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Old 17-12-2019, 10:34 PM
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Wavytone is offline
Join Date: Jul 2008
Location: Killara, Sydney
Posts: 4,147
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

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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