My monthly trip to London for the Royal Astronomical Society Meeting allowed me not only to get out of the office for the day but also to attend a nice talk by Alberto Vecchio about yesterday’s amazing results.
I hear that we will be having champagne at the club later on to celebrate. In the meantime here’s a little Haiku I wrote on the theme:
Two black holes collide
A billion years ago.
LIGO feels the strain.
Some more reaction to the LIGO result…
Clifford Will is the Editor-in-Chief of Classical and Quantum Gravity
As if celebrating the 100th birthday of general relativity weren’t enough, the LIGO-Virgo collaboration has provided “the icing on the cake” with today’s announcement of the first direct detection of gravitational waves. At press conferences in the USA and Europe, and in a paper in Physical Review Letters published afterward, the team announced the detection of a signal from a system of two merging black holes.
The signal arrived on 14 September, 2015 (its official designation is GW150914), and was detected by both the Hanford and Livingston advanced detectors of the LIGO observatory (the advanced Virgo instrument in Italy is not yet online). It was detected first by
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So the eagerly awaited press conference happened this afternoon. It started in unequivocal fashion.
“We detected gravitational waves. We did it!”
As rumoured, the signal corresponds to the coalescence of two black holes, of masses 29 and 36 times the mass of the Sun.
The signal arrived in September 2015, very shortly after Advanced LIGO was switched on. There’s synchronicity for you! The LIGO collaboration have done wondrous things getting their sensitivity down to such a level that they can measure such a tiny effect, but there still has to be an event producing a signal to measure. Collisions of two such massive black holes are probably extremely rare so it’s a bit of good fortune that one happened just at the right time. Actually it was during an engineering test!
Here are the key results:
Excellent signal to noise! I’m convinced! Many congratulations to everyone involved in LIGO! This has been a heroic effort that has taken many years of hard slog. They deserve the highest praise, as do the funding agencies who have been prepared to cover the costs of this experiment over such a long time. Physics of this kind is a slow burner, but it delivers spectacularly in the end!
You can find the paper here, although the server seems to be struggling to cope! One part of the rumour was wrong, however, the result is not in Nature, but in Physical Review Letters. There will no doubt be many more!
And right on cue here is the first batch of science papers!
No prizes for guessing where the 2016 Nobel Prize for Physics is heading, but in a collaboration of over 1000 people across the world which few will receive the award?
So, as usual, I had a day filled with lectures, workshops and other meetings so I was thinking I would miss the press conference entirely, but in the end I couldn’t resist interrupting a meeting with the Head of the Department of Mathematics to watch the live stream…
P.S. A quick shout out the UK teams involved in this work, including many old friends in the Gravitational Physics Group at Cardiff University (see BBC News item here) and Jim Hough and Sheila Rowan from Glasgow. If any of them are reading this, enjoy your trip to Stockholm!
Follow @telescoperRegardless of what will or will not be announced on Thursday, I thought it would be worth sharing this nice colloquium talk by Dr Alan Weinstein of Caltech about the search for gravitational waves, featuring the Laser Interferometric Gravitational-wave Observatory (LIGO). I’ve picked this not only because it’s a nice and comprehensive overview, but also that Professor Weinstein doesn’t call them gravity waves!
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This morning I heard the same rumour from two distinct (and possibly independent) sources. That’s not enough to prove that the rumour is true, but perhaps enough to make it repeating here.
The rumour is that, on Thursday 11th February in Washington DC at 10.40am 10.30am local time (15.40 15.30GMT), the Laser Interferometry Gravitational Wave Observatory (LIGO) will announce the direct experimental detection of gravitational waves.
If true this is immensely exciting, but I reiterate that it is, for the time being at least, only a rumour.
I will add more as soon as I get it. Please feel free to provide updates through the comments. Likewise if you have information to the contrary…
UPDATE: 9th February 2016. An official announcement of the forthcoming announcement has now been announced. It will take place at 10.30 local time in Washington (15.30 GMT), although it is believed the first ten minutes will involve a couple of songs by the popular vocal artist Beyoncé.
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The other day I was chatting to a group of our 4th-year MPhys students about the process for applying (and hopefully being interviewed) for a PhD. This is the time when students in the UK have started to apply and are awaiting decisions on whether they have to go for an interview. Final decisions are usually made by the end of March so those with interviews have a busy couple of months coming up.
I actually quite enjoy doing PhD interviews, because that involves giving excellent young scientists their first step on the ladder towards a research career. I’m sure it’s not so pleasant for the candidates though. Nerves sometimes get the better of the students in these interviews, but experienced interviewers can calibrate for that. And if you’re nervous, it means that you care…
Anyone reading this who is nervous about doing a PhD interview (or has experienced nerves in one they’ve already had) might reflect on my experience when I was called to interview for a PhD place in Astronomy at the University of Manchester way back in 1985. I was very nervous before that, and arrived very early for my grilling. I was told to wait in a sort of ante-room as the previous interview had only just started. I started to read a textbook I had brought with me. About five minutes later, the door of the interview room opened and the interviewers, Franz Kahn and John Dyson, both of whom are sadly no longer with us, carried out the unconscious body of the previous candidate. It turned out that, after a couple of friendly preliminary questions, the two Professors had handed the candidate a piece of chalk and told him to go to the blackboard to work something out, at which point said candidate had fainted. When it was my turn to be handed the chalk I toyed with the idea of staging a mock swoon, but resisted the temptation.
The question, in case you’re interested, was to estimate the angle through which light is deflected by the Sun’s gravity. I hadn’t done any general relativity in my undergraduate degree, so just did it by dimensional analysis which is easy because an angle is dimensionless. That gets you within a factor of a two of the correct answer which, in those days, was pretty goood going for cosmology. That seemed to go down well and they offered me a place … which I turned down in favour of Sussex.
In those days, before detailed information about research in University departments was available online, the interview generally consisted of a discussion of the various projects available and a few odd questions about Physics (and possible Astronomy) to see if the candidate was able to think on their feet (i.e. without fainting).
Nowadays it’s a bit different. You can still expect a bit of questioning about undergraduate material but that is normally preceded by the chance to talk about your final-year project. One reason for that is that selectors are interested in project work because it can provide evidence of an aptitude for research. The other is simply that it gives the candidate a chance to get over any initial nerves by talking about something that they hopefully know well, as they will have been working on it for some time.
My first piece advice for students who have been offered an interview, therefore, is to prepare a short (~10 minute) verbal summary of your project work so you’re not wrong-footed if asked to talk about it.
Students nowadays are also expected to know a bit more about the thesis topic in advance, so my second tip is to read up a bit of background so you can talk reasonably intelligently about the proposed research. If, for example, you have decided to work on Dark Energy (as many seem to these days), you won’t come across very well if you don’t know what the main issues are. What’s the observational evidence? What kind of theories are there? What are the open questions? Same goes for other fields. It also will do no harm if you read a couple of recent papers by your prospective supervisor, for reasons of flattery if nothing else.
Anyway, I think those are the two main things. If anyone has other advice to offer prospective PhD students, please feel free to add via the comments box.
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A frequent complaint raised by students of Astronomy is that astronomers insist on using funny units. Chief among them is the use of magnitudes to quanitify the brightness of an object. Why not use the observed intensity (or brightness or flux) of the light from the star, which can be expressed straightforwardly in SI units, instead of faffing around with a clunky logarithmic measure? The reason we use the magnitude scale is primarily historical and based on the fact that the eye’s response to light is more-or-less logarithmic and that in the days before calculators it was easier to deal with very large and very small numbers using logarithms.Most relevant calculations involve divisions and multiplications which become subtractions and additions when you use logarithmic quantities.
It was Norman Pogson who first suggested that a magnitude scale be defined such that a difference of five magnitudes should correspond to a factor of 100 in actual brightess. This was because the brightest naked-eye stars – those of first magnitude – are about 100 times brighter than the faintest naked-eye stars, which are of sixth magnitude. That was in 1856 and we’ve been stuck with it ever since!
Although the magnitude system may appear strange, it’s not really that hard to use when you get used to it. A beginner really just needs to know a few key things:
and 
respectively then 
where 
and 
are respectively the fluxes received from the two stars;Got it?
To test your understanding you could try these little problems. To warm up you might look at I posted the first of them a while ago. Anyway, here we go:
Answers through the comments box please! The first correct entry wins a year’s free subscription to the Open Journal of Astrophysics…
UPDATE: Apologies for having forgotten about this post for ages. The answers are:
Fascinating demonstration of critical opalescence..
One feature of the teaching at Dalhousie University’s Physics Department is a laudable emphasis on demonstrations.
Visiting Professor Tom Duck there, I was delighted to be shown a demonstration I had heard of, but never seen: the phenomenon of critical opalescence in carbon dioxide.
I have written about critical opalescence previously on this blog (here) and with more pictures (here), so I won’t repeat most of that.
In my previous articles I described the phenomenon in two immiscible liquids which is an exact analogy for the physics of critical opalescence in a pure substance. But it’s not what physics students read about in text books.
Michael: What are you going on about?
The phenomenon occurs when one heats a liquid in a container with a small amount of free space.
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The Times Higher has given me yet another reason to be disgruntled this week, in the form of an article that talks about the possible effect of the proposed Teaching Excellence Framework (TEF) on “creative” subjects. What bothers me about this piece is not that it criticises the TEF – I think that’s an unworkable idea that will cause untold damage to the University system if, as seems likely, it is railroaded through for political reasons – but that the author (Nigel Carrington, Vice-Chancellor of the University of Arts London), like so many others, lazily implies that STEM disciplines are not creative. I think some of the most intensively creative people in the world are to be found in science and engineering and creativity is something we try very hard to nurture in students at Sussex University regardless of discipline.
Anyway, while feeling grumpy about this article, I remembered this video of an interview with the great jazz pianist, Bill Evans. Jazz is undoubtedly an intensely creative form, not only because it requires spontaneous real-time conversion of ideas into sounds. Evans talks with great passion and insight about creativity in music-making, but the striking thing about what he says at the very beginning about the need to analyse your subject at a very elementary level before proceeding in order to create something that’s “real” applies equally well to, e.g. theoretical physics as it does to jazz.
In the following section he reiterates this point, but also stresses the discipline imposed by a particular form and why this does not limit creativity but makes it stronger.
It’s better to do something simple that is real. It’s something you can build on. because you know what you’re doing. Whereas, if you try to approximate something very advanced and don’t know what you’re doing, you can’t build on it.
No matter how far I might diverge or find freedom in this format, it only is free insofar that it has reference to the strictness of the original form. That’s what gives it its strength.
In much the same way, theoretical physics is not made less creative because it has to obey the strict rules of mathematics but more so. This is true also in the fine arts: the more limited the canvas the more creative the artist must be, but it also applies to, e.g. engineering design. Self-teaching is important in STEM subjects too: the only really effective way of learning, e.g. physics, is by devoting time to working through ideas in your own mind, not by sitting passively in lectures.
All subjects require technical skill, but there is more to being a great jazz musician than mastery of the instrument just as there’s more to being a research scientist than doing textbook problems. So here’s to creativity wherever it is found, and let’s have a bit more appreciation for the creative aspects of science and engineering!
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Interesting piece by Buchert et al. about the role of inhomogeneities in cosmology….
Yes! The biggest problem in cosmology—the apparent acceleration of the expansion of the Universe and the nature of dark energy—has stimulated a debate about “backreaction”, namely the effect of inhomogeneities in matter and geometry on the average evolution of the Universe. Our recent paper aims to close a chapter of that debate, to encourage exciting new research in the future.
Although matter in the Universe was extremely uniform when the cosmic microwave background radiation formed, since then gravitational instability led to
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In the Dark 