Do Interesting Things · Study guides
25 things worth wondering about
How big is the universe? What is consciousness? Why do civilizations rise and fall? What gives life meaning? These short guides take on twenty-five of the biggest questions people ask, from black holes and DNA to the Industrial Revolution, AI and the future of medicine, in plain language with the key numbers.
Each topic opens a page with four parts:
Each topic also comes as slides (PDF), a Word document for printing and a PowerPoint. Your best test score is saved on your own device and shows beside each topic.
Twenty-five topics, about ten minutes each. Start anywhere, or open them all in one page.
Open all 25 topics in one pageThe observable universe is about 93 billion light-years across and holds hundreds of billions of galaxies or more. How astronomers measure such distances, why the universe is wider than its age would suggest, and what looking far away really means.
DNA carries the instructions to build and run every living thing using just four chemical letters. How the code works, what the Human Genome Project found, and why the origin of life is still one of science's biggest open questions.
Black holes pack so much mass into so little space that not even light escapes. How they form, the first photographs of them, gravitational waves, and how Einstein's discovery that gravity slows time keeps your phone's GPS accurate.
Splitting uranium atoms releases enormous energy, a direct example of Einstein's E = mc². How fission and a chain reaction work, how a reactor turns that heat into electricity, and why a few pounds of fuel can do so much.
At the scale of atoms, particles act like waves, can be in more than one state at once, and stay linked across distances. The key ideas in plain language, and how quantum physics makes transistors, lasers, LEDs and MRI machines possible.
Your brain weighs about three pounds yet uses a fifth of your body's energy. How neurons talk to each other, what the major parts do, how the brain rewires itself as you learn, and why consciousness is still one of science's hardest puzzles.
AI systems now write code, read X-rays, recognize speech and help scientists. How machine learning works in plain terms, the milestones from 1956 to today, what AI is good and bad at, and the open questions about jobs, discovery and decisions.
The heart beats about 100,000 times a day, tens of thousands of miles of blood vessels deliver oxygen, and feedback loops hold your temperature and blood sugar steady. The body seen through an engineer's eyes.
Why do living things age? Scientists point to DNA damage, worn-down telomeres, worn-out cells and changing metabolism. What researchers have learned, what the record lifespan is, and the everyday habits with the strongest evidence for a longer healthy life.
Modern humans appeared in Africa about 300,000 years ago. How our ancestors spread across the world, what we inherited from Neanderthals, and how language, farming and writing changed everything in a remarkably short time.
Ancient civilizations built pyramids, roads, laws and philosophies that still shape us. A tour of five great civilizations, what made them strong, and the common reasons they declined, from overreach to climate and disease.
Christianity, Islam, Hinduism, Buddhism and Judaism have shaped law, art, holidays and how people think about right and wrong. A respectful overview of each faith's origins, central beliefs and how many people follow it today.
Writing let people store knowledge beyond one lifetime, and mathematics let them build, trade, navigate and eventually compute. How writing began with tally marks and clay tablets, where our numbers and zero came from, and how the printing press spread it all.
Starting in Britain in the 1700s, machines and steam power moved work from farms and homes into factories. The key inventions, how railroads and electricity spread the change, and how it raised living standards while bringing new problems.
Wars have been fought over land, resources, security, ideas and power. The common causes historians identify, the two World Wars and the Cold War in brief, and how nuclear deterrence and international institutions shaped the decades since 1945.
A modern chip packs billions of transistors onto a sliver of silicon. What a transistor does, how chips are made, Moore's law, and why semiconductors now power everything from phones and cars to satellites, medical scanners and AI.
Twelve people walked on the Moon between 1969 and 1972, and people have lived aboard the International Space Station since 2000. What it would take to return to the Moon and reach Mars, and the engineering and medical problems that must be solved first.
Fusion joins light atoms together, the process that powers the Sun. Why it is so hard to do on Earth, the 2022 experiment that produced more energy than its laser delivered, how fusion differs from fission, and how far it is from powering homes.
Robots build cars, assist surgeons, explore Mars and move packages in warehouses. How a robot senses and acts, where robots work today, and how combining them with AI could change factories, farms and homes.
Earth's climate depends on how the atmosphere, oceans, land, ice and living things trade heat, water and carbon. How the greenhouse effect keeps the planet livable, how the water and carbon cycles work, and what scientists measure to understand change.
Astronomers have confirmed thousands of planets around other stars, some in zones where water could stay liquid. How we find them, the Drake equation and the Fermi paradox, how scientists search for signals and signs of life, and why there's still no confirmed evidence.
Money, banking, debt, inflation and trade touch nearly every part of daily life. What money really is, how banks and central banks work, why prices rise, why countries trade, and why economies grow and sometimes fall into recession.
CRISPR lets scientists edit DNA precisely, immunotherapy trains the body to fight cancer, and mRNA vaccines can be designed in days. What these tools are, the first approved treatments, and the ethical questions they raise.
Pandemics, solar storms, grid failures, war and other shocks can disrupt the systems we depend on. A calm look at the major risks, historical examples, and the practical steps that make families and communities more resilient.
Why do we exist, and what makes a life meaningful? How religion, philosophy and science each approach the question, what famous thinkers have proposed, and what long-running studies say about what makes people's lives feel worthwhile.