If we lived light years from Earth, how would we know there’s life here? Let’s take a look at the search for extraterrestrial life on habitable exoplanets, and discover what biosignatures would show someone else that we’re here.

Humans have a hard time with really big numbers, especially when it comes to DEEP TIME. The history of the Earth took a lot longer than you think, trust me. But I’m here to help you put it in perspective. With some string.

Honeycomb. Strawberries. Flower pods. Some people find these things incredibly scary. We call this extreme fear trypophobia. But why does it exist?

You may have heard that a kilogram of feathers weighs the same as a kilogram of steel, but that all depends on where you weigh them. This video is all about the difference between mass and weight, and how weirdly awesome Earth’s gravity really is.

More people have food allergies than ever before. Peanuts, tree nuts, shellfish, eggs, and even milk… the list of possibly dangerous foods seems to get longer every day. But why do some people’s bodies have deadly reactions food? And why are food allergies on the rise? In this video we explain what food allergies really are, and what the difference is between food allergy and food intolerance. Some fellow YouTubers tell us their stories of what it’s like to live with food allergies, and we bring you the best current science on how to prevent food allergies in kids and adults. It’s a tough nut to crack.

Air. I bet you never even notice that it’s there. Yet you are swimming in an ocean of it every day. If there’s a literal ton of air pressing down on you all the time, so why don’t we feel it? We look back at the history of physics to learn how we figured out air pressure, why vacuums don’t suck, and how people like Galileo, Torricelli, and Otto von Guericke changed science forever with a few simple experiments.

The monarch butterfly migration is one of nature’s greatest events. This orange-winged wonder travels up to 4,500 km from all over North America to spend the winter hanging from oyamel fir trees in central Mexico’s mountain forests. I got to go there. Seeing tens of millions of butterflies dangling from the treetops is a truly breathtaking sight. But how does an animal with a brain the size of a poppy seed navigate to this one special place, especially since the last monarchs to make the trip lived 4 or 5 generations earlier? Get ready for an amazing story of science, instinct, and navigation.

We’ve all gotten dizzy before… but have you ever gotten WEIRD DIZZY? I teamed up with Vanessa Hill from BrainCrat to answer the question “why do we get dizzy?” and in the process we learned about some very strange and hilarious ways to get extra-special dizzy! Get ready to learn about your vestibular system, the system that lets you know where your body is in space. You don’t even notice your vestibular system is there… until it stops working right!

I love coffee. Like, a lot. You know who else loves coffee? Astronauts! And also the people who help them do awesome things in space (I think NASA might be powered by coffee). But how do astronauts actually drink coffee in space, aboard the International Space Station, in microgravity? I visited astronaut Don Pettit to learn about his invention for having a cup o’ Joe in orbit. This is some awesome science.

The eyes are often the first thing we see when we look at someone. And when you look at them up close, everyone’s eye color is a kaleidoscope of shapes and hues. How does eye color work? The answer involves some very cool physics, and probably isn’t what you were taught in school. And you’ve probably wondered how is eye color inherited, or why some people have blue eyes even if their parents’ eyes are brown? Get ready for a long look deep into the genetics and physics of eye color.

A massive new study has just been released showing that human activities are threatening Earth’s other life forms in some very bad ways. One million species may be at risk of extinction. Just let that sink in. Isn’t the Anthropocene awesome? Check out the study below to learn more and find out how we can stop it.

Butterfly metamorphosis is still a bit of a mystery. What happens inside a chrysalis to turn a caterpillar into a beautifully painted butterfly? Does it really turn to soup? I visited Dr. Arnaud Martin, who uses the CRISPR genetic modification technology to learn about how genes build bodies. Dr. Martin uses CRISPR to disrupt certain genes, and then looks for changes in butterfly wing patterns, creating designs we never see in nature. This tells us which genes control which part of the "wing painting" process. In the process of visiting Dr. Martin’s lab, I had my mind blown about what REALLY happens during butterfly metamorphosis. You will too.

Ever feel like you aren't totally yourself? Well, maybe you aren't. In this video, we explore the idea of human chimeras. In mythology, the "Chimaera" was a beast made from different animals combined into one. But in biology, a chimera is a single organism whose body is made from parts of two or more genetically distinct individuals of the same species. Biological chimeras were once thought to be rare, but modern genetics has shown us that these genetic mashups are so common, that you yourself may actually be a chimera. And even if you don't have part of another body in you, your body is certainly not just one thing. We also discuss the idea of mosaicism and how it relates to cancer, Tasmanian devils, and circus sideshow attractions.

It took about a century for black holes to go from impossible, to theoretical, to real. And it was just this year, in 2019, when we finally saw the first picture of a black hole! But how to you take a photo of something so massively dense that not even light can escape its gravitational pull? You use a telescope the size of the Earth!

Fifty years ago, we sent the first astronauts to walk on the moon’s face. But what they brought back is just as important as what got them there. I’m talking about moon rocks, guys. And I got to go visit NASA’s lunar sample vault to learn more about them! NASA’s moon rock collection has helped us learn so much about the early solar system, the formation of rocky planets like ours, and where our moon came from. And let me tell you, the story of our moon is a VIOLENT one. It involves the word “magmoon”. That’s an awesome word! Enjoy this video, and I hope you learn not just some lunar geology, but also how exploring the moon helped change what the space program was all about.

It never gets dark anymore. Not REALLY dark, anyway. Not like it used to. Most humans on Earth live under light polluted skies. That's because, for the past century and a half, since the dawn of electric light, we’ve been losing our connection to the night. We need artificial light for modern society, of course. The problem is, we need darkness for our health, and for the health of wildlife and ecosystems, and we’re not getting enough of it. I traveled to McDonald Observatory in far west Texas, one of the darkest places in North America, to learn what people are doing in order to preserve dark skies, and to see truly dark skies for myself (and so I could show them to you!). This video features time lapse night sky images that I’ve been collecting for the past few years, and I hope they make you feel something special. Turn out the lights, keep looking up, and don’t be afraid of the dark.

Looking up at the stars makes you wonder: what and who is out there? And why haven’t we seen any other intelligent civilizations given the vast size and age of the universe? They’re complicated questions and although we haven’t met any other space-faring species we do have a way of calculating just how many alien civilizations might be out there as well as some rather frightening ideas as to why we might not have met them.

Why the forest is more than the trees

I met Molly Burke a few months ago. She’s awesome. I absolutely love what she’s done on YouTube to bring awareness to living with disability, and turning it into ability. And her guide dog Gallop is awesome too! When Molly and I first met, we started talking about how she navigates the world, because I’m a nerd and I always steer the conversation toward science. I was not prepared for what she told me. She said she uses echolocation! Molly’s brain has adapted to listen to sounds in her environment in ways that most of us sighted people can’t even imagine. I went to meet her in LA and brought a special surprise, to see if my brain could learn what hers has.

What is “egg-shaped” even? I used to think it was the shape of a chicken egg. Then one day I saw a collection of eggs from lots of different bird species, and I realized just how many different kind of egg shapes there really are! I had to know why. And it turns out a couple teams of scientists had wondered the same thing. Here’s what science says about why eggs are egg-shaped, if that's even a thing, which I’ve learned it might not be. Evolution of bird eggs, go!

It sounds like such an incredible fact. “Our own cells are outnumbered by our microbes 10 to 1!” I don’t remember where I first heard it. But I read it in science papers and articles by journalists, so I believed it without question. I even made one of my first videos based on this fact. Problem is, this fact is not true. So how did it remain firmly planted in our common knowledge for almost four decades without any scientific scrutiny? And how can you prepare yourself to not be fooled by other scientific urban legends? I look at a few of the most famous incorrect factoids in science, and give a few suggestions for how to make our common knowledge more correct.

Money. We all use it. But is it real? I mean, you can touch a coin or bill, but who decided that’s worth anything? And what about all those 1’s and 0’s getting swapped and traded by computers thousands of times per second? How are those worth anything? We trace the history of money, from physical barter to bitcoin, and discover that money isn’t just a lie we all agree to share, it’s been built on the back of technology and invention for millennia.

Earth’s climate is changing in a big way, and it’s because there's more carbon dioxide in the atmosphere than at any point in our species’ history. But Earth’s climate has changed before. How do we know that this time we’re the cause? We know thanks to tiny bubbles of ancient atmosphere trapped in ice.

Greetings, fellow Homo sapiens. Our species is the only remaining member of the genus of upright, walking apes known as Homo. Where did we come from? Our history just got a whole lot more complicated (in a good way) thanks to some incredible new fossils unearthed in South Africa over the past few years. I got to visit them, and the scientists who discovered them, to learn their story and ours. Meet your cousin: Homo naledi

Why are trees and other plants green? Seems like a simple question. But the answer is full of surprises. Using a special camera that can pick up light just beyond the visible range, into the near-infrared, you’ll get to see trees like you’ve never seen them before. And these other-worldly images can teach us not only why trees are green on Earth, but what color photosynthetic life on other planets might be.

What color is a banana? Duh, it’s yellow. But what is yellow? Now that you mention it, how do we see color in the first place? That’s the series of questions that led me to making this video. It started simple and took me down a rabbit hole of decoding our visual system. Turns out it’s way more interesting than I ever thought possible. You might even call it complex. In fact, it’s a wonder it even works. Biology… wow, right?

If you were taking an engineering class in school and you turned in the human body for your final exam… you would get like, a C+. Or maybe a B- at best. That’s because the human body is full of design flaws. Except they aren’t really design flaws, because the human body wasn’t designed. It was evolved, and it is still evolving. And that means some of our parts don’t work as well as they could, they just work well enough. Here’s a rundown of a few of the human body’s biggest evolutionary fails!

People say insects are the food of the future. They’re more environmentally sustainable and more humane than other sources of animal protein. Can they really catch on in western diets? I’m a pretty adventurous eater, but I’ve never actually tried edible insects. So when I got invited to an edible insect Thanksgiving feast, I had to say yes. Along the way I learned that eating bugs isn’t really that new for humans, and that this really could be a delicious food we all eat in the near future.

If everyone would just put more in the recycling bin instead of the trash can, the world would be a better place. Right? Well, that’s not exactly true. For many items that end up in the recycling bin, you’ve actually created more trash by trying to recycle them. You’ve also made it harder to recycle the stuff that CAN be saved, and basically demonstrated that recycling is broken… at least the way we do it today. Here’s how we can fix it.

I’m guessing you’re pretty familiar with ice. We use it in our drinks, slip on it, skate on it, worry about climate change melting it. But have you ever stopped to really think about this stuff? The freezing and melting of water affects so much of our world. It’s ice crystals in thunderclouds that create lightning. Ice is powerful enough crack boulders, float stones, and alter entire landscapes. Ice is such a common substance, you'd think we'd know everything about it by now. But it has some secrets and weird properties we’ve only just begun to figure out. One question about ice that's, still not totally answered, is one of the most obvious: why is ice slippery? It's a more complicated answer than it seems!

Half a century ago, astronauts got on top of a really big rocket and sent a tiny little capsule on a 384,000 km trip to the moon and back. And they were able to do it because a lot of extremely smart and dedicated people pushed engineering and chemistry to the limits in order to create a 36-story tower of carefully-controlled space fire powerful enough to escape Earth’s gravity. I went to NASA in Houston to talk to astronaut Don Pettit about how they did it, and if we’ll be able to do it again.