For young readers

1. It's all about relationships

Think about your family. Each person is real on their own, but what makes them a family is how they are connected: who is a parent, who is a brother, who is a cousin. Scientists Matthew and Melissa Gelfman think the universe works the same way. Every tiny particle is real, but what the universe does comes from how the particles are connected to one another. They made a giant chart that compares every kind of particle with every other kind, the way you might compare every player on a team with every other player.

Try this. Make a chart of your family or your class. Write the names along the top and down the side, and in each square write one way those two people are connected. You have just made a matrix, the same kind of chart scientists use.

2. Space is always full

Is a glass that is half water and half air half empty? No, it is completely full: part water, part air. Space is like that. Even where it looks empty, it is full. Imagine a sealed bag of water with toys floating in it. There is no gap between the water and the toys. In this picture, space is the water.

Try this. Fill a clear bottle halfway with water and close it. Turn it over. The water and the air move around, but the bottle is always full.

3. Push and pull

Blow up a balloon. The air inside pushes out, and the rubber pulls in. If the push wins, the balloon pops. If the pull wins, it gets smaller. Everything in the universe is a balance of push and pull. A star is a ball where the push is winning a little, so light and heat leak out, and that is why stars shine. A black hole is where the pull wins completely, so not even light can get out. Even a tiny proton, far too small to see, is a balance: the bits inside push out and a strong force pulls them back in.

Try this. Squeeze a balloon gently with both hands and feel it push back. That push against your pull is the balance.

4. Why light bends near the Sun

Put a pencil in a glass of water and it looks bent. That is because light slows down in water. Space near something very heavy, like the Sun, acts a little like water for light. Light passing close to the Sun slows and bends. Scientists first measured this in 1919 during a solar eclipse, and the amount matches the math on this website.

Try this. Look at a straw in a glass of water from the side. The straw looks broken where it enters the water. Light is bending.

5. Particles that share a secret

Some particles are linked in a special way called entanglement. Imagine a coin seen in two mirrors. If one mirror shows heads, you instantly know the other shows tails. Nothing flew between the mirrors; it was always one coin. Entangled particles behave like that, even when they are very far apart. The scientists behind this website think gravity, the pull that keeps your feet on the ground, comes from all the entanglement in the universe added together.

6. Ripples that never stop

Drop two pebbles in a still pond. Where the ripples cross, you get bumps, dips and saddle shapes, and the pattern keeps moving. But the pond as a whole stays flat. Space is like that pond: lumpy and changing up close, flat when you look at the whole thing. That is the “Transitioning” in the name of the theory.

Try this. Fill a baking tray with water and tap it gently at two corners. Watch where the ripples cross.

7. How it all began

Long ago, everything in the universe was squeezed together, held in so tightly that it could not stay that way. Then it let go. Think of a water balloon dropped on the ground: it bursts, and the water spreads out in waves. There is the same amount of water as before, just spread out. The universe has been spreading out ever since, for about 13.8 billion years.

8. How do scientists know if they are right?

A good scientific idea does not just explain what we already know. It also makes a guess about something nobody has measured yet. If the guess turns out wrong, the idea is wrong, and scientists learn from it. This theory makes a guess about neutrinos, the lightest and shyest particles known. It says how heavy they should be and in what order. A huge experiment in China called JUNO will check that guess in the next few years.

Try this. Make a prediction: how many seconds will it take an ice cube to melt in your hand? Write it down, then test it. That is how science works.