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Course: Computer science theory > Unit 3
Lesson 1: Ancient information theory- What is information theory?
- Origins of written language
- History of the alphabet
- The Rosetta Stone
- Source encoding
- Visual telegraphs (case study)
- Decision tree exploration
- Electrostatic telegraphs (case study)
- The battery and electromagnetism
- Morse code and the information age
- Morse code Exploration
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Visual telegraphs (case study)
The history of visual telegraphs. Created by Brit Cruise.
Want to join the conversation?
- Why is there a picture of a flea at7:26? It has no relation to the video, as far as I'm aware.(41 votes)
- I think the key is "improving the capability of human vision using lenses".
My guess is that this is one of the first small scale drawings of a flea.(110 votes)
- Am I the only one who can't make any sense of the Bi-Literal Cipher?(10 votes)
- It's simply a unique combination of a' and b's to represent each letter for example, try making your own:
A = aaaaa
B = aaaab
C =aaaba
and so on.
This way I could send you something like
aaaab aaaba aaaba = B C C(26 votes)
- Without telescopes, how could the Greeks accurately recognize which flares were lit for the Polybius square? I imagine that misreading the states of 10 flares from a long distance could potentially spell disaster in a scene of war.(16 votes)
- I'm not one hundred percent certain, but you must remember, the torches were much bigger. They probably made smoke signals, which can be seen from much farther away.(14 votes)
- why couldn't they have used colored smoke, one color to a meaning.(7 votes)
- They absolutely could have. Provided the recipient could see/understand the different colors, works great.
A traffic signal is a modern method of this exact thing--each color means a certain set of information.(6 votes)
- why is there a flea at7:26there is no connection what so ever.(5 votes)
- At this point in the video Brit is talking about Robert Hooke, who used microscopes and telescopes in his work. The drawing of the flea, as seen through a microscope, is a sketch by Hooke.(7 votes)
- Brit said that there was an invention which brought us into the information age. What was it?(5 votes)
- Maybe it's the realization that nothing can be as important as something? I know it's not really an invention, but it can still help a large amount. Or what about binary code?(1 vote)
- 6:45the origin of Morse code?(5 votes)
- Good observation. That's one of the earliest records of a single difference being used to convey the alphabet. However...Morse code is different from this example in one simple, yet important way.(5 votes)
- what did he say at0:16to0:40(4 votes)
- When he says belief state he is just meaning what you believe. So if you believe something is true your belief state is that the answer is "true", if you then get evidence that the answer is false, you belief state would change to "false". So by noticing a difference in something over a distance such as a flame your belief about something can change.(5 votes)
- what age are we right now?(2 votes)
- Age like the next chapter in the history of the world type of age? Assuming you're talking about that type of age, it's actually sort of divided right now. Each age is defined by the major geological force in that time period. Every time that changes, the age changes. That is why it's called an Ice Age. It's because the major geological force of that time was ice and glaciers. Ok, now after that brief explanation on ages, back to your question. Currently, most scientists agree that we are now in the Age of the Anthropcene, or the Age of Mankind. Congratulations, you and I are the major geological forces of today. However, most scientists disagree on the beginning of this age. Some believe that we have been majorly affecting the world since the Industrial Revolution in the mid-1800's. Others think that nuclear warfare has changed this world the most, and place the beginning of the Anthropcene in 1945 with the first detonation of a Weapon of Mass Destruction on a populated area. These are the two main ideas for the beginning of the Anthropcene, although there are other suggestions, such as the invention of gunpowder or the computer. I guess you could even make an argument with the invention of the excavator, treecutter, and other mass nature-destroyers. With these machines we are cutting down and reshaping acres and acres of land every single second.(7 votes)
- How can Polybius describe a technology developed by Eneus tacitus when Polybius was born in 200 B.C and tacitus is from 4th century B.C?(3 votes)
- The 4th century B.C. is 499 - 400 B.C. 200 B.C. came after 4th century B.C. That's because 200 B.C. means 200 years before the birth of christ and 4th century B.C. is 499 - 400 years before the birth of christ.(1 vote)
Video transcript
- [Narrator] The signal fire
is no doubt one of the oldest technologies for transmitting information. Perhaps dating back to the
first controlled use of fire. It allows one person to
influence another's belief state across a distance. Because, with the ability to
notice either the presence or absence of something, we
are able to switch between one of two belief states. One difference, two states. And if we look back in
history, we find that this was of great importance to military powers, which all rely on
effective communications. And a great place to begin
is with the Greek myth of Cadmus, a Phoenician prince
who introduced the phonetic letters to Greece. The Greek alphabet borrowed
from the Phoenician letters, along with light and cheap papyrus, affected the transfer of power from the priestly
to the military class. And Greek military history
provides clear evidence of the first advancements
in communications stemming from the use of signal torches. Polybius was a Greek
historian born in 200 BC. He wrote the histories,
which is a treasure trove of detail related to the
communication technologies of the time. He writes, "The power of
acting at the right time "contributes very much to
the success of enterprises. "And fire signals are the
most efficient of all devices "which aid us to do this." However, the limitation of a
signal fire was clear to him. He writes, "It was possible
for those who had agreed "on this to convey information that, say, "a fleet had arrived, but
when it came to some citizens "having been guilty of
treachery, or a massacre having "taken place in town, things
that often happen but cannot "all be foreseen, all such
matters defied communication "by fire signal." A fire signal is great
when the space of possible messages is small. Such as enemy has arrived or not arrived. However, when the message
space, which is the total number of possible messages,
grows there was a need to communicate many differences. And in the histories, Polybius
describes a technology developed by Aeneas Tacticus,
one of the earliest Greek writers on the art of war
from the fourth century, BC. And his technology was
described as follows. "Those who are about to
communicate urgent news to "each other by fire signal
should procure two vessels "of exactly the same width and depth. "And through the middle should
pass a rod graduated into "equal sections, each
clearly marked off from the "next, denoted with a Greek letter." Each letter would correspond
to a single message in a look-up table which contained
the most common events that occur in war. To communicate they
would proceed as follows. "First the sender would
raise his torch to signal "he had a message. "Then receiver would then
raise his torch signalling "he was ready to receive it." Then the sender would lower
his torch and they would both begin to drain their
vessels from a board hole of equal size at the bottom. Now, when the event is
reached, the sender raises his torch to signal that they
should both stop the flow of water. This results in equal water
levels, denoting a single shared message. This ingenious method
used differences in time to signal messages. However it's expressive
capability was limited, mainly due to it's speed. Polybius then writes of
a newer method originally devised by Democritus,
which he claims was, "Perfected by myself and
quite definite and capable "of dispatching with
accuracy every kind of urgent "message." His method, now known
as the Polybius square, works as follows. Two people separated by a
distance each have 10 torches separated into two groups of five. To begin, the sender raises
a torch and waits for the receiver to respond. Then the sender lights a
certain number from each group of torches and raises them. The receiver then counts
the number of torches lit in the first group. This number defines the row
position in an alphabetic grid they share. And the second group of
torches signifies the column position in this grid. The intersection of the row
and column number defines the letter sent. Realize this method can be
thought of as the exchange of two symbols. Each group of five torches is a symbol, which was limited to five differences, from one to five torches. Together these two symbols
multiply to give five times five equals 25 differences. Not five plus five. This multiplication
demonstrates an important combinatorial understanding in our story. It was explained clearly
in a sixth century BC Indian medical text
attributed to Sushruta, an ancient Indian sage, as follows. "Given six different spices
how many possible different "tastes can you make?" Well, the process of making
a mixture can be broken down into six questions. Do you add A, yes or no? Do you add B? C? D? E? And F? Realize this multiplies
into a tree of possible answer sequences. Two, times two, times two, times two, times two, times two equals 64. 64 different sequences of
answers are therefore possible. Realize that given N yes or no questions, there are two to the
power of N possible answer sequences. Now in 1605 Francis Bacon
clearly explained how this idea could allow one to send
all letters of the alphabet using only a single difference. With his bilateral cipher,
Bacon wrote famously, "The transposition of two
letters by five placings "will be sufficient for 32 differences. "For by this art a way
is opened whereby man may "express and signify the
intentions of his mind "at any distance of place
with objects which are "capable of a two fold difference only." This simple idea of using
a single difference to communicate the alphabet
really took flight in the 17th century due to the
invention of the telescope by Lippershey in 1608 and Galileo in 1609. Because quickly the magnification
power of the human eye jumped from three to eight
to 33 times and beyond. So the observation of a single
difference could be made at a much greater distance. Robert Hooke, an English
polymath interested in improving the capability of
human vision using lenses, ignited progress when he told
the Royal Society in 1684 that suddenly quote,
"With a little practice, "the same character may
be seen at Paris within a "minute after it hath
been exposed at London." This was followed by a
flood of inventions to pass differences more effectively
across greater distances. One technology from 1795
perfectly demonstrates the use of a single difference to
communicate all things. Lord George Murray's shutter
telegraph was Britain's reaction to the Bonaparte's
threat to England. It was composed of six
rotating shutters which could be oriented as either open or closed. Here each shutter can be thought
of as a single difference. With six shutters we have six
questions, open or closed? Providing us with two to the power of six, or 64 differences. Enough for all letters, digits, and more. Now realize that each
observation of the shutter telegraph can also be thought
of as the observation of one of 64 different paths
through a decision tree. And with a telescope it was
now possible to send letters at an incredible distance between beacons. However, an observation in
1820 lead to a revolutionary technology, which forever
changed how far these differences could travel
between signalling beacons. This ushered in new ideas
which launched us into the information age.