The history of light if funny.
First people thought it was a particle, as per corpuscular theory of light, notably Newton supported the corpuscular theory of light.
But then evidence of the diffraction of light start to become unbearably strong, culminating in the Arago spot.
And finally it was undertood from Maxwell's equations that light is a form of electromagnetic radiation, as its speed was perfectly predicted by the theory.
But then evidence of particle nature started to surface once again with the photoelectric effect. Physicists must have been driven mad by all these changes.
The Quantum Story by Jim Baggott (2011) page 2 mentions how newton's support for the corpuscular theory of light led it to be held for a very long time, even when evidence of the wave theory of light was becoming overwhelming.
Video 1. The Story of Light by Bell Labs (2015) Source. Gives some ideas of the history of fiber optics. Features: Herwig Kogelnik.
Video 1. Replicating the Fizeau Apparatus by AlphaPhoenix (2018) Source. Modern reconstruction with a laser and digital camera.
Video 2. Visualizing video at the speed of light - one trillion frames per second by MIT (2011) Source. Fast cameras. OK, this takes it to the next level.
It is so mind blowing that people believed in this theory. How can you think that, when you turn on a lamp and then you see? Obviously, the lamp must be emitting something!!!
Then comes along this epic 2002 paper: "Fundamentally misunderstanding visual perception. Adults' belief in visual emissions". TODO review methods...
In special relativity, it is impossible to travel faster than light.
One argument of why, is that if you could travel faster than light, then you could send a message to a point in Spacetime that is spacelike-separated from the present. But then since the target is spacelike separated, there exists a inertial frame of reference in which that event happens before the present, which would be hard to make sense of.
Even worse, it would be possible to travel back in time:
Figure 1. Spacetime diagram illustrating how faster-than-light travel implies time travel. Legend an explanation are shown in this answer.
Notably used for communication with submarines, so in particular crucial as part of sending an attack signal to that branch of the nuclear triad.
This is likely the easiest one to produce as the frequencies are lower, which is why it was discovered first. TODO original setup.
Also because it is transparent to brick and glass, (though not metal) it becomes good for telecommunication.
Some notable subranges:
Micro means "small wavelength compared to radio waves", not micron-sized.
Microwave production and detection is incredibly important in many modern applications:
Microwave only found applications into the 1940s and 1950s, much later than radio, because good enough sources were harder to develop.
One notable development was the cavity magnetron in 1940, which was the basis for the original radar systems of World War II.
Apparently, DC current comes in, and microwaves come out.
TODO: sample power efficienty of this conversion and output spectrum of this conversion on some cheap device we can buy today.
Video 1. Magnetron, How does it work? by Lesics (2020) Source.
Finance is a cancer of society. But I have to admit it, it's kind of cool. The secret world of microwave networks (2016) Fantastic article.
Video 1. Lasers Transmit Market Data and Trade Execution by Anova Technologies (2014) Source. Their system is insane. It compensates in real time for wind movements of towers. They also have advanced building tracking for things that might cover line of sight.
Video 1. How Microwaves Work by National MagLab (2017) Source. A bit meh. Does not mention the word cavity magnetron!
420 to 680 nm for sure, but larger ranges are observable in laboratory conditions.

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