Double Slit Experiment - radioactive particles

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Hello,
Quick question:
Will radioactive particles give interference pattern if there is no measuring device?
 
174
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By measuring device do you mean the screen the particles are projected on? How would you see the interference pattern if there is no measuring device?
 
29
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No, I mean the device, whose task is to determine through which slit the radioactive particle pass by.
The point is that in case of the radioactive particles measuring device can be passive, which means that measurement does not affect the measured object.
 
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f95toli

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There is no such thing as a "passive" measurement device. So, if you can determine "which path" information there won't be an interference pattern.
 
29
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You mean that there is no a passive measurement devices, because an act of measurement collapses a wave function?
So, if there is a measuring device and information about a particle passing by slit isn't store anywhere, then will an interference pattern occur?
 
26
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He's trying to say that the very act of measurement collapses the wave function, so ANY measuring device would interfere with the results.
 
29
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Thanks for your reply.
I'm trying to make some sens out of this but it is pretty hard, because there is so many contradiction.
Let me ask you question in order to clarify issue regarding the measurement problem:
By saying "act of measurement" you mean:
1. the measurement device;
2. reviving an information.


________
Sorry for my bad english
 
53
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Before I chip in, I should warn you that I'm not a proper physicist or anything, so I could very well be wrong. If I am I am sure someone will correct me though.

With regards to the measurement problem, the way I've made sense of it is that before a particle interacts in a given situation there are certain properties that you can't know exactly, such as position. Not just because it's too hard to measure them, but because the particle itself doesn't even have an exact position or whatever. In order to make a measurement you force the particle to make some sort of interaction, and so it has to make up its mind what it's doing. So it's not just because humans want to look at it, the particle has been forced to make a choice because of an interaction, and so the wave function for all of this fuzzy information has to collapse. Before the interaction, the particle has made no commitment about what is going to happen to it, so to speak. So any time a particle has to "make up its mind" the wave function collapses, and when you measure something, you force the particle to make up its mind. A particle will choose what information it has when it interacts, and a measurement device makes particles interact so that we can see this information. The measurements have been made whether we look at them or not, so storing the measurements without looking would be no different to making the measurements and looking - either way the particles in question have interacted with the measuring device. It's the interaction that collapses the wave function, not us looking at it.

Like I said, I'm pretty sure this is all right, but I am still very much on the learning curve myself, so anyone please correct me if I am wrong.
 
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29
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Thanks, it sounds ok to me, but still I am a little confused (btw, I'm not a physicist too).
At the beginning of this topic I have mentioned about the radioactive particles. What makes radioactive particles different from electrons? You don't need to send photons or other particles to get information about it's position because radioactive particle is already sending them.
What also bothers me in your description is why structure of the measuring device is so much different from the structure of the plate with slits that it collapses the wave function to one particular state? I guess that leads us again to the problem of measurement and what exactly it is.
 
442
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Hello,
Quick question:
Will radioactive particles give interference pattern if there is no measuring device?
It's quite simple, if we have made a measurement or we know which slit the particle/photon has gone through then we will have a 'wave pattern' ahead of us onto the screen.On the other hand add another slit and repeat the experiment,this time you'll notice the appearance of interference pattern,all due to the uncertainty of which slit it has gone through because we did not define a position to the wave function.The larger the particle is the less noticeable are the 'pattern/fringe differences'.

Regards,
ibysaiyan
 
442
0
Before I chip in, I should warn you that I'm not a proper physicist or anything, so I could very well be wrong. If I am I am sure someone will correct me though.

With regards to the measurement problem, the way I've made sense of it is that before a particle interacts in a given situation there are certain properties that you can't know exactly, such as position. Not just because it's too hard to measure them, but because the particle itself doesn't even have an exact position or whatever. In order to make a measurement you force the particle to make some sort of interaction, and so it has to make up its mind what it's doing. So it's not just because humans want to look at it, the particle has been forced to make a choice because of an interaction, and so the wave function for all of this fuzzy information has to collapse. Before the interaction, the particle has made no commitment about what is going to happen to it, so to speak. So any time a particle has to "make up its mind" the wave function collapses, and when you measure something, you force the particle to make up its mind. A particle will choose what information it has when it interacts, and a measurement device makes particles interact so that we can see this information. The measurements have been made whether we look at them or not, so storing the measurements without looking would be no different to making the measurements and looking - either way the particles in question have interacted with the measuring device. It's the interaction that collapses the wave function, not us looking at it.

Like I said, I'm pretty sure this is all right, but I am still very much on the learning curve myself, so anyone please correct me if I am wrong.
Actually in QM the particles are said to have any of the probable outcome i.e are in any of the quantized state until the wave-function is collapsed,which is of course by measuring. (I maybe wrong)
 

DrChinese

Science Advisor
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Thanks, it sounds ok to me, but still I am a little confused (btw, I'm not a physicist too).
At the beginning of this topic I have mentioned about the radioactive particles. What makes radioactive particles different from electrons? You don't need to send photons or other particles to get information about it's position because radioactive particle is already sending them.
What also bothers me in your description is why structure of the measuring device is so much different from the structure of the plate with slits that it collapses the wave function to one particular state? I guess that leads us again to the problem of measurement and what exactly it is.
Forget radioactive particles, they have nothing to do with the issue. Most quantum particles will exhibit interference through a suitable sized double slit. So let's use photons (particles of light) as an example.

Assume you send photons through a double slit apparatus with polarizering filters behind each of the slits. If the polarizers are aligned parallel, you DO get an interference pattern. If the polarizers are aligned anti-parallel (crossed), you do NOT get an interference pattern. When they are crossed, you have the ability to determine which slit so the pattern disappears.

If you consider this result, you will see that the presence of the polarizer itself does NOT cause the pattern to appear or not. It is the ability to obtain knowledge of the path by the relative orientation of the 2 polarizers. So I would say it is incorrect to say that the measurement apparatus disturbs the results, since it is the same apparatus either way.
 
911
1
Well put Dr Chinese.

The perpendicular Vs parallel --> seems to suggest that interference pattern happens only between photons (or to be more accurate.....between the Maxwell light wave) that are polarized in the same direction?

Maybe a perpendicular polarizer introduces some sort of phase difference?
 
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