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nouveau_riche
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how is observer defined in context to quantum physics?
does it have to b a conscious observer?
does it have to b a conscious observer?
Polyrhythmic said:It doesn't have to be a conscious observer. Contrary to what many popular myths suggest, consciousness is not part of quantum mechanics. What we mean by observation is anything that is mathematically equivalent to applying an operator on a quantum mechanical state. For example, applying the position operator and getting its eigenvalue is equal to measuring a particle's position. .
nouveau_riche said:what makes something(event) as mathematically equivalent to applying an operator?
I like Serena said:The example that I like is the experiment where electrons are shot through a double-slit, impacting on a photographic plate behind it.
In the dark, you'll get an interference pattern.
In the light (with a short wavelength), you'll get a particle impact pattern.
In light with a long wavelength (in which an observer would not be able to distinguish through which slit the electron goes), you'll get an interference pattern again.
This is without anyone actually watching!
It's enough that someone might be able to see through which slit the electron goes. Weird huh!
Polyrhythmic said:That's one of the axioms of quantum mechanics, measurements correspond to eigenvalues of hermitian operators. I guess you should read an introductory text to the subject in order to understand what is going on.
nouveau_riche said:not much...I like Serena said:The example that I like is the experiment where electrons are shot through a double-slit, impacting on a photographic plate behind it.
In the dark, you'll get an interference pattern.
In the light (with a short wavelength), you'll get a particle impact pattern.
In light with a long wavelength (in which an observer would not be able to distinguish through which slit the electron goes), you'll get an interference pattern again.
This is without anyone actually watching!
It's enough that someone might be able to see through which slit the electron goes. Weird huh!
if an observer is not interested in measuring the position of photon then even the short wavelength will cause an interference...weird?
I like Serena said:There!
Dr. Quantum thinks it's weird!
(Just found this on facebook! )
nouveau_riche said:suppose the intereference experiment is set up again,the light used is of very high frequency(so that it's wavelength could match with that of slits) ,now the distance at which interefence pattern is seen is at max distant from slit(max in sense that pattern can b seen nicely).,now one of the observer set up apparatus to see the intereference pattern while the other one set up an apparutus to measure position of photon(to see from which slit it passes through)
question is-will the interference pattern b lost or both will see their portion of reality ?
I like Serena said:Hmm, afaik the measurement making it observable which slit the electron passes through, collapses the electron's wave function, so regardless of the other observer, the interference pattern would be lost.
Do you have information that this is otherwise?
I like Serena said:Hmm, afaik the measurement making it observable which slit the electron passes through, collapses the electron's wave function, so regardless of the other observer, the interference pattern would be lost.
nouveau_riche said:out of many answers that i have received for the above experiment many say that it's impossible to set up an apparatus like that ,one observer have to eliminate the other
like refer
https://www.physicsforums.com/showthread.php?t=434366&page=2
I like Serena said:I've read the thread you mentioned and I have to say I have trouble understanding what is said exactly. As yet I see no reason to change my previous statement.
Here's a section of the wikipedia article that supports my statement:
http://en.wikipedia.org/wiki/Double-slit_experiment#Relational_interpretation
nouveau_riche said:the important point to b highlighted here is that both observer aren't aware of the act of measurement made by the other one,so if the pattern get lost ,the other observer get's to know the history of interaction of that particle
I like Serena said:Hmm, afaik the measurement making it observable which slit the electron passes through, collapses the electron's wave function, so regardless of the other observer, the interference pattern would be lost.
Do you have information that this is otherwise?
nouveau_riche said:i would prefer the paragraph in that wiki link that could justify ur point.
I like Serena said:Feynman also quotes Heisenberg who said:
"It is impossible to design an apparatus to determine which hole the electron passes through, that will not at the same time disturb the electrons enough to destroy the interference pattern."
DrChinese said:That *may* be true for electrons, but definitely is not for photons as described above. That is definitely NOT why the interference is destroyed, it is the obtaining of which path information that causes that to occur.
I like Serena said:Please elaborate? I don't understand.
DrChinese said:Take a double slit setup using light. Place one polarizer over the left slit at angle L, another over the right slit at angle R. When L-R=0 (parallel), there IS interference. When L-R=90 degrees (crossed), there is NO interference. Obviously, the presence or absence of a polarizer does not change anything unless which slit information is gained. That becomes progressively more feasible as L-R goes from 0 to 90 degrees. In other words: you *could* know which path (100% certain) by checking the polarization of the detected photon when L-R=90 (crossed), even if you didn't.
In other words, the particle goes through the same apparatus whether the polarizers are parallel or crossed. So clearly the apparatus itself is not altering the particles as they go through more in one case than in another. And yet when they are parallel, no which path information is gained and interference is produced. And vice versa when crossed.
Conceptually, you could do the same thing with electrons (using S-G method) although I doubt it is practical. I am not trying to dispute Heisenberg (or Feynman) but the analogy is not correct regardless. Early quantum theorists used it to help describe how things work, but with the advent of entanglement experiments it is clear that the apparatus definitely is not the source of this effect. It is the overall context (configuration) of the setup and the Heisenberg Uncertainty Principle at work. Which is to say I have no idea what is happening.
IllyaKuryakin said:Maybe it has to do with the transfer of information, or change in entropy, between the particle and it's environment.
DrChinese said:Take a double slit setup using light. Place one polarizer over the left slit at angle L, another over the right slit at angle R. When L-R=0 (parallel), there IS interference. When L-R=90 degrees (crossed), there is NO interference. Obviously, the presence or absence of a polarizer does not change anything unless which slit information is gained. That becomes progressively more feasible as L-R goes from 0 to 90 degrees. In other words: you *could* know which path (100% certain) by checking the polarization of the detected photon when L-R=90 (crossed), even if you didn't.
In other words, the particle goes through the same apparatus whether the polarizers are parallel or crossed. So clearly the apparatus itself is not altering the particles as they go through more in one case than in another. And yet when they are parallel, no which path information is gained and interference is produced. And vice versa when crossed.
Conceptually, you could do the same thing with electrons (using S-G method) although I doubt it is practical. I am not trying to dispute Heisenberg (or Feynman) but the analogy is not correct regardless. Early quantum theorists used it to help describe how things work, but with the advent of entanglement experiments it is clear that the apparatus definitely is not the source of this effect. It is the overall context (configuration) of the setup and the Heisenberg Uncertainty Principle at work. Which is to say I have no idea what is happening.
nouveau_riche said:suppose the intereference experiment is set up again,the light used is of very high frequency(so that it's wavelength could match with that of slits) ,now the distance at which interefence pattern is seen is at max distant from slit(max in sense that pattern can b seen nicely).,now one of the observer set up apparatus to see the intereference pattern while the other one set up an apparutus to measure position of photon(to see from which slit it passes through)
question is-will the interference pattern b lost or both will see their portion of reality ?
nouveau_riche said:i still don't have a satisfying answer for this experiment...the only thing i am asking is the reason if this experiment is not possible?
I like Serena said:Oh sorry, I guess I was not clear enough before. :shy:
The experiment is possible.
The answer is that both observers would always see the same reality.
I take it both observers have their own light source that they use to see the electron?
The actual observers would not play a role - only their light source would.
The first light source would try to illuminate the electron in such a way that it becomes observable through which slit the electron goes.
The second light source would illuminate the electron near the screen, but would not show through which slit the electron went.
It is the first light source that determines everything!
If it's on and bright enough it will destroy the interference pattern.
The second light will show that result.
If the first light is off, there will be an interference pattern.
The second light will show that result.
Does this satisfy you?
nouveau_riche said:i am quite not happy with ur assumption,use a single light source
I like Serena said:Well, I'm quite not happy that you are quite not happy.
With a single light source the results will be the same.
Cheers!
nouveau_riche said:i think both will going to see the same thing:no interference pattern
I like Serena said:Yep! :)
Any light source that makes it observable through which slit an electron goes, destroys the interference pattern (for all observers).
nouveau_riche said:but there's another experiment i got which i think could give real weirdness...\
"consider the same interference experiment,the interference pattern produced is used to illuminate the next source in series,which then produces a new interference pattern,this gets cascaded say 10 times and the final interference pattern is obtained on the wall.
now ,the observer, observing the final interference pattern is not known of the fact that there's another observer measuring the particle position in the first stage of interference,and viceversa
"will ur answer b the same(no interference pattern) or something else?
and if u think that the experiment is not possible,state the reason along
i think the result will still b the same as it was with previous experimentI like Serena said:This experiment can be done just fine, although you seem to be mixing electrons with photons.
But that's not really a problem, it doesn't really matter which of them you use.
Cascading through a number of interference patterns will reduce the chance that a photon/electron will reveal which slit an electron/photon goes through.
I believe that the result will be a mixture of an interference pattern and a destroyed interference pattern (for all observers).
In quantum physics, an observer is defined as any entity that can measure or observe a physical system. This can include a human observer, a measuring instrument, or even a particle interacting with the system.
The presence of an observer is crucial in quantum physics as it collapses the wave function of a system, determining its state and properties. Without an observer, a system can exist in multiple states simultaneously, known as superposition.
No, an observer in quantum physics does not have to be conscious. It can be any entity capable of interacting with a system and obtaining information about its state. However, the act of observation does require some form of measurement or detection.
Yes, the presence of an observer can affect the outcome of a quantum experiment. This is because the act of observation collapses the wave function and determines the state of the system. The observer's measurement can also introduce uncertainty and change the outcome of the experiment.
The observer effect and the uncertainty principle are closely related in quantum physics. The act of observation introduces uncertainty into the measurement, and the more precisely we measure one property of a system, the less precisely we can measure another. This is known as the Heisenberg uncertainty principle.