公共英语五级考试冲刺7

>>公共英语考试试题：公共英语五级考试冲刺7

>>公共英语考试辅导课程

第2题：Reading Comprehension(子母填空):

Quantum World

If successful scientific theories can be thought of as cures for stubborn problems, quantum physics was the wonder drug of the 20th century. It successfully explained phenomena such as radioactivity and antimatter, and no other theory can match its description of how light and particles behave on small scales.

But it can also be mind-bending. Quantum objects can exist in multiple states and places at the same time, requiring a mastery of statistics to describe them. Rife with uncertainty and riddled with paradoxes, the theory has been criticised for casting doubt on the notion of an objective reality -- a concept many physicists, including Albert Einstein, have found hard to swallow.

Today, scientists are grappling with these philosophical conundrums, trying to harness quantum's bizarre properties to advance technology, and struggling to weave quantum physics and general relativity into a seamless theory of quantum gravity.

The birth of an idea

Quantum theory began to take shape in the early 20th century, when classical ideas failed to explain some observations. Previous theories allowed atoms to vibrate at any frequency, leading to incorrect predictions that they could radiate infinite amounts of energy -- a problem known as the ultraviolet catastrophe.

In 1900, Max Planck solved this problem by assuming atoms can vibrate only at specific, or quantised, frequencies. Then, in 1905, Einstein cracked the mystery of the photoelectric effect, whereby light falling on metal releases electrons of specific energies. The existing theory of light as waves failed to explain the effect, but Einstein provided a neat solution by suggesting light came in discrete packages of energy called photons -- a brain wave that won him the Nobel Prize for Physics in 1921.

Quantum weirdness

In fact, light's chameleon -- like ability to behave as either a particle or a wave, depending on the experimental setup, has long stymied scientists. Danish physicist Niels Bohr explained this wave-particle duality by doing away with the concept of a reality separate from one's observations. In his "Copenhagen interpretation", Bohr argued that the very act of measurement affects what we observe.

One controversial experiment recently challenged this either/or scenario of light by apparently detecting evidence of both wave- and particle-like behaviour simultaneously. The work suggests there may be no such thing as photons light appears quantised only because of the way it interacts with matter.

Other interpretations of quantum theory of which there are at least half a dozen deal with the measurement problem by suggesting even more far-fetched concepts than .a universe dependent on measurement. The popular many worlds interpretation suggests quantum objects display several behaviours because they inhabit an infinite number of parallel universes. Uncertainty rules

For about 70 years, this wave-particle duality was explained by another unsettling tenet of quantum theory the Heisenberg uncertainty principle. Formulated by Werner Heisenberg in 1927 and recently made more precise, the theory puts an upper limit on knowledge. It says one can never know both the position and momentum of a quantum object measuring one invariably changes the other.

Bohr defeated Einstein in a series of thought experiments in the 1920s and 1930s using this principle, but more recent work suggests the underlying cause of the duality seen in experiments is a phenomenon called entanglement.

Entanglement is the idea that in the quantum world, objects are not independent if they have interacted with each other or come into being through the same process. They become linked, or entangled, such that changing one invariably affects the other, no matter how far apart they are something Einstein called "spooky action at a distance".

This may be involved in superconductivity and may even explain why objects have mass. It also holds promise for "teleporting" particles across vast distance assuming everyone agrees on a reference frame. The first teleportation of a quantum state occurred in 1998, and scientists have been gradually entangling more and more particles, different kinds of particles, and large particles.

Secure networks

Entanglement may also provide a nearly uncrackable method of communication. Quantum cryptographers can send "keys" to decode encrypted information using quantum particles. Any attempt to intercept the particles will disturb their quantum state -- an interference that could then be detected.

In April 2004, Austrian financial institutions performed the first money transfer encrypted by quantum keys, and in June, the first encrypted computer network with more than two nodes was set up across 10 kilometres in Cambridge, Massachusetts, US.

But keeping quantum particles entangled is a tricky business. Researchers are working on how to maximise the particles' signal and distance travelled. Using a sensitive photon detector, researchers in the UK recently sent encrypted photons down the length of a 100-kilometre fibre optic cable. Researchers in the US devised a scheme to entangle successive clouds of atoms in the hopes of one day making a quantum link between the US cities of Washington, DC, and New York.

Lightning-fast computers

Quantum computers are another long-term goal. Because quantum particles can exist in multiple states at the same time, they could be used to carry out many calculations at once, factoring a 300-digit number in just seconds compared to the years required by conventional computers.

But to maintain their multi-state nature, particles must remain isolated long enough to carry out the calculations -- a very challenging condition. Nonetheless, some progress has been made in this area.

1小题>

Quantum physics ______.

A provided medical cures for persisting problems

B first appeared as a wonder drug in the 20th century

C described some phenomena no other previous theories had ever explored

D gave the best description of some behaviors of light and particles so far

2小题>

Quantum physics is a concept that ______.

A is very difficult to understand

B demands abundant statistics to master

C describes the objective nature of the real world

D has been rejected by many scientists

3小题>

Scientists are ______.

A frustrated by the philosophical problems related to quantum physics

B working to make use of quantum in developing technology

C trying to identify quantum's properties

D struggling to clarify how quantum physics and general relativity could form a new theory

4小题>

According to theories before quantum theory, atomic energy could lead to ______.

5小题>

The contribution Einstein has made is that he discovered the ______, and thus solved the problem with new ideas about light

6小题>

Niel Bohr believed that there is a close correlation between the ______ and ______.

7小题>

Niel Bohr developed his theory by using the ______.

8小题>

Recent studies suggest that quantum objects are ______, hence the duality in experiments.

9小题>

In what field(s) has entanglement been applied in practice?

10小题>

What can be done to improve the implication of entanglement-based communication? Name one.

11小题>

In what aspect could quantum computers surpass conventional computers?

第3题：Use of English:

Scientists Say Plants Helped Ants Evolve

Ants evolved far earlier than (1) believed, as far back as 140 million to 168 million years ago -- and they have plants to (2) for their diversity, U.S. researchers reported on Thursday.

Researchers at Harvard University used a genetic clock to reconstruct the history of ants, and found that the ant family (3) arose more than 40 million years (4) than previously thought. The family did not diversify into different genera and species (5) flowering plants came (6) the scene, they said.

The study sheds light on one of the (7) important and numerous animals, which includes hundreds of (8) species.

"We (9) that ant diversification took off (10) 100 million years ago, along with the rise of flowering plants, the angiosperms," Naomi Pierce, a professor of biology who (11) the study, said in a statement.

"These (12) provided ants with new habitats (13) in the forest canopy and in the more complex leaf litter on the forest floor, and the herbivorous insects that evolved alongside flowering plants provided food for (14) ."

Writing in Friday's (15) of the journal Science, the researchers said they reconstructed the ant family tree (16) DNA sequencing of six genes from 139 ant genera, encompassing 19 of 20 ant subfamilies around the world.

Such "molecular clocks" are (17) used, alongside fossil and other evidence, to (18) how old species are. They work on the basis that DNA mutates at a steady and calculable (19) .

"Ants are a dominant feature of nearly all terrestrial ecosystems, and yet we know surprisingly little about their evolutionary history: the major groupings of ants, how they are (20) to each other, and when and how they arose," said graduate student Corrie Moreau.

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