Euclid launched: the space telescope that must unravel one of the greatest mysteries of our universe | Science & Planet

LOOK. Watch the launch of the Euclid space telescope here

Space telescope Euclid, named after the ancient Greek mathematician Euclid, will measure the structure of the universe on the largest scale. This will produce an extremely detailed map with 2 billion galaxies, a large part of the observable universe. And that map also tells you how all those galaxies have developed over the past, say, 10 billion years.

Scientists hope this will help solve pressing cosmological issues. Enigmatic dark matter, dark energy, gravity and the development of the universe: it remains shrouded in mystery. These are five fundamental questions that Euclid sets out on.

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Our universe consists of many stars and galaxies, plus some clouds of dust and gas. However? If you ask a cosmologist this is far from the right answer. All those galaxies are just what we can see. But that’s less than five percent of what really needs to be.

At least twenty percent of the universe must consist of ‘dark’ matter. Stuff we can’t see but can measure the gravitational effects of. And then there is a lot of dark energy, a mysterious dispersive force that ensures that the expansion of the universe is accelerating. Scientists have no idea what it is for either.

Viewed on the largest scale, the galaxies in our universe form a kind of cobweb, also called the cosmic web. But the gravitational pull of all those galaxies together is simply not enough to form such a structure, explains René Laureijs, project scientist at Euclid.

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According to many scientists, invisible ‘dark matter’ must exist between and around the galaxies. Its gravity is measurable, but what it consists of is completely unknown. By looking closely at the gravitational effects of this dark matter, Euclid will map its distribution. That helps answer the question of what it’s made of.

In the 1920s, astronomer Edwin Hubble discovered that all galaxies are flying away from us. So the universe is expanding, like a balloon being inflated. In the late 1990s, scientists discovered, against all odds, that this inflation is accelerating.

The unknown, dispersive force responsible for this, they called dark energy. Where gravity attracts, dark energy pushes everything apart. This constant pushing seems to be inherent in empty space itself. The more empty space there is, the more dark energy there is. And so everything is pushed apart faster and faster.

On Earth, we do not notice any dark energy at all. Even between, for example, neighboring galaxies, the gravitational pull is still much stronger. Only on the largest cosmic scale does dark energy play a leading role.

Dark energy therefore ensures that the universe is expanding faster and faster. But that acceleration only started about six billion years ago, when the universe was roughly half the age it is today. Then dark energy became stronger than gravity.

To understand more about this mysterious form of energy, scientists want to discover, among other things, whether dark energy is constant or undergoes changes, says Laureijs. In the latter case, the cosmological theories must be reconsidered.

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Because the universe is so big and because light needs time to reach us, looking deep into the universe is also seeing far back in time. Euclid will look back to that moment six billion years ago, when dark energy became so strong that it began to interfere with the development of the universe.

The effects of dark matter and the formation of galaxies in a web-like structure are all related to gravity. We mainly understand gravity thanks to Einstein’s general theory of relativity. But is this theory also valid on the very largest cosmic scale? Cosmologists don’t know for sure.

With Euclid, scientists can watch the formation of the very largest cosmic structures over billions of years. They may find indications with Euclid that gravity on a cosmic scale works slightly differently than previously thought. And even then the theories have to be overhauled.

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