Sathya’s Cosmic Sirens

Bit busy today so I thought I’d just post this talk by Cardiff’s own Prof. Bangalore Sathyaprakash at last year’s TEDX event in Cardiff.
The title is Cosmic Sirens although given that the topic is gravitational waves I hope that “sirens” isn’t intended to mean those entirely mythical entities that lure unsuspecting PhD students to their ultimate destruction…

Anyway, here’s the blurb:

In 1916 Einstein predicted that dynamical mass distribution generates ripples in the very fabric of spacetime that propagates outwards at the speed of light.

For over two decades B.S. Sathyaprakash (Sathya for his family and friends) is engaged in research to detect these ripples called gravitational waves, from cataclysmic cosmic events such as exploding stars, colliding black holes and the big bang. His personal goal is to observe and understand black holes and gravity using gravitational radiation. He is the head of the gravitational physics group at Cardiff University — a centre for modelling astronomical sources of gravitational radiation, discovering innovative algorithms to search for this radiation and analyzing data from gravitational-wave detectors using massive computer clusters.

Although there is firm indirect evidence that certain astronomical systems do emit gravitational waves, so far no one has detected them directly. Sathya and his team are part of a worldwide effort, called the LIGO Scientific Collaboration, to detect these elusive waves using kilometer long laser interferometers in the US, Europe and Japan. Recently, Sathya helped develop the science case for building such a detector in India. He has been involved in the European design study of a third generation underground detector with a 30 km baseline called the Einstein Telescope, chairing the group that developed the science case for this ambitious venture.

And here is the actual talk..

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Gravity Waves Detected!

At last, for all you sceptics out there, Hurricane Sandy has finally provided definitive proof of the existence of gravity waves, clearly visible to the South West of the storm…

Apologies if you thought I meant gravitational waves. The confusion was entirely intentional.

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R.I.P. Leonid Grishchuk

As I was travelling to Heathrow airport in order to fly to the USA (from where I am posting this message), I heard the sad news of the death of a dear and respected colleague, Professor Leonid Petrovich Grishchuk.

Leonid was a  Distinguished Research Professor here in Cardiff from  1995 until his retirement in 2009 and was frequently to be found in the department after that. You can read more of his scientific biography and wider achievements here, but it should suffice to say that he was a pioneer of many aspects of relativistic cosmology and particularly primordial gravitational waves. He was also a larger-than-life character,  held in great affection by many scientists and friends around the world.

My first experience of Leonid was many years ago at a scientific meeting at which I attempted to give a talk. Leonid was in the audience and he interrupted me,  rather aggressively. I didn’t really understand his question so he had another go at me in the questions afterwards. I don’t mind admitting that I was quite upset with his behaviour. I think a large fraction of working cosmologists have probably been “Grischchucked” at one time or another. Later on, though, people from the meeting were congregating at a bar when he arrived and headed for me. I didn’t really want to talk to him as I felt he had been quite rude. However, there wasn’t really any way of escaping so I ended up talking to him over a beer. We finally resolved the question he had been trying to ask me and his demeanour changed completely. We spent the rest of the evening having dinner and talking about all sorts of things and were good friends ever since. Over the years I’ve learned that this is very much a tradition amongst Russian scientists of the older school. They can seem very hostile – even brutal – when discussing science, but that was the way things were done in the environment where they learned their trade.  In many cases the rather severe exterior masks a kindly and generous nature, as it certainly did with Leonid. Leonid’s confrontational behaviour was partly sport – once you got used to that twinkle in his eye it was impossible to take offence – but partly a genuine desire to cut away the flannel and get to the heart of things. He detested bullshit and had no time for people who traded in it.

Here’s a picture of Leonid taken a few years ago with his longstanding friend Professor Kip Thorne.

Some months ago Leonid was struck down by a brain tumour, against which he struggled bravely. On Monday this week, however, the doctors were forced to admit that the treatment had failed and Leonid could not live much longer. Fortunately his death, when it came, was peaceful. He passed away in his sleep on Wednesday night.

Farewell, Leonid. We’ll all miss you.

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Wavy Gravy

I was looking through my collection of old CDs last night and saw a track on Kenny Burrell’s classic album Midnight Blue with the title Wavy Gravy. I hadn’t noticed the name before, but thought it might do as a theme tune for my Cardiff colleagues who work on gravy waves  gravitational waves…

Anyway, the album was recorded at the Van Gelder Studio, Englewood Cliffs, New Jersey on April 06-07, 1963, and originally released on Blue Note (4123). The complete personnel listing is: Kenny Burrell (guitar); Stanley Turrentine (tenor saxophone); Major Holley, Jr. (bass); Bill English (drums); Ray Barretto (congas).

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Bad News for Astrophysics from ESA

Just a quick post to pass on the news (which I got from Steinn Sigurdsson’s blog) that the ESA Executive (see correction in comments below) Space Science Advisory Committee (SSAC) of the European Space Agency (ESA) has made a recommendation as to the next large mission to be flown. The short list consisted of a mission to Jupiter’s moons (JUICE), an X-ray observatory (ATHENA), and a gravitational wave observatory (NGO). The last two of these are severely de-scoped versions of missions (IXO and LISA respectively) that had to be re-designed in the aftermath of decisions made in the US decadal review not to get involved in them.

Not unexpectedly, the winner is JUICE. Barring a rejection of this recommendation by the ESA Science Programme Committee (SPC) this will be the next big thing for ESA space science.

The School of Physics and Astronomy at Cardiff University has a considerable involvement in gravitational wave physics, so the decision is disappointing for us but not entirely surprising. It’s not such a big blow either, as we are mainly involved in ground-based searches such as LIGO.

The biggest local worry will be for the sizeable community of X-ray astronomers in the UK. With no big new facilities likely for well over a decade one wonders how the expertise in this area can be sustained into the future, even if LOFT is selected as one of the next medium-sized missions. Or, given that STFC funding is already spread extremely thin, perhaps this is time for the UK to organize a strategic withdrawal from X-ray astronomy?

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Gravity waves goodbye to LISA?

It seems that we’re not allowed to have any good news these days without a bit of bad to go with it. This week it has emerged here and there that the US National Aeronautics and Space Administration (better known as NASA) is pulling the plug on one of the most exciting space missions on its drawing board. Feeling the pressure of budget constraints and a ballooning overspend on the James Webb Space Telescope (JWST), NASA has decided not to participate further in the Laser Interferometric Space Antenna, a.k.a. LISA. The project teams working on LISA have been disbanded, and the shutters have been pulled down on a project which would have revolutionised astrophysics by opening up new possibilities of observing astronomical objects using gravitational waves, rather than electromagnetic radiation.

This does not mean that LISA is necessarily completely dead. For one thing, it was always planned to be a partnership between NASA and its European counterpart ESA (the European Space Agency); you can find ESA’s LISA page here. In fact a technological demonstrating mission LISA-Pathfinder, operated by ESA, is scheduled for launch in 2013.
It remains possible that ESA will proceed on its own with some version of LISA, although given its own financial constraints it is unlikely that it will be able to fund the full original mission concept. The best we can hope for, therefore, is probably some slimmed-down low-budget version and perhaps an even later launch date.

I still hold out some hope that LISA might come out of mothballs when gravitational waves are actually detected. This may well be accomplished by Advanced LIGO, a ground-based interferometric system based in the states, although it has to be said that gravitational waves have been “on the brink of detection” for at least 30 years and still haven’t actually been found. When detection does become a reality it might galvanise NASA into finding room in its budget again.

This news will be a particularly concern for the sizeable Gravitational Physics group here in the School of Physics & Astronomy at Cardiff University. However, LISA was very much in the planning and development stages so it won’t impact their current work. I haven’t had the chance to discuss the news about LISA with members of this group, so I’d be interested to receive comments from them, or indeed anyone else who knows more about what NASA’s decision may or not mean for the future of gravitational wave physics.

Black Hole Hunter

A discussion yesterday with one of my colleagues in the gravitational physics group here in Cardiff gave me the idea of including a little advert here for a fun website called Black Hole Hunter.

The site was developed as a part of the Royal Society Summer Exhibition 2008, Can you hear black holes collide? presented by Cardiff University, and the Universities of Birmingham, Glasgow and Southampton in the UK in collaboration with the Albert Einstein Institute and Milde Marketing in Germany.

The idea is to use your skill, judgement and lugholes to detect the gravitational wave signal from the merger of two black holes in the noisy output of a gravitational wave detector. The image on the left shows the pattern of gravitational radiation as calculated numerically using Einstein’s general theory of relativity. Why not give it a try and see how you get on?

You can play here.

Much Ado About a Null Result

In today’s Nature there’s an article outlining the current upper limits on the existence of a stochastic cosmological background of gravitational waves. The basis of the analysis presented in the paper is a combination of data from two larger international collaborations, called VIRGO and LIGO. Cardiff University is a member of the latter, so I suppose I should be careful about what I say…

These experiments have achieved incredible sensitivity – they can measure distortions that are a tiny fraction of an atomic nucleus in scale – but because gravity is such a very weak force they still haven’t managed to find direct evidence of gravitational waves. The next generation of these laser interferometers – Advanced LIGO – should get within hailing distance of a detection but in the meantime we have to do with upper limits. Since the sensitivity of the instruments is so well calibrated, the lack of a signal can yield interesting information. The Nature paper is quite interesting in that it summarizes the constraints that can be placed in such a way on some models of the early Universe. Mostly, though, these are “exotic” models that have already been excluded by other means. If I’ve got my sums right the stochastic gravitational wave background expected to be produced within the standard “concordance” cosmology, in which gravitational wave modes are excited by cosmic inflation, is at least three orders of magnitude lower than current experimental sensitivity.

I can’t resist including the following excerpts from a press release, produced by the Media Relations Department at Caltech whose spin doctors have apparently been hard at work.

Pasadena, Calif.—An investigation by the LIGO (Laser Interferometer Gravitational-Wave Observatory) Scientific Collaboration and the Virgo Collaboration has significantly advanced our understanding the early evolution of the universe.

Analysis of data taken over a two-year period, from 2005 to 2007, has set the most stringent limits yet on the amount of gravitational waves that could have come from the Big Bang in the gravitational wave frequency band where LIGO can observe. In doing so, the gravitational-wave scientists have put new constraints on the details of how the universe looked in its earliest moments.

Much like it produced the cosmic microwave background, the Big Bang is believed to have created a flood of gravitational waves—ripples in the fabric of space and time—that still fill the universe and carry information about the universe as it was immediately after the Big Bang. These waves would be observed as the “stochastic background,” analogous to a superposition of many waves of different sizes and directions on the surface of a pond. The amplitude of this background is directly related to the parameters that govern the behavior of the universe during the first minute after the Big Bang.

and

“Since we have not observed the stochastic background, some of these early-universe models that predict a relatively large stochastic background have been ruled out,” says Vuk Mandic, assistant professor at the University of Minnesota.

“We now know a bit more about parameters that describe the evolution of the universe when it was less than one minute old,” Mandic adds. “We also know that if cosmic strings or superstrings exist, their properties must conform with the measurements we made—that is, their properties, such as string tension, are more constrained than before.”

This is interesting, he says, “because such strings could also be so-called fundamental strings, appearing in string-theory models. So our measurement also offers a way of probing string-theory models, which is very rare today.”

“This result was one of the long-lasting milestones that LIGO was designed to achieve,” Mandic says. Once it goes online in 2014, Advanced LIGO, which will utilize the infrastructure of the LIGO observatories and be 10 times more sensitive than the current instrument, will allow scientists to detect cataclysmic events such as black-hole and neutron-star collisions at 10-times-greater distances.

“Advanced LIGO will go a long way in probing early universe models, cosmic-string models, and other models of the stochastic background. We can think of the current result as a hint of what is to come,” he adds.

“With Advanced LIGO, a major upgrade to our instruments, we will be sensitive to sources of extragalactic gravitational waves in a volume of the universe 1,000 times larger than we can see at the present time. This will mean that our sensitivity to gravitational waves from the Big Bang will be improved by orders of magnitude,” says Jay Marx of the California Institute of Technology, LIGO’s executive director.

“Gravitational waves are the only way to directly probe the universe at the moment of its birth; they’re absolutely unique in that regard. We simply can’t get this information from any other type of astronomy. This is what makes this result in particular, and gravitational-wave astronomy in general, so exciting,” says David Reitze, a professor of physics at the University of Florida and spokesperson for the LIGO Scientific Collaboration.

If hyperbole is what you’re looking for, go no further. There’s nothing wrong with presenting even null results in a positive light but, I don’t think this paints a very balanced picture of the field. For examples, early Universe models involving cosmic strings were already severely constrained before these results, so we know that they don’t have a significant effect on the evolution of cosmic structure anyway.

Clearly the political intention was to flag the importance of Advanced LIGO, although even that will probably be unable to detect the cosmological gravitational-wave background.  Overstatements contained in press releases of this type usually prove counterproductive in the long run.

Leonid’s Shower

Yesterday (17th April) was the last day of our Easter vacation – back to the grind on Monday – and it was also the occasion of a special meeting to mark the retirement of Professor Leonid Petrovich Grishchuk.

Leonid has been a Distinguished Research Professor here in Cardiff since 1995. You can read more of his scientific biography and wider achievements here, but it should suffice to say that he is a pioneer of many aspects of relativistic cosmology and particularly primordial gravitational waves. He’s also a larger-than-life character who is known with great affection around the world.

Among other things, he’s a big fan of football. He still plays, as a matter of fact, although he generally spends more time ordering his team-mates about than actually running around himself. One of his retirement presents was a Cardiff City football shirt with his name on the back.

My first experience of Leonid was many years ago at a scientific meeting at which I attempted to give a talk. Leonid was in the audience and he interrupted me,  rather aggressively. I didn’t really understand his question so he had another go at me in the questions afterwards. I don’t mind admitting that I was quite upset with his behaviour. I think a large fraction of working cosmologists have probably been Grischchucked at one time or another.

Later on, though, people from the meeting were congregating at a bar when he arrived and headed for me. I didn’t really want to talk to him as I felt he had been quite rude. However, there wasn’t really any way of escaping so I ended up talking to him over a beer. We finally resolved the question he had been trying to ask me and his demeanour changed completely. We spent the rest of the evening having dinner and talking about all sorts of things and have been friends ever since.

Over the years I’ve learned that this is very much a tradition amongst Russian scientists of the older school. They can seem very hostile – even brutal – when discussing science, but that was the way things were done in the environment where they learned their trade.  In many cases the rather severe exterior masks a kindly and generous nature, as it certainly does with Leonid.

I also remember a spell in the States as a visitor during which I heard two Russian cosmologists screaming at each other in the room next door. I really thought they were about to have a fist fight. A few minutes later, though, they both emerged, smiling as if nothing had happened…

Appropriately enough Leonid’s bash was held immediately after BritGrav 9, a meeting dedicated to bringing together the gravitational research community of the UK and beyond, and to provide a forum for the exchange of ideas. It aimed to cover all aspects of gravitational physics, both theoretical and experimental, including cosmology, mathematical general relativity, quantum gravity, gravitational astrophysics, gravitational wave data analysis, and instrumentation. I chaired a session during the meeting and found Leonid in characteristic form as a member of the audience, never shy with questions or comments, and quite difficult to keep under control.

I enjoyed the meeting because priority was given to students when allocating speaking slots. I think too many conferences have the same senior scientists giving  the same talk over and over again. Relativists are also quite different to cosmologists in the level of mathematical rigour to which they aspire.  You can bullshit at a cosmology conference, but wouldn’t get away with it in front of a GR audience.

On the evening of 16th April we had a public lecture in Cardiff by Kip Thorne on The Warped Side of the Universe: from the Big Bang to Black Holes and Gravitational Waves and Kip also gave a talk as part of the subsequent meeting on Friday in Leonid’s honour.

Kip and Leonid are shown together a few years ago in the photograph to the left here. The rest of the LPGFest meeting was interesting and eclectic, with talks from mathematical relativists as well as scientists in diverse fields who had come over from Russia specially to honour Leonid. We later adjourned to a “Welsh Banquet” at the 15th Century Undercroft of Cardiff Castle for dinner accompanied by something described as “entertainment” laid on by the hosts. That part was quite excruciating: like Butlins only not as classy. Heaven knows what our distinguished foreign visitors made of it, although Leonid seemed to think it was great fun, and that’s what matters.

Once the dinner was over it was time for Leonid to be showered with gifts from around the world and, by way of a finale, he was serenaded with a version of From Russian With Love, by Bernie and the Gravitones. Now at last I understand what the phrase “extraordinary rendition” means.

Clover and Out

One of the most exciting challenges facing the current generation of cosmologists is to locate in the pattern of fluctuations in the cosmic microwave background evidence for the primordial gravitational waves predicted by models of the Universe that involve inflation.

Looking only at the temperature variation across the sky, it is not possible to distinguish between tensor  (gravitational wave) and scalar (density wave) contributions  (both of which are predicted to be excited during the inflationary epoch).  However, scattering of photons off electrons is expected to leave the radiation slightly polarized (at the level of a few percent). This gives us additional information in the form of the  polarization angle at each point on the sky and this extra clue should, in principle, enable us to disentangle the tensor and scalar components.

The polarization signal can be decomposed into two basic types depending on whether the pattern has  odd or even parity, as shown in the nice diagram (from a paper by James Bartlett)

The top row shows the E-mode (which look the same when reflected in a mirror and can be produced by either scalar or tensor modes) and the bottom shows the B-mode (which have a definite handedness that changes when mirror-reflected and which can’t be generated by scalar modes because they can’t have odd parity).

The B-mode is therefore (in principle)  a clean diagnostic of the presence of gravitational waves in the early Universe. Unfortunately, however, the B-mode is predicted to be very small, about 100 times smaller than the E-mode, and foreground contamination is likely to be a very serious issue for any experiment trying to detect it.

An experiment called Clover (involving the Universities of  Cardiff, Oxford, Cambridge and Manchester) was designed to detect the primordial B-mode signal from its vantage point in Chile. You can read more about the way it works at the dedicated webpages here at Cardiff and at Oxford. I won’t describe it in more detail here, for reasons which will become obvious.

The chance to get involved in a high-profile cosmological experiment was one of the reasons I moved to Cardiff a couple of years ago, and I was looking forward to seeing the data arriving for analysis. Although I’m primarily a theorist, I have some experience in advanced statistical methods that might have been useful in analysing the output.  It would have been fun blogging about it too.

Unfortunately, however, none of that is ever going to happen. Because of its budget crisis, and despite the fact that it has spent a large amount (£4.5M) on it already,  STFC has just decided to withdraw the funding needed to complete it (£2.5M)  and cancel the Clover experiment.

Clover wasn’t the only B-mode experiment in the game. Its rivals include QUIET and SPIDER, both based in the States. It wasn’t clear that Clover would have won the race, but now that we know  it’s a non-runner  we can be sure it won’t.