Submitted by Max-Phallus t3_10rza78 in askscience
mckulty t1_j6yxzj8 wrote
> I've always imagined radio signals as enormous photons
No bigger or smaller than other photons, just a different color.. infra-infra-infra-red.
> and we can generate very complicated wave forms with radio.
Whoa hoss. We can generate very complicated AUDIO waveforms superimposed on a carrier of radio but the CARRIER remains a sine wave and varies its amplitude (AM) or frequency (FM) in synch with the AUDIO waveform it encodes.
Since there are blue photons (400 nm) and red photons (700 nm) we can combine them but they still behave like two different photons and stimulate two different photopigments inside the eye.
> So can we form complex wave form light?
No. I don't think photons interact that way, creating the harmonics that distinguish a flute tone from an oboe. IF they did, it would be in the [Edit:] ultraviolet range
> Are there natural phenomenon which produce odd looking wave forms?
Photons are wavicles and appear to contain only one wavelength.
> Does a refraction grating separate out different wavelength photons,
*diffraction Yes, unavoidably because each color diffracts to a different degree. So the grating pattern gets lost. To get a useful grating patterns you need monochromatic light.
Max-Phallus OP t1_j6z45xi wrote
Thanks for the answer. I think it highlights some holes in my understanding though.
While we do mostly think of AM and FM radio transmissions; we can pass any waveform into an antenna.
Is the output from that antenna a variable waveform photon, or is it multiple photons of different wavelengths being produced at once.
Or is it pretty much semantics? Where a variable waveform is just one waveform, but it can be described as multiple photons of different wavelengths, as per it's Fourier transform?
Apologies if I'm being dim.
nicholsz t1_j6zbtu8 wrote
>Is the output from that antenna a variable waveform photon, or is it multiple photons of different wavelengths being produced at once.
Not just multiple, preposterous numbers of photons are output by radio transmitters; numbers like 10^34 photons per second
The variable waveform isn't from approximating the signal with a series of sine waves like Fourier analysis. It's from changing the wavelength of the photons you're spewing out (in the case of FM), or from increasing / decreasing the number of photons you're spewing out (in the case of AM)
mckulty t1_j702zhy wrote
> Is the output from that antenna a variable waveform photon, or is it multiple photons of different wavelengths being produced at once.
A photon is a fixed unit of energy whose energy is proportional to its color.
If the station is an AM station, the photon are pumped out as if the woofer were attached to a photon pump, pushing more photons out on the upwave, and pulling back to create a relative rarity of photons on the downwave. The audio modulates the amplitude of the output signal (# of photons). The carrier remains on one frequency, as tightly controlled as possible - "1410 on your radio dial" 1411 is a little staticky, 1415 is worse, and 1450 is a whole nother station. Carriers run from 680kHz to 1500 kHz.
If the station is an FM station, it still pumps out photons but the audio isn't encoded in the amplitude of the waves. Instead a signal is generated at say 95Mhz, but it's allowed to warble, to swing 0.1 Mhz either way. Music is encoded onto the warble, so that high notes are one wavelength and low notes are slightly different, a continuum that lets you trace out the audio waveform.
So the FM station pumps out a steady energy but the wavelength warbles between 95.0 and 95.1, so that a curve y=f-95.0 plots the musical waveform. It's a little more ocmplex bc they actually create two signals on either side of 95.0, 94.9 for left and 95.1 for right. Or VV.
If I haven't totally munged this explanation, perhaps someone can explain how volume is encoded in FM.
Otherwise-Way-1176 t1_j6z9sqq wrote
>No. I don't think photons interact that way, creating the harmonics that distinguish a flute tone from an oboe.
What does this mean? The sound that we hear from an oboe or a flute consists of multiple frequencies added together.
You can certainly produce multiple frequencies of light and have them all arrive at your receiver - say the human eye - together. For example, light from a fluorescent light bulb and light from the sun.
>So can we form complex wave form light?
Depends what you mean by complex. Evanescent waves have an imaginary number in their propagation constant. So if by complex you mean includes complex numbers, then certainly it’s possible with light.
If by complex the OP simply means complicated, then I would argue that sunlight is already quite complicated. Unpolarized monochromatic light can be modeled as a sine wave with a slowly varying phase, which in Fourier space provides a small bandwidth around the central frequency which is very similar to FM radio, but of course the fluctuations are random so we couldn’t dig out some sort of audio signal from it.
mckulty t1_j6znp7k wrote
> What does this mean? The sound that we hear from an oboe or a flute consists of multiple frequencies added together.
Yes, we call them harmonics, and they are the basis for octaves resulting from dividing a string into two (880hz A) or three (1320hz E) or four (1760hz A) etc parts.
So the harmonics are always higher frequency than the principal pitch, and and the first harmonic is always twice the value of the principal, eg middle C to C above middle C.
But visible light doesn't allow even the first harmonic, because 400 nm to 800 nm would make the first harmonic infrared.
So if you COULD modulate a radio wave with harmonics, which you can't, it won't create any new colors or visible whizbang.
Otherwise-Way-1176 t1_j70a0qc wrote
I understand what harmonics are. I couldn’t figure out what point you were making.
But the original question was about radio waves, which are not visible light.
So I still don’t understand why you’re making the argument that it’s impossible to have a photon at one frequency and then another photon at 2x that frequency, just because they wouldn’t both be in the range our eyes can see.
mckulty t1_j6zov2e wrote
> If by complex the OP simply means complicated
No he means formed, like the difference between the waveform pattern for a tuning fork (smooth sinusoidal) vs complicated like an oboe. The flute pattern below shows strong influence from the third harmonic.
https://i.imgur.com/Qp13d3Y.png
I don't know of any way to impose harmonics like that on a photon, but I'm willing to listen if someone says otherwise.
Otherwise-Way-1176 t1_j70aiag wrote
All you have to do is allow more than one photon and it’s trivial to produce a complex waveform. Radio waves that actually arrive at an antennae in real world applications consist of more than 1 photon, so I don’t understand why you’re so attached to this idea that it has to be all packed into just one photon.
Sound waves are not carried by particles, so I don’t see why you’re insisting on this single photon restriction.
mckulty t1_j70jflh wrote
I'm missing something but too tired to care. Of course light reinforces and cancels like any other wave.
> Sound waves are not carried by particles
Um, they don't do well in a vacuum.
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