In which John Green teaches you about population. So, how many people can reasonably live on the Earth? Thomas Malthus got it totally wrong in the 19th century, but for some reason, he keeps coming up when we talk about population. In 1800, the human population of the Earth passed 1 billion, and Thomas Malthus posited that growth had hit its ceiling, and the population would level off and stop growing. He was totally right. Just kidding, he was totally wrong! There are like 7 billion people on the planet now! John will teach a little about how Malthus made his calculations, and explain how Malthus came up with the wrong answer. As is often the case, it has to do with making projections based on faulty assumptions. Man, people do that a lot.

This week, we're headed to the Americas to learn about the theater that existed there prior to the arrival of Europeans, how the theater of the Spanish influenced it, and the impact of Sor Juana Inez de la Cruz, playwrighting Spanish nun extraordinaire.

So, who was this Presocrates guy? Just kidding!
Long ago, some philosophers worked very hard to separate myths from what they actually knew about nature.
Thales theorized that everything in the world is made of water. Pythagoras was a mathematical-mystical vegetarian. And Democritus, we all know and love as the Atom Guy…
Meet the Presocratics!

A lot of work goes into managing our impact on the environment and its impact on us. That work is the work of environmental engineers. In this episode we’ll explore water quality, air quality, noise pollution, waste management, and more.

Today we’re going to begin our discussion of probability. We’ll talk about how the addition (OR) rule, the multiplication (AND) rule, and conditional probabilities help us figure out the likelihood of sequences of events happening - from optimizing your chances of having a great night out with friends to seeing Cole Sprouse at IHop!

Today we're going to introduce bayesian statistics and discuss how this new approach to statistics has revolutionized the field from artificial intelligence and clinical trials to how your computer filters spam! We'll also discuss the Law of Large Numbers and how we can use simulations to help us better understand the "rules" of our data, even if we don't know the equations that define those rules.

Today, Carrie Anne is going to start our overview of the fundamental building blocks of programming languages. We’ll start by creating small programs for our very own video game to show how statements and functions work. We aren’t going to code in a specific language, but we’ll show you how conditional statements like IF and ELSE statements, WHILE loops, and FOR loops control the flow of programs in nearly all languages, and then we’ll finish by packaging up these instructions into functions that can be called by our game to perform more and more complex actions.

We’ve spent most of this series talking about computers. Which makes sense - this is Crash Course COMPUTER SCIENCE after all. But at their core computers are tools employed by humans and humans are pretty complicated. So today, we’re going to discuss some psychological considerations in building computers like how to make them easier for humans to use, the uncanny valley problem when humanoid robots gets more and more humanlike, and strategies to make our devices work better with us by incorporating our emotions and even altering our gaze. Oh, and we'll talk about Carrie Anne's all time favorite user interface design principle - knurling.

What’s the difference between race and ethnicity? Today we’ll look at how definitions of races and ethnicities have changed over time and across places. We also discuss the terms minority and minority-majority and how races are defined in the United States.

We’re continuing our discussion of nineteenth-century American theater with a look at some upsetting parts of the US's theatrical past. In the nineteenth century, race and racism contributed to a unique and troubling performance culture, which helped create and spread racist stereotypes that are still with us today.

And just - to be super clear - the stuff we’re talking about in this episode is … tough. The images are upsetting, and much of the language is … fraught, to put it lightly. So, just an up front content warning, so you know what’s coming up.

We can’t talk about race without also discussing racism, so today we are going to define and explain prejudice, stereotypes, and racism. We’ll look at five theories for why prejudice exists. We’ll discuss discrimination and the legacies of institutional racism. We’ll also provide an overview of four types of racial interaction: pluralism, assimilation, segregation, and genocide.

In which John Green teaches you about railroads, and some of the ways they changed the world, and how they were a sort of microcosm for the Industrial Revolution as a whole. Prior to the invention of steam powered railroads, pretty much all locomotion had been muscle-powered. You either walked where you wanted to go, or rode on an animal to get where you were going. The railroad changed human perception of time and space, making long distance travel much faster and easier. Railroads also changed habits, including increasing reading. People needed some sort of distraction to ensure they didn't have to talk to other people on the train. Like any new technology, railroads also scared people. All kinds of fears surrounded rail travel, but over time, people got over them. And the quality of boiler manufacturing improved, so the trains exploded less often, which also made people feel safer.

There are a lot of events in life that we just can’t predict, but just because something is random doesn’t mean we don’t know or can’t learn anything about it. Today, we’re going to talk about how we can extract information from seemingly random events starting with the expected value or mean of a distribution and walking through the first four “moments” - the mean, variance, skewness, and kurtosis.

Today we’re going to start thinking about materials that are used in engineering. We’ll look at mechanical properties of materials, stress-strain diagrams, elasticity and toughness, and describe other material properties like hardness, creep strength, and fatigue strength.

In the late 19th and early 20th centuries, theater was evolving rapidly in Europe. Impresarios like Georg II, Duke of the Duchy of Saxe Meinengen (in what is now Germany), were pushing theater troupes to new heights of realism. New methods of staging, acting, set building, and even rehearsing were making plays more realistic than ever. These practices spread to France with Andre Antoine's Theatre Realisme, and from there spread across Europe.

Today we’re going to create memory! Using the basic logic gates we discussed in episode 3 we can build a circuit that stores a single bit of information, and then through some clever scaling (and of course many new levels of abstraction) we’ll show you how we can construct the modern random-access memory, or RAM, found in our computers today. RAM is the working memory of a computer. It holds the information that is being executed by the computer and as such is a crucial component for a computer to operate. Next week we’ll use this RAM, and the ALU we made last episode, to help us construct our CPU - the heart of a computer.

Today we're going to introduce one of the most flexible statistical tools - the General Linear Model (or GLM). GLMs allow us to create many different models to help describe the world - you see them a lot in science, economics, and politics. Today we're going to build a hypothetical model to look at the relationship between likes and comments on a trending YouTube video using the Regression Model. We'll be introducing other popular models over the next few episodes.

Today we’re turning our sociological eye to another major social institution: religion. We’ll use symbolic interactionism to help us understand the dichotomy of the Sacred vs. the Profane. We’ll compare the perspectives of structural functionalists and conflict theorists on whether religion improves social cohesiveness or increases social stratification. We’ll also explore how religious practice in the US differs across race and class lines.

In which John Green teaches you about the European Renaissance. European learning changed the world in the 15th and 16th century, but was it a cultural revolution, or an evolution? We'd argue that any cultural shift that occurs over a couple of hundred years isn't too overwhelming to the people who live through it. In retrospect though, the cultural bloom in Europe during this time was pretty impressive. In addition to investigating what caused the Renaissance and who benefitted from the changes that occurred, John will tell you just how the Ninja Turtles got mixed up in all this.

Replication (re-running studies to confirm results) and reproducibility (the ability to repeat an analyses on data) have come under fire over the past few years. The foundation of science itself is built upon statistical analysis and yet there has been more and more evidence that suggests possibly even the majority of studies cannot be replicated. This "replication crisis" is likely being caused by a number of factors which we'll discuss as well as some of the proposed solutions to ensure that the results we're drawing from scientific studies are reliable.