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Author Topic: Does the double slit experiment work at low radio frequencies?  (Read 20712 times)

Offline lightarrow

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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

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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

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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

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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
 

Offline JP

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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

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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*.

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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

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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 »
 

Offline lightarrow

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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

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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

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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

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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

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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
 

Offline yor_on

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Offline JP

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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

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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.
 

Offline JP

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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

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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 »
 

Offline JP

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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

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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.
 

Offline yor_on

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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.
 

Offline lightarrow

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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

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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.

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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

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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

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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?
 

Offline JP

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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.
 

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Does the double slit experiment work at low radio frequencies?
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