[Merged] Double slit experiment

[khol]

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! (:

[SilentHunter]

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/home/baez/physics/Quantum/see_a_photon.html

[Still Waters]

Is this any help?

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

[khol]

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

[khol]

Is this any help?

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

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

[Still Waters]

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.

[Emma_Acid]

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.

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??

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.

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.

[sepulchrave]

Emma_Acid is correct.

But...

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).

[SilentHunter]

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.

[SilentHunter]

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.

[Celestae]

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.

[Leonardo]

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.

[khol]

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.

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

[SilentHunter]

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.

[khol]

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!

[Emma_Acid]

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

All due respect, I don't think you grasp the basics. It has nothing to do with anyone being "in the room" or not. That's not what interferes with the system.

[Professor Buzzkill]

All due respect, I don't think you grasp the basics. It has nothing to do with anyone being "in the room" or not. That's not what interferes with the system.

I understood his post perfectly. I think you are being deliberately obstructive.

If you run an unmonitored experiment, then view the results you get one outcome. You run the exact same experiment while monitoring, you get a different outcome, yet all you are doing is actually "viewing" the experiment in process.

The thing that gets me in the double slit experiment is; if you send a single particle through the slits, what is causing the interference pattern? Where is the interference coming from? Surely not the particle itself?

Quantum mechanics is magic in the sense that tiny particles "know" things. They "know" interference patterns despite there being nothing to interfere with. They "know" if they are being watched. Explain that.

"If you think you understand quantum mechanics, you don't understand quantum mechanics." Richard Feynman

Edited November 27, 2013 by Professor Buzzkill

[Professor Buzzkill]

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.

Talking of entanglement. Is it true that if you have two entangled particles, you could theoretically send one particle to the other side of the universe, destroy the remaining one on earth and instantaneously destroy the one 1,000,000 light years away?

If so then how is this information transferred across such distances at an instantaneous rate, let alone faster than light?

Edited November 27, 2013 by Professor Buzzkill

[Emma_Acid]

I understood his post perfectly. I think you are being deliberately obstructive.

Wasn't responding to you, and I'm not being deliberately anything.

If you run an unmonitored experiment, then view the results you get one outcome. You run the exact same experiment while monitoring, you get a different outcome, yet all you are doing is actually "viewing" the experiment in process.

I'm afraid you don't understand it. It is nothing to do with "viewing" the experiment. Its nothing to do with being "in the same room". It has nothing to do with consciousness, nothing to do watching anything happen. It has nothing to do with a person being there at all.

When you are dealing with fundamental particles, when you measure those particles, the very act of measuring them disturbs them. It's like measuring a car's velocity by stepping out into the middle of the road. Yes, you will learn its velocity, but you will also disrupt the car's journey. Unfortunately, with fundamental particles, you cannot just sit by the side of the road and watch them whiz by.

The thing that gets me in the double slit experiment is; if you send a single particle through the slits, what is causing the interference pattern? Where is the interference coming from? Surely not the particle itself?

As far as I understand it, its the probability of the particle going through multiple slits that causes the pattern. But I'm not an expert (despite years of reading on the subject) and am ready to be corrected.

The thing that gets me in the double slit experiment is; if you send a single particle Quantum mechanics is magic in the sense that tiny particles "know" things. They "know" interference patterns despite there being nothing to interfere with. They "know" if they are being watched. Explain that.

They don't "know" things, and quantum physics is not "magic". You can't invent your own faulty definitions of something and then ask someone else to explain them.

"If you think you understand quantum mechanics, you don't understand quantum mechanics." Richard Feynman

Ah, the 'quote fallback', a logical fallacy in itself. Yes, QM is difficult to understand. No, that does not mean the door is wide open for any crack hypothesis you want to throw at it.

[Rlyeh]

The thing that gets me in the double slit experiment is; if you send a single particle through the slits, what is causing the interference pattern? Where is the interference coming from? Surely not the particle itself?

Quantum mechanics is magic in the sense that tiny particles "know" things. They "know" interference patterns despite there being nothing to interfere with. They "know" if they are being watched. Explain that.

Kind of like a ball knows when you've kicked it?

[Rlyeh]

Talking of entanglement. Is it true that if you have two entangled particles, you could theoretically send one particle to the other side of the universe, destroy the remaining one on earth and instantaneously destroy the one 1,000,000 light years away?

No, but you have destroyed the entanglement.

http://van.physics.illinois.edu/qa/listing.php?id=24514

[spacecowboy342]

I understood his post perfectly. I think you are being deliberately obstructive.

If you run an unmonitored experiment, then view the results you get one outcome. You run the exact same experiment while monitoring, you get a different outcome, yet all you are doing is actually "viewing" the experiment in process.

The thing that gets me in the double slit experiment is; if you send a single particle through the slits, what is causing the interference pattern? Where is the interference coming from? Surely not the particle itself?

Quantum mechanics is magic in the sense that tiny particles "know" things. They "know" interference patterns despite there being nothing to interfere with. They "know" if they are being watched. Explain that.

"If you think you understand quantum mechanics, you don't understand quantum mechanics." Richard Feynman

The particles don't know they are being watched. If you set up a wave detector you find waves. If you set up a particle detector you find particles. This is regardless if there is a human in the room or not. The uncertainty principle says the more you know about either position or momentum the less you know about the other. So detecting a particle (finding position) means you lose the wave.

http://Abyss.uoregon.edu/~js/21st_century_science/lectures/lec13.html

[Professor Buzzkill]

Kind of like a ball knows when you've kicked it?

Not at all. Unless the ball went through both goal posts and kicked itself.

[khol]

there are aspects to this experiment i believe that are eluding to a deeper reality

i suppose this is obviously the case...sub atomic particles appear to be non-local which goes against the grain of our everyday perceptions

the "quantum eraser" experiment..a modification of the double slit.. shows that that there is no way classical physics can explain the outcome

when we can finally begin to understand whats going on here,its exciting to speculate what we will learn of the universe and our place in it

www.lifesci.sussex.ac.uk/home/John_Gribbin/quantum.htm#Solving

Edited November 28, 2013 by khol

[Rlyeh]

Not at all. Unless the ball went through both goal posts and kicked itself.

With a lot of help from you.