Double Slit Experiment

[Qfwfq]

So if I understand correctly what you are saying.

 

The power of thought doesn't effect the experiment.

 

It is only effected by the physical actions of the experimenter.

 

I find this whole matter doesn't exist, unless you are looking at it, hard to believe.

Quite right Abstruce.

 

The particle exists, but it would be paradoxical to claim, under certain circumstances, that it has values of certain things, such as position, more than can be predicted by the quantum formalism.

 

There is already an old thread in Philosophy of Science, entitled Schrödinger's Cat.

[CraigD]

The easiest way that I understand the observation changing the path is using the Uncertainty Principle.

There is a electron, I want to know its velocity and position. To measure one of these you would shine a particular frequency of light on it and observe how it refects. To do this most accurately you would want a higher frequency because electrons are so small BUT the higher the frequency used the more energy in the photon and the more it will disrupt the path of the electron.

So the more accurately you try to measure the position the less accurately you know its velocity and vise versa.

This example, or one similar to it, is often given to illustrate H’s Uncertainty Principle. It is attractive, because it is purely a classical mechanical explanation – it requires no mention of a quantum wave function, considering the electron (in this example) to have a precise, though unknowable, position as a function of time, both before and after the measurements.

 

The Uncertainty Principle is really stating something more fundamental – no matter how one detects the position of anything. In its current, quantum mechanical form, it’s an exact description of decoherence - how a quantum wave function is modified by a measurement.

 

From The wikipedia article “Uncertainty principle” : The uncertainty principle in quantum mechanics is sometimes erroneously explained by claiming that the measurement of position necessarily disturbs a particle's momentum. Heisenberg himself may have initially offered explanations which suggested this view. That this disturbance does not describe the essence of the uncertainty principle in current theory has been demonstrated above.

 

So we who offer the “bumped by a photon” illustration are, if incorrect, in good company, as Heisenberg himself perhaps and many of his contemporaries certainly accepted it. The illustration hasn’t survived the rigor that it was subjected to as physicists continued to formalize quantum Physics.

 

The idea has “cross pollinated” into other disciplines, however, in a form where the illustration is accurate: in Statistics and the social sciences, the term “uncertainty principle” is sometimes used to describe the collection of survey data’s effect on the population being observed, such as when subjects lie when answering embarrassing survey questions in front of a live interviewer, or change their normal behavior when they’re aware of being observed. An negative consequence of the term’s use in the social sciences is that many people educated in them misunderstand its use in Quantum Physics, spreading and perpetuating acceptance of the “bumped by a photon” illustration as accurate.

[Abstruce]

Sanctus

 

I e-mailed Dr. Wolf who appeared in the movie "What the Bleep do we Know" just to see what response I would get.

 

Fred Alan Wolf Ph.D.

Have Brains / Will Travel

San Francisco

mailto:[email protected]

web page: http://www.fredalanwolf.com

 

> -----Original Message-----

> From: John Quest [mailto:[email protected]]

> Sent: Thursday, February 02, 2006 11:38 AM

> To: 'fred alan wolf'

> Subject: Dr. Quantum

>

>

>

Second Question

> > It is evident that Quantum Mechanics and Celestial Mechanics have a

> > great deal in common.

> > We know nature has a strange replitory cycle.

> > Do not Galaxies resemble molecules?

>

> Fred Alan Wolf : Not very much other than they are things

> bound together. Molecules bind due to quantum physics forces

> while galaxies bind due to gravitational forces. All

> molecules of any substance are exactly alike--not so for galaxies.

>

> John Quest: My Question was miss-stated. What I meant to ask was do not

> Galaxies resemble that of living cells?

 

Fred Alan Wolf : No.

 

> John Quest: What I am comparing the atom with would be a planetary

> system, I would compare a Solar system with a molecule, I

> would then compare a Galaxy with a cellular structure.

>

> John Quest: I know I sound nuts when I say this it goes against

> everything in accepted scientific theory.

 

Fred Alan Wolf :It is no nuts it just based on the thinking of 18th century physics.

 

> John Quest: I contend there is no difference between the strong nuclear

> force and gravity. They are two of the same thing on two

> different dimensions.

> Both have an attractive effect on neutrally charged mass.

 

Fred Alan Wolf : No that is wrong too. You can believe what you want but why postulate on matters that have been well-researched? Gravity electromagnetic, weak, and strong nuclear forces are very different. Otherwise we wouldn't be struggling so hard to find a unified field which to date has not be successful. I am sure all of the forces are the same at some level, but to prove that either by experiment or theory has not worked to date.

 

> John Quest: If this un orthodox approach were considered just for a

> second we might have a unification hypothesis.

 

Fred Alan Wolf : Do you ever read anything such as Brian Greene's book the elegant universe? Your thoughts are very naive.

 

John Quest: Yes I have and I study it every chance I get. Here is my favorite website on the subject.

 

http://www.pbs.org/wgbh/nova/elegant/program.html

 

> John Quest: "As far as the laws of mathematics refer to reality, they are

> not certain, as far as they are certain, they do not refer to

> reality." AE

>

> John Quest: I feel in my hart the answer is a simple one and we as humans

> are trying our best to complicate the issue.

 

Fred Alan Wolf : This sounds very trite and has been quoted I would guess a million times in the last year. Things are complex in that we fail to understand them. Even when we do understand them they often remain complex, meaning not simple. I think simplicity is important but complexity leads to a richer experience of life. Humans simply want to know what's going on?

 

> Dedicated to a life of Abstruse thinking, John Quest.

 

Fred Alan Wolf : Quest you may be but it doesn't appear that you are questing in the right direction.

 

*******************************************************

 

The only thing I am trying to bring to light here is now we have M theory in the Elegant Universe.

 

ARE NOT CELLS ENCLOSED BY MEMBRANES???? HELLO MC FLY!!!:cup:

 

Dr. Wolf seems to be a fundamentalist of his own discipline and I can understand how that happens.

 

I am not making any claims here I am only trying to initiate thought in new directions.

[CraigD]

So if I understand correctly what you are saying.

 

The power of thought doesn't effect the experiment.

 

It is only effected by the physical actions of the experimenter.

 

I find this whole matter doesn't exist, unless you are looking at it, hard to believe.

Quite right Abstruce.

 

The particle exists, but it would be paradoxical to claim, under certain circumstances, that it has values of certain things, such as position, more than can be predicted by the quantum formalism.

 

There is already an old thread in Philosophy of Science, entitled Schrödinger's Cat.

The role of a “conscious observer” in explaining the effect of measurement on a particle – decoherence or “collapsing the wave function” – has always been a troubling aspect of various interpretations of quantum physics. Theorists have long sought and continue to seek a formalism without the “ghost” of consciousness, and in the past couple decades, have made significant progress in showing decoherence to be a statistical phenomenon related to the number of interacting particles in a system.

 

If a conscious observer were truly the “trigger” for decoherence, building quantum computers would be much easier than it is proving (see ”problems with quantum computing” in the wikipedia article “quantum computing”) Even with all the engineering measure taken to isolate the computing elements – qbits – of these devices from interaction with other particles, it's difficult maintaining coherence for more than a fraction of a second, even though isolating these elements from human awareness is trivially easy (closed windows and blindfolds would do the job).

 

This makes sense when you consider that a “conscious observer” such as a human being is, in a quantum mechanical sense, merely a large ensemble of interacting particles. Other ensembles – a large rock, for instance – are as capable of causing decoherence as a human observer is.

[Abstruce]

Quite right Abstruce.

 

The particle exists, but it would be paradoxical to claim, under certain circumstances, that it has values of certain things, such as position, more than can be predicted by the quantum formalism.

 

There is already an old thread in Philosophy of Science, entitled Schrödinger's Cat.

 

Yes, I understand the cat in the box paradox.

 

Philosophy is sometimes better left to Religion.

 

The imagination is priceless and it paves the way to new scientific theory, yet if we concentrate too hard on the un-knowns it seems we have a tendency to complicate the issue, until it is difficult to comprehend, then we call it in some cases scientific theory.

[Qfwfq]

Even with all the engineering measure taken to isolate the computing elements – qbits – of these devices from interaction with other particles, it difficult maintaining coherence for more than a fraction of a second, even though isolating these elements from human awareness if trivially easy (closed windows and blindfolds would do the job).

That's exactly why the cat is either dead or alive.

 

There's no need for the fabled conscious observer. The observer is anything interacting that can distinguish one eigenvalue from another. It in turn can be observed by something else etc.... The whole cat will never be in a coherent state, even less in a coherent superposition of two coherent states.

[InfiniteNow]

So if I understand correctly what you are saying.

 

The power of thought doesn't effect the experiment.

 

It is only effected by the physical actions of the experimenter.

What is the power of thought? I never really said that it didn't have an effect, especially since we still struggle to adequately define thought/mind/consciousness/being/etceteras, however, I can see how that might have been implied. I was (as I now understand mistakenly) advocating the whole "push it off course" idea. However, of course the experiment is not ONLY effected by the actions/thoughts of the experimenter, but that very well may have an influence.

 

 

To me, the Uncertainty Principle is intuitively beautiful. You want to measure momentum? Well, that means it's moving and doesn't occupy just one position... it is travelling along a path, not stationary on one point. You want to measure position? Well, that means it's not moving so much and sort of remains where it is. This is way too simplex to adequately describe the full implications, but that's what I see.

 

Going into the quantum side, and wave function concept, Shroedinger's cat is a wonderful thought experiment. Is the cat dead, is the cat alive? :cup:

 

It's both until you measure it, until you open the box. The thing is, it's also ALL OTHER possibilities that we haven't yet listed... inside the box (until we actually open it) is also a dog, a giraffe, a five-course meal, Claudia Schiffer, a time machine, my great great great great grandmother reading Hitchhiker's guide to the galaxy...

It's uncertain until measured, which collapses the wave function of all those other possibilities. That's where the observer has impact... it's only from the observers reference that the other possibilities went away. To anyone else not looking in the box, it still might contain Claudia Schiffer.

[Jay-qu]

The matter is discussed quite well in the Feynman lectures.

My cousin got the entire written works of the lectures - its quite a read! I'm going to borrow them as he finishes reading them

[Abstruce]

Going into the quantum side, and wave function concept, Shroedinger's cat is a wonderful thought experiment. Is the cat dead, is the cat alive? :cup:

 

It's both until you measure it, until you open the box. The thing is, it's also ALL OTHER possibilities that we haven't yet listed... inside the box (until we actually open it) is also a dog, a giraffe, a five-course meal, Claudia Schiffer, a time machine, my great great great great grandmother reading Hitchhiker's guide to the galaxy...

It's uncertain until measured, which collapses the wave function of all those other possibilities. That's where the observer has impact... it's only from the observers reference that the other possibilities went away. To anyone else not looking in the box, it still might contain Claudia Schiffer.

 

The point of view that this thought experiment most clearly refutes is that the laws of physics are different for experiments than for other interactions.

 

An autopsy would (if a thought experiment could actually kill a cat) show a time of death that would be before the opening of the box.

 

The experiment contains an improper equation, the probability factor is not 50% it is a variable based on time.

 

F=S/D/T (F factor, S current state divided by D rate of decay,

divided by time)

 

So if you put a live cat in the box and open as soon as you shut the box then the cat is Alive. The longer you leave the Cat in the box the higher the probability rate that the cat will be dead.

 

This experiment must be based on a probability variable and not an act of human thought.:)

[InfiniteNow]

The point of view that this thought experiment most clearly refutes is that the laws of physics are different for experiments than for other interactions.

 

An autopsy would (if a thought experiment could actually kill a cat) show a time of death that would be before the opening of the box.

 

The experiment contains an improper equation, the probability factor is not 50% it is a variable based on time.

 

F=S/D/T (F factor, S current state divided by D rate of decay,

divided by time)

 

So if you put a live cat in the box and open as soon as you shut the box then the cat is Alive. The longer you leave the Cat in the box the higher the probability rate that the cat will be dead.

 

This experiment must be based on a probability variable and not an act of human thought.:cup:

Abstruce,

Time of death and rate of decay has nothing to do with the heart of the Schroedinger cat in the box idea. You can't measure that either until the box has been opened.

 

The issue (as far as I understand it) is "what's the state of the cat, given a poison set to break open at a given point, before you open the box?" Did the poison kill the cat? did the cat survive the poison? did the poison even break open as it was supposed to? The cat occupies this super-position of states until the box is open, and is all possibilities at once.

[Abstruce]

Abstruce,

Time of death and rate of decay has nothing to do with the heart of the Schroedinger cat in the box idea. You can't measure that either until the box has been opened. .

 

InfiniteNow, I'm sorry, I don't understand.

 

A cat is placed in a sealed box. Attached to the box is an apparatus containing a radioactive nucleus and a canister of poison gas.

 

If you know what the radioactive nucleus is before you put it in the box then you probably are going to know it's stability.

 

The experiment is set up so that there is a 50% chance of the nucleus decaying in one hour. If the nucleus decays, it will emit a particle that triggers the apparatus, which opens the canister and kills the cat.

 

Ok so if you have a 50% chance that the cat will be dead in one hour, 100% the cat will be dead in two hours therfor the answer is quantum.

 

According to quantum mechanics, the unobserved nucleus is described as a superposition (meaning it exists partly as each simultaneously) of "decayed nucleus" and "undecayed nucleus". However, when the box is opened the experimenter sees only a "decayed nucleus/dead cat" or an "undecayed nucleus/living cat."

 

If this farie tail were true, the cat would die as soon as you close the lid. I do not see this as a problem of super position. I see it as a problem of caos. It is true that you do not know if the Cat is dead or alive from the time you close the lid, you do know the longer you wait to open the lid the greater the probability the cat will be dead. Terefore time is a variable in the experiment.

 

If you put a die in a box and shake it, you will not know what number faces up untill you open the box. You can make an educated guess at a number between 1 and 6 with an accracy of 1/6.

 

The issue (as far as I understand it) is "what's the state of the cat, given a poison set to break open at a given point, before you open the box?" Did the poison kill the cat? did the cat survive the poison? did the poison even break open as it was supposed to? The cat occupies this super-position of states until the box is open, and is all possibilities at once.

 

All you have to do to solve the cat problem is use a glass box. :Waldo:

[CraigD]

Ok so if you have a 50% chance that the cat will be dead in one hour, 100% the cat will be dead in two hours therfor the answer is quantum.

A small quibble about probability – The probability that a single atom of an isotope with a half life of 1 hour will have decayed after 1 hour is 50%. The probability that it will have decayed after 2 hours is 75%. The probability that it will have decayed after n hours is 1-.5^n, (eg: after 24 hours, 1-.5^24 = about 99.999994%). Even after millions of years, there is a miniscule, but non-zero, probability that it will not have decayed.

According to quantum mechanics, the unobserved nucleus is described as a superposition (meaning it exists partly as each simultaneously) of "decayed nucleus" and "undecayed nucleus". However, when the box is opened the experimenter sees only a "decayed nucleus/dead cat" or an "undecayed nucleus/living cat."

 

If this farie tail were true …

Fantastic as it seems, what InfiniteNow describes agrees with the most widely accepted interpretation of Quantum Physics.

 

What all this counterintuitive quantum stuff – coherence, decoherance, superposition of states, collapse of superposition of states, etc. – with its confusing and seemingly supernatural allusions to consciousness and observers, is increasingly coming to be understood as having to do with limited information. In this page, hard SF writer Greg Egan attempts the daunting task of explaining this. Though I’m not in Egan’s league when it comes to popularizing Physics (being more of a pop Physics consumer than producer), this thread provides an irresistible opportunity to attempt it, so here goes:

 

Quantum coherence exists only when all of the information in system is available. This is illustrated by both dual slit experiments and the Schrödinger’s Cat thought experiment.

• Dual slit
  • If both slits are unobstructed, the target photographic film contains all the information about the photons that have interacted with it. The system exhibits coherence, so even if no more than a single photon is permitted in it at a time, an interference pattern forms on the film.
    
  • If one slit is obstructed, half of information about the photons that pass through the unobstructed slit to interact with the film (or fail to pass through the obstructed slit, and do not), so no interference pattern forms.
    

  [*]Schrödinger’s Cat

  • If the contents of the box containing cat, 50%-chance-of-killing-the-cat-machine, and whatever else is in it (a comfy pillow, perhaps, some catnip, or even a few more cats or a human being or two) are in complete isolation from the rest of the universe – that is, no fundamental particle of them have interacted and become entangled with any particles outside of the box – then all of the information about the box is inside of the box. The system exhibits coherence, and the cat, machine, etc. are in a superposition of all possible states.
    
  • When the box is opened, its particles interact with those outside the box. Information about the system is lost. Coherence is lost. The superposition collapses into one of the possible states – dead cat, live cat, live cat sleeping, live cat playing with catnip, etc.
    

[Qfwfq]

No need to use so much bold Abstruce, please don't get upset if you disagree with someone.

 

The matter is certainly not a fairy tale for objects that can be in a coherent state, experiments have even been done on many-atom objects but not quite the size of a cat. In the macroscopic world quantum formalism applies but decoherence rapidly rushes in to dominate.

 

Suppose the autopsy determines the cat as being dead since ten minutes after closing the box, which remained closed for an hour. If it weren't for decoherence one could say that's one of the many component states the cat was in. To be precise, in fact, the states "dead" and "live" would each be categories of states. When the box has been opened but the autopsy hasn't yet been performed, the cat would still be in a superposition of many different states of the "dead" category. Again, that's if it weren't for decoherence.

[Qfwfq]

Quantum coherence exists only when all of the information in system is available.

I'd say there's a difference between a state not being coherent and a state not being prepared.

 

A small and simple system can easily be in a coherent state, even if you or I don't know which it's in. Suppose you know which, while I don't even know that you're performing the experiment. Is the state coherent or is it not?

[Qfwfq]

:Waldo:

 

I left out a very fundamental thing! AAMOF it's something that's all too easy to let slip and not many are aware of in the first place.

 

The deep dire secret is that even a prepared state is a superposition. Even if you know the eigenvalues of a complete set of compatible observables, there are other observables of which the object can't be in an eigenstate. In essence, that's what Heisenberg's principle means.

[EWright]

If you change the frequency of photons being fired through the slits, does the interference pattern change as well?

[Qfwfq]

Of course!

 

For each point of the screen consider the difference of path from each slit in terms of wavelength, this gives you the phase difference.