Archive for Roger Penrose

Hawking Points in the CMB Sky?

Posted in Astrohype, Bad Statistics, The Universe and Stuff with tags , on October 30, 2018 by telescoper

As I wait in Cardiff Airport for a flight back to civilization, I thought I’d briefly mention a paper that appeared on the arXiv this summer. The abstract of this paper (by Daniel An, Krzysztof A. Meissner and Roger Penrose) reads as follows:

This paper presents powerful observational evidence of anomalous individual points in the very early universe that appear to be sources of vast amounts of energy, revealed as specific signals found in the CMB sky. Though seemingly problematic for cosmic inflation, the existence of such anomalous points is an implication of conformal cyclic cosmology (CCC), as what could be the Hawking points of the theory, these being the effects of the final Hawking evaporation of supermassive black holes in the aeon prior to ours. Although of extremely low temperature at emission, in CCC this radiation is enormously concentrated by the conformal compression of the entire future of the black hole, resulting in a single point at the crossover into our current aeon, with the emission of vast numbers of particles, whose effects we appear to be seeing as the observed anomalous points. Remarkably, the B-mode location found by BICEP 2 is at one of these anomalous points.

The presence of Roger Penrose in the author list of this paper is no doubt a factor that contributed to the substantial amount of hype surrounding it, but although he is the originator of the Conformal Cyclic Cosmology I suspect he didn’t have anything to do with the data analysis presented in the paper as, great mathematician though he is, data analysis is not his forte.

I have to admit that I am very skeptical of the claims made in this paper – as I was in the previous case of claims of a evidence in favour of the Penrose model. In that case the analysis was flawed because it did not properly calculate the probability of the claimed anomalies in the standard model of cosmology. Moreover, the addition of a reference to BICEP2 at the end of the abstract doesn’t strengthen the case. The detection claimed by BICEP2 was (a) in polarization not in temperature and (b) is now known to be consistent with galactic foregrounds.

I will, however, hold my tongue on these claims, at least for the time being. I have an MSc student at Maynooth who is going to try to reproduce the analysis (which is not trivial, as the description in the paper is extremely vague). Watch this space.

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Shooting at the Cosmic Circles

Posted in Astrohype, Bad Statistics, The Universe and Stuff with tags , , , , on May 11, 2011 by telescoper

Another brief update post of something that whizzed past while I was away and thought I’d mention now that I’m back.

Remember the (now infamous) paper by Gurzadyan and Penrose about evidence for the Conformal Cyclic Cosmology that I blogged about last year?

The original analysis was comprehensively dissected and refuted by a number of papers within a few days of its appearance – see here, here and here – only for Gurzadyan and Penrose to dig an even bigger hole for themselves with a nonsensical reply.

Undaunted, the dynamic duo of Gurzadyan and Penrose have produced yet another paper on the same subject which came out just as I was heading off on my hols.

There has subsequently been another riposte, by Eriksen and Wehus, although I suspect most cosmologists ceased to care about this whole story some time ago. Although it’s a pretty easy target, the Eriksen-Wehus reply does another comprehensive demolition job. The phrase “shooting fish in a barrel” sprang to my mind, but from facebook I learned that the equivalent idiomatic expression in Italian is sparare sulla Croce Rossa (i.e. shooting on the Red Cross). Perhaps we can add a brand new phrase for “taking aim at an easy target” – shooting at the cosmic circles!

I was struck, however, by the closing sentences of the abstract of Eriksen-Wehus reply:

Still, while this story is of little physical interest, it may have some important implications in terms of scienctific sociology: Looking back at the background papers leading up to the present series by Gurzadyan and Penrose, in particular one introducing the Kolmogorov statistic, we believe one can find evidence that a community based and open access referee process may be more efficient at rejecting incorrect results and claims than a traditional journal based approach.

I wholeheartedly agree. I’ve blogged already to the effect that academic journals are a waste of time and money and we’d be much better off with open access and vigorous internet scrutiny. It may be that this episode has just given us a glimpse of the future of scientific publishing.

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Doubts about the Evidence for Penrose’s Cyclic Universe

Posted in Bad Statistics, Cosmic Anomalies, The Universe and Stuff with tags , , , , , , on November 28, 2010 by telescoper

A strange paper by Gurzadyan and Penrose hit the Arxiv a week or so ago. It seems to have generated quite a lot of reaction in the blogosphere and has now made it onto the BBC News, so I think it merits a comment.

The authors claim to have found evidence that supports Roger Penrose‘s conformal cyclic cosmology in the form of a series of (concentric) rings of unexpectedly low variance in the pattern of fluctuations in the cosmic microwave background seen by the Wilkinson Microwave Anisotropy Probe (WMAP). There’s no doubt that a real discovery of such signals in the WMAP data would point towards something radically different from the standard Big Bang cosmology.

I haven’t tried to reproduce Gurzadyan & Penrose’s result in detail, as I haven’t had time to look at it, and I’m not going to rule it out without doing a careful analysis myself. However, what I will say here is that I think you should take the statistical part of their analysis with a huge pinch of salt.

Here’s why.

The authors report a hugely significant detection of their effect (they quote a “6-σ” result; in other words, the expected feature is expected to arise in the standard cosmological model with a probability of less than 10-7. The type of signal can be seen in their Figure 2, which I reproduce here:

Sorry they’re hard to read, but these show the variance measured on concentric rings (y-axis) of varying radius (x-axis) as seen in the WMAP W (94 Ghz) and V (54 Ghz) frequency channels (top two panels) compared with what is seen in a simulation with purely Gaussian fluctuations generated within the framework of the standard cosmological model (lower panel). The contrast looks superficially impressive, but there’s much less to it than meets the eye.

For a start, the separate WMAP W and V channels are not the same as the cosmic microwave background. There is a great deal of galactic foreground that has to be cleaned out of these maps before the pristine primordial radiation can be isolated. The fact similar patterns can be found in the BOOMERANG data by no means rules out a foreground contribution as a common explanation of anomalous variance. The authors have excluded the region at low galactic latitude (|b|<20°) in order to avoid the most heavily contaminated parts of the sky, but this is by no means guaranteed to eliminate foreground contributions entirely. Here is the all-sky WMAP W-band map for example:

Moreover, these maps also contain considerable systematic effects arising from the scanning strategy of the WMAP satellite. The most obvious of these is that the signal-to-noise varies across the sky, but there are others, such as the finite size of the beam of the WMAP telescope.

Neither galactic foregrounds nor correlated noise are present in the Gaussian simulation shown in the lower panel, and the authors do not say what kind of beam smoothing is used either. The comparison of WMAP single-channel data with simple Gaussian simulations is consequently deeply flawed and the significance level quoted for the result is certainly meaningless.

Having not looked looked at this in detail myself I’m not going to say that the authors’ conclusions are necessarily false, but I would be very surprised if an effect this large was real given the strenuous efforts so many people have made to probe the detailed statistics of the WMAP data; see, e.g., various items in my blog category on cosmic anomalies. Cosmologists have been wrong before, of course, but then so have even eminent physicists like Roger Penrose…

Another point that I’m not sure about at all is even if the rings of low variance are real – which I doubt – do they really provide evidence of a cyclic universe? It doesn’t seem obvious to me that the model Penrose advocates would actually produce a CMB sky that had such properties anyway.

Above all, I stress that this paper has not been subjected to proper peer review. If I were the referee I’d demand a much higher level of rigour in the analysis before I would allow it to be published in a scientific journal. Until the analysis is done satisfactorily, I suggest that serious students of cosmology shouldn’t get too excited by this result.

It occurs to me that other cosmologists out there might have looked at this result in more detail than I have had time to. If so, please feel free to add your comments in the box…

IMPORTANT UPDATE: 7th December. Two papers have now appeared on the arXiv (here and here) which refute the Gurzadyan-Penrose claim. Apparently, the data behave as Gurzadyan and Penrose claim, but so do proper simulations. In otherwords, it’s the bottom panel of the figure that’s wrong.

ANOTHER UPDATE: 8th December. Gurzadyan and Penrose have responded with a two-page paper which makes so little sense I had better not comment at all.


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