Archive for Joao Magueijo

Nailing Cosmological Jelly to the Wall

Posted in The Universe and Stuff with tags , , on November 28, 2016 by telescoper

When asked to provide comments for a recent piece about cosmology in New Scientist, all I could come up with was the quote in the following excerpt:

But no measurement will rule out inflation entirely, because it doesn’t make specific predictions. “There is a huge space of possible inflationary theories, which makes testing the basic idea very difficult,” says Peter Coles at Cardiff University, UK. “It’s like nailing jelly to the wall.”

Certain of my colleagues have cast doubt on whether I am qualified to comment on the nailing of jelly to the wall, so I feel obliged to share the results of my highly successful research into this in the form of the following photograph:
orange_jelly_nailed_to_wall

I regret that I was unable to find any Dark Jelly, so had to settle for the more familiar baryonic type. Also, for the record, I should point out that what is shown is actually jelly concentrate. A similar experiment with the more normal diluted form of jelly was somewhat less successful.

I hope this clarifies the situation.

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Astronomy (and Physics) Look-alikes, No. 35

Posted in Astronomy Lookalikes with tags , on July 30, 2010 by telescoper

I wonder if anyone else has noticed the remarkable resemblance between these two international celebrity heart-throbs? I wonder if by any chance they might be related?

Enrique Iglesias

Joao Magueijo

Darwin and After

Posted in Biographical, Science Politics with tags , , , , , , , , on October 10, 2009 by telescoper

Another sign that the academic year is back into full swing is that the monthly meetings of the Royal Astronomical Society have started up again after the usual summer hiatus. Since I’ve got a very heavy week coming up, I thought I’d take the advantage of a bit of breathing space in my timetable to attend yesterday’s meeting and catch up with the gossip at the Club afterwards.

The highlight of the day’s events was the annual George Darwin Lecture which was given this year by Neil Gehrels from the NASA Goddard Space Flight Center on the subject Gamma Ray Bursts and the Birth of Black Holes: Discoveries by SWIFT. This is a very hot topic (of course) and the lecture did full justice to it. The RAS has two other “prize” lectures – the Gerald Whitrow Lecture and the Harold Jeffreys Lecture – which are used to invite eminent speakers from around the world. They’re not always successful as lectures because the speakers sometimes try to make them too specialised and too detailed, but this one was exceptionally clear and well delivered. I enjoyed it, as well as learning a lot; that’s the essence of a good lecture I think.

The main task for visiting speakers when it comes to the George Darwin Lecture is to give their talk without revealing the fact that they hadn’t realised that Charles Darwin had a famous astronomical son!

Then to the Athenaeum, for drinks and dinner, where the current financial crisis at STFC was in the background of a lot of the conversation. Rumours abounded but I didn’t pick up any hard information about what is likely to happen to our funding next year. I suspect that’s because even STFC doesn’t know. After a bit of wine, though, conversation moved onto other,  less depressing, things including football, cheese and the Welsh landscape.

The colleague sitting next to me (an old friend from Queen Mary days, now at Imperial College) reminded me that in January last year Joao Magueijo invited me to give the vote of thanks at his inaugural lecture (as long as I promised to try to make my speech as short and as funny as possible). It turns out his lecture was only twenty minutes long, which didn’t give as much time as I’d hoped to think of something to say so I resorted to a couple of off-colour jokes and a facetious remark about how the brevity of Imperial’s lectures explained why their students never seemed to know anything. I got a very good laugh from the packed lecture theatre, but was told off afterwards by a senior physicist from the Imperial physics department. That particular episode is something I often think about, the pomposity of some of the staff reminding me that I’m not unhappy at not getting a job there I applied for a few years ago.

Actually, I just remembered that they took pictures at the party afterwards so here’s one of me and Joao having a chuckle afterwards. Notice I had put a tie on for the occasion, but Joao’s wardrobe is strictly T-shirts only.

37079699

After Friday’s dinner (roast partridge, if you want to know) I got the last train back to Cardiff from Paddington, snoozing comfortably for a large part of the journey. On time until just outside Cardiff Central, the train then sat motionless on the track almost within sight of the platform owing to the presence of a broken down goods train in front of us. We finally got into the station 50 (FIFTY) minutes late, and I didn’t get home until well after 2am.

The Axle of Elvis

Posted in Cosmic Anomalies, The Universe and Stuff with tags , , , , , , on August 6, 2009 by telescoper

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 before.

Before explaining what this is all about, let me just briefly introduce a bit of lingo. The pattern of variations fluctuations in the temperature of the cosmic microwave background (CMB) across the sky, such as is revealed by the Wilkinson Microwave Anisotropy Probe (WMAP), is usually presented in terms of the behaviour of its spherical harmonic components. The temperature as a function of position is represented as a superposition of spherical harmonic modes labelled by two numbers, the degree l and the order m. The degree basically sets the characteristic angular scale of the mode (large  scales have low l, and small scales have high l). For example the dipole mode has l=1 and it corresponds to variation across the sky on a scale of 180 degrees; the quadrupole (l=2) has a scale of 90 degrees, and so on. For a fixed l the order m runs from -l to +l and each order represents a particular pattern with that given scale.

The spherical harmonic coefficients that tell you how much of each mode is present in the signal are generally  complex numbers having real and imaginary parts or, equivalently, an amplitude and a phase.  The exception to this are the modes with m=0, the zonal modes, which have no azimuthal variation: they vary only with latitude, not longitude. These have no imaginary part so don’t really have a phase. For the other modes, the phase controls the variation with azimuthal angle around the axis of the chosen coordinate system, which in the case of the CMB is usually taken to be the Galactic one.

In the simplest versions of cosmic inflation, each of the spherical harmonic modes should be statistically independent and randomly distributed in both amplitude and phase. What this really means is that the harmonic modes are in a state of maximum statistical disorder or entropy. This property also guarantees that the temperature fluctuations over the sky should be described by  a Gaussian distribution.

That was perhaps a bit technical but the key idea is that if you decompose the overall pattern of fluctuations into its spherical harmonic components the individual mode patterns should look completely different. The quadrupole and octopole, for example, shouldn’t line up in any particular way.

Evidence that this wasn’t the case started to emerge when WMAP released its first set of data in 2003 with indications of an alignment between the modes of low degree. In their  analysis, Kate Land and Joao Magueijo dubbed this feature The Axis of Evil; the name has stuck.They concluded that there was a statistically significant alignment (at 99.9% confidence) between the multipoles of low degree (l=2 and 3), meaning that the measured alignment is only expected to arise by chance in one in a thousand simulated skies. More recently, further investigation of this effect using subsequent releases of data from the WMAP experiment and a more detailed treatment of the analysis (including its stability with respect to Galactic cuts) suggested that the result is not quite as robust as had originally been claimed. .

Here are the low-l modes of the WMAP data so you see what we’re talking about. The top row of the picture contains the modes for l=2 (quadrupole) and l=3 (octopole) and the bottom shows l=4 and l=5.

 

The two small red blobs mark the two ends of the preferred axis of each mode. The orientation of this axis is consistent across all the modes shown but the statistical significance is much stronger for the ones with lower l.

It’s probably worth mentioning a couple of neglected aspects of this phenomenon. One is that the observed quadrupole and octopole appear not only to be aligned with each other but also appear to be dominated by sectoral orders, i.e those with m=l. These are the modes which are, in a sense, opposite to the zonal modes in that they vary only with longitude and not with latitude. Here’s what the sectoral mode of the quadrupole looks like:

map22

Changing the phase of this mode would result in the pattern moving to the left or right, i.e. changing its origin, but wouldn’t change the orientation. Which brings me to the other remarkable thing, namely that the two lowest modes also have  correlated phases. The blue patch to the right of Galactic centre is in the same place for both these modes. You can see the same feature in the full-resolution map (which involves modes up to l~700 or so):

I don’t know whether there is really anything anomalous about the low degree multipoles, but I hope this is a question that Planck (with its extra sensitivity, better frequency coverage and different experimental strategy) will hopefully shed some light on. It could be some sort of artifact of the measurement process or it could be an indication of something beyond the standard cosmology. It could also just be a fluke. Or even the result of an over-active imagination, like seeing Elvis in your local Tesco.

On its own I don’t think this is going to overthrow the standard model of cosmology. Introducing extra parameters to a model in order to explain a result with a likelihood that is only marginally low in a simpler model does not make sense, at least not to a proper Bayesian who knows about model selection…

However, it is worth mentioning that the Axis of Evil isn’t the only cosmic anomaly to have been reported. If an explanation is found with relatively few parameters that can account for all of these curiosities in one fell swoop then it would stand a good chance of convincing us all that there is more to the Universe than we thought. And that would be fun.