#21  
Old 30-10-2019, 08:32 PM
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doppler (Rick)
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Another interesting thing about photons is they make everything look "solid". Even though the atoms that make up everything that we see are mostly empty space, the void is filled with the electromagnetic fields generated by the electrons within the atom. These affect light waves as they move through materials, preventing them from passing straight through unimpeded. Switching to radiation of shorter wavelength, like X-rays or gamma rays, allows even relatively dense materials to become transparent.
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Old 01-11-2019, 04:24 PM
morls (Stephen)
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Very helpful information, thanks everyone
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Old 17-12-2019, 04:25 PM
bgilbert (Barry gilbert)
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The Nobel Laureate, Willis Lamb junior Wrote a paper titled "Anti photon", where he suggested the word ''photon" should be banned from the lexicon. I agree with Lamb, but for stronger reasons.
Maxwell's Equations can explain almost everything that the photon is normally used for.
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Old 17-12-2019, 05:00 PM
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Quote:
Originally Posted by bgilbert View Post
... Maxwell's Equations can explain almost everything that the photon is normally used for.
Well.... it is true for practical purposes (RF etc) but it is not enough. QED explains the rest.
And Standard model goes even deeper....
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Old 17-12-2019, 05:37 PM
bgilbert (Barry gilbert)
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If its good enough for RF, then Its good enough for for all other forms of electromagnetic radiation, they are the same. RF engineers don't use the concept of the photon and do pretty well, Wi-Fi , 5G, VDSL and radio astronomy etc.
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Old 17-12-2019, 07:53 PM
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If its good enough for RF, then Its good enough for for all other forms of electromagnetic radiation, they are the same. RF engineers don't use the concept of the photon and do pretty well, Wi-Fi , 5G, VDSL and radio astronomy etc.
Yes, but that is not the whole story.

We are talking here physics, not RF engineering.
(BTW, I am RF engineer by profession).
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Old 17-12-2019, 10:34 PM
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As both physicist (first degree) and electrical engineer (second degree).. a photon is both, yet neither provides a complete description.

The wave description explains many phenomena nicely such as diffraction, superposition (interference), coherence (lasers), maxwells equations, antenna theory and ties in nicely with quantum mechanics.

But there are other aspects that are explicable as particle, but not wave...
- Slit experiments with single photons show that when one is detected (ie arrives at a sensor) the entire wave function collapses, ie on conversion of the photon to an electron, the wave ceases to exist. The wave is physically distributed over macroscopic distances (two slits) yet when absorbed at a sensor resulting in an electron (essentially a very small particle) the entire wave collapses. In this respect the photon behaves as a particle. Yet, when there are two slits, the photon must pass through one, or other to reach the sensor, yet somehow it "knows" the presence of the other slit. With multiple photons in succession, the two-slit interference pattern pattern is produced.
- The photo-electric effect of metals is explicable using Einsteins particle representation;
- A photon also has measurable momentum when it strikes a macroscopic object, which is very much a particle behaviour.

Then there are small groups of photons - solitons - which are important for high data transmission rates in optical fibres.

Morls... yes photons carry information. While the pure theory is taught in physics, information theory is an electrical engineering topic not taught in science degrees.

Direction, polarisation, energy (frequency/wavelength), relative phase and group velocity, periodic changes in brightness and the waveform or the timing between pulses (eg eclipsing binary stars, Cepheid variable stars, and pulsars), the rise and decay rates of big pulses (supernovae), the Doppler shift (rotating stars and binaries) as well as the gravitational redshift (distant galaxies) all convey information.

Frequency-shifts or relative-phase shifts can convey information (for example a laser beam through an optical fibre can be used to sense mechanical strain or vibrations along the length of the figure and the time-of-flight can locate the position along the fibre).

There is the frequency distribution (spectrum) of the observed light, that also conveys information.

And lastly to warp your mind, 2-dimensional Fourier transforms can be used to do real-time filtering of images, and holograms can be used to model 3-D objects.

Direction is useful in astronomy - for example the bending of starlight by gravity first predicted by Einsteing, verified at an eclipse in 1919, and subsequently the gravitational lensing of distant galaxies by foreground ones.

For an example in which direction alone is used to encode 10 bits see https://www.technologyreview.com/s/6...f-information/

These all make the binary pulses (0 or 1) used to encode data on CD's and DVD's look rather primitive compared to what could really be stored on a macroscopic object if several of the above techniques could be combined reliably.

Last edited by Wavytone; 17-12-2019 at 11:13 PM.
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Old 18-12-2019, 11:29 PM
bgilbert (Barry gilbert)
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Moris,

did you take the advice of Alex, and look at; 'Photon' on Wiki.
It might be more productive than listening to some of us sparring.
At all cost maintain your curiosity and even skepticism and don't be
"bullied by erudite sycophants to the standard model. Progress is often
achieved by overturning existing well established theories
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Old 21-12-2019, 10:41 AM
bgilbert (Barry gilbert)
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Max Plank and Albert Einstein had a serious disagreement about the nature of "the light quanta". Plank insisted quantization only occurred in 'matter', at the point of creation or detection of the radiated field. Moreover, the radiated field behaved entirely according to Maxwell’s equations, and therefore, was not quantized. Einstein was not convinced, and continued with the notion that the field itself was quantized.

The term "photon" was later adopted for the "light quanta" by the scientist, Gilbert N Lewis. It took some years before the notion of the "photon " was finally accepted by the mainstream scientists, but Max Plank was not one of them. The relationship between Max and Albert was never the same after this disagreement.


It is interesting to note, that Niels Bohr, who later was to be an adversary of Albert’s, resisted the notion of Albert’s "photon", for quite some time, before finally acquiescing.

Towards the end of Albert’s life he was said to have stated;

"All the fifty years of conscious brooding have brought me no closer to answer the question, “What are light quanta?” Of course today every rascal thinks he knows the answer, but he is deluding himself."
— Albert Einstein

Last edited by bgilbert; 22-12-2019 at 12:07 AM.
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Old 28-10-2020, 11:13 PM
bgilbert (Barry gilbert)
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Is the laser a quantum device?

The laser was developed in spite of quantum mechanics (QM), not as a result of QM.
H R Townes, the inventor of the laser, happened to mention to Niels Bohr what he was working on, Niels replied that it could not possibly work because of the uncertainty principle. Thankfully Townes ignored Niels Bohr.
Neils Bohr also told Hanbury Brown that his proposal to measure the diameter of stars using intensity correlations could not possibly work, because of the uncertainty principle. Hanbury ignored Niels and spent 17 years at Narrabri successfully measuring star diameters.
Twenty years later an absurd theory of bunching, based on erroneous measurements of arrival statistics for laser light was developed, to explain the Hanbury Brown Twiss effect. This effect was also thought to explain the operation of the laser.
QM has now incorporated a QM interpretation of the Hanbury Brown Twiss effect into its vocabulary.

Barry
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