Clover and Out

One of the most exciting challenges facing the current generation of cosmologists is to locate in the pattern of fluctuations in the cosmic microwave background evidence for the primordial gravitational waves predicted by models of the Universe that involve inflation.

Looking only at the temperature variation across the sky, it is not possible to distinguish between tensor  (gravitational wave) and scalar (density wave) contributions  (both of which are predicted to be excited during the inflationary epoch).  However, scattering of photons off electrons is expected to leave the radiation slightly polarized (at the level of a few percent). This gives us additional information in the form of the  polarization angle at each point on the sky and this extra clue should, in principle, enable us to disentangle the tensor and scalar components.

The polarization signal can be decomposed into two basic types depending on whether the pattern has  odd or even parity, as shown in the nice diagram (from a paper by James Bartlett)

The top row shows the E-mode (which look the same when reflected in a mirror and can be produced by either scalar or tensor modes) and the bottom shows the B-mode (which have a definite handedness that changes when mirror-reflected and which can’t be generated by scalar modes because they can’t have odd parity).

The B-mode is therefore (in principle)  a clean diagnostic of the presence of gravitational waves in the early Universe. Unfortunately, however, the B-mode is predicted to be very small, about 100 times smaller than the E-mode, and foreground contamination is likely to be a very serious issue for any experiment trying to detect it.

An experiment called Clover (involving the Universities of  Cardiff, Oxford, Cambridge and Manchester) was designed to detect the primordial B-mode signal from its vantage point in Chile. You can read more about the way it works at the dedicated webpages here at Cardiff and at Oxford. I won’t describe it in more detail here, for reasons which will become obvious.

The chance to get involved in a high-profile cosmological experiment was one of the reasons I moved to Cardiff a couple of years ago, and I was looking forward to seeing the data arriving for analysis. Although I’m primarily a theorist, I have some experience in advanced statistical methods that might have been useful in analysing the output.  It would have been fun blogging about it too.

Unfortunately, however, none of that is ever going to happen. Because of its budget crisis, and despite the fact that it has spent a large amount (£4.5M) on it already,  STFC has just decided to withdraw the funding needed to complete it (£2.5M)  and cancel the Clover experiment.

Clover wasn’t the only B-mode experiment in the game. Its rivals include QUIET and SPIDER, both based in the States. It wasn’t clear that Clover would have won the race, but now that we know  it’s a non-runner  we can be sure it won’t.

31 Responses to “Clover and Out”

  1. Anton Garrett Says:

    Sad news, very sorry to hear it.

    Suppose my hope is correct that a flat universe is a basic consequence of a better theory than we have today, rather than a consequence of inflation. Would that make a difference to the data that experiments of this sort would log?


    • telescoper Says:

      Inflation or not, a detection of B-mode polarization would tell us a lot. Even if there is no primordial B-mode polarization it can be generated at later times and on smaller angular scales by gravitational lensing by intervening matter. So there should be a signal if you believe there are galaxies, even if you don’t believe in inflation.

  2. Chris Crowe Says:

    Indeed a disappointment, as I was hoping to work with Anthony Challinor on this at the IoA. Desipte the extremely difficult removal of foregrounds and lensing contributions, even an upper limit on r would have told us a lot about excluding particular models of inflation. I suppose Clover is dead in its current form, but perhaps something can be resurrected in some alternate (read: cheaper) form. I will remain hopeful!



  3. […] a little rusty. For a much more expert view on this, visit Peter Coles’ excellent blog In The Dark. Hopefully, though, I should be able to cure this “between” state sooner or later, but […]

  4. Peter – this is pretty grim. Any details on the process ? And had 4.5M actually already been spent, or is it just that the estimated total cost went up from 4.5 to 7 ? Those are quite different things.

  5. telescoper Says:


    I don’t know that much about the process but it has been rumbling on for some time now. Science Board voted to cancel the experiment and the decision was recently ratified by Council.

    The £4.5M has already been spent and the experiment is basically built; the extra money was needed to set things up and run it because the costs rose during the project. It may be possible to use the kit for something else in due course, but the original experiment is dead unless someone else can be found as a partner, which is unlikely in the current climate.

    Of course this also sticks the boot into the careers of the many talented people involved in designing and building Clover.


  6. Anton Garrett Says:

    Any chance of finding partners somewhere in the world to join the project? They would put in the missing money and share the credit, maybe getting a disproportionately good deal but better for the team than the present situation?

  7. telescoper Says:

    I haven’t given up hope but I think this possibility is a little remote. Maybe, however, a little bit of Obama’s stimulus package might find its way into pure science. Knowing the desperate situation Clover is in, anyone with cash could drive a hard bargain.

  8. Chris Crowe Says:

    I’m sure most of you will have seen this before

    Click to access file_27824.pdf

    It makes for very sombre reading. Not only does it depress people like me who are hoping to pursue a career in research, but it has also deterred [very bright] friends of mine who were originally considering research careers in physics following their Msc/PhD. How long are these cuts going to continue? Is the crisis peaking now, or is the worst yet to come? We are steering a generation of budding new scientists away from areas where they can actually make a difference. Where will the UK stand in the physics community in 20 years time? A lot lower down in the list if you ask me….

  9. […] You may have heard rumours that the Clover experiment has been cancelled, and indeed Peter C has just written about it. My colleague Alan Heavens was perturbed by this turn of events, so I invited him to write about […]

  10. Just to correct an earlier comment – according to our information, Science Council did not vote to cancel Clover, they still rated it as first rate science and timely, but could not afford it and so had to refer it to STFC Council. STFC Council then cancelled it for financial reasons.

    Almost all of the initial grant had been spent and further funds committed by STFC. The instrument is in the early assembly phase, with almost all hardware built, and was due to be shipped at the end of the year.

  11. telescoper Says:


    The link you added is to a document written in January 2008. If you think that paints a bleak picture then just wait and see what comes out from STFC over the next few weeks and months…


  12. […] In the Dark A blog about the Universe, and all that surrounds it « Clover and Out […]

  13. Bryn Jones Says:

    This is indeed unfortunate news, though somehow not as surprising as it should be.

    The story reminds me to some extent of my experiences a little over a year ago. I had just had my laborious attempts at Gemini Phase II observing preparations approved by a support scientist when I learnt that the U.K. had been expelled from the Gemini project. Fortunately, that immediate fiasco was resolved and the U.K. continued as a Gemini partner in the short term.

    However, the abandonment of Clover is more significant and will have serious implications for the university departments affected. Spending a majority of the cost of a project, amounting to many millions of pounds, and then abandoning that project, does not constitute an appropriate use of taxpayers’ money. I wonder whether House of Commons committees might show an interest in this, including the Public Accounts Committee (as well, of course, as that for Innovation, Universities, Science and Skills).

    We have been in the STFC funding fiasco for some time now, and much of the research community will have looked at the value of the pound falling while thinking of the CERN, ESA and ESO subscriptions (although some protection from the exchange rate change may now be put in place). A strategic shift in the science budget away from research to economic and societal impact may put significant further pressure on the existing astronomy programme. And this will come on top of long-standing (decade long) strategic problems such as inadequate resources for the scientific exploitation of existing astronomical facilities and the careers crisis.

    Things do not look good for British astronomy.

  14. Steve Masey Says:

    Hi Peter,

    Chris at Cambridge directed me to your weblog, I do part III Maths with him. A very interesting page you have here, it is a shame that all these cuts have to be made. Whose fault is it? Surely the falling pound cannot be entirely to blame? I don’t think I will want to get involved in astronomy for fear of no money!

    Interesting stuff anyway, I will certainly put the word around about this page.



  15. […] Just a quick note for those interested in the story of Clover, Physics World have run a news item on their website and I’m told there will be a story in […]

  16. Peter Proudlove Says:

    Does anyone know how James Bartlett gets those pretty shadows on his diagram?

  17. telescoper Says:


    The falling pound isn’t entirely to blame. When STFC got its funding allocation in 2007 after the Comprehensive Spending Review, there was a well-advertised shortfall which required it to slash the science budget and also look for savings at the laboratories it inherited from the old CCLRC (including RAL and Daresbury). My understanding is that none of these savings has actually been made. The falling pound has compounded the failure of STFCs management to deal with the issues it promised to deal with over a year ago.

    My opinion is that STFC got a very raw deal from the government, and its management has been unable to deal with the problem which has consequently got worse. I wish I could believe that the government will come to our rescue, but if there is to be increased government spending on research it is not very likely that this government will let it go to pure science rather than applied research. That’s a big contrast with the USA, where Obama’s stimulus package includes quite a bit for fundamental physics.

    Perhaps the UK government is telling us all that it wants us to start the brain drain all over again….


  18. What a disappointment, so many people have worked so hard on this project. I know someone who works for ExxonMobil, do you think there’s much point in sending a mailshot? 🙂


  19. […] At Full Blast Yesterday, Paolo Calisse and I were paid a visit by a reporter (Martin Shipton) and a photographer from Welsh newspaper The Western Mail who wanted to cover the sad story of Clover. […]

  20. Bryn Jones Says:

    Phillip Helbig has made some very good points, concentrating on the careers crisis. We have large numbers of younger researchers struggling to get the patronage or lucky break to advance their careers towards the objective of getting one of the relatively small permanent lecturing positions needed to give them the freedom and stability to succeed in research.

    I’m not going to add to that discussion here because, firstly, the main article was concerned with the specific problems with Clover funding, and secondly, because the careers crisis deserves a much more dedicated discussion than we have room for here. I shall only say that we must have very great sympathy for those people who have contributed to Clover and will now find themselves out of work. I shall also add that one of the reasons that the careers crisis in basic research continues is that most of the people who suffer do not complain enough to the right people: there needs to be much more campaigning and action.

  21. Bryn Jones Says:

    We have some very pertinent points above.

    Another set of pertinent comments on the careers crisis in astronomy appeared in an earlier post on this blog:

  22. telescoper Says:

    If you think the careers crisis is bad right now, just wait until the news gets out that STFC is thinking of cancelling the next astronomy grants round.

  23. […] there seems to be a shift from science-driven to technology-driven projects,  signalled by the cancellation of projects such as Clover to save a couple of million, and the allocation of funds to projects such as Moonlite which is […]

  24. […] How Loud was the Big Bang? The other day I was giving a talk about cosmology at Cardiff University’s Open Day for prospective students. I was talking, as I usually do on such occasions, about the cosmic microwave background, what we have learnt from it so far and what we hope to find out from it from future experiments, assuming they’re not all cancelled. […]

  25. […] discussion to those who know more about it – good coverage of the situation over on Andy and Peter’s blogs and on Paul Crowther’s […]

  26. […] Our head of school, Walter Gear, has got his phone call telling him that our attempt to resurrect Clover will not be funded. Disappointing, but not entirely […]

  27. […] the past few years, the UK community has been in near-constant turmoil – grants were cut, projects cancelled, consortia pulled out of – all worsened by a variety of factors from the economic crisis, […]

  28. […] a few people have been asking me whether the UK’s cancelled B-mode experiment, Clover, could have detected what BICEP2 may  have found; I’m still not convinced, by the way. If […]

  29. […] wrote at some length about the cancellation of the Clover experiment here. In a nutshell, however, Clover involved the Universities of Cardiff, Oxford, Cambridge and […]

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