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Thread: Radio waves..

  1. #1
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    Radio waves..

    I was just wondering, when a radio wave is emitted from a radio station fifty miles away from my house, is it in a quantum superposition until it gets detected
    by my antenna in my front room ?

    Cheers
    Far away is close at hand in images of elsewhere...

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    Yes and no.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by kevin1981 View Post
    I was just wondering, when a radio wave is emitted from a radio station fifty miles away from my house, is it in a quantum superposition until it gets detected
    by my antenna in my front room ?

    Cheers
    Not unless it's a quantum radio station!

    Seriously, "radio wave photons" are emitted in the bazillions by the likes of your local radio station, and they interact with molecules in the air, birds, insects, your neighbor's porch, etc before they generate a current in your antenna ... So, no.

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    I’m going to go with yes.

    Going from emitter to aerial, clearly each photon is going to pass through a lot of intervening stuff (mostly air) as Jean mentions.

    However, I don’t see this as significantly different from the typical double-slit experiment which is also performed in air, and so each photon also has to pass through the air without losing its superposition. To break superposition, the photon must have some actual effect on the object it is passing by, and that doesn’t happen significantly with air.

    So I reckon when a photon hits your antenna, it’s only at that moment that it won’t hit another antenna on the other side of the city.


    EDIT TO ADD: On reflection, two other points to consider: First, the double slit experiment has been performed not just with air, but with solid glass covering the slits, and still the interference pattern is displayed. Secondly, and perhaps more importantly, there is a BIG difference between the double-slit experiment in the lab and the OP's question - namely distance. In the lab, the light only goes through a few metres of air, whereas the radio station would be many miles. It could be like a foggy day - light travels fine over a hundred metres, but gets swallowed over a kilometre.

    So how many photons, having a small level of interaction with air but over much greater distances, can retain their superposition?

    I'm going to say some ...

    ... Probably


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    Last edited by Ufonaut99; 2019-Jun-13 at 10:30 PM.

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    Quote Originally Posted by Ufonaut99 View Post
    To break superposition, the photon must have some actual effect on the object it is passing by, and that doesn’t happen significantly with air.
    It only needs to interact, there's no lower threshold that I know of.
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    Quote Originally Posted by Noclevername View Post
    It only needs to interact, there's no lower threshold that I know of.
    As I think I understand quantum theory, any given photon either interacts or it doesn't. It doesn't matter how many zillions of atoms it has bypassed between the transmitter and the receiver.

    In my opinion the OP topic here is an academic curiosity for the purposes of radio engineering and technology, because the quantum character can be safely ignored at radio frequencies. If we were transmitting x-rays, it would be very different.

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    Quote Originally Posted by Noclevername View Post
    It only needs to interact, there's no lower threshold that I know of.
    This maybe be because of my lack of a physics background, but Iím not quite getting what you guys are talking about. What is the difference between ďinteract withĒ and ďhave an actual effect onĒ?


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    Quote Originally Posted by Jens View Post
    This maybe be because of my lack of a physics background, but I’m not quite getting what you guys are talking about. What is the difference between “interact with” and “have an actual effect on”?
    Ufonaut99 said that radio interacting with air molecules does not have a "significant" effect. I was rebutting that by saying (admitting I may be refuted by someone smarter) that the interaction doesn't need to be "significant" by our macro standards, it just has to be an interaction in order to collapse the superposition.

    But there has to be some measurable interaction between radio and air, or weather would not alter radio's effective range.
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    Quote Originally Posted by Noclevername View Post
    (admitting I may be refuted by someone smarter)
    Not necessarily smarter. Just more knowledgeable, perhaps (than either of us, I mean).
    As above, so below

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    Quote Originally Posted by Jens View Post
    Not necessarily smarter. Just more knowledgeable, perhaps (than either of us, I mean).
    If they're knowledgeable about quantum physics, I'd give even odds they're smarter, too.
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    Quote Originally Posted by Noclevername View Post
    But there has to be some measurable interaction between radio and air, or weather would not alter radio's effective range.
    Indeed. Absorption and scattering by matter (water, mainly, in ordinary circumstances) make a wavelength-dependent difference, and explain why kilometer-scale terrestrial wireless communication favours longer wavelengths. During WWII, failed attempts to push radar to 1.25 cm stimulated research that resulted in Bloch and Purcell winning a Nobel in 1952 for the discovery of nuclear magnetic resonance. That's very much a quantum phenomenon (NMR, that is, not winning the Nobel).

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    Quote Originally Posted by Geo Kaplan View Post
    Indeed. Absorption and scattering by matter (water, mainly, in ordinary circumstances) make a wavelength-dependent difference, and explain why kilometer-scale terrestrial wireless communication favours longer wavelengths. During WWII, failed attempts to push radar to 1.25 cm stimulated research that resulted in Bloch and Purcell winning a Nobel in 1952 for the discovery of nuclear magnetic resonance. That's very much a quantum phenomenon (NMR, that is, not winning the Nobel).
    I find that interesting, I thought I understood the resonance part of how NMR works but how is it a quantum effect?
    sicut vis videre esto
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    Quote Originally Posted by profloater View Post
    I find that interesting, I thought I understood the resonance part of how NMR works but how is it a quantum effect?
    Oh thinking more it"s electrons jumping quantum levels and the tuned frequency of that effect, so I think I understand now, maybe?
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
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    Quote Originally Posted by Noclevername View Post
    Quote Originally Posted by Ufonaut99 View Post
    To break superposition, the photon must have some actual effect on the object it is passing by, and that doesnít happen significantly with air.
    It only needs to interact, there's no lower threshold that I know of.
    ...
    But there has to be some measurable interaction between radio and air, or weather would not alter radio's effective range.
    We may be agreeing vociferously !

    For any individual photon, I also don't see a difference between "interact" having "some actual effect". In a double-slit experiment in a lab, over the course of a few metres, there is a pretty low probability of any given photon having any "effect" or "interaction" with any molecule of air. For those few where that probability becomes reality, then certainly their superposition is broken, but that doesn't happen significantly often enough to change the fact that we see an interference pattern. I also agree about the weather bit as well (which is why I'd added that bit about distance to the post).

    Quote Originally Posted by Noclevername View Post
    If they're knowledgeable about quantum physics, I'd give even odds they're smarter, too.
    And certainly agree about that as well !

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    Quote Originally Posted by profloater View Post
    Oh thinking more it"s electrons jumping quantum levels and the tuned frequency of that effect, so I think I understand now, maybe?
    Think spin, not jumping of electrons, for NMR. Spin is a quintessential QM property.

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    Some confusion, I think.

    Superposition is different from what happens in the double slit experiment; one way to see this is to remember that the interference patterns are the same, even when thereís ever only one photon in the device at any time.

    Entangled is often used in the same sentence/para as superposition. AFAIK, radio photons, from your local station, are not, ever, entangled ... so thereís no superposition to lose/destroy/collapse...

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    Quote Originally Posted by Jean Tate View Post
    Some confusion, I think.
    Yes, l was kind of puzzled by the question, but I didnít think about it that carefully. But yes, it seems that people interpreted it as meaning wave-particle duality, but I donít think that would change. But as far as entanglement, I donít think they are entangled in the first place.


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    Quote Originally Posted by Jean Tate View Post
    Entangled is often used in the same sentence/para as superposition. AFAIK, radio photons, from your local station, are not, ever, entangled ... so thereís no superposition to lose/destroy/collapse...
    Entangled and superposition are often used together, but superposition is not only restricted to entangled particles; it can apply to a single particle as well. For example, we can talk of the spin of a single electron being in a superposition of both up and down before measurement.

    My take of the OP was nothing to do with entanglement, but the question of a single photon being in a superposition of location, as I said in my original answer : when a photon hits your antenna, itís only at that moment that it wonít hit another antenna on the other side of the city.

    That issue certainly occurs within the double-slit experiment. When a particle is fired, if passes through both slits simultaneously. A split second before it hits the detector screen, it is not at a fixed spot but instead still spread along the wave. Both of these are the same kind of superposition as our radio-emitted photon before itís interaction with the aerial.






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    Note that interference does NOT require single photon!

    Consider electromagnetic waves - low frequency electromagnetic fields emitted by different antennae and presumably consisting of different photons will interfere precisely the same way as parts of a wave emitted by the same antenna that possibly might be parts of the same photon.

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    Okay, thanks as always..

    So what would you say about this view..

    The radio station antennae emits an electromagnetic wave and when that interacts with my antenna the wave collapses into a definitive point, which we call a particle.
    Far away is close at hand in images of elsewhere...

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    Quote Originally Posted by kevin1981 View Post
    Okay, thanks as always..

    So what would you say about this view..

    The radio station antennae emits an electromagnetic wave and when that interacts with my antenna the wave collapses into a definitive point, which we call a particle.
    There's no collapsing into a point. Erase that notion from your mind. You've somehow confused Copenhagen-interpretation "probability waves" with radio waves. Not the same things at all.

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    Really.. I thought they were the same thing
    Far away is close at hand in images of elsewhere...

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