# How do we measure distance in space? • 2014 • TED-Ed

Category: Physics
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When we look at the sky, we have a flat, two-dimensional view. So how do astronomers figure the distances of stars and galaxies from Earth? Yuan-Sen Ting shows us how trigonometric parallaxes, standard candles and more help us determine the distance of objects several billion light years away from Earth.

## TED-Ed • 0 • 74 episodes •

How do we measure distance in space?

When we look at the sky, we have a flat, two-dimensional view. So how do astronomers figure the distances of stars and galaxies from Earth? Yuan-Sen Ting shows us how trigonometric parallaxes, standard candles and more help us determine the distance of objects several billion light years away from Earth.

2014 • Physics

How many ways can you arrange a deck of cards?

One deck. Fifty-two cards. How many arrangements? Let's put it this way: Any time you pick up a well shuffled deck, you are almost certainly holding an arrangement of cards that has never before existed and might not exist again. Yannay Khaikin explains how factorials allow us to pinpoint the exact (very large) number of permutations in a standard deck of cards.

2014 • Math

Is math discovered or invented?

Would mathematics exist if people didn't? Did we create mathematical concepts to help us understand the world around us, or is math the native language of the universe itself? Jeff Dekofsky traces some famous arguments in this ancient and hotly debated question.

2014 • Math

The History of Keeping Time

Where did time-telling come from? What are time zones and why are there so many of them? Get the answers to these questions and more in this journey through the history of time -- from sundials to hourglasses to modern clocks.

How playing an instrument benefits your brain

When you listen to music, multiple areas of your brain become engaged and active. But when you actually play an instrument, that activity becomes more like a full-body brain workout. What's going on? Anita Collins explains the fireworks that go off in musicians' brains when they play, and examines some of the long-term positive effects of this mental workout.

How to understand power

Every day, we move and operate within systems of power that other people have constructed. But we’re often uncomfortable talking about power. Why? Eric Liu describes the six sources of power and explains how understanding them is key to being an effective citizen.

How big is infinity?

Using the fundamentals of set theory, explore the mind-bending concept of the "infinity of infinities" -- and how it led mathematicians to conclude that math itself contains unanswerable questions.

The death of the universe

The shape, contents and future of the universe are all intricately related. We know that it's mostly flat; we know that it's made up of baryonic matter (like stars and planets), but mostly dark matter and dark energy; and we know that it's expanding constantly, so that all stars will eventually burn out into a cold nothingness. Renée Hlozek expands on the beauty of this dark ending.

What's an algorithm?

An algorithm is a method of solving problems both big and small. Though computers run algorithms constantly, humans can also solve problems with algorithms. David J. Malan explains how algorithms can be used in seemingly simple situations and also complex ones.

The physics of sperm vs. the physics of sperm whales

Traveling is extremely arduous for microscopic sperm -- think of a human trying to swim in a pool made of...other humans.

The loathsome, lethal mosquito

Everyone hates mosquitos. So shouldn't we just get rid of them?

The mighty mathematics of the lever

Archimedes once said “Give me a place to stand, and I shall move the Earth.”

The language of lying

We hear anywhere from 10 to 200 lies a day. And although we’ve spent much of our history coming up with ways to detect these lies by tracking physiological changes in their tellers, these methods have proved unreliable. Is there a more direct approach?

How do the lungs work?

When you breathe, you transport oxygen to the body’s cells to keep them working, while also clearing your system of the carbon dioxide that this work generates. How do we accomplish this crucial and complex task without even thinking about it? Emma Bryce takes us into the lungs to investigate how they help keep us alive.

What does the liver do?

There’s a factory inside you that weighs about 1.4 kilograms and runs for 24 hours a day. It’s your liver: the heaviest organ in your body, which simultaneously acts as a storehouse, a manufacturing hub, and a processing plant.

How a wound heals itself

Our skin is the largest organ in our bodies, with a surface area of about 20 square feet in adults. When we are cut or wounded, our skin begins to repair itself through a complex, well-coordinated process. Sarthak Sinha takes us past the epidermis and into the dermis to investigate this regenerative response.

The Higgs Field, explained

One of the most significant scientific discoveries of the early 21st century is surely the Higgs boson, but the boson and the Higgs Field that allows for that magic particle are extremely difficult to grasp. Don Lincoln outlines an analogy (originally conceived by David Miller) that all of us can appreciate, starring a large dinner party, a raucous group of physicists, and Peter Higgs himself.

Schrödinger's cat: A thought experiment in quantum mechanics

Austrian physicist Erwin Schrödinger, one of the founders of quantum mechanics, posed this famous question: If you put a cat in a sealed box with a device that has a 50% chance of killing the cat in the next hour, what will be the state of the cat when that time is up?

Particles and waves: The central mystery of quantum mechanics

One of the most amazing facts in physics is that everything in the universe, from light to electrons to atoms, behaves like both a particle and a wave at the same time. But how did physicists arrive at this mind-boggling conclusion?

Einstein's brilliant mistake: Entangled states

When you think about Einstein and physics, E=mc^2 is probably the first thing that comes to mind. But one of his greatest contributions to the field actually came in the form of an odd philosophical footnote in a 1935 paper he co-wrote -- which ended up being wrong.

What is the Heisenberg Uncertainty Principle?

The Heisenberg Uncertainty Principle states that you can never simultaneously know the exact position and the exact speed of an object.

What can Schrödinger's cat teach us about quantum mechanics?

The classical physics that we encounter in our everyday, macroscopic world is very different from the quantum physics that governs systems on a much smaller scale (like atoms).

Music and Math: The genius of Beethoven

How is it that Beethoven, who is celebrated as one of the most significant composers of all time, wrote many of his most beloved songs while going deaf?

The 2,400-year search for the atom

How do we know what matter is made of? The quest for the atom has been a long one, beginning 2,400 years ago with the work of a Greek philosopher and later continued by a Quaker and a few Nobel Prize-winning scientists. Theresa Doud details the history of atomic theory.?

What is Fat?

As the narrative goes, fat is bad. Well, it's actually more nuanced than that. The type of fat you eat is more impactful on your health than the quantity. George Zaidan examines triglycerides, the varied molecules that make up fat, and how to identify which types of fat you are consuming.

Why we love repetition in music

How many times does the chorus repeat in your favorite song? How many times have you listened to that chorus? Repetition in music isn’t just a feature of Western pop songs, either; it’s a global phenomenon. Why? Elizabeth Hellmuth Margulis walks us through the basic principles of the ‘exposure effect,’ detailing how repetition invites us into music as active participants, rather than passive listeners.

A different way to visualize rhythm

In standard notation, rhythm is indicated on a musical bar line. But there are other ways to visualize rhythm that can be more intuitive. John Varney describes the ‘wheel method’ of tracing rhythm and uses it to take us on a musical journey around the world.

Dead stuff: The secret ingredient in our food chain

When you picture the lowest levels of the food chain, you might imagine herbivores happily munching on lush, living green plants. But this idyllic image leaves out a huge (and slightly less appetizing) source of nourishment: dead stuff. John C. Moore details the "brown food chain," explaining how such unlikely delicacies as pond scum and animal poop contribute enormous amounts of energy to our ecosystems.

How do you know you exist?

How do you know you’re real? Is existence all just a big dream? Has some mad scientist duped us into simply believing that we exist? James Zucker investigates all of these questions (and more) in this mind-boggling tribute to René Descartes’s "Meditations on First Philosophy."

Population pyramids: Powerful predictors of the future

Population statistics are like crystal balls -- when examined closely, they can help predict a country's future (and give important clues about the past). Kim Preshoff explains how using a visual tool called a population pyramid helps policymakers and social scientists make sense of the statistics, using three different countries' pyramids as examples.

From the top of the food chain down: Rewilding our world

Our planet was once populated by megafauna, big top-of-the-food-chain predators that played their part in balancing our ecosystems. When those megafauna disappear, the result is a "trophic cascade," where every part of the ecosystem reacts to the loss. How can we stay in balance? George Monbiot suggests rewilding: putting wolves, lions and other predators back on top -- with surprising results.

The fundamentals of space-time (Part 2)

Light always travels at a speed of 299,792,458 meters per second. But if you're in motion too, you're going to perceive it as traveling even faster -- which isn't possible! In this second installment of a three-part series on space-time, CERN scientists Andrew Pontzen and Tom Whyntie use a space-time diagram to analyze the sometimes confounding motion of light.

The evolution of the human eye

The human eye is an amazing mechanism, able to detect anywhere from a few photons to a few quadrillion, or switch focus from the screen in front of you to the distant horizon in a third of a second. How did these complex structures evolve? Joshua Harvey details the 500 million year story of the human eye.

The Benefits of a Good Night's Sleep

It’s 4am, and the big test is in 8 hours. You’ve been studying for days, but you still don’t feel ready. Should you drink another cup of coffee and spend the next few hours cramming? Or should you go to sleep? Shai Marcu defends the latter option, showing how sleep restructures your brain in a way that’s crucial for how our memory works.

8 traits of successful people

Ten years of research and 500 face-to-face-interviews led Richard St. John to a collection of eight common traits in successful leaders around the world.

How spontaneous Brain Activity Keeps You Alive

The wheels in your brain are constantly turning, even when you're asleep or not paying attention. In fact, most of your brain’s activities are ones you’d never be aware of … unless they suddenly stopped. Nathan S. Jacobs takes us inside the always active, surprisingly spontaneous brain.

GPS location apps on a smartphone can be very handy when mapping a travel route or finding nearby events. But how does your smartphone know where you are?

The Distracted Mind

Everyone knows we're not supposed to multitask while driving, but do you know why? It turns out your brain literally can't focus on too much at once.

Why do buildings fall in earthquakes?

Earthquakes have always been a terrifying phenomenon, and they’ve become more deadly as our cities have grown — with collapsing buildings posing one of the largest risks. But why do buildings collapse in an earthquake? And how can it be prevented? Vicki V. May explains the physics of why it is not the sturdiest buildings, but the smartest, that will remain standing.

The Five Major World Religions

It's perfectly human to grapple with questions, like 'Where do we come from?' and 'How do I live a life of meaning?' These existential questions are central to the five major world religions -- and that's not all that connects these faiths. John Bellaimey explains the intertwined histories and cultures of Hinduism, Judaism, Buddhism, Christianity and Islam.

After drinking a few glasses of water on a hot day, you might be struck with a sudden ... urge. Behind that feeling are two bean-shaped organs that work as fine-tuned internal sensors.

Should you trust your first impression?

You can't help it; sometimes, you just get a bad feeling about someone that's hard to shake. So, what's happening in your brain when you make that critical (and often lasting) first judgment? Peter Mende-Siedlecki shares the social psychology of first impressions -- and why they may indicate that, deep down, people are basically good.

The last banana: A thought experiment in probability

Imagine a game of dice: if the biggest number rolled is one, two, three, or four, player 1 wins. If the biggest number rolled is five or six, player 2 wins. Who has the best probability of winning the game? Leonardo Barichello explains how probability holds the answer to this seemingly counterintuitive puzzle.

What does the pancreas do?

Beneath your ribs, you’ll find, among other things, the pancreas -- an organ that works a lot like a personal health coach.

The operating system of life

Humans, octopi and pine trees alike are all made up of cells, tiny but sophisticated systems that keep life going. Cells are almost like tiny factories run by robots, with the nucleus, DNA, proteins, lipids, and vitamins and minerals all playing critical roles. George Zaidan and Charles Morton lay out the blueprint of a cell and explain how biochemistry binds all life together.

Like an actor's script, a sheet of music instructs a musician on what to play (the pitch) and when to play it (the rhythm). Sheet music may look complicated, but once you've gotten the hang of a few simple elements like notes, bars and clefs, you're ready to rock.

Why sitting is bad for you

Sitting down for brief periods can help us recover from stress or recuperate from exercise. But nowadays, our lifestyles make us sit much more than we move around. Are our bodies built for such a sedentary existence?

What is Alzheimer's disease?

Alzheimer's disease is the most common cause of dementia, affecting over 40 million people worldwide. And though it was discovered over a century ago, scientists are still grappling for a cure.

What Happened to Antimatter?

Particles come in pairs, which is why there should be an equal amount of matter and antimatter in the universe. Yet, scientists have not been able to detect any in the visible universe. Where is this missing antimatter?

The real story behind Archimedes’ Eureka!

When you think of Archimedes’ Eureka moment, you probably imagine a man in a bathtub, right? As it turns out, there's much more to the story. Armand D'Angour tells the story of Archimedes' biggest assignment -- an enormous floating palace commissioned by a king -- that helped him find Eureka.

Underwater astonishments

David Gallo shows jaw-dropping footage of amazing sea creatures, including a color-shifting cuttlefish, a perfectly camouflaged octopus, and a Times Square's worth of neon light displays from fish who live in the blackest depths of the ocean.

Why are manhole covers round?

Why are most manhole covers round? Sure it makes them easy to roll, and slide into place in any alignment. But there’s another, more compelling reason, involving a peculiar geometric property of circles and other shapes. Marc Chamberland explains curves of constant width and Barbier’s theorem.

Questions of good and evil, right and wrong are commonly thought unanswerable by science. But Sam Harris argues that science can -- and should -- be an authority on moral issues, shaping human values and setting out what constitutes a good life.

What is leukemia?

Stem cells found in the bone marrow are crucial for our health because they are needed to become new blood cells that sustain and protect our bodies. But when the transformation goes wrong, harmful mutations can cause the cells to start replicating without control -- a type of cancer known as leukemia. Danilo Allegra and Dania Puggioni explain how this happens and how certain treatments provide hope for those suffering from the disease.

How to Make a Baby (In a Lab)

Infertility affects 1 in 8 couples worldwide. But in the last 40 years, more than 5 million babies have been born using in vitro fertilization (IVF). How does it work? Nassim Assefi and Brian A. Levine detail the science behind making a baby in a lab.

Some people love the feeling of cracking their knuckles, while others cringe at the sound. But what causes that trademark pop? And is it dangerous? Eleanor Nelsen gives the facts behind joint popping.

How does the thyroid manage your metabolism?

Nestled in the tissues of your neck is a small, unassuming organ that wields enormous power over your body: the thyroid. Emma Bryce explains how the thyroid, like the operations manager in a company, is tasked with making sure that all the cells in your body are working properly.

What really happens to the plastic you throw away

We’ve all been told that we should recycle plastic bottles and containers. But what actually happens to the plastic if we just throw it away? Emma Bryce traces the life cycles of three different plastic bottles, shedding light on the dangers these disposables present to our world.

The famously difficult green-eyed logic puzzle

One hundred green-eyed logicians have been imprisoned on an island by a mad dictator. Their only hope for freedom lies in the answer to one famously difficult logic puzzle. Can you solve it? Alex Gendler walks us through this green-eyed riddle.

What is a Calorie?

We hear about calories all the time: How many calories are in this cookie? How many are burned by doing 100 jumping jacks, or long-distance running, or fidgeting? But what is a calorie, really? And how many of them do we actually need? Emma Bryce explains how a few different factors should go into determining the recommended amount for each person.

2015 • Health

The benefits of good posture

Has anyone ever told you, “Stand up straight!” or scolded you for slouching at a family dinner? Comments like that might be annoying—but they’re not wrong. Your posture is the foundation for every movement your body makes and can determine how well your body adapts to the stresses on it. Murat Dalkilinç gives the pros of good posture.

2015 • Health

Who am I?

Throughout the history of mankind, the subject of identity has sent poets to the blank page, philosophers to the agora and seekers to the oracles. These murky waters of abstract thinking are tricky to navigate, so it’s probably fitting that to demonstrate the complexity, the Greek historian Plutarch used the story of a ship.

2015 • Brain

How smart are dolphins?

Dolphins are one of the smartest animal species on Earth. In fact, their encephalization quotient (their brain size compared to the average for their body size) is second only to humans. But exactly how smart are they? Lori Marino details some incredible facts about dolphins.

2015 • Nature

In previous decades, most news with global reach came from several major newspapers and networks with the resources to gather information directly. The speed with which information spreads now, however, has created the ideal conditions for something called circular reporting. Noah Tavlin sheds light on this phenomenon.

2015 • People

Can you ever travel from one place to another? Ancient Greek philosopher Zeno of Elea gave a convincing argument that all motion is impossible - but where's the flaw in his logic? Colm Kelleher illustrates how to resolve Zeno's Dichotomy Paradox.

2013 • Math

The mathematical secrets of Pascal’s triangle

Pascal’s triangle, which at first may just look like a neatly arranged stack of numbers, is actually a mathematical treasure trove. But what about it has so intrigued mathematicians the world over?

2015 • Math

3 tips to boost your confidence

When faced with a big challenge where potential failure seems to lurk at every corner, you’ve probably heard the advice, “Be more confident!” But where does confidence come from, and how can you get more of it? Here are three easy tips to boost your confidence.

2015 • Lifehack

The moon illusion

Have you noticed how the full moon looks bigger on the horizon than high overhead? Actually, the two images are exactly the same size -- so why do we perceive them differently? Scientists aren't sure, but there are plenty of intriguing theories. Andrew Vanden Heuvel unravels the details of focus, distance and proportion that contribute to this mystifying optical illusion.

2013 • Brain

The Arctic vs. the Antarctic

How can you tell the two poles apart? Where are the penguins? What about the bears? The Arctic pole is located in the Northern Hemisphere within the deep Arctic Ocean, while the Antarctic pole is smack in the middle of the ice-covered Antarctica. Camille Seaman describes how enterprising people and organisms have found ways to reside around both poles despite the frigid temperatures.

2013 • Nature

Would you opt for a life with no pain?

Imagine if you could plug your brain into a machine that would bring you ultimate pleasure for the rest of your life. The only catch? You have to permanently leave reality behind. Hayley Levitt and Bethany Rickwald explore Robert Nozick’s thought experiment that he called the Experience Machine.

2015 • Brain

The Sun’s surprising movement across the sky

Suppose you placed a camera at a fixed position, took a picture of the sky at the same time every day for an entire year, and overlaid all of the photos on top of each other. What would the sun look like in that combined image? A stationary dot? A circular path? Neither. Oddly enough, it makes a ‘figure 8’ pattern, known as the Sun’s analemma.

2015 • Astronomy

What would happen if you didn’t sleep?

In the United States, it’s estimated that 30 percent of adults and 66 percent of adolescents are regularly sleep-deprived. This isn’t just a minor inconvenience: staying awake can cause serious bodily harm. Claudia Aguirre shows what happens to your body and brain when you skip sleep.

2015 • Health

Our hard-wired stress response is designed to gives us the quick burst of heightened alertness and energy needed to perform our best. But stress isn’t all good. When activated too long or too often, stress can damage virtually every part of our body. Sharon Horesh Bergquist gives us a look at what goes on inside our body when we are chronically stressed.

2015 • Health

Meet the tardigrade, the toughest animal on Earth

Without water, a human can only survive for about 100 hours. But there’s a creature so resilient that it can go without it for decades. This 1-millimeter animal can survive both the hottest and coldest environments on earth, and can even withstand high levels of radiation. Thomas Boothby introduces us to the tardigrade, one of the toughest creatures on Earth.

2017 • Nature

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Time and Distance

Professor Marcus du Sautoy tells the story of the metre and the second - how an astonishing journey across revolutionary France gave birth to the metre, and how scientists today are continuing to redefine the measurement of time and length, with extraordinary results.

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Can We Travel Faster than Light?

It's called the speed limit of the universe. Einstein blew all of our minds when he worked out the Theory of Relativity, and showed that space and time were malleable substances. He also theorized that we as humans can never travel faster than the speed of light, which leaves the stars and other galaxies almost impossibly out of our reach. But the dreams of Star Wars and Star Trek are not dead. In fact, there could be ways to travel faster than the speed of light - and some of them are already being tested in labs around the world.

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