What's the physics behind being able to make a container light-tight with a couple of right angle corners yet radio waves seem to leak out like water?
Difference 1 is the wavelength. Light has a wavelengths of 400-700nm, whereas radio waves used by phones have wavelengths in the mm and cm range.
If structures are of similar size to the wavelength, then waves can "bend around" obstacles. This effect is called diffraction and can be observed with sound waves, electromagnetic waves, water waves, etc.
Difference 2 is the photon energy / frequency. How well radiation is absorbed depends on the photon energy. There are lots of molecules that absorb visible light very well, so it's easy to make surfaces that absorb light. But there are few things that absorb radio waves as well, so it's hard to make things that neither reflect nor transmit radio waves.
I remember going caving and we would have to go 100m or more through many different turns before we all turned our lamps off and truly experienced perfect dark.
A hole/leak in the metal wall of a Faraday cage is going to be a lot more reflective and can easily act like a crude waveguide[1].
[1] https://en.wikipedia.org/wiki/Waveguide_%28radio_frequency%2...
Our eyes simply aren't very sensitive instruments. And the visible part of the spectrum is uncharacteristically full of 'noise', so it makes some sense that our eyes don't need to detect any signals that are too far below the noise-floor.
That makes me wonder. How much 'darker' is any given bit of radio spectrum as compared to the visual spectrum earth at night.
I take umbrage with that statement! Our eyes are exquisitely sensitive, and most importantly, have staggering dynamic range.
Our eyes are capable of perceiving a single photon [1], albeit noisily (I've been lucky enough to have performed this experiment myself!).
But the greatest thing about our eyes is the dynamic range: the difference in brightness between a moonless, starry night (which we are perfectly capable of navigating by eyesight) and a bright sunny day is nine orders of magnitude. A bright day is a billion times brighter!
Show me an RF receiver or light camera with that dynamic range!
The one place our eyes are limited is in frequency range.
The magnitude of the dynamic range is even more impressive if converted to 'stops' from photography, yielding about 30 stops (1 stop halves the light). Whereas a really good camera will do about 15 stops. Though I suppose that the camera gets 15 stops in a single 'scene'. Whilst the 30 stop figure for the human eye does not hold up if half your vision is taken up by daylight and the other half by a night sky. For a single 'scene' I think it becomes hard to define the dynamic range of a human eye though.
If the signal gets choppy and you miss some of it, how do you know what you missed?
`..--- -.... ----- -----` (2600) could come through as `..- -. —` (Uno). Uno is a valid word, so passes validation, but it’s the wrong message.
What Reed-Solomon allows us to do is pad the message with n% of error correcting ‘bits’. That way, if >100-n% of the message gets through, the whole message can be reconstructed from whatever bits that made it. And if not enough of the message made it, it immediately fails the validation check and so you know you must resend the message.
It’s so handy and so solid that it’s used almost everywhere. From optical discs to ECC ram to radio communications and a bunch more.
There is:
- lines-of-sight propagation in free space,
- reflect from the surfaces like light (spectacular reflection)
- microwaves can be channeled trough tubes (think sound waves). If you fold a conductive material like tin foil multiple times, it can still work as a wave guide and escape.