Wikipedia:Reference desk/Archives/Science/2021 July 22

= July 22 =

Radio waves and information
So in Layman's terms, what's the basis for how radio waves hold and transfer information? Like for smartphones and Internet. And can it be done for other wavelengths? If the answer is yes, I'm sure it won't be done for a lot due to health reasons, but if radio waves can transfer information, then what about wavelengths as light? Does that mean we can use a flashlight to transfer information as well? 67.165.185.178 (talk) 11:23, 22 July 2021 (UTC).
 * Light can be and is used quite effectively - see Fiber-optic cable. Wikignome Wintergreen talk 13:24, 22 July 2021 (UTC)


 * Very simply you can switch the flashlight on and off and transmit a message via Morse code. That is obviously very slow but it is a form of amplitude modulation, which is one method of transmitting information by radio waves (AM radio). Another method is frequency modulation (FM radio), which is quite a bit harder to do with optical light. --Wrongfilter (talk) 13:43, 22 July 2021 (UTC)
 * I'll just point out that Morse code transmission by flashing lights is not just a hypothetical example; it's been used importantly, principally at sea, as seen in the movie The Hunt for Red October, for example. --184.147.181.169 (talk) 00:16, 23 July 2021 (UTC)


 * In basic terms, waves can be combined and uncombined through a mathematical process called fourier series. The theoretical basis is that literally any arbitrary function can be represented by a superposition of multiple sine waves and that composing and decomposing such functions is done by simple addition of the waves.  Information of any kind is embedded in a carrier wave (this is what you "tune" your radio to) and then some electronics in the receiver extracts the information by decomposing the waves from the carrier wave.  On paper fourier series is messy, but it takes a relatively few, simple electronic components to perform the process physically and extract information from radio waves.  -- Jayron 32 14:25, 22 July 2021 (UTC)
 * If you had a top-quality digital sound file of someone tapping the C4 key of a piano once (no pedal), and similar files for each note and you knew which parts of which files should be playing when, then could you also sum them into a graph of any arbitrary sound? i.e. metal or JFK speeches. Sagittarian Milky Way (talk) 16:20, 22 July 2021 (UTC)
 * Yes, you could. It needn't be a sine wave, you can compose any arbitrary function using any arbitrary wave form or set of arbitrary wave forms and you can also reverse the process (in theory, though it could get very mess in practice).  I highly recommend 3blue1brown's videos on the Fourier series process, he takes it from a wide variety of angles (historical development via the heat equation, modeling fourier series using computer graphics, the equations behind it, etc. etc. etc.)  If you want a good demonstration of how to create arbitrary plots using the Fourier series process, Here is a video where he uses the concepts of Fourier to tell a computer how to draw any arbitrary picture using nothing but harmonic functions (essentially sine functions).  It's quite beautiful.  This video is a bit lengthier, but in it he explains how he made those animations, and the math behind it.  -- Jayron 32 16:30, 22 July 2021 (UTC)
 * edit: I linked to the wrong article. I have corrected my links above.  It's the Fourier series I meant to link to, the Fourier transform which I originally cited is a related concept, but not as applicable here. -- Jayron 32 16:38, 22 July 2021 (UTC)
 * 10.1109/50.54508 is an example of FM of light near the visible range. DMacks (talk) 16:01, 22 July 2021 (UTC)

Okay 1 thing that radio waves cannot be used as light waves, is that light also behaves as particles (photons). So can't use light waves as radio waves since light will not go through a solid object. Can there be the equivalent of photons for radio waves? 67.165.185.178 (talk) 23:40, 22 July 2021 (UTC).
 * Radio wave radiation IS photons. And wave at same time (wave-particle duality) Sagittarian Milky Way (talk) 00:02, 23 July 2021 (UTC)
 * Okay, so photons at radio-wavelengths can go through solid objects? 67.165.185.178 (talk) 06:10, 23 July 2021 (UTC).
 * Light can go through glass bricks. Also AM radio stations emit wavelengths up to 555+ meters, good for quantum tunneling through and diffracting around anything opaque to them up to the size of buildings. Sagittarian Milky Way (talk) 06:31, 23 July 2021 (UTC)
 * Okay, I was gonna say, we don't see wavelengths at radio-frequency, this is the same for light-wavelengths? Meaning the only aspect we see of light is the photon-part of it. I wonder if light-wavelengths are the safest wavelengths radiation. 67.165.185.178 (talk) 06:42, 23 July 2021 (UTC).
 * Standard radio waves can be blocked by large objects. For example, when driving through a tunnel. ←Baseball Bugs What's up, Doc? carrots→ 06:44, 23 July 2021 (UTC)
 * Light can pass through a sheet of glass, which is quite solid. It can't pass through a wooden fence. Radio waves will pass through a wooden fence, but not through a metal wire mesh fence. Light has no trouble passing through that metal wire mesh fence (through the holes). It all comes down to wavelength, the scale of the object and its electrical properties. Both light and radio behave both as electromagnetic waves and as a stream of photons. For radio waves a wave description is almost always more useful. For light it's different. Detecting light is almost always done as a particle, but to describe refraction and reflection you need a wave description. Gamma rays are usually best described as a stream of photons. PiusImpavidus (talk) 08:26, 23 July 2021 (UTC)
 * Faraday cage for the metal fence thing, radio waves really don't like to pass through electrically conductive grids of holes smaller than their wavelength. Sagittarian Milky Way (talk) 15:52, 23 July 2021 (UTC)
 * Hence, as an illustrative example, the mesh in the glass doors of microwave ovens. {The poster formerly known as 87.81.230.195} 90.197.27.141 (talk) 14:22, 24 July 2021 (UTC)
 * Similarly, in some reinforced concrete buildings, you get really bad mobile phone reception, even if there's good reception outside, because the decimeter sized meshes of iron rods in the walls is close enough in scale to the microwave wavelengths used for mobile phone. – b_jonas 11:41, 27 July 2021 (UTC)
 * As for the original question, (1) we are already using significantly different frequencies of radio waves and microwaves for transferring information, from 30 kHz to 3 GHz. These propagate to different distances, partly because of how they disperse in the atmosphere, partly from how they bounce from the ground, surface of seas, and the ionosphere.  Lower frequencies are generally used for longer distances but also lower communication bandwidth.
 * Near infrared (300 THz) is also used for communication, notably for handheld remote controls for home appliances. There is, notably, a gap between microwaves and near infrared which isn't used, because the atmosphere is too opaque to them.  Anything higher frequency than visible light isn't generally used for communications as far as I know; instead some higher frequencies are used for medical imaging, passive astronomical obsercations, or analyzing crystal structure.  – b_jonas 12:09, 27 July 2021 (UTC)