清华科技英语阅读2
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Page 38
1. He argued that even if the universe…
Page 40
Quantum effects
Random fluctuations Spatial variation: cause inflation to end at different times in different regions Gives birth to stars and galaxies
Page 42
Coins analogy
There is no way to judge which coin is more likely when the number of coins is infinite. There is no way to judge which kind of island is more likely in an eternally inflating universe.
Originally from Schrodinger (08-141935)
When two systems ... enter into temporary physical interaction ... and when after a time of mutual influence the systems separate again, then they can no longer be described in the same way as before, viz. by endowing each of them with a representative of its own. I would not call that one but rather the characteristic trait of quantum mechanics, the one that enforces its entire departure from classical lines of thought. By the interaction the two representatives [the quantum states] have become entangled.
Entanglement
In classical physics, electrons spin around a fixed axes of rotation. To measure the a particle spin, you need to choose a direction and the outcome depends on whether the direction you choose aligns to the particle’s axis. If you measure both electrons horizontally, you see both spinning in opposite direction; if you measure them vertically, you detect no spin at all for either. In quantum physics, the particles have no fixed axes of rotation, they will always spin in opposite ways. If you measure one particle horizontally and the other vertically, you will still detect some spin for each. This might be where entanglement fits in.
The Cover of Nature in October 2006 (vol 2 no. 10)
Entanglement (缠绕)
Entanglement binds together individual particles into an indivisible whole. A classical system is always divisible; whatever its collective properties arise from components with their own certain properties. But an entangled system cannot be broken down in this way. Even when the entangled particles are far apart, they still behave as a single entity, leading to what Einstein called “spooky action a distance”, and went to his grave denying.
Entanglement (缠绕)
The connections between ordinary objects are fleeting and superficial. Two atoms may collide and separate, never to meet again. Others can stick together by virtue of the chemical bonds they form, until the day that bond is broken. But there is another type of connection that is far more powerful and romantic. Certain objects can become linked by a mysterious process called entanglement. Particles that become entangled are deeply connected regardless of the distance between them. If they become separated by the width of the Universe, the bond between them remains intact. These particles are so deeply linked that it’s as if they somehow share the same existence. Physicists do not yet fully understand the nature of entanglement but there is growing evidence that it is a fundamental property of the universe. Unfettered by the restrictions of space, entanglement may be the ghostly bedrock upon which reality is built.
Page 41
2. we could ignore bad inflation if it were incompatible with life. In that case, … 3. not only is bad inflation more likely than good inflation, but no inflation is more likely than either. 4. In 2008 Gary W. Gibbons of the university of Cambridge …
Group Discussion
Alternative explanations: p 42-43
1. special initial state hypothesis 2. weighing measure 3. volume measure 4. anthropic principle measure
Text 2, Topic 1
Living in a quantum world
Schodinger’s cat
Schrödinger's Cat: A cat, a flask of poison and a radioactive source are placed in a sealed box. If an internal monitor detects radioactivity, the flask is shattered, releasing the poison that kills the cat. The Copenhagen interpretation of quantum mechanics implies that after a while, the cat is simultaneously alive and dead. Yet, when we look in the box, we see the cat either alive or dead, not both alive and dead.
Selected English Readings for Science and Technology
Presented by Dr. James Zhang
Autumn 2012 - Spring 2013
பைடு நூலகம்
Text 1, topic one
Title: The inflation debate -- Detailed study of some difficulties
Experiments on entanglement
Quantum salt: Gabriel Aeppli (2003)
Larger system like atoms in the salt at low temperature can remain entangled when the information leakage is reduced or somehow counteracted. The 10 to the 20th power atoms of salt formed a huge entangled state to help the atoms in the salt to act in unison.
Decoherence (离散)
Decoherence can be viewed as the loss of information from a system into the environment, since every system is loosely coupled with the energetic state of its surroundings. Larger things seem to be more susceptible to decoherence than smaller ones, which justifies why physicists get away with regarding quantum mechanics as theory of the microworld. But in many cases, information leakage can be slowed or stopped, and then the quantum world reveals itself to use in all its glory. But the difficulty of preserving entanglement by slowing or stopping decoherence is a major challenge for us to seek to exploit these novel effect fro practical use, such as quantum computers.