The Origin of the World

You probably know how tall you are. You know your weight and how far it is to school or the nearest supermarket, and how to get there. You know the units used to measure distances and weights, and that your day has a beginning and an end. You can see colours and hear sounds. All this is possible because we humans perceive our surroundings with our senses. And that helps us find our way around the Earth.

For a long time, people believed that Earth was the center of the universe and that the sun, moon and all the stars hung above us like ornaments from a dome. They believed that gods pulled the sun across the sky during the day and carried it back to its starting point in the east at night.

Today we know that Earth is by no means the centre of the universe, but a tiny speck of dust in an unimaginably vast universe. We know that Earth revolves around the Sun, and that our Sun is just one of countless stars.

We humans have learned a lot about the universe, but there is still much we do not know. Our senses are not enough to understand what space is like. We have learned to use telescopes and electronic equipment and to make mathematical calculations. Even so, much of it is simply beyond comprehension. Distances in space are so vast that we no longer measure them in meters or kilometers, but in astronomical units and light-years. An astronomical unit is the distance from Earth to the Sun—150 million kilometers. A light-year is the distance light can travel in one year.

Since light travels at a speed of 300,000 kilometres per second, it covers 9,460,800,000,000 kilometres in a year. We usually write this unimaginably large number as 9.46 trillion. We cannot grasp such a distance with our senses. Even more so when scientists tell us that the universe is at least 93 billion light-years across.

We also cannot imagine how it all began: the entire universe as we know it today, with its immense dimensions, is said to have once been concentrated in a single point, thousands of times smaller than a pinhead and many billions of degrees hot.

Before that, there was supposedly nothing—no space and no time. Then this tiny point exploded in a Big Bang. In less than a second, space grew larger than our Milky Way is today. It has been expanding at tremendous speed ever since. The expansion is still continuing today, even though about 13.8 billion years have passed since the Big Bang. We do not know whether space has an edge, how long it will continue to expand, or whether it might eventually contract again.

One second after the Big Bang, stable particles formed that we call protons and neutrons. After three minutes, the universe had cooled a little; it was "only" about 1 billion degrees Celsius. The protons and neutrons could now join together, forming hydrogen and helium nuclei.

After another 300,000 years, the temperature was still about 3,000 degrees Celsius. Hydrogen and helium nuclei could now capture electrons and form atoms. Clouds of hydrogen and helium formed. And the stars developed from these gases.

The Big Bang is still a theory, not an established fact. Most scientists currently consider it to be correct. Others have their doubts. Since a theory is accepted only until it is shown to be wrong, we cannot rule out the possibility that new discoveries will be made in the future. - Image: pixabay.com

✍️ The Big Bang

For a long time, people believed that the Earth was a ___.
We now know that it is a ___.
The distances in ____ are enormous.
An astronomical unit is the distance between ____ and the Sun.
A light-year is a distance of ____ kilometers.
The universe is at least ____ light-years across.
The point from which the universe developed was only as big as ____.
At the beginning of all time there was the ____.
About ____ years have passed since then.
Before, it was probably simply ____.
Three minutes after the Big Bang, the universe was ____ hot.
Since then, the stars have formed from the gases ___ and ____.

Complete the sentences and write out the text.

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