COVER FEATURE: 22 THINGS WE DON’T KNOW!

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1What caused the Big Bang? According to the theory, everything that exists, including space, time and all the matter in the universe, expanded from a tiny single point in a mind-boggling moment we call the Big Bang. But as for what, if anything, caused the Big Bang – we have absolutely no idea!

2Do aliens exist? Our galaxy, the Milky Way, is very big and has existed for more than 13 billion years. It contains hundreds of billions of stars and planets, and mathematical probability suggests that at least one of those planets should contain intelligent alien life. However, so far, we have yet to meet any aliens or detected any signs that they exist. One reason for this could be that space is just too big (the Milky Way alone is 100,000 light years across), and so even if aliens are out there, and sending messages into space, they just haven’t had time to reach us yet.

3Was Mulan a real person? Disney’s warrior heroine is based on a real Chinese folk

From how life on Earth began to whether aliens exist, we investigate some of the universe’s great unsolved mysteries…

It is likely that alien life exists somewhere in the universe.

song from the 5th or 6th century. The song describes a real time and place. But Mulan’s name doesn’t appear in a text about important women in the clan. So whether Mulan was a real historical figure remains a mystery.

4What would happen if a spaceship fell into a black hole?

Scientists think that any object falling into a black hole would be stretched out by the enormous pull of its gravity like a long piece of spaghetti, in a process called spaghettification. However, no one knows what would happen next because we have no information about what may or may not exist on the other side. Though some theories suggest that black holes could provide a gateway to an entirely different universe.

‘I like a universe that includes much that is unknown.’ CARL SAGAN, ASTRONOMER

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5Where is Cleopatra’s tomb? Cleopatra was the last pharaoh of ancient Egypt. She died in 30 BCE and ancient historians wrote that her tomb was filled with treasures including gold, silver, emeralds and ivory. Archaeologists think Cleopatra’s tomb is buried underground somewhere near the Egyptian port of Alexandria, but it has yet to be discovered.

6Could we bring dinosaurs back to life?

Fans of the Jurassic Park movies will be familiar with the idea that, one day, scientists will use an extract of a dinosaur’s DNA or genetic code to bring it back to life. At the moment, however, this is unlikely, partly because DNA is easily damaged and would probably have broken down in the millions of years since the dinosaur died. Could scientists of the future find a new way to bring dinosaurs back?

7How does gravity work? Gravity is an invisible force of attraction that exists between any two objects or particles in the universe that have mass. When you throw a ball up in the air, for example, it is the gravitational force created by Earth’s greater mass that pulls it back down to Earth. But although we understand how gravity behaves, and can observe and predict its effects, we don’t know by what physical mechanism it happens. All we can say for now is that gravity exists.

Dinosaurs lived on Earth for about 165 million years. Could they ever return? Above: cats are one of several animals that are thought to dream while they are asleep. Right: a green iceberg.

8Is there a lost city of Atlantis?

According to legend, Atlantis was an ancient city that was swept beneath the sea by a tsunami, or giant wave, thousands of years ago. Will the lost city ever be found? Most experts doubt Atlantis was a real place so it seems unlikely.

9Was Robin Hood a real person? Many people have heard the tales of Robin Hood, a well-meaning outlaw in 14th-century England who lived in a forest and robbed from rich people to give money to the poor. Do you believe the stories? Lots of historical documents refer to a ‘Rabunhod’, but this may just be a nickname for a robber.

1O Will we ever decipher Minoan writing?

The ancient Minoan civilisation, which flourished on the island of Crete between about 3,000 BCE and about 1,100 BCE had two writing systems. One, known as Linear A, used symbols to represent sounds and some objects such as cows, pigs and grain. Historians have yet to fully decipher Linear A, although they can translate Linear B, another ancient writing system which was adapted from Linear A. So, one day, it’s possible someone could crack the code.

11 Why are some icebergs green? Most large

icebergs are blueish in colour but some in Antarctica are green. They are

sometimes called jade bergs because they look similar in colour to the gemstone jade. Scientists don’t know why these icebergs are green but one theory is that yellow-ish red minerals scraped up by glaciers mix with the normal blue colour of icebergs, turning them green.

12 Why do humans (and animals) dream?

they’re asleep. And behaviour that suggests dreaming has been observed in animals, including cats, rats and birds. Yet despite decades of research, scientists still can’t say for sure exactly why and how we dream. One theory is that dreams help the brain to organise all the sensory information it has received during the day, before storing some of it as memories.

13 Did the Hanging Gardens of Babylon exist?

One of the Seven Wonders of the Ancient World, the Hanging Gardens were said to be beautiful tiered gardens in in the city of Babylon. Some sources claim they were destroyed by an earthquake in the 1st century CE. However, no evidence of the Hanging Gardens has ever been found.

‘We’re not afraid to admit what we don’t know – there’s no shame in that. The only shame is to pretend that we have all the answers.’ NEIL DEGRASSE TYSON, ASTROPHYSICIST

14 How did life on Earth begin?

The earliest known signs of life on Earth are the remains of microbes found in rocks thought to be around 3.5 billion years old. There are lots of theories, but exactly how life first emerged remains one of science’s great unanswered questions.

15 What is dark energy? According to

the laws of gravity, the rate at which the universe is expanding should be slowing down. However, it’s actually speeding up! Why? Scientists have no idea, although they have named the force causing this mysterious acceleration dark energy.

16 How do animals migrate? Many animals

migrate thousands of miles each year to escape seasonal changes in temperature, find food or breed. But how do they find their way to the same places year after year? Different animals have different ways of navigating, such as sensing the position of the Sun and stars, and even using Earth’s magnetic field. However, scientists still know relatively little about how these migratory behaviours evolved and are passed down to new generations of animals.

17 Why did some Maya cities collapse?

The Maya were one of the great civilisations in Mesoamerica, a region stretching between what is now Mexico and

Central America. From about 800 to 950 CE, Mayan cities went

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A temple in the abandoned Mayan city of Tikal in Guatemala.

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into decline and some were abandoned. Historians have put forward various theories for this – including drought, land erosion and warfare – but the mystery of what caused this dramatic collapse remains unsolved.

18 Why do scorpions glow in moonlight?

Although nobody knows for certain, scientists think that chemicals in the scorpion’s skin convert faint ultraviolet light from the stars into a blue-green light which makes them glow. How this benefits the scorpion is also unclear. The scorpion’s glow may help it confuse potential predators.

19 Will computers become smarter than humans?

In some ways, computers are already cleverer than humans. They can make calculations faster, memorise more information and even beat us at strategy games such as Go and chess. Yet despite all the recent advances in computer technology, no one has built a computer as complex as the human brain – at least not yet.

20 Who wrote the Iliad and the Odyssey?

These famous epic poems are usually credited to the ancient Greek poet Homer. However, most historians agree that the same person couldn’t have written both poems. And some experts think that Homer never existed at all!

21 Who built the rock churches of Lalibela?

There are 11 impressive churches in the Ethiopian city of Lalibela that were carved from rock more than 800 years ago. No one knows who built them and some locals believe they were made by angels.

‘For every complex problem in life there’s always a simple answer – and it’s always wrong.’ SUSAN GREENFIELD, SCIENTIST

22 How will the universe end? Most scientists

agree that the universe will end at some point billions of years in the future. But no one knows precisely when or how this will happen. One theory says that the current expansion of the universe will slow down and reverse, pulling all its matter together again. Another theory says that the universe will continue to expand until it loses all its energy. A third theory says the universe’s expansion will accelerate until stars, planets and even atoms are torn apart. Which theory is correct? We don’t know, so you’ll have to wait and see…