Science > Physics > Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment)
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Science > Physics |
| User: |
"Ravindra" |
| Date: |
13 Apr 2006 04:41:42 AM |
| Object: |
Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
Have couple of questions:
1. Lets assume a scenario of performing Double slit experiment starting
with bullet size partciles emitted from the gun one after another.
Obviously the interference pattern will not be observed. Now start
repeating the experiment by gradually decreasing the bullet size till
it becomes the size of an electron. Interference will appear. But there
is certain critical size of the particle at which this conversion
should happen. Anyone aware of this size?
2. A follow-up to my previous one, does interference depends on size of
the particle / mass of the particle? Lets say I have condensed the mass
of bullet into the size/volume of an electron and fire this in the
double slit experiment. Would interference be still observed ( ofcourse
assuming that the affect of gravity on this mass be nullified by some
experimental setup, say)
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| User: "Greg Neill" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
13 Apr 2006 07:39:21 AM |
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"Ravindra" <kmsravindra@gmail.com> wrote in message
news:1144921301.998543.71500@g10g2000cwb.googlegroups.com...
Have couple of questions:
1. Lets assume a scenario of performing Double slit experiment starting
with bullet size partciles emitted from the gun one after another.
Obviously the interference pattern will not be observed. Now start
repeating the experiment by gradually decreasing the bullet size till
it becomes the size of an electron. Interference will appear. But there
is certain critical size of the particle at which this conversion
should happen. Anyone aware of this size?
2. A follow-up to my previous one, does interference depends on size of
the particle / mass of the particle? Lets say I have condensed the mass
of bullet into the size/volume of an electron and fire this in the
double slit experiment. Would interference be still observed ( ofcourse
assuming that the affect of gravity on this mass be nullified by some
experimental setup, say)
Look up de Broglie wavelength.
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| User: "LawsonE" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
13 Apr 2006 05:33:54 AM |
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"Ravindra" <kmsravindra@gmail.com> wrote in message
news:1144921301.998543.71500@g10g2000cwb.googlegroups.com...
Have couple of questions:
1. Lets assume a scenario of performing Double slit experiment starting
with bullet size partciles emitted from the gun one after another.
Obviously the interference pattern will not be observed. Now start
repeating the experiment by gradually decreasing the bullet size till
it becomes the size of an electron. Interference will appear. But there
is certain critical size of the particle at which this conversion
should happen. Anyone aware of this size?
What is the "size" of a radio-wave photon? I think it is far larger than a
bullet.
2. A follow-up to my previous one, does interference depends on size of
the particle / mass of the particle? Lets say I have condensed the mass
of bullet into the size/volume of an electron and fire this in the
double slit experiment. Would interference be still observed ( ofcourse
assuming that the affect of gravity on this mass be nullified by some
experimental setup, say)
I think its a specific behavior/property of photons and other such
"particles" that is being measured in this kind of experiment. The "size" of
the particle isn't relevant to whether or not the slit experiment works at
all: its the other properties. The size might be relevant to how you need to
set up the experiment to find the effect, but thats about it. Ditto with the
mass: that changes the requirements for the experimental setup, but unless
the "particle" is of a certain type or types, you won't find the
interference pattern no matter how you set things up.
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| User: "Ravindra" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
17 Apr 2006 02:22:23 AM |
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Does this mean that hypothetically can I setup an experiment, where I
can see an interference of even macro sized particles ( lets say the
size of dust particles?)
If not, I am interested in knowing what properties set the particles
distinguish this?
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| User: "Materion" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
17 Apr 2006 07:30:49 AM |
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Ravindra wrote:
Does this mean that hypothetically can I setup an experiment, where I
can see an interference of even macro sized particles ( lets say the
size of dust particles?)
Sure, you can set up interference experiments with macro-sized
particles. Bullet-shaped particles are however not the best types of
particles. Prefer particles whose mathematical representation is nearer
to a vector than to a point or a sphere, for example needles, rods or
even baseball bats. Let then the orientation of this object be steered
by the phase of a pilot wave (acoustic, hydraulic, electromagnetic...).
The rod-like particles will then impinge on the target depending on the
phase of the wave at that point. Different orientations of the rod mean
different collision distributions. The detection probability on the
target will follow the interference pattern.
If not, I am interested in knowing what properties set the particles
distinguish this?
As explained above, you need vector-shaped particles whose evolution
follow quantum rules. Decoherence occurs when these particles run out
of phase with the pilot wave.
--
Arjen Dijksman
--------------------------------
Materion physics, the search for a satisfactory explanation of natural
phenomena at http://materion.free.fr
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| User: "Ravindra" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
17 Apr 2006 11:59:47 PM |
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But I meant can we hypothetically setup a double slit thought
experiment atleast ( choosing the correct size of the slit opening)
with needles and rods? What I meant here also was that would there be
interference when only both the slits are open and we dont find
interference when we close one of the slits...Would the same
explanation as that of electron travelling through the slits hold good
for macro sizes atleast in a thought experiment? If this is not
possible, then what is the critical size below which can we find the
interference pattern in a double slit experiment and the reason for the
same?
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| User: "Greg Neill" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
18 Apr 2006 06:25:32 AM |
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"Ravindra" <kmsravindra@gmail.com> wrote in message
news:1145336387.092915.238400@t31g2000cwb.googlegroups.com...
But I meant can we hypothetically setup a double slit thought
experiment atleast ( choosing the correct size of the slit opening)
with needles and rods? What I meant here also was that would there be
interference when only both the slits are open and we dont find
interference when we close one of the slits...Would the same
explanation as that of electron travelling through the slits hold good
for macro sizes atleast in a thought experiment? If this is not
possible, then what is the critical size below which can we find the
interference pattern in a double slit experiment and the reason for the
same?
Did you look up De Broglie?
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| User: "LawsonE" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
18 Apr 2006 04:45:43 AM |
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"Ravindra" <kmsravindra@gmail.com> wrote in message
news:1145336387.092915.238400@t31g2000cwb.googlegroups.com...
But I meant can we hypothetically setup a double slit thought
experiment atleast ( choosing the correct size of the slit opening)
with needles and rods? What I meant here also was that would there be
interference when only both the slits are open and we dont find
interference when we close one of the slits...Would the same
explanation as that of electron travelling through the slits hold good
for macro sizes atleast in a thought experiment? If this is not
possible, then what is the critical size below which can we find the
interference pattern in a double slit experiment and the reason for the
same?
I don't think its size, but the quality of quantum coherence (?). A radio
wave might have a huge size, but still show the interference pattern.
Apparently buckyballs below a certain temperature can also show this
pattern. Even larger molecules might show this pattern as well in the right
conditions, but perhaps even small fragments of DNA molecules couldn't.
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| User: "Materion" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
18 Apr 2006 10:18:48 AM |
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Ravindra wrote:
But I meant can we hypothetically setup a double slit thought
experiment atleast ( choosing the correct size of the slit opening)
with needles and rods?
Yes, if the rotating needles' orientation remains in phase with the
wave's phase, you will have a greater impact probability at crests. We
need to set up a pilot wave with wavelength longer then the length of
the needles. The greater the wavelength, the easier we will distinguish
the crests.
What I meant here also was that would there be
interference when only both the slits are open and we dont find
interference when we close one of the slits...
Yes, if we close one slit, the phase of the pilot-wave at the target
varies periodically and so do the orientations of the rotating needles
at the target. When we open both slits, a standing wave is built up. If
the needles' orientation follows the phase of the standing wave on its
path, the interference pattern appears due to the impinging needles.
Would the same
explanation as that of electron travelling through the slits hold good
for macro sizes atleast in a thought experiment?
In my opinion yes. For needles steered by a pilot wave, the
interference pattern disappears in the cases described by Feynman in
his lectures:
-when you close one slit,
-when you try to detect the needle at one slit with another projectile
needle that disturbs it in such a way that its orientation cannot stay
in phase with the wave.
If this is not
possible, then what is the critical size below which can we find the
interference pattern in a double slit experiment and the reason for the
same?
Only practical/technological constraints could dictate a critical size
(energy of the wave to steer the vector-like projectile, size of the
screen...).
--
Arjen Dijksman
--------------------------------
Materion physics, the search for a satisfactory explanation of natural
phenomena at http://materion.free.fr
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| User: "Ravindra" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
19 Apr 2006 01:04:36 AM |
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I think I got some clarity with the probability waves explanation and
at the same time got some more questions as well...
Lets assume that the electrons are fired one after the other in the
double slit experiment...Probability waves explain the interfernce
pattern observed and the reasoning goes that the probability wave of a
single electron would travel through both the slits and hence it
interferes causing an interference pattern. When we put a detector at
one of the slits ( either direct / indirect detection of the electron),
the interference pattern is not found because the probability wave
sharpened into the slit where we detected this electron...Till here it
is fine...
Case 1. Lets say we repeat the same experiment ( thought experiment!)
with needles fired one after another...Going by the same probability
wave explanation should we identify interference pattern with needles?
( lets say I chose all the required distances, slit separation width,
screen size all of those etc., hypothetically) ...
OR
Case 2. We dont observe interfernce because I can clearly see with my
eyes which slit the needle is passing through ( it is visible) without
any need of detectors!!
Case 3. Lets say I repeat Case 2 with needles but now in a closed
chamber and I cannot see till the entire experiment is over so that
Case 2 is no longer valid. Now will I see the interference pattern? If
yes, then I have some more questions:
a. In case of electrons it is understood that a detector presence /
presence of light disturbs/alters the probability wave of an electron (
Using uncertainity principle)
b. But in the case of needles, I am not using any detector but is
clearly visible to the naked eye to see the needle as to which slit it
is passing thorugh...So how can the mere act of seeing without any
presence of detectors etc., alter the probability wave of needles?
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| User: "Materion" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
19 Apr 2006 07:21:48 AM |
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Hello Ravindra. You wrote:
I think I got some clarity with the probability waves explanation and
at the same time got some more questions as well...
Lets assume that the electrons are fired one after the other in the
double slit experiment...Probability waves explain the interfernce
pattern observed and the reasoning goes that the probability wave of a
single electron would travel through both the slits and hence it
interferes causing an interference pattern.
The wave indeed travels through both slits but the electron passes
through one or the other, cf. Bell's quotation in his 1986 paper "Six
possible worlds of quantum mechanics":
"De Broglie showed in detail how the motion of a particle, passing
through just one of two holes in screen, could be influenced by waves
propagating through both holes. And so influenced that the particle
does not go where the waves cancel out, but is attracted to where they
cooperate. This idea seems to me so natural and simple, to resolve the
wave-particle dilemma in such a clear and ordinary way, that it is a
great mystery to me that it was so generally ignored."
When we put a detector at
one of the slits ( either direct / indirect detection of the electron),
the interference pattern is not found because the probability wave
sharpened into the slit where we detected this electron...Till here it
is fine...
It's not the detector's presence that destroys the interference
pattern, it is the impulse of the photons fired by the detector that
knocks the electron out of phase with the wave.
Case 1. Lets say we repeat the same experiment ( thought experiment!)
with needles fired one after another...Going by the same probability
wave explanation should we identify interference pattern with needles?
( lets say I chose all the required distances, slit separation width,
screen size all of those etc., hypothetically) ...
Yes, if the rotating needles stay in phase with the wave.
OR
Case 2. We dont observe interfernce because I can clearly see with my
eyes which slit the needle is passing through ( it is visible) without
any need of detectors!!
The photons we detect with our eyes coming off the path of the needle
do not have enough impulse to knock the needle out of phase with the
pilot wave. The interference pattern is not destroyed.
Case 3. Lets say I repeat Case 2 with needles but now in a closed
chamber and I cannot see till the entire experiment is over so that
Case 2 is no longer valid. Now will I see the interference pattern?
Yes, like in case 2.
If yes, then I have some more questions:
a. In case of electrons it is understood that a detector presence /
presence of light disturbs/alters the probability wave of an electron (
Using uncertainity principle)
It is indeed the presence of light that alters the probability wave of
the electron, not the detector's presence.
b. But in the case of needles, I am not using any detector but is
clearly visible to the naked eye to see the needle as to which slit it
is passing thorugh...So how can the mere act of seeing without any
presence of detectors etc., alter the probability wave of needles?
Well, the mere act of observing with your eyes does not alter the
probability wave of such macro-sized objects. Detecting the path of the
needles with other needles would.
--
Arjen Dijksman
-------------------
Wire grid and needle with angle theta: | | | |/| | | | | |
State vector of plane rotating needle steered by wave with phase phi:
|theta> = exp(i*phi) cos(theta) |0> + sin(theta) |1>
|0> = state vector for undetected needle (theta = 0)
|1> = state vector for detected needle (theta = pi/2)
More on http://materion.free.fr
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| User: "Ravindra" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
20 Apr 2006 05:34:08 AM |
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"Well, the mere act of observing with your eyes does not alter the
probability wave of such macro-sized objects. Detecting the path of the
needles with other needles would." As I understand how can the
"probability" wave NOT get altered, if I am able to exactly see the
position of the needle with my eyes / any other detector! So the
probability wave should collapse and hence the interference should not
be observed as per my thinking...
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| User: "Materion" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
20 Apr 2006 08:10:59 AM |
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Ravindra wrote:
As I understand how can the
"probability" wave NOT get altered, if I am able to exactly see the
position of the needle with my eyes / any other detector! So the
probability wave should collapse and hence the interference should not
be observed as per my thinking...
Collapsing the probability wave when detecting the path of a particle
is always the case in the submolecular world, because you may only use
submolecular particles in order to detect that path. You always knock
the particle out of coherence with its probability wave (collapsing) if
you wish to have sufficient resolution.
For the experiment with macro-sized rotating needles, you may use
particles that are much and much less energetic than the needles,
leaving therefore the path and the rotational mode of the needle
unaltered. But imagine you have only similar needles in order to detect
the path of the needle (like in the submolecular world you have only
fundamental particles or nuclei...). You will then always knock the
needle out of its pilot wave and collapse the probability wave.
Therefore, it is not the fact of *detecting* a particle that collapses
the wavefunction, it is the fact of *disturbing* the detected particle
with another particle of the same energetic range that collapses the
wavefunction.
--
Arjen Dijksman
-------------------
Wire grid and needle with angle theta: | | | |/| | | | | |
State vector of plane rotating needle steered by wave with phase phi:
|theta> = exp(i*phi) cos(theta) |0> + sin(theta) |1>
|0> = state vector for undetected needle (theta = 0)
|1> = state vector for detected needle (theta = pi/2)
More on http://materion.free.fr
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| User: "Ravindra" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
21 Apr 2006 12:19:36 AM |
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Thanks Arjen for making this clear...I hope this is "real"
fact...because when I read the book "the fabric of cosmos- by Briane
Green " the understanding that I got was otherwise where the detection
of electron at any slit in the double slit experiments through indirect
techniques (where the motion of the electron was left undisturbed,
through the use of some reflectors etc.,) showed NO interference
eventhough the electron was left undisturbed. There are some
experiments that are described in this book to demonstrate this.
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| User: "Materion" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
21 Apr 2006 03:06:21 AM |
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Ravindra wrote:
Thanks Arjen for making this clear...I hope this is "real"
fact...because when I read the book "the fabric of cosmos- by Briane
Green " the understanding that I got was otherwise where the detection
of electron at any slit in the double slit experiments through indirect
techniques (where the motion of the electron was left undisturbed,
through the use of some reflectors etc.,) showed NO interference
eventhough the electron was left undisturbed. There are some
experiments that are described in this book to demonstrate this.
That are interesting experiments. Could you tell me more about them? (I
also ordered the book.) It seems to me hardly understandable to detect
an electron at a slit leaving that electron undisturbed, even through
indirect detection. But why not;-)
--
Arjen Dijksman
------------------
Feynman in chapter 1.6 of his Quantum Lectures on Physics:
*When we do not see the electron, no photon disturbs it, and when we do
see it, a photon has disturbed it*
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| User: "Ravindra" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
22 Apr 2006 06:28:35 AM |
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The book has a good detail of the experiment though I will just brief
the concept here...
This is the variation of the double slit experiment...wherein there is
a light source and the light is impinged onto a beam splitter that will
send the beam one way or the other. This beam is in turn focused onto a
screen by reflectors placed on either side...the book has a diagram
that makes it very clear to understand this setup. Now something called
as "downconverter" are placed in the path of the beam from the
reflector to the screen. What this will do is to take an input as one
photon and produces 2 identical ( twin) photons...The twin photon is
called as idler photon. By detecting the idler photon, we can clearly
know if the photon has travelled through the right reflector / left
reflector without disturbing/detecting the path of the original
photon...When the idler photon was detected and hence indirectly it was
known if the photon travelled through the left / right relfector, to
the surprise there was no interference pattern observed!! The
explanation for this given is that out of the many possible different
history paths, one history path has gained significance because of the
fact that it got observed and hence the probability wave got
collapsed...so no interference was observed. When the idler detector
was removed, interferece pattern appeared!! ( again the origin photon
was not disturbed!)
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| User: "Materion" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
22 Apr 2006 04:21:14 PM |
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Hello Ravindra,
It seems to me that the experiment you are talking about is the one
performed by Mandel's team in Rochester (X. Y. Zou, L. J. Wang, and
L. Mandel, 1991, http://prola.aps.org/abstract/PRL/v67/i3/p318_1).
I found a good description in
http://www.physics.uiuc.edu/People/Faculty/Profiles/Branning/Mandel_Tribute.pdf,
paragraph *A Mind-Boggling Experiment*.
In such experiments, it is important to first analyze why interference
appears. In a double slit experiment, interference occurs between the
waves emanating from both possible paths of the photon.
In Mandel's experiment, interference occurs if the idler wave from
down converter 1 (PDC NL1 in figures 2 and 3 of above paper) crosses
the path of the signal wave at PDC NL2. In the configuration of figure
2 (no interference), even if we detect that the signal photon has
travelled through path 2, leaving it undisturbed, there is no altering
of interference pattern. In the configuration of figure 3 (interference
due to idler wave 1 affecting the phase and polarization of the waves
emanating from PDC NL2), destruction of the interference pattern occurs
through blocking idler wave 1, not through the process of detecting the
photon on path 2.
Does this explanation relate to the one given in *The Fabric of the
Cosmos*?
Applying the needle/pilot wave analogy on Mandel's experiment is much
trickier than for the simple double slit experiment. One needs to
modelize the down-converting process in the crystals...
--
Arjen Dijksman
--------------------------------
Materion physics, the search for a satisfactory explanation of natural
phenomena at http://materion.free.fr
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| User: "Ravindra" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
24 Apr 2006 07:26:13 AM |
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Yes the terminology matches but i guess the experiments in the book are
different from what is narrated...Probably the concept is also slightly
different...In *fabric of cosmos*, the interference of the signal
photos was observed when the idler photons were left undetected...but
in the exaclty same setup if the idler photons were detected ( its just
a on/off switch on the idler detector lying completly outside the
experiment...thoerectically it can be light years away as well!) then
there is no interference observed...the book explains it better!
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| User: "Materion" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
07 May 2006 04:54:42 PM |
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Hello Ravindra,
I received "The Fabric of the Cosmos" and read its interesting 7th
chapter. Brian Greene develops on the conventional dichotomic (wave
*or* particle) approach. As he indicates in note 2 of this chapter, we
should "bear in mind, though, that in Bohm's approach, ... particles
are accompanied by probability waves; that is, Bohm's theory always
invokes particles *and* waves, whereas the standard approach envisions
a complementarity that can roughly be summarized as particles *or*
waves." And further in note 13: "it is definitely worth keeping this
alternative approach in mind, if only as a foil against rash
conclusions about what quantum mechanics unavoidably implies".
The delayed choice and quantum eraser experiments refered to in this
chapter seem weird with the conventional "wave *or* particle" approach
but natural in a "wave *and* particle" approach.
The quantum eraser experiment discussed in "The Fabric of Cosmos"
(slight differences) was not Mandel's as I guessed in a previous post,
but was performed by a team at the University of Rochester (note 5 of
chapter 7), see:
A Delayed Choice Quantum Eraser, by Yoon-Ho Kim, R. Yu, S.P. Kulik,
Y.H. Shih, Marlan O. Scully
http://arxiv.org/abs/quant-ph/9903047
You wrote:
In *fabric of cosmos*, the interference of the signal
photos was observed when the idler photons were left undetected...
Well, my conclusion is different after reading subchapter "Shaping the
Past" of "Fabric of the Cosmos" and the original report by Kim et al.
Brian Greene writes: "the totality of impact positions of the signal
photons will look like the data in Figure 7.5a, showing not the
slightest hint of an interference pattern". In fact, it should be
emphasized that in this experiment, one never detects an interference
pattern at the detector collecting the signal photons. The interference
pattern concerns coincidence counts between signal and idler photons.
It is built up at the "quantum eraser" beam splitter (labeled *c* in
the book) by the idler photons, not at the signal detector.
I suspect interference effects of the idler pilot wave traveling both
ways (phase difference of pi between left and right detector). The
report does not give enough data in order to analyze it suitably
(nature of the beam splitters: polarizing or non-polarizing; distances
between the BBO down-converter and the prism...).
Regards.
--
Arjen Dijksman
--------------
J.S.Bell, "Six possible worlds of quantum mechanics", 1986:
"While the founding fathers agonized over the question
'particle' or 'wave'
de Broglie in 1925 proposed the obvious answer
'particle' and 'wave'.
Is it not clear from the smallness of the scintillation on the screen
that we have to do with a particle? And is it not clear, from the
diffraction and interference patterns, that the motion of the particle
is directed by a wave?
De Broglie showed in detail how the motion of a particle, passing
through just one of two holes in screen, could be influenced by waves
propagating through both holes. And so influenced that the particle
does not go where the waves cancel out, but is attracted to where they
cooperate. This idea seems to me so natural and simple, to resolve the
wave-particle dilemma in such a clear and ordinary way, that it is a
great mystery to me that it was so generally ignored."
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| User: "Ravindra" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
08 May 2006 05:16:48 AM |
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Yes Arjen, infact reading Fabric of Cosmos was an exciting journey for
me as well especially thru these chapters.
After referring thru several books that explain this double slit
experiment from various perspectives and *combined*
with my earlier questions on macro particles, how do you think that we
should we conclude this whole thing?
Please throw some light on it ;-)
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| User: "Materion" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
24 Apr 2006 02:53:24 PM |
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Ravindra wrote:
Yes the terminology matches but i guess the experiments in the book are
different from what is narrated...Probably the concept is also slightly
different...In *fabric of cosmos*, the interference of the signal
photos was observed when the idler photons were left undetected...but
in the exaclty same setup if the idler photons were detected ( its just
a on/off switch on the idler detector lying completly outside the
experiment...thoerectically it can be light years away as well!) then
there is no interference observed...the book explains it better!
That's OK. I'll read Brian Green's explanation as soon as I'll get the
book. Maybe I'll continue this thread at that time;-) Keep on
questioning nature with your own insight! It's much better to find it
out by yourself then to take for granted other one's explanations.
Regards.
--
Arjen Dijksman
--------------
"John Bell's legacy: questioning quantum mechanics is fruitful", Alain
Aspect 2003, Introduction to the 2nd edition of "Speakable and
Unspeakable in Quantum Mechanics".
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| User: "Ravindra" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
24 Apr 2006 11:44:58 PM |
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I completely agree with both of you...
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| User: "Ravindra" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
03 May 2006 03:59:57 AM |
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I happen to get hold of this book and read the chapter that you were
mentioning about...
After reading thru some references and books, probably I can summarize
my understading of the result of this discussion this manner...
We should not genaralize by saying interference cannot be observed by
watching "things"...It should be specific only to the particles that
get disturbed due to presence of light / photons on that particles.
However we can still genaralize it in this fashion probably and I want
to throw a wild guess...Not sure if this would be correct.
Lets say I happen to choose the slit opening and the inter-split
distance in such a fashion that we can observe interference even with
bullets ( applying DeBroglie's wavelength logic for bullet path and all
that!)...
But this interference would be again such that a photon / light
collision with the bullet might disturb the bullet path (and hence
disturbs the interference because the slit width and the inter-split
distance might be so small that even a collision by light can disturb
the bullet path to an extent that interference is no longer
observed...same as the case with electrons..The difference being that
in the case of electrons, the particles are at a micro level whereas
the inter-slit distance can be at a macro level whereas in the case of
bullets, the inter-slit widths will be at a micro level and particles
at a macro level!!) Wondering if this had opened a new perspective of
looking at this experiment!?
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| User: "Materion" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
07 May 2006 04:01:35 AM |
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Ravindra wrote:
I happen to get hold of this book and read the chapter that you were
mentioning about...
After reading thru some references and books, probably I can summarize
my understading of the result of this discussion this manner...
We should not genaralize by saying interference cannot be observed by
watching "things"...It should be specific only to the particles that
get disturbed due to presence of light / photons on that particles.
Yes, or get disturbed by other means of observation (electrons,
protons...).
However we can still genaralize it in this fashion probably and I want
to throw a wild guess...Not sure if this would be correct.
Lets say I happen to choose the slit opening and the inter-split
distance in such a fashion that we can observe interference even with
bullets ( applying DeBroglie's wavelength logic for bullet path and all
that!)...
But this interference would be again such that a photon / light
collision with the bullet might disturb the bullet path (and hence
disturbs the interference because the slit width and the inter-split
distance might be so small that even a collision by light can disturb
the bullet path to an extent that interference is no longer
observed...same as the case with electrons..The difference being that
in the case of electrons, the particles are at a micro level whereas
the inter-slit distance can be at a macro level whereas in the case of
bullets, the inter-slit widths will be at a micro level and particles
at a macro level!!) Wondering if this had opened a new perspective of
looking at this experiment!?
This is indeed another perspective;-) But bullets won't do if we keep
in mind the coherence between the particle and its environment. I
prefer the rotating arrow or needle that may stay in coherence with its
environment (pilot wave...) if it is not disturbed by impinging noise
particles. Did you refer to the bullet's interference pattern in
subchapter 1-6 of Feynman's Quantum Lectures on Physics, figure 1-5?
Feynman lectured on it in the 60's. I am not sure he would have held
that passage if he lectured today. He probably would have mentioned the
idea of decoherence, alike Brian Greene in "The Fabric of Cosmos" (cf.
post scriptum).
--
Arjen Dijksman
--------------
Brian Greene in "The Fabric of Cosmos", 2004, chapter 7:
"Although photons and air molecules are too small to have any
significant effect on the motion of a big object like this book or a
cat, they are able to do something else. They continually "nudge" the
big object's wavefunction, or, in physics-speak, they disturb its
*coherence*: they blur its orderly sequence of crest followed by trough
followed by crest."
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| User: "PD" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
24 Apr 2006 08:34:03 AM |
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Ravindra wrote:
Yes the terminology matches but i guess the experiments in the book are
different from what is narrated...Probably the concept is also slightly
different...In *fabric of cosmos*, the interference of the signal
photos was observed when the idler photons were left undetected...but
in the exaclty same setup if the idler photons were detected ( its just
a on/off switch on the idler detector lying completly outside the
experiment...thoerectically it can be light years away as well!) then
there is no interference observed...the book explains it better!
Well, that's why Brian Greene's book is a best-seller. It's his aim to
explain it better.
But if you want to understand it more *deeply* and to see the details
of how it is actually tested, then you need to dive into the papers.
This is like everything in physics (or anything else, for that matter).
A popularization will be more accessible, but offers only a shallow
understanding. Real scientific literature will provide deeper
understanding, but will be less accessible. There is no shortcut.
PD
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| User: "PD" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
19 Apr 2006 07:19:28 AM |
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Ravindra wrote:
I think I got some clarity with the probability waves explanation and
at the same time got some more questions as well...
Lets assume that the electrons are fired one after the other in the
double slit experiment...Probability waves explain the interfernce
pattern observed and the reasoning goes that the probability wave of a
single electron would travel through both the slits and hence it
interferes causing an interference pattern. When we put a detector at
one of the slits ( either direct / indirect detection of the electron),
the interference pattern is not found because the probability wave
sharpened into the slit where we detected this electron...Till here it
is fine...
Case 1. Lets say we repeat the same experiment ( thought experiment!)
with needles fired one after another...Going by the same probability
wave explanation should we identify interference pattern with needles?
( lets say I chose all the required distances, slit separation width,
screen size all of those etc., hypothetically) ...
OR
Case 2. We dont observe interfernce because I can clearly see with my
eyes which slit the needle is passing through ( it is visible) without
any need of detectors!!
Case 3. Lets say I repeat Case 2 with needles but now in a closed
chamber and I cannot see till the entire experiment is over so that
Case 2 is no longer valid. Now will I see the interference pattern? If
yes, then I have some more questions:
a. In case of electrons it is understood that a detector presence /
presence of light disturbs/alters the probability wave of an electron (
Using uncertainity principle)
b. But in the case of needles, I am not using any detector but is
clearly visible to the naked eye to see the needle as to which slit it
is passing thorugh...So how can the mere act of seeing without any
presence of detectors etc., alter the probability wave of needles?
Stop. Run, do not walk, to the nearest 2nd-hand bookstore and purchase
a copy of Feynman's book, The Character of Physical Law.
There is a lovely chapter in there that talks extensively about the
double-slit experiment and what happens if you watch the "things" pass
through the slits.
PD
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| User: "Materion" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
19 Apr 2006 07:47:07 AM |
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I have not read that book of Feynman, but I am a freak of his Quantum
Lectures on Physics. Feynman's explanations of the double-slit
experiment are indeed masterpieces. Does that chapter in "The Character
of Physical Law" treat the question otherwise than in the first chapter
of his Quantum Lectures? If not, even if it might give very good
insight on the question, I doubt if it will answer Ravindra's questions
on macro-sized particles interfering with a wave.
--
Arjen Dijksman
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| User: "Henning Makholm" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro |
17 Apr 2006 05:11:24 AM |
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Scripsit "Ravindra" <kmsravindra@gmail.com>
Does this mean that hypothetically can I setup an experiment, where I
can see an interference of even macro sized particles ( lets say the
size of dust particles?)
Practically you're going to get in trouble observing any interference
when the de Broglie wavelength of the object becomes much smaller than
the extension of the object itself.
Leaving classical interference patterns aside, I think I have read of
experiments demonstrating quantum coherent behavior for massive
systems several milimeters across (small drops of supercooled helium
IIRC).
--
Henning Makholm "No one seems to know what
distinguishes a bell from a whistle."
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| User: "Ian Stirling" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
13 Apr 2006 03:37:55 PM |
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Ravindra <kmsravindra@gmail.com> wrote:
Have couple of questions:
1. Lets assume a scenario of performing Double slit experiment starting
with bullet size partciles emitted from the gun one after another.
Obviously the interference pattern will not be observed. Now start
repeating the experiment by gradually decreasing the bullet size till
it becomes the size of an electron. Interference will appear. But there
is certain critical size of the particle at which this conversion
should happen. Anyone aware of this size?
Interference has been observed with C70
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| User: "PD" |
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| Title: Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment) |
18 Apr 2006 11:13:22 AM |
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Ravindra wrote:
Have couple of questions:
1. Lets assume a scenario of performing Double slit experiment starting
with bullet size partciles emitted from the gun one after another.
Obviously the interference pattern will not be observed. Now start
repeating the experiment by gradually decreasing the bullet size till
it becomes the size of an electron. Interference will appear. But there
is certain critical size of the particle at which this conversion
should happen. Anyone aware of this size?
Not in the particle size per se, but its momentum.
When the slit separation becomes comparable to the deBroglie wavelength
(h/p) of the particle, then interference effects will become apparent.
2. A follow-up to my previous one, does interference depends on size of
the particle / mass of the particle? Lets say I have condensed the mass
of bullet into the size/volume of an electron and fire this in the
double slit experiment. Would interference be still observed ( ofcourse
assuming that the affect of gravity on this mass be nullified by some
experimental setup, say)
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