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[Merged] Double slit experiment


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#1    khol

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Posted 24 November 2013 - 06:16 PM

to all you physicists out there
whats the final consensus on this experiment
i've read one member here mention how its not human observation that dictates wave or particle..more like having the right measuring instrument to perform such a delicate observation without interacting with it
well how more delicate can one get then our eye sight?
if the experiment is performed in an enclosed room with no measuring device we get interference
when its performed again with no measuring device and observed by us we get a particle..in other words we are the measuring device
now is it our physical observation causing the collapse or not?
if so how would we be interacting with it
your thoughts are appreciated! (:


#2    SilentHunter

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Posted 24 November 2013 - 09:01 PM

View Postkhol, on 24 November 2013 - 06:16 PM, said:

to all you physicists out there
whats the final consensus on this experiment
i've read one member here mention how its not human observation that dictates wave or particle..more like having the right measuring instrument to perform such a delicate observation without interacting with it
well how more delicate can one get then our eye sight?
if the experiment is performed in an enclosed room with no measuring device we get interference
when its performed again with no measuring device and observed by us we get a particle..in other words we are the measuring device
now is it our physical observation causing the collapse or not?
if so how would we be interacting with it
your thoughts are appreciated! (:

The human eye has cells in it that can sense a single photon - http://math.ucr.edu/...e_a_photon.html


#3    Still Waters

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Posted 24 November 2013 - 09:50 PM

Is this any help?

http://www.unexplain...howtopic=225231

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#4    khol

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Posted 25 November 2013 - 12:07 AM

View PostSilentHunter, on 24 November 2013 - 09:01 PM, said:

The human eye has cells in it that can sense a single photon - http://math.ucr.edu/...e_a_photon.html
fair enough but am I missing something?..sensing single photons doesn't explain how the observation collapses the wave function


#5    khol

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Posted 25 November 2013 - 12:10 AM

View PostStill Waters, on 24 November 2013 - 09:50 PM, said:

thanks but video would not open up
i've watched similar video's on this topic but am still perplexed how our interaction effects the outcome of the experiment


#6    Still Waters

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Posted 25 November 2013 - 11:29 AM

View Postkhol, on 25 November 2013 - 12:10 AM, said:

thanks but video would not open up
Oops, sorry I didn't notice. The video owner seems to have blocked it from public viewing since it was last posted.

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#7    Emma_Acid

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Posted 25 November 2013 - 11:49 AM

View Postkhol, on 24 November 2013 - 06:16 PM, said:

i've read one member here mention how its not human observation that dictates wave or particle..more like having the right measuring instrument to perform such a delicate observation without interacting with it

The thing about this sort of experiment, is that at the scale of sub atomic particles, any measurement interferes with the particle.


View Postkhol, on 24 November 2013 - 06:16 PM, said:

if the experiment is performed in an enclosed room with no measuring device we get interference


How do you measure something with no measuring device??


View Postkhol, on 24 November 2013 - 06:16 PM, said:


when its performed again with no measuring device and observed by us we get a particle..in other words we are the measuring device


You can't observe this sort of thing with no measuring device. You can't sit there and watch photons travelling across a room.


View Postkhol, on 24 November 2013 - 06:16 PM, said:


now is it our physical observation causing the collapse or not?

No. Because you can't measure it without the measuring equipment. So your point is invalid.

"Science is the least subjective form of deduction" ~ A. Mulder

#8    sepulchrave

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Posted 25 November 2013 - 12:45 PM

Emma_Acid is correct.

But...

View Postkhol, on 24 November 2013 - 06:16 PM, said:

to all you physicists out there
whats the final consensus on this experiment
Since you asked...

Every system exists in a single, specific state at all times. However this state does not need to be specific for any arbitrary basis set. When you perform a measurement, the very act of measuring the system corresponds to a sudden (and, in the limit of a perfect measurement, a discontinuously sudden) change in that system's environment such that the only stable state a system can be in is one of the basis states for that measurement.

Wave/particle duality is the most famous example of this. When a system is in empty space, the natural state for this system to be in is a plane wave. The true, singular state of the system could be expressed as a superposition of plane waves, but as long as the system is in empty space this superposition will be unstable - random fluctuations will eventually collapse the system to a singular plane wave state.

If you attempt to measure the linear momentum of a singular plane wave state you will get a specific answer 100% of the time. If you attempt to measure the linear momentum of a superposition of plane wave states, the very act of measuring will collapse the system to a singular plane wave state (i.e. only one of the plane waves involved in the superposition will be ``selected''). Subsequent measurements of momentum will reveal the exact same linear momentum 100% of the time.

Every wave state can also be expressed as a superposition of particle states. This is just a mathematical trick - it is irrelevant until we attempt to measure the position of the system.

How do we measure the position of something? We set up a confined box and then check if the system is inside it (the smaller the box, the more precise our measurement). But we can't do this without changing the environment - in other words, we no longer have empty space. It is this change, this abrupt attempt to confine the system, that causes the system to collapse into a position state (or a superposition of smaller number of position states, if our position measurement was somewhat vague).

Once we remove the box, and return to empty space, the system will start to ``spread out'' and gradually evolve back into a plane wave state.

There is a lot of fuss made over wave/particle duality because ordinary people can grasp the meaning of ``waves'' and ``particles''. But waves and particles are just two of an infinite number of possible ``basis sets'' for  a system.

Two other classic quantum mechanical systems are the quantum harmonic oscillator and the orbitals of a hydrogen atom. Neither of these two sets of solutions are plane waves or particles, and in fact we could perfectly legitimately describe every plane wave as a superposition of quantum harmonic oscillator states, or every hydrogen atom orbitals.

The ``natural'' state of a system is an eigenfunction of the system's Hamiltonian. If the quantity you want to measure is an eigenvalue of these states, then your measurement will not affect the system (i.e. a momentum measurement on a system in empty space, a position measurement on a system in an infinitely deep and infinitesimally narrow potential well, an ``excitation number'' measurement on a quantum harmonic oscillator, or an angular momentum measurement on a hydrogen atom orbital).


#9    SilentHunter

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Posted 25 November 2013 - 02:36 PM

View PostEmma_Acid, on 25 November 2013 - 11:49 AM, said:

The thing about this sort of experiment, is that at the scale of sub atomic particles, any measurement interferes with the particle.

How do you measure something with no measuring device??

You can't observe this sort of thing with no measuring device. You can't sit there and watch photons travelling across a room.

No. Because you can't measure it without the measuring equipment. So your point is invalid.

That barrier was overcome quite early in the development of quantum mechanics. By entangling two atoms you no longer needed to disturb the orginal particle as you could measure its partner. In fact it led to the discovery of quantum teleportation.


#10    SilentHunter

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Posted 25 November 2013 - 02:41 PM

View Postkhol, on 25 November 2013 - 12:07 AM, said:

fair enough but am I missing something?..sensing single photons doesn't explain how the observation collapses the wave function

The wavefunction is an probability equation. Its impossible to gain information on a probability and leave it intact. The information gaining collapses it leaving one of its outcomes. Hence, measuring brings into existance a particle from a wave by discarding the rest of the wave.

The wave and probability equation are the same thing.


#11    Celestae

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Posted 25 November 2013 - 02:43 PM

I'm no Physicist not by a long stretch, but a couple of years back I read a book Called "The End of Mr Y" by Scarlett Thomas. it was really interesting... one of those fiction books that's written to incorporate a non fiction theory.

Anyway, it was really interesteding and did actually touch quite heavily on  Quantum Physics, and its possible connection to Spirituality, they talked about this very same  experiment where particles behave differently under observation,as if they do exactly what the observer expects them to do.

I'm sure it is much more complex than that, but as I said, I'm no Physicist.


#12    Leonardo

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Posted 25 November 2013 - 02:56 PM

View PostSilentHunter, on 25 November 2013 - 02:36 PM, said:

That barrier was overcome quite early in the development of quantum mechanics. By entangling two atoms you no longer needed to disturb the orginal particle as you could measure its partner. In fact it led to the discovery of quantum teleportation.

This is not entirely true. Entanglement causes the entangled states to assume a singular value - in essence you cause two states (each object having one) to become one state. Measurement of this state on any one 'entangled' object necessarily affects that state, and because the other object exhibits the same state it is 'disturbed'.

This effect is Einstein's "spooky action at a distance". Because the entangled objects share the same state (and value of that state), interference of one object causes the same effect on the other simultaneously - no matter the distance between them.

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#13    khol

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Posted 25 November 2013 - 03:02 PM

View PostEmma_Acid, on 25 November 2013 - 11:49 AM, said:

The thing about this sort of experiment, is that at the scale of sub atomic particles, any measurement interferes with the particle.


[/size]

How do you measure something with no measuring device??




You can't observe this sort of thing with no measuring device. You can't sit there and watch photons travelling across a room.


[size=4]

No. Because you can't measure it without the measuring equipment. So your point is invalid.
i guess what i was referring to is alowing the experiment to run without observation and then after time "pull the plug"
then going into the room to see the result..should be interference..no?
if we stay in the room and observe we get a particle pattern


#14    SilentHunter

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Posted 25 November 2013 - 03:10 PM

View PostLeonardo, on 25 November 2013 - 02:56 PM, said:

This is not entirely true. Entanglement causes the entangled states to assume a singular value - in essence you cause two states (each object having one) to become one state. Measurement of this state on any one 'entangled' object necessarily affects that state, and because the other object exhibits the same state it is 'disturbed'.

This effect is Einstein's "spooky action at a distance". Because the entangled objects share the same state (and value of that state), interference of one object causes the same effect on the other simultaneously - no matter the distance between them.

Yes, you got me on that one. The measuring device does make the same changes in both the observed and unobserved atom if they were entangled.


#15    khol

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Posted 25 November 2013 - 03:18 PM

View Postsepulchrave, on 25 November 2013 - 12:45 PM, said:

Emma_Acid is correct.

But...

Since you asked...

Every system exists in a single, specific state at all times. However this state does not need to be specific for any arbitrary basis set. When you perform a measurement, the very act of measuring the system corresponds to a sudden (and, in the limit of a perfect measurement, a discontinuously sudden) change in that system's environment such that the only stable state a system can be in is one of the basis states for that measurement.

Wave/particle duality is the most famous example of this. When a system is in empty space, the natural state for this system to be in is a plane wave. The true, singular state of the system could be expressed as a superposition of plane waves, but as long as the system is in empty space this superposition will be unstable - random fluctuations will eventually collapse the system to a singular plane wave state.

If you attempt to measure the linear momentum of a singular plane wave state you will get a specific answer 100% of the time. If you attempt to measure the linear momentum of a superposition of plane wave states, the very act of measuring will collapse the system to a singular plane wave state (i.e. only one of the plane waves involved in the superposition will be ``selected''). Subsequent measurements of momentum will reveal the exact same linear momentum 100% of the time.

Every wave state can also be expressed as a superposition of particle states. This is just a mathematical trick - it is irrelevant until we attempt to measure the position of the system.

How do we measure the position of something? We set up a confined box and then check if the system is inside it (the smaller the box, the more precise our measurement). But we can't do this without changing the environment - in other words, we no longer have empty space. It is this change, this abrupt attempt to confine the system, that causes the system to collapse into a position state (or a superposition of smaller number of position states, if our position measurement was somewhat vague).

Once we remove the box, and return to empty space, the system will start to ``spread out'' and gradually evolve back into a plane wave state.

There is a lot of fuss made over wave/particle duality because ordinary people can grasp the meaning of ``waves'' and ``particles''. But waves and particles are just two of an infinite number of possible ``basis sets'' for  a system.

Two other classic quantum mechanical systems are the quantum harmonic oscillator and the orbitals of a hydrogen atom. Neither of these two sets of solutions are plane waves or particles, and in fact we could perfectly legitimately describe every plane wave as a superposition of quantum harmonic oscillator states, or every hydrogen atom orbitals.

The ``natural'' state of a system is an eigenfunction of the system's Hamiltonian. If the quantity you want to measure is an eigenvalue of these states, then your measurement will not affect the system (i.e. a momentum measurement on a system in empty space, a position measurement on a system in an infinitely deep and infinitesimally narrow potential well, an ``excitation number'' measurement on a quantum harmonic oscillator, or an angular momentum measurement on a hydrogen atom orbital).
facinating stuff tho i still struggle with the concepts! what got me going on this is this idea of biocentrism which being a layman in these areas i find kinda ridiculous...as great and fantastic that would be it puts humans on a pedastal again...we have this urge or impulse to find meaning and justify our existance..i think people gravitate to experiments like the double slit to prove there ideas without fully understanding the experiment...i will go back to my premise on everything..US =  highly evoved ape...done   thanks!





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