Double Slit Explanation Overdue!

AlfieGee

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Hey guys, this is my first post, go easy on me :)

Over the last century or so there does not seem to have been much progress made as to explaining the results of the double slit experiment.

References to this experiment are very common, as are the detailed explanations of what happens. However, there does not seem to be much discussion as to why this is the case.

When you think of how far we have progresses in various other scientific fields, it seems strange that, what is arguably, the most important experiment ever done still lacks any kind of accepted explanation?

OK, to the crunch.... I have recently read Thomas Campbell's My Big TOE (Theory of Everything) and somewhere in amongst the various parts which make up his TOE he provides an explanation as to the reason why the double slit experiment's results are as they are.

Now I dont want to get into all the other stuff in his book (not yet anyway) but this got me thinking that this is the first explanation that I have actually ever come across in all the quantum physics books I have read.

Even if we assume all of his Virtual Reality and OBE stuff is dubious to say the least, the idea that reality is computer like and efficiently only renders matter when required (ie when it is observed or measured) seems like a very interesting proposition?

Maybe Ive just been reading the wrong books :) but I would be interested what others thought about this .....?
 
AlfieGee said:
Hey guys, this is my first post, go easy on me :)

Over the last century or so there does not seem to have been much progress made as to explaining the results of the double slit experiment.

References to this experiment are very common, as are the detailed explanations of what happens. However, there does not seem to be much discussion as to why this is the case.

When you think of how far we have progresses in various other scientific fields, it seems strange that, what is arguably, the most important experiment ever done still lacks any kind of accepted explanation?
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I'm not sure why you would think it is the most important experiment ever done.

As to an explanation, it's not that it isn't being investigated, it's that scientists don't understand everything about light yet. The double-slit experiment shows that a quantum of light behaves both like a wave and like a particle, depending on what its interacting with.

In normal life, we deal with things more or less our own size. What this experiment suggests is that the things that things more or less our own size are made of do not behave like stuff our size behaves.
 
godless dave said:
I'm not sure why you would think it is the most important experiment ever done.

As to an explanation, it's not that it isn't being investigated, it's that scientists don't understand everything about light yet. The double-slit experiment shows that a quantum of light behaves both like a wave and like a particle, depending on what its interacting with.

In normal life, we deal with things more or less our own size. What this experiment suggests is that the things that things more or less our own size are made of do not behave like stuff our size behaves.
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Its not just about light. From electrons, all the way up to 114 atom molecules, have been used in double slit experiments.

In normal life, things more or less our own size are made from small things that behave like this?. Yes... that is why this is hugely important... I dont get your point?
 
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AlfieGee said:
Hey guys, this is my first post, go easy on me :)

Over the last century or so there does not seem to have been much progress made as to explaining the results of the double slit experiment.

References to this experiment are very common, as are the detailed explanations of what happens. However, there does not seem to be much discussion as to why this is the case.
Click to expand...

"Why" is very loaded word. Why do things fall? Why is the standard model the way it is?

Why an interference pattern is formed is quite well understood in the context of current physics. Why no interference pattern is formed when the particle is interfered with is also well understood in the context of current physics.

Are you asking why physics are the way they are?
 
Quantum physics books for the layman are not the same as quantum physics. The latter predicts the two slit results just fine. It's just not terribly expressible in words, but it would be a bit presumptuous to expect nature to be fully expressible in the language we use for our everyday lives.
 
RussDill said:
"Why" is very loaded word. Why do things fall? Why is the standard model the way it is?

Why an interference pattern is formed is quite well understood in the context of current physics. Why no interference pattern is formed when the particle is interfered with is also well understood in the context of current physics.

Are you asking why physics are the way they are?
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Yes, I suppose I am asking why physics is the way it is , in this particular instance, and seems to work differently, based on whether there is an observer or not.

Stating that the two possible outcomes are both independently describable is not the same as stating why the act of observing influences which of the outcomes actually happens?
 
One might advise ditching the Copenhagen Interpretation then.
 
edd said:
Quantum physics books for the layman are not the same as quantum physics. The latter predicts the two slit results just fine. It's just not terribly expressible in words, but it would be a bit presumptuous to expect nature to be fully expressible in the language we use for our everyday lives.
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So you are saying that "real" quantum physics is happy with the reason why this happens but it is not even remotely describable in words to non quantum physicists and that I just have to take their word for it?

A proportion of the books I have read are written by qualified physicists, yet they gave no indication that the double slit experiment was a done deal and fully explained (but only if you were a quantum physicists).
 
AlfieGee said:
So you are saying that "real" quantum physics is happy with the reason why this happens but it is not even remotely describable in words to non quantum physicists and that I just have to take their word for it?

A proportion of the books I have read are written by qualified physicists, yet they gave no indication that the double slit experiment was a done deal and fully explained (but only if you were a quantum physicists).
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Feynman's Sum Over Histories mathematical theory is one of the most successful Physics theories ever.

Just because it can't be put into language and conflicts with how our brains evolved to conceptualize the world, isn't the theory's fault!

http://www.internationalskeptics.com/forums/showthread.php?p=8941794

Many of our most successful scientific theories are like this!
 
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AlfieGee said:
Yes, I suppose I am asking why physics is the way it is , in this particular instance, and seems to work differently, based on whether there is an observer or not.
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It's not actually an observer that makes the difference. It's taking a measurement that makes the difference, and this effect occurs regardless of whether or not any observer exists to view the results.

But it's still called the observer effect because you can't observe which slit the particle passes through without some kind of measuring device to detect it, and if you don't plan to observe it, you wouldn't bother using a measuring device.
 
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What JDC said. It's describable in mathematics and you don't take the physicists' words for it - you take experimental results for it. If you want a better 'why' still then I would refer back to AlfieGee.

I'll accept happily that the interpretation of QM is not a done deal but that's a broader question with far more interesting bizarreness involved than the double slit alone, and the mathematics doesn't really care about it.
 
There is a very easy explanation for the double slit experiment.

See my sig.
 
This is an alternative interpretation I've been mulling over:

Measuring which path the particle takes does not destroy interference. Instead, it simply adds an essentially random phase to the particle, due to the fact that the wave function of the measurement apparatus it interacts with has a random phase. But interference patterns only emerge after repeated measurements. If you could prepare your measurement apparatus in an identical state each time, you would see an interference pattern. But since you can't, repeated measurements essentially average over all possible interference patterns for different phase shifts, and that gives the same result as no interference pattern.
 
edd said:
Quantum physics books for the layman are not the same as quantum physics. The latter predicts the two slit results just fine. It's just not terribly expressible in words, but it would be a bit presumptuous to expect nature to be fully expressible in the language we use for our everyday lives.
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I regard this rather like programming in BASIC.

If you could speak/write English, even if you had no computer programming experience, you could look at a simple BASIC subroutine and get a reasonable idea of what it was doing...

10 INPUT A
20 INPUT B
30 C = A*B
40 PRINT C
50 GOTO 10

However, if you now express it in terms of hexadecimal codes (assembly language)

5E FD A9 45 D3 B7.....

....it suddenly becomes unintelligible to anyone who doesn't know how to read it.

BASIC is the analogue of "quantum physics for the layman"

ASSEMBLY LANGUAGE is the analogue of quantum physics for the quantum physicist
 
I recommend Feynman's excellent and very straightforward (and also quite short) book for the layman QED.

Here's a link to the book on amazon.

Here's a link to the youtube video of the lectures that the book was based on:

http://www.youtube.com/watch?v=eLQ2atfqk2c


This comes as close as anything I've seen to give me some idea of "why" that the OP is asking about, though your mileage may vary.
 
Gord_in_Toronto said:
It's just the way the Universe is made. :con2:

Get over it. :w2:
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My alternative explanation is that the double slit experiment proves that the universe is broken. Sooner or later the cosmic repairman will fix it, and then we'll be able to figure out exactly where those particles are.
 
I'm struggling with the meaning of the word "explanation" in the question at hand.
A charged particle moving in a magnetic field experiences a force perpendicular both to the direction of the field and the motion of the particle using the right hand rule. So, one might say the "explanation" for the behavior of the particle is expressed in Maxwell's equations. If, however, we are asking why there is a force in the first place, why is it perpendicular, why the right hand rule? Then, I believe there is no answer or "explanation."
Similarly, the mathematics of QM "explains" the behavior of a particle in the double split experiment. Indeed, QM was developed, in part, to provide such an "explanation" and it does so remarkably well. However, if we are asking why the particle behaves as it does, we are back to asking something like why Maxwell's equations are what they are.
 
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Perpetual Student said:
I'm struggling with the meaning of the word "explanation" in the question at hand.
A charged particle moving in a magnetic field experiences a force perpendicular both to the direction of the field and the motion of the particle using the right hand rule. So, one might say the "explanation" for the behavior of the particle is expressed in Maxwell's equations. If, however, we are asking why there is a force in the first place, why is it perpendicular, why the right hand rule? Then, I believe there is no answer or "explanation."
Similarly, the mathematics of QM "explains" the behavior of a particle in the double split experiment. Indeed, QM was developed, in part, to provide such an "explanation" and it does so remarkably well. However, if we are asking why the particle behaves as it does, we are back to asking something like why Maxwell's equations are what they are.
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I think this is probably the most appropriate comment to my original post. I am indeed interested in the "why" behind all the maths. It doesnt seem any of the maths is really getting anywhere as to the "why" is it ?

So... Ive got Tom Campbells My Big Toe "why" regarding the double slit. What are my other options here? Are there any that are considered plausible?
 
AlfieGee said:
I think this is probably the most appropriate comment to my original post. I am indeed interested in the "why" behind all the maths. It doesnt seem any of the maths is really getting anywhere as to the "why" is it ?
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The mathematics can only model the behavior. Why does an electron have 9.11×10−28 g. mass instead of some other amount? If there is a model to provide an answer to that, then we would ask why that model and not some other model?
So... Ive got Tom Campbells My Big Toe "why" regarding the double slit. What are my other options here? Are there any that are considered plausible?
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I'm not familiar with that. About a year ago, I gave up on popular descriptions of QM and decided to study the real thing. It's been rewarding for me.
 
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Meadmaker said:
My alternative explanation is that the double slit experiment proves that the universe is broken. Sooner or later the cosmic repairman will fix it, and then we'll be able to figure out exactly where those particles are.
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Golly. Do you know what guys charge per nanosecond? There is no way anyone can afford a fix. We'll just have to live with it. :covereyes
 
to "explain" QM for example the double slit, I'm assuming you mean make a representational video of what happens on atomic or sub-atomic scale. No progress has been made in that endeavor because 1) as mentioned above, the equations do it just fine and 2) the fact that we can't play a video in our mind of the event is not a concern, actually it's not considered worthy of research funding.

Here's a simpler example; you've probably read how string theory might work mathematically but it requires 11 dimensions instead of the 4 known ones. The closest anyone comes to 'explain' that is to say the other 7 are very, very small (not joking here!) Clearly, you wouldn't waste your time trying to visualize what a 5th dimension looks like. So most physicists view the double slit in the same way. Of course, QM is experimentally proven and string is still a theory, not even testable currently.
Here's more Feynman as educator- http://www.youtube.com/watch?v=hUJfjRoxCbk
 
AlfieGee said:
Over the last century or so there does not seem to have been much progress made as to explaining the results of the double slit experiment.

QUOTE]

Welcome AlfieGee.

Google 'Bian Cox night with the stars' it was on BBC iplayer so not sure you'll be able to see it but there are clips on youtube. He did a lecture at the Royal Institution of Great Britain which even a duffy like me could follow:p Fasinating stuff.
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orange31 said:
Here's more Feynman as educator- http://www.youtube.com/watch?v=hUJfjRoxCbk
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He's great, ain't he?

What was particularly interesting about that lecture, was that I don't remember seeing elsewhere the simple disproof of the hidden variable theory he describes; i.e. if you could discover the values of the hidden variables that determine the particle's path, you could predict which slit the particle would go through - but that would mean that you wouldn't get the interference pattern, because you can't get an interference pattern if the particle goes through one slit or the other - so there can't be any hidden variables that could tell you the path the particle will take...

So why Bell's Inequality? Was Feynman referring to a simpler form of the hidden variable theory, or something different?
 
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The real secret is... there is no slit.

Huh. That doesn't sound as profound as I was hoping it would.
 
AlfieGee said:
I think this is probably the most appropriate comment to my original post. I am indeed interested in the "why" behind all the maths. It doesnt seem any of the maths is really getting anywhere as to the "why" is it ?

So... Ive got Tom Campbells My Big Toe "why" regarding the double slit. What are my other options here? Are there any that are considered plausible?
Click to expand...

There is no 'why' in physics. There is only 'how'.
 
Try Brian Cox and Jeff Forshaw “The Quantum Universe: Everything that can happen does happen”. Allen Lane. ISBN 978-1-846-14432-5 Hardback – a paperback edition is also available.
 
What's to explain? QM describes the probability of any particle arriving at any particular point, and this is best described as a wave. In reality, if you restrict the flow of particles, it is possible to observe the arrival of individual photons. Each provides an individual instance of observation (in tune with Heisenberg), over time it buids up to the response predicted by QM. There is no discrepancy to explain. Get over it.
 
AlfieGee said:
Hey guys, this is my first post, go easy on me.
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I have several problems with this post.

First, why should we “go easy on you” because “this is [your] first post”. Nobody in this forum cares whether it is or is not. Post rubbish, and take the flack. Enough people have had a go at me.

Secondly, I’ve looked at Thomas Campbell's web material. Anyone who goes down that route isn’t really worth bothering with.

I’ve just ordered a copy of Park’s “Voodoo Science”. I hope it lives up to its reviews. Maybe you should read it too.
 
Here is a great explanation of the problem with 'Why?' questions, also by Feynman:

 
A lot of efforts to interpret quantum mechanics sometimes seem to me like efforts to force it into a classical-physics mold. That seems to me because our intuitions and many of the simpler physical theories are all classical-limit ones, and also because of wanting to avoid bringing in any mathematics.

For my part, I prefer to avoid trying to interpret quantum mechanics, because of the interpretation problems I've mentioned. It can give me a headache.

Quantum mechanics is very counterintuitive, but it has very good theoretical foundations and very good experimental support, and that's usually good enough in practice.
 
lpetrich said:
A lot of efforts to interpret quantum mechanics sometimes seem to me like efforts to force it into a classical-physics mold. That seems to me because our intuitions and many of the simpler physical theories are all classical-limit ones, and also because of wanting to avoid bringing in any mathematics.
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I think this is absolutely key. Trying to explain something like the Double Slit Experiment in terms of our everyday experience is like asking the question "What color is ultraviolet light". Ultraviolet doesn't have a color, because color is a function of human perception and humans cannot perceive ultraviolet light. Trying to intuitively understand quantum mechanics is like trying to visualize what the color of ultraviolet light is, our brains have not evolved to deal with these things except through abstraction.
 
AlfieGee said:
I think this is probably the most appropriate comment to my original post. I am indeed interested in the "why" behind all the maths. It doesnt seem any of the maths is really getting anywhere as to the "why" is it ?
Click to expand...

But what does this have to do with the double slit experiment? You could just as easily ask "Why gravity?" or "Why does F = ma?" or literally any other question beginning with "why". We have a perfectly good description of what happens with the double slit experiment and what results you will get, and that's all the answer you will ever get from physics about anything. It just doesn't seem to make sense to single out this particular thing for a special "why?" when there's just nothing special about it.
 
Cuddles said:
But what does this have to do with the double slit experiment? You could just as easily ask "Why gravity?" or "Why does F = ma?" or literally any other question beginning with "why". We have a perfectly good description of what happens with the double slit experiment and what results you will get, and that's all the answer you will ever get from physics about anything. It just doesn't seem to make sense to single out this particular thing for a special "why?" when there's just nothing special about it.
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I think the difference is that gravity and force operate at human scale, but if you throw golf balls through a wall with two slots in it, you don't get an interference pattern. For things that work the way we are familiar with, people don't feel they need an explanation, but for anything "weird", they do. It's not logical, but it's the way people think.
 
Wavelike nature of what one would expect to be particles:

Electron diffractionWP
Neutron diffractionWP
Fullerene Diffraction - that's soccer-ball-shaped C60 molecules

I remember a physics professor who had called a photon a "blob of light", and that seems like the closest one can get while still being nontechnical.
 
AlfieGee said:
Yes, I suppose I am asking why physics is the way it is , in this particular instance, and seems to work differently, based on whether there is an observer interaction or not.
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The situation may be worse than you imagine.

In the first case, the electron first interacts with itself while in wave mode, forming the interference potential. Apparently self-interaction does not require being in particle mode. Nor does being forced to split into two separate self-interfering waves when it goes through the slits count as requiring a switch to particle mode. Apparently. But then it switches to particle mode when it strikes the plate while randomly varying it's particular location on the plate, thereby requiring multiple shots to form the interference pattern.

:wwt

In the second case, the electron interacts with the detector at the slit by allowing itself to be counted as a particle, which (I suppose) forces it to go through the slit with the detector. Then I'm not sure what it does; it either remains a particle after being counted or switches back to wave mode and then back again to particle mode when it hits the plate.

:wwt

All of which strikes me as rather odd, bordering on arbitrary complexity and Einstein-despised dice-throwing. Why not just be a damn particle all the time if you will have to be one every time you interact? What's with all the switching back and forth? Can they not move as particles? Do they have to switch to particle mode, stop, interact, switch back to wave mode, and move on?

:boggled: Surely not.
 
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