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Quantum Mechanics: How the penny dropped

tvellalott
Posts: 10,864
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1/31/2011 1:02:05 AM
Posted: 5 years ago
http://en.wikipedia.org...

It was this simple experiment which gave me a practical application for the one of the principles of quantum mechanics.

My boss explained to me that if a stream of photons (such as from a laser) is fired at the double slit paper, the light behind starts out as two lines and spreads off until the light is lost. In other words, the light behaves like a wave.

However, if some device of measurement or analysis is used on the photon beam, the light immediately behaves as a particle and the spread off disappears leaving only two lines.

In simple terms, by observing the photons you cause them to act differently.

Science is awesome.
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Atheism
Posts: 2,033
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1/31/2011 1:11:41 AM
Posted: 5 years ago
"It is a widespread misunderstanding that, when two slits are open but a detector is added to the experiment to determine which slit a photon has passed through, then the interference pattern no longer forms and the experimental apparatus yields two simple patterns, one from each slit, superposed without interference[12][citation needed]. Such a result would be obtained only if the results of two experiments were superposed in which either one or the other slit is closed."
I miss the old members.
belle
Posts: 4,113
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1/31/2011 1:12:51 AM
Posted: 5 years ago
yes, and no. you have to be specific about what you mean by "observe". looking at it ain't gonna cut it :P
evidently i only come to ddo to avoid doing homework...
tvellalott
Posts: 10,864
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1/31/2011 1:14:12 AM
Posted: 5 years ago
At 1/31/2011 1:12:51 AM, belle wrote:
yes, and no. you have to be specific about what you mean by "observe". looking at it ain't gonna cut it :P

You're right. I'm still sketchy about this. I've always kind of avoided it because I didn't understand. I suppose it would have to be a device that measures the photon distrubution between the two slits?
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Puck
Posts: 6,457
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1/31/2011 1:15:36 AM
Posted: 5 years ago
At 1/31/2011 1:14:12 AM, tvellalott wrote:
At 1/31/2011 1:12:51 AM, belle wrote:
yes, and no. you have to be specific about what you mean by "observe". looking at it ain't gonna cut it :P

You're right. I'm still sketchy about this. I've always kind of avoided it because I didn't understand. I suppose it would have to be a device that measures the photon distrubution between the two slits?

Yup. Observe means interact in QM.
CosmicAlfonzo
Posts: 5,955
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1/31/2011 1:24:34 AM
Posted: 5 years ago
Ah, quantum mechanics... The science of trying to find variables unaccounted for..

Everything is a wave, maaaaan. The colder you get, the more obvious this becomes. When everything is all hot, the vibrations are so fast that everything looks more and more like a particle.

We're all like, part of this one big note, dude.. and like, everything is just an overtone. Blow your mind, dawg foo ganstas

How do I know this? I fap to the rhythm of the big note. It is a very hard rhythm to fap to, but if you get it just right, you'll sh!t bricks.
Official "High Priest of Secular Affairs and Transient Distributor of Sonic Apple Seeds relating to the Reptilian Division of Paperwork Immoliation" of The FREEDO Bureaucracy, a DDO branch of the Erisian Front, a subdivision of the Discordian Back, a Limb of the Illuminatian Cosmic Utensil Corp
belle
Posts: 4,113
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1/31/2011 1:26:37 AM
Posted: 5 years ago
At 1/31/2011 1:14:12 AM, tvellalott wrote:
At 1/31/2011 1:12:51 AM, belle wrote:
yes, and no. you have to be specific about what you mean by "observe". looking at it ain't gonna cut it :P

You're right. I'm still sketchy about this. I've always kind of avoided it because I didn't understand. I suppose it would have to be a device that measures the photon distrubution between the two slits?

yeah, it would have to be some particle interacting with the photon in some way, us then noticing the change in that particle; the interference pattern is broken because the interaction with the particle changes the path of the photon
evidently i only come to ddo to avoid doing homework...
Caramel
Posts: 855
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1/31/2011 9:12:47 AM
Posted: 5 years ago
"However, if some device of measurement or analysis is used on the photon beam, the light immediately behaves as a particle and the spread off disappears leaving only two lines."

I don't believe this is true at all. The magnificent thing about the experiment isn't how light behaves both as particles and waves from different perspectives; it is that light will create an interference pattern on the screen even when only a single photon is emitted. There isn't anything for it to interfere with, yet it still creates the interference pattern - therefore the photon actually travels through each slit separately and simultaneously. I believe this has something to do with sum over histories but I can't be bothered to remember.
no comment
CosmicAlfonzo
Posts: 5,955
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1/31/2011 6:08:36 PM
Posted: 5 years ago
Particles are just overlapping waves. Everything is made up of waves.
Official "High Priest of Secular Affairs and Transient Distributor of Sonic Apple Seeds relating to the Reptilian Division of Paperwork Immoliation" of The FREEDO Bureaucracy, a DDO branch of the Erisian Front, a subdivision of the Discordian Back, a Limb of the Illuminatian Cosmic Utensil Corp
SuperRobotWars
Posts: 3,906
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1/31/2011 6:26:23 PM
Posted: 5 years ago
At 1/31/2011 6:08:36 PM, CosmicAlfonzo wrote:
Particles are just overlapping waves. Everything is made up of waves.

Does this imply that by changing the resonance and frequency of waves that make up matter we can move at light speed?
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: At 12/6/2011 2:21:41 PM, badger wrote:
: ugly people should beat beautiful people ugly. simple! you'd be killing two birds with the one stone... women like violent men and you're making yourself more attractive, relatively. i met a blonde dude who was prettier than me not so long ago. he's not so pretty now! ha!
:
: ...and well, he wasn't really prettier than me. he just had nice hair.
Cliff.Stamp
Posts: 2,169
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1/31/2011 8:35:12 PM
Posted: 5 years ago
At 1/31/2011 9:12:47 AM, Caramel wrote:

I don't believe this is true at all. The magnificent thing about the experiment isn't how light behaves both as particles and waves from different perspectives; it is that light will create an interference pattern on the screen even when only a single photon is emitted. There isn't anything for it to interfere with, yet it still creates the interference pattern - therefore the photon actually travels through each slit separately and simultaneously.

Exactly right, this is the infinite history model proposed by Feynman, the wave function only collapses (becomes a distinct observable) if it is measured and determined which slit the photon traveled through. At this point there is no infinite history probability as it is now determined where the photon traveled. This measurement therefore collapses the wave function from all the things it could have been and it simply acts as how it actually is and no interference pattern can be formed. This is related to the entanglement problem which convinced Einstein that Quantum Theory had to be wrong as it made no sense.
Illegalcombatant
Posts: 4,008
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4/12/2011 6:01:17 AM
Posted: 5 years ago
Pennies don't drop in QM, they disappear then reappear than show up in different locations at the same time then travel back in time.
"Seems like another attempt to insert God into areas our knowledge has yet to penetrate. You figure God would be bigger than the gaps of our ignorance." Drafterman 19/5/12