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After a Short Delay, Quantum Mechanics Becomes Even Weirder!

The newest revelations in the scientific world -- post articles, discussions and your own ideas.

Postby SmokinJoe » Wed Apr 20, 2011 6:18 pm

According to quantum mechanics, light can be either a graceful rippling wave or a hail of bulletlike particles, depending on how you look at it. Now, an experiment shows that an observer can make the choice retroactively, after light has entered a measuring apparatus. The result shows that reality is truly in the eye of the beholder.

A single dollop of light, or photon, must be described by a flowing quantum wave that gives the probability of finding it at any particular place and time. At the same time, the photon acts a bit like an indivisible bullet: When observed with a particle detector, it produces a distinct signal, like a pebble pinging off a car door. And things get weirder. The quantum wave can split in two and recombine, like ripples flowing around a stump in a pond, to create striking "interference" effects that determine which way the recombined wave flows. On the other hand, it's simply impossible to split a photon at a fork in the road. If there is no way to eventually put the pieces back together, the photon acts like a particle and goes one way or the other.

Even weirder still, the choice to allow the waves to recombine or not can be made even after the photon passes the fork where it should have split--or not. Famed physicist John Archibald Wheeler realized that nearly 30 years ago and dreamed up an experiment to prove the point. Now Jean-François Roch of the Ecole Normale Supérieure de Cachan in France and colleagues have performed the experiment. The researchers shot photons one by one at a half-silvered mirror, or "beam splitter," to cleave the quantum wave describing each photon. After traveling different distances, the two halves sloshed back together at a second beam splitter 50 meters away, which could recombine them. The experimenters could randomly switch this second beam splitter on and off electronically well after the photon had passed the first one.

If the second splitter was on, interference between the two pieces directed the recombined wave of probability toward one or the other of two detectors, depending on the difference in the path lengths. If the second beam splitter was turned off so the waves couldn't recombine, then the photon took one path or the other with 50-50 probability, and equal numbers of photons reached detectors. The results, reported this week in Science, prove that the photon does not decide whether to behave like a particle or a wave when it hits the first beam splitter, Roch says. Rather, the experimenter decides only later, when he decides whether to put in the second beam splitter. In a sense, at that moment, he chooses his reality.

Others had tried to perform Wheeler's experiment but had lacked the single-photon source and other elements to really do it right, says Arthur Zajonc, an experimenter at Amherst College in Massachusetts. "This is the experiment you wanted to do, but it was too hard," he says. The experiment will likely become a classic cited in textbooks, Zajonc says: "It's going to be seen as a kind of a landmark.



http://news.sciencemag.org/sciencenow/2 ... l?etoc&eaf
Dawkins thinks belief in God is an excuse to evade thinking in the scientific world. Sadly, he is ignorant to the list of christian scientists who have contributed & founded many of the sciences he himself believes in. How ironic.
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Postby DIss0n80r » Wed Apr 20, 2011 6:45 pm

Interesting. Maybe the wavelike nature indicates an essential unity while the discrete particle nature are instantiations within the flow of time.
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Postby chrisv25 » Wed Apr 20, 2011 9:47 pm

this experiment has been done previously. If you read between the lines, it's not the nature of the particle that changes; it is our mathematical interpretation of the wave that can change. A photon is a particle, whose position in time can be described with the mathematics of maxwell's wave function.

They are simply saying that we don't know what happens between the emitter and the detector, and any attempts to describe it with our current mathematical techniques fail or produce bizarre results. There are several ways around it that are used in supercomputers, ways of viewing the mathematics in new and different ways, that remove the most of the uncertainty. The light particles do however behave this way for real and you can not understand it without the language of math, they are however only particles and never waves.

I tried to explain that the best i could in layman's terms, i do not however know if i am clear.
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Postby bionic » Wed Apr 20, 2011 11:27 pm

spiraling particles, maybe..like when you toss a football? (or the way snowlfakes fall in spirals because of the spin of the earth)

like particles riding on waves?

I am WAY overreaching the bounds of my brain's humble abilities, here.
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Postby chrisv25 » Thu Apr 21, 2011 7:34 am

bionic wrote:spiraling particles, maybe..like when you toss a football? (or the way snowlfakes fall in spirals because of the spin of the earth)

like particles riding on waves?

I am WAY overreaching the bounds of my brain's humble abilities, here.
:D


it would be more correct to think of a single particle as occupying all the paths from the light source to the target at once, that's why we can treat it as a wave with math (and why lenses bend light); it is a field of probability.

though this interpretation has flaws too.
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Postby DIss0n80r » Thu Apr 21, 2011 9:00 am

chrisv25 wrote:this experiment has been done previously. If you read between the lines, it's not the nature of the particle that changes; it is our mathematical interpretation of the wave that can change. A photon is a particle, whose position in time can be described with the mathematics of maxwell's wave function.

They are simply saying that we don't know what happens between the emitter and the detector, and any attempts to describe it with our current mathematical techniques fail or produce bizarre results. There are several ways around it that are used in supercomputers, ways of viewing the mathematics in new and different ways, that remove the most of the uncertainty. The light particles do however behave this way for real and you can not understand it without the language of math, they are however only particles and never waves.

I tried to explain that the best i could in layman's terms, i do not however know if i am clear.


No, you're doing pretty good. :thumbup:
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Postby DIss0n80r » Thu Apr 21, 2011 9:01 am

chrisv25 wrote:
bionic wrote:spiraling particles, maybe..like when you toss a football? (or the way snowlfakes fall in spirals because of the spin of the earth)

like particles riding on waves?

I am WAY overreaching the bounds of my brain's humble abilities, here.
:D


it would be more correct to think of a single particle as occupying all the paths from the light source to the target at once, that's why we can treat it as a wave with math (and why lenses bend light); it is a field of probability.

though this interpretation has flaws too.


You're referring to superposition?
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Postby chrisv25 » Thu Apr 21, 2011 10:03 am

DIss0n80r wrote:You're referring to superposition?


most definitely.
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Postby SmokinJoe » Thu Apr 21, 2011 4:12 pm

Would Shrodinger still think it's preposterous? :P :shock: :lol:
Dawkins thinks belief in God is an excuse to evade thinking in the scientific world. Sadly, he is ignorant to the list of christian scientists who have contributed & founded many of the sciences he himself believes in. How ironic.
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Postby chrisv25 » Sat Apr 23, 2011 5:50 am

SmokinJoe wrote:Would Shrodinger still think it's preposterous? :P :shock: :lol:


yeah he really wanted wave mechanics to win, but the discovery of fission pretty much nailed the last nail in the coffin of Schroedinger and friends.

and I think Einstein would have had a royal screaming hissy fit about Frank Wilczek using m=e/c^2 to hypothesize that mass is the result of energy at the quark level.
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