---23/06/22 17:15:30----------------------

Now we are going to talk about the animated movie Wall-E

Here you have the song that comes after the movie:

https://www.youtube.com/watch?v=hscu7cc1_2Y

You have robot Eve and robot Wall-E, they both go through paintings. Each of these paintings is coming from a different time:

First you have the paintings on the walls of caves (caves are like big holes in mountains and people lived there) That was some 40000 years ago. These were painted during the ice age, when half of Europe was under a big block of ice. These are the first examples of big art, paintings that are very big, on the walls of caves - that's where we got culture from, and some people say that language came from this time.

Then at 00:19 you are in painting that is just like the painting on the walls of a pyramid in ancient Egypt (from 5000-2300 years ago) Egypt was one of the first places with cities and one of the first languages that wrote things down. History starts, when we can find books. Books that people people wrote at the same time. Everything before that is the time before history - pre-history.

At 00:30 you get into a painting from classical Greece, from some 2400 years ago. You see a lot of ornaments; this is the culture that tells us how to think. They taught us philosophy and mathematics, and critical thinking - that's when you ask questions why things are the way they are. The Jews were also good at critical thinking - the prophets would ask the kings of Israel questions, and even challenged them - they would tell the king if he did something bad!

at 00:44 you are in a mosaic, that is a picture that is made from very little stones, they like these in ancient Rome (2500-1600 years ago) Rome built a big empire, and united many people - most countries in Europe say that they come from this time.

at 01:00 comes a painting from China, the picture has very fine lines. The picture is drawn on paper and people in China invented paper. They also invented minimalism - that's art that is trying to use as few tools as possible.

at 1:17 we get back to Europe during the renaissance - that's between six hundred and three hundred years ago in Italy. That's when Europe got back to the tradition of ancient Greece and ancient Rome, and when we learned about new things, like science. Artists learned about perspective, depth and Humanism - that people are the most important and should come first.

at 1:30 we get into 19th century France - the early impressionist; they taught us to draw what we feel, and not just what we see.

at 1:40 they are in a painting by Monet, many many small dots, like pixels.

at 1:47 they are in a field with sun flowers, just like Van Gogh

at 2:08 in a surrealist painting, where the roots of the tree come all into the boot where Wall-E found the plant/flower. Surrealist means that this is not real, trees don't have roots like this. You draw like this if you want to show ideas, not things that exist in the real world.

You see that two robots are going through a journey, as if they learn again what humans learned through their own way/journey, and all that through the eyes of art. Art is like a kind of time machine, if you look at both the art and its time. And that's what we will talk about now...

The very first art that we know about is here, it comes from three million years ago!

This small stone is a crystal, it looks a bit like a face, and the people of three million years ago added some scratches, to make it look more like a face. This crystal was found in a cave. But it does not come from that cave. You can find crystals like that, but they are some 30 kilometer away. This means they had to take and move the stone all by themselves!

Is that art? The stone could mean a lot to the people who brought it to the cave - they found it far away and had to keep it!

These people were before Humans, they are called Australopithecus - we know very little about this kind of people, we have only the bones of the head, and some tools that they made. https://simple.wikipedia.org/wiki/Australopithecus

Here is some more art from a very long time ago:

This is the "Venus of Berekhat Ram" : a stone figure of a women that was found in Israel, you can see it in the Israel museum in Jerusalem, it is from 280000 years ago! It had some paint on it, so many scientist think that this was art.

There are many museums in the world, but you need to go to Jerusalem, if you want to see the first art ever!

This was before Humans- but we know much more about the artist!

This is Homo Erectus scientists found much more than the bones of a head here, we know that he could walk and stand straight on his feet (that's what the name Homo Erectus says) https://simple.wikipedia.org/wiki/Homo_erectus

We think they looked like this

People know that they got out of Africa, they got to Europe and Asia, and even crossed the sea to the island of Java.

You need boats to cross the sea to that Island, it is too hard to swim that distance!

They made very complicated tools like this one:

And this:

It takes hundred of hours to make one like this, you need to plan what to do. You also need to teach your children how to make these, so they must have known how to talk, somehow. Maybe they were talking by making signs with their hands, but we don't know exactly.

But we don't know for sure, they all died, and now we have no Homo Erectus to ask...

We don't know how Homo Erectus talked to each other. Some scientist say that they must have had some language - to teach their kids how to make complicated tools.

They didn't have a larynx and a complicated tongue. A larynx is what you have in your throat, you need that to make sounds for speaking

But you can teach a Gorilla or a Bonobo some sign language. Sign language is what Humans who can't speak use.

Here is an example of American Sign language - that's how you talk with a person who can't speak.

https://www.youtube.com/watch?v=p0ufyoe0URA

Here is Koko - she was a Gorilla who learned human sign language! She could tell us simple stuff.

https://www.youtube.com/watch?v=FqJf1mB5PjQ

Maybe Homo Erectus could talk about more complicated things with his hands! He had a bigger brain and could stand on his feet - that means that his hands were not busy with moving him from one point to the other.

Also Homo Erectus knew how to make fire, that means he could cook his food. Cooked food has more energy in it, so he didn't have to eat plants all day.

---28/06/22 01:45:44----------------------

Now fast forward to the ice age - you already have Humans in Europe - Homo Sapiens, that's us.

At the time of the ice age you had a very large block of ice. This block of ice was covering half of Europe. The weather was much colder than now. The ice age was from 60.000 years ago until 10.000 years ago.

In Germany you can sometimes see some very big stones, in a place where you don't have any mountains. These big stones are near Berlin. They got there because this big block of ice moved the stones from far far away!

Now a lot of things happened during the ice age, things were very cold and people had to fight hard to survive. At this time they make tools that get much more complicated.

You can use these to catch fish. They also had bows and arrows!

People were hunting big animals, like Bison, Reindeer and stone age Rhinos with a big horn. You had to take these stones and glue them onto a stick, then some of these spears could be used for throwing, with some of them you can't do that - you take that spear and run up to the animal and stick it into it.

Some 30.000 year ago they also made music! This is a flute made out of some piece of bone

And 20.000 years ago we got dogs! Once there were only wild wolfs, no dogs. Dogs were wolfs, who got used to living with people!

Now some scientists say that that that's the time when people learned how to speak!

But the biggest thing that archaeologists found are drawings in caves - a cave is a hole in a mountain. Some of the drawings are from 40.000 years ago! You can find the paintings in some caves in Spain and France. You can also see paintings in the Sahara dessert - that was not a desert at the time, it had grass and lots of animals were living there.

Look at this painting of a bison from the Altamira cave in Spain (from 14000 years ago)

You see they knew about perspective - look at the legs, the leg that is near to us is drawn stronger. And it's a three dimensional painting - some parts are near to us, some are further away.

How did they do it? They used ochre color - you take some special stone/clay that has some iron in it - that's why it is red. You need to turn it into dust and add some fat to it - the fat makes the color stick to the wall. You can also make a paint that is made from charcoal - that is wood after you burn it, then it turns black and you can make a some black paint out of it.

Then they took some paint and blew the paint onto the wall by moving the air with their mouths. As if they breathe life into the painting! That's not just some wall, it's the ceiling - above their heads. So they had to use lamps to put some light into the cave.

Why did they do these paintings? We don't know for sure, but we are guessing. There is a science called anthropology - scientists go to far away places like the amazon and Australia and Africa, some groups of people live there as if in the stone age - they did not have any contact with anyone else. The anthropologists live with them, learn their language and their culture. This way we can guess what the people were thinking some 30000 years ago.

Archaeologists dig up stuff, and they can also tell from what time it was. They use different tricks to do that.

There is also another direction - we think about the art, how does art work? What does it mean? How does it move us?

Linguists think about language, and where it came from and how language is working. That means they also think about the way we think.

You see that this is a big puzzle, and you get ideas from many areas of study. More about this in the next lesson.

---29/06/22 05:01:30----------------------

here someone made art with a cup of coffee and some milk foam.

What has that got to do with the history of art? The first cave paintings appear 40.000 years ago, but Homo Sapiens already exists for some two or three hundred thousand years, does it mean that art was a very late invention?

We don't know, it can be that people had some art before, just that we don't know about it. The cats on top of the coffee will not survive for a hundred thousand years, maybe people did some other art earlier, like painting on their own bodies or painting on baskets.

We don't know for sure, but they found ochre paint that comes from earlier than 285.000 years ago, it is much older than the cave paintings! What do you do with paint? Something that has to do with art!

Now what is art? You draw something, it looks like it is real, but the painting is not real.

This is a painting from 1928 by Rene Margarite. The text on the painting is in French, it says: "this is not a pipe". People asked the painter: but we can see a pipe on the painting - this is a pipe! Rene answered: if it is a pipe, then take it and smoke it!

You see that art is a bit different, or very different from a real thing. It is a symbol. Art is about the artist talking to the people who see the painting - the artist wants to tell us something. The artist can talk about something real, but also about his feelings. The artist always wants to make us feel something, when we look at his art. Art is a tool, that is used by the artist to talk with us!

The cats in the coffee cup tell us: this is cute! Or the artists wants to say "i put in a lot of work in this cup, you want to drink the coffee, but how can you take it and destroy my art?" or maybe it means something else...

Pablo Picasso said that "art is a lie that helps the artist to tell the truth" - the picture is not the same as the real thing, often the artist is using tricks that help him to tell us something, but these tricks move the painting away from the real thing.

People get very exited about the old paintings on the caves - it tells us that people from 40.000 years ago thought abstract ideas - that is about things that you can't touch or use as tools. That means that they thought just like us!

Dolev asked me about the scratch marks on one of the tools:

Thats a good question. Yesterday I saw something on youtube. Genevieve von Petzinger is looking at symbols drawn in caves, she made a catalog of all symbols that she found. https://www.youtube.com/watch?v=hJnEQCMA5Sg

She says that the sign with the dots is very often found!

maybe even possible that these scratches count something, or that it is for beauty.

Geneve became a big star in anthropology for asking your question!

No one was bothering with the signs, everyone was cool with the paintings. Now they say that Genevieve is a big star, because some six and half million people saw her talk on youtube! She was asking just the same questions as you do!

---01/07/22 05:24:13----------------------

Back to the cave paintings, you can see a many drawings of animals, they are drawing a lot of details. This means they are naturalistic pictures - they try to look like they look in nature.

Like the Bisons in Altamira cave - they are sometimes drawing around cracks in the stones.

Or in Chaveaux cave

Look at the horns of the animal in the last picture - that's a trick. You see the animal from the side, but the artist is drawing two horns, you would see only one horn from this perspective!

Also see this one from Lascaux cave

Like with Mickey mouse - you would not see both ears from the side. The same trick here:

People are often drawn in the same picture, but in less details. This means they are often more abstract.

Also you have a lot of signs, maybe they stand in for people,

Maybe they wanted to draw the soul of the animal, maybe they had a fascination for the strength of animals and people were less interesting. Maybe their religion would not allow drawing people, we have that in Judaism.

That may be like a smiley. I would be afraid to see a real person with a face like this

But we know what it says, so we are not afraid...

You also have a figure of a person who as if he is a lion. Maybe they already had abstract thought back 30.000 years ago. Maybe this is a kind of priest, a Shaman.

People were thinking in concepts, if they combined a person who is just like them and a lion - the king of the animals. Maybe that's their idea of superman...

Most of the stuff here comes from a video lecture, they have a university course on the history of art on youtube. Here is one of the first lectures

https://www.youtube.com/watch?v=P_tkKoXDfdg&list=PLjxfpwtKvIlmbzrwkUuhVRI2X2V4t5QWE&index=3

There are lots of ideas on the meaning of all this. I think that I would have to read more about the subject, before I tell you stuff about the meaning of it.

In science you would take many details and look at them together:

what were the people eating? You can take a place where they put their garbage and look at the bones of the animals, they can tell the kind of animals from the bones!
Are they drawing animals that they eat?
You can think about other cultures that are in far away places, like Africa or the Amazonas, and compare what they are doing.
You can compare pictures from different places and different times, and see how they changed through time.
what kind of tools are people using? Sometimes you can find differences between the stone tools - tools from east Africa are a little bit different from the tools that they find in west Africa, so they had different cultures, and we see that from the difference in the stone tools! A lot later people start to make pots/pottery (that was just some seven thousand years ago). Scientist study the types of pots, the drawings that were made on the pots - all this gives you a lot of clues on the culture that people had, during the same time as they find other things, at the same spot!
Lots of possible ways to search for answers.

https://www.youtube.com/watch?v=ns3YRpeeGwI Like in the movie AI, you have aliens that study a robot made by Humans, the Humans are no longer there, so they want to find out about our culture. Then the Aliens all come together and stand in a circle, each one knows a different part of the puzzle, and they tell their part of the big picture to all the other guys.

That's their kind of science, just like ours...

My daughter Dolev added about the sign language of Koko the Gorilla: That's right, but Koko doesn't know how to create new words, she only knows how to use words that she learned. The closest she got to creating a new word was to say bird water - while talking about a bird in a water. Also she doesn't use a grammar to combine the words.

I answered: That is right. In the English language that's a big error. But there are other languages where the order of words is not important. But you are right, these languages have a grammar too, just that it looks different. Here is wikipedia talking about the order of word. https://en.wikipedia.org/wiki/Word_order There are different rules for language. Grammar is a way of taking words and putting them together.

In the English language you say: "She loves him"

the word "She" is the Subject - that is the word for a person or a thing that is doing something
the word "loves" is a Verb, that is a word that describes an action, something that we do.
the word "him" is an Object. That is a word that tells who gets the action, who is acted upon. That means that English is an Subject-Verb-Object language, because that is the order that words appear in.

In Japanese or Mongolian you would say "She him loves" - that is a subject-object-verb language

But there are languages, where the order of words does not matter, but they have other rules of grammar, rules of putting words together! You have a free word order in the Russian language, and other languages that are similar to Russian. In these languages you have more kinds of word forms, this helps you to find matching words, and this helps you to figure out the meaning.

Language is very important, because it also tells us about the way that we think.

---03/07/22 07:18:28----------------------

Before we study language in more detail, what is so special about language?

What can we do that animals can't do? Lets first see what animals can do:

There are some monkeys on Koshima Island, in Japan The mother monkeys taught their kids to wash sweet potatoes in the sea water. Sea water is salty, and the potatoes taste better that way! Teaching your kids how to do stuff is culture, some animals have their own culture! https://www.youtube.com/watch?v=gz8FlSKJ2JE&t=120s
Chimpanzees make tools, some groups of Chimps can make fifteen tools, they even can sharpen a stick and hunt with the stick
lots of animals can communicate somehow. When a craw dies, other craws come together and are very sorry about what happened. They seem to be talking with each other and try to understand what happened.

Also look at this craw, how it is throwing little stones into the bottle, the stones push the water out of the bottle so that the craw can drink it! https://www.youtube.com/watch?v=NGaUM_OngaY

you saw Koko the Gorilla, talking with her hands while making signs, the same language as used by blind people.
they say that elephants can recognize themselves. When you put an Asian elephant in front of a mirror, and he has some spot on his face, now the elephant cleans herself up, that means she knows that she is looking at an image of herself! Scientist say that she is aware of herself (though I am not sure why they think that)

here is a nice video - the elephant is looking at herself in the mirror, it takes some time, but then she understand that she is looking at herself! https://www.youtube.com/watch?v=NygmdjerkLQ

look at how Suda the Elephant is painting pictures with her trunk! https://www.youtube.com/watch?v=7XOl48ssdyo

But there are limits. Animals don't know about symbols, or abstract thought. It would be hard for Koko to talk about things that happened in the past, for example. Also the sentences that Koko was making were very very simple.

We need complex language to talk about more complex stuff, and we can do that; That's what makes us special!

(I learned most of the stuff here from a book "Are we smart enough to know how smart animals are?” by Frans De Waal)

Another form of animal communication. Liraz gave some cat food to Kitty, the street cat. Then she brought all her relatives as well - all the kitties look similar. They all want to eat cat food!

One cat is waking me up at six a clock in the morning, with a loud cry of Miiaaau, she says that again and again and she is loud, in a screechy voice.

Another one is waiting silently, but then she is making noise by scratching the window.

A third one is also saying Miau, but only once.

I can tell who it is, by the way that they talk to me!

Here they are (I have a deal with them - they get some cat food, but the cats need to get rid of any mice, or other animals...)

---04/07/22 12:21:56----------------------

Now some more about language, now that we know how special it is!

Grammar is a set of rules that helps with making a sentence from words; Last lesson we saw some rules, like Subject-Verb-Object, in English we say "She loves him". "she him loves" is a wrong sentence in English, but you could have the same order of words in Japanese.

A grammar is a set of rules for putting words together.

Lets make a grammar, first lets talk about how a rule looks like:

Each of these rules is a rewrite rule: A rewrite rules - you have one or more symbols to to the right of the := sign, if these symbols appear in the text in the same order, then they are rewritten into only one symbol - the symbol that stands to the left of the := sign.

    Sentence := Noun-phrase Verb-phrase

    Noun-phrase := Noun

    Noun-phrase := Determiner Noun

Also there are two rules with Noun-phrase on the left sign, that means that one of them can apply - depending on if you have a single Noun in the text, or a pair of Determiner and Noun.

Next there are rules for words. It is used when you have any one of the words that stand to the right of the := sign, each possible choice of words is standing between the | sign.

    Noun := I | cat | spaghetti | home | computer

    Determiner := my | his | her

    Verb := go | eat | swim | jump | drink

Now look like these rules are used with the following sentences. The sentence "I go home".


                              Sentence
                              /    \
                      Noun-phrase  Verb-phrase
                          /       /     \
                        Noun    Verb    Noun
                        |        |        |
                        I        go      home

You get something like a tree, when you apply all of the rules!

You get something very similar for the next sentence

                              Sentence
                              /    \
                      Noun-phrase  Verb-phrase
                          /       /     \
                        Noun    Verb    Noun
                        |        |        |
                        I        eat      spaghetti

Now look at the following sentence "my cat eats spaghetti"

                                     Sentence
                                  /           \
                                /               \
                          Noun-phrase         Verb-phrase
                          /        \          /       \
                       Determiner   Noun     Verb     Noun
                        |           |        |        |
                        my         cat      eats    spaghetti

Words that are related have a small tree of their own, like "my cat" and "eats spaghetti"

Here you see such a small tree.

                         Noun-phrase      
                          /        \         
                       Determiner   Noun     
                        |           |       
                        my         cat

The word "my" and "spaghetti" are not closely related, but you see a connection - to connect them you need to go up until the top of the tree!

The tree for the grammar is showing you two things: - the order of the words - the order of thought: related words are in a small tree, close to each other, they explain one another!

People thought that this is a big deal, and they built a big theory around this!

The big deal is that you can describe a lot of sentences this way, even sentences that you have never heard before! You say that a language is 'generative' - if you can use it to create all kinds of new sentences, you can even make up sentences that don't make sense, but they are by the rules. "my spaghetti drink computer" - doesn't make sense, but these rules allow it!

A second question is: how do most children manage to learn all the rules of language so quickly, in the first few years of their life?

But we leave that for the next lesson....

One interesting thing: a grammar like this is always used to describe a programming language, that is a language used to write computer programs. The grammar helps us to create a language used for talking to the computer!

---04/07/22 22:35:39----------------------

Children learn language when they are very young.

Noam Chomsky is a linguist - a scientist who studies language. He says that we learn language very fast - much faster than we should learn it. He says that some kind of general grammar rules are built right into our brains, and that this explains why we are learning so fast.

He also says that language developed suddenly, as a kind of mutation. A friend of mine, who is very religious actually likes this - he says that this similar to the Bible and how God created language, all of a sudden! (all that despite the fact that Noam Chomsky doesn't believe in God at all) What i learn from this is that there are very different kind of ways on how to look at things!

Other linguist don't agree, so they fight it out among themselves.

You can learn some more about Noam Chomsky and his ideas here: https://www.youtube.com/watch?v=Q-B_ONJIEcE

There are many other linguists with different ideas, and we can also learn what they say, if you are interested...

Another detail: they say it shows that we have some built-in ability for learning language. Nicaraguan sign language https://en.wikipedia.org/wiki/Nicaraguan_Sign_Language

Nicaragua is a country; it had a big group of people who can't talk, who are deaf. The deaf people made up a sign language of their own, without anyone teaching them, all by themselves! And this language has all the features of a real language, just like all the other six thousand languages in the world!

Dolev asked a question! "If that is so then why are so many languages different in the way that you can arrange words in order to make an understandable sentence?"

That is a wonderful question! I am glad you asked!

Chomsky says there is a 'surface grammar' - a grammar for each language, but then there is a more abstract 'deep structure grammar' that is universal, common to all languages. The problem is that no one could find this deep structure grammar.

Then he changed it: he says what makes up the deep structure grammar are tricks for learning grammar. There is a rule for "merge" - building a substitution rule like

Sentence := Noun-phrase Verb-phrase

And there is a rule for recursion - recursion means rules for building sentences that contain other sentences. like "Dolev said that her friends said that the sun is rising".

But then this also has other problems: there should be some more common mechanism in the brain like "universal grammar", something that could be used for other things like vision, general problem solving, but there isn't. Also as I said, all these substitution rules don't work for languages with a free word order, like Russian (there are other structural grammars that work better here, like dependency grammars)

Still, people like what Chomsky did - he asked a lot of good questions like:

how do children learn language?
how is syntax represented in the brain?
what things are common between languages?

---05/07/22 00:35:13----------------------

Now back to art:

Something important happened some twelve thousand years ago. The ice age came to an end, it became warmer.

Now all the action happened in the sahara dessert - at that time it wasn't a dessert at all! There was grass everywhere, they had lots of animals there.

We know it from the paintings that people left on the walls of rocks (they also find old bones of elephant, rhinos, gazelles, giraffes - in places where there is a desert)

These paintings are now standing in the middle of the desert. There was no desert anywhere near the place, at the time when they were drawn!

At that same time something big happens: people start to do something new:

People start to have herds of animals, like sheep and goats, just like the forefathers of Israel - Abraham, Isaac, and Jacob! Now people had more time, as they didn't have to hunt and gather all day! Hunting and gathering takes up a lot of time, so you have little time for anything else.

You see interesting things in the paintings - there are more humans around, and they draw them in more detail!

This woman is sitting or dancing - painting from a famous site, Tassili n'Ajjer, in the land of Algeria.

It takes a long time until people start to plant their food, that is called agriculture. It takes some more years, you only get there three to five thousand years after that!

Something very happens in art, people start to build big monuments made out of big stones, maybe these are temples? (this kind of art is called Megalithic - Mega means big, lithic means a thing made from stone)

Göbekli Tepe in Turkey from 10.000 years ago!

In Israel we have Atlit-yam, that's place that is now under the sea, near Haifa - also from some 9000 years ago

You have lots of interesting old things in Israel. People had to get to Israel, if they want to go in and out of Africa! We were a big cross road! The weather is also great - it is not very hot and not very cold!

Stonhenge, in Great Britain - the earliest stones are from five thousand years ago, it took them a thousand years to build it

Why did people do all that? Scientist think that this is how we got society: once upon a time people lived in small groups, very small bands of people, or villages with up to a hundred people in it. Now you can trust everyone in a small group - you know each other well, some of the people are your relatives. Trust is that you can believe what they say, you don't have to think all the time that they want to cheat you.

Later the groups get bigger, and everyone is doing some special kind of work: some people are good at making clothes, so they make clothes all day. Some people are good at herding sheep, so that's what they do all day. These people have to exchange things - I give you my stuff and you give you your stuff, they need to trade what they got! At this moment trust becomes important, there is a big problem, if you can't trust anybody. Try to be afraid of everybody - now life is very hard if you do that, cooperation becomes impossible, if you have that!

Now people need some common ideas, a common religion. And they do big projects together to build these temples - in the process they learn to trust each other. So maybe this process of building art created our first societies! You see that art is very important...

It's not just a nice painting - people really put a lot of meaning into art!

---06/07/22 04:46:33----------------------

Remember we talked about how to grow food?

You need a lot of people to build these big monuments, because only lots of people working together can change the shape of these big stones and move them. It needs a group of hundreds of people who all live together. You need some specialists for carving the images on the blocks - specialists are people who are good at doing a thing. That's because they do it every day.

Now scientists thought a group of hunters and gatherers can't do this, because they can't get enough food to feed this big group of people! They would spend all of the day with finding food! It turns out that things are complicated.

Remember Göbekli Tepe in Turkey

from 10.000 years ago?

Scientists looked at the garbage from that place, and it turns out that they were eating gazelles. Gazelles are wild animals, they don't live in herds. You need to hunt a gazelle if you want to eat it, so these people did not have herds of gazelles.

A gazelle likes to jump around, and people can't keep them in herds, like sheep. The gazelles don't go were we want to go, they go to some other place.

What happened? You can do a lot to make it easier for the gazelles to grow, so that it is easier to hunt them. - you can kill all the animals that eat gazelles, there will be more gazelles for hunting, if the predators don't eat them - you can burn the wild grass in the steppe. The next year it will be easier for the grass to grow, and there will be more grass. This means more food for gazelles. This way you get more gazelles for hunting (Indians in America used to did this, so that they had more Bisons for hunting - you see, that needs a lot of planning, people were very clever, for quite some time!)

But then this explanation also has a problem: you can't do these tricks for a long time, If you burn the steppe for several times, then the land becomes tired, and the grass will not grow again. Erosion starts - that's when the wind is blowing the soil away, and you get a lot of dust. That's how big steppes can turn into deserts.

In the end it is hard to know for sure what happened. We can only make guesses. We don't know the exact history of the people who lived there.

One of the guesses is that they needed these very big art project in order to build a society - a society is a big group with thousands of people. Maybe that's the way to bring in lot of people and unite them for the project, you see these big buildings in lots of a places, all over the world, so maybe this is a stage that people had to go through...

You had these big art project in a lot of places, like the Easter Island - in the middle of the Pacific ocean!

Easter island is very far away in the pacific ocean, if you have a spacecraft, and you need to get rid of it, then you fly it to point Nemo - that's a point that is very far way from any land. This way the spacecraft will not fall on the head of anybody. Here is a map with point Nemo and Easter Island.

Here is an old Soviet/Russian space station called "Mir" - it is burning, while the pieces of the space station are falling on their way to point Nemo.

But later there came another big change: some five thousand years ago people learned how to write, they learned how to do that in both Egypt and in Mesopotamia (that is the land in Iraq). That is the start of history: from that moment we can look at texts that were written by the people who lived at the time! Before writing we can't know anything for sure, all we can do is make fancy guesses...

---07/07/22 05:47:41----------------------

Now lots of things happen between 12000 years ago until 5000 years ago (that's the time when we get the big civilizations of Egypt and Mesopotamia - the land in modern Iraq)

Lots of things happen during this time:

The city of Çatalhöyük in Turkey, it is from 9500 years ago, and some 5000 people lived in houses, that's a big group of people! The houses were built very close to each other, the wall of one house would also be the wall of the next house. But they sometimes had squares of empty space between the houses, sometimes they had big holes between houses - they would put their garbage in these holes. People moved from the roof of one house to the roof of the next house - they didn't have streets between the houses.

That's what they found

They think it looked like this

Usually a family lived in a house, the houses were all of equal size, that would mean that people were more or less equal - they didn't have very big houses for the rich people! That's a very strange thing - you don't have that very often, this is very unusual!

People also started with agriculture - growing plants for eating, they had rooms for storing wheat, barley and fruit. But they also held sheep and some of them were hunting.

You didn't have big city walls around this city for protection. Maybe the way they built the houses was a kind of protection - you would have to fight for each house, they were built very close to each other.

Also each family was making their own tools, they did not have specialists who would only do one kind of tool. More on that later.

Do you remember the story of Atlantis? The Greek philosopher Plato told a story of a city on an Island that was called Atlantis, the island later sank in the sea. Plato told, that they didn't have rich or poor people in Atlantis, so maybe that's a bit like the city of Çatalhöyük.

Dolev is asking "Maybe they were just communists?"

Answer: Maybe, but in the Soviet Union a director of a factory had a bigger house than a factory worker. Another thing: in old societies they were bringing presents to the graves, if a person dies, then he got presents, for the afterlife. But in Çatalhöyük they did not find much of a difference with these presents. You also don't have much of a difference in other societies - mostly simple societies in far away places. Maybe Çatalhöyük was somewhere in between - it was still a very simple society, but things were about to get much more complicated in the future. In English they say "strange things happen at sea" this means that things can get complicated - if you look at something specific.

Another place: the towers of Jericho from 10000 years ago. Jericho is a town near the dead sea - it is the place where people are living for a very long time, the oldest town on earth!

The tower was 8.5 meter high, when it was built. But then you had more and more soil forming around the place, so that it lies deep under the earth.

You need a hundred people building that, they would all have to spend a hundred days to build that. So they must to have some kind of organization: someone needs to prepare the food, others need to gather that food and store it somewhere. Lots of action!

Why would they build this wall? Usually you have that to defend against enemies, but we don't know for sure - they didn't find any enemies around the place. You can also use the tower and the walls as protection against floods - that is when the water is rising high. Some scientist say that big city walls are not only built against enemies - you need them to keep your own people from running away! Or maybe it had something to do with astronomy - we can only guess, they didn't know how to write things down ten thousand years ago.

Another big change: people start to make pottery, that is somewhere like 8500 years ago.

Here is one of the first pots, they found it near Kibbutz Shaar Hagolan in Israel, it is some 8400 years old, so it is a very old pot!

That is a big change: now from that moment archaeologists start to find pots and broken pieces of pots - they find these in a lot of places. There are a lot of ways to make pots, and people also make nice decorations and drawings on the pots, each culture has its own way of making pots, and you find the pieces of pots in lots of archaeological sites!

You can use these peaces of pots to guess about the date of what you found - when it happened. If you find stuff with the same pieces of pots, then they are from the same time!

You can also say, if these people were trading stuff with other people. Sometimes you can find a pot from a different culture, that shows what kind of trade was going on!

Also pottery may be a sign of specialization - some people start to make pots all day, others make tools, there may be other professions as well. The pottery is getting more complicated, and you need people who really know how to do this stuff, you can't make all of your tools, as before.

All this stuff helps you to find layers: new soil/earth is forming, and old stuff is buried under the earth (like at Jericho, where the big towers got buried in the ground). Now you can find different layers - different areas that have common style of pottery. This way you can group the stuff that you find by time! Troy is a town in Turkey, you remember the story of the Troyan horse? That's the place!

They found some ten different layers there, each one is coming from a different time period and a different kind of culture. Things get very complicated, if you have that many layers.

Like with the movie Shrek - here Shrek is explaining that he is a very complicated person, because he is having many layers

https://www.youtube.com/watch?v=-FtCTW2rVFM&t=37s

---14/07/22 03:58:45----------------------

There are a lot of ways to make a pot, each different way will give you a different kind of pot, you can tell a lot by looking at the pot and the way it was made:

This is how pottery is made, wikipedia tells us a lot about pottery in ancient Egypt: https://en.wikipedia.org/wiki/Ancient_Egyptian_pottery

First you have to find the clay - that's the stuff used to make pots; in Egypt you can do that by two ways
- get the clay from the Nile river; the river moves the stuff from the mountains down to the sea. The river has much more water in the spring, that's when the water is spilling over into the land around the river, a lot of land is covered with water. You can then find the clay, when the water gets back into the river. Nile clay was used for simple stuff that simple people bought for themselves. Firing will turn this clay into a dark red or brown pot - here is a pot made out of nile clay
- you can dig up the clay from the earth, this is Marl clay - you have to carry the clay for some distance, it was used for very expensive pots, Firing will turn this clay into a white or cream colored pot, here is a pot made out of marl clay
Next step: you need to prepare the clay, you can do this in two ways:
- make the clay dry, break the clay into very small pieces and remove small stones and dirt with a sift.
- put the clay in water, now you have to wait and remove the dirty water, do so again and again.
later you need to add some stuff, to make it easier to form the clay. This is called stuff is called temper - it can be made out of bones, out of coal, out of sandstone now comes an important part: you need to remove all the air bubbles from that block before using the clay. You can get an explosion without this step - the air bubbles will grow when heated, so that your pot will explode in the fire! You have to be very careful, also this step takes a lot of time, knead the clay again and again.

next you need to form the pot from the wet clay, again lots of possibilities.
- Form it by hand. If you make a pot on your own then you will most likely use this method.

Even today you have people who work like this. This picture is not from long ago, this is near the Amazon river in south America.

You can do better, welcome to the potter wheel! - use a rotating base, like this one, this is a very early method, it was even used before the time of the Pharaos, some six thousand years ago! - or you can use a slow potter wheel. You need one hand to turn the wheel, and you have to use your other hand to form the clay.

This potter wheel is an important tool, you can use that in a small factory. In a factory each person does only a single small part of the process, one person is preparing the clay, the other is forming and so on. You can make many many pots this way, when many people are working togather like this, this is called mass production. They had it since the Old Kingdom of Egypt - some 4600 years ago, when the pyramids where built!

The fast potter wheel, you can turn it with your feet and you both hands to form the clay, they had this sine the new kingdom of Egypt - some 3500 years ago, it took a thousand years to come up with this invention.

Next stage: the clay is still wet, it has lots of water in it. You can now decorate the pot, scratch something into the clay

Now is the time when you can also polish the pot and put on stuff to make it shine

Another detail: the base of the pot is being finished - the base is a tricky part, it needs a lot of work - even at this stage.
Next stage: Drying: You can't put it into the fire right now, the clay still has lots of water, the fire would turn the water into steam, and your pot would explode. Now you need to be careful - if the clay dries too much, then the pot will shrink. In the summer you have to put it into the shade, for several days.
Next stage: Firing: put the pot into the fire, so that it gets hard. But you need to turn on the heat slowly - there is still some water in the clay that needs to turn into steam. Again there are several methods to fire the pottery:
- an open fire, put some wood into the pot,
  
  - even used today, in Mali.
  
  Pots made like this often have a black rim on the top Still, there are lots of trick that can make a big different - more details: https://ancientpottery.how/open-fire-pottery/
- larger scale production: a Kiln - here you can control how much oxygen gets near the pot, while it is hot. This can be used to change the color of the pot. You also have more control on how the fire is burning, this gives you pots of better quality. You can know that each pot got the same amount of heat.
  
  This tool is also a sign of mass production in factories - a very advanced trick!
- Next stage: a kiln that separates the fire from the pots, this way you got even better quality pots - the flames of the fire don't leave flecks or smudges on the pot.

Archaeologists have a way to classify pottery, by the way it is made, by the quality of the clay, etc. This helps them to tell the culture and time period when it was made. Now you need to have such a classification for each culture, the pots in Egypt have their own classification, now Greece or Mesopotamia is a whole different story!

Pottery was important in Egyptian religion - they had the god Khnum, this one is one of the more important ones: he was responsible for flooding the river Nile -that's when all the land of Egypt gets a lot of fertilizers and you can then find the Nile clay, after the water returns back into the river. The symbol of Khnum was the potters wheel. He was also responsible for making the bodies of children - out of clay, on his potters wheel. The goddess Isis would later breathe life into them.

Pottery is also important in Jewish religion, Abraham worked at the shop of his father Terah, in the city of Ur, where they made idols out of clay. That's where Abraham found out that all the other gods were fake!

---17/07/22 05:42:22----------------------

Another big change after the ice age: how do we get our food?

Hunting and gathering is not that bad, people spend some twenty hours per week working here that means they work four hours per day, less than we do! They have a lot of time, but they do need a lot of skills for that:

they need to make their own tools.
If you want to hunt animals, then you need to know a lot about animals, how they behave.
They need to know lots of stuff about the different plants - as they have to search for them.
They know how to find their way in strange place, that's very important! There is a people in Australia, the Kuuk Thaayorre people. They don't have words for "right" and "left", but they know how to say North/South/East/West. These people feel very bad when they don't see the sun - they don't know how to tell directions, but they know how to find their way, much better than us! They always know where to go!

Look at this - it's a very interesting talk by linguist Lera Broditsky https://www.youtube.com/watch?v=RKK7wGAYP6k She is asking an interesting question: do people think the same in all languages, or do some languages make us think differently? In other words: can a language change the way we think? Gradpa Ilja always says that he got another life, each time when he learned another language - he knows some seventeen languages!

Dolev is asking a question: But they could see the moon at night, why do they feel bad when they don't see the sun?

That's right! But with the sun there is something that you can know for sure: in the morning it is in the east, and in the evening it is in the west. But the moon is walking around the sky in complicated ways, and it is more difficult to tell the direction by looking at the moon. People who life in Europe have the northern star - you can find a star that is always in the north, but the sky to the south of the equator is looking very different, i am not sure if they have such a star in Australia. Also Professor Boroditsky says that the concept of time is also connected to where the sun is - at least for the Kuuk Thaayorre people.

If you get lost - here is how you can find the North Star.

It is the last star in the constellation of Ursa Minor (that name is in Latin, it means the 'little Bear') Or you take the constellation of 'the Plough' and then go three times the length of the distance of the outer stars. Then you know where north is (but not if you go south of the equator)

Still lots of changes happened, with the ice age. People started to change the environment: we learned how to get animals to live with us, that means how to domesticate animals.

People had their first dogs some 20.000 years ago, they are the first domestic animal! Scientist know this: they study how the genes of the animal change, and how fast this is happening.

Dogs helped people with hunting, they have a much better nose then us. Dogs also told them if something dangerous is coming! Some Indians/native Americans treat their dogs as family members! They have big dogs, they helped to carry stuff around and helped the Indians to move quickly. That's an Alaskan Malamut, but that's a very big doggy.

Scientists say that both wolfs and dogs have a common great great grand daddy - the stone age wolf. You see, they are similar!

At some stage this stone age wolf became used to live with humans, that's when we had the first dogs. Some people say that dogs domesticated us. That's because people had to live in the same place, when they domesticated other animals and plants, like sheep and goat for example - and that caused some really big changes!

We know that wolfs and humans have lots in common:

we both hunt in groups,
we have to coordinate our action, there is a leader who tells others what to do. Now wolfs and humans came closer together and have a lot of contact: sometimes the wolf look out for hunting people, when the humans are finished hunting, then the wolfs can eat what is left of the dead animals.

Now also people do what the wolfs are doing, we learned from the wolfs: sometimes Indians in America where wearing wolf pelts, to get closer to groups of Bisons,

Also sometimes there are outcast wolf - that's when the group of wolfs doesn't like a wolf, so that he has to live on on his own. These outcast wolfs would have a reason to come closer to people, so that they can get a bone from us. Maybe the kids of the wolf were less wild, they would be used to life with humans.

Dolev is asking a question: How could dogs domesticate us, if we did that with other animals?

The dogs were the first domesticated animals, and I think that people would not know how to do this. I think that has to do with one of the theories: that wolfs got near to people - to get what is left over from what the people eat, and that people got near wolfs - to learn from hunting them. The other theory also says, that the outcast wolf got nearer to us - that means it was his initiative, kind of. In the end that's kind of a joke, but I am not sure. When I walk out our dog Nella, then she always knows where to go. Maybe the dogs/wolfs had a plan? Who knows, they can't talk...

https://www.youtube.com/watch?v=7DwmrQr11eo&t=621s Here is a funny story - I am sending the interesting part - where they author is having a discussion with a chief from the ice age. The funny story is that the dogs were the first, and then people would domesticate other animals. However the first domesticated animal would have been very difficult, that would be something new!

Some sixty years ago scientists managed to domesticate wild foxes. A domesticated fox wags its tail and likes to be with us, just like dogs. It took some twenty to thirty generations of foxes. At each generation they choose the foxes who are most friendly, these foxes will be the fathers and mothers of the next generation of foxes. This is called selective breeding.

https://www.youtube.com/watch?v=X-EXeZXwO08

Dimitry Belyaev managed to get tame foxes. https://en.wikipedia.org/wiki/Dmitry_Belyayev_(zoologist) Actually some seventy years ago he had a lot of trouble. The Soviet Union didn't like geneticists, during the government of Stalin. The most famous geneticist Nikolai Vavilov was thrown into jail and died of hunger. https://en.wikipedia.org/wiki/Nikolai_Vavilov Belyaev didn't get into jail, but he was in some serious trouble, because he was a geneticist. But thankfully they changed this policy, after the death of Stalin.

https://www.youtube.com/watch?v=HsIibD-TLcM

Dolev is asking a question: Why would they select breed the foxes, if they are not sure about genetics?

That's complicated. In the Soviet Union there were were different levels of allowed disagreement, at different times.

if you say that are against communism then you are in very deep trouble
if you are a member of the communist party, then they had discussions on what to do, but only until 1929.
if you were a scientists, then you could disagree with other scientists, mostly.

But then things got worse: in the nineteen thirties stalin became very paranoid, he feared that a different politician would replace him. And that's why he started the great terror waves of 1936-1939. That's when your great granddads got killed. Your great granddads thought that communism is a good idea, and moved to the soviet union, but that was a big mistake.

Now about genetics: at some time Genetics was allowed and welcomed - it promised to give you better sorts of grain. But then came a guy called Lysenko. Lysenko said that you can change plants by changing their environment - by educating the plants, he said that he can get better sorts of grain - faster. That is of course rubbish, but he managed to convince the communist party bosses that this is the right way.

All the geneticists were in deep trouble from this point, until the death of stalin. https://en.wikipedia.org/wiki/Lysenkoism

Dolev is asking a question: "Lysenko said that you can change plants by changing their environment - by educating the plants" Isn't that what Darwin is saying? Aren't you explaining natural selection? Also aren't the plants mutating and only successful adaptations would survive?

There is a difference between Lamarck and Darwin.

Lamarck said - an organism can learn something - and their kids will have what the parents learned in their life, that their offsprings will inherit what their parents have learned. https://en.wikipedia.org/wiki/Lamarckism Darwin says - if you are born with the right traits, and these traits can help you with surviving, then you will give these traits to your kids, and they have a better chance to go on, etc.

The funny thing is: Darwin once thought that Lamarck has point. But that is not true.

https://en.wikipedia.org/wiki/Vernalization Some seeds of wheat have to be put in the cold, for some time. This helps them to grow/flower. Now Lysenko said that these seeds have learned something, and that the next generation will have the same traits - that's what Lamark would have said. But it didn't work.

A lot of changes happened after the end of the ice age, some 11.700 years ago.

People domesticated other animal, sheep, goats, pigs. Sheep didn't have long hair - people also did the selective breeding trick, then we got sheep with long hair, we can then use the hair for making clothes.

People started to grow grass with grains - like wheat and barley. They always took the biggest grains to plant for the next season - this way they selected for the largest grain sizes. This way the grain sizes got bigger.

That's not a simple thing, it took a few thousand years to get these results!

At some stage people started to life at the same place, in houses. You can't move around all the time, when you need to take care of your animals and your wheat...

Dolev is asking: but is that a good thing? Is it of benefit?

Is has some good points, and some bad points.

the bad point: you have much less freedom. You need to work in big societies, they tell you what to do (mostly). Big groups of people get sick and infect one another. You also need to get clean water and get rid of the waste - people didn't know how to do this for a very long time.
the good point: You can store grain for a long time. Remember the dreams of Joseph and the Pharao in the Bible? Pharaoh had a dream of seven good years, and then seven bad years with bad harvests would come to Egypt. Jospeh explained this dream. He told Pharaoh to build cities to store the grain surplus from the good years. That means a big deal: if you are a hunting/gathering then you need to move often, when you run out of food. Also some Indian tribes in America even used to eat their poor dogs, when they couldn't find anything to eat. You have fewer of these problems with agriculture.
what about wars? Scientist in Australia watched how hunter gatherers make war. They make a lot of noise, they swear a lot, throw a few stones, and then they go away. It looks they are more peaceful, no way!

Archaeologists find a lot of buried bones of the dead ones with very bad injuries, you get these injuries/wounds at times of wars. The problem is that they make war all the time - there is a good chance that you will die in any one of these small wars. Civilized people have fewer wars, but the fighting gets much worse - they fight for longer periods of time, they have better weapons, they have larger armies. A more advanced civilization can get a bigger army, and has better weapons. On the other hand: you also have be more afraid to start a war, it is a very dangerous business.

They call that a 'trade off', you have two choices - each choice has its good sides and its bad sides. You need to decide which choice is the better one. Apparently people choose the way that could feed their kids, some scientists say that population pressure had a big role in the way that cities were formed.

In technology you have lots of trade offs - engineering is the art of making the best out of available trade off.

---19/07/22 04:54:05----------------------

We learned about very first cities, like Çatalhöyük - that's the point where people started to grow grains and when they were keeping animals like sheep, goats and piggies.

People in Turkey had enough rain for their fields, they don't have to add additional water - no need for irrigation (irrigation is when you add water to the fields, so that the plants can grow - that's a lot of work). No you can't work the field all the time: once every few years you need to give the land a rest, the land needs to gather new fresh organic matter. All this is called Fallow agriculture https://en.wikipedia.org/wiki/Fallow In the Jewish religion we have the Shmita year - https://en.wikipedia.org/wiki/Shmita every seven year the land should rest - exactly for this purpose! 2021-2022 is such a Shmita year.

Another important thing: how did people get plants big grain sizes and animals, such as sheep with long hair?

Gregor Mendel lived some hundred and fifty years ago, and he did some important experiment with pea plants, (here is a nice youtube video https://www.youtube.com/watch?v=3f_eisNPpnc )

Mendel also wanted to know something: sometimes traits in a family disappear for a generation, then they come back in the next generation. How is that possible?

Mendel did thousands of experiments with pea plants. Pea plants grow fast, and have lots of traits, such as:

The color and shape of the pea's pod

The color and shape of the seed

The color of the flower

Now lets look at the flowers, first he selected for the same color, he got two kind of peas, One kind of peas always gives you a purple color flower, when they mate with other plants of their group. They have a gene that tells the flower to be purple, lets calls the group R,R The other kind of peas always gives you a white color flower, when they mate with other plants of their group, They have a gene that tells the flower to be white, lets call the group r,r

This is called true breeding.

Now lets breed the peas with the blue color flower with the peas of the white color flower - this is called hybridization

Now the first generation all has purple flower plants, that's because they get a mixed gene - one from each parent that looks like this:

R,r or r,R - each one has the capital letter R that tells the flower to be purple (The first letter is the gene that it got from mummy plant, the second letter is the gene that they got from daddy plant) The expression of the R gene for the purple color is called the dominant gene - it is stronger, and that's why you use the capital letter R. The expression of the r gene (the one that stands for the white flower) is the weaker one, the recessive gene - if you have both the dominant and the recessive gene, then the recessive gene remains silent.

Now lets only breed plants from this generation, and you get something interesting.

One fourth of the flowers are white again!, that's because when you mix them:

        R,r    r,R   (this axis is the daddy plant)
      -------------
R,r  |  R,R    R,r
     |
r,R  |  r,R    r,r 

M
u
m
m
y

p
l
a
n
t

a
x
i
s

One fourth of all flowers is r,r - they are again white peas! And they will remain so, if you interbreed only within these white ones! Congrats, Mendel now got a model that explains what happened, that's what they call science!
He got an explanation, even without explaining how it works exactly - people had to work for another hundred years to get there, and that was a lot of work...

You also have more complicated situations - other than complete domination

Also, you sometimes get girl cats with three colors, but boy cats can't be like this. See https://en.wikipedia.org/wiki/Calico_cat

There are lots of possibilities....

Did you know that you can tell where a giraffe comes from - all by looking at the pattern of it's skin? from here: https://earthlymission.com/regional-giraffe-patterns-throughout-africa/

People from a long time ago had some idea of all this, you can read it in the Bible!

Jacob was the son of Isaac, our forefather. He worked fourteen years to marry Rachel and Leah. Then they had a problem: Jacob didn't have any sheep or goats of his own, and his big family didn't have much to eat! He couldn't go his own way, he would have to work for his stepfather Lavan forever. Now Lavan liked to pull tricks on Jacob, he told him: "here are these goats and sheep - they are all have the dominant gene that makes them of a single color. But you can have all the goats and sheep with the spots, that's the recessive gene" He didn't use these word, but that was the message. Now Jacob worked a lot of years caring for the animals, and he probably knew something about Mendel's laws. In the end he got a big group of spotted goats and sheep. That's the way we have a Jewish people, because we wouldn't have one if Jacob would not have found anything to eat... You see: a long long time ago these were very important things to a lot of people! People cared about this stuff!

Dolev: (About the giraffes) that is gorgeous! As if they have different imprints.

They say there are regional differences, they don't say why.

I was surprised when I first came to Israel: pigeons look different in Israel and in Germany!

In Berlin they are bigger, and the color is a little bit different: https://www.exberliner.com/berlin/berlin-pigeons/

And our pigeons look slightly different https://www.shutterstock.com/video/clip-8297344-closeup-shot-pigeon-walking-on-floor-israel

There is an interesting things about islands in the sea: animals on islands are often smaller than on a continent! https://en.wikipedia.org/wiki/Insular_dwarfism Even big dinosaurs were smaller on islands!

Another important thing: you can keep a lot of grains in places of storage. This gives you a big advantage:

you don't have to be hungry, even if there is one bad harvest. You still have something to eat!
you don't have to move around all the time. Hunter gatherers are always moving - if they can't find their food in one place, then they move to some other place.

Still living in cities has a lot of risks

people live in a small space, they didn't have to put their garbage somewhere, and they didn't have toilets. It is also a big problem to get clean water to everybody. As a result people were often sick, and there were diseases, when many people get sick, just like with Corona!
people have to work more hours, much more than they used to work as hunters and gatherers.
you can have a bad year, where there is little rain. The plants will not grow and people will stay hungry.
there are more risks: things can go bad, like when a war happens

Now 8200 years ago the weather changed, it became drier for many years, that's called the 8.2k event https://en.wikipedia.org/wiki/8.2-kiloyear_event That's the point when people left the city of Çatalhöyük, but people still lived in smaller villages - they didn't die out. It took about a hundred years for the climate to get better! Progress took a big break.

The weather is relatively good for a long long time, from 8200 years ago to 6200 years ago it gets better again. That's when we see some progress!

By the way: once every 1500-2000 years there is a big change in the weather, it is getting cold for a few years, or even up to a hundred years. That's a hard time for civilization.

See this table from wikipedia (i changed the notes a bit)

https://en.wikipedia.org/wiki/Bond_event#List

No |Time | Time G(AD, BC) |Gap from previous event|Notes

0	≈ −0.5 ka	≈ 1500 AD	900 years	See Little Ice Age[12] (The Mongolian empire dies, lots of antisemitism in Europe - they are blaming it on the Jews, Nasty witch hunts)
1	≈ −1.4 ka	≈ 600 AD	1400 years	See Migration Period[12] and Late Antique Little Ice Age (the Western Roman empire has a hard time and dies)
2	≈ −2.8 ka	≈ 800 BC	1400 years	See Iron Age Cold Epoch.  https://en.wikipedia.org/wiki/Iron_Age_Cold_Epoch
                                        Bronze age collapses somewhere around 1200-1150BC, what about the weather? https://en.wikipedia.org/wiki/Late_Bronze_Age_collapse (spoiler - it did have a role, but you need more than one thing to kill a bronze age state)
3	≈ −4.2 ka	≈ 2200 BC	1700 years	See 4.2-kiloyear event; collapse of the Akkadian Empire and the end of the Egyptian Old Kingdom.
4	≈ −5.9 ka	≈ 3900 BC	2300 years	Sahara desert reforms by 3500–3000 BC, Ubaid culture ends? Early Bronze Age begins ~3300 BC.
5	≈ −8.2 ka	≈ 6200 BC	1200 years	See 8.2-kiloyear event (people leave Çatalhöyük)
6	≈ −9.4 ka	≈ 7400 BC	1100 years	Erdalen event of glacier activity in Norway,[15] as well as a cold event in China.[16]
7	≈ −10.3 ka	≈ 8300 BC	800 years	
8	≈ −11.1 ka	≈ 9100 BC	---	Transition from the Younger Dryas to the Boreal.[17]

Next comes the Ubaid period (some 8500 to 5800 years ago), it is called like this, because archeologist found the first stuff at a place called Tel-Ubaid in Iraq. https://en.wikipedia.org/wiki/Ubaid_period

now people start to do something new in Mesopotamia (that is Greek and means the land between the rivers; Meso - in the middle; Potamoi - rivers in Greek) Now we see a very complicated culture!

The fields don't get enough rain there, so you need to bring the water from the river. It starts to get complicated - they need to build complicated canals. Now that is a lot of work, many people need to dig these canals. Also you have to repair them a lot - that's also a lot of work.

You need to build big walls around the main river, so that the water does not spill over. Also a big river can change it's course - the river can change the way that it is flowing. You can't have that with agriculture. Building that kind of thing means a lot of work! Then you build smaller canals that get their water from the big canal. These also need to be reparied.

You need gates between the bigger canal and smaller canals; They opened the gates and the small canals get more water

You even have a minecraft version - to learn about water management from six thousand years ago! https://education.minecraft.net/en-us/worlds/mesopotamia

Someone has to organize people for all this work, you need a lot of workers. Some people say it all started with the temples.

You see the first big temples built in the city of Eridu:

You have buildings for storing grain - granaries. These are near temples. Even at Çatalhöyük they had special rooms for storing grain, they also found strange figures of animals - it is possible that this is a sign of a temple and that it all started with temples.
They now need to count things, these are tokens made of clay. Each clay token is several centimeters big, and the number of scratches mean a number.

A temple has to count the number of things that it gets/stores. A trader is a man who travels to far a way places, he brings stuff from far away and needs to exchange that for something of value, so that he has something to bring back. A trader needs to count the number of things that he receives. You can also find these tokens in the bigger houses of the chiefs.

The form of the token may tell us what is counted

flat disk mean measures of grain
egg shaped tokens mean jars with oil
cylinder tokens mean a number of sheep

That's the first way to write things down, before they invented writing! They call it proto-writing system (a system used before writing)

At some stage people find seals - a seal is a form, and you can press it into clay so as to leave an impression.

Later you get cylinder seal impressions like this one:

How do you make an impression like this? You take a cylinder made out of stone or metal and roll it over the clay. The cylinder has a form, and you then see a picture left in the clay! Here is a seal from much later - but it's the same idea.

That's the cylinder seal of queen Puabi from 4600 years ago (from the Sumerian culture, that was a bit later) https://en.wikipedia.org/wiki/Puabi (Who found the seal? Leonard Woolley - an archaeologist who inspired the Indiana Jones movies! Cool dude! https://www.nationalgeographic.com/history/article/150514-indiana-jones-archaeology-exhibit-national-geographic-museum ) Queen Puabi also had some jewels, made of gold:

Seals are used by important people who have something to say. A seal imprint tell us "this item is now under under my responsibility and that's me, look at the picture!", it is like writing a name under a document, a signature! It's a big deal that we found these seals: it means that the rich and important ones were different from the rest of the people. Not like at Çatalhöyük, they had more equality.

seals and tokens are combined: you take a few tokens, put them into a small pot, or clay ball - the clay ball contains a message. Then you sign the clay ball with your seal - the seal tells you that the message is real, and that it has not been faked!

Actually we have something similar, in our time: Digital signatures!! Lets say there is a picture of me. I want to make sure, that people know my real picture, and that everyone knows that this picture has not been faked. Now I can make a digital signature of the picture, and everyone else can check if the signature was made by me. That's like an imprint of a cylinder seal on a pot of clay with tokens - the same principle! In our time the technology of digital signatures is used in lots of areas: electronic books, digital television, voting systems. I can tell you more about it in another lesson, if you want.

People start to live in a number of cities, with some four to seven thousand people: cities like Eridu and early Uruk. Now these cities didn't have big walls around them. That means they didn't have to defend themselves. I think that is very important (will tell later).
you need better tools for working the land, someone has to build ploughs, sickles, pots for storing grain.

Here are some tools used for agriculture - made of clay and then put into fire so that it gets hard (like pottery)

People start to specialize - they work all day in only one area, they do what they have learned to do. Someone is a potter, someone is working in the field, someone is weaving clothes, they do that all day!

trade: you start to bring stuff from far away places, also some places specialize at doing the stuff that they are good at!

South Mesopotamia is good at making food: they make grain, pots, clothes

North Mesopotamia is good at making metals: they make copper and tools out of copper. Copper is the first metal used by people, it is a bit soft and melts at lower temperatures - it is easier to work with copper. But you still need to heat that stuff to 1100C, that's very very hot! The northern town of Değirmentepe was mining copper, so that they have something to trade. That's specialization - you need to bring in food from other places!

some people have more to say than others. You see that some houses are bigger than others - the chief lives here. Still there is no big difference between the rich and the poor. Still they don't find any exotic materials or goods that are created only for the very rich. Also they didn't see a big difference in the graves for the dead - no big difference in the gifts that they put in a grave.
Pottery: this time we got pottery! You need pots and jars to store things in, and to move them from place to place.

They also invent the potters wheel, at some stage there are mass produced pots and bowls. That means they already had factories, where each one was doing just a small part in making the product - that's how many people work together. They can make a lot of pottery this way. An interesting thing: these mass produced items don't have any decoration. There is no time for that!

For example they found lots of bowls of the same time and shape - at the mining city of Değirmentepe. That may be a way to give the same amount of food to each of the workers who worked at the mine.

(found lots of information here: https://belleten.gov.tr/tam-metin/61/eng https://www.thoughtco.com/clay-tokens-mesopotamian-writing-171673 )

You see that things are getting complicated - there are many systems that need to work together for all this to work! But then it all stops when the weather turns bad with the 5.9k climate event. https://cof.quantumfuturegroup.org/events/5370 But we will see the next series, in a few hundred years, with the Sumerian civilization.

Now they still didn't invent writing, so that scientists have to guess about a lot of details.

An interesting thing: they cities of this period were populated for some 1200 years, without breaks. The archeologists didn't find signs of wars - in other places they often find layers when the cities was destroyed and later rebuild, this is a sign of a war. But they don't find this with the Ubaid period towns ! Also the cylinder ceal impression do not show weapons, or scenes of war (but you get a lot of that in the next culture) Is it possible that the cities of this period did not fight wars against one another? Lots of open questions.

Also they didn't find city walls, a city wall has two functions; one is to keep the enemy out of the city, it is for defending a city. The other role is to keep your own people from running away. They didn't have that!

There is a theory of Hydraulic civilizations - these are complex cultures that need a complicated system of canals. The canals must bring all the water for agriculture. The theory says, that these cultures are very centralized. They must have a king who can tell everyone what to do. They need this in order to get the workers needed for building these big canals, it's a lot of work to build and keep them! Everyone has to do what the king says, otherwise he will not get water for his field, no questions asked. The theory says that these cultures are always despotic - they have a central ruler who can do whatever he wants. The king often counts as a god or is a relative of one. Now i read a few articles, but it does not seem to be the case with the Ubaid culture.

Here is an interesting article, it tries to gives an answer: http://www.columbia.edu/itc/anthropology/v3922/pdfs/stein_gil.pdf The Ubaid culture had some tricks: Gil Stein says there were two centers of power: the temple and the chief of the tribe.

The family of the chief is often a big one. They have big families, and they can tell their family members to work on the common canal. This gives the family of the chief a lot of weight.
Land owned by the temple is a kind of common land. The granaries kept by the temple are very important - in bad times a person can get some of the stored grain. This gives a lot of authority to the temple: they can tell the people to work this temple land, it's kind of a common land.
The chief can play tricks: they tell us about an example from modern Irak, in our time - but from the same place. The Chief is administrating the land of the religious leader. He gives some grain/money for keeping up the temple, but he can keep the rest for himself. Now this sponsorship also gives the chief some authority: he can now call all the other tribesmen and tell them to work on the land owned by the religious leader. In Hebrew this is called 'a combination' (kombina)

Now the Ubaid culture had a lot of 'soft power' they had could pursuade the northern towns to join their culture, without war! They see that the culture in these northern areas changes from an older culture - the Halaf culture) to the Ubaid culture, again without signs of war and destruction. It can be, that people worked for the temple, for the common good of everyone, not because someone forced them to do so!

But I don't understand the following: In the Sumerian and Babylonian culture they had a big problem: People from the mountains, who don't live in cities would make war against them. One can gain a lot by attacking cities, you can get a lot of stuff from looting the cities. If this is true, then they would need to have a big army, and there would be a chance of defeat, meaning layers of destruction. A big army would mean that they could force people to do stuff against their will - meaning despotism would be a thing.

In any case, we know much more about the next culture, the Sumerians. That's because the Sumerians learned how to write! We have to guess less with the Sumerian culture, because the Sumerian culture has it's own voice - the things they wrote down. Also cities got ten times bigger - the city of Uruk had some fifty thousand people, they had to get ten times more food for them! It also becomes harder to rule over a big number of people.

(the next section is probably not very educational, won't send that to my kids...)

Here is a song by Randy Newman - he is the artist who wrote and sang all the songs in the "Toy Story" movies. He wrote:

Now they're gone, they're gone, they're really gone
You've never seen anyone so gone
They're a picture in a museum
Some lines written in a book
But you won't find a live one no matter where you look

The song is written about the Indians in America. I think that the song is also about other cultures, who didn't know how to write (or who did know that, just that we can't understand what they wrote). Here is the song: "The great nations of europe" :: https://www.youtube.com/watch?v=q3hMA76mBGE

.. and you won't hear that song in a "Toy Story" movie either ...

A short short break: let's talk about digital signatures. That's a bit like the method of signing a clay jar with a cylinder seal. There is a difference: our digital signatures are using math and are using a computer. But there is a common thing: they both try to solve the problem of trust by means of technology. The problem is: here is a message. Now I am sending this message to someone else who is far away. Now how can he know, that this message is from me? And that's a very old problem, people thought about it some six or seven thousand years ago, that's before the invention of writing!

Digital certificates are used in all sort of things: Digital money like bitcoin and ethereum, voting system, you are also using that when you buy stuff online!

Let's first talk about encryption and decryption:

In simple systems you are using the same key for encrypting and decrypting a message. Let's say you use a substitution cipher - the key is the way how you swap letters: for example swap A with the letter Z, B with the letter Y, C with the letter X, and so on. Now the same method/key is used to decrypt the message. That has a problem: if you have caught the guy who has encrypted the message, then you can beat him with a stick and force him to tell you the key. Now you can read this message, and all other messages that were encrypted in the same way! This method has a name, it is called rubber-hose cryptanalysis, because you beat the information out with a stick. (a rubber-hose is a hard stick made of rubber, that one hurts a lot!) : https://en.wikipedia.org/wiki/Rubber-hose_cryptanalysis

That's why they invented asymmetric encryption - here you have two totally different keys, one is used for encryption, and the other is used for decryption. One of the keys is public - everyone can know them, the other one is private - it is a big secret.

Now lets create such a pair of keys with the openssl program, from the command prompt. (here they tell you haw to install it on windows: hhttps://wiki.openssl.org/index.php/Binaries )

This command is creating the private key (and the public key) - it puts them into file privkey-ID.pem This private key file is your cylinder seal, your digital identity, your preccccious ring. You keep it just for yourself!

openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048  -out privkey-ID.pem -text

Lets look at the parts of this command, each part has something to say:

openssl - that's the name of the program that does cyptogrphic stuff
genpkey  - that's the name of the action, we want to create a private key
-algorithm RSA - tells what kind of key is created, by the RSA algorithm
-pkeyopt rsa_keygen_bits:2048  - tells you that the private key will have 2048 bits (the more bits there are in the key, the harder it is to break the encrypted message)

Now lets get the public key with the following command. The public key will be in file pubkey-ID.pem You can give the public key to everyone, who needs to interact with your digitial identity.

openssl pkey -in privkey-ID.pem -out pubkey-ID.pem -pubout

Lets look at the parts of this command, each part has something to say:

openssl - that's the name of the program that does cyptogrphic stuff
pkey - we want to do do something with the private/public key
-in privkey-ID.pem  - the output file, it will the the private ke
-pubout - show the public key part

Now let's use the public key to encrypt the message - you give this public key to everyone who can send a message to you. If they catch him, then they can't get the other part that is needed to decrypt other messages that were encrypted with the same key!

let make a text file with a secret message - and put the text into the file message_to_send.txt

echo "Attack at dawn" >message_to_send.txt

Now let's encrypt the file with the public key!

openssl rsautl -encrypt -inkey pubkey-ID.pem -pubin -in message_to_send.txt -out encrypted.bin

The encrypted file is something binary, no way to know what it means, without the private key (the decryption key)

That's a hexadecimal dump, it shows what is in a binary file, which is not text:

hexdump -C encrypted.bin
00000000  b8 c9 e1 00 c5 c7 22 7b  b5 e3 91 80 94 e7 be be  |......"{........|
00000010  41 41 3a df 96 97 1b 69  90 bc b7 94 af 41 af c7  |AA:....i.....A..|
00000020  07 97 5b 42 bd c4 18 f2  3b 78 fd 92 12 a5 2f a9  |..[B....;x..../.|
00000030  69 45 42 d3 26 0b d4 58  5b 29 16 e0 35 c1 a5 92  |iEB.&..X[)..5...|
00000040  bf 25 7e 3c 6d 4f 03 ea  11 65 90 db 0d fd be f1  |.%~<mO...e......|
00000050  c6 12 97 9d 16 ac c0 52  30 25 b7 46 d7 21 03 59  |.......R0%.F.!.Y|
00000060  bc 31 5a 0e 91 ff 63 db  e5 0d 04 07 a8 90 5d 1b  |.1Z...c.......].|
00000070  67 64 11 de d0 d3 c1 80  db 7c 45 c1 b8 cf ec 99  |gd.......|E.....|
00000080  39 fc 33 39 90 1d 94 5b  dc ce 53 49 2f 95 74 82  |9.39...[..SI/.t.|
00000090  ba e3 26 d0 cc b6 20 51  63 7d 39 7f 77 e6 44 c2  |..&... Qc}9.w.D.|
000000a0  dd d7 a0 7a 0b 19 67 29  d1 5a cd 3a b2 f1 75 39  |...z..g).Z.:..u9|
000000b0  f5 fb 92 b5 fc 0f 29 0d  09 e7 70 35 c3 72 11 99  |......)...p5.r..|
000000c0  13 b0 d9 02 a1 df 40 95  79 d2 45 c5 4f 36 68 8c  |......@.y.E.O6h.|
000000d0  a0 4b 60 25 40 09 c4 cd  66 8d c5 2d e2 f6 cd bc  |.K`%@...f..-....|
000000e0  39 f1 58 1b 87 f9 9e b4  41 fc 37 78 70 ae 70 5e  |9.X.....A.7xp.p^|
000000f0  a2 a1 55 bb 01 29 71 0b  03 a1 c2 89 dd 27 fb 1a  |..U..)q......'..|
00000100

Now let's decrypt the thing with the private key, only I can decrypt and read the original message, as I didn't give the private key to anyone else!

openssl rsautl -decrypt -inkey privkey-ID.pem  -in encrypted.bin
lets attack at dawn

Now lets create a Digital signature: let's say that I have a picture of me: me.jpeg - I wan't to say that this is my picture, not a fake one.

Now I take my picture as input (file me.jpeg) and use the private key (file privkey-ID.pem) - that's my digital cylinder seal, to create the digital signature sign.sha256 The digital signature is a file. It proves that the image my image, it's like an imprint of the cylinder seal

The resulting signature is in the file sign.sha256

openssl dgst -sha256 -sign privkey-ID.pem  -out sign.sha256 me.jpeg

What happened behind the scenes?

First we take the picture file me.jpeg as create a number that stands for the image.

An example:

here we create a sha512 digest of the text 123456 - the result is a number that is 1024 bits long (that's 128 bytes 1024/8=128 )

echo '123456' | openssl dgst -sha512
1caced6fca2237153d65adfb0f3dbe33b9375e9eb6df17c379f80cd37deb6e6a70159c7e898576db568b871ca1c2ffd1a2cc3205f1b50be5396096335fc29c40

Now we just add the digit 7 to the text, and we get a totally different value of the digest!

echo '1234567' | openssl dgst -sha512
a6e0dd4375374d5a37c8395d86e6e0b4baa8ba56da30a7193a6eea4022855477fdf90ee00685ef57f134a649fc2ac08e712fc525e975ce23a88ba0ef0f0d742e

This is done on purpose: you have a very very small chance, that two different input files will result in the same number! You can learn more about message digests in this video: https://www.youtube.com/watch?v=DMtFhACPnTY (also Computerphile is a nice channel for learning about computers! https://www.youtube.com/user/Computerphile )

The second step is that this large number is encrypted with your precious private key (the cylinder seal) to produce the digital certificate as a result (the imprint of the cylinder seal on the clay tablet) This step makes sure, that no one has changed this number, you will see why this is needed. Note the difference - we encrypt with the private key (our big secret), previously we encrypted with the public key! That's because we want everyone to check on us, they can only do that with the public key.

Everyone who has both the picture and the public key can now check, if the picture was signed by me (only I have the private key)

Here is the steps they have to do:

first decrypt the encrypted digest with the public key, so they have the original digest. Now they can be sure that no one changed this number!
they also compute the digest from the picture
if these two values match, then the picture was signed by me!

That is called 'verification of a signature', it is done in one step:

openssl dgst -sha256 -verify pubkey-ID.pem -signature sign.sha256 me.jpeg

Now we have learned about something completely different. Isn't that cool?

---03/08/22 00:47:25----------------------

What happened after the 5.9 kiloyear event, when the weather was bad for a hundred years? https://en.wikipedia.org/wiki/Bond_event#5.9_kiloyear_event

Africa had some big changes: the Sahara used to be a green place with lots of grass and animals - then it turned into a dessert. People who lived in the Sahara had to go to to other places - some of them go to the Nile river, with lots of water. That's were we have Egypt. https://en.wikipedia.org/wiki/African_humid_period

Some of the art from the Sahara looks similar to early Egyptian art - from the time of the early Pharaos!

https://youtu.be/GtFiVcU6THw?t=631

But other scientists say, that Egypt got many ideas from Mesopotamia/middle east.

The next season of civilization starts a few hundred years later, that was about 5300 years ago, and it goes on until 4200 years ago https://en.wikipedia.org/wiki/4.2-kiloyear_event

Now you get the Sumerian culture in Mesopotamia, and in Egypt we get the Old Kingdom - the age of the first Pharaos, who united Egypt into a single country. However the Sumerians and Egyptians didn't start from zero - they continued with the knowledge from the previous season!

Both cultures invented their own form of writing, so now these cultures have their own voice, we also know a lot more about these cultures!

Mesopotamians scratched signs on clay tablets

Here is the sign for head - first it looked like a drawing, in later times it got more abstract, but it got easier to write down!

Egypt had hieroglyphs - these were written on papyrus scrolls.

Thats the Rhind Papurus - it's about mathematics https://en.wikipedia.org/wiki/Rhind_Mathematical_Papyrus

Some interesting facts:

They found a board game from 4500 years ago, luckily they also found the instructions for the game, again on a clay tablet. Look at the The Royal game of Ur - looks like fun! https://www.youtube.com/watch?v=WZskjLq040I&t=82s (this link skips the introduction)

They even had a notation of music, notes from some 3400 years ago - also on clay tables https://www.openculture.com/2014/07/the-oldest-song-in-the-world.html Here they played the musics, from these notes! https://www.youtube.com/watch?v=9c-hmFN610g

King David also made music with a Lyre!

It seems that we have more written texts from Mesopotamia - clay tables can get really hard and survive for a lot of time. Also: if the library with tablets burns down because of a fire, then the tablets become very hard and last longer. Papyrus scrolls are harder to keep that long, also they burn quite well, unfortunately.

However we seem to have more works of art from Egypt - they have built some great monuments in stone, whereas Mesopotamia was building everything out of clay bricks - these don't last for quite as long.

Some common things between Egypt and Mesopotamia: things start to get big. Cities get ten times larger than in the previous age - tens of thousand or even hundreds of thousand of people life in Ur - in Mesopotamia, and in Thebes - the big city of lower Egypt.

Now any organization has a big problem, when it grows ten times it's size: you can even see that today, with high tech companies. The problem is that these companies no longer know how to make decisions: anything that worked when the company was smaller stops working! In a small company could make a meeting, where everyone could say something? In a large company there are many more managers, no one can keep track if everybody says something! Also look at schools: the teachers have a big problem with very big classes - how do you keep all the kids listening? What happens when someone asks a question? It is much harder to teach in a big class compared to a small class (Now you should value your summer school, where you can ask questions - you never had it so good ;-) )

You see that everything is different, this time. They got a thing called the state, and had to invent laws and other rules - and they had to write them down and keep people who would enforce them! That would mean - to check if the rules are followed and to punish everyone who does not follow the rules.

Dolev says: I think they had papyrus scrolls in the library of Alexandria

Me-answering: yes, but they all burned down, when the arabs took Alexandria. https://en.wikipedia.org/wiki/Library_of_Alexandria#Arabic_sources_on_Muslim_invasion0

Their leader said: "If those books are in agreement with the Quran, we have no need of them; and if these are opposed to the Quran, destroy them."

Dolev says: I know, that's quite upsetting. Maybe the scrolls had a lot of information that made them mad?

Me-answering: That's an interesting question, it is hard to know what people thought when they wrote them down. Who could write things down? Only few people knew how to write, writing was a difficult thing and you had to learn it for many years. Those who could write would work for the state. But there are interesting episodes when they do tell about what people thought. We will talk about it later.

For example there was king Urukagina in the city of Lagash. https://en.wikipedia.org/wiki/Urukagina He made a lot of changes: he made the first laws ever, and wanted to help normal people. for example the tablets say that he made changes, so that "The widow and the orphan were no longer at the mercy of the powerful man" An orphan is a child who has no father and mother, a widow is a woman who was married to a man who died later. Here is a lecture on cuneiform writing - it is very difficult, some signs are words - like hieroglyphs. Some signs are syllables, but without vowels - like in Hebrew writing. but sometimes different signs mean the same thing - and it all changed a lot during the three thousand years, when they used cuneiform. https://www.youtube.com/watch?v=PfYYraMgiBA

The city of Ur may have looked like this, the big temple/ziggurat is at the center. That may be the place where Abraham broke the idols!

Egypt had these big pyramids, the big ones were built 4500 years ago. They had free people working there, not slaves - it was a big honor to work at this site.

You may think it was a waste to build these? Maybe that is not the case. Building these huge pyramids may have had the same role as all the other megalithic structures that we see all over the word. Maybe they brought the people of north and south Egypt together. (I think that was very clever: they didn't have these in Mesopotamia - and all city states there were fighting against each other, bitterly)

I think you even have that today - look at the space race in the twentieth century. Ask any Russian and any American: Who has send the first man to space? the Russian will answer proudly - that was us! Who has send the first man to the moon - the American will answer proudly: that's us, of course! The space race was not only a weapon in the cold war between the USA and the Soviet Union, it was a tool for building a feeling of being "us" and feeling of being part of something big - a collective identity.

Look at any of the TV series for pre-school kids: they all have an episode about Christmas and an episode about going to the moon. You need to start with building this sense of being "us" at a very young age...

Also: some things seem to be the same, in the words of King Salomon in the Bible: That which has been is that which shall be; and that which has been done is that which shall be done: and there is no new thing under the sun. In Hebrew: מַה שֶּׁהָיָה הוּא שֶׁיִּהְיֶה, וּמַה שֶּׁנַּעֲשָׂה הוּא שֶׁיֵּעָשֶׂה, וְאֵין כָּל חָדָשׁ תַּחַת הַשָּׁמֶשׁ.

Europe discovered the old cultures of Egypt and Mesopotamia some two hundred hears ago. That's when Europe had it's time of big changes - the age of steam and steel. I think that digging up stuff from a very long time ago helped people to understand the big changes in their own life time.

The steam engine allowed us to use a lot of energy. You just need to move the coal and make a fire. The fire heats up a big closed pot with water, the water turns into steam and the steam engine is using that pressure to turn the big wheel around and around!

The next picture shows you how it worked:

This power was first used to drive machines for making clothes

The long sticks at the top were turning, then this movement was passed to the machines at the floor through these long bands. That's a very dangerous way to work!

Later they used steam engines to build train, this is a train from around 1870 - it is not the first train.

That picture is from 1964 - that was six years before I was born. I even travelled on a steam powered train as a kid, in East Germany, in the nineteen eighties. That's not that long ago - that was just some forty years ago! They already had better engines, but they kept the steam engine for a long long time, as they had a lot of coal at the place. (just like in "Thomas & Friends")

They built some some really big things made out of steel and iron:

Like the Eiffel tower in 1889, the tower is much bigger than the pyramids!

Or the Brooklyn Bridge in New York - built in 1883

Back to five thousand years ago: the big changes came because of a new material called Bronze:

We already talked about copper, that is a metal, and it is a bit soft. There is another metal - tin, it is much softer than copper. Now take 90-95% copper and 10-5% tin, heat them up with the same fire at the same place, and the two become liquid and mix. Then wait until this mixture gets colder, so that it turns hard again. Now you get a new material - bronze.

Bronze is much harder than copper or tin, so you can use it to make weapons and tools.

This is a plough from Egypt. They use it to dig up the earth before planting, so that the plants can grow better. A plough with a piece of bronze is much better than one made of wood - it can be used for a long time. https://en.wikipedia.org/wiki/Ard_(plough)#History

This is a bronze axe from Egypt

That's a Khopesh - a bronze sword from old Egypt

And these are bronze swords from Greece

And they could kill people at a distance, with bows and arrows. The arrows must have a arrow head made of bronze. This picture is from the kingdom of Akkadia, in northern Iraq.

The big deal is to get these metals - you need to travel a lot. You can dig up copper from under the ground in many places places. You can find it in Timna, in Israel https://en.wikipedia.org/wiki/Timna_Valley#Copper_mining - some 9000 years ago they were already digging up copper at that place! You can also get copper in Cyprus - in Greece, or in Turkey - at the Taurus mountains, and in other places.

Now finding tin is a bigger problem - there is less of it, and you need to go to much longer distances in order to find tin. You need to go to the mountains of Afghanistan, Spain, Turkey, England - they found tin from England in a sword from Mesopotamia, one that was made thousands of years ago!

So you need to have a big system for organizing trade over long distances: you need to make stuff that you can give people in far away places, stuff that they want - so that they will give you the tin and copper in return. You need big ships to move over the sea and caravans to move the stuff through deserts, you need to get the money for all this, somehow, you need to make sure that no one will take this expensive stuff from you, while you are travelling. You need even more details for all this to work!

They found a lot of stuff under the see, near Turkey https://en.wikipedia.org/wiki/Uluburun_shipwreck It comes from a ship that sank in a storm. The museum in the city of Bodrum tries to show you how this ship looked like:

You can't have all this trading at long distances without a big system. A system is like a big machine - you need a lot of parts that work together.

---10/09/22 13:30:08----------------------

One very important thing during the bronze age was to have big parties (no one could dig canals the whole year through!). That's one of the reason of having a calendar, it tells you when you should have a festival!

In Egypt they had the Opet festival , it was a religious festival and it happened during the flooding of the river Nile. Here the Pharaoh was having a ritual marriage to the main god Amun-Re, that's a kind of renewal that happened each year.

A lot of a land around the river Nile is under water, when the river Nile is carrying more water - during the flood season. During this time you can't do much work in the fields, so there is a lot of time for festivals! Sometimes the party would go on for a long time: under Pharaoh Tutmose III the Opet festival lasted 11 days, during the time of Pharaoh Ramses III they partied for 24 days!

Pharaoh would have his party at the temple of Karnak (see these big columns? That was a big building project during the new kingdom, when they stopped building pyramids), but they also had a party in all the other parts of Egypt.

The river Nile is getting a lot of water between the months of May and August, these are the months when there is a lot of rain in central Africa. The water of the Nile comes from the mountains and the Victoria lake - that is the second largest lake in the world! Also between May and August it is raining a lot in these parts of Africa, it is often raining for the whole day! This rain season is called the Monsoon season.

Mesopotamia and later Babylon had two big festivals, both with the same name - the Akitu festival. One festival was during spring, during the month of Nissan, that's when they start to plant barley seeds. The spring festival was also a kind of renewal - the king of Babylon receives his right to rule from the priests of the god marduk. The festival took twelve days, and you didn't have to work at three of these days! During this time the king would tell about changes in his government, announce treaties with other states or announce that some political prisoners are now free. The second festival was in fall, during the month of Tashrity(Tishrei) - that's when the religious year starts again.

That sounds very similar to the Jewish festivals of Pesach and Rosh Hashanah, even the names of months are the same, we got a very similar calendar as in Babylon - after returning from Babylonian captivity!! See the table here: https://en.wikipedia.org/wiki/Babylonian_calendar#Months

Now lets look at the calendars:

In Egypt they had a calendar that describes the movement of the earth around the sun. It takes the earth some 365 days and one quarter day to turn around the sun. If you do it right, then you need to add a leap day, as the days don't add up exactly to describe the movement of the earth around the sun. Now In Egypt a week had ten days, a month had 30 days (three weeks for a month). Four months make a season (60 days for a season), They had four seasons, now that makes 360 days per year. This means that they had to add another five days of festivals at the end of the year (another party!) But they didn't know about leap years

The Egyptian calendar keeps getting out of step with the real year, we now avoid this by adding an extra day for each leap year, but they didn't have a leap year in ancient Egypt! But there is a workaround, if you know how to look at the stars! Most stars keep moving around the sky, except for Polaris - that's the northern star. If you make a photograph with a long exposure then you see how the stars are moving around the northern star.

You see that the stars keep disappearing from the skyline. During some days you can't see some of the stars at all! This happens quite regularly, as the stars are very far away from the sun.

Each one of the stars appears in the sky, and for the next 70 nights it will stay visible, Then the star will disappear and stay invisible for the next 90 nights. After that the star will appear again.

This dancing of the stars happens, because the axis of the earth is on an angle relative to the movement of the earth around the sun. Because of this we see a slightly different picture of the sky, as the earth is travelling around the sun. This angle is also causing the different seasons of the year, because we get different amounts of sunlight, when we look at the sun under a small angle (summer time) and under a big angle (winter time).

One star that was important in Egypt was Sirius - it is the brightest star in the sky (actually these are two stars, a very big Sirius-A star and a very small and hot Sirius-B star. These stars turn around each other, but they didn't know that in ancient Egypt)

The star of Sirius is this very bright star in the constellation of 'The great dog' (Canis Major in Greek) - and it appears again - the next full moon after that will be the festival of Opet. These tricks help them to ignore the leap year problem!

It seems that the Egyptians didn't care that their calendar got out of sync, as long as they knew when to have the festival and when to plant the crops!

In Babylon they had a calendar by tracking the moon. The moon rotates around the earth, and that takes 29.53 days. Each day the sun shines on the moon under a different angle, that's why the image of the moon keeps growing bigger, until you get a full moon. And then it keeps growing smaller.

Now once in a while you need to add a leap month (like Adar II) in order to keep this synchronized with the cycle of the earth around the sun. Somehow this system worked better then the Egyptian calendar, which got out of sync because of the missing leap year business.

Once again you need to track the movement of the stars, to get it right. The Iku star in the constellation of Pegasus would rise, that's when you can have the spring festival of Akitu!

Star tables:

The Egyptian priests had to follow the movement of the stars in the sky. They had a kind of clock that can tell the time of year, if you know how to look at the stars!

Remember the cycle: each star appears in the sky, will stay visible for the next 90 nights, then the same star disappears and will stay invisible for the next 70 nights, then it reappears again. Now the star stays visible: it will appear in the sky at a slightly different time: after ten days the same sky will appear in the sky at a different hour of the night.

The Egyptians picked a set of stars to track through the whole year, this group of star is called the Decans, now they all summed it up in a table:

Here you have a big table. The horizontal line is the time of year. You divide the year into months, each month is divided into three weeks.

Now the vertical line is dividing the night into twelve hours of equal length.

Each square of the table has the name of a star in it: Look at the column - it's the week of the year, look at the row - it's the hour of the night, when the star named by the square appears in the sky! During the next week that same star is rising an hour later, and so on, until the star disappears from the sky - that's why the stars keep shifting in the table.

How did they know the hour of the night? With a water clock!

You fill the big bowl with water, and there is a hole in the bottom of the bowl. The water is slowly falling out of the bowl. Now you look at the level of the water as it appears on the marks drawn in the bowl, there is a special mark for each hour of the night. Now you can tell the hour of the night by looking at the text written right near the mark that you can see right above the water!

But the nights are not of the same length, a night in winter is longer than in summer. They fixed that: you can see different rows of marks, each row is used during a different time of the year.

So now it gets a bit circular: you need to know the time of the year, in order to know what the current hour of the night is. And you use this information to get the current date - from the star table. I don't quite know how all of this worked in detail, but some priests in ancient Egypt had a lot of fun with all of this

By the way: all this had a lot of religious meaning in Egypt - when a star disappeared from the sky it would 'go into the underworld/hell' and when it appears in the sky again it would be 'reborn'. (that's how they did propaganda during the bronze age...)

There is a youtube lecture here, maybe you manage to understand more than me... https://www.youtube.com/watch?v=Ak07dI-TALU

Now lets look at the number systems

In Egypt they kept counting to ten, but they had different signs for every power of ten, they had a special sign for a hundred and another sign for one thousand. If you want to say two hundred then just draw two signs for one hundred.

Wikipedia is explaining this in a picture.

I like the sign for one million, it looks as if the guy is raising his hands and saying "that's too much!"

Now the whole thing gets complicated, when you want to have fractions, like one half or one third - so people tried to avoid these situations. You can look at it here, I didn't understand the concept of fractions... https://en.wikipedia.org/wiki/Egyptian_numerals

Now what about Babylonia? Here they didn't count to ten, they counted to sixty!

Actually we still have a bit of that today, you have sixty seconds in a minute, sixty minutes in an hour. You have 360 degrees in a circle. (all because the Babylonians were experts in astronomy, and astronomy had something to do with measuring time and space)

Why sixty? We don't know for sure, but we can guess:

Maybe because of the lunar calendar, a lunar month is 29 years long, so the closes round number is thirty, two months are about sixty days.

Now there is a better reason, I have written a small program, it takes all the numbers between one and one hundred, for each number it shows which other numbers can divide the given number, without a fraction.

Sixty is the smallest number between one and one hundred that can be divided by seven numbers - 2, 3, 4, 5, 6, 10, 12, 15, 20, 30

That's very practical - you can avoid fractions in lots of situations. Lets say that take a loan of sixty shekel (the unit of money in Babylonia was the Shekel, just like in Israel, today. What a coincidence!) Now after a year I have to add a tenth of that sum to what I owe you - you get 10% interest rate. No problem, sixty divides by ten. So you have more possibilities to use that number system without dealing with fractions!

What about numbers that are bigger than sixty? There was a clever trick (that's the first time the trick was used, and we still use it today).

What if you want to show the number sixty five? Now that's 60 * 1 + 5 so they would write it as

Actually that is quite similar to what we are doing now, with the base of ten: 65 = 6 * 10 + 5

Now lets write the number of seconds in one day: that's

NumberOfSecondsInAMinute * NumberOfMinutesInAnHour * NumberOfHoursInADay = 60 * 60 * 24 + 0 * 60 + 0 = 86400

Now we learn about a new cuneiform symbol - that would be what we have for zero in a decimal system, a placeholder!

- that is zero, but only for the purpose of writing the number

Back to our number:

60 * 60 * 24 + 0 * 60 + 0 = 86400

In cuneiform that's written as:

Now that zero is only a place holder, it is not a number - that's for good reasons.

The Greeks used the Babylonian number system. Alexander conquered the Persian empire in 334BC, after that the Greek learned a lot from Babylonian mathematics and astronomy. Now they also used the Babylonian number system, just because it was much better than what they had!

The problem with zero

Some stuff here is taken from a book by "Zero: The Biography of a Dangerous Idea" by Charles Seife, I am trying to retell some of it in simple words.

We know about the natural numbers, These are the numbers 1,2,3,.... Now 0 is the number right before 1 - it describes the amount of ... nothing.

In ancient Egypt they did have a concept of zero, but just as a starting point, Today we measure the height in geography as 'meters above the sea level', where the 'sea level' is zero is the starting point, the baseline.

That is the symbol for zero, Even the great pyramids had this on their lowest level, it's their baseline, the lowest level of the pyramid.

The Egyptians didn't use this symbol when they did math. The Babylonian zero was only a placeholder, it was not used as a number that denotes nothing. For good reason:

Multiplying any number with zero gives zero, lets see why.

We have the rule of associativity: a * (b + c) = a * b + a * c

For example: 2 * (3 + 5) = 2 * 3 + 2 * 5 = 6 + 10 = 16

Now lets have: a * b = a * (b + 0) = a * b + b * 0

           a * b = a * b + b * 0

That means: b * 0 = 0 - anything else would have broken the rules.

That's a big deal:

Lets take the line of numbers 1..2..3..4..5..6...

Imagine that the line of numbers is a band made of rubber that can be stretched, if we multiply each of the numbers by three then that's as if we make the rubber band three times longer, we stretch it by three times!

3..6..9..12..15..24.....

Now if we multiply this infinite rubber band of numbers by zero then everything collapses into just one point - zero. As if all the numbers fell into a black hole, just like this!

Now that's still nothing - division by zero brings total chaos into the kingdom of numbers.

Now lets assume 2 * 3 = 6 The inverse of multiplication is division: 2 = 6 / 3

Let's assume that zero plays by the same rule

2 * 0 = 0 so therefore 2 = 0 / 0

3 * 0 = 0 so therefore 3 = 0 / 0

4 * 0 = 0 so therefore 4 = 0 / 0

So any number is zero divided by zero. Also any number is equal to any other number! You can't have this chaos! Therefore the only way is to forbid this. You are not allowed to divide by zero - it brings total chaos into the world of numbers, that' even worse than a black hole!!!

(or in other words: if you just stepped into a black hole, then there is no way out :-) )

The book gives an example of a big warship, that's a ship almost as big as a city - and it stopped moving at all. Because some important computer program stopped working - the program divided by zero, and that kills any computer program! Dividing by zero is not allowed!!!

Some say that the ship had to be pulled by another ship, because it could not move on its own, and they didn't know how to fix the problem with the computer https://medium.com/dataseries/when-smart-ships-divide-by-zer0-uss-yorktown-4e53837f75b2

How did people start to think in terms of numbers?

The first person to think of mathematical proofs was Thales https://en.wikipedia.org/wiki/Thales_of_Miletus

Thales came from the Greek town of Miletus, which is in Ionia - now that is part of Anatolia in Turkey. By the way: In Israel Greece is known as יוון - javan, this name comes from the place name Ionia. These guys liked to travel!

Now Thales had a lot of money, so he could travel to Egypt (traveling did cost a lot of money!). In Egypt he learned a lot about geometry. The Egyptians knew a lot about calculating the volume of pyramids and other geometric objects. That was very important, because how would you build something big without knowing how many stones are needed to build the thing?

Now Thales did something new - he says that you can proof complicated things from simple facts. For example: you know that Socrates is a Man and that all man have to die, this means that you can say that Socrates will have to die - you just took two facts and combined them. That's the magic of logical thinking, and Thales used that to proof things in Geometry, this turns out to be a kind of superpower!

He used this superpower to find the height of the great Pyramid. He did that by measuring the length of the shadow of the pyramid, also he looked at the shadow of a similar triangle and took its measure, then he calculated the height of the pyramid.

height-of-pyramid / shadow-of-pyramid = height-of-stick / shadow-of-stick = ratio

height-of-pyramid = length-of-shadow-of-pyramid * ratio

In the next lesson we will learn, how Thales proofed this. (that's will be important to understand why the Greeks liked ratios, some greek philosophers like Pythagoras thought that everything in the world is a ratio. Now zero breaks this concept, because you can't divide by zero! but we will get to that.

Thales found is the following, as a preparation of the proof:

you cut an angle with three parallel lines A1-B1, A2-B2 A3-B3 (these three lines are parallel - they will never meet each other on the plane), Thales now says: if A1-A2 is equal to A2-A3 then B1-B2 is equal to B2-B3

Lets prove that!

Now lets draw two lines B1-L and B2-M these two lines are parallel to A1-A3.

Now we see that the angle B1 K B2 is equal to angle A1 A2 B2, also angle B2 M B2 is equal to angle A1 A3 B3 - because they are formed by parallel lines.

Now that's the reason by angle B1 K B2 is equal to angle B2 M B3

Also the segment B2 M is equal to B1 K - because they are equal to the parallel segments A1 A2 and A2 A3 (remember that was one of the conditions)
Also angles K B1 B2 is equal to angle M B2 B3 - they are formed by parallel lines.

Now we know if two triangles have a common side and two common angles with that side, then these triangles are equal, so we just proved that segment B1 B2 is equal to B2 B3

Now this preparation is used in the following proof:

If C B is parallel with C1 B1 then (A C1) / (A C) = (A B1) / (A B)

You got the idea? This is what Thales used to measure the height of the pyramid! If you look at triangle formed by the pyramid and its shadow and at the triangle formed by the stick and its shadow then these are two similar triangles, if you know the length of the two shadows and the length of the stick, then you can find the length of the pyramid!

Let's use the last statement to prove this one!

Let's find a common divisor of length P, so that AC = P * n and A C1 = P * m

Then let's draw parallel lines through all of the points along the C line, where these points have a distance to A of P * x.

Now on the other side, on the B you get a segment of line K that is formed by the smallest triangle.

Now A B = n * k and A B1 = m * k

We get the same proportions!

(A B1) / (A B) = (m * k) / ( n * k) = m / n

Fractions lead to the philosophers of Athens

This stuff became very important, let's see how:

This is a painting by Raphael, it was painted some two thousand years after Thales. This painting is very famous, it is the first painting that is using the tool of perspective (things that are near to us are drawn bigger than things that are far away - these are drawn smaller, just like they do appear in the real world!)

The picture is showing the Greek philosophers that came after Thales.

Pythagoras is the philosopher in the lower left corner, he lived right after Thales - and not far from city of Miletus (that's where Thales lived).

Pythagoras did think and do a lot of crazy things, he made up his own kind of religion. That was a bit dangerous - Pythagoras and his pupils had to move away from where they lived, they had to do so several times.

Now Pythagoras is famous for having made a religion out of numbers, and especially fractions!

Pythagoras liked music: they had an instrument called the Lyre - it has seven strings. There is a course on youtube that teaches how to play that instrument! https://www.youtube.com/watch?v=1ShcYrFPlbw

The lyre is a bit like a guitar: You need to press on a part of the string, then you pluck the other end of the string. The string that is on the other part of the finger is making a sound, as it is vibrating up and down. These vibrations move the air around the string up and down - that's how a sound is made.

Now you get different sounds. If the finger is leaving a short string then you get a note with a higher sound - the string is moving very fast. If you are leaving a longer string then you get a note that sounds lower.

The sound of the string depends on the ratio between the length of the whole string and the length of the remaining string!

Pythagoras said that everything in music is a number - think of the ratio of the whole string to the length of the part that is making the sound. Now Pythagoras also said that everything else in the world is also ruled by numbers! For example he said that the sun and all of the planets are turning around the same point in space. He said that the sun and the planets are making music as they move around this central point - that is the music of the heaven (or the music of the spheres in heaven - they didn't have a word for space)

All of this became very important - Plato was an important philosopher (actually you see him right in the middle of the picture of Raphael, Plato is the guy right in the middle! (Funny that he isn't the biggest one in the picture) Plato said that the most important things in the world are abstract ideas - and that everything that is real is only a shadow of an abstract idea. That's very similar to what Pythagoras said - as numbers and rules for numbers are similar to abstract ideas.

Pythagoras made one of the first schools of philosopher - for a very long time people studied his philosophy but also other things like mathematics and geometry. At least a third of what is written in the big book on geometry by Euclid came from this school of philosophers!

Now all of this world view breaks down with zero as a number - you can't divide by zero! There are even more problems - not every number can be written down as a ratio between two integers. The square root of two is not a rational number! Hippasus of Metapontum proved that, and Pythagoras and his friends didn't like it at all. Some say that they killed Hippasus, others say that he only had to go away - but it must have been very nasty, to say the least!

The proof that the square root of two is not a rational number

This means that the square root of two can't be written as a fraction a / b where a and b are natural numbers. That was a dangerous truth, the friends of Pythagoras didn't like that at all, as it would break the religion that their leader made up!

A very good proof is here - that's a great site for learning mathematics! Normally they like to skip over steps in mathematical proofs - they don't do that here!!! https://www.homeschoolmath.net/teaching/proof_square_root_2_irrational.php

Lets say that the square root of two can be written as a fraction a / b - where a and be can't be written down as a product of two other numbers (this means that a and b can't be simplified). The task is now to proof that this is not possible. If we manage to find such a contradiction, then then we found that the square root of two is not a rational number.

We start with the hypothesis:

square-root(2) = a / b ; lets square both sides of the equation

2 = (a * a) / (b * b)

2 * (b * b) = (a * a) - we just multiplied both sides of the equation with (b * b), and that cancelled the lower part of the right hand side.

This means that a * a is an even number - because you can write a * a as a product of two with another number!

If a is not even then a * a is not even (adding a not even number to itself many times makes a not even number). So that means that a is an even number!

So lets say that a = 2 * aa This means that a can be simplified (this contradicts with the problem statement)

Now lets show that b can be simplified too!

Now we know that 2 = (a * a) / (b * b)

2 = (2 *aa) * (2 * aa) / (b * b) = (4 * aa * aa) / (b * b)

2 = 4 * aa * aa / b * b

1 = 2 * aa * aa / b * b

b * b = 2 * aa * aa

Now we know that b is also an even number!

that means that b can also be written as the product of two numbers, it can be simplified!

Now we found an error - if both a and b are even numbers, then they can be written as the product of two other numbers. At the beginning it was said that this can't be, we found a contradiction!

if we found an error - a contradiction, then that means that two can't be written as a fraction of two natural numbers, it is irrational.

Here you have a homework exercise: Irving Finkel is working at the British Museum, he is telling us about a board game from the Neo-Babylonian or Achemeneid empire - some 2500 years ago, or earlier. https://www.youtube.com/watch?v=WZskjLq040I&t=225s

Your exercise: understand the rules and make a board for this game, then play it with your friends or brothers/sisters.

The link is to the place in the video where Ivring Finkel is telling us about the rules of the game.

The other guy is Tom Scott, he is a programmer. Here he is telling us about computer programs that work with time and time zones. Different cultures have different calendars, which means a lot of fun. See this video: https://www.youtube.com/watch?v=-5wpm-gesOY

Now he doesn't tell us about calendars that have to do with the movement of stars: the ancient Egyptian calendar, the Babylonian Calendar and nowadays the Persian/Iranian calendar - they set the start of the new year when a certain star appears in the sky (we talked about this before). That means a lot of additional fun.

There is a clever trick for working with leap seconds. On some days they have to add an extra second to a day, to keep the calendar synchronized with the movement of the earth around the sun. That's when you would get a date like 23:59:60 - at the end of the day. Many computers can't have that, the programs will start to have bugs. The trick is to make make the computer clock a bit slower, for each hour the computer clock will be 1/24th of a second slower. By the end of the day they have spent the extra second with this delay (24 * 1/24 = 1) and all the computers are happy again!

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Now lets look at the calendars:

Star tables:

Now lets look at the number systems

The problem with zero

More problems with zero

How did people start to think in terms of numbers?

Fractions lead to the philosophers of Athens

The proof that the square root of two is not a rational number

Back to the Arts