Is there an Elephant in the Room?

A couple of weeks ago I was in Cambridge giving a talk at a nice cosmology meeting housed in the splendid Centre for Mathematical Sciences. How the other half lives. The building is not only palatial, it is also very well designed for informal interactions and discussions. When I was a student at Cambridge this building didn’t exist and the Department of Applied Mathematics and Theoretical Physics was housed in rather ramshackle but characterful buildings in Silver Street, right in the city centre. I don’t know what department is there now.

I gave a talk with the title “Fishing for Elephants in the CMB”. I always think it’s a good idea not to give too much away in the title, although perhaps in this case I went a bit too far. Quite apart from the mixed metaphor, it doesn’t really give any clue at all as to what I was talking about. Mind you, I’m not sure at the end of the talk the audience was any the wiser either.

The idea for the title came from the phrase “There’s an Elephant in the Room”, a curious expression that even has its own wikipedia entry, as well as being the title of the picture shown here made by the artist Banksy. It refers to something that is large and obvious, but is being ignored for some reason, usually because it is considered impolite to draw attention to it. My talk of course wasn’t about real elephants but the possibility that there may be a metaphorical one in the field of cosmology, something that is consciously ignored by most of the community.

In yesterday’s post, I referred to the importance of the cosmic microwave background in establishing the so-called “concordance model” of cosmology. But as well as providing compelling evidence in support of this theory, the CMB has also thrown up a few bits of evidence that are quite difficult to reconcile with the standard description of the Universe.

Perhaps the most famous of these anomalies is the so-called “Axis of Evil“, which is an unexplained alignment of features in the pattern of temperature fluctuations observed across the sky by the Wilkinson Microwave Anisotropy Probe (WMAP) satellite. In the concordance picture, the fluctuations are basically random so there shouldn’t be coherent alignments like this.

But the Axle of Elvis isn’t the only curiosity in the cosmology shop. There is also a significant asymmetry between North and South on the sky (with respect to the ecliptic plane) when the two celestial hemispheres should be statistically indistinguishable if the standard model is correct.

There also exists a peculiar cold spot. Of course a fluctuating temperature pattern must contain places colder than average and places hotter than average. However, the standard model assumes these are drawn from a Gaussian (or “normal“) distribution, in which large fluctuations are extremely rare. The cold spot we see in the WMAP is colder than the coldest cold spot expected if the standard model is right, with odds of greater than 1000:1 against.

And there’s more. Statistical measures of the fluctuation pattern, such as the correlation function, pixel variance and quadupole moment, all give results for the real sky that are discordant with theory, although admittedly some are more significant than others. There are others too but I have no time to go into them, except to say that they may be related to the ones I’ve already mentioned, or at least share a common cause.

So what’s going on? The most conservative view is that there is nothing in the data that can’t be explained by the standard model and what we are seeing is a consequence of over-interpreting one or two chance coincidences. In the words of Fred Menger

If tortured sufficiently, data will confess to anything.

There may indeed be some truth to this, but serious attempts have been made to assess the statistical significance of the various results and my personal reaction is that, while coincidences do happen, it is unwise to dismiss 1000:1 results as mere flukes. On the other hand, these assessments are difficult and the significance may have been miscalculated.

More likely is the presence of some slight unidentified systematic artefact in the data. Not being an experimentalist it’s unfair to cast doubts on the brilliant work of the WMAP team, but one should keep an open mind about this possibility.

But as a theorist I have to admit that the most exciting possibility is that, lurking out there somewhere, are clues to a radical departure from orthodox theory. Many suggestions have been made, and no doubt most of them will be shown to be wrong. But the most dramatic thing that can happen in science is when the only game in town is “none of the above” and we are forced to think outside the box altogether.

I’m certainly not going to argue that we need to ditch the standard model or that cosmologists should all become obsessed with these tantalising conundrums. But in focussing exclusively on questions related to the standard model and its parameters, we may be throwing away a great deal of potentially exciting information. Every now and again, it’s worth checking your waste basket in case there’s something in it that you really shouldn’t have binned.

I realise that there are probably too many mixed metaphors in this piece. They’re a habit of mine and when you get to my age it’s difficult to change. After all, you can’t teach an old leopard to change its spots in midstream.



17 Responses to “Is there an Elephant in the Room?”

  1. Hello, nice of you to mention “radical departure from orthodox theory.” Physicists always enjoy citations of their work.

  2. […] in the cosmic microwave background sky. I blogged about this some time ago, under the title of Is there an Elephant in the Room?, so it’s interesting to see a different take on it. Interest in this issue has been […]

  3. […] are some important gaps, including some puzzling anomalies, and the precise nature of many of its constituents is yet to be understood, but the establishment […]

  4. […] to the Science and Technology Facilities Council to fund research over the next three years into departures from the concordance cosmological model has actually been […]

  5. […] of the primordial density perturbations. In reality the data contains tentative evidence of strange alignments, such as the so-called “Axis of Evil” discovered by Kate Land and Joao Magueijo. These […]

  6. […] on the curiosities we find in the cosmic microwave background that I’ve mentioned here and there, but it seems to peak at too low a frequency to account for much of the overall microwave sky […]

  7. […] there is the issue that I talked about in my seminar in London and have actually blogged about (here and there) previously, which is why the Universe appears to be a bit lop-sided and asymmetrical […]

  8. […] have been written about the possibility of a lop-sided universe that I’ve blogged about here and there, and which is a major topic of current cosmological […]

  9. […] signal in the ecliptic plane”. I thought I’d mention it here because it relates to an ongoing theme of mine, and I’ll refrain from commenting on the poor grammatical construction of the […]

  10. […] I actually agreed with quite a lot of what he said, and certainly think the subject needs people willing to question the somewhat shaky foundations on which the standard concordance cosmology is […]

  11. […] There isn’t much actual cosmology done in Ireland (North or South) so my brief as invited speaker was to give an overview of the current state of the field for astronomers who are not  experts in cosmological matters. I therefore gave a summary of the concordance model which I’ve blogged about before and then made some comments about things that might point to a more complete theory of the Universe. I also mentioned some of the anomalies in the cosmic microwave background that I’ve also blogged about on here. […]

  12. […] I gave my (usual) talk about cosmic anomalies (which I’ve blogged about before), but there were also interesting talks about possible interpretation of the positron excess […]

  13. […] An interesting paper on the arXiv yesterday gave me a prod to expand a little on one of the cosmic anomalies I’ve blogged about […]

  14. […] it among the list of cosmological anomalies that I’ve blogged about before (for example, here, here and here). I find them interesting but don’t lose sleep worrying that the standard […]

  15. […] pattern of temperature fluctuations in the cosmic microwave background (CMB). See my other posts here, here, here, here and here for related […]

  16. Are you familiar with the Partition Function table which shows how each number is partitioned according to its stage value? Have a look at this for outside the box – page 19-23

  17. […] then finally, there is the issue that I have ablogged about (here and there) previously, which is why the Universe appears to be a bit lop-sided and asymmetrical […]

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