I n finiteSpace The universe is a vast expanse of space that contains all matter and energy from the smallest particle to the biggest galaxy It contains all the planets the Sun stars asteroids our Milky Way Galaxy and all the other galaxies too No one knows how big the universe is Astronomers believe that it is still growing outward in every direction How did it all begin No one knows that for sure either Most scientists believe that at first everything was one incredibly solid heavy ball of matter This ball exploded billions of years ago and the universe was born The moment of this explosion is called the big bang It is from this moment that time began After the explosion the early universe was small and extremely hot As it cooled it expanded and pieces spread out Small pieces formed the basic S EA R C H LIG H T If the universe is still growing is it moving toward or away from the Earth 8
UNIVERSE elements hydrogen and helium Other pieces began to join together and objects began to form Over billions of years the objects became galaxies stars and planets This is still only a theory an idea But different parts of it have proved true over the years Astronomers try to investigate the theory all the time One way they do this is to use a spectroscope A spectroscope measures the color of light coming from an object Changes in the color indicate whether an object is moving away from or toward the Earth Because of spectroscope readings scientists believe that the universe is still growing outward in every direction LEARN MORE READ THESE ARTICLES GALAXIES SOLAR SYSTEM STARS D I D YO U K N O W ieve that much of the universe may be made of something Scientists bel l e d d a r k m a t t e r T h i s h i d d e n mass may be a substance that human cal beings have never before encountered balloon blow it up and watch the dots spread apart thing else You can see how this works if you put black dots on a Answer Everything in the universe is moving away from every 9
TheInvisibleMag n e t Raise your arm Keep it in that position for as long as you can What happens After some time your arm begins to hurt Something seems to be pulling it down Soon enough you have to lower your arm It’s a force called gravity that causes you to lower your arm Gravity acts something like a magnet tugging away at your arm as if it were a piece of metal We can’t see gravity or touch it We can only feel it The Earth has gravity that pulls down on everything on or near it It is this force that keeps us all on Earth The Moon and the Sun also have gravity All bodies in the universe have gravity In fact gravity helps hold all of them together Sir Isaac Newton first introduced the idea of gravity and Albert Einstein added to Newton’s ideas Gravity works in a two-way system This means that all bodies have a pull on each other For example Earth’s gravity forces the Moon to circle around it all the time In return the Moon’s gravity attracts the waters of Earth’s oceans to cause tides The force of gravity becomes weaker and weaker as we move away from its source That is partly why astronauts can float around in outer space They are too far away for the Earth to have much pull on them What do you think would happen if there were no gravity on Earth LEARN MORE READ THESE ARTICLES ALBERT EINSTEIN MOON SIR ISAAC NEWTON 10
GRAVITY DID YOU KNOW The 1961 Disney movie The Absent Minded Professorintroduced one of the most far-fetched and hilariously popular antigravity schemes flubber a superbouncy flying-rubber formula S EA R C H LIG H T Why do you think a ballpoint pen won’t work when you try to write with its point facing upward The upside-down pen’s point soon runs out of ink the wrong end of a pen that’s not facing toward the ground Answer Gravity causes the ink in the ballpoint pen to flow to 11
