- By Jonathan Amos
- BBC Science Correspondent
A European space telescope is about to launch from Florida in a quest to solve one of the biggest questions in science: what is the Universe made of?
The Euclid mission will create a massive 3D map of the cosmos in an effort to tie together some of the properties of so-called dark energy and dark matter.
Together, these phenomena appear to control the shape and expansion of everything we see out there.
Researchers admit, however, they know almost nothing about them.
Neither dark energy nor dark matter is directly observable.
The huge knowledge gap means we can’t explain our origins, says Prof Isobel Hook.
Euclid’s insights will be our best bet to get on the path to understanding, believes the astronomer at UK’s Lancaster University.
“It’s like getting on a ship before people know where the land is in different directions. We’re going to map the Universe to try to understand where we fit into it and how we got here – how we got there. the entire Universe from the point of the Big Bang to the beautiful galaxies we see around us, the Solar System and even life,” he told BBC News.
The €1.4bn (£1.2bn) Euclid telescope is poised to lift off on a Falcon-9 rocket from Cape Canaveral at 11:11 local time (15:11 GMT/16:11 BST).
Euclid will be sent to an observing position about 1.5 million km from Earth, opposite the planet from the Sun.
Although primarily a project of the European Space Agency (Esa), the mission has significant scientific and engineering input from the US space agency (Nasa) as well.
How would Euclid analyze the dark cosmos?
Previous experiments have suggested dark energy accounts for about 70% of all energy in the Universe; dark matter about 25%; with all visible material – the stars, gas, dust, planets, us – accounting for the remaining 5%.
To unravel the nature of the mysterious 95%, Euclid would conduct a six-year, two-pronged survey.
A key task is to map the distribution of dark matter, the matter that cannot be detected directly but that astronomers know is there because of its gravitational effects on the matter we can see.
Galaxies, for example, could not hold their shape if not for the presence of some additional “scaffolding”. This is assumed to be dark matter – whatever that is.
Although this material is not directly visible, telescopes can plot its distribution by looking for the subtle way its mass distorts the light coming from distant galaxies. The Hubble Space Telescope is famously the first to do this for a small patch of sky – just two square degrees.
Euclid would do this across 15,000 square degrees of the sky – a little over a third of the sky.
Central to all this is the telescope’s VIS, or visible, camera, whose development has been led from the UK.
“The images it will produce are enormous,” said Prof Mark Cropper from UCL’s Mullard Space Science Laboratory. “You’d need more than 300 high-definition TVs to actually display just one picture.”
Dark energy is a very different concept from dark matter.
This mysterious “force” appears to be accelerating the expansion of the Universe. Recognition of its existence and impact in 1998 earned the Nobel Prize to three scientists.
Euclid would investigate the phenomenon by mapping the three-dimensional distribution of galaxies.
The patterns in the large voids that exist between these objects can be used as a kind of “yardstick” to measure expansion over time.
Again, ground-based surveys did this for small volumes of sky; However, Euclid will measure the precise positions of about two billion galaxies out to about 10 billion light-years from Earth.
“We can ask some interesting questions,” said Prof Bob Nichol from Surrey University.
“Is the acceleration the same at all points in the Universe? Now, we pretty much average everything we measure. But what if the acceleration there is not the same as here? That would be discovery science,” he told BBC News.
Euclid can’t necessarily say “this is the nature of dark matter and dark energy”, but what it should do is narrow the range of models and ideas that flood current thinking. It will focus the attention of theorists and experimentalists.
For example, it could introduce some new thinking on how to identify particles currently thought to represent the bulk of dark matter. All searches to date have come up empty.
And as for dark energy, Euclid could tell scientists that, far from being some intrinsic property of the vacuum of space – their current best guess – this unknown force has a better explanation in a modified theory of gravity. This too will be the science of discovery.
“One possibility is that dark energy is actually a fifth force, a new force in the Universe that only works on large scales, so it doesn’t influence life here on Earth,” said Prof Mark McCaughrean, ESA’s senior advisor for in science and exploration. .
“But, of course, this has a huge influence on the fate of our Universe – how far will it expand? Will it continue to accelerate forever, getting bigger and bigger? Or maybe everything will collapse again.”
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