approach resolves the paradox around information loss from black holes. “Many worlds should be taken seriously,” he says.
1. Which word in the article is similar in meaning to the underlined word in Paragraph 2?| A．Assumption (Paragraph 2) | B．Interpretation (Paragraph 4) |
| C．Evaporation (Paragraph 5) | D．Contradiction (Paragraph 7) |
| A．There is a firewall. | B．No observer will split. |
| C．No information is lost. | D．The wave function collapses. |
| A．introduce an independent scientist |
| B．support the many-worlds interpretation |
| C．question whether many worlds really exist |
| D．argue against the information loss from black holes |
| A．Rules of quantum mechanics. |
| B．A new understanding of the black hole. |
| C．Hawking’s interpretation of the black hole. |
| D．The development of the global wave function. |
2 . The temperature of the Sun is over 5,000 degrees Fahrenheit at the surface, but it rises to perhaps more than 16 million degrees at the center. The Sun is so much hotter than the Earth that matter can exist only as a gas, except at the core. In the core of the Sun, the pressures are so great against the gases that, despite the high temperature, there may be a small solid core. However, no one really knows, since the center of the Sun can never be directly observed.
Solar astronomers do know that the Sun is divided into five layers or zones. Starting at the outside and going down into the Sun, the zones are the corona, chromosphere, photosphere, convection zone, and finally the core. The first three zones are the regarded as the Sun’s atmosphere. But since the Sun has no solid surface, it is hard to tell where the atmosphere ends and the main body of the Sun begins.
The Sun’s outermost layer begins about 10,000 miles above the visible surface and can be seen during an eclipse (日食) such as the one in February 1979. Other time, the corona can be seen only when special instruments are used on cameras and telescopes to shut out the glare of the Sun’s rays.
The corona is a brilliant, pearly white, filmy light as bright as the full Moon. Its beautiful rays are a sensational sight during an eclipse. The corona’s rays flash out in a brilliant fan. The corona is thickest at the sun’s equator (赤道).
The corona rays are made up of gases streaming outward at tremendous speeds and reaching a temperature of more than 2 million degrees Fahrenheit. The rays of gas thin out as they reach the space around the planets. By the time the Sun’s corona rays reach the Earth, they are weak and invisible.
1. What is the second paragraph mainly about?| A．How the Sun evolved. |
| B．The structure of the Sun. |
| C．Why scientists study the Sun. |
| D．The distance of the Sun from the planets. |
| A．corona | B．chromosphere |
| C．photosphere | D．core |
| A．Paragraph 1. | B．Paragraph 2. |
| C．Paragraph 3. | D．Paragraph 4. |
3 . Earth is constantly being hit by space rocks. Several tons rain down on the planet each day in the form of dust. And larger strikes have created more visible features, including giant craters. But which of our planet’s extraterrestrial scars is the oldest?
Researchers reported on Tuesday in Nature Communications that they have pinpointed it, in Western Australia. It was caused by an impact more than 2.2 billion years ago. Interestingly, that timing roughly coincides with the end of one of our planet’s ice ages. An impact in the ice would have liberated an enormous amount of water vapor, the researchers suggest, perhaps enough to alter Earth’s climate.
The Yarrabubba impact structure, about a day’s drive northeast of Perth, isn’t much to look at today. The original crater, believed to have been roughly 40 miles in diameter, is long gone. That’s because the combined effects of wind, rain, glaciation and plate tectonics have washed several miles off the surface of the planet, effectively erasing the crater. The extent of erosion suggests that the impact structure is very, very old.
Existing clues yield “a pretty giant” age range of about a billion and a half years, said Timmons Erickson, a geochronologist at NASA Johnson Space Center in Houston and the study’s lead author. But Dr. Erickson knew that it was possible to do far better, by reading the tiny geological clocks that hide within rocks.
In 2014, Dr. Erickson collected roughly 200 pounds of granitic rocks from Yarrabubba. Back in the laboratory, based on a series of experiments, Dr. Erickson and his team calculated that the Yarrabubba impact occurred 2.229 billion years ago, with an uncertainty of 5 million years. The nextoldest impact structure, Vredefort Dome in South Africa, is over 200 million years younger.
The age of the Yarrabubba impact structure happens to line up with the end of an ice age, which makes for a compelling coincidence, Dr. Erickson said: “Would an impact event like Yarrabubba be enough to terminate a glacial time in Earth’s history?”
To help answer that question, the scientists modeled the effects of a roughly fourmilewide impact object striking ice sheets of different thicknesses. They found that more than 100 billion tons of water vapor would have been jetted into the upper atmosphere. Water vapor is an effective greenhouse gas; suddenly having much more of it in the atmosphere could have caused a warming that ended an ice age, the team suggested. That idea still needs to be tested with climate models, the researchers noted.
Christian Koeberl, a geochemist at the University of Vienna and not involved in the research, agreed. Inferring what might have happened to Earth’s ancient climate is “Where things get a lot more speculative,” he said.
1. Which of the following statements is TRUE?| A．Craters are formed when the Earth is struck by rocks. |
| B．The Yarrabubba impact is a very popular tourist attraction in Australia. |
| C．We cannot see the original crater of the Yarrabubba impact because of erosion. |
| D．The age of the crater can be accurately measured by the degree of the erosion. |
| A．Dr. Erickson has accurately measured Yarrabubba impact with his experiments. |
| B．A sudden release of much water vapor might have resulted in the ending of an ice age. |
| C．Sufficient evidence has proved that the Yarrabubba impact had ended an ice age. |
| D．Considering the uncertainty, Vredefort Dome might still hold the title of being the oldest. |
| A．He criticized the research for its inaccuracy. |
| B．He applauded the novelty of the researchers’ approach. |
| C．What happened to earth’ climate billions of years ago has come to light. |
| D．He acknowledged the difficulty involved in further investigations. |
| A．Earth’s Oldest Impact |
| B．How To Warm a Planet |
| C．Giant Craters On Earth |
| D．Earth’s Geological Erosion |
4 . Back in 2015 my colleague Adam Frank of the University of Rochester and I were having lunch near Columbia University's campus in New York City. As at Fermi's lunch 65 years earlier, the conversation was about the nature of spacefaring species. And inspired by Fermi's mental calculation, we were trying to craft an investigative strategy that made the fewest possible unsubstantiated assumptions and that could be somehow tested or constrained with real data. At the center of this exercise was the simple thought that waves of exploration or settlement could come and go across the galaxy, with humans happening to come into being in one of the lonely periods.
This idea relates to Hart's original fact: that there is no evidence here on Earth today of extraterrestrial（外星的）explorers. But it goes further by asking whether we can obtain meaningful limits on galactic（星系的）life by constraining the exact length of time over which Earth might have gone unvisited. Perhaps long, long ago extraterrestrial explorers came and went. A number of scientists have, over the years, discussed the possibility of looking for artifacts that might have been left behind after such visitations of our solar system. The necessary scope of a complete search is hard to predict, but the situation on Earth alone turns out to be a bit more manageable. In 2018 another of my colleagues, Gavin Schmidt of NASA's Goddard Institute for Space Studies, together with Adam Frank, produced a critical assessment of whether we could even tell if there had been an earlier industrial civilization on our planet.
As fantastic as it may seem, Schmidt and Frank argue—as do most planetary scientists—that it is actually very easy for time to erase essentially all signs of technological life on Earth. The only real evidence after a million or more years would boil down to isotopic or chemical stratigraphic anomalies—odd features such as synthetic molecules, plastics or radioactive fallout. Fossil remains and other paleontological markers are so rare that they might not tell us anything in this case.
Indeed, modern human urbanization covers only on order of about 1 percent of the planetary surface, providing a very small target area for any paleontologists（古生物学家）in the distant future. Schmidt and Frank also conclude that nobody has yet performed the necessary experiments to look exhaustively for such non-natural signatures on Earth. The bottom line is, if an industrial civilization on the scale of our own had existed a few million years ago, we might not know about it. That absolutely does not mean one existed; it indicates only that the possibility cannot be completely eliminated.
1. The word “unsubstantiated”（in paragraph 1）is closest in meaning to ________.| A．unconscious | B．unknown | C．unnatural | D．unsupported |
| A．No other species have ever settled on Earth except human beings. |
| B．Extraterrestrial explorers come and go at increasingly short intervals. |
| C．No spacefaring species have visited the Earth since humans emerged. |
| D．Extraterrestrial explorers once built an industrial civilization on Earth. |
| A．turn to isotopic or chemical stratigraphic anomalies |
| B．find as many signs of technological life as possible |
| C．unearth more fossil remains than we do now |
| D．leave behind synthetic things like plastics |
| A．Human urbanization should be expanded for the sake of research. |
| B．We cannot say for sure that no civilization existed before ours. |
| C．Non-natural signatures on Earth have been studied exhaustively. |
| D．An industrial civilization came into being a few million years ago. |
