Archive for July, 2013

Article of the Day!

Posted in The Universe and Stuff with tags , , , , , , on July 31, 2013 by telescoper

Back in the office today, the heatwave having given way to grey drizzle and cool breezes (at least for the time being). I’ve got stacks of paperwork to catch up on, but fortunately I’ve got time to post a quick congratulatory message to Ian Harrison, who is author of today’s NASA ADS Article of the Day! Ian is a PhD student in the School of Physics & Astronomy at Cardiff University and was supervised by me until I abandoned ship to come here to Sussex earlier this year; he’s got a postdoctoral research position lined up in the Midlands (Manchester) when he finishes his thesis. The other author, Shaun Hotchkiss, is coming to Sussex as a postdoctoral researcher in October.

Anyway, the paper is a nice one, called A consistent approach to falsifying ΛCDM with rare galaxy clusters. Here’s the abstract:

We consider methods with which to answer the question “is any observed galaxy cluster too unusual for ΛCDM?” After emphasising that many previous attempts to answer this question will overestimate the confidence level at which ΛCDM can be ruled out, we outline a consistent approach to these rare clusters, which allows the question to be answered. We define three statistical measures, each of which are sensitive to changes in cluster populations arising from different modifications to the cosmological model. We also use these properties to define the “equivalent mass at redshift zero” for a cluster — the mass of an equally unusual cluster today. This quantity is independent of the observational survey in which the cluster was found, which makes it an ideal proxy for ranking the relative unusualness of clusters detected by different surveys. These methods are then used on a comprehensive sample of observed galaxy clusters and we confirm that all are less than 2σ deviations from the ΛCDM expectation. Whereas we have only applied our method to galaxy clusters, it is applicable to any isolated, collapsed, halo. As motivation for future surveys, we also calculate where in the mass redshift plane the rarest halo is most likely to be found, giving information as to which objects might be the most fruitful in the search for new physics.

In case you’re wondering, the rather Popperian nature of the title is not the reason why I’m not among the authors. I’m just not the sort of supervisor who feels he should always be an author of papers done by his research students even when they had the idea and did all the work themselves. From what I’ve heard talking to others, we’re a dying breed!

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Blue, the Hotel Cat

Posted in Uncategorized with tags , on July 30, 2013 by telescoper

I’m in Edinburgh Airport waiting for a flight home after a day spent conducting a PhD Examination at the Royal Observatory. I stayed overnight last night at a nice B&B and made the acquaintance of a handsome cat called Blue, a fine example of a British Shorthair..

The Road to Edinburgh

Posted in Biographical with tags , on July 29, 2013 by telescoper

And so, after a pleasantly relaxing weekend in Newcastle after the end of last week’s conference in Durham, the latest leg of my little UK tour finds me in the fine city of Edinburgh. I originally intended to travel by train, but my folks offered to drive me here instead. Unfortunately the weather wasn’t all that great:

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It took a bit longer to get here than I’d hoped, which left me feeling a bit guilty that they had to turn right around and go back (after a spot of refreshment near the hotel) while I had a short nap in the cosy B&B kindly booked for me by the Royal Observatory. Anyway, I have quite a bit of work to do this evening and tomorrow. After that I’ll be flying back to Gatwick and thence to Brighton, where I’ve got even more to catch up on. There’s no rest for the Head of School…

No more ripples?

Posted in Biographical, The Universe and Stuff with tags , , , on July 27, 2013 by telescoper

Well, that’s the Ripples in the Cosmos meeting in Durham over and done with, and I’m back in Newcastle for a few days before moving on to Edinburgh next week. I’m not sure I’ll be able to blog much over the next few days because my internet connectivity will be a bit limited.

Anyway, the meeting was very exciting, as you can tell from the picture showing me (with the beard) and Brian Schmidt (with the Nobel Prize):

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Yesterday it was my job to round off the meeting with some concluding remarks leading into a panel discussion. I have to admit that although the programme for the conference was clearly designed in order to generate provoke discussion, I was a little disappointed that so few people said anything controversial. I’ve long held that there are too many cosmologists willing to believe too much, and this was further evidence that the scepticism that is a necessary part of a healthy science has been replaced by widespread conformity, especially among the young;
when I was a lad the students and postdocs were a lot more vocal at meetings than they are now. Perhaps this is characteristic of a change in culture of cosmology? To get a job nowadays it’s virtually essential to climb onto one of the big bandwagon projects, and to keep your place you have to toe the party line, refrain from rocking the boat, not speak out of turn, and avoid making ripples (That’s enough metaphors. Ed).

Anyway, I think there are still a great many things in modern cosmology we don’t understand at all, and I think a few more of the older generation should show the way by questioning things in public. In fact only got asked to do the concluding remarks because Jim Peebles was unable to come to the meeting. Jim’s an immensely distinguished physicist who has probably done more than any other living person to develop the standard cosmology, but he’s also never been afraid to play devil’s advocate. We need more like him, willing to articulate the doubts that too many of us feel the need to suppress.

It’s amazing how much progress we have made in cosmology over the last few decades, but we shouldn’t use that as an excuse to get complacent. Cosmology is about the biggest questions in science. That alone makes it an exciting subject to work in. It’s an adventure. And the last thing you want on an adventure is for the journey to be too comfortable.

The Lindisfarne Gospels

Posted in Art, History with tags , , , , on July 25, 2013 by telescoper

450px-Lindisfarne_Gospels_folio_209vOne of the interesting things going on in Durham during the week of this conference is an exhibition relating to the Lindisfarne Gospels. This extraordinary book was written around 715AD, just after the death of St Cuthbert. For those of you not familiar with Lindisfarne, or “Holy Island” as it is often called, it’s a small island off the Northumbrian coast, connected to the mainland by a causeway which is covered by the tide twice a day.

Although the Lindisfarne Gospels are about 1300 years old, the colours remain extremely vivid. It’s a remarkable thing to look at the pages on view in the exhibition to see the marks made by a human hand all that time ago; it’s difficult not to wonder about the life of the person who devoted what must have been a huge amount of time compiling this exquisite work.

Incidentally, St Cuthbert’s remains now lie in a tomb inside Durham’s magnificent cathedral, of which we have a fine view from the balcony of the Calman Learning  Centre during the coffee breaks:

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The Mysterious Mr Ripples

Posted in Biographical, The Universe and Stuff with tags , , on July 24, 2013 by telescoper

So here I am in the fine city of Durham, in the North Midlands, for a meeting entitled Ripples in the Cosmos. I travelled by plane from Gatwick to Newcastle on Sunday afternoon, and got there eventually – after a two-hour delay caused by the aircraft we were meant to fly on having a technical problem and needing to be replaced by another. Anyway, I spent Sunday with my folks. Thinking it was only going to be a half-hour drive to Durham, we left early on Monday morning so I’d be in time to chair the first session.

Unfortunately, major roadworks on A1 intervened and we got stuck in traffic near the Metro Centre in Gateshead. Fortunately, various people at the conference caught my Twitter updates and a deputy was arranged. I got there about 30 minutes late and I took over after the coffee break.

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After the day’s conference I wandered up to Durham Caste (left), where I had a room booked for the week. However, when I got there they had no record of my reservation. The porter was very helpful and let me connect to my email to check, and I retrieved the confirmation of my booking. In exasperation, I looked through the papers he had relating to room bookings, and found one in the name of “Mr Ripples”. Not even “Professor Ripples”, mark you.

 

The mysterious Mr Ripples not having appeared to claim his room I surmised that the similarity of his name to the title of the conference might indicate that perhaps some administrative error might have been made. The porter agreed, changed the name from Mr Ripples to Professor Coles and gave me a key.

Anyway, Durham Castle is a rather splendid place to stay.  Breakfast is to be had in grand surroundings complete with walls decorated with suits of armour, swords and other historical weapons. This environment, together with the continuing warm weather, as well of course as the excellent conference talks, has made this very enjoyable week so far.  Apart from the nagging doubt that Mr Ripples could suddenly turn up and demand his room, the only problem is the ringing of bells all through the night.

The conference dinner is this evening, and it’s in the Great Hall of Durham Castle so I won’t have far to stagger home to bed…

Newsflash: Direct Detection of B-mode Polarization

Posted in The Universe and Stuff with tags , , , , , on July 23, 2013 by telescoper

I’m not meant to be blogging these days but I thought I’d break radio silence to draw attention to a new paper on the arXiv by Hanson et al. from SPTpol, an experiment which aims to measure the polarization of the cosmic microwave background using the South Pole Telescope. One of the main aims of experiments such as this is to measure the so-called “B-mode” of polarization (the “curl” component of the polarization signal, which possesses a handedness) because this holds the key to direct detection of a number of interesting cosmological phenomena such as the existence of primordial gravitational waves.  However, primordial effects aren’t  the only way to generate B-mode polarization. Other “foreground” effects can do the job too, especially gravitational lensing can also generate a signal of this form. These “late-time” effects have to be understood before the primordial contribution can be isolated.

Before today there was no direct measurement of B-mode polarization at all, primordial nor not.

The abstract basically says it all:

Gravitational lensing of the cosmic microwave background generates a curl pattern in the observed polarization. This “B-mode” signal provides a measure of the projected mass distribution over the entire observable Universe and also acts as a contaminant for the measurement of primordial gravity-wave signals. In this letter we present the first detection of gravitational lensing B modes, using first-season data from the polarization-sensitive receiver on the South Pole Telescope (SPTpol). We construct a template for the lensing B-mode signal by combining E-mode polarization measured by SPTpol with estimates of the lensing potential from a Herschel-SPIRE map of the cosmic infrared background. We compare this template to the B modes measured directly by SPTpol, finding a non-zero correlation at 7.7 sigma significance. The correlation has an amplitude and scale-dependence consistent with theoretical expectations, is robust with respect to analysis choices, and constitutes the first measurement of a powerful cosmological observable.

This measurement is not unexpected. Indeed, the B-mode contribution from lensing by the known distribution of galaxies can be calculated fairly straightforwardly because the physics is well understood; failure to find the expected signal would therefore have been somewhat embarrassing.  It’s a different story for the primordial B-mode because that depends strongly on what is going on in the very early universe, and that is much less certain. Although the new result doesn’t itself tell us anything new about the very early Universe it is definitely an important step on the way, and it’s a fairly safe prediction that there will be a great deal of activity and interest in CMB polarization over the next few years, including next year’s planned release of polarization data from Planck.

I’ll also note the use of Herschel-SPIRE images in tracing the galaxy images, in deference to my former colleagues in Cardiff who played a key role in developing that instrument!