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From: Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>
Newsgroups: sci.electronics.design
Subject: Re: Quantum mystics
Date: Mon, 10 Jun 2024 18:26:49 -0000 (UTC)
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Martin Brown <'''newspam'''@nonad.co.uk> wrote:
> On 10/06/2024 17:25, Jeroen Belleman wrote:
>> On 6/10/24 16:20, john larkin wrote:
> 
>>> But photon entanglement can't be explained, or even thought about, in
>>> classic-physics terms.
>>> 
>>> Nor can single-photon interferance.
>>> 
>>> Just accept and enjoy it.
>> 
>> That's false! Entanglement and interference can easily be understood
>> in terms of waves and quantized detectors. It's the QM view, with its
>> imagined photon particle flying everywhere at once that is confusing.
> 
> But that world view is backed up by experiments.
> 
> Particles can behave as waves and waves can behave as particles 
> depending on the experiment. The particle isn't "everywhere at once" 
> either it is trapped in a spherical shell radius vt expanding around its 
> point of origin with the amplitude of the wavefunction representing the 
> chances of finding it at any particular position.
> 
>> What size do you imagine a photon to be?
> 
> Depends on the wavelength of the photon but to have a well defined 
> frequency the amplitude envelope has to be a good few wavelengths long 
> and to agree with causality the leading edge must be zero until 
> sufficient time has passed from its emission to reaching its target. I 
> expect that there is a canonical shape for a photon amplitude envelope 
> for given df/f but I don't know what it is or if it has ever been computed.
> 
> This aspect of size of a photon always seemed very awkward to me when 
> working at 21cm neutral hydrogen and measuring what are essentially tiny 
> correlations in narrowband random noise from extremely remote mostly 
> point sources over a large number of different antenna pairs. What is 
> pretty clear is that the correlations of such signals are good enough 
> even on planetary dimensions for VLBI to work!

Sticking with the semiclassical picture of photodetection is good, because
it avoids almost all of the blunders made by the photons-as-billiard-balls
folk, but it doesn’t get you out of the mystery. 

The really mysterious thing about photodetection is that a given photon (*)

incident on a large lossless detector gives rise to exactly one detection
event, with probability spatialy and temporally weighted by E**2. 

Doesn’t seem so bad yet, but consider this:
If the detector is large compared with the pulse width/c, distant points on
the detector are separated by a spacelike interval. 

That means that so when point A detects it, there is no way for the
information reach point B before the end of the pulse, when E drops to
zero, and yet experimentally point B doesn’t detect it. 

(*) a quantized excitation of a harmonic oscillator mode of the EM field in
a given set of boundary conditions)

Cheers 

Phil Hobbs 
-- 
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics