Schrödinger's Rabbits The Many Worlds of Quantum (2004) / Chapter Skim
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3 Collapse by Inference
3 Collapse by Inference
Pages 27-39
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From page 27... ...
If the partides are arge things like bowling balls or oven-ready Chickens, you can imagine all sorts of simple gadgets that cou d do the job—a lever that the object pushes as it passes, a beam of infrared light that it interrupts, a weightdetecting platform, and so on. If the objects are small things like electrons, Me tedmology becomes a bit more subtLe, but there is still a range of choices: various different electrical and magnetic effects can be used.
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From page 28... ...
This is disconcerting, but there is still a way to ding to Me dassical picture. Any kind of detector—even of Me most passive sort—has some effect on its surroundings, even when it is not detecting anyffiing.' lust possibly, even Me most innocuous detector somehow disrupts any guide waves passing nearby, whidh explains why a detector beside one of Me slits is sufficient to destroy the whole of the interference pattern.
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From page 29... ...
The guide wave behaves in Me fashion we have come to expect —for example, it will generate an interference pattern if we make it pass through a pair of slits. But when one of Me electrons eventually gets measured—for example, by hitting a detector we have placed somewhere in We dhamber—something very remarkable happens.
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From page 30... ...
Imagine a blind scientist investigating We properties of waves using a ripple tank, a shallow tank of water that is agitated to create patterns of waves on Me surface. (These devices still exist, and were the best way to study wave patterns until modern computer simulations overtook them.
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From page 31... ...
But if this instant collapse did not happen, a terrible hole would open up in Me fabric of quantum medhanics. By making simultaneous measurements on each of a widely separated particle pair, you could gain more knowledge about them than Heisenberg's uncertainty principle allows.
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From page 32... ...
Indeed, turning Einstein's original thought experiment into a doable laboratory test turned out to be immensely hard. Quantum limitations apart, tiny things like individual atoms and photons are tridky things to measure in the hot, noisy environment of the Earffi's surface.
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From page 33... ...
At intermediate angles Me probability that the photon will pass throuf h unscathed is given by cosZfz~, where ~ is Me ang e between the photon polarization and Me direction of the filter's axis. Whatever happens to Me photon, Me interaction with Me filter resets Me angle of its arrow, so that single bit of information—transmitted or rejected, which we can record as the number O or I—is all Me information about its polarization that we can ever actually read from an individua photon.
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From page 34... ...
To set up this useful device, imagine a spaceship orbiting slightLy earthward of the midpoint between Earth and Mars, which we will assume are currently 200 million miles apart so that light takes approximately 20 minutes to travel between them. The spaceship has an apparatus for emitting polarization-correlated photon pairs, which reach Earth and Mars resp ectively about 10 minutes later, but with We Earth one arriving just before its Martian twin.
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From page 35... ...
There doesn't have to be any kind of link or conspiracy between Me photons to produce Me correlation. If each photon independentdy for ows Me rule "If I meet a filter at the same angle as my polarization vector, I get transmitted with 100 percent probability; if I meet a filter at 45 degrees to my vector, I get transmitted with 50 percent probabi ity; if I meet a filter at 90 degrees to my vector, I get transmitted with 0
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From page 36... ...
If Me two lottery cards of Me conjuring tridk are replaced by polarizing filters that are dialed to Me positions of the spots my partner and I pink, then however Me photons are internally programmed—by whatever rules the lottery card color gets filled in—it should be impossible to Choose angles 6 degrees apart and yet get the same result 99 percent of the time, as happens in Me conjuring show and also with
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From page 37... ...
Collapse by Inference /37 TABLE 3-2 Second Attempt at Faster-Than-Light Signaling Our Filters Are Your Photon is at Relatve My Photon Transmitted with Overall Result Angle is Probability % at This Angle 0 Transmitted 100 50/50 Reflected 0 6 Transmitted 99 So/50 Reflected 1 12 Transmitted 96 50/50 Reflected 4 1 B Transmitted 90 50/50 Reflected 10 24 Transmitted B3 50/50 Reflected 17 30 Transmitted 75 50/50 Reflected 25 36 Transmitted 65 50/50 Reflected 35 42 Transmitted 55 50/50 Reflected 45 45 Transmitted 50 50/50 Reflected 50 4B Transmitted 45 50/50 Reflected 55 54 Transmitted 35 50/50 Reflected 65 60 Transmitted 25 50/50 Reflected 75 66 Transmitted 17 50/50 Reflected B3 72 Transmitted 10 50/50 Reflected 90 7B Transmitted 4 50/50 Reflected 96 B4 Transmitted 1 50/50 Reflected 99 90 Transmitted 0 50/50 Reflected 100 Probabilities are rounded to the nearest percent.
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From page 38... ...
We have encountered two mysteries in this chapter. The first was that observing one slit of a two-slit apparatus can seemingly change the behavior of partides that go through the other slit, an arbitrary distance away.
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From page 39... ...
One sudh hypothesis is ffiis: "The acquisition of knowledge about a system by an observer, even inferential knowledge, can somehow Change the behavior of that system—or at any rate what Me observer subsequentLy sees—in a way unprecedented in dassical physics, where We observer plays no special role:'
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