If you travel back in time, what is the most unbearable thing for you? Presumably most people will say: "No WiFi!" For modern people, life without fast information is simply unimaginable
However, many film and television dramas also tell us that when there is no WiFi, there are still many ways to quickly transmit information, such as lights.
In the ancient costume film "Twelve Hours in Chang'an", the lookout tower of Chang'an City uses 12 squares to convey information, and each square can be lit or extinguished with lights. There are as many as 2 in total.12A combination of permutations to represent various types of information, or to convey 12 bits of information.
Is this method really reliable?
Did the ancients really use these methods to communicate?
In the absence of mobile phones and the Internet, can the artificial and primitive way of sending messages in the two films really be used? In fact,This is also the "visible light communication" that many researchers have been trying in recent years, also known as LiFi(Light Fidelity)But many times, they are not so reliable and practical
Take "Twelve Hours in Chang'an" as an example. According to historical records, no one really invented or used this "lookout tower grid" system during the Tang Dynasty. For a long time in ancient times, the beacon tower was really widely used in the wild.
When transmitting information between beacon towers, it is generally not used to encode multiple lamps, but to use the intensity of beacon fire and wolf smoke to indicate different signals. In the "Mozi Orders", it is recorded that "when you see a knight holding a chute, when you enter the country, you will raise two chutes, when you enter the country, you will raise three chutes, when you enter the chute, you will raise four chutes, and when you enter the city, you will raise five chutes." One chute means a pile of firewood, and five chutes means five piles of firewood.
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