For example, if you've ever opened an electronic device and seen squiggly traces everywhere, it's because of light speed[0]. When signals get fast enough, you have to make sure the traces have the same length to within a fraction of a millimeter. Otherwise, the signals on two traces arrive at different times and nothing works.
[0](electrons move at ~c, more or less)
There's a significant delay in satellite communications, on the order of milliseconds. It takes several seconds to reach the moon. 20 minutes to Mars, a few hours to Jupiter. Famously 8 minutes to the sun. The nearest galaxy is 1.5 million years away.
Consider how stupefyingly large our solar system is. Then consider how insanely huge the galaxy is: 90,000ly. It takes ninety thousand years for a photon to go from one edge of the galaxy to another. Then compared to the universe at large, our galaxy is essentially a single point.
Light is extremely slow and the universe is vast beyond our meat brain's ability to comprehend.
Pedantic: electrons (in a wire) move at relatively ordinary speeds. Wikipedia says this [0]:
>The drift velocity in a 2 mm diameter copper wire in 1 ampere current is approximately 8 cm per hour. AC voltages cause no net movement. The electrons oscillate back and forth in response to the alternating electric field
Think of it more like a long row of billiard balls. You hit the first one, it moves a little, then it hits the next one, that one moves a little etc. Except the "hit" is just getting closer to the next electron to make it move (like if they were magnets).
At least that's my understanding of it.
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Maybe "hit" is the correct word? Isn't it the same forces at play that stop my hand from going through the table?
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So switching circuits need to take into account "transmission line" effects.