ESA Endorses Euclid

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.

3 Responses to “ESA Endorses Euclid”

  1. Anton Garrett Says:

    Do they intend to flash-test your office computer, thereby wrecking it? I know of one university in which this lunacy would have happened but for some fairly high-level intervention.

    • telescoper Says:

      Well, I don’t know what they did but it’s taken me well over an hour to get my internet connection back.

  2. There are two interesting measurements to be done. First, find out whether the equation-of-state parameter is approximately -1 or -1 to very good accuracy. IIRC it was Richard Battye in his summary talk at the last MOND cosmology meeting who pointed out that most such measurements give -1 as best-fit value but with relatively large error bars: one would then expect a broader distribution of best-fit values. This will essentially answer the question whether dark energy (top of the list for worst “scientific terms”; as Sean Carroll pointed out, essentially everything has energy and many things are dark—“smooth tension” sounds better and is more accurate) is the cosmological constant or something else. Second, assumng that it is the cosmological constant, it would be nice to know whether Omega(matter) and lambda together are very close to one or slightly smaller or slightly larger since (assuming a simple topology) this determines whether the universe is finite or infinite.

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