Archive for Euclid

The Great Dark Energy Poll

Posted in The Universe and Stuff with tags , , on June 8, 2017 by telescoper

Yesterday was a very busy day: up early to check out of my hotel and head to the third day of the Euclid Consortium meeting for the morning session, then across to the Institute of Physics for a Diversity and Inclusion Panel meeting, then back to the Euclid Consortium meeting for the last session of the day, then introducing the two speakers at the evening event, then to Paddington for the 7.15 train back to Cardiff. I was not inconsiderably tired when I got home.

I had to bale out of the evening session to get the train I was booked on, but it seemed to be going well. Before I left, Ofer Lahav asked for an informal show of hands about a few possibilities relating to the nature of Dark Energy. Since today is polling day for the 2017 General Election, I thought it might be a good idea to distract people from politics for a bit by running a similar poll on here.

There are lots of possibilities for what dark energy may turn out to be, but I’ve decided to allow only six broad classes into which most candidate explanations can be grouped:

  1. The cosmological constant, originally introduced as a modification of the left hand side of Einstein’s general theory of relativity – the side that describes gravity – but more often regarded nowadays as a modification of the right-hand-side representing a vacuum energy. Whichever interpretation you make of this, its defining characteristic  is that it is constant.
  2.  Modified gravity,  in other words some modification of the left-hand-side of Einstein’s equations that manifests itself cosmologically which is more complicated than the cosmological constant.
  3. Dynamical dark energy, i.e. some other modification of the energy-momentum tensor on the right-hand side of Einstein’s equation that looks like some form of “stuff” that varies dynamically rather than being cosmologically constant.
  4.  Violation of the cosmological principle by the presence of large-scale inhomogeneities which result in significant departures from the usual Friedman-Robertson-Walker description within which the presence of dark energy is
  5. Observational error, by which I mean that there is no dark energy at all: its presence is inferred erroneously on the basis of flawed measurements, e.g. failure to account for systematics.
  6.  Some other explanation – this would include the possibility that the entire standard cosmological framework is wrong and we’re looking at the whole thing from the wrong point of view. If you choose this option you might want to comment through the box below what you have in mind.

Well, there are the six candidates. Make your choice:

Cosmology beyond the Centenary of Λ

Posted in The Universe and Stuff, Talks and Reviews with tags , , on June 6, 2017 by telescoper

I didn’t expect to be doing anything other than listening to the talks and getting updated on the progress of the Euclid project at this meeting in London, but this morning I was roped in to introduce a public event tomorrow evening, called Cosmology beyond the Centenary of Λ:


This will take the form of a dialogue/discussion/debate between two leading cosmologists taking a `big picture’ view of the state of cosmology now and likely future developments. I’m sure it will be very friendly so I won’t use any form of language that suggests confrontation but it features, in the red corner, George Efstathiou of the University of Cambridge and, in the blue corner, Ofer Lahav of University College London.

Incidentally, I posted some months ago about the fact that this is the centenary year of Einstein’s introduction of the cosmological constant into the field equations of general relativity in this paper:


I recommend anyone attending this Euclid meeting and indeed anyone with a passing interest in cosmology to read that paper – it’s very different from what you might probably imagine it to be!

A Tale of Two Cities 

Posted in The Universe and Stuff, Biographical with tags , , on June 5, 2017 by telescoper

“It was the best of times, it was the worst of times..”

As planned on Saturday evening I stayed at home,  cooked myself dinner, opened a bottle of wine, and watched an old film on DVD. Self-indulgent, I know, but a good way to  have a pleasant evening while avoiding  the crowds at the UEFA Champions League final.

Some time after 10pm  I checked Twitter to see what the score was (4-1 to Real Madrid), and just to check that nothing untoward had happened before or during the match.

It hadn’t, but that was exactly when news was coming in of another terrorist attack in London, this time on London Bridge and in the area of Borough Market. Stories were initially very confused, and I went to bed before a clear picture emerged.

I checked the news feeds again when I woke up and felt the saddest I’ve ever been on a birthday, but still determined to go to Der Rosenkavalier. The best way for us all to beat terrorism is to carry on regardless.

Likewise I didn’t think twice about coming to London today for the Euclid meeting this week. That said, I did arrive very late. Torrential rain overnight in Cardiff, combined with a blocked gutter, led to a flood in my kitchen. I had to call a useful person to fix it the problem, which delayed me by a few hours. Fortunately it was only rainwater in the leak, not nasty stuff backed up from the drain.

Now I’m in London where it is also tipping down, but at least I’m in a pleasant hotel and looking to get a good night’s sleep. The sound of rain can be restful, at least when it’s not flooding your kitchen.

I made my way to the hotel, which is in Bayswater, after a wine and nibbles reception at the workshop. I have never stayed here before and it took a while to find. I was a bit nervous too, as the place is remarkably cheap by London standards. Before correctly locating the hotel I wandered into another establishment on the same street with a similar name. It was quite obviously a brothel, and they politely directed me to the correct address. The hotel turned out to be fine, though obviously without any of the ‘extras’ that would have been available at the other place.

I can’t stay the whole week here as I have to get back to Cardiff to vote on Thursday, but it’s been nice to catch up with news of the Euclid mission and to meet some old friends. There are about 400 cosmologists here in London for this meeting, some of them familiar some of them less so. The mission won’t be launched until 2021 at the earliest, and it’s unlikely I’ll be involved very much, but it’s still exciting to see it all taking shape.

To Edinburgh for Euclid

Posted in The Universe and Stuff with tags , , on December 17, 2015 by telescoper

This morning I flew from London Gatwick to Edinburgh to attend the UK Euclid meeting at the Royal Observatory, which lasts today and tomorrow. It turns out there were two other astronomers on the plane: Alan Heavens from Imperial and Jon Loveday from my own institution, the University of Sussex.

The meeting is very useful for me as it involves a number of updates on the European Space Agency’s Euclid mission. For those of you who don’t know about Euclid here’s what it says on the tin:

Euclid is an ESA mission to map the geometry of the dark Universe. The mission will investigate the distance-redshift relationship and the evolution of cosmic structures by measuring shapes and redshifts of galaxies and clusters of galaxies out to redshifts ~2, or equivalently to a look-back time of 10 billion years. In this way, Euclid will cover the entire period over which dark energy played a significant role in accelerating the expansion

Here’s an artist’s impression of the satellite:


Do give you an idea of what an ambitious mission this is, it basically involves repeated imaging of a large fraction of the sky (~15,000 square degrees) over a period of about six years. Each image is so large that it would take 300 HD TV screens to display it at full resolution. The data challenge is considerable, and the signals Euclid is trying to measure are so small that observational systematics have to be controlled with exquisite precision. The requirements are extremely stringent, and there are many challenges to confront, but it’s going well so far. Oh, and there are about 1,200 people working on it!

Coincidentally, this very morning ESA issued a press release announcing that Euclid has passed its PDR (Preliminary Design Review) and is on track for launch in December 2020. I wouldn’t bet against that date slipping, however, as there is a great deal of work still to do and a number of things that could go wrong and cause delays. Nevertheless, so far so good!



ESA Endorses Euclid

Posted in Science Politics, The Universe and Stuff with tags , , , , , , on June 20, 2012 by telescoper

I’m banned from my office for part of this morning because the PHYSX elves are doing mandatory safety testing of all my electrical whatnots. Hence, I’m staying at home, sitting in the garden, writing this little blog post about a bit of news I found on Twitter earlier.

Apparently the European Space Agency, or rather the Science Programme Committee thereof, has given the green light to a space mission called Euclid whose aim is to “map the geometry of the dark Universe”, i.e. mainly to study dark energy. Euclid is an M-class mission, pencilled in for launch in around 2019, and it is basically the result of a merger between two earlier proposals, the Dark Universe Explorer (DUNE, intended to measure effects of weak gravitational lensing) and the Spectroscopic All Sky Cosmic Explorer (SPACE, to measure wiggles in the galaxy power spectrum known as baryon acoustic oscillations); Euclid will do both of these.

Although I’m not directly involved, as a cosmologist I’m naturally very happy to see this mission finally given approval. To be honest, I am a bit sceptical about how much light Euclid will actually shed on the nature of dark energy, as I think the real issue is a theoretical not an observational one. It will probably end up simply measuring the cosmological constant to a few extra decimal places, which is hardly the issue when the value we try to calculate theoretically is a over a hundred orders of magnitude too large! On the other hand, big projects like this do need their MacGuffin..

The big concern being voiced by my colleagues, both inside and outside the cosmological community, is whether Euclid can actually be delivered within the agreed financial envelope (around 600 million euros). I’m not an expert in the technical issues relevant to this mission, but I’m told by a number of people who are that they are sceptical that the necessary instrumental challenges can be solved without going significantly over-budget. If the cost of Euclid does get inflated, that will have severe budgetary implications for the rest of the ESA science programme; I’m sure we all hope it doesn’t turn into another JWST.

I stand ready to be slapped down by more committed Euclideans for those remarks.

Dark Energy’s Day

Posted in The Universe and Stuff with tags , , , on October 4, 2011 by telescoper

Following hard on the heels of the announcement of a Nobel Prize for cosmology earlier this morning, the European Space Agency has this afternoon officially announced the two candidates which have been chosen for its next M-class missions from a shortlist of three.

One of the successful candidates, EUCLID, is directly relevant to the topic covered by the Nobel Prize announced this morning. “Euclid will address key questions relevant to fundamental physics and cosmology, namely the nature of the mysterious dark energy and dark matter. Astronomers are now convinced that these substances dominate ordinary matter. Euclid would map the distribution of galaxies to reveal the underlying ‘dark’ architecture of the Universe.”

Now that it’s definitely been selected, I hope to devote time in due course for a longer post about EUCLID’s capabilities and intentions, but in the meantime I’ll just say that it’s been a very good day for Dark Energy.

P.S. The other successful candidate is called Solar Orbiter. Commiserations to advocates of the third mission on the shortlist of three, PLATO. Close, but no cigar…

Cosmic Vision

Posted in Science Politics, The Universe and Stuff with tags , , , , , , , , , on February 20, 2010 by telescoper

It’s nice to have a bit of science stuff to blog about for a change. Just this week the European Space Agency (ESA) has  announced the results of its recent selection process for part of its Cosmic Visions programme, which represents ESA’s scientific activity for the period 2015-2025.

The selection process actually began in 2007, with over 50 proposals. This list was then whittled down so that there were six candidate missions under consideration for the so-called M-class launch slots (M meaning medium-sized), and three in the L-class list of larger missions. The latest exercise was to select three of the M-class missions for further study. They succeeded in selecting three, but have also kept another, much cheaper, mission in the frame.

As far as I understand it, only two M-class missions are actually envisaged so the race isn’t over yet, but the missions still in the running are:

PLATO.  The PLATO mission is planned to study planets around other stars. This would include terrestrial planets in a star’s habitable zone, so-called Earth-analogues. In addition, PLATO would probe stellar interiors by through stellar seismology. In some sense, this mission is the descendant of a previous proposal called Eddington. (PLATO stands for PLAnetary Transits and Oscillations of stars – I’ll give it 3/10 for quality of acronym).

EUCLID. Euclid would address key questions relevant to fundamental physics and cosmology, namely the nature of the mysterious dark energy and dark matter. Astronomers are now convinced that these substances dominate ordinary matter. Euclid would map the distribution of galaxies to reveal the underlying ‘dark’ architecture of the Universe. I don’t think this is meant to be an acronym, but I could be wrong. Perhaps it’s European Union Cosmologists Lost in Darkness?

SOLAR ORBITER. Disappointingly, this is neither an acronym nor a Greek person. It would take the closest look at our Sun yet possible, approaching to just 62 solar radii. It would deliver images and data that include views of the Sun’s polar regions and the solar far side when it is not visible from Earth.

These are the three main nominations, but the panel also decided to endorse another mission, SPICA, because it is much cheaper than the approximately 500 Million Euro price tag on the other contenders. SPICA would be an infrared space telescope led by the Japanese Space Agency JAXA. It would provide ‘missing-link’ infrared coverage in the region of the spectrum between that seen by the ESA-NASA Webb telescope and the ground-based ALMA telescope. SPICA would focus on the conditions for planet formation and distant young galaxies.

Many of Cardiff’s astronomers will be very happy if SPICA does end up being selected as it is the one most directly related to their interests and also their experience with Herschel which is, incidentally,  continuing to produce fantastic quality data. If SPICA is to happen, however, extra money will have to be found and that, in the current financial climate, is far from guaranteed.

Which of these missions will get selected in the end is impossible to say at this stage. There are dark mutterings going on about how realistic is the price tag that has been put on some of the contenders. Based on past experience, cost overruns on space missions are far from unlikely and when they happen they can cause a great deal of damage in budgets. Let’s hope the technical studies do their job and put realistic figures on them so the final selection will be fair.

Whatever missions fly in the end, I also hope that the Science and Technology Research Council (STFC) – or whatever replaces it – remembers that these are science missions, and its responsibility extends beyond the building of instruments to fly on them. Let’s to hope we can count on their support for research grants enabling us to answer the science questions they were designed to address.