Double slit - revisited
mercury
or Young experiment) always done with small distance d (um) between
the slits (of course here and after the radiation considered is
assumed monochromatic and the experiment is carried in vacuum).
As far as one has a spherical (or plane) wave from the source then
even if d is great (provided d=N.L/2 where N is a great integer and L
is the wavelength) there should INTFR.
One can argue that the radiation wave is not perfectly spherical (or/
and) there is a phase difference if d is great.
But then the complete field (wave) is comprised by the waves for
separate photons and each photon’s wave (probability amplitude) is
perfectly spherical and in fact just separate photons interfere (with
themselves).[Everybody knows this statement of Dirac in his QM]. I
believe this is the major reason for INTFR (and although it is known
that different photons can also interfere I think this a rare case??).
So if the complete field (wave) is comprised by the waves for separate
photons – every wave will interfere with itself and there must be
INTFR picture even if d is great.
Another aspect is that one can also carry the experiment with single
(one after one) photons for great d.
In the first case (dense radiation – e.g. sunlight, laser) there is
surely no INTFR and for single photons I think also no INTFR (I’m not
sure).
So theoretically there must be INTFR (even is d is large) but
experimentally is not observed.
The question is: Is this true and if so then why?
ken...@erinet.com
The paper in the following link provide a physical explanation for the
double slit experiment.
http://www.modelmechanics.org/2008experiment.pdf
Ken Seto
Rich L.
No, what you are describing is incompatible with experiment. Light
will form interference at any distance, as long as the DIFFERENCE in
path length along the two interfering paths is less than the coherence
length of the light source used. In the case of lasers, the coherence
length can be quite long (roughly the inverse of the line width of a
single mode laser). This can be up to meters for very quiet/stable
lasers. In the case of white light, you can see "white light fringes"
in a Michelson Interferometer, but the path difference must be no more
than a few microns (the coherence length of "white" light). This can
even be done using sunlight.
There is also no restriction on light intensity. Intensity has no
effect on interference what so ever. You can get interference fringes
with very intense lasers, or at light levels so low that only one
photon at a time can be in the apparatus. This has been demonstrated
by experiment (for example see "http://en.wikipedia.org/wiki/Double-
slit_experiment" down about 80% through the article). You might be
confusing the ability to recognize an interference pattern (which you
cannot do with a single photon) with the prediction of the
probabilities for an individual photon appearing in different
locations on the detector (which is verified by experiment).
It has even been demonstrated that you can see interference between
different light sources, i.e. lasers, provided they are stable enough
that they can be considered to be coherent for reasonable periods of
time. See for example "http://en.wikipedia.org/wiki/Hong%E2%80%93Ou
%E2%80%93Mandel_effect" .
Rich L.
glen herrmannsfeldt
> On Oct 6, 9:16 am, mercury <il...@abv.bg> wrote:
>> Why is the interference (INTFR) from two slits (double slit experiment
>> or Young experiment) always done with small distance d (um) between
>> the slits (of course here and after the radiation considered is
>> assumed monochromatic and the experiment is carried in vacuum).
> No, what you are describing is incompatible with experiment. Light
> will form interference at any distance, as long as the DIFFERENCE in
> path length along the two interfering paths is less than the coherence
> length of the light source used. In the case of lasers, the coherence
> length can be quite long (roughly the inverse of the line width of a
> single mode laser). This can be up to meters for very quiet/stable
> lasers. In the case of white light, you can see "white light fringes"
> in a Michelson Interferometer, but the path difference must be no more
> than a few microns (the coherence length of "white" light). This can
> even be done using sunlight.
(snip)
Yes, but note that the laser principle means mulitple photons.
I am not sure if the OP was asking about single photon or multiple
photon interference, though.
-- glen
mercury
Do you mean interference experiment with the distance 'd' between the
slits macroscopic? Why not? In fact I remembered later the Arago
(Poisson) spot. Is this not interference with long d? It must work
with slits too.
I wonder - is this done with separate photons (Arago and double slit
with long d)? I think it will work - in fact the spot in the center of
the shadow of Arago's experiment must be from interference of separate
photons which interfered with themsleves.
> Light will form interference at any distance, as long as the DIFFERENCE in
> path length along the two interfering paths is less than the coherence
> length of the light source used.
Do you mean by distance - the distance light travels after splitting
to the INTFR spot or the distance between the slits? Why question is
about the latter.
> In the case of lasers, the coherence length can be quite long (roughly the inverse of the line width of a
> single mode laser). This can be up to meters for very quiet/stable
> lasers. In the case of white light, you can see "white light fringes"
> in a Michelson Interferometer, but the path difference must be no more
> than a few microns (the coherence length of "white" light). This can
> even be done using sunlight.
A question: Is the coherence length the same when one reduces the
intensity of a laser to single photons?
>
> There is also no restriction on light intensity. Intensity has no
> effect on interference what so ever. You can get interference fringes
> with very intense lasers, or at light levels so low that only one
> photon at a time can be in the apparatus. This has been demonstrated
> by experiment (for example see "http://en.wikipedia.org/wiki/Double-
> slit_experiment" down about 80% through the article). You might be
> confusing the ability to recognize an interference pattern (which you
> cannot do with a single photon) with the prediction of the
> probabilities for an individual photon appearing in different
> locations on the detector (which is verified by experiment).
>
> It has even been demonstrated that you can see interference between
> different light sources, i.e. lasers, provided they are stable enough
> that they can be considered to be coherent for reasonable periods of
> time. See for example "http://en.wikipedia.org/wiki/Hong%E2%80%93Ou
> %E2%80%93Mandel_effect" .
>
> Rich L.- Hide quoted text -
>
> - Show quoted text -
Rich L.
> On Oct 9, 12:51 am, "Rich L." <ralivings...@sbcglobal.net> wrote:
> > On Oct 6, 9:16 am, mercury <il...@abv.bg> wrote:
> > > Another aspect is that one can also carry the experiment with single
> > > (one after one) photons for great d.
> > > In the first case (dense radiation – e.g. sunlight, laser) there is
> > > surely no INTFR and for single photons I think also no INTFR (I’m not
> > > sure).
> > > So theoretically there must be INTFR (even is d is large) but
> > > experimentally is not observed.
> > > The question is: Is this true and if so then why?
>
> > No, what you are describing is incompatible with experiment.
>
> Do you mean interference experiment with the distance 'd' between the
> slits macroscopic? Why not? In fact I remembered later the Arago
> (Poisson) spot. Is this not interference with long d? It must work
> with slits too.
> I wonder - is this done with separate photons (Arago and double slit
> with long d)? I think it will work - in fact the spot in the center of
> the shadow of Arago's experiment must be from interference of separate
> photons which interfered with themsleves.
I'm confused about your question. I thought you were suggesting that
if the distance 'd' between slits was sufficiently large that you
would no longer see interference. My answer was that this is not
true, that you can see interference with any spacing between the
slits. See further answer below...
> > Light will form interference at any distance, as long as the DIFFERENCE in
> > path length along the two interfering paths is less than the coherence
> > length of the light source used.
>
> Do you mean by distance - the distance light travels after splitting
> to the INTFR spot or the distance between the slits? Why question is
> about the latter.
I'm talking about the Path Difference, the difference in distance that
the light travels to go from the source to each of the slits and then
to the detector. Note that no matter how large 'd' is, you can always
find points where the path difference is small. (Whether the
intensity of light there is significant is another question.)
...
> A question: Is the coherence length the same when one reduces the
> intensity of a laser to single photons?
Yes.
Rich L.
mercury
Exactly this. But I was wondering about experimental evidence - e.g.
some old papers about DSE with large d.
The spot right between the slits (on the screen) would not depend on
the coherence length.
>My answer was that this is not true, that you can see interference with any spacing between the
> slits. See further answer below...
>
> > > Light will form interference at any distance, as long as the DIFFERENCE in
> > > path length along the two interfering paths is less than the coherence
> > > length of the light source used.
Can we imagine the wave (amplitude of probability) as a blowing sphere
with thickness = coherence length?
>
> > Do you mean by distance - the distance light travels after splitting
> > to the INTFR spot or the distance between the slits? Why question is
> > about the latter.
>
> I'm talking about the Path Difference, the difference in distance that
> the light travels to go from the source to each of the slits and then
> to the detector. Note that no matter how large 'd' is, you can always
> find points where the path difference is small. (Whether the
> intensity of light there is significant is another question.)
>
> ...
>
> > A question: Is the coherence length the same when one reduces the
> > intensity of a laser to single photons?
>
> Yes.
Are then 2 photon different by their coherence length?
>
> Rich L.- Скриване на цитирания текст -
>
> - Показване на цитирания текст -
Rich L.
Actually if you are trying to make sense of the idea of "photons", you
will have to talk to someone else. I have gradually come to the
conclusion that the idea of a photon as a particle of light is a
mathematical abstraction that in reality does not make sense. As
applied here, the concept of coherence length doesn't make sense as
applied to a "photon". The coherence length is a property of the
light source, and you will see interference, or not, depending on this
property of the source. You really can't say that a photon carries
the coherence length.
As for the two slits, I'm not aware of exactly that experiment being
done on a large scale, but there are many examples of interference
over separations of thousands and millions of wavelengths of the
light. One example is the LIGO experiment where the interferometer
arms are 4 km (2.5 miles) long and after passing out and back this
distance they definitely see interference. I have also read of
observations of light interference fringes being observed on earth
when stars are occulted by the moon. I'm not sure that directly
relates to your question, however. On a much smaller scale, large
diffraction limited telescope (e.g. Hubble) would not achieve such
resolution if there were not interference between light reflected off
opposite sides of the primary mirror.
Rich L.
glen herrmannsfeldt
(snip)
> Actually if you are trying to make sense of the idea of "photons", you
> will have to talk to someone else. I have gradually come to the
> conclusion that the idea of a photon as a particle of light is a
> mathematical abstraction that in reality does not make sense. As
> applied here, the concept of coherence length doesn't make sense as
> applied to a "photon". The coherence length is a property of the
> light source, and you will see interference, or not, depending on this
> property of the source. You really can't say that a photon carries
> the coherence length.
(snip of LIGO example)
> On a much smaller scale, large
> diffraction limited telescope (e.g. Hubble) would not achieve such
> resolution if there were not interference between light reflected off
> opposite sides of the primary mirror.
Yes, the ability to focus and detect light through one large
slit is pretty much the same as for two slits. Many of the hubble
photons will be 15e9 years old. For a good (diffraction limited)
telescope, the resolution depends on the ability of the photon
wave function, as distributed across the telescope aperture,
to interfere constructively at the focal point, and destructively
at all other points.
-- glen
Tom Roberts
> I have gradually come to the
> conclusion that the idea of a photon as a particle of light is a
> mathematical abstraction that in reality does not make sense.
Yes. But if you think of photons as excitations in the field, then things make
much more sense. As it is a quantum field, its excitations are quantized. For
instance, this makes it clear how photons relate to the field inside a
resonator, and why only certain modes occur. Thinking of EM radiation as "a
particle" or as "a bunch of very small BBs" cannot do that.
[BBs are small spheres about 4 mm in diameter.]
> As
> applied here, the concept of coherence length doesn't make sense as
> applied to a "photon". The coherence length is a property of the
> light source, and you will see interference, or not, depending on this
> property of the source. You really can't say that a photon carries
> the coherence length.
Hmmmm. In the sense that the source excites the field, the photons from the
source do "carry" properties of the source, including such aspects as direction,
distribution of wavelengths, and coherence length. After all, since all of those
properties affect the interference between/among photons far from the source,
they must somehow "carry" them all. Note that "carry" is really the wrong word
here; say, rather, that photons from a given source have properties related to
that source, because the form of excitations in the field depends on the details
of how the field is excited by the source. Coherence length is BOTH a property
of individual photons, AND a statistical aspect of the collection of photons
from a given source (related to the width of the wavelength distribution). IOW:
in order to generate a narrow distribution of wavelengths, the source must
excite the field differently from a source that generates a wide distribution.
[We know it is not purely a statistical property, because
experiments with individual photons show interference.]
This is just one more case in which the "ether/or" structure of the English
language does not capture the subtleties of quantum phenomena. The so-called
"particle/wave duality" is basically a LANGUAGE issue.
Tom Roberts
glird
> On 10/12/10 10/12/10 - 11:39 PM, Rich L. wrote:
>
> > I have gradually come to the
> > conclusion that the idea of a photon as a particle of light is > > a mathematical abstraction that in reality does not make
> > sense.
>
> Yes. But if you think of photons as excitations in the field,
> then things make much more sense.
Yes.
> As it is a quantum field, its excitations are quantized.
A "field" is a local volume of space. A "quantum" is a quantity. Is
a "quantum field" a quantity of space? (If so, why complicate things
by adding the word "quantum", when the word "filed" already denotes
exactly that? If not, then what IS a quantum field?
> For instance, this makes it clear how photons relate to the
> field inside a resonator, and why only certain modes occur.
Clear as mud. If you disagree, explain how a photon relates to a
field inside or outside a resonator.
> Thinking of EM radiation as "a particle" or as "a bunch of
> very small spheres" cannot do that.
A photon is a quantity of energy. If you think a quantity of energy
is a particle, explain how a aquantity of the ability to do work can
exist in a void. If you think it is a particle, explain what it is
made of.
>>< As applied here, the concept of coherence length doesn't make sense as applied to a "photon". �The coherence length is a property of the light source, and you will see interference, or not, depending on this property of the source. �You really can't say that a photon carries the coherence length.>
>
>< In the sense that the source excites the field, the photons from the source do "carry" properties of the source, including such aspects as direction, distribution of wavelengths, and coherence length. >
if a photon has a wavelength then why deny that light is a wave
system? If light IS a wave system, then what waves? (As written
elsewhere,"A wave avoids a void because a void cannot wave. (In a
void, avoid a void.)"
>< After all, since all of those properties affect the interference between/among photons far from the source, they must somehow "carry" them all. Note that "carry" is really the wrong word here; say, rather, that photons from a given source have properties related to that source, because the form of excitations in the field depends on the details of how the field is excited by the source. >
Yes, a quantum of energy does have the property of its source, which
is h = 2 pi r m c(fs).
> <The Coherence length is BOTH a property of individual photons, AND a statistical aspect of the collection of photons
from a given source (related to the width of the wavelength
distribution).. .
Wtf does that mean?
> < IOW: in order to generate a narrow distribution of wavelengths, the source must excite the field differently from a source that generates a wide distribution.>
BS!!
The distribution of wavelengths of a photon is a function of the
velocity of the incident atom, regardless of what the wavelength was
on emission.
> � � � � [We know it is not purely a statistical property, because
> � � � � �experiments with individual photons show interference.]
The walls of a hole don't count? Name an experiment, based on ONE
photon alone, that shows interference.
glird
Oh No
>On Oct 13, 5:43�pm, Tom Roberts <tjrob...@sbcglobal.net> wrote:
>> On 10/12/10 10/12/10 - 11:39 PM, Rich L. wrote:
>>
>> > I have gradually come to the
>> > conclusion that the idea of a photon as a particle of light is > >
>> >a mathematical abstraction that in reality does not make
>> > sense.
>>
>> Yes. But if you think of photons as excitations in the field,
>> then things make much more sense.
>
> Yes.
>
>> As it is a quantum field, its excitations are quantized.
>
> A "field" is a local volume of space.
No. A field is a function on a region of space.
>A "quantum" is a quantity.
No. Here quantum is just an adjective meaning pertaining to quantum
theory.
>Is
>a "quantum field" a quantity of space? (If so, why complicate things
>by adding the word "quantum", when the word "filed" already denotes
>exactly that? If not, then what IS a quantum field?
put the above together. If you want to understand this subject and take
part in meaningful discussions you must actually study the subject.
> A photon is a quantity of energy. If you think a quantity of energy
>is a particle, explain how a aquantity of the ability to do work can
>exist in a void.
clearly it can only do work when it interacts with other matter, which
means it can't do work when it is in a void.
>If you think it is a particle, explain what it is
>made of.
it is a fundamental particle, and hence it is made of itself.
>> � � � � [We know it is not purely a statistical property, because
>> � � � � �experiments with individual photons show interference.]
>
>The walls of a hole don't count? Name an experiment, based on ONE
>photon alone, that shows interference.
>
Tom said "individual photons", not "an individual photon".
Regards
--
Charles Francis
moderator sci.physics.foundations.
charles (dot) e (dot) h (dot) francis (at) googlemail.com (remove spaces and
braces)
Tom Roberts
not. This is a re-send. -- TR
Rich L. wrote:
> One of my problems with the photon as a particle idea is how can it maintain
> the appearance of coherence length far from the source?
That's merely one of the many reasons why photons are not "particles". As I said
before, many of the common notions about particles do not apply to photons. As I
said before, thinking of them as excitations in a quantum field resolves most of
the problems (once one understands what that means :-)).
Given a source and its characteristics, then the wave function for a single
photon is a function on spacetime with support that is moving along a null
geodesic, and is elongated along its direction of propagation; the amount of
elongation is related to the coherence length of the source.
Don't think of the wavefunction as related to "where the photon is", but rather
related to the "probability of detecting the photon" [#] -- because that
probability depends not only on properties of the photon but also on properties
of the detector.
[#] And even here, my use of "the" is problematical. In general
one cannot discuss individual photons; often one cannot even count
them. This problem is linguistic; the math is clear and precise.
> The photon is an excitation of the quantum field, which consists of many many
> cavity modes.
Not really. In open space there is no "cavity", and even inside an actual
cavity, the field excitations are not really restricted to the modes of the
cavity -- only the PERSISTENT STANDING WAVES are so restricted. But propagating
light beams are not such standing waves.
Instead, think of such "modes" as merely being Fourier components. After all,
any function can always be Fourier decomposed into such modes.
> Infinitely many in the case of free space (unless the universe is finite, but
> that is of no practical importance). Each cavity mode is a precise frequency
> and thus should not show a finite coherence length.
Yes. Which is why thinking exclusively in terms of modes is not fruitful when
considering coherence length. For coherence length to be meaningful, it must be
significantly smaller than any relevant "cavity". That implies one should use a
Fourier integral, not a discrete Fourier analysis. Then it becomes clear that
outside the region of support for the wavefunction (in space), all the basis
functions of the F.I. cancel each other.
Why did I specify "(in space)" there? -- because we often
write wavefunctions in momentum space, which is related to
configuration space by a Fourier integral. This stuff is
A LOT more complicated than I am discussing here....
> This suggests that when we talk of a "single photon in the experiment at a
> time" that we must be talking about a superposition of many cavity modes.
> But to do this you can no longer say "a photon is a photon". That is, each
> "photon" can have very different propertied depending on what mix of modes go
> into it. A photon from an incandescent light bulb will be different from a
> photon from a laser.
Hmmm. You are conflating several different concepts here. As I said above,
thinking in terms of "modes' is not always fruitful, and this is a case in
point. But yes, the photon WAVEFUNCTIONS from a laser and from an incandescent
bulb are quite different from each other. But no detector "detects" the
wavefunction, it detects photons, and THE DETECTOR cannot tell them apart (even
though an analyst can do so by looking at the functional forms of their
wavefunctions). This depends in part on the detector's capabilities -- a
wavelength-sensitive detector can determine STATISTICALLY that their wavelength
distributions are quite different, but cannot tell for certain whether any
individual hit came from the lamp or the laser (though for a wavelength far from
the laser's center one can guess it came from the bulb with a high likelihood of
being correct).
Of course light is highly directional, and one can use direction
to distinguish two sources. But again this is only statistical,
and one cannot tell for certain from which source a given hit came.
Even from the side of the laser, there is a minuscule but nonzero
probability that a photon tunneled through the opaque housing....
> Unless you pass the light bulb photon through a narrow bandwidth filter in
> which case it can be turned into a narrow band photon indistinguishable from
> the laser photon.
To a detector they were already indistinguishable, as individual hits. It is
only statistically that the laser and bulb can be distinguished.
> Describing a photon as a mixture of cavity modes is like specifying the
> position of something with a vector defined in terms of a specified basis.
> The only difference is that the basis has infinitely many dimensions, one
> corresponding to each cavity mode.
Sure. That's what Fourier analysis is. But instead of an ordinary vector space
in which the basis consists of N vectors, this is a Hilbert space in which the
basis consists of an infinite number of functions (speaking loosely, and
omitting some caveats).
> I think it is a mistake to think that any one particular basis represents
> the fundamental character of what is going on [...]
Sure. That is what wavelet analysis is all about. The Fourier basis set
{sin(...), cos(...)} are a convenient basis because they have definite
frequencies, but they are by no means the only useful basis set. But as you
realize, they have infinite duration in time -- most wavelet analyses use basis
functions with a finite frequency spread and a finite duration.
> It is when you try to conceptualize photon as something like an electron or
> proton, like an elementary particle with a frequency parameter that can take
> on any frequency but is otherwise identical to any other "photon" with the
> same frequency that the concept falls apart.
Actually that falls apart for electrons and protons, too. Quantum object simply
are NOT "very tiny particles", they are something completely different -- so
different that your everyday life has not prepared you to understand them; you
must study quantum theory. There is no shortcut to understanding.
> I think that we may be blinding ourselves to what is really going on by
> trying to fit the square peg of a photon concept into the round hole of EM
> behavior.
Hmmmm. Electromagnetism is the essence of photon behavior. But a classical
description of EM has no hope of describing or explaining photons. Nor do your
rather naive notions.
> I'm suspecting that there is a slightly more sophisticated concept that is a
> little closer to what is really happening.
Yes. As I have indicated, your notion of "photons" falls far short of what they
actually are in quantum theory.
For starters, Feynman's book _QED_ is an excellent overview. But
I know of nobody who has successfully studied this on their own
and fully grasped the subtleties of quantum theory. The guidance
of an experienced and knowledgeable professor seems mandatory
(along with the study groups that form in graduate school)....
Tom Roberts
maxwell
A mathematical field is a continuous function of all the spatial
separation variables. This may be used to describe the variation of
potential over space, when it is being used simply as a mathematical
intermediary in a larger calculational context.
Or, a field may be used to represent the reality of an ontogical
entity, as Maxwell did for representing the luminiferous aether in his
EM theory. Such a usage implies other physical consequences above and
beyond the mathematical implications.
The question is: which usage is the psi function playing in QM or QFT?
Rich L.
> NOTE TO MODERATOR: I don't know if this was affected by your server problem or
> not. This is a re-send. -- TR
>
> Rich L. wrote:
> > One of my problems with the photon as a particle idea is how can it maintain
> > the appearance of coherence length far from the source?
>
> That's merely one of the many reasons why photons are not "particles". As I said
> before, many of the common notions about particles do not apply to photons. As I
> said before, thinking of them as excitations in a quantum field resolves most of
> the problems (once one understands what that means :-)).
Tom,
Thanks for the detailed response. I think our ideas about photons as
particles are largely in agreement (i.e. that it is often misleading
to talk about them as physical particles). I'm personally not that
enthusiastic about thinking about them as quantum field excitations
either, and I think that is one place where we differ, but I don't
intend to argue that point too strenuously since the QFT point of view
is clearly very successful and I do not have a convincing alternative,
yet.
My thinking is inspired by a number of quantum mechanical effects that
seem to challenge our ideas about causality and locality. For example
the correlation experiments that test Bell's Inequality. The usual
interpretation of these experiments has a disturbance leaving the
source at event "O" at t0 and propagating independently to observers
at events "A" and "B" with space-like separation. The often cited
Copenhagen interpretation is that the detection of the first photon at
either A or B then influences the outcome at the other detector. This
is not a relativistically consistent picture, however, because a
different observer can see the influence the other way around just by
passing by the experiment at an appropriate speed and direction.
My choice is to modify the concept of locality, and I am trying to
develop this idea into a consistent and useful interpretation. This
is inspired by the notion in relativity that the proper distance
between O and A or B is zero since O is on the past light cones of
both A and B (two separate light cones that intersect at O). If we
consider this proper distance as the distance that is important in
electromagnetic interactions, then the correlation is not surprising.
>From the point of view of O both A and B are adjacent (in this sense)
and O could coordinate the transfer of the photon energy to give the
observed correlation. This does not have to violate causality, i.e.
it does not require that O have any knowledge of the state of A or B.
O could, for example, "try" to emit photons in any direction but will
only emit them if a suitable receiver can be found on it's future
light cone. By "try" I don't mean to be anthropomorphic, but more
statistical: it will eventually transfer the photon energy to some
available receiver, but exactly when and where is randomly determined
but biased by physical distance to each possible receiveing charge
(really all charges in the universe) This is a little bit like the
"Pilot Wave" theory of Bohm but somewhat less deterministic.
This idea is also inspired by the observation that an excited atom in
a resonant cavity that cannot support the emitted photon wavelength
from the atom will suppress the decay of that atom. I.e., the atom
will emit photons only if an accepting charge can be located in the
future. The correlation in these experiments would then be explained
by the atom not emitting photons towards A and B unless O was
polarized appropriately and also that A and B were oriented
appropriately to accept photons with that orientation.
Some pluses to this idea, in my mind are:
-It eliminates any discussion of how the photon propagates from O to A
or B, since in the EM sense the emitter and absorbers are "zero
distance" apart.
-it also explains "delayed choice" experiments, since the photons are
exchanged only when the path of "propagation" from the receiver to the
emitter is open as seen by the receiver (this is always true in the
delayed choice experiments)
-it explains why an excited atom will not emit when in a cavity that
won't support the photon (although I have to admit that there are
consistent QM arguments for this one, related to the uncertainty
principle)
-it can explain Rabi oscillations in a very natural way
some negatives that do bother me are:
-it implies that the state of A and B are 'fixed' already when the
photons are emitted by O. For example, if the photon is from the
cosmological background radiation, and we are receiving it now, this
implies that the receiving atoms state was already set billions of
years ago. This certainly messes with most peoples ideas of causality
and especially self determination...
-it isn't immediately clear to me how to calculate the probabilities
in a way that duplicates the calculations of QED, but I'm working on
that.
I recognize that there are aesthetic reasons to not like this
concept. Do you know of any hard observational reasons why this
picture cannot be valid? I'm certainly not convinced myself, but I
want to explore the idea for a while and see where it goes.
Rich L.
Oh No
>> Rich L. wrote:
>> > One of my problems with the photon as a particle idea is how can it maintain
>> > the appearance of coherence length far from the source?
>>
>> That's merely one of the many reasons why photons are not "particles". As I said
>> before, many of the common notions about particles do not apply to photons. As I
>> said before, thinking of them as excitations in a quantum field resolves most of
>> the problems (once one understands what that means :-)).
>
>Tom,
>
>Thanks for the detailed response. I think our ideas about photons as
>particles are largely in agreement (i.e. that it is often misleading to
>talk about them as physical particles).
I find there is really only one common notion of particles which does
not apply to photons, and that this notion equally does not apply to
other particles such as electrons. This is the notion that particles
have to exist in space. Space (or spacetime) I see as an emergent
property from the interactions of many particles. This being so, we
cannot talk of where particles are in space, but only of where they
might be found in measurement. I.e. a fundamental property of quantum
mechanics becomes immediately apparent.
Of course exactly how all this happens, and we get from it not only the
precise mathematical structures of qm, qft, and relativistic spacetime
is not so obvious. But it can be understood if you put enough work into
it.
maxwell
> Thus spake Rich L. <ralivings...@sbcglobal.net>
Reality precedes measurement & supersedes humanity.
Since animals function well in the world & they don;t measure anything
(that presumes the concept & manipulation of number) then space & time
ARE the foundations of reality, not the result of measurement.
Man is not the measure of all things but ego believes so.
Particles always exist at a unique location in space at any one
instant in time - this os their one unique, defining feature.
Electrons ARE particles!
Oh No
>On Oct 30, 7:09 am, Oh No <N...@charlesfrancis.wanadoo.co.uk> wrote:
>> I find there is really only one common notion of particles which does
>> not apply to photons, and that this notion equally does not apply to
>> other particles such as electrons. This is the notion that particles
>> have to exist in space. Space (or spacetime) I see as an emergent
>> property from the interactions of many particles. This being so, we
>> cannot talk of where particles are in space, but only of where they
>> might be found in measurement. I.e. a fundamental property of quantum
>> mechanics becomes immediately apparent.
>>
>> Of course exactly how all this happens, and we get from it not only the
>> precise mathematical structures of qm, qft, and relativistic spacetime
>> is not so obvious. But it can be understood if you put enough work into
>> it.
>>
>> Regards
>Reality precedes measurement & supersedes humanity.
>Since animals function well in the world & they don;t measure anything
>(that presumes the concept & manipulation of number)
Not at all. We measure everything in our surroundings all the time. That
is how we know that one object is further away than another.
>then space & time
>ARE the foundations of reality, not the result of measurement.
>Man is not the measure of all things but ego believes so.
Then you should recognise that space and time cannot be the foundations
of reality, but are rather just man-made organisational principles which
we use to interpret the world.
>Particles always exist at a unique location in space at any one
>instant in time - this os their one unique, defining feature.
This we know is false as a matter of absolute scientific fact.
Tom Roberts
> Thus spake maxwell <sp...@shaw.ca>
>> Particles always exist at a unique location in space at any one instant in
>> time - this os their one unique, defining feature.
>
> This we know is false as a matter of absolute scientific fact.
Not really. All that we actually know is that in our best current models that
claim is false, and that those models are so well supported experimentally that
there is no known way to construct a viable theory in which this claim is true.
(Here "viable" means "consistent with all known experiments".)
There is no such thing as "absolute scientific fact", because science does not
deal with certainties, only MODELS. Don't believe everything you hear on television.
There are some things which are established so solidly that it is
downright perverse to withhold one's agreement, until and unless
definitive evidence to the contrary is presented. This is one of
them.
Tom Roberts
ben6993
> Thus spake maxwell <s...@shaw.ca>
>
> - Show quoted text -
The Rasch paired comparisons method can be used to provide sports
tables in which the outcomes are more like physical measurements than
normal sports tables. E.g. http://www.winsteps.com/ncb.htm for a
basketball table.
But are the physical outcomes so envied in psychological measurement
(I doubt if sports organisers have the same envy) themselves relying
on something like a Rasch calculation. Is a Rasch analysis equivalent
to the step of collapsing a wave function by measurement.
In a sports competition each team has matches which they can win lose
or draw. This set of match results represents the raw data. The
final results table shows the relative standings for all teams, and
are the calculated outcomes. A rasch table shows positions of teams on
an interval scale. This last step is equivalent to our common sense
knowledge of space and time positions.
Relative separations of particles may be like the raw sports data, and
turned by measurement into spacetime locations in each of the four
dimensions. As a league position is only a limited summary of the
intricacy of the qualities of a sports team, perhaps spacetime
location is only a limited summary of the qualities of a particle's
place. I.e the four dimensions may arise as a consequence of the
calculations.
Rich L.
The fact that electrons demonstrate interference proves that they do
NOT have to be in one place at one time. In a two slit experiment, or
Davisson–Germer experiment, the results can only make sense if the
electron is in some sense at two or more places at the same time.
Rich L.
glen herrmannsfeldt
(snip)
> The fact that electrons demonstrate interference proves that they do
> NOT have to be in one place at one time. In a two slit experiment, or
> Davisson?Germer experiment, the results can only make sense if the
> electron is in some sense at two or more places at the same time.
The usual explanation is that the electron goes through both slits.
I am not sure that means at the same time, though.
How about this experiment (probably easier with photons):
Take the two slit experiment, but alternately open and close
the slits at a very high speed. Is it still possible to
get interference?
-- glen
Materion
>
> The fact that electrons demonstrate interference proves that they do
> NOT have to be in one place at one time. In a two slit experiment, or
> Davisson–Germer experiment, the results can only make sense if the
> electron is in some sense at two or more places at the same time.
>
> Rich L.
Interference can be obtained with single particles that are located at
one place at a time, see Couder's experiments on bouncing droplets:
http://www.physorg.com/news78650511.html
Arjen
Oh No
>Oh No wrote:
>> Thus spake maxwell <sp...@shaw.ca>
>>> Particles always exist at a unique location in space at any one
>>>instant in time - this os their one unique, defining feature.
>> This we know is false as a matter of absolute scientific fact.
>
>Not really. All that we actually know is that in our best current models that
>claim is false, and that those models are so well supported experimentally that
>there is no known way to construct a viable theory in which this claim is true.
>(Here "viable" means "consistent with all known experiments".)
No. We no more than that. Not simply that there is no such known theory,
but that there can be no such theory consistent with experiment.
>
>There is no such thing as "absolute scientific fact", because science does not
>deal with certainties,
That is saying that science is not science. The fact that you do not
recognise science is not enough to show that science cannot exist.
Rich L.
Yes, provided that from the view of the detecting screen the two slits
appear to be open at the same time as the photon is detected. By
"same time" here I mean on the detectors past light cone at that
moment.
Rich L.
Rich L.
This appears to be a situation that simulates the Bohm Pilot Wave
theory of quantum mechanics. It seems to me that what was
demonstrated isn't really a quantum mechanical effect but merely an
interaction between the water wave and the oil droplet. In any case,
you can't do a similar experiment with photons or subatomic particles
because the act of observing their location (a measurement) completely
scrambles the wave function and the interference effect is lost.
Rich L.
Tom Roberts
> The usual explanation is that the electron goes through both slits.
> I am not sure that means at the same time, though.
In quantum theory it means you cannot ask the question about time of passage.
Nor can you ask "which slit?" (To ask such questions you must make appropriate
measurements, and that changes the physical situation and the resulting pattern
in the detector.)
> How about this experiment (probably easier with photons):
> Take the two slit experiment, but alternately open and close
> the slits at a very high speed. Is it still possible to
> get interference?
It depends on how quickly you can open and close them, and on the ratio of the
time duration that both are open (partially) to the duration that one is
definitely closed. Both partially open will give interference, one definitely
closed will not; you can get a combination of two 1-slit patterns and a 2-slit
pattern. If you wait to open one until the other has been definitely closed for
at least the transit time of the light from source to detector, then you won't
get any interference; shorter durations of both definitely closed will require a
complete analysis.
Tom Roberts
maxwell
to view an electron being at two points in space at the same time -
this is rank mysticism.
The failure to imagine a solution is not a proof that there is no
alternative solution - classic false logic.
maxwell
> On Oct 30, 11:03嚙窮m, maxwell <s...@shaw.ca> wrote:
>
>
>
>
>
> > On Oct 30, 7:09嚙窮m, Oh No <N...@charlesfrancis.wanadoo.co.uk> wrote:
>
> > > Thus spake Rich L. <ralivings...@sbcglobal.net>
>
> > > >> Rich L. wrote:
> > > >> > One of my problems with the photon as a particle idea is how can it maintain
> > > >> > the appearance of coherence length far from the source?
>
> > > >> That's merely one of the many reasons why photons are not "particles". As I said
> > > >> before, many of the common notions about particles do not apply to photons. As I
> > > >> said before, thinking of them as excitations in a quantum field resolves most of
> > > >> the problems (once one understands what that means :-)).
>
> > > >Tom,
>
> Davisson嚙瘦ermer experiment, the results can only make sense if the
> electron is in some sense at two or more places at the same time.
>
> Rich L.
This proves nothing. Delayed action at a distance on a complex
object, such as a screen (not a simple object, like 2 holes) offers
all sorts of opportunity for explanations.
Tom Roberts
> Thus spake Tom Roberts <tjrobe...@sbcglobal.net>
>> Oh No wrote:
>>> Thus spake maxwell <sp...@shaw.ca>
>>>> Particles always exist at a unique location in space at any one
>>>> instant in time - this os their one unique, defining feature.
>>> This we know is false as a matter of absolute scientific fact.
>> Not really. All that we actually know is that in our best current models that
>> claim is false, and that those models are so well supported experimentally that
>> there is no known way to construct a viable theory in which this claim is true.
>> (Here "viable" means "consistent with all known experiments".)
>
> No. We no more than that. Not simply that there is no such known theory,
> but that there can be no such theory consistent with experiment.
I doubt very much you have such a proof.
>> There is no such thing as "absolute scientific fact", because science does not
>> deal with certainties,
>
> That is saying that science is not science.
Not at all. I am merely pointing out that science is about MODELS OF THE WORLD,
not about certainty, "truth" or "absolute scientific fact" (which, as I pointed
out, is really an oxymoron). Some of those models are so good and well tested
that for all practical purposes they can be used as if they were certain and
"true", but that does not change the FACT that they are not. ALL models are
contingent.
As I said, don't believe everything you hear on television.
Tom Roberts
Tom Roberts
> Interference can be obtained with single particles that are located at
> one place at a time, see Couder's experiments on bouncing droplets:
> http://www.physorg.com/news78650511.html
Interesting. But that is not at all the same as quantum interference, and the
article does not claim that it is. This is just a classical system in which the
influence of waves on a particle is important to its motion. The math for this
bears a resemblance to the math for quantum systems, but the analogy is by no
means exact.
Tom Roberts
Tom Roberts
> The definition of a particle (see above) means that it makes NO sense
> to view an electron being at two points in space at the same time -
> this is rank mysticism.
You are confused -- an electron is not a particle in the sense of the definition
you gave. Wishing it were so does not make it so. The fact that physicists call
electrons "particles" is due to the use of a different definition of the word. I
prefer the term "quantum objects" to avoid your mistake of using the wrong meaning.
> The failure to imagine a solution is not a proof that there is no
> alternative solution - classic false logic.
Sure. As I pointed out earlier in this thread. But to date nobody has come up
with a theory that conforms to your definition and also agrees with all of the
experiments.
It is EXCEEDINGLY difficult to construct a theory that agrees with all of the
experiments in the sub-atomic realm. You cannot expect to also be able to
dictate the behavior of the components of such a theory -- nature is under no
compulsion to behave according to the way you happen to define words. And nature
is under no compulsion to behave the same way at all scales that she happens to
behave at ordinary human scales (where common word definitions evolve); indeed
it is QUITE CLEAR that the sub-atomic realm is INCREDIBLY different from our
everyday lives.
Tom Roberts
ben6993
>
> > - Show quoted text -
>
> The Rasch paired comparisons method can be used to provide sports
> tables in which the outcomes are more like physical measurements than
> basketball table.
>
> But are the physical outcomes so envied in psychological measurement
> (I doubt if sports organisers have the same envy) themselves relying
> on something like a Rasch calculation. Is a Rasch analysis equivalent
> to the step of collapsing a wave function by measurement.
>
> In a sports competition each team has matches which they can win lose
> or draw. This set of match results represents the raw data. The
> final results table shows the relative standings for all teams, and
> are the calculated outcomes. A rasch table shows positions of teams on
> an interval scale. This last step is equivalent to our common sense
> knowledge of space and time positions.
>
> Relative separations of particles may be like the raw sports data, and
> turned by measurement into spacetime locations in each of the four
> dimensions. As a league position is only a limited summary of the
> intricacy of the qualities of a sports team, perhaps spacetime
> location is only a limited summary of the qualities of a particle's
> place. I.e the four dimensions may arise as a consequence of the
>
> - Show quoted text -
Sorry for replying here to my own earlier posting about the analogy of
rasch pairs with wave collapse, but I woke today realising I can add
that there are other similarities wrt localness and uncertainty of
position. The Rasch pairs method can give sports teams relative
standings (equivalent to 'collapsed' positions) on an interval scale
whereas the set of match outcomes in terms of wins, losses and draws
for pairs of teams is the raw data (equivalent to wave functions).
[The method is also used in educational research.] Normal tables of
sports team results have total team points which are not truly on an
interval scale.
The Rasch method has to be used locally else the interval scale
outcome is unavailable. Take a top class league of teams, with its
normal quota of exciting topsy-turvy surprising match results, and add
one very poor team which is beaten by every other team. We know that
the poor team is in last place, i.e. we have an ordinal scale result,
but we do not know by how much that team is worse just from a set of
100% lost matches, i.e. we do not have an interval scale result. To
find the true position of the poor team on an interval scale we need
to compare it with similarly poor
teams where it should win some matches and lose some. So Rasch pairs
needs to be used locally. To try to apply that analogy from Rasch
back into physics, it is as if measuring the distances of stars within
a galaxy were achievable on an interval scale but trying to see how
far away was a star in another galaxy could not give any useful
results. Not just that we haven't applied the measurement and
collapsed the wave, but that even after measurement and collapse there
would not be enough information to give its position accurately as it
is not local. Collapse being only possible locally to a measurement.
Another problem which can make an interval scale outcome of positions
unavailable is if the data have a Guttmann structure, in this case the
data will 'overfit' the Rasch model. We get this if the top team
beats all other teams, the 2nd team beats all the lower teams, etc.
etc. All we can get out of this is a rank order of teams. Any hope
of finding proper distances between teams is lost. This is connected
to the issue of locality. Even though the teams are nominally in the
same league they are not similar enough in quality to be considered
truely local. There is no uncertainty in the outcomes. More
uncertainty is equivalent to more locality. To get useful Rasch
results you need some uncertainty. Applying this aspect from Rasch to
physics, it means that without some uncertainty you would lose the
ability to use your rulers for measuring lengths. Heisenberg's
uncertainty is not just a nuisance preventing your desired accuracy,
it is a requirement to get an interval scale.
Rasch outcomes come with a standard error. Applying the standard
error back into physics would seem to perhaps be analgous to the
Planck length. In Rasch, the standard error varies by sports team and
depends on the set of raw data of match results. Following that
analogy back to physics the planck length could be expected to vary
and depend on local data. It also means that there should be
uncertainty in the positions in the raw data i.e. wave functions
should truly exhibit uncertainty, not merely uncertainty in the
collapsed positions. Well we know there is
uncertainty in wave functions as they can be used to indicate
probabilities of positions, but I mean that it may be wrong in
principle to think that there might be underlying precision of form in
higher dimensional structures of matter that we just can't see from
here.
Materion
The act of detecting the location of a bouncing droplet with particles
at the same scale (other droplets) destroys the coherence between wave
and droplets and the interference effect is completely lost.
Arjen
Oh No
>Oh No wrote:
>> Thus spake Tom Roberts <tjrobe...@sbcglobal.net>
>>> Oh No wrote:
>>>> Thus spake maxwell <sp...@shaw.ca>
>>>>> Particles always exist at a unique location in space at any one
>>>>> instant in time - this os their one unique, defining feature.
>>>> This we know is false as a matter of absolute scientific fact.
>>> Not really. All that we actually know is that in our best current
>>>models that
>>> claim is false, and that those models are so well supported
>>>experimentally that
>>> there is no known way to construct a viable theory in which this
>>>claim is true.
>>> (Here "viable" means "consistent with all known experiments".)
>> No. We no more than that. Not simply that there is no such known
>>theory,
>> but that there can be no such theory consistent with experiment.
>
>I doubt very much you have such a proof.
Rather than doubting things, it would be better to study them.
>>> There is no such thing as "absolute scientific fact", because
>>>science does not
>>> deal with certainties,
>> That is saying that science is not science.
>
>Not at all. I am merely pointing out that science is about MODELS OF
>THE WORLD, not about certainty, "truth" or "absolute scientific fact"
>(which, as I pointed out, is really an oxymoron).
No. The word "science" means literally "knowledge", meaning that it is
indeed about certainty, rather than about simply belief, or faith.
>Some of those models are so good and well tested that for all practical
>purposes they can be used as if they were certain and "true", but that
>does not change the FACT that they are not. ALL models are contingent.
>
>As I said, don't believe everything you hear on television.
Actually, you are the one citing common dogma.
maxwell
Tom, because it is difficult does not make it impossible. I am making
solid progress starting from viewing the electron as a particle and
adding extra properties that are not present in the Newtonian model
i.e. the electron is NOT a boring lump of stuff, like a billiard
ball. The atomic world is only different because the electron's mass
is so small that ALL interactions effect its behavior, including ALL
attempts to measure it. If you start with a theory of measurement at
the human scale then don't be surprised at the results. I suggest you
broaden your scope.
Tom Roberts
> My thinking is inspired by a number of quantum mechanical effects that
> seem to challenge our ideas about causality and locality. For example
> the correlation experiments that test Bell's Inequality. The usual
> interpretation of these experiments has a disturbance leaving the
> source at event "O" at t0 and propagating independently to observers
> at events "A" and "B" with space-like separation.
Not a "disturbance", but rather a quantum object.
> The often cited
> Copenhagen interpretation is that the detection of the first photon at
> either A or B then influences the outcome at the other detector.
The quantity measured is not merely the presence of a photon, but rather its
spin. AFAIK the "spooky" correlation of these experiments that violates the Bell
inequalities is always between spins of entangled quantum objects (even though
the inequalities are more general than just spins).
Please remember the original genesis of spin -- Dirac's need to find a "square
root" of the Klein-Gordon equation. He found algebraic operators that were able
to obtain the appropriate type of "square root", which could only be implemented
in a non-abelian group (the canonical representation is related to 4-component
spinors). It was later discovered (by Wigner, I believe) that the basis states
of these spinors behave exactly as if they have intrinsic angular momentum
(which is why it is called "spin"). And then all sorts of puzzling atomic
spectroscopy results suddenly became clear and understandable, as did the
structure of the periodic table and some details of electron scattering.
So spin is really a rather strange beast.... For instance its genesis was pure
relativity and the need for Lorentz invariance of the equations, but the most
common use of this stuff is as the Clebsch-Gordan coefficients [#] of non-rel QM
and the way they explain atomic spectroscopy and the details of the scattering
of elementary particles.
[#] These are actually the structure coefficients of the
various representations of the Lorentz group. How and why that
appears in a NON-relativistic theory of QM for atomic systems
is an interesting story....
> This
> is not a relativistically consistent picture, however, because a
> different observer can see the influence the other way around just by
> passing by the experiment at an appropriate speed and direction.
Yes. That's why non-rel QM is not a fundamental theory of physics; it is in
essence the low-speed and low-energy limit of QED.
> in relativity that the proper distance
> between O and A or B is zero since O is on the past light cones of
> both A and B (two separate light cones that intersect at O).
Hmmmmm. That's only true for experiments using photons traveling in vacuum. Some
of these experiments transport them in fiber optic cables, and I believe that
other experiments use electrons. Moreover, the experiments are about SPIN
CORRELATIONS, not electromagnetic interactions.
> [...] some negatives that do bother me [about his idea] are:
> -it implies that the state of A and B are 'fixed' already when the
> photons are emitted by O.
That is ruled out by experiments. Look at the "delayed choice" type of EPR
experiments.
> For example, if the photon is from the
> cosmological background radiation, and we are receiving it now, this
> implies that the receiving atoms state was already set billions of
> years ago.
But you ought to be consistent. In your approach, it was "set" _ZERO_ time ago
because the source is on the past lightcone of the receiving atom. These photons
are traveling in vacuum (well, presumably close enough...). This is no different
in principle from source and receiver being separated by millimeters -- it only
differs in scale.
> This certainly messes with most peoples ideas of causality
> and especially self determination...
But so do quantum mechanics and QED. At least they have the virtue of being
consistent with the experiments within their domains.
Tom Roberts
Rich L.
> Rich L. wrote:
> > ... The usual
> > interpretation of these experiments has a disturbance leaving the
> > source at event "O" at t0 and propagating independently to observers
> > at events "A" and "B" with space-like separation.
>
> Not a "disturbance", but rather a quantum object.
I think I'm working on an interpretation that is part way between the
"disturbance propagating in space-time" and "a quantum object". The
picture I'm trying to develop is of a discrete transfer of energy from
O to A and B as a more or less instantaneous (in some sense) event.
The trick is to account for the observed correlations in a
relativistically consistent way.
> > The often cited
> > Copenhagen interpretation is that the detection of the first photon at
> > either A or B then influences the outcome at the other detector.
>
> The quantity measured is not merely the presence of a photon, but rather its
> spin. AFAIK the "spooky" correlation of these experiments that violates the Bell
> inequalities is always between spins of entangled quantum objects (even though
> the inequalities are more general than just spins).
...
True, but not central to the problem. In the case of photons (which
is all that has been tested this way) the correlation is with
polarization. You could argue that polarization is related to the
spin of the photon, but again that is irrelevant to the argument. The
key thing is the correlation between A and B when they are not
causally connected except through O.
>...
> So spin is really a rather strange beast....
Without a doubt...
...
> > in relativity that the proper distance
> > between O and A or B is zero since O is on the past light cones of
> > both A and B (two separate light cones that intersect at O).
>
> Hmmmmm. That's only true for experiments using photons traveling in vacuum. Some
> of these experiments transport them in fiber optic cables, and I believe that
> other experiments use electrons. Moreover, the experiments are about SPIN
> CORRELATIONS, not electromagnetic interactions.
This is true, and this bothers me somewhat. On the other hand there
seems to be a difference in the interactions between the "photon" and
the glass and the act of being absorbed or detected. Consider a
simpler case, the reflection of a photon from a metallic mirror. The
photon is interacting with many many electrons in the metal mirror
simultaneously. After reflection the photon is then propagating at
the speed of light again towards the detector. From the point of view
of the detector, the source of the photon is the image of the true
source in the mirror, and that image is on the past light cone of the
detector. Never the less, the emitter and absorber can be time-like
separated (e.g. they could be right next to each other, connected
optically only by the reflection). This argument can be extended to
many reflections. Refraction can be considered to be a continuous
bulk interaction with electrons. Detection, on the other hand, is the
termination of the energy transfer.
I don't consider this a very convincing argument, but it's the best I
have so far.
> > [...] some negatives that do bother me [about his idea] are:
> > -it implies that the state of A and B are 'fixed' already when the
> > photons are emitted by O.
>
> That is ruled out by experiments. Look at the "delayed choice" type of EPR
> experiments.
I disagree on this. In the "delayed choice" experiments, if you look
at the event from the point of view of the detector there is no
paradox. Remember that the only thing the detector sees is its own
past light cone. At the moment that the detector detects a photon in
these experiments, the detector can "see" the emitter directly. There
is nothing surprising. I think the paradox implied by these
experiments is the result of looking at it from the wrong point of
view, that of the emitter at the moment of emission.
Our concept of causality and the way time works needs revision. I am
convinced of this. We tend to think in terms of disturbances
propagating into the future, unaffected by the future. The Aspect
experiments show that this doesn't work, that the future has subtle
effects on current events. This is quite different from our every day
experience, but quantum mechanical events are different. The
correlations we see cannot happen unless there is some interaction
from the future, but it is subtle.
This touches on one of the main concepts I am trying to develop, that
we should not be thinking in terms of "now" in the sense of
synchronized clocks like we do in special relativity, but rather in
terms of the past light cone. Especially when you get into general
relativity there really is no workable concept of "now". The only
thing that has any meaning is the past light cone.
> > For example, if the photon is from the
> > cosmological background radiation, and we are receiving it now, this
> > implies that the receiving atoms state was already set billions of
> > years ago.
>
> But you ought to be consistent. In your approach, it was "set" _ZERO_ time ago
> because the source is on the past lightcone of the receiving atom. These photons
> are traveling in vacuum (well, presumably close enough...). This is no different
> in principle from source and receiver being separated by millimeters -- it only
> differs in scale.
Exactly! If you think about the apparent paradoxes in quantum
mechanics as if there is instantaneous communication along the light
cone, many of them make perfect sense, such as the Aspect experiments,
delayed choice experiments and Rabi oscillations.
> > This certainly messes with most peoples ideas of causality
> > and especially self determination...
>
> But so do quantum mechanics and QED. At least they have the virtue of being
> consistent with the experiments within their domains.
As far as I can tell, the interpretation I'm working on is consistent
with experiments as well. Note that Bohm's pilot wave theory was
shown to be completely consistent with observed physics. What I'm
thinking about would actually be a simplification of that idea, just
by recognizing that events on the light cone can be considered to be
co-located, in a sense, at least for EM interactions.
I'm not ready to say I think this is correct yet (I'm more
conservative than that), and I certainly am not ready to ask anyone
else to believe these ideas, but I am interested in hearing criticism
and arguments. Thanks for responding,
Rich L.
Rich L.
...
> As far as I can tell, the interpretation I'm working on is consistent
> with experiments as well. Note that Bohm's pilot wave theory was
> shown to be completely consistent with observed physics. What I'm
> thinking about would actually be a simplification of that idea, just
> by recognizing that events on the light cone can be considered to be
> co-located, in a sense, at least for EM interactions.
> Rich L.
I mis-spoke (mis-typed?) in the above. Instead of the Bohm pilot wave
theory I meant the Transactional Interpretation of Quantum Mechanics
(TIQM).
Rich L.
brad
> �After reflection the photon is then propagating at
> the speed of light again towards the detector. �From the point of view
> of the detector, the source of the photon is the image of the true
> source in the mirror, and that image is on the past light cone of the
> detector.
Hasn't the original EM radiation been absorbed and what is
subsequently
observed has been reemitted from internal electrons in the mirror (at
least
a metal one) as they drop back down into a ground state? Essentially
the
image is correlated new photons?
>
> Our concept of causality and the way time works needs revision. �I am
> convinced of this.
In my opinion we conflate two "types" of time. One type measures
intervals
we use for living.
The other type is related to the gravitational field and accelerated
motion. Because we
live inside a gravitational well we don't intuitively recognize that
Time varies according to
ones' position.
It seems logical that every location in the Universe must realize its
own measure of Time
according to its relationship to its local gravitational well.
Because a reference frame can be chosen for any location in the
Universe that yields
an inertial point of view, so also can we choose to find references
that force us to
accept that any reference frame can be considered to be accelerated.
It implies that every location in the Universe must evolve to its own
clock!
When we look out into the Universe we must be seeing only a
statistical representation of its
evolution! To attempt to turn the clock back to a BB is to apply our
own colloquial view of Time
to the Universe.
Brad
Alex
...
>
> A mathematical field is a continuous function of all the spatial
> separation variables. This may be used to describe the variation of
> potential over space, when it is being used simply as a mathematical
> intermediary in a larger calculational context.
>
> Or, a field may be used to represent the reality of an ontogical
> entity, as Maxwell did for representing the luminiferous aether in his
> EM theory. Such a usage implies other physical consequences above and
> beyond the mathematical implications.
>
> The question is: which usage is the psi function playing in QM or QFT?
It is an *auxiliary* mathematical object, which:
1. is supposed to describe the system's state
2. has no *direct* meaning by itself (in particular because it is complex
and defined in the *configuration* space of the system, not in the physical
space)
3. the physical properties are bilinear forms of psi and operators, which
are real function of space, time, spin and other variables.
Because of (2), a quantum system is *not* a wave in the physical space. It
follows, in particular, that all the interpretations of the double slit
through difraction and interference of waves have an heuristic at best.
The only correct explanation of the results of double slit experiments is
obtained by solving - numerically if necessary - the Schrödinger equation
with boundary conditions for the specific experimental setup.
Alex
maxwell
> On Wed, 27 Oct 2010 12:57:22 CST, maxwell wrote:
>
>
>
>
> > A mathematical field is a continuous function of all the spatial
> > potential over space, when it is being used simply as a mathematical
> > intermediary in a larger calculational context.
>
> > Or, a field may be used to represent the reality of an ontogical
> > entity, as Maxwell did for representing the luminiferous aether in his
> > beyond the mathematical implications.
>
> > The question is: which usage is the psi function playing in QM or QFT?
>
> It is an *auxiliary* mathematical object, which:
>
> 1. is supposed to describe the system's state
>
> 2. has no *direct* meaning by itself (in particular because it is complex
> and defined in the *configuration* space of the system, not in the physical
> space)
>
> 3. the physical properties are bilinear forms of psi and operators, which
> are real function of space, time, spin and other variables.
>
> Because of (2), a quantum system is *not* a wave in the physical space. It
> follows, in particular, that all the interpretations of the double slit
> through difraction and interference of waves have an heuristic at best.
>
> The only correct explanation of the results of double slit experiments is
> with boundary conditions for the specific experimental setup.
>
> Alex
Agreed, Alex. All this math is a fiction - just stages in a math
calculation. Only in Platonia (the timeless world of the
mathematicians) do calculational symbols take on the role of reality.
The real world is discrete but mathematicians having been developing
continuum math for centuries & will not admit this is only an
approximation to reality.
Materion
Some thoughts about what you wrote.
On Nov 5, 6:32 pm, Alex <alexlREM...@REMOVEsolnet.ch> wrote:
> On Wed, 27 Oct 2010 12:57:22 CST, maxwell wrote:
>
> > ...
>
> > The question is: which usage is the psi function playing in QM or QFT?
>
> It is an *auxiliary* mathematical object
All mathematical objects are auxiliary to physical natural reality.
> , which:
>
> 1. is supposed to describe the system's state
Yes.
> 2. has no *direct* meaning by itself (in particular because it is complex
> and defined in the *configuration* space of the system, not in the physical
> space)
Complex values and configuration space have a direct meaning when
describing physical objects. Complex values = amplitude, phase and
angle differences. Configuration space: physical space organized by
allowed measurement values.
> 3. the physical properties are bilinear forms of psi and operators, which
> are real function of space, time, spin and other variables.
physical properties are described by ...
> Because of (2), a quantum system is *not* a wave in the physical space. It
> follows, in particular, that all the interpretations of the double slit
> through difraction and interference of waves have an heuristic at best.
Because of (2), a wave in the physical space is an analogy of a
quantum system. OK for heuristic property of interpretations: it is
therefore very important to develop such interpretations.
> The only correct explanation of the results of double slit experiments is
> obtained by solving - numerically if necessary - the Schrödinger equation
> with boundary conditions for the specific experimental setup.
A mathematical explanation is auxiliary, see (1). It is a convenient
(formal) interpretation among others, which benefits when seen in a
wider context of other interpretations.
Regards,
Arjen
Alex
> All mathematical objects are auxiliary to physical natural reality.
To the physical reality - yes, but not to a physical theory. A physical
theory is a mathematical formalism plus the *interpretation* of (some) the
symbols. Interpretation means pointing to what element of realitx the
symbol is supposed to correspond.
About interpreting the solutions of the Schrödinger equation (SE) for a
system of particles as a real wave in the physical space:
In classical physics one studies sound waves in the air and other gases, in
liquids and solids, electromagnetic waves. One desribes them through
various wave equarions. The solutions of those equations represent some
kind of disturbation (instantaneous values of pressure, of displacement, of
the electric/magnetic fields) and are purely real functions (that is
numbers). It is true that, in some cases, one attempts to solve the wave
equations by trying complex solutions, but at the end one retains as
solution the real part only. The use of complex functions is a purely
mathematical device, a *method* of solving those (real) equations.
The solutions of the SE, however, are *essentially* complex: their real or
imaginary parts taken separately are not solutions of the SE. The SE
contains an "i", the imaginary "unit", and this is one of the causes of the
fact that the solutions are essentially complex. The wave equations of the
"classical waves" do not contain "i". Therefore, psi cannot be interpreted
as a true wave.
> Complex values and configuration space have a direct meaning when
> describing physical objects. Complex values = amplitude, phase and
> angle differences.
Those are *mathematical* interpretations of complex numbers, not physical.
> Configuration space: physical space organized by
> allowed measurement values.
The configuration space of a system of N particles is 3*N-dimentional; the
physical space is 3-dimentional. For N>1 the configuration space is no kind
of "organization" of the physical space.
> physical properties are described by ...
Correction accepted.
> ... a wave in the physical space is an analogy of a
> quantum system. OK for heuristic property of interpretations: it is
> therefore very important to develop such interpretations.
It *was* important - during the construction of what is now called "the old
QM", as a heuristic tool. The wave analogy brakes completely for N > 1.
>> The only correct explanation of the results of double slit experiments is
>> obtained by solving - numerically if necessary - the Schrödinger equation
>> with boundary conditions for the specific experimental setup.
>
> A mathematical explanation is auxiliary, see (1). It is a convenient
> (formal) interpretation among others, which benefits when seen in a
> wider context of other interpretations.
To *explain* a phenomenon within a physical theory means showing how this
phenomenon *follows* from the theory ( theory = mathematical formalism +
physical interpretation) and additional, system-specific, assumptions.
Regards
Alex
Alex
> All this math is a fiction ...
Absolutely not.
> The real world is discrete but mathematicians having been developing
> continuum math for centuries & will not admit this is only an
> approximation to reality.
Mathematical tools to takle descreteness do exist. What does not exist is
the proof that the continuum hypothesis is false at *any* level of
approximation of the real world.
Alex
Oh No
There certainly is, and can be, no proof that the continuum hypothesis
is true. Surely science should only consider what can be proven, one way
or the other. Otherwise it is mere speculation. However, I do not think
it is true that there is no proof that the continuum hypothesis is
false. It appears to me that the mathematics of quantum theory is true
precisely because there is no underlying continuum, which would enable
us to say, as we cannot, that particles have precise position.
Tom Roberts
> All this math is a fiction
Say, rather, that it is a MODEL. After all, making models is the only way we
humans have of understanding the world we inhabit.
Tom Roberts
Tom Roberts
> I do not think
> it is true that there is no proof that the continuum hypothesis is
> false. It appears to me that the mathematics of quantum theory is true
> precisely because there is no underlying continuum, which would enable
> us to say, as we cannot, that particles have precise position.
Quantum Field Theory models the world as a 4-d spacetime manifold, which is
necessarily continuous. The mathematics of quantum theory inherently depends on
this (continuous) manifold. Yet it is still true that particles do not have
precise positions. The presence of a (continuous) spacetime manifold in this
model does not mean that particles (quantum objects) have precise positions --
they don't. The simple reason for this is that in QFT a particle's position is
not a function on the manifold, it is an operator on the appropriate Hilbert space.
Your first sentence implies that you think there is a proof that the continuum
hypothesis is false. Presumably you are thinking of some underlying theory of
which QFT is some limit. Until you actually produce such a theory and
demonstrate that limit, there _IS_ no such proof. Good luck -- a lot of smart
people have been trying to do that for many decades....
[I'm ignoring the obvious fact that there can be no "proof" about
the structure of the world we inhabit; at best all we humans can
have are models valid in a given domain....]
Tom Roberts
Alex
> Thus spake Alex <alexl...@REMOVEsolnet.ch>
>>Mathematical tools to takle descreteness do exist. What does not exist is
>>the proof that the continuum hypothesis is false at *any* level of
>>approximation of the real world.
>>
>
> There certainly is, and can be, no proof that the continuum hypothesis
> is true. Surely science should only consider what can be proven, one way
> or the other. Otherwise it is mere speculation. However, I do not think
> it is true that there is no proof that the continuum hypothesis is
> false.
But I did not claim such a thing: please note that there is no full stop
after the word "false" in *my* claim.
> It appears to me that the mathematics of quantum theory is true
> precisely because there is no underlying continuum, which would enable
> us to say, as we cannot, that particles have precise position.
I am not sure what you mean by your claim that in the mathematics of the
quantum theory "there is no underlying continuum." I'll only note that
<psi> is a function of 3*N+1 parameters which are supposed to be
continuous. So that at least the underlying configuration space and the
time arre supposed to be contiinuums.
Alex
Oh No
>On 11/8/10 11/8/10 - 9:06 AM, Oh No wrote:
>> I do not think
>> it is true that there is no proof that the continuum hypothesis is
>> false. It appears to me that the mathematics of quantum theory is true
>> precisely because there is no underlying continuum, which would enable
>> us to say, as we cannot, that particles have precise position.
>
>Quantum Field Theory models the world as a 4-d spacetime manifold,
>which is necessarily continuous.
One should distinguish mathematical structure, which is just idea, from
reality, which is something more than idea. QFT contains this
mathematical structure. It does not say that the mathematical structure
is a description of reality.
>The mathematics of quantum theory inherently depends on this
>(continuous) manifold. Yet it is still true that particles do not have
>precise positions. The presence of a (continuous) spacetime manifold in
>this model does not mean that particles (quantum objects) have precise
>positions -- they don't. The simple reason for this is that in QFT a
>particle's position is not a function on the manifold, it is an
>operator on the appropriate Hilbert space.
Saying something is an operator on a Hilbert space is just mathematical
jargon. That is not part of a model of the world, to use your own word,
because a model is, by definition, an imitation of reality.
>
>Your first sentence implies that you think there is a proof that the
>continuum hypothesis is false. Presumably you are thinking of some
>underlying theory of which QFT is some limit. Until you actually
>produce such a theory and demonstrate that limit, there _IS_ no such
>proof. Good luck -- a lot of smart people have been trying to do that
>for many decades....
That is already done. *If you wish to say otherwise, then you must find
a mathematical fault.
> [I'm ignoring the obvious fact that there can be no "proof" about
> the structure of the world we inhabit; at best all we humans can
> have are models valid in a given domain....]
I wish you would get off this one about models, because it is really
rather trivial. Certainly we can believe that reality is just a dream,
or that a tree does not continue to be when there is no one to observe
it if we so desire. But that takes us outside of the realm of science,
which assumes that there is a reality and that we can study it.
Oh No
>On Mon, 8 Nov 2010 09:06:26 CST, Oh No wrote:
>
>> Thus spake Alex <alexl...@REMOVEsolnet.ch>
>
>>>Mathematical tools to takle descreteness do exist. What does not exist is
>>>the proof that the continuum hypothesis is false at *any* level of
>>>approximation of the real world.
>>>
>>
>> There certainly is, and can be, no proof that the continuum hypothesis
>> is true. Surely science should only consider what can be proven, one way
>> or the other. Otherwise it is mere speculation. However, I do not think
>> it is true that there is no proof that the continuum hypothesis is
>> false.
>
>But I did not claim such a thing: please note that there is no full stop
>after the word "false" in *my* claim.
Then I am not parsing your sentence correctly. Perhaps you could expand
and clarify your point. If you mean that the continuum hypothesis is
true at some level of approximation, then I would have said that is
trivial. I thought you meant to deny that.
>
>> It appears to me that the mathematics of quantum theory is true
>> precisely because there is no underlying continuum, which would enable
>> us to say, as we cannot, that particles have precise position.
>
>I am not sure what you mean by your claim that in the mathematics of the
>quantum theory "there is no underlying continuum." I'll only note that
><psi> is a function of 3*N+1 parameters which are supposed to be
>continuous. So that at least the underlying configuration space and the
>time arre supposed to be contiinuums.
Before attempting to understand quantum theory, it is in my view
undoubtedly a good idea to have a clear understanding of the Bayesian
interpretation of probability theory. We can have continuous probability
distributions for the reason that probabilities are ideas, products of
mind, not elements of reality.
In the same way we can have a mathematical notion of a continuum in
quantum theory, and we can define wave functions on this continuum
(whose only role is to generate probabilities) without suggesting that
this continuum is a part of nature. When I said "there is no underlying
continuum", I meant to imply that there is no underlying continuum as an
objective, or substantive, part of nature.
maxwell
No, its not a model; its proponents add a lot more than mathematics.
Like Maxwell's "gears & wheels" - that was a model of the aether.
A set of mathematical symbols & logic rules is just math, not a model.
A model is an abstraction from reality - it offers insights &
understanding.
Newton's theory of gravitation was a model - it was very insightful.
Tom Roberts
> On Nov 8, 8:58 am, Tom Roberts<tjrob...@sbcglobal.net> wrote:
>> On 11/6/10 11/6/10 - 1:09 PM, maxwell wrote:
>>> All this math is a fiction
>> Say, rather, that it is a MODEL. After all, making models is the only way we
>> humans have of understanding the world we inhabit.
>
Yes, it is. That what all theories of physics are, MODELS.
The purpose of a model is to be able to use it to make predictions about the
world we inhabit.
> its proponents add a lot more than mathematics.
That doesn't matter; indeed, more than mere mathematics is necessary for a set
of equations to be a physical theory -- one must describe what the symbols in
them mean.
In math, the symbols have no meanings; in physical theories, the symbols used in
the equations are related to quantities we can observe in the world.
> Like Maxwell's "gears& wheels" - that was a model of the aether.
Sure. There are many kinds of models. Theories of physics are mathematical models.
> A set of mathematical symbols& logic rules is just math, not a model.
Sure. But physical theories are equations and descriptions of the symbols that
appear in them, relating the symbols to quantities we can observe in the world
we inhabit.
> A model is an abstraction from reality - it offers insights&
> understanding.
Right. All physical theories are like that (well, at least the good ones :-)).
> Newton's theory of gravitation was a model - it was very insightful.
Sure. SR, GR, QED, and the standard model are even more so.
Tom Roberts
Alex
> If you mean that the continuum hypothesis is
> true at some level of approximation,...
Yes, this is what I mean.
> ... then I would have said that is
> trivial.
Then we do agree at least on this trivial matter :-)
>>I am not sure what you mean by your claim that in the mathematics of the
>>quantum theory "there is no underlying continuum."
>... When I said "there is no underlying
> continuum", I meant to imply that there is no underlying continuum as an
> objective, or substantive, part of nature.
You said that *in the mathematics* of the QT there is no underlying
continuum. Do you mean that the mathematics of, for example QM and QED,
does *not* assume the continuity of some elements of reality, respectively
of their mathematical correspondent? I claim that the mathematics of QM and
QED *assumes* that the real space is a continuum, and represents it in the
formalism by an 3-dim Euclidean space.
If you agree with this and consider it trivial too, then we agree on a
second trivial matter, which is wonderful :-)
Regards
Alex
Tom Roberts
>> which is necessarily continuous.
>
> One should distinguish mathematical structure, which is just idea, from
> reality, which is something more than idea.
Hmmm. Close, but not right. You allude to the difference between world and model
-- what you call "idea" is part of what the rest of us call "model". But there
is no method of comparison between "idea"/model and "reality" by which one could
apply "more than" -- they are COMPLETELY DISPARATE AND INCOMMENSURATE.
The statement "three is more than blue" is just as nonsensical as
your "reality is something more than idea". For instance, "reality"
has nothing whatsoever to do with "idea".
> QFT contains this
> mathematical structure. It does not say that the mathematical structure
> is a description of reality.
No; I never said or implied that it did. But QFT does provide techniques to use
the model to make predictions about experimental results in the world we
inhabit. And those techniques inherently rely on "this mathematical structure"
(the spacetime manifold). So it is not pure fantasy, either -- it is part of the
model.
Later on you say that my discussion of the relationship between models and the
world is "really rather trivial", yet right here you show that you do not really
understand it. The manifold, and the rest of the mathematical structure of QFT,
are parts of the model called QFT, which _IS_ a description of "reality", within
its domain. That is, the model enables one to make predictions about
experimental results in the world we inhabit. But that does not mean that the
model actually corresponds to any physical phenomena in the world, or that any
part of the model has such a correspondence. All we know is that this particular
model gives accurate predictions of experimental results within its domain of
applicability.
>> in QFT a
>> particle's position is not a function on the manifold, it is an
>> operator on the appropriate Hilbert space.
>
> Saying something is an operator on a Hilbert space is just mathematical
> jargon.
No. It is "saying something" about how position is modeled in this particular
model. My point was that this refutes your implication that the presence of a
continuous manifold implies positions can be specified to infinite precision --
in this model that manifold is not used to specify positions of objects, it is
merely a base manifold to which the fields are referenced. The fields are
functions on the manifold [#], but positions are not modeled that way.
[#] Or equivalently, the fields are the fibers of a fiber bundle
on that manifold, or sections of the bundle (depends on how words
are used).
> That is not part of a model of the world, to use your own word,
> because a model is, by definition, an imitation of reality.
See -- there you go again, not understanding what a model actually is. I repeat:
in this context a model is a set of equations, and descriptions of their
symbols, that permit one to make predictions about experimental results in the
world we inhabit.
Your word "imitation" is both too strong and too weak: it is too strong in that
we humans can never know how well such an "imitation" might be; after all, all
we ever know about the relationship between model and world is how accurately
the model works and what domain it covers -- we have no access to "what is
really out there". Your word "imitation" is too weak, in that a mere "imitation"
could not generate predictions about experiments in the real world, and could
not teach us something about understanding our models of the world.
>> Your first sentence implies that you think there is a proof that the
>> continuum hypothesis is false. Presumably you are thinking of some
>> underlying theory of which QFT is some limit. Until you actually
>> produce such a theory and demonstrate that limit, there _IS_ no such
>> proof. Good luck -- a lot of smart people have been trying to do that
>> for many decades....
>
> That is already done. *If you wish to say otherwise, then you must find
> a mathematical fault.
> http://rqgravity.net/Papers
.... that will take a while ...
>> [I'm ignoring the obvious fact that there can be no "proof" about
>> the structure of the world we inhabit; at best all we humans can
>> have are models valid in a given domain....]
>
> I wish you would get off this one about models, because it is really
> rather trivial.
But you keep getting it wrong. This is a fundamental limitation of humans and
their attempts to understand the world they inhabit -- it is ESSENTIAL to
understanding modern physics.... It is also a major departure from "classical"
physics, by which I mean roughly before the 1920s or so -- back then they really
thought they were describing how the world actually worked; it was with quantum
theory, its successes, and its structure that we learned how limited we humans
really are....
> Certainly we can believe that reality is just a dream,
> or that a tree does not continue to be when there is no one to observe
> it if we so desire. But that takes us outside of the realm of science,
> which assumes that there is a reality and that we can study it.
That has NOTHING WHATSOEVER to do with what "model" means in physics.
Tom Roberts
Oh No
>On Tue, 9 Nov 2010 15:00:45 CST, Oh No wrote:
>
>> If you mean that the continuum hypothesis is
>> true at some level of approximation,...
>
>Yes, this is what I mean.
>
>> ... then I would have said that is
>> trivial.
>
>Then we do agree at least on this trivial matter :-)
Excellent.
>
>>>I am not sure what you mean by your claim that in the mathematics of the
>>>quantum theory "there is no underlying continuum."
>
>>... When I said "there is no underlying
>> continuum", I meant to imply that there is no underlying continuum as an
>> objective, or substantive, part of nature.
>
>You said that *in the mathematics* of the QT there is no underlying
>continuum. Do you mean that the mathematics of, for example QM and QED,
>does *not* assume the continuity of some elements of reality, respectively
>of their mathematical correspondent? I claim that the mathematics of QM and
>QED *assumes* that the real space is a continuum, and represents it in the
>formalism by an 3-dim Euclidean space.
>
>If you agree with this and consider it trivial too, then we agree on a
>second trivial matter, which is wonderful :-)
I don't think we agree on this much more subtIe issue. Mathematics, on
its own, makes no assumptions outside of its own structures. The
correspondence between mathematics and reality is strictly philosophy,
not mathematics.
There may be many physicists who assume that the continuum which appears
in the mathematical structure of QFT corresponds to an element of
reality. That is not, however, the "official" position of quantum field
theorists, who are more likely to say that only the numerical
predictions corresponding to experimental results correspond to elements
of reality.
My position is neither of those. I construct the mathematical structures
of QFT from assumptions in which particles are treated as elements of
reality, and the spacetime continuum is not.
Oh No
>> mathematical structure. It does not say that the mathematical structure
>> is a description of reality.
>
>No; I never said or implied that it did. But QFT does provide
>techniques to use the model to make predictions about experimental
>results in the world we inhabit. And those techniques inherently rely
>on "this mathematical structure" (the spacetime manifold). So it is not
>pure fantasy, either -- it is part of the model.
>
>Later on you say that my discussion of the relationship between models
>and the world is "really rather trivial", yet right here you show that
>you do not really understand it. The manifold, and the rest of the
>mathematical structure of QFT, are parts of the model called QFT, which
>_IS_ a description of "reality", within its domain. That is, the model
>enables one to make predictions about experimental results in the world
>we inhabit. But that does not mean that the model actually corresponds
>to any physical phenomena in the world, or that any part of the model
>has such a correspondence.
You just said it did. I.e. that the predictions correspond to
experimental results. If there were no correspondence it would not be a
model of anything at all.
>
>>> in QFT a
>>> particle's position is not a function on the manifold, it is an
>>> operator on the appropriate Hilbert space.
>> Saying something is an operator on a Hilbert space is just
>>mathematical
>> jargon.
>
>No. It is "saying something" about how position is modeled in this
>particular model.
You are abusing the word "model" which implies a correspondence between
the model and the thing being modelled. It is invariably the case that
parts of a model model nothing at all.
>My point was that this refutes your implication that the presence of a
>continuous manifold implies positions can be specified to infinite
>precision -- in this model that manifold is not used to specify
>positions of objects, it is merely a base manifold to which the fields
>are referenced. The fields are functions on the manifold [#], but
>positions are not modeled that way.
Please don't put words into my mouth. It does not help any form of
intelligent discussion
> [#] Or equivalently, the fields are the fibers of a fiber bundle
> on that manifold, or sections of the bundle (depends on how words
> are used).
Reliance on jargon is unimpressive.
>> That is not part of a model of the world, to use your own word,
>> because a model is, by definition, an imitation of reality.
>
>See -- there you go again, not understanding what a model actually is.
>I repeat: in this context a model is a set of equations, and
>descriptions of their symbols, that permit one to make predictions
>about experimental results in the world we inhabit.
If you mean to say that qft is just a bunch of algorithms which give
experimental results, then you should say that. It would a) be much
more conventional, and b) avoid abusing the word model.
>
>>If you wish to say otherwise, then you must find
>> a mathematical fault.
>> http://rqgravity.net/Papers
>
>.... that will take a while ...
>
I'm afraid so. But no one suggested this could be easy.
>
>>> [I'm ignoring the obvious fact that there can be no "proof" about
>>> the structure of the world we inhabit; at best all we humans can
>>> have are models valid in a given domain....]
>> I wish you would get off this one about models, because it is really
>> rather trivial.
>
>But you keep getting it wrong. This is a fundamental limitation of
>humans and their attempts to understand the world they inhabit -- it is
>ESSENTIAL to understanding modern physics.... It is also a major
>departure from "classical" physics, by which I mean roughly before the
>1920s or so -- back then they really thought they were describing how
>the world actually worked; it was with quantum theory, its successes,
>and its structure that we learned how limited we humans really are....
What you mean is, we found a theory we couldn't understand, so we
developed a philosophy that physics does not need to be understood.
Sorry, I am not going to accept that philosophy. I say it is perfectly
possible to understand why an underlying reality consisting
fundamentally of particles and in which space and spacetime are emergent
gives rise to precisely the mathematical structures of quantum field
theory which we verify through experiment. We do have to dispense with
preconceptions. That is not easy. It is possible, nonetheless.
>> Certainly we can believe that reality is just a dream,
>> or that a tree does not continue to be when there is no one to observe
>> it if we so desire. But that takes us outside of the realm of science,
>> which assumes that there is a reality and that we can study it.
>
>That has NOTHING WHATSOEVER to do with what "model" means in physics.
However it does have a great deal to do with the rise of half baked
philosophies to cope with the fact of failure to understand the meaning
of modern physical theory.
Alex
>>...I claim that the mathematics of QM and
>>QED *assumes* that the real space is a continuum ...
> ... Mathematics, on
> its own, makes no assumptions outside of its own structures.
Speaking even more strictly, mathematics makes no assumption whatsoever,
only people do ;-)
Quite obviously, what I meant is that physicists , in their search for
adequate mathematical objects, choose those which are supposed -
hypothetically - to "represent" some treats of reality. If the resulting
theory is successful, they conclude that their assumptions were, probably
and contextually, correct. Otherwise, the re-examine every assumption, not
forgetting, however, that extraordinary claims require extraordinary
evidence ;-)
> correspondence between mathematics and reality is strictly philosophy,
> not mathematics.
True, it is not mathematics. Neither is this correspondence pure
philosophy (unless you mean "natural philosophy" :-). Specifying this
correspondence is an indispensable *constituent* of a physical theory.
Indeed, a physical theory must specify to what elements of reality do (some
of) the mathematical constructs correspond.
> [Some] theorists ... say that only the numerical
> predictions corresponding to experimental results correspond to elements
> of reality.
*Before* comparing numerical prediction, and producing experimental
results, the physicist have to first make assumptions as to *what*
construct of the formalism (to measure and then) to compare with what
element of reality.
If (at lest some of) the elements of your formalism are not interpreted,
you won't be able to test anything. An uninterpreted formalism is not
testable. Testability *presupposes" interpretation. An uninterpreted
formalism is pure mathematics.
> ... I construct the mathematical structures
> of QFT from assumptions in which particles are treated as elements of
> reality, and the spacetime continuum is not.
I assume you wished to say that you were not assuming apriori that the
space-time is a continuum. Or you try to suggest that space and time are
*not* real (in at least *some* sense) ?
Regards
Alex
Oh No
>On Thu, 11 Nov 2010 05:28:29 CST, Oh No wrote:
>
>>>...I claim that the mathematics of QM and
>>>QED *assumes* that the real space is a continuum ...
>
>> ... Mathematics, on
>> its own, makes no assumptions outside of its own structures.
>
>Speaking even more strictly, mathematics makes no assumption whatsoever,
>only people do ;-)
>
>Quite obviously, what I meant is that physicists , in their search for
>adequate mathematical objects, choose those which are supposed -
>hypothetically - to "represent" some treats of reality. If the resulting
>theory is successful, they conclude that their assumptions were, probably
>and contextually, correct.
This is perhaps how things once were, but the more modern position of
physicists is to make no assumption regarding the meaning of their
assumptions (sorry), and only require correspondence between predictions
and experiment.
>> correspondence between mathematics and reality is strictly philosophy,
>> not mathematics.
>
>True, it is not mathematics. Neither is this correspondence pure
>philosophy (unless you mean "natural philosophy" :-).
yes
>Specifying this
>correspondence is an indispensable *constituent* of a physical theory.
>Indeed, a physical theory must specify to what elements of reality do (some
>of) the mathematical constructs correspond.
>
>> [Some] theorists ... say that only the numerical
>> predictions corresponding to experimental results correspond to elements
>> of reality.
>
>*Before* comparing numerical prediction, and producing experimental
>results, the physicist have to first make assumptions as to *what*
>construct of the formalism (to measure and then) to compare with what
>element of reality.
Oh, don't take me too far down this route. This is not my position, and
I do not even believe that these theorists are capable of maintaining a
consistent argument regarding their position. In practice they run away
from such arguments saying "philosophy is not physics", "it is not the
business of physics to discuss such questions". As far as I can tell
many of them are quite happy to be inconsistent, because they will say
that "the fundamental entities are fields", and at the same time say
that "there is no fundamental description of matter, only correspondence
between prediction and experiment". I merely remark that this is the
modern "orthodox" position. Tom may have more wish to defend it than I.
>
>If (at lest some of) the elements of your formalism are not interpreted,
>you won't be able to test anything. An uninterpreted formalism is not
>testable. Testability *presupposes" interpretation. An uninterpreted
>formalism is pure mathematics.
>
>> ... I construct the mathematical structures
>> of QFT from assumptions in which particles are treated as elements of
>> reality, and the spacetime continuum is not.
>
>I assume you wished to say that you were not assuming apriori that the
>space-time is a continuum. Or you try to suggest that space and time are
>*not* real (in at least *some* sense) ?
Difficult to say "not real", because reality contains things which are
composed of other things, and which are such that our idea of them is
clearly an approximation. One has to say something like "not elemental",
or "not fundamental", or "emergent", meaning that the concept has no
meaning in a fundamental description, but does have meaning when the
properties of elemental quantities are combined (much as "wood" has no
immediate meaning in a description of matter as composed of electrons,
protons and neutrons).
Alex
>>physicists , in their search for
>>adequate mathematical objects, choose those which are supposed -
>>hypothetically - to "represent" some treats of reality.
> This is perhaps how things once were, but the more modern position of
> physicists is to make no assumption regarding the meaning of their
> assumptions (sorry), ...
Whole theories with not a single interpreted symbols ? Those are unrestable
and lead nowhere. Waste of - mostly - taxpayer's money.
>>> correspondence between mathematics and reality is strictly philosophy,
>>> not mathematics.
>>
>>True, it is not mathematics. Neither is this correspondence pure
>>philosophy (unless you mean "natural philosophy" :-).
>
> yes
Yes ... what?
Regards
Alex
Oh No
>On Fri, 12 Nov 2010 04:19:04 CST, Oh No wrote:
>
>>>physicists , in their search for
>>>adequate mathematical objects, choose those which are supposed -
>>>hypothetically - to "represent" some treats of reality.
>
>> This is perhaps how things once were, but the more modern position of
>> physicists is to make no assumption regarding the meaning of their
>> assumptions (sorry), ...
>
>Whole theories with not a single interpreted symbols ? Those are unrestable
>and lead nowhere. Waste of - mostly - taxpayer's money.
I'm afraid so. This does, imv, have a great deal to do with the reasons
for lack of progress in theoretical physics for the last 50 or so years.
>
>>>> correspondence between mathematics and reality is strictly philosophy,
>>>> not mathematics.
>>>
>>>True, it is not mathematics. Neither is this correspondence pure
>>>philosophy (unless you mean "natural philosophy" :-).
>>
>> yes
>
>Yes ... what?
>
Yes, that is what I mean.
Alex
>>>>> correspondence between mathematics and reality is strictly philosophy,
>>>>> not mathematics.
>>>>
>>>>True, it is not mathematics. Neither is this correspondence pure
>>>>philosophy (unless you mean "natural philosophy" :-).
>>>
>>> yes
>>
>>Yes ... what?
>>
> Yes, that is what I mean.
I still don't know what you mean :-(
"Natural philosophy" is simply an older term for, mainly, physics.
Therefore, your agreement referrs to which one of those two claims ?:
- correspondence between mathematics and reality is the field of pure
philosophy, or
- correspondence between mathematics and reality is the field of physics,
which is my position
Regards
Alex
Oh No
I mean correspondence between mathematics and reality is the field of
natural philosophy.
To me natural philosophy includes discussions on the interpretation of
physics. Such discussions are, for example, very much a part of this ng,
but they are not much accepted on s.p.research, which takes a more
narrow view of what is meant by physics.
Alex
>>Therefore, your agreement referrs to which one of those two claims ?:
>>
>>- correspondence between mathematics and reality is the field of pure
>>philosophy, or
>>- correspondence between mathematics and reality is the field of physics,
>>which is my position
>>
>
> I mean correspondence between mathematics and reality is the field of
> natural philosophy.
Just for the record: taking iton account the context of our discussion, we
are talking specifically about:
the correspondence between the *mathematical formalism of
a physical theory* and reality (also called "interpretation")
and not about correspondence between mathematics and reality *in general*.
Regards
Alex
Oh No
no correspondence with reality in general.
glird
>
><When I said "there is no underlying
continuum", I meant to imply that there is no underlying continuum as
an objective, or substantive, part of nature. >
That implication is false.
There IS a continuous material everywhere. It is the conducting
medium of light. It exerts an expansive pressure -- the "psi" in
Schrodinger's probability paper -- from every point in the space it
fills. It is this material out of which particles, including atoms
and molecules, are made.
The fact that Physics denies that this substance exists doesn't
change any of those things.
glird
Daniel Baumgarten
If there is a continuous material everywhere, then discrete quanta
cannot possibly be composed of it. A continuum is infinitely divisible,
and a quantum is not divisible at all. The reason for denying the
substantive actuality of a continuum is precisely that nowhere in nature
is anything observed to be infinitely divisible. That property is purely
a convenience of abstraction.