Why don't the Slits collapse the wave function?

In summary: However, I think the author is confusing the observer effect with the measurement effect. The observer effect occurs when the experimenter affects the outcome of the measurement. The measurement effect occurs when the detector detects the photon. The two are not the same.In summary, the video explained the wave-like behavior of subatomic particles in a concise and easy to understand way. The explanations of quantum properties were accurate and concise. The way they described subatomic behavior was easy to digest from a layman's perspective. One thing I don't understand is how the screen with the slits do not collapse the wave function until there is a measurement. Wouldn't bouncing off the sides of the slit constitute some sort of interaction? I hope I get this right
  • #36
Hans de Vries said:
One could imagine that some time in the, not so far away, future such an experiment using Extreme Ultra Violet photons and a nanotechnology slit plate could do measurements with the required sensitivity.
Not in my wildest imagination whould I expect to ever see technology that sensitive. We are looking at the movement of the mass of a wall holding a slit being moved by just a small few photons that by chance happen to all deflect the same way before others cancel the effect by going the other way. I would expect tempature alone to swamp the detail needed.
 
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  • #37
RandallB said:
Not in my wildest imagination whould I expect to ever see technology that sensitive. We are looking at the movement of the mass of a wall holding a slit being moved by just a small few photons that by chance happen to all deflect the same way before others cancel the effect by going the other way. I would expect tempature alone to swamp the detail needed.
To stimulate your imagination then: The "wall" would be in the order
of 40 nm wide with nano technology and EUV photons. There are several
ways of measuring forces and/or displacements with extreme precision.

Measuring the effects of single particles is not so exceptional anymore.
The record measurement of the electron's gyromagnetic anomaly was
measured with a precision of 12 digits by observing a single electron
in a Penning trap for a long enough time. Regards, Hans.
 
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  • #38
ueit said:
Sum over histories is, according to Feynman, just a method of calculation, nothing more. The mechanism behind the quantum phenomena is unknown and, as I've argued before, there is no reason to assume it is non-local.

If you can test the specific assumption (in this case: sum over histories), and the results are as predicted by theory, how can you say it is not physical?

As for the requirement of 4D spacetime, it is a bit premature to require that there be no additional dimensions. Maybe there are more.
 
  • #39
The interference pattern is real, is it not? I therefore deduce the slit is also real, and the interference pattern is a causal consequence of photon-slit interactions.
 
  • #40
Hans de Vries said:
To stimulate your imagination then: The "wall" would be in the order
of 40 nm wide with nano technology and EUV photons. There are several
ways of measuring forces and/or displacements with extreme precision.

Measuring the effects of single particles is not so exceptional anymore.
The record measurement of the electron's gyromagnetic anomaly was
measured with a precision of 12 digits by observing a single electron
in a Penning trap for a long enough time.
To Bring your imagination Back to Reality then;
consider the total mass of the 40 nm THICK wall holding the slit (we only need one here) that will be moved by the deflection of the one or two photons we detect going to one side.
I can only guess what you might imagine; but do you actually think that the movement of the wall caused by just a couple of photons we be nearly as large as a precision of 12 digits
 
  • #41
Chronos said:
The interference pattern is real, is it not? I therefore deduce the slit is also real, and the interference pattern is a causal consequence of photon-slit interactions.

The interference is not an artifact of interaction with the slit per se. If it was, then a single slit would also produce interference.

That is not say that the *shape* of the interference pattern is not influenced by the shape of the slit. Diamond shaped slits produce diamond shaped patterns.
 
  • #42
DrChinese said:
The interference is not an artifact of interaction with the slit per se. If it was, then a single slit would also produce interference.
But a single slit does give an interferance pattern. The applet at http://www.physics.northwestern.edu/ugrad/vpl/optics/diffraction.html" ; is a nice tool to show how both types of patterns must be considered to define the Complete Pattern that will be produced.
 
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  • #43
RandallB said:
But a single slit does give an interferance pattern. The applet at http://www.physics.northwestern.edu/ugrad/vpl/optics/diffraction.html" ; is a nice tool to show how both types of patterns must be considered to define the Complete Pattern that will be produced.

Hi RandallB,

I must be an idiot, because I tinkered with that applet and couldn't find that result.

I would guess that there is some interference in a single slit, but that the effect on total intensity would be minimal (and would not be visually evident to the resulting pattern).
 
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  • #44
DrChinese said:
I must be an idiot, because I tinkered with that applet and couldn't find that result.

I would guess that there is some interference in a single slit, but that the effect on total intensity would be minimal (and would not be visually evident to the resulting pattern).
I find the best viewing comes if you:
Leave wave length at 1
Slits at n = 2
Change slit separation to d=30
Change Slit width between a = 4, 8, & 12 (my favorite is 3.8)

Then alternate which boxes you check you check at the bottom.

The pure single slit plot shows the area that the pure n-slit graph must fit under for the complete pattern.
As you can see in most cases real experiments are done in the center area, being careful not to let the value of “a” slit width get to big. Or the single slit dispersion interference will move toward the center with both a ‘null’ spot getting in the way and a lowering of the relative intensity as compared to dead center. Either affect would ruin the purpose of most experiments.
But I would like to see an experiment looking past the first single slit null at about 45 to 50 degrees using 3.8 width slits in a 2 slit. Maybe I should ask DrDave to do it; but it looks like a particularly difficult test to run for real.

Note: The display does have a code error in that when putting in a slit separation of 30 it actually represents a slit separation of 15. (30 should give 60 peaks from end to end for the pure n-slit not 30 peaks)
 
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  • #45
RandallB said:
But a single slit does give an interferance pattern.

The single-slit pattern is qualitatively very different from the double-slit one. How can one account for this difference via interactions with the slit edges?
 
  • #46
kliide said:
One thing I don't understand is how the screen with the slits do not collapse the wave function until there is a measurement. Wouldn't bouncing off the sides of the slit constitute some sort of interaction?

The slits do collapse the wavefunction: into to delta functions located at the slits. This is because the slits measure position, and delta functions are the eigenfunctions of position.
 
  • #47
jtbell said:
The single-slit pattern is qualitatively very different from the double-slit one. How can one account for this difference via interactions with the slit edges?
Single slit diffraction & interference is rather basic stuff just google or start at http://en.wikipedia.org/wiki/Slit_experiment"
 
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  • #49
RandallB said:
I've never seen a documented example of non-local correlation proven to be based on a local mechanism. At least not a "truly local" mechanism. (I understand there are "local mathematical constructs" such as BM, MWI, etc. that could work in a reality with additional dimensions to allow for guide waves etc.)
You site as an example “the speed of gravity: infinite in Newtonian gravity, c in GR”? – I don’t see how that relates to correlations being based on a true naive Einstein local mechanism. Do you have a link or other resource pertaining to your point here?
From this article:

http://arxiv.org/PS_cache/gr-qc/pdf/9909/9909087.pdf"

It is certainly true, although perhaps not widely enough appreciated, that observations are incompatible with Newtonian gravity with a light-speed propagation delay added in [3,4].
If one begins with a purely central force and puts in a finite propagation speed by hand, the forces in a two-body system no longer point toward the center of mass, and the resulting tangential accelerations make orbits drastically unstable.

As a warm-up, let us first consider electrodynamics. It is well known that if a charged source moves at a constant velocity, the electric field experienced by a test particle points toward the source’s “instantaneous” position rather than its retarded position. Lorentz
invariance demands that this be the case, since one may just as well think of the charge as being at rest while the test particle moves. This effect does not mean that the electric field propagates instantaneously; rather, the field of a moving charge has a velocity-dependent component that cancels the effect of propagation delay to first order

Finally, let us return to the question asked in Ref. [1]: what do experiments say about the speed of gravity? The answer, unfortunately, is that so far they say fairly little. In the absence of direct measurements of propagation speed, observations must be filtered through theory, and different theoretical assumptions lead to different deductions. In particular, while the observed absence of aberration is consistent with instantaneous propagation (with an extra interaction somehow added on to explain the gravitational radiation reaction), it is also consistent with the speed-of-light propagation predicted by general relativity. Within the framework of general relativity, though, observations do give an answer. The Einstein field equations contain a single parameter cg, which describes both the speed of gravitational waves and the “speed of gravity” occurring in the expression for aberration and in the velocity-dependent terms in the interaction. This parameter appears in the
gravitational radiation reaction in the form c−5 g , as in eqn. (3.3), and the success of the theory in explaining the orbital decay of binary pulsars implies that cg = c at the 1% level or better [22].

I think this is a good example of how a local mechanism can produce non-local correlations. If you agree that GR is correct and not just a "local mathematical construct" my point is proven.

I don't understand your question about the "true naive Einstein local mechanism".a
 
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  • #50
ueit said:
I think this is a good example of how a local mechanism can produce non-local correlations. If you agree that GR is correct and not just a "local mathematical construct" my point is proven.

You need to understand Bell better. The question is NOT whether it is possible to get an apparently "non-local" correlation from a purely local mechanism. Bell states specifically that you cannot get QM's predictions from a LOCAL and REALISTIC theory. That is a completely different issue altogether!

So your point continues to miss the mark wide, and that is why it is not generally accepted science. Your "citations" add nothing to the debate.
 
  • #51
DrChinese said:
You need to understand Bell better. The question is NOT whether it is possible to get an apparently "non-local" correlation from a purely local mechanism. Bell states specifically that you cannot get QM's predictions from a LOCAL and REALISTIC theory. That is a completely different issue altogether!

So your point continues to miss the mark wide, and that is why it is not generally accepted science. Your "citations" add nothing to the debate.

GR is both local and realistic, do you agree?

Gravity appears to be non-local, that is, if I am on Mars and you on Earth we could establish our instantaneous position by using accelerometers. We would find that the directions these instruments show are always correlated (parallel).

Now, let's make Bell's assumption. For whatever reason (say evolutionary adaptation) we strongly believe that the planets are moving because of our will, that is, their positions are just like the detector orientations in EPR experiments. It is easy to see that in this case the only way to make sense of the correlations is to assume non-locality. Sort of Bell theorem for gravity.
 
  • #52
DrChinese said:
If you can test the specific assumption (in this case: sum over histories), and the results are as predicted by theory, how can you say it is not physical?

Sum over histories requires a particle to travel an infinite distance in a finite amount of time, in other words, it has to travel at infinite speed. A particle has mass/energy and mass/energy cannot travel faster than c. Therefore, the assumption is falsified by relativity.
 
  • #53
ueit said:
Sum over histories requires a particle to travel an infinite distance in a finite amount of time, in other words, it has to travel at infinite speed. A particle has mass/energy and mass/energy cannot travel faster than c. Therefore, the assumption is falsified by relativity.


The what with the which, there? :confused:
 
  • #54
ueit said:
GR is both local and realistic, do you agree?

Gravity appears to be non-local,
No it is not, see other threads on indeterminate background of GR.
And as you claim gravity appears to be non-local are you saying GR is not a proper description of gravity or disagreeing with yourself and that GR is non-local.
 
  • #55
RandallB said:
No it is not, see other threads on indeterminate background of GR.
The background is dynamic in GR, I don't see how this is relevant. Although some solutions in GR seem to allow for non-locality, they are entirely speculative. As applied to my example, GR is a local mechanism (each planet follows the local space curvature), explaining an "apparently" non-local force (as required in Newtonian gravity). Isn't this what you’ve asked me for?
Include the "free will" assumption and you have a nice analogy with Bell's theorem.
 
  • #56
ueit said:
Isn't this what you’ve asked me for?
... a nice analogy with Bell's theorem.
No it is not.
Gravity and GR with planets have nothing to do with non-local (or local) correlations. You’ve shown no analogy with Bell's theorem here.
 
  • #57
ueit said:
GR is both local and realistic, do you agree?

Gravity appears to be non-local,...

GR is a local realistic theory, athough it is not part of the domain that is QM.

Gravity has never been found to have a non-local component by any known experiment result. Not sure what any of this has to do with this thread.
 
  • #58
RandallB said:
To Bring your imagination Back to Reality then;
consider the total mass of the 40 nm THICK wall holding the slit (we only need one here) that will be moved by the deflection of the one or two photons

A cube with 40 nm sides can be accelarated to up to 400 nm/s by a single
EUV photon. That's ten times its size per second. Nowadays we can detect
displacements well below an Angstrom ...


Regards, Hans.
 
  • #59
DrChinese said:
GR is a local realistic theory, athough it is not part of the domain that is QM.

Gravity has never been found to have a non-local component by any known experiment result. Not sure what any of this has to do with this thread.
In Newtonian physics the speed of gravity was infinite. If you use a limited speed, let's say c, the planetary orbits become unstable.
In GR this "seemingly" infinite speed of gravity was explained by a local mechanism.
This is an example where a non-local effect in an old theory is known to be the result of a local mechanism in a new theory. This is what I was asked for:

I've never seen a documented example of non-local correlation proven to be based on a local mechanism.

I do not claim that this is what happens in the EPR experiment although it is possible (if a GR-like theory can be created for the EM field). It is only an analogy to point to the fact that, in the absence of direct confirmation of non-locality, it is premature to consider non-local correlations as evidence for non-locality.

P.S.

I'll not be able to post here for about four days, I'll answer then if necessary.
 
  • #60
ueit said:
I'll not be able to post here for about four days, I'll answer then if necessary.
No need to reply - I think it is clear you do not understand the term "correlation" from the origianal question
 
  • #61
Hans de Vries said:
A cube with 40 nm sides can be accelarated to up to 400 nm/s by a single EUV photon. That's ten ...
Not on point,
1) that little cube a slit does not make, you will need much more mass than that even for a singlr slit.
2) You do not get to use ALL the energy of the photon, only what counts for momentum concervation do to the deflection of the photon going through the slit to go off to the right or left. (Rerun the test if you get one going straight ahead) MUCH smaller than your number.

Your better than that, do all the math if your going to do it.
 
  • #62
RandallB said:
Not on point,
1) that little cube a slit does not make, you will need much more mass than that even for a singlr slit.
2) You do not get to use ALL the energy of the photon, only what counts for momentum concervation do to the deflection of the photon going through the slit to go off to the right or left. (Rerun the test if you get one going straight ahead) MUCH smaller than your number.

Your better than that, do all the math if your going to do it.

Your response is fast but both points are wrong.

1)

EUV radiation has a wavelength in the order of 10 nm. "Double split"
experiments can be (and have been) performed with a single wire.
This is enough to create two different paths, In this case the wire
can be in the order of 10nm to 20nm thick.

2)

Of course the deflection momentum is less as the total momentum
but certainly not "MUCH" smaller under the proposed dimensions.

Two split interference pattern with 1 wavelength separation:
http://www.calvin.edu/~lmolnar/anim/circ3.gif (10 nm separation)

Two split interference pattern with 2 wavelengths separation:
http://www.calvin.edu/~lmolnar/anim/circ4.gif (20 nm separation)
Regards, Hans
 
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  • #63
ueit said:
In Newtonian physics the speed of gravity was infinite. If you use a limited speed, let's say c, the planetary orbits become unstable.
In GR this "seemingly" infinite speed of gravity was explained by a local mechanism.

I don't think you have a sufficient grip on GR. GR is a local theory which respects c. Under GR, planets DO have stable orbits. GR has absoultely nothing to do with Bell's Theorem. I do not understand what GR has to do with this discussion.
 
  • #64
All I think ueit is trying to say, is that prior to GR we had a non-local model for explaining gravitational interactions. Then GR came along and gave us a local theory that explained gravitational interactions.

Perhaps he/she is trying to draw analogies between pre-GR gravity to current understanding of QM, and post-GR gravity to some as-of-yet-unknown-paradigm of QM which would be local and realist. The specific details are, of course, different, but perhaps he/she is merely trying to draw an analogy.

But I must say I'm not entirely sure if that is exactly what ueit is trying to say.
 
  • #65
masudr said:
All I think ueit is trying to say, is that prior to GR we had a non-local model for explaining gravitational interactions. Then GR came along and gave us a local theory that explained gravitational interactions.

Perhaps he/she is trying to draw analogies between pre-GR gravity to current understanding of QM, and post-GR gravity to some as-of-yet-unknown-paradigm of QM which would be local and realist. The specific details are, of course, different, but perhaps he/she is merely trying to draw an analogy.

But I must say I'm not entirely sure if that is exactly what ueit is trying to say.

That's exactly what I want to say, thanks!
 
  • #66
ueit said:
That's exactly what I want to say, thanks!

OK, historical point noted.

However, that is exactly why Bell's Theorem is so amazing. We now know that a local realistic theory (like GR: which respects c and has definite values for the gravitational tensors at all times) cannot reproduce the results of QM. This is a very surprising result, and I think it is counterintuitive. That is why it is also so controversial.
 
  • #67
Hans de Vries said:
Your response is fast but both points are wrong.
Great then instead of computer generated diagrams --
What go you expect the details of the real experiment are going to be?

What Hz or energy of a photon do you propose send through the slit?
What angle of deflection will you wait to see a single one of these photons deflect?
What Momentum must go into the slit to account for the change of momentum in the deflected photon?
THEN how far will the slit assembly move based on:

Size of complete slit assembly: That is COMPLETE dimensions and mass including the target cross hairs or index used to make the slit location measurements from, AND the mounting points and any friction to be accounted for from whatever holds the slit assembly in place?

What will you be using as the measuring system to make the two location measurements of that slit index both before and after each potential test photon passes though?
And what effects will this measuring system have on the total slit system?

I presumably that measuring system will involve a stream photons, smaller with higher energy than the larger lower energy photon we are testing.
I assume we will have a large number of location measurements to record before we get a pair with a proper deflected photon.

How do you account for any momentum imparted to the slit from the measuring system including any scattering (oops more random deflections) of the higher energy photons used to make these measurements? Can we say about how many of these higher energy photons will be needed to make each measurement?

I know details, details….
But as I said before; not in my wildest dreams do I expect this kind of test to every be done.
 
  • #68
RandallB said:
Great then instead of computer generated diagrams --
What go you expect the details of the real experiment are going to be?

What Hz or energy of a photon do you propose send through the slit?

Since the first post I talked about EUV photons which have a wavelength
of about 10nm.

RandallB said:
What angle of deflection will you wait to see a single one of these photons deflect?
What Momentum must go into the slit to account for the change of momentum in the deflected photon?
Again, from the very first post you could deduct a split separation in
the order of the wavelength of the photon which means a wide range
of angles. It doesn't matter at all what the exact distribution is as long
as the angle of deflection isn't extreemly small as you wrongly suggested.

http://www.calvin.edu/~lmolnar/anim/circ3.gif (10 nm separation)
http://www.calvin.edu/~lmolnar/anim/circ4.gif (20 nm separation)

RandallB said:
THEN how far will the slit assembly move based on:

Size of complete slit assembly: That is COMPLETE dimensions and mass including the target cross hairs or index used to make the slit location measurements from, AND the mounting points and any friction to be accounted for from whatever holds the slit assembly in place?

What will you be using as the measuring system to make the two location measurements of that slit index both before and after each potential test photon passes though?
And what effects will this measuring system have on the total slit system?

it can move arbitrary far depending on the time you have.

Imagine it as a scattering experiment then, with the nanoslits scattering
one way and the EUV photon the other way. If the nanoslits move
several times their own size per second, as I showed, then you don't
need much time to get a good resolution on a detector screen designed
to detect "nanoslits" impacts.

RandallB said:
I presumably that measuring system will involve a stream photons, smaller with higher energy than the larger lower energy photon we are testing.
I assume we will have a large number of location measurements to record before we get a pair with a proper deflected photon.

How do you account for any momentum imparted to the slit from the measuring system including any scattering (oops more random deflections) of the higher energy photons used to make these measurements? Can we say about how many of these higher energy photons will be needed to make each measurement?

No higher energy photons needed at all...Regards, Hans.
 
  • #69
Hans de Vries said:
as long as the angle of deflection isn't extreemly small as you wrongly suggested.
Never made such a suggestion - and you are still completely missing the point, as if you didn't understand what or how the HUP works, and have not thought it through COMPLETLY. But have your way, start a new thread when you or one of yours actually runs such an experiment some day in the future, I’ll unsubscribe here, this thread is long enough as it is.
 
  • #70
DrChinese said:
However, that is exactly why Bell's Theorem is so amazing. We now know that a local realistic theory (like GR: which respects c and has definite values for the gravitational tensors at all times) cannot reproduce the results of QM. This is a very surprising result, and I think it is counterintuitive. That is why it is also so controversial.
No, we don't know that. You forget that such a theory does not allow "free will", there is no statistical independence between detector orientations and the particle source. I know, you will say that no such theory was put forward but this is not so surprising given the number of physicists working on LHV theories.
I wonder if a better understanding of the measurement process (describing all experimental setup in terms of particles/fields and not macroscopic instruments) couldn't reveal the mechanism involved in EPR.
 
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