Euclid telescope prepares for launch

In just a few weeks, hopefully, a new European Space Agency telescope will be sent into space in a bid to explore the dark side of the cosmos. It is hoped that the Euclid mission will help shed new light on both dark energy and dark matter, which are two of the Universe’s biggest enigmas. The spacecraft’s telescope has two cameras: one to see visible light and the other to measure the distance between us and distant galaxies. Euclid will eventually settle at a point between Earth and the Sun which has one of the best views out into the cosmos.

Guadalupe - So there are two instruments that we have on board. One is a camera. So in that camera we will just take a picture where we will see galaxies in the sky. From that picture, we can actually obtain the position. So basically the altitude and the latitude the galaxy is placed in the sky. With the other instrument, we will measure the distance between us and that galaxy. And we already have three dimensions. With that, we can construct a map. The good thing about this map is that we can infer where that matter is located. We will do that not only by studying the position of the galaxies in the pictures, but also the shape of the galaxies. We know that the light that it is arriving from us, from really distant galaxies, that the form has deviated from due to the matter that is in the universe between those galaxies and us. By starting this cosmic history, we can study the evolution. So basically the speed at which the universe is expanding, that will help us to analyse dark energy. And then by inferring the distribution of matter overall in this map, we can actually extract some properties from that matter.

Chris - So if we look at really, really far away galaxies, the light we're seeing from those has been travelling for a long time. So we are seeing a long way back in the past when we look at those galaxies. When we look at nearer galaxies, that light's been travelling less far, so it's younger. So you can then see the effect of any influence on the growth of the universe in the meantime because it will be more manifest in the older ones than the younger ones. And that enables you to, I suppose, recapitulate what the universe has gone through as it's aged.

Guadalupe - Exactly. That is exactly the point.

Chris - We think the universe is about 13.8 billion years old. We know it grew really fast when it was first born at the big bang, then it slowed down a bit and now we think it's speeding up again. When in the timeline, between 13.8 billion years ago and now, are you looking and why do you think that we are seeing this acceleration of the universe the way that we are?

Guadalupe - So we are looking between now and 10 billion years in the past, and this is exactly the time range in which we believe that dark energy has started dominating and therefore the universe started accelerating its expansion. This is the moment that we are really interested in looking at because the structure that we see in our universe has already formed. So galaxies had already formed, clusters of galaxies had already formed, and we can actually study the distribution of this matter in the universe, which is the main measurement that we want to achieve with Euclid.

Chris - Was there no dark energy around before about 10 billion years ago then, or was there just not as much of it and that's why the trajectory changed at that point?

Guadalupe - So dark energy is really puzzling. Even though we believe that at the beginning of the universe still 70% of it was dark energy, that ingredient, despite being dominant, wasn't the one that had the largest influence in the expansion of the universe and on how it was evolving in time. However, right now is when it has started dominating the ratio of expansion. And this is why our model does not only need to explain why our universe is accelerating its expansion right now, but also why, at the beginning, other ingredients such as our ordinary matter, or matter in general, played a more significant role in the past.

Chris - It's really interesting that you say that because previously many physicists have said, the more universe we get, the more it grows, the more dark energy we get and that's why things are speeding up. But you've made a subtle point, which is saying the dark energy hasn't changed, but it's how it behaves, or how the universe responds to that dark energy, that has changed and that is accelerating. The response, the sensitivity to the amount of dark energy is increasing, so it's having or wielding more of an influence now than it did.

Guadalupe - Exactly. So this is why this relation to how much the universe was growing and how much the universe's space was being created had some influence in the expansion of the universe. It's because we thought, "okay, we don't know what dark energy is, but at the beginning of the universe, space time was definitely smaller and now it's getting bigger and it is getting bigger in an accelerated way. So what are we having now that we didn't have before" More empty space. And this is why we try to postulate that this dark energy is somehow associated with the energy of emptier space. And this is why we are starting to see how its role is more dominant now just by simply thinking, "okay, now there is more empty space." However, it's really tricky to keep this theory on hold because you need to actually make a relation between vacuum energy and also the quantum world. So you need to come back to quantum physics and if you actually make some predictions of how important the energy of the vacuum can actually be from the quantum physics point of view, it is not enough to explain what we are seeing right now at our universities. This is why it is one of the biggest mysteries that we have right now in more than cosmology.

Chris - So when will Euclid take to the skies and when will you begin to see first light? When are you going to first begin to get data flowing back from the instruments?

Guadalupe  -So the project will be six years, and this is actually all the time that we need to take pictures of this one third of the sky. So Euclid won't have holidays. There will be a possibility of having four years extension to this mission, but we will need to decide on the scientific goals after that. But, in principle, we're going to be busy for six years.