How can you see something that’s invisible? Well, with Euclid! This future ESA telescope will map the structure of the Universe and teach us more about invisible dark matter and dark energy. Scientific coordinator of Euclid and Leiden astronomer Henk Hoekstra explains how this works.
Something strange is going on
Why do we assume that dark matter exists, if we have never seen it or even measured it? ‘We are orbiting the center of our galaxy at 220 kilometers per second,’ says Hoeksta. A bizarre speed, which fortunately we don’t notice. Still, something strange is going on. ‘Based on the number of stars in our Milky Way, the stars at the edge of the Milky Way should have a much lower speed, but they move as fast as the Sun. Yet these stars are not being slung into the Universe. Something is holding them together.’
Basically, there can only be one explanation: there is matter that you cannot see, but that exerts extra gravity. In other words, dark matter. Hoekstra: ‘Or the theory of gravity is wrong. But everything indicates that dark matter exists, only we still don’t know what it is. What we do know is that it does not absorb light or interact with it. So that literally makes it invisible.’ If this is not strange enough: since 1998 we know that the expansion of the Universe is accelerating. To explain this an even more mysterious ingredient is needed: ‘dark energy,’ a term that simply encompasses all ideas that astronomers and physicists are currently studying.
The matter we cannot see
In this 5-minute TED-Ed movie, James Gillies explains what dark matter and dark energy are.
Why we need Euclid
‘We have some knowledge-gaps and these cannot be filled with existing observations. So the only way forward is to take better measurements.’ And that’s where Euclid comes in, the satellite that the European Space Agency will launch in 2022. At a distance of 1.5 million kilometers from Earth, Euclid will map a third of the sky. So we can answer questions such as: How is the structure in the Universe formed under the influence of gravity? How is all matter distributed in the Universe? And how does that change over time? Hoekstra: ‘An answer to the last question enables us to test models for dark energy directly.’
Hoekstra is one of the four cosmology coordinators and leader of the project ‘weak lensing’. ‘We are going to investigate how dark matter distorts space,’ he says.
Euclid is a pioneering mission to observe billions of faint galaxies and investigate the origin of the Universe’s accelerating expansion, as well as the mysterious nature of dark energy, dark matter and gravity. Credit: ESA
The Universe is like a tank of water filled with coins
But how does this work? Hoekstra continues: ‘Mass distorts space and time around it. You can measure that effect, even if you can’t see the dark matter.’ He uses an enlightening analogy to explain this. ‘Compare it to a tank of water containing a coin. If you tap that container, the water ripples and deforms the coin. Take several pictures of the coin and you’ll see that the coin looks different every time.’
‘Suppose you’ve got a lot of coins and you know they’re originally round, then you can figure out how much water there is in that tank.’ With dark matter it’s exactly the same, says the cosmologist. ‘Dark matter causes galaxies in the background to slightly deform. We can measure that distortion with Euclid by averaging the shapes of as many galaxies as possible.’
The more the better
The more dark matter there is somewhere, the more the underlying galaxies are distorted. In this way, you can determine the distribution of dark matter in the Universe. But first, a lot of sharp pictures are needed. ‘The more galaxies we measure, the more reliable the results. So we are talking about big data, not only because of the amount of data but also because of its complexity. The number of pictures that the Hubble telescope collected over the past 25 years is what we will collect in a few days.’
The biggest astronomy collaboration ever
Not only is the amount of data large, so is the number of astronomers participating in Euclid. ‘It’s the largest astronomy team in the world, with about 1500 scientists, engineers, and technicians. However, the number of astronomers benefiting from Euclid will be much greater: the data will eventually be published publicly and can be used for various purposes, such as discovering the most distant quasars and identifying massive stars in nearby galaxies. ‘In the beginning, the data will only be available for Euclid participants, after that we will have so-called data releases. In order to give people an idea of the first results, we will also have some quick releases. And those will be phenomenal,’ a beaming Hoekstra predicts.
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10 Comments
According to hindu mythology earth is floating in kshir sagar(ocean), so it might be possible that universe is that ocean which everthing(sun, blackole, planets etc.) is floating in that ocean.
Author should refer https://en.wikipedia.org/wiki/Kshir_Sagar
I am an Hindu and strongly beleive that universe is nothing but an ocean and in this ocean
everthing is floating, as per Hindu mythology there are seven ocean.
One day future humans will surely get to know that how much knowledge hinduism has about universe and God.
Dark matter is a supersolid that fills ‘empty’ space and is displaced by visible matter. The supersolid dark matter displaced by the quarks the Earth consist of, pushing back and exerting pressure toward the Earth, is gravity. The supersolid dark matter displaced by the quarks a galaxy consists of, pushing back and exerting pressure toward the galaxy, causes the stars in the outer arms to orbit the galactic center at the rate in which they do.
The missing mass associated with dark matter is the mass of the supersolid dark matter connected to and neighboring the galaxy which is displaced by the galaxy. Diffuse galaxies do not displace the supersolid dark matter enough for it to be measured, resulting in the mistaken notion the galaxies are devoid of the missing mass. Compact galaxies displace the supersolid dark matter to such a great extent that the galaxies appear to be mostly the missing mass.
Curved spacetime is a geometrical representation of gravity. Displaced supersolid dark matter is gravity.
Actually, it’s now believed that dark gravity, which reaches through multi-dimensions, accounts for much of these galactic anomalies, and warps spacetime in consistent geometric patterns that exert the pressure you’re attributing to supersolid dark matter displaced by the quarks.
The supersolid dark matter displaced by visible matter occurs in three dimensional space. No need for gravity to be reaching through multi-dimensions. Gravity does not warp spacetime. Gravity is warped spacetime. More correctly, what is referred to geometrically as warped spacetime physically exists as displaced supersolid dark matter.
The displaced supersolid dark matter ‘displaces back’, causing gravity. The displaced supersolid dark matter ‘displacing back’ is the pressure associated with gravity.
You are correct and I misspoke. As you say, gravity IS warped spacetime, which by default makes it multi-dimensional and eliminates the need for dark matter. Dark gravity is now beginning to be credited for many of the anomalies that have been mistakenly attributed to dark matter.
Hahahaha! Just out of curiosity, I looked up the term “dark gravity.” Lo and behold, there is such a thing! At least, it’s actually been proposed as an alternative to dark matter. I mean, I was just making stuff up above, but hey, guess that’s what most everyone else is doing in the science-free fantasy land of astrophysics, where those with the biggest imaginations rule.
Gravity IS NOT warped spacetime as spacetime is a mathematical construct only. The SUPERSOLID spacetime DISPLACED by the quarks the Earth consists of, pushing back and exerting pressure toward the Earth, IS gravity.
“Basically, there can only be one explanation.” This statement alone totally discredits pretty much everything associated with their explanation, and has zippo to do with real science. In fact, it’s actually the polar opposite of science. I mean, seriously, just let that close minded statement sink in a bit. We’re talking about THE UNIVERSE. And yet these people unquestioningly proclaim, “there can only be one explanation.” No hubris here folks, lol.
Well, overlooking the fact that you’ve said two polar opposite statements, I do think you’re on to something. You say spacetime is a mathematical construct only. Now, replace the word “spacetime” with pretty much every other sacred belief held in astrophysics, like black holes, dark matter, dark energy, big bang, on and on, and you’d be spot on. They’re ALL mathematical constructs that are totally divorced from legitimate scientific methods. You’re a prime example actually of the current state of this field, so locked into your above stated beliefs that anything that doesn’t agree with them is immediately discounted. Science is a discipline based on skepticism, and one should foremost be skeptical of one’s own assumptions and beliefs. You can gather supportive evidence for literally any belief or theory or assertion, but the only real measure for how good they are is how difficult they are to scientifically disprove, as in a controlled laboratory experiment. Astrophysics is virtually devoid of laboratory experimentation for the vast majority of the current beliefs that are held about the universe, no way to even begin to design experiments to disprove it, so it’s a free for all, anything goes field based on speculation and imaginary dark forces.
Dark matter and dark energy are still, in terms of their real identifies, extremely mysterious and very complex. However there are ultimate explanations. My second book to be published soon, whuch has taken me 4 years will once for all scientifically describe both dark matter and dark energy in very clear terms. Then we will all, philosophers, writers, scientists, intellectuals and the people realise we do have a universe and a world, more extraordinary and meaningful than what philosophers and scientists believe so far. That is why I had to publish my scientific papers and two cosmology books.