Does the double slit experiment work at low radio frequencies?

  • 61 Replies
  • 20987 Views

0 Members and 1 Guest are viewing this topic.

*

Offline Geezer

  • Neilep Level Member
  • ******
  • 8328
  • "Vive la résistance!"
    • View Profile
Would it be possible to run a version of the double-slit experiment http://en.wikipedia.org/wiki/Double-slit_experiment using much lower frequencies than visible RF, perhaps in the microwave range?

If so, would we expect to observe the same results that we observe with visible RF?
There ain'ta no sanity clause, and there ain'ta no centrifugal force ćther.

*

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • 12188
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
" The way to show wave nature of light is with interference experiments (ie double slit). This would actually be much easier to do with radio waves, given their longer wavelength.

The particle nature you can show via quantization, as in the photoelectric effect. So you'd need an absorber of radio waves. It would be very difficult to perform, especially with the cosmic microwave background radiation cuddling  everything up.

The second is defined as a certain number of oscillations of a particular transition in a cesium atom. So if you stimulate that transition, and with very sensitive detectors show that the radiation emitted is quantized, then you're done."

This document describes experiments done with light and microwaves and how it brings the students to the conclusion that both are the same differing only in wavelength/frequency. Light and Electromagnetic Waves Teaching in Engineering Education

And here is another experiment with interference patterns contra 'particles' that to me seem too point to Feynman's 'many paths' ( That light goes all possible 'ways' simultaneously but with different probability, 4-real :) to explain why it acts like it does. single photons two ways.
« Last Edit: 30/12/2009 21:52:54 by yor_on »
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

*

Offline Geezer

  • Neilep Level Member
  • ******
  • 8328
  • "Vive la résistance!"
    • View Profile
This would actually be much easier to do with radio waves, given their longer wavelength.

Cool! Has anyone actually done it?
There ain'ta no sanity clause, and there ain'ta no centrifugal force ćther.

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
Would it be possible to run a version of the double-slit experiment http://en.wikipedia.org/wiki/Double-slit_experiment using much lower frequencies than visible RF, perhaps in the microwave range?
If so, would we expect to observe the same results that we observe with visible RF?
Yes. Yes.
http://phoenix.phys.clemson.edu/labs/224/diffraction/index.html
http://www.thenakedscientists.com/HTML/content/kitchenscience/exp/measuring-the-speed-of-light/

*

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • 12188
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Ah, lightarrow found them :)

When I looked I didn't find any such experiment with really long wavelengths, I thought it might be due to that as you increase the wavelength also will increase the distance between the fringes? (fringe=One of the light or dark bands produced by the interference and diffraction of light).

But I did find this proposal which seems really interesting.
A Cosmic-Scale Double-Slit Experiment

Searching I found this really nice description of waves too for those of you, like me :) that like to have a little  'something' to look at when discussing.

As for my comment yesterday about my last link, shoving support for 'many paths'. The support is in 'Shock # 1:'  being presented there, not in 'Shock # 2:' that can be discussed as it is not exactly true as presented.

"It is a widespread misunderstanding that, when two slits are open but a detector is added to the experiment to determine which slit a photon has passed through, then the interference pattern no longer forms and the experimental apparatus yields two simple patterns, one from each slit, superposed without interference. Such a result would be obtained only if the results of two experiments were superposed in which either one or the other slit is closed. However, there are many other methods to determine whether a photon passed through a slit, for instance by placing an atom at the position of each slit and monitoring whether one of these atoms is influenced by a photon passing it. In general in such experiments the interference pattern will be changed but not be completely wiped out. Interesting experiments of this latter kind have been performed with photons[7] and with neutrons.[8]"

Double-slit_experiment
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

*

Offline Geezer

  • Neilep Level Member
  • ******
  • 8328
  • "Vive la résistance!"
    • View Profile
Thanks for the refs Yor_on and Lightarrow. I'll look at them next year [:D]
There ain'ta no sanity clause, and there ain'ta no centrifugal force ćther.

*

Offline LeeE

  • Neilep Level Member
  • ******
  • 3382
    • View Profile
    • Spatial
I actually remember doing a practical microwave diffraction experiment at school - we used what looked like a section of birdcage i.e. vertical steel bars spaced about 1 cm apart for our diffraction grating.  We also used a lens made out of paraffin wax for microwave refraction too, iirc.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

*

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
Interference and diffraction effects happen for all electromagnetic radiations at all frequencies.  However if you are talking about observing the non intuitive quantum effects these are only observable for frequencies at which individual quanta can be detected which requires at least infra red frequencies although the quantum effects would still occur at low frequencies.
Learn, create, test and tell
evolution rules in all things
God says so!

*

Offline Geezer

  • Neilep Level Member
  • ******
  • 8328
  • "Vive la résistance!"
    • View Profile
Interference and diffraction effects happen for all electromagnetic radiations at all frequencies.  However if you are talking about observing the non intuitive quantum effects these are only observable for frequencies at which individual quanta can be detected which requires at least infra red frequencies although the quantum effects would still occur at low frequencies.

Oh! Yes, I was referring to particle like behaviour. Is this limitation simply because we don't have photon detectors that work at lower frequencies?

There ain'ta no sanity clause, and there ain'ta no centrifugal force ćther.

*

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
You must remember that the energy of an electromagnetic photon is planck's constant multiplied by the frequency of the photon (h x nu) so as the frequencies get lower the energy of individual photons get smaller.  this makes it more difficult to detect low frequency photons individually.

The non intuitive quantum process involves observing that individual photons passing through the apparatus are subject to interference and diffraction that is an individual photon is always in some way an extended object.

I am surprised that so many people are fixated in some way on this experiment because quantum mechanics is clearly a non local process.  In some ways I think that the converse experiment with matter is far more surprising. 

ALL material objects like electrons have a wavelength that depends on their momentum in the frame of reference of the experiment  that is the slower the particles move, the longer their wavelength.  They are therefore also subject to interference and diffraction and individual electrons passing through an apparatus will generate interference patterns. 

Even more counter-intuitive this process applies to all individual bodies like human beings (and schrodinger's cat) however as the bodies get more massive the wavelengths are exceedingly short and the effective diffraction and interference patterns undetectably small.  However this experiment has been performed using quite large complex molecules like buckyballs
« Last Edit: 04/01/2010 09:33:39 by Soul Surfer »
Learn, create, test and tell
evolution rules in all things
God says so!

*

Offline litespeed

  • Sr. Member
  • ****
  • 419
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #10 on: 04/01/2010 17:58:07 »
SS

You seem well versed in this subject. Perhaps you would comment on something that has always perplexed me. Do photons have dimensions? This perplexes me because photons vary in wave length by orders of magnitude.

My GUESS is that photons do not have dimension, but leave a variety of measurable wave lengths in the electomagnetic field as they pass.

*

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
Does the double slit experiment work at low radio frequencies?
« Reply #11 on: 04/01/2010 18:51:19 »
To be totally pedantic quantum mechanics implies that all the particles in the universe, that is both massive particles like protons and electrons or massless like photons, exist to a certain extent throughout the entire universe, because all the integrals that define the properties of a particle extend to infinity.

The "size" of a particle could be considered as the range of distance over which it was reasonably probable that something  (another particle or an experimental structure) could interact with this particle.

This size is a function of the particle's "wavelength" when considered as a wave, that is a few wavelengths.  The precise number of wavelengths depends on how long you are prepared to spend looking for it  The longer you spend looking the "bigger" the particle gets!

remember also the wavelength of matter particles like electrons and protons gets shorter the more massive the particle is and the slower it is moving.

Electrons have a low mass and therefore have quite long wavelengths.  This is why they exist in orbitals which extend a considerable distance from the nucleus and defines how big atoms are.

Protons and neutrons  are much more massive and interacting with very much higher energies in the nucleus and that makes a nucleus small.

So for massive particles the lighter the particle and the slower it is moving the "bigger" it gets. 

For very slow moving atoms in extremely cold "Bose Einstein condensations"  atoms can become so "big" that they are in effect visible to the naked eye!


Let me point out though that this increase in "size" does not mean that the atom itself has changed in any way. it is just like Schrodinger's cat which is simultaneously alive and dead at the same time the atom exists everywhere in a large volume of space with a reasonably high degree of probability and is linked with many other atoms and cannot be distinguished from them it is a total quantum entity.
Learn, create, test and tell
evolution rules in all things
God says so!

*

Offline litespeed

  • Sr. Member
  • ****
  • 419
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #12 on: 04/01/2010 23:48:32 »
SS

I must confess a particular hostility to Schrodinger's cat. I think it was a condescending analogy, at best. However, a photon traveling through space leaves behind it an unambiguous residue of wave length. I find this oddly in sync with string theory. Specifically, the wave length is perfectly measurable, but is the residual product of something that has no size; it only has resonance that is left in its wake.

For instance. We talk of electromagnetic waves that measure peak to valley in METERS.  The thing that left that wave has nothing more then an intrinsic resonance of indeterminate size, and certainly not one meter long. Further, the 'item' that left the meter sized wave in its wake does not seem to have been reduced in energy at all.

One important question is how the PHOTON is affected AFTER its residual wave has been absorbed by the appropriate antenna. The antenna can only absorb the energy if it is tuned to the resonant length frequency. Yet that frequency can only be absorbed AFTER it is created in space time once the photon has passed. Accordingly, once the wave has been created, absorbed by the antenna, the photon must subsequently dissipate. 

Sounds once again to me like "spooky action at a distance". To quote Albert. Accordingly, it seems to me that photons are firmly anchored to space time and can be destroyed and converted to electromechanical energy AFTER they have crossed the appropriate length antenna.

This sounds to me very much the converse to entangled particles.
« Last Edit: 05/01/2010 00:00:46 by litespeed »

*

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
Does the double slit experiment work at low radio frequencies?
« Reply #13 on: 05/01/2010 10:38:04 »
I do not understand properly what you are trying to say.  You do not seem to have the correct mental image of what is going on. 

You seem to be obsessed with the concept of a point particle.

Photons don't leave electromagnetic waves in their tracks.  The electromagnetic waves ARE the photons.   In the case of radio waves vast numbers of coherent photons.  The best way of thinking of photons is as wave packets of energy which start small build to a peak and die away as they pass.  A bit like sets of waves in the ocean.

As I pointed out above all photons and particles do have a physical size and radio wave photons can be very large indeed with the tiny energy of the photon effectively spread over volumes greater than one kilometer. 

The concept of a point particle like an electron is not that the particle is a mathematical point it is just that to the current detail of our measurements the particle is structureless in that its charge behaves like a physical point but it clearly has structure in the form of its spin but the details of this are only covered by the many billions of string theories from which we have yet to refine a complete model

Learn, create, test and tell
evolution rules in all things
God says so!

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #14 on: 05/01/2010 12:15:06 »
SS

You seem well versed in this subject. Perhaps you would comment on something that has always perplexed me. Do photons have dimensions? This perplexes me because photons vary in wave length by orders of magnitude.

My GUESS is that photons do not have dimension, but leave a variety of measurable wave lengths in the electomagnetic field as they pass.
There isn't any valid model of photon, at the moment, so it's meaningless to talk about its dimensions (meaningless in the sense I specified). No one can prove that photons are point-like and no one can disprove that they are extended objects. Maybe they don't even exist, as bodies flying from source to detector. What we know about photons is related to how a source of light or a light detector gives away/absorbs energy and momentum.
(Before you could reply about momentum I remind you that classical electromagnetic waves have momentum too).

*

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
Does the double slit experiment work at low radio frequencies?
« Reply #15 on: 05/01/2010 22:52:38 »
I do not think that you are being very sensible light arrow.

How do you define the size of an object?

The only way I can understand it is that it is the volume in which other objects can interact with it.  If you define size in this way all particles have clearly defined sizes.  these may well vary under different experimental conditions but that is quite reasonable.  the sizes that I have been defining are those well established by experimental science and nothing to do with any theory.
« Last Edit: 05/01/2010 23:01:14 by Soul Surfer »
Learn, create, test and tell
evolution rules in all things
God says so!

*

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • 12188
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #16 on: 07/01/2010 12:53:16 »
Soul Surfer, I didn't know why, but you got me confused when you wrote that you could see an atom in a Bose Einstein condensation.

"At extremely low temperatures or at small size scales, on the other hand, the usefulness of classical mechanics begins to wane. The crisp analogy of atoms as Ping-Pong balls begins to blur. We cannot know the exact position of each atom, which is better thought of as a blurry spot. This spot-known as a wave packet-is the region of space in which we can expect to find the atom. As a collection of atoms becomes colder, the size of each wave packet grows. As long as each wave packet is spatially separated from the others, it is possible, at least in principle, to tell atoms apart.

When the temperature becomes sufficiently low, however, each atom's wave packet begins to overlap with those of neighbouring atoms. When this happens, the atoms "Bose - condense" into the lowest possible energy state, and the wave packets coalesce into a single, macroscopic packet. The atoms undergo a quantum identity crisis: we can no longer distinguish one atom from another."

So in a way you might call that a 'super atom' but seen from another perspective you don't have 'atoms' any more. You have a geometrically constricted 'fog' without any specific atoms visible.
Bose Condensate described

As for "The electromagnetic waves ARE the photons." Maybe, in a way, just as the 'super atom' can be said to be a lot of atoms interacting under a very specific condition joining into a new inseparable state containing new properties. But there is a particle/wave duality existing that hasn't been explained, even though there are yet unproven theory's trying to do so, like string theory that you mention.
Atomic Particles, Photons and Heisenberg’s Uncertainty Principle (HUP)

----Quote from it--

"These experimental observations were in direct opposition to those expected for a wave theory of radiation. In wave theory, no threshold energy would be required for photoelectron release. A wave with low energy would simply operate long enough to contribute sufficient energy to cause the electron to be ionized. The kinetic energy of the photoelectrons would be expected to increase with the intensity of the radiation “waves”.

Another effect that the wave theory of radiation cannot explain is the transmission of the Sun’s rays through what is virtually a perfect vacuum between the star and the Earth in which there is nothing in which waves can form and carry the transmitted energy, unlike that which occurs in the oceans."

--end of quote..


Then you state "As I pointed out above all photons and particles do have a physical size and radio wave photons can be very large indeed with the tiny energy of the photon effectively spread over volumes greater than one kilometer. " Seen as a wave this is perfectly correct, as HUP comes into play.

As for what decides a photons wavelength, it's called the 'wave vector'. And the definition of that is mostly applicable to monochromatic light (Lasers)and is a generalization of a vector representation of a wave. A theoretical model in other words neither proving nor disproving it as the sole fact.
« Last Edit: 07/01/2010 14:09:46 by yor_on »
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #17 on: 07/01/2010 18:41:43 »
I do not think that you are being very sensible light arrow.

How do you define the size of an object?

The only way I can understand it is that it is the volume in which other objects can interact with it. 
And so how would you define a photon's size?

*

Offline litespeed

  • Sr. Member
  • ****
  • 419
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #18 on: 07/01/2010 22:19:06 »
SS - Thanks for your forbearance! I am trying to work this out, really I am ;)

OK. Lets talk about a single, very long radio wave photon that is absorbed by a an appropriate antenna. 1) Will a single such photon have enough energy to be converted into a single, corresponding; small electric current?

If so, at some point the entire photon is converted instantaneously to something else. However, as you point out, a single photon could be miles long. So. Does it make any sense to even discuss whether the entire photon must reach the antenna first, or that it can be converted as soon as the front of the 'wave' interacts with the antenna?






*

Offline Geezer

  • Neilep Level Member
  • ******
  • 8328
  • "Vive la résistance!"
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #19 on: 07/01/2010 22:22:23 »
(HUP)
----Quote from it--


"Another effect that the wave theory of radiation cannot explain is the transmission of the Sun’s rays through what is virtually a perfect vacuum between the star and the Earth in which there is nothing in which waves can form and carry the transmitted energy, unlike that which occurs in the oceans."


Yor_on - Perhaps you can help me understand something that I seem to get stuck on all the time.

Space is described as a vacuum (not made by Electrolux of course [;D]) and, therefore, waves cannot form in something that has no "substance". (So far so good.)

However, it also seems to be well accepted that mass/matter "distorts" space to produce gravity.

So, why would photons not just be another aspect of the distortion of space? In that case, photons might merely be energy propagating through space in some manner that we don't understand. We clearly don't know what makes gravity work, so why would photons be any different?

We also know that matter and energy are somewhat convertible, and we have vivid demonstrations that prove this. So, why would all matter not simply be energy that is somehow "locked up" in space? In other words, all matter is just another aspect of space itself.

Or did I just reinvent string theory?
There ain'ta no sanity clause, and there ain'ta no centrifugal force ćther.

*

Offline litespeed

  • Sr. Member
  • ****
  • 419
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #20 on: 07/01/2010 22:40:49 »
Geezer,

I always assumed light travels through space/time almost as if it were the Either Michaelson and Morely were looking for. The only thing is M&M did not understand that matter traveling through space/time interact with it.

And it is true light travels at different speeds when you put certain transparent mass in front of it. At least I think that is true. If so, matter can interact with light without absorbing it. It sort of makes sense to me since mass interacts with space/time by bending it.

*

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • 12188
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #21 on: 08/01/2010 11:54:26 »
Geezer I find it questionable too :)
Not your statement, but what a vacuum really is. My thoughts on it is that if distance and motion is something defined to SpaceTime under our arrow of time (-past--'now'-> future-->)and elastic, then at and possibly 'under' Planck size and without any 'arrow of time' there should be other definitions and what we call distance here might not exist at all, as it craves a times arrow to exist. So I sort of agree with that you said :)
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

*

Offline LeeE

  • Neilep Level Member
  • ******
  • 3382
    • View Profile
    • Spatial
Does the double slit experiment work at low radio frequencies?
« Reply #22 on: 08/01/2010 17:43:36 »
The issue with waves in a vacuum is that classical waves are not a fluctuation within the medium, but a fluctuation of the medium itself, so if there's no medium there's nothing to be 'waved'; you can't wave a flag if there's no flag to be shaken about.

If space-time is a medium, then it needs to consist of something.  That though, is rather like saying the a distance or a length of one foot/metre/whatever needs to be made of something and is not just the distance between two points; it's like the difference between the distances marked off along a rule or tape measure, and the material that makes up the matter of the rule or tape measure itself.

As it is though, it seems to be that the distance between two points exists regardless of whether the rule or tape measure is there to measure it (which is not to say that the distance remains the same regardless of whether the rule or tape measure is there and when it's not, and depending upon where you're watching it all from).
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

*

Offline Geezer

  • Neilep Level Member
  • ******
  • 8328
  • "Vive la résistance!"
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #23 on: 08/01/2010 18:27:26 »
The more closely we examine matter, the less tangible it appears. I seems to me that all particles are simply different manifestations of energy in "space". Of course, this requires that "space" actually is something. But there are indications that it actually is - gravity seems to suggest that it is, as do the wave characteristics of photons and all particles.

The fact that we don't observe space as "something" is hardly surprising if everything is actually made from space itself.

If you assume for a moment that this model is valid, many things do seem to fall into place. Of course the big question then becomes "what the heck is space?"
There ain'ta no sanity clause, and there ain'ta no centrifugal force ćther.

*

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
Does the double slit experiment work at low radio frequencies?
« Reply #24 on: 09/01/2010 23:30:10 »
Light arrow the "size" of a photon is approximately the wavelength multiplied by the reciprocal of the fractional  bandwidth of the frequency of the photon over which the observation is made.  Say for example I was observing radio signals at 100Mhz,  this is around the frequency of FM radio,  the wavelength is around 3 metres and, if I observed the signal with a receiver with a bandwidth of 10MHz, that is one tenth of the frequency.  The receiver therefore needs about ten waves to respond.  So the "size" of the photons being observed is about ten wavelengths, that is, around thirty metres.

I have illustrated this using radio waves because it was low frequencies that were being discussed in the origin of the question.

One question that has always intrigued me  is "Is  bandwidth a fundamental property of photons?"  That is is a photon originating from a broad band or rapid process at a particular frequency fundamentally different from one originating from a narrow band process.  for example broadband and narrowband processes occur at all frequencies radio light and gamma rays a broadband photon is emitted very quickly and has very few waves in its wave packet but a narrow band one may have many orders of magnitude more waves in its wave packet.  look up mossbauer effect where gamma ray sources and detectors can be "tuned" in to each other using mechanical motion and the gravitational red shift due to the earth's gravitational field measured in the laboratory.
« Last Edit: 09/01/2010 23:32:47 by Soul Surfer »
Learn, create, test and tell
evolution rules in all things
God says so!

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #25 on: 10/01/2010 02:28:04 »
Light arrow the "size" of a photon is approximately the wavelength multiplied by the reciprocal of the fractional  bandwidth of the frequency of the photon over which the observation is made.  Say for example I was observing radio signals at 100Mhz,  this is around the frequency of FM radio,  the wavelength is around 3 metres and, if I observed the signal with a receiver with a bandwidth of 10MHz, that is one tenth of the frequency.  The receiver therefore needs about ten waves to respond.  So the "size" of the photons being observed is about ten wavelengths, that is, around thirty metres.
I think that you are very optimistic in the possibility of making such kind of considerations, but maybe, who know, you could be right.
In this moment there is one thing that doesn't convince me: you say that the receiver would need n wavelenghts to respond, but such kind of "delay" has never been observed experimentally, for what I know: photons can be detected at every instant of time.

*

Offline litespeed

  • Sr. Member
  • ****
  • 419
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #26 on: 10/01/2010 20:50:24 »
All this stuff about wave lengths is fascinating, and brings up memories of tuning or 'trimming' antennae for enhanced reception for specific wave lengths. As I recall, you could have full wave length antennae, 1/2 wave, 1/4 wave etc.

In the context we are now discussing this is very weird. Specifically, either the antenna could absorb a single photon or it could not. If it required more then one photon to complete 'the wave length' how were they stored up?

I have a guess. My guess is that individual radio frequency photons can be absorbed entirely by antennae of various lengths, but the output of the antenna is largely a function of the RESONANT effect between the frequency of the photon and the natural frequency of the antenna.

Any thoughts on this.......

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #27 on: 11/01/2010 00:19:43 »
All this stuff about wave lengths is fascinating, and brings up memories of tuning or 'trimming' antennae for enhanced reception for specific wave lengths. As I recall, you could have full wave length antennae, 1/2 wave, 1/4 wave etc.

In the context we are now discussing this is very weird. Specifically, either the antenna could absorb a single photon or it could not. If it required more then one photon to complete 'the wave length' how were they stored up?

I have a guess. My guess is that individual radio frequency photons can be absorbed entirely by antennae of various lengths, but the output of the antenna is largely a function of the RESONANT effect between the frequency of the photon and the natural frequency of the antenna.

Any thoughts on this.......
A photon don't have a frequency by itself. It's the electromagnetic radiation associated with the photon/photons which have a frequency.

*

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
Does the double slit experiment work at low radio frequencies?
« Reply #28 on: 11/01/2010 18:46:16 »
All photons must have a fundamental frequency because that is what defines the energy in that photon.  The energy in any photon is always Planck's constant multiplied by its frequency.  that is one of the most fundamental laws of quantum physics and has been proved many times over
Learn, create, test and tell
evolution rules in all things
God says so!

*

Offline JP

  • Neilep Level Member
  • ******
  • 3366
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #29 on: 11/01/2010 21:50:05 »
Lightarrow and Soul Surfer,

I think you're both right, from different points of view.  What we classically consider frequency is the number of oscillations per second of a classical monochromatic electromagnetic wave that pass a given point.

A photon has a frequency that determines its energy from E=hf, where E is energy, h is Planck's constant, and f is frequency.  In addition to determining the energy, this frequency appears in the description of the photon according to quantum electrodynamics.  The mathematics of a photon look similar to the mathematics of a quantum harmonic oscillator, where the photon has a frequency just like a harmonic oscillator has a frequency.  However, the photon is not modeled by a nice classical wave that oscillates a certain of number of times per second. 

The two types of frequency are related to each other, however.  If you add up photons of a given frequency in the right way (called a coherent state) they should sum up to give what looks like a classical wave with that frequency, although this wave will have quantum noise present.  A classical wave has high enough amplitude that the quantum noise is negligible and the classical model holds.

Read this for an overview: http://en.wikipedia.org/wiki/Coherent_state  The first figure on the right demonstrates how a collection of photons can form a classical wave.


*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #30 on: 11/01/2010 22:44:28 »
Lightarrow and Soul Surfer,

I think you're both right, from different points of view.  What we classically consider frequency is the number of oscillations per second of a classical monochromatic electromagnetic wave that pass a given point.

A photon has a frequency that determines its energy from E=hf, where E is energy, h is Planck's constant, and f is frequency.  In addition to determining the energy, this frequency appears in the description of the photon according to quantum electrodynamics.  The mathematics of a photon look similar to the mathematics of a quantum harmonic oscillator, where the photon has a frequency just like a harmonic oscillator has a frequency.  However, the photon is not modeled by a nice classical wave that oscillates a certain of number of times per second. 
Exactly, infact it's modeled by *nothing*.

Quote
The two types of frequency are related to each other, however.  If you add up photons of a given frequency in the right way (called a coherent state) they should sum up to give what looks like a classical wave with that frequency, although this wave will have quantum noise present.  A classical wave has high enough amplitude that the quantum noise is negligible and the classical model holds.

Read this for an overview: http://en.wikipedia.org/wiki/Coherent_state  The first figure on the right demonstrates how a collection of photons can form a classical wave.
From which you can infer that a photon is not a coherent state and so it couldn't have a single frequency even if it were an electromagnetic pulse, but it's not...

*

Offline Geezer

  • Neilep Level Member
  • ******
  • 8328
  • "Vive la résistance!"
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #31 on: 12/01/2010 04:19:30 »
Exactly, infact it's modeled by *nothing*.



Lightarrow - are you saying there is no model of a photon? I'm not sure I understood your point. Thanks, G
« Last Edit: 12/01/2010 06:19:26 by Geezer »
There ain'ta no sanity clause, and there ain'ta no centrifugal force ćther.

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #32 on: 12/01/2010 18:43:34 »
Exactly, infact it's modeled by *nothing*.
Lightarrow - are you saying there is no model of a photon? I'm not sure I understood your point. Thanks, G
Exactly.

*

Offline JP

  • Neilep Level Member
  • ******
  • 3366
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #33 on: 13/01/2010 16:12:57 »
Exactly, infact it's modeled by *nothing*.
Lightarrow - are you saying there is no model of a photon? I'm not sure I understood your point. Thanks, G
Exactly.

Lightarrow, I think I see what you're getting at, but I don't really agree with your statement that a photon is modeled by "nothing."  There is a perfectly good model for photons via quantum electrodynamics (as a Fock state containing 1 photon).  They certainly aren't simple particles zipping between sources and detectors, and the position representation of the photon isn't clear to me (I've browsed over some books that do define it, or make approximations so that a photon can be treated over space, but I'm not well-versed in these techniques).  However, photons can be modeled and the models appear to be extremely accurate. 

I think the best way to talk about photons is in terms of them being tiny packets of energy that can be emitted or absorbed at a point, but do something strange (although we can model it) in between emission/absorption. 

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #34 on: 13/01/2010 20:10:35 »
Lightarrow, I think I see what you're getting at, but I don't really agree with your statement that a photon is modeled by "nothing."  There is a perfectly good model for photons via quantum electrodynamics (as a Fock state containing 1 photon).  They certainly aren't simple particles zipping between sources and detectors, and the position representation of the photon isn't clear to me (I've browsed over some books that do define it, or make approximations so that a photon can be treated over space, but I'm not well-versed in these techniques).  However, photons can be modeled and the models appear to be extremely accurate. 
Ok, but when a non-specialist (as me) asks about a model of the photon, he/she usually mean "something like a particle, made (or not) of other particles" and I think it's important to remark the fact such a kind of model for a photon doesn't exist.

1. We don't know which shape has a photon (if it has one).
2. We don't know how big is a photon (if it has dimensions).
3. We don't know if it is a corpuscle travelling from source to detector, on the contrary, it seems that we are not allowed at all to say it's such a kind of thing...

Photons are Much more complicated objects than what non-specialists usually think it is, and often even for specialists...
« Last Edit: 13/01/2010 20:12:14 by lightarrow »

*

Offline JP

  • Neilep Level Member
  • ******
  • 3366
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #35 on: 13/01/2010 23:20:57 »
Then it sounds like we agree.  [:)]

*

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • 12188
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #36 on: 14/01/2010 22:38:53 »
This is a very nice thread
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

*

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • 12188
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

*

Offline JP

  • Neilep Level Member
  • ******
  • 3366
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #38 on: 08/03/2011 22:28:04 »
Could you explain a bit more, Yor_on?  Which post here makes you think that a classical explanation of the photoelectric effect is being proposed?

*

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • 12188
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #39 on: 08/03/2011 23:30:01 »
"The photoelectric effect posed a significant challenge to the study of optics in the latter portion of the 1800s. It challenged the classical wave theory of light, which was the prevailing theory of the time. It was the solution to this physics dilemma that catapulted Einstein into prominence in the physics community, ultimately earning him the 1921 Nobel Prize."

That one states quite clearly that there is a fundamental difference between photons and waves as I understands it? And I got the feeling that the consensus here was that 'photons' are a misconception rereading it? Then there has to be a equivalent wave definition for the photoelectric effect. So I looked but didn't find it? And no JP, it wasn't a reply to you particularly, just a question of mine.
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

*

Offline JP

  • Neilep Level Member
  • ******
  • 3366
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #40 on: 08/03/2011 23:49:36 »
I don't think anyone was trying to say photons were a misconception.  Certainly what I meant, and what I think the the other posters meant, was that photons aren't as simple as many lay-explanations make them out to be.  They aren't, for example, little bullets zipping around. The QM description of them is a lot more complex than that.

However, they do certainly exist and are probably best thought of in terms of the photoelectric effect: as the smallest packets of energy of light available.

*

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • 12188
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #41 on: 08/03/2011 23:58:06 »
Well, if you go by both waves and photons interactions you have one, as I see it, clear difference. Photons do their work 'instantly' (less than 10-9 s) as far as I now, waves don't. When it comes to how we model them outside a interaction we can't say we observe them.
=

Ah, this might sound like I don't have any use for waves. Well, if so, neither do I have it for photons :)
My personal favorite for the moment is the idea of a universe where we have pointlike insertions made into causality chains by our arrow, following a thin line. Not that I understands how it does it? But i think it allows for both phenomena to exist, and I don't have to care that much about what happens where we don't observe, as that doesn't need to exist. To me the interactions will be defined by the need for them, you could say that the relations crave them, or that our arrow creates them through the shape it has. Feynman used many paths and probability to explain it, but in my universe that becomes too many paths simultaneously, so I'll stick to those 'points made' that we 'observe', sort of :)

And if the arrow act this way macroscopically, giving us one timely procession, could I look at what happens in a QM perspective as something (time) 'widening' becoming 'whole processes'. Doesn't make much sense, does it? It's more of a feeling I have than anything touchable, but to me time is a very weird thing and the arrow even worse. It sort of would make time into a cone where we always are at its 'tip' with its base being somewhere at string theory or loop quantum theory where all shapes becomes the same, as observed from us. I know, that's pretty weird.
« Last Edit: 09/03/2011 00:35:58 by yor_on »
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

*

Offline JP

  • Neilep Level Member
  • ******
  • 3366
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #42 on: 09/03/2011 03:32:00 »
Well, if you go by both waves and photons interactions you have one, as I see it, clear difference. Photons do their work 'instantly' (less than 10-9 s) as far as I now, waves don't. When it comes to how we model them outside a interaction we can't say we observe them.

Maybe it's the same kind if language issue at work here that I talked about in the "aether" thread.  Photons have a QM wave function and by the rules of QM, that wave can interact instantly and at a point.  Classical EM waves don't have these properties, since they have to play by classical rules.  Maybe it's unfortunate that the term "wave function" brings to mind classical waves, since they don't mean the same thing or play by the same rules. 

The full quantum theory, when applied, also explains why classical waves work so well for so many things.  It also explains why they don't work well for quantum effects, such as the photoelectric effect.
« Last Edit: 09/03/2011 03:40:02 by JP »

*

Offline Geezer

  • Neilep Level Member
  • ******
  • 8328
  • "Vive la résistance!"
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #43 on: 09/03/2011 06:59:27 »
What what it's worth, it strikes me that a nanosecond is a really long time. The semiconductor guys have been counting in picoseconds for a long time.
There ain'ta no sanity clause, and there ain'ta no centrifugal force ćther.

*

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • 12188
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #44 on: 09/03/2011 13:35:08 »
This sums it up nicely

"The mechanism whereby the Maxwellian fields (which are continuous in space and time) interact with electric charge is via the Lorentz force law. In brief, the Maxwell/Lorentz force on charged particles occurs continuously in space and time. In Einstein's explanation of the photoelectric effect, the interaction between the field and a charged particle occurs impulsively, essentially at a given point in space/time."

As for how long 'instant' is? I used the links definition in my post. But I don't know how long it takes in 'reality'. If you look you will see that it states 'less than'? But as we are talking freeing 'electrons' that are particles of matter from a metal it needs to take some measurable time I think, as we will have an acceleration.
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #45 on: 09/03/2011 15:31:43 »
Although. Thinking of it Are you saying that you can explain the the photoelectric effect by waves now?
Certainly.
The "photon" concept is not required at all. How many people (including me) deceived for so many years  [:)] [>:(]

People much more prepared than me says the prove it's in Mandel and Wolf "Optical Coherence and Quantum Optics" (section 9.3):
http://www.amazon.com/Optical-Coherence-Quantum-Optics-Leonard/dp/0521417112#reader_0521417112

Unfortunately I don't have that book, but I don't have reasons not to believe it.

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #46 on: 09/03/2011 15:39:23 »
Well, if you go by both waves and photons interactions you have one, as I see it, clear difference. Photons do their work 'instantly' (less than 10-9 s) as far as I now, waves don't. When it comes to how we model them outside a interaction we can't say we observe them.
As yor_on wrote, how long 'instantly' is? It seems it's not exactly zero seconds.

Quote
The full quantum theory, when applied, also explains why classical waves work so well for so many things.  It also explains why they don't work well for quantum effects, such as the photoelectric effect.
But a "semiclassical" approach, where a classical EM field and a detector treated quantistically, really seems to work (see my previous post).

*

Offline JP

  • Neilep Level Member
  • ******
  • 3366
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #47 on: 09/03/2011 15:45:31 »
Part of it's available on google books.

The semiclassical treatment works to an extent, but it has some issues, as they note in that chapter.  I haven't gone through the details, though.

*

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • 12188
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #48 on: 09/03/2011 20:07:05 »
So we have a Quantum Mechanical approach to Waves explaining Photons? A contradiction in terms that one :)

QM = quanta, explaining Photons aka 'light quanta' as, ah, Waves?

Ahem?
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

*

Offline JP

  • Neilep Level Member
  • ******
  • 3366
    • View Profile
Does the double slit experiment work at low radio frequencies?
« Reply #49 on: 09/03/2011 21:12:23 »
All the semiclassical model is explaining there is the photoelectric effect.  As you say, obviously photons themselves require the field to be quantized, since they're quanta.

But it's very interesting that the effect can be modeled without photons!  All my courses on QM used the photoelectric effect as a starting point for requiring quantized light.