George's Secret Key to the Universe

by Stephen Hawking

  Annie waved to Saturn and shouted, “Hello, Saturn!” so loudly that George’s hands automatically tried to cover his ears, but he couldn’t because of his helmet, so instead he yelled back, “Don’t shout!”

  “Oh, I’m sorry,” she said. “I didn’t mean to.”

  As they whizzed past Saturn, George saw that Annie was right—the comet didn’t fall all the way onto the giant planet but cruised straight past it. With some distance now, he could see that Saturn not only had rings, but also a moon, like the Earth. Looking closer, he could hardly believe his eyes! He saw another moon, and another and yet another! In total, he saw five large moons and even more small ones before Saturn was too far away for him to keep counting. Saturn has at least five moons! he thought. George hadn’t known that a planet other than the Earth could have even one moon, let alone five! He looked at Saturn with respect as the giant planet with rings shrank into the distance behind them until it was just a bright dot in the starry background.

  SATURN

  Saturn is the sixth closest planet to the Sun.

  Average distance to the Sun: 888 million miles (1,430 million km)

  Diameter at equator: 74,898 miles (120,536 km) corresponding to 9.449 diameters at equator on Earth

  Surface area: 83.7 × Earth’s surface area

  Volume: 763.59 × Earth’s volume

  Mass: 95 × Earth’s mass

  Gravity at the equator: 91.4% of Earth’s gravity at Earth’s equator

  It takes Saturn 29.46 Earth-years to circle around the Sun.

  Structure: Hot, rocky core that is surrounded by a liquid metal layer that is itself surrounded by a liquid hydrogen and helium layer. There then is an atmosphere that surrounds it all.

  Winds have been recorded at speeds up to 1,116 mph (1,795 km/h) in Saturn’s atmosphere. By comparison, the strongest wind ever recorded on Earth is 231 mph (371.68 km/h) at Mount Washington, New Hampshire, USA, on April 12, 1934. It is believed that wind speeds can sometimes reach over 300 mph (480 km/h) inside tornadoes. However devastating these are, these winds are still very slow compared to Saturn’s winds.

  So far, Saturn has 59 confirmed moons. Seven of them are round. Titan, the largest, is the only known moon within the Solar System to have an atmosphere. In volume, Titan is more than three times bigger than our Moon.

  The comet was now traveling straight again. In front of them, the Sun was bigger and brighter than before, but still very small compared to its size when seen from the Earth. George spotted another bright dot that he hadn’t noticed before, a dot that was quickly growing bigger as they approached it.

  “What’s over there?” he asked, pointing ahead and to the right. “Is that another planet?”

  But there was no reply. When he looked around, Annie had gone. George untied himself from the comet and followed the trail of footprints she had left in the icy powder. He carefully gauged the length of his steps so that he wouldn’t find himself flying off the comet again.

  After climbing carefully over a small icy hill, he saw her. She was peering into a hole in the ground. Around the hole were bits and pieces of rock that seemed to have been spat out by the comet itself. George walked over and looked down into the hole too. It was a few feet deep, with nothing much to be seen at the bottom.

  “What is it?” he asked. “Have you found something?”

  “Well, you see, I went for a walk—,” Annie started to explain.

  “Why didn’t you tell me?” George interrupted her.

  “You were shouting at me about not shouting!” said Annie. “So I thought I’d just go by myself. Because then there’d be no one to get mad at me,” she added pointedly.

  “I’m not mad at you,” said George.

  “Yes, you are! You’re always angry with me. It doesn’t make any difference if I’m nice to you or not.”

  “I’m not angry!” shouted George.

  “Yes, you are!” shouted back Annie, balling her gloved hands into fists and shaking them at George. As she did so, something extraordinary happened. A little fountain of gas and dirt blew up from the ground just next to her.

  “Now look what you’ve done!” complained George. But as he spoke, another little fountain erupted through the rock right next to him. It formed a cloud of dust that slowly dispersed.

  “Annie, what’s happening?” he asked.

  “Um, it’s nothing,” replied Annie. “This is all fine, don’t worry.” But she didn’t sound very sure. “Why don’t we go and sit down where we were before?” she suggested. “It’s nicer over there.”

  But as they walked back, more and more little geysers of dust erupted around them, leaving a haze of smoke in the air. Neither of them felt very safe, but neither of them wanted to admit it. They just walked more and more quickly toward the place where they’d been sitting before. Without saying a word, they anchored themselves to the comet once more.

  In the sky, the bright dot George had seen growing had become much bigger. It now looked like a planet with red and blue stripes.

  “That’s Jupiter,” Annie said, breaking the silence. But she was whispering now. She didn’t sound like the confident show-off she had been earlier. “It’s the biggest of the planets, about twice the volume of Saturn. That makes it more than a thousand times the volume of Earth.”

  “Does Jupiter have moons too?” George asked.

  “Yes, it does,” replied Annie. “But I don’t know how many. I didn’t count them last time I was here, so I’m not sure.”

  “Have you really been here before?” George looked suspicious.

  “Of course I have!” said Annie indignantly. George wasn’t sure he believed her.

  Once again, the comet and Annie and George started to fall. As they fell, George gazed at Jupiter. Even by Saturn’s standards, Jupiter was enormous.

  As they flew by, Annie pointed out a big red mark on Jupiter’s surface.

  “That thing,” she said, “is a huge storm. It’s been going on for hundreds and hundreds of years. Maybe even more, I don’t know. It’s over twice the size of the Earth!”

  As they moved away from Jupiter, George counted how many moons he could spot.

  “Four big ones,” he said.

  “ ‘Four big ones’ what?”

  “Moons. Jupiter has four big moons and lots and lots of little moons. I think it has even more moons than Saturn.”

  “Oh, okay,” said Annie, who was sounding nervous now. “If you say so.”

  George was worried—it wasn’t like Annie to agree with anything he said. He noticed she had shuffled a little closer to him. She slipped her hand in its space glove into his. All around them, new jets of gas and dust were springing up out of the rock, each one spitting out a small cloud. A thin haze was forming over the whole comet. “Are you all right?” he asked Annie. She had stopped showing off and being rude, and he felt sure something was very wrong.

  “George, I—,” Annie started to reply, when a huge rock smashed into the comet behind them, shaking the ground like an earthquake and sending up even more dust and ice into the haze.

  Looking up, George and Annie saw there were hundreds and hundreds of rocks, all coming toward them at high speed. And there was nowhere to hide.

  “Asteroids!” cried Annie. “We’re in an asteroid storm!”

  JUPITER

  Jupiter is the fifth closest planet to the Sun.

  Average distance to the Sun: 483.6 million miles (778.3 million km)

  Diameter at equator: 88,846 miles (142,984 km), corresponding to 11.209 diameters at equator on Earth

  Surface area: 120.5 × Earth’s surface area

  Volume: 1,321.3 × Earth’s volume

  Mass: 317.8 × Earth’s mass

  Gravity at the equator: 236% of Earth’s gravity at Earth’s equator

  Structure: Small (compared to the overall size of the planet) rocky core surrounded by a liquid metal layer that smoothly turns into a liquid hydrogen layer as height increases. This liquid then smoot
hly turns into an atmosphere made of hydrogen gas, which surrounds it all. Even though it is bigger, Jupiter’s overall composition is similar to Saturn’s.

  The Great Red Spot on Jupiter’s surface is a giant hurricane-type storm, a storm that has lasted for more than three centuries (it was first observed in 1655), but it may have been there for even longer. The Great Red Spot storm is huge: more than twice the size of the Earth. Winds on Jupiter often reach 620 mph (1,000 km/h).

  It takes Jupiter 11.86 Earth-years to circle around the Sun.

  So far, Jupiter has 63 confirmed moons. Four of them are big enough to be round and were seen by the Italian scientist Galileo in 1610. These are collectively known as the Galilean moons. They are Io, Europa, Ganymede, and Callisto, and they are about the same size as our Moon.

  “What do we do?” yelled George.

  “Nothing,” shrieked Annie. “There’s nothing we can do! Try not to get squashed! I’ll call Cosmos to get us back.”

  The comet shot through the asteroids with incredible speed. Another large rock hit the comet just in front of them, raining down smaller rocks on their space suits and helmets. Through the voice transmitter in his helmet, George heard Annie scream. But suddenly the scream went silent—the noise just stopped like a radio being switched off.

  George tried to say something to Annie through the voice transmitter, but she didn’t seem to hear him. He turned to look at her. He could see she was trying to speak to him from inside the glass space helmet, but he couldn’t hear anything she said. He shouted as loudly as he could: “Annie! Get us home! Get us home!” But it was no use. He could see now that the tiny antenna on her helmet was snapped in half. That must be why he couldn’t talk to her! Did this mean she couldn’t talk to Cosmos either?

  Annie was nodding like crazy and holding on to George very tightly. She was trying as hard as she could to summon Cosmos to come and get them both, but the computer wasn’t answering. As George feared, the device that linked her both to him and to Cosmos had been broken by the rocks raining down on them. They were stuck on the comet, flying through an asteroid storm, and it seemed there was no way out. George tried to call Cosmos himself, but he didn’t know how to do it or whether he even had the right equipment. He got no reply. Annie and George hung on to each other and squeezed their eyes shut.

  But just as suddenly as the storm had started, it stopped again. One minute rocks were thudding down on the comet all around them, the next the comet had flown out of the other side of the storm. Looking around, George and Annie realized how very lucky they had been to escape. The rocks were forming a huge line that seemed to extend all the way through space. They were mainly large and scattered thinly along the line, except where the comet had flown through. The rocks here were much smaller but more densely packed.

  However, they were still far, far from safe. Jets of gas from the comet were now shooting out everywhere. Soon one could erupt right underneath them. It was now so hazy from all the explosions that they could hardly see the sky. Just the Sun and a faint little blue dot that was slowly getting bigger.

  George turned back to Annie and pointed at the blue dot ahead. She nodded and tried to spell out a word with the finger of her space glove in the air. George could only make out the first letter—E. As they got closer to it, the comet tilted slightly toward it, and George suddenly realized what Annie was trying to tell him. It was E for Earth! The tiny blue dot in front of him was the planet Earth. It was so small compared to the other planets, and so beautiful. And it was his planet and his home. He desperately wanted to be back there now, this very second. He wrote “Cosmos” in the air with his space glove. But Annie just shook her head and wrote the word “NO” with her finger.

  ASTEROID BELT

  Asteroids are objects that orbit the Sun but are not big enough to be round and to be called planets or dwarf planets. There are millions of them around the Sun: 5,000 new asteroids are discovered every month. Their size varies from a few inches across to several hundred miles wide.

  There is a ring full of asteroids that circle the Sun. This ring lies between Mars and Jupiter. It is called the Asteroid Belt. Even though there are a lot of asteroids in the Asteroid Belt, it is so huge and spread out that most of the asteroids there are lone space travelers. Some places, however, may be more crowded than others.

  Around them on the comet, conditions were getting worse by the second. Hundreds and hundreds of fountains of gas and dust were erupting all over it. They huddled together, two castaways in space, with no idea how to get out of the awful trouble they had landed themselves in.

  At least, George thought, in a strange, dreamlike way, I’ve seen the Earth from space. And he wished he could have told everyone back home how tiny and fragile the Earth was compared to the other planets. But there was no way they could get back home now. The fog of dust and gas was now so thick that they had even lost sight of the Earth’s blue color. How could Cosmos have let them down like this?

  George was just wondering if this was the last thought he’d ever have when suddenly a doorway filled with light appeared on the ground next to them. Through it came a man in a space suit, who unhooked them both from the comet and, one at a time, picked them up and threw them through the door. A split second later, Annie and then George landed with a bump on the floor of Eric’s library. The man who had grabbed them quickly followed and the doorway slammed shut behind him. Pulling off his space helmet and glaring down at George and Annie, who were sprawled on the library floor in their space suits, Eric shouted, “What on Earth did you think you were doing?!”

  “What on Earth did you think you were doing?!”

  Eric was so angry that, for a moment, George wished he were still on the roller-coaster comet, heading straight for the heart of the Sun.

  “Actually, we weren’t on the Earth,” murmured Annie, who was struggling out of her suit.

  “I heard that!” George hadn’t thought Eric could get any angrier than he already was, but now he looked so furious, George thought he might explode. He half expected to see great jets of steam burst out of his ears, just like the ones on the comet.

  “Go to your room, Annie,” ordered Eric. “I’ll talk to you later.”

  “But Da-ddy … ,” Annie began. But even she fell silent under Eric’s glare. She pulled off her heavy space boots, wriggled out of her suit, and shot out of the door like a streak of blond lightning. “Bye, George,” she muttered as she ran past him.

  “As for you … ,” said Eric in such a menacing tone that George’s blood ran cold. But then he realized Eric wasn’t talking to him. He was looming over Cosmos, casting threatening looks at the computer screen.

  “Master,” said Cosmos mechanically, “I am just a humble machine. I can only obey the commands I am given.”

  “Ridiculous!” cried Eric wildly. “You are the world’s most powerful computer! You let two children travel into outer space by themselves. If I hadn’t come home when I did, who knows what might have happened? You could have—you should have—stopped them!”

  “Oh dear, I think I am about to crash,” replied Cosmos, and his screen suddenly went blank.

  Eric clutched his head in his hands and staggered around the room for a minute. “I can’t believe this,” he said, as though to himself. “Terrible, terrible!” He groaned loudly. “What a disaster!”

  “I’m very sorry,” said George timidly.

  Eric whipped around and stared at him. “I trusted you, George,” he said. “I would never have showed you Cosmos if I’d thought that the minute my back was turned, you would sneak through the doorway into outer space like that. And taking a younger child with you! You have no idea how dangerous it is out there.”

  George wanted to shout that this was so unfair! It wasn’t his fault—it was Annie who had pushed them both through the doorway into outer space, not him. But he kept quiet. Annie, he figured, was in enough trouble already without him making it worse.

  “There are things in out
er space you can’t even imagine,” continued Eric. “Extraordinary, fascinating, enormous, amazing things. But dangerous. So dangerous. I was going to tell you all about them, but now …” He shook his head. “I’m going to take you home.” And then Eric said a terrible thing. “I need to have a word with your parents.”

  As George found out afterward, Eric had more than just one word with his parents. In fact, he had quite a few, enough to make them feel very disappointed in their son. They were very hurt that despite all their good intentions about bringing up George to love nature and hate technology, he’d been caught red-handed at Eric’s house playing with a computer. A valuable and delicate one no less; one that wasn’t for kids to touch. Worse, George had invented some kind of game (Eric had become somewhat vague at this point), which he’d persuaded Annie to join in, and this game had been very dangerous and very silly. As a result, the two children were both grounded and not allowed to play together for a whole month.

  “Good!” said George when his dad told him what his punishment would be. At that moment he never wanted to see Annie again. She’d got him into so much trouble already, and yet George had been the one to take all the blame.

  “And,” added George’s dad, who was looking very angry and bristly today with his big, bushy beard and his itchy, hairy homemade shirt, “Eric has promised me he will keep his computer locked up so neither of you will be able to get near it.”

  “No-o-o!” yelled George. “He can’t do that!”

  “Oh yes he can,” said George’s dad very severely. “And he will.”

  “But Cosmos will get lonely all by himself!” said George, too upset to realize what he was saying.

  “George,” said his dad, looking worried, “you do understand that this is a computer and not a living being we’re talking about? Computers can’t get lonely—they don’t have feelings.”

  “But this one does!” shouted George.

  “Oh dear,” sighed his dad. “If this is the effect that technology has on you, you see how right we are to keep you away from it.”