Back to Mississippi

First time I went to Oxford Mississippi was 7 years ago, as a visiting master student at The University of Mississippi or, as it is more commonly known, OleMiss. I arrived there around May and, as in most college towns like Oxford, the city emptied right after the term finished, few days after my arrival. This is to say, nothing much was going on in Oxford at that time; nonetheless during my six-month visit there I managed to meet very interesting people, live curious experiences, have fun, and specially work hard in what has later become my field of research. Looking back, I had really a great time.

This is why i'm so excited to come back in Oxford MS tomorrow to attend the Workshop "Testing General Relativity with Astrophysical Observations".

The beautiful logo of the workshop recalls the iconographic Southern magnolia with the trajectory of an extreme mass-ratio inspiral, i.e. the evolution of a stellar-mass compact object orbiting a supermassive black hole like the one at the center of the Milky Way. [credits: Ana Sousa]

This workshop will bring together experts in tests of general relativity, modified theories of gravity and astrophysics. The aim is to foster informal discussions on the current status of experimental constraints on Einstein’s theory and their prospects for the near future, when advanced gravitational-wave observatories will be operational.

The list of participants is impressive and the program promises this will be a fun and fruitful meeting. For me this will also be a special experience, as at Olemiss I met some of my scientific advisors, some closest collaborators and also good friends.

Oxford has been named by USA Today as one of the top six college towns in the U.S. and it is also known as the hometown of  Nobel-prize winning author William Faulkner, as well as residence of novelist and politician John Grisham. However, as a 23-yr old student, I like to remember myself walking around the Olemiss campus while listening to Afroman's hits, which are definitely less literate but undeniably fun. Here is an example, particularly apt for this occasion:

OK, the lyrics is bitter and somehow sexist but, hell, Mississippi is not only Oxford!

I better stop here and continue preparing my slides for this meeting....

The Unbearable Baldness of Black Holes

One of the most awe-inspiring properties of black holes is their absolute simplicity, or as John Wheeler famously put it, "black holes have no hair". As their progenitor collapses, its memory is forever lost, and all that remains is a quiescient, bald black hole. In a new article in Physical Review Letters, a team of scientists (that only by chance includes me...) has shown that black holes can nevertheless "grow hair" in the presence of matter, connecting them to the rest of the host galaxy.

Black holes are almost xeroxed copies of one another, differing at most in mass and rotation. These objects are described by a solution discovered by Roy Kerr in 1963. Remarkably, Kerr black holes are ubiquitous in almost any other theory of gravity, to the extend that the "Kerr hypothesis" is the current paradigm in astrophysics. 

First time I saw this picture was in one of Stephen Hawking's popular-science books, probably 'Brief History of Time'. It is supposed to describe the 'baldness' that this post refers too, am I the only one finding it a bit pathetic? :)

We have shown that in simple and attractive extensions of Einstein's theory (known as scalar-tensor gravity) black holes may not be described by the Kerr metric, as was previously thought. The crucial ingredient is the matter surrounding astrophysical black holes, typically in the form of accretion disks. The presence of matter triggers an instability that forces the bald Kerr black hole to develop a new charge -- a "scalar hair" -- connecting it to the matter around it and possibly to the entire galaxy. 

This hair growth is accompanied by a peculiar emission of gravitational waves, potentially by upcoming laser interferometers, which may test the Kerr hypothesis and probe the very foundations of gravity.

Read what real outreach journalists wrote on this on:

NewScientist

Huffington Post

Portuguese newspaper Público

The Gravitational Universe

May 24th, 2013, 12:00 CEST is the deadline for submission of the eLISA white paper to the European Space Agency (ESA).

Quoting the webpage of the project: "Gravity is the dominant force in the universe. We propose the first ever mission to survey the entire universe directly with gravitational waves, to tell us about theformation of structure and galaxies, stellar evolution, the early universe, and the structure and nature of spacetime itself. Most importantly, there will be enormous potential for discovering the parts of the universe that are invisible by other means, such as black holes, the Big Bang, and other, as yet unknown objects. 

The European Space Agency has recently launched the process for choosing candidates for the next large mission launch slots. The first step in this process is the submission of white papers advocating science themes. The eLISA team will submit a compelling science case, which will be addressed by our eLISA mission concept in 2028."

79 authors and 80 contributors have worked intensively to produce this impressive white paper. The proposed mission itself is epic:

"Today we can see the beauty of the universe with modern telescopes in many wavelengths. Observing the universe with gravitational waves—which are analogous to acoustic waves—will allow us to hear the universe for the first time. 

eLISA will be the first observatory to directly detect low frequency gravitational waves. It will measure the relative displacement of free-falling test masses, one million kilometers apart, by means of laser interferometry. This will enable us to determine parameters like mass, spin, orbital elements, and luminosity distance of the sources with unprecedented precision. Large parts of the technologies necessary for such a mission have already been developed, and will be tested in space by LISA Pathfinder in 2015."

Almost 1000 scientists worldwide are supporting the mission, including Stephen Hawking, Edward Witten, Nobel Laureate Gerard 't Hooft and many of the most renewed faculties of Physics and Astrophysics worldwide.

If you want to learn what all of this is for, check out the project webpage!

Visiting the Pi

Let me state it clearly. The Perimeter Institute is A M A Z I N G. The institute and its facilities are just one of best places for a scientist to work. The building itself is a piece of art, and the interior is even better. 

Front view of the Perimeter Institute. The yellow glasses are those that reflect light from outside, but  one can actually look through from the interior. Most offices sport huge pairs of these glasses facing a quite and beautiful lake.

They stole the name of one of the conference rooms from our blog!

This is just one of the many places where scientists may gather together, chatting and discussing. The entire building is full of blackboards, sofa chairs and couches like those in the picture. Not to mention a pool table, a fully equipped kitchen (with fireplace for the winter!) a squash and basketball pitch and a gym with huge glasses facing the lake... This place is like the Google company of theoretical physics.

The lake next to the institute. Besides scientists and various other geeks, the area is inhabited by gooses 

PS: If you are curious, here is the video of the talk I gave on Thursday.

Unlock the Gravitational Universe - Black Holes, Compact Binaries, the Big Bang

This trailer is not for a movie, it's not for a TV show and it's not for a computer game. This trailer is for the largest instrument ever built by humanity. An enormous space-based gravitational wave detector that will measure distortions of space-time, revolutionize astronomy, our understanding of physics, and the past and future of our cosmos. That's it really.....enjoy! :)

LISA Mission / eLISA Mission

Song: "First Hero" by Vera Ohl (musicfox UG)

Ginjinha physics in Lisbon

Most of the participants of the "Strong Gravity Beyond to GR: from theory to observations" Workshop,
having a typical Ginginha in Lisbon's city center.

The workshop is going great, as you may see. Besides drinking ginjinhas, all talks have been excellent and plenty of interesting discussions are going on. This totally compensates for the 18h/day-effort that we are putting on it!

This picture was taken 10 sec after the previous one. Funny thing: the guy on the bottom left, the lady at the center and the two guys on the right (who were not in the previous one) are just pedestrians who joined the photo for the sake of it, without even paying the workshop fee!

Workshop + School in Lisbon

Next two weeks will be very busy in Lisbon (i'm flying back tomorrow). Next week at IST we have the pleasure to host and organize the first "Strong Gravity Beyond GR: from theory to observations" workshop.

The workshop logo. Here is the webpage

The purpose is to organize a friendly and relaxed meeting for a limited number of scientists who work on gravitational theories aiming at correcting General Relativity and on experimental tests of gravity in general. Next few years will witness a wealth of new astrophysical data: second-generation interferometers promise to detect gravitational waves for the first time, very precise observations of the Milky Way center will allow to infer the properties of the supermassive black hole lurking at it and the exponential grow of cosmological observations will open new windows through which "The Theory" of gravity will reveal itself. This is just the perfect time to organize such a meeting in Europe! I'll try to report on the ongoing events, although each time i promise that I failed miserably...

The logo of the NR/HEP2: Spring School

Moreover, in two weeks from now the IST will host a Spring School on topics at the edge between Numerical Relativity and High Energy physics. The NR/HEP2: Spring School is an event organized within a long-term initiative involving the Universities of Aveiro, Instituto Superior Técnico in Lisbon, Rome Sapienza”, Barcelona, Belém do Pará in Brazil, Mississippi and the DAMTP at Cambridge U. Five intense days of lectures are scheduled and, beside one silly guy, i guarantee the speakers are all excellent and it will be fun.

Anyway, these are wonderful excuses for me to take a rest from Boston and enjoy Portuguese weather, food and friends... more soon from Lisboa!

De devulgationi eloquentia

Our gravity group in Lisbon have just published a series of short movies where many group members describe some general aspect of Einstein's theory and beyond.

Have a look at Videoteca do Gravitão, muito boa!

Check out all cool resources at our group's outreach webpage

LIGO Magazine

Here the annoucement by Gabriela Gonzalez (LSC spokesperson):

The US-based Laser Interferometer Gravitational-Wave Observatory (LIGO) is supported by an international group of more than 800 scientists from about 80 institutions, the LIGO Scientific Collaboration (LSC, http://www.ligo.org).

Following the examples of other large science projects we decided to create the LIGO Magazine, a regular publication to exchange information, news and stories from and with the LSC community. The inaugural issue is now available, with more than 30 pages of entertaining stories and fascinating photos from the installation of the Advanced LIGO detectors.

We believe that the magazine is also a good way to find out more about LIGO and the gravitational wave community, and to satisfy your general interest in science and technology. Therefore the magazine is available as a free download (pdf file) at: http://www.ligo.org/magazine/

We hope you find it inspiring and entertaining. Let us know what you think and do tell your friends and colleagues by forwarding this link to them.

Light David defeats the supermassive Goliath [on NewScientist]

read the coverage

There must be something wrong in science if the NewScientist published this weird coverage on massive photons around black holes.

First, even my grandma knows that "black holes tend not to exist" [cit.], so that putting bounds on the mass of the photon using observations of supermassive black holes, as the author apparently do, doesn't sound very likely.
Second, I know personally most of the authors and at least one of them is dangerously close to be a crackpot, to be polite.

Thus, i strongly suggest you not to read the original paper, or to read it just for fun, and never ever trust those authors!

Btw, if you are not disgusted enough, here you can find another view on the problem.

Matters of Gravity

Last issue appeared some days ago here 

Issued twice a year, Matters of Gravity is a newsletter mainly organized by the Topical Group in Gravitation of the American Physics Society (APS). You might find summaries of meetings and workshops, announcements for prizes and grants and, most importantly, some scientific gossip.

Here you can find issues since 2006, while here there are the previous ones (started in 1991).

Recommended by us

“Questioning the Foundations The submission deadline for this year’s FQXi essay context on the question “Which of Our Basic Physical Assumptions Are Wrong?” has just passed. They got many thought-provoking contributions, which I encourage you to browse here. The question was really difficult for me. Not because nothing came to my mind but because too much came to my mind! Throwing out the Heisenberg uncertainty principle, Lorentz-invariance, the positivity of gravitational mass, or the speed of light limit – been there, done that. And that’s only the stuff that I did publish...

(Continue to read on BackReaction)                                                                                                                                 ”

Sparse Swedish Thoughts

• My talk is in a couple of hours, i should finish it instead of writing here
• Stockholm is just amazing: it looks like nobody is really rich and nobody is poor. On average everybody is wealthy enough and the standard deviation is tiny. I guess that's the secret of this country (plus the fact it's just 10 millions people)

"Blond girls... blond girls everywhere"

New insights on the matter-gravity coupling paradigm

Back in October 1915, Albert Einstein published his revolutionary theory of gravity, General Relativity. His first version of the equations named after him were actually not compatible with local energy conservation. The second version was modified accordingly and claims that geometry is proportional to matter content. The fundamental geometric object is the so called metric, which prescribes how to measure length and time intervals. As John A. Wheeler said, 'Matter tells space how to curve, and space tells matter how to move.' This is the tenor of the Einstein equations. Furthermore, the metric itself is dynamical and contributes to the energy, warping the spacetime. This is encoded in the nonlinear nature of the geometrical part of the Einstein equations.

Although Einstein's equations successfully describe a lot of astrophysical or cosmological phenomena, it is worth noting that there is something missing in the theory. For instance, galactic rotation curves can be understood only by postulating the existence of some weakly interacting, nonvisible dark matter. The birth of the universe requires an inflationary period, which in turn requires new matter content. In fact, the most successfully tested sector of Einstein's theory is vacuum, as most experiments are performed outside of matter.

On another hand, it seems legitimate to wonder why an intrinsically nonlinear theory should couple linearly to the matter content. This should be valid in some regime but there is no reason to impose it. Modified theories of gravity usually propose to change the geometrical description, generally leading to strong experimental constraints. Instead, the coupling between matter and geometry is most often left unchanged. A modification of this coupling deserves a comprehensive analysis, which is the purpose of our letter 'New insights on the matter-gravity coupling paradigm.'

We were working on a particular alternative theory, namely the Eddington-inspired-Born-Infeld theory, when we realized that it can be interpreted as a standard General Relativity model, but with a modified coupling. This model was brought up to date in 2010 by Banados and Ferreira, who showed that in some situations singularity problems can be avoided. Using the reinterpretation of the model, we put forward the mechanism behind the singularity avoidance and explicitly show the effect of the coupling modification.

Even better, we provide a relation between how matter affects the geometry and how we perceive matter. Indeed, if the coupling to geometry changes, we must interpret measurements in a different way. Otherwise one is led to the (probably false) conclusion that spacetime is curved by a matter source different from the one directly seen... This sounds familiar? It should! Indeed, modified couplings are yet quite unexplored, experimentally viable, and might provide new perspectives to currently unanswered questions, e.g., mimic the new kinds of matter proposed in cosmology.

arXiv link