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My question seems obvious but nobody is talking about it. The way I understand it, an electromagnetic wave collapses to a particle when observed. This goes for electrons and photons but I imagine the same is true across the EM spectrum.

When I send a wireless transmission and it's observed, some amount of energy within the wave is lost. Does this not imply a limit to the number of observers to my transmission?

Say I have a circumference of observers that are really small. I can fit almost an unlimited number of observers here. Won't there be a limit to the amount of energy the wave can give to the observers? The energy lost during the "collapse" is probably negligible. But theoretically energy is lost when I observe it, right?

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    $\begingroup$ Yes, if you put the transmitter into what is in effect a Faraday cage of receiving antennas, you will be limited. Yet commercial radio stations routinely serve 1000s of listeners. Why? The density of receive antennas is really really small. $\endgroup$
    – Jon Custer
    Commented Mar 21 at 16:20
  • $\begingroup$ @JonCuster This should be an answer. $\endgroup$
    – Vincent Thacker
    Commented Mar 21 at 16:38
  • $\begingroup$ @JonCuster In fact a Hertzian dipole that is tuned to a single frequency can be infinitesimally small within the confines of Maxwell's equations. The problem is having an infinitesimally small dipole with finite bandwidth whose matching circuit is lossless. $\endgroup$
    – hyportnex
    Commented Mar 21 at 16:40
  • $\begingroup$ A photon collapses to a local location ... where it excites an electron, the photon does not become a particle. The electron is always a particle with wave properties, it collapses to a local location into an atom. $\endgroup$
    – PhysicsDave
    Commented Mar 21 at 16:48
  • $\begingroup$ If your transmitter is one atom large and you excite it one time you will only communicate to one receiver ..... if you excite it many times then many receivers are possible. $\endgroup$
    – PhysicsDave
    Commented Mar 21 at 16:51

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Niels Nielsen's answer correctly points out that for any practical problem, it doesn't make sense to count photons of radio-frequency electromagnetic radiation. But just because the theory has no practical value in some situation, that doesn't mean it's wrong.

Suppose we're talking about WMVP Chicago, USA. Their antenna nominally radiates 50kW at 1MHz. According to Max Planck, that should be $7.54 \times{} 10^{31}$ photons per second. If you know how much energy your receiver needs to catch in some definite span of time in order to reliably decide whether or not WMVP is on the air, then that certainly does put an upper bound on the number of receivers that could possibly accomplish the feat all at the same time.

I suspect that if you put realistic numbers into it though, the upper bound is going to be such a huge number that it essentially will be meaningless outside of any conversation where you hoped the response would go any deeper than, "Gee Wiz! That's a lot of radios."

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The physical model of wave function collapse into a particle upon observation is the wrong one to use for describing how electromagnetic waves interact with matter. The standard text which describes the correct model is the ARRL publication, The ARRL Antenna Book.

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  • $\begingroup$ Indeed, I love the Antenna Handbook. A half-decent rig does fine on a received power in the microWatt level, so it takes a lot of antennas to capture more than a very very small fraction of a 50W transmitter, much less an amateur legal max of 1500W. $\endgroup$
    – Jon Custer
    Commented Mar 21 at 16:45
  • $\begingroup$ @JonCuster- right on, daddy-o! $\endgroup$
    – niels nielsen
    Commented Mar 21 at 18:54

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