Onde Gravitazionali: la musica dello spaziotempo

Dopo l'incredibile rivelazione delle onde gravitazionali, gli amici dell'Associazione Astronomiamo mi hanno ricontattato per organizzare una serata online all'interno dei loro "Incontri di Astronomia". Ho accettato molto volentieri, visto il grande impegno ed entusiasmo che questa associazione mette nella divulgazione scientifica.

Ecco il video della serata, disponibile anche sul loro sito. Buona visione (specie per mia nonna!)

Recommended by us: Time to move on?

''Cosmology and particle physics have long been dominated by theoretical paradigms: Einstein's general theory of relativity in cosmology and the Standard Model of particle physics. The time may have come for paradigm shifts. Does cosmological inflation require a modification of Einstein's gravity? Have experiments at the LHC discovered a new particle beyond the Standard Model? It is premature to answer these questions, but we theorists can dream about the possibilities.''
 

Full conference proceeding  here.

Hey Grandma look: I finally study something that exists!

So much has been already written about today's announcement of the first direct discovery of the gravitational waves from two merging black holes by the advanced LIGO detector. Some examples:

[1], [2], [3] (this beautiful piece by my friend and colleague Emanuele Berti)

In Italian press: [1], [2], [3]

Exactly 100 years ago, Albert Einstein proved that his theory of gravity, General Relativity, predicted the existence of gravitational waves.

This is nothing but one of the most outstanding historic discoveries in science. However, since you can find much deeper posts on this topic, here are some random, not-so-serious, thoughts hastily written down while watching today's live streaming announcement (sorry for typos, this is written on the wings):

1) Look Grandma: I finally study something that exists!
[Last time someone told my grandma that maybe black holes didn't exist after all.. she literally cried!]

2) Wow, my field of research has finally become mainstream! [is this good of bad? Anyway, the largest lecture hall at the Physics Department at Sapienza was full 30 mins before the live streaming..that's pretty uncommon for something related to gravity...]

3) The first direct detection of gravitational waves is really great, but what is emitting these waves is even more interesting: these are two black holes orbiting each other, loosing energy through gravitational-wave emission and finally merging to form a final big black hole. All of this is beautifully predicted by Einstein's theory of General Relativity and required several decades of theoretical, experimental and computational work.

4) Now everyone claims they have predicted that the signal from a binary black hole merger would have been detected. Truth is, just 6 months ago nobody would have bet on this particular source.

5) Related to this, isn't it amazing how physics works? It takes just a single observation to completely change the paradigm that theorists have built over decades. Just 6 months ago very few people would have predict that LIGO -even in the case of a detection- would have been able to test General Relativity or just to make some science or astrophysics out of this discovery. Well, judging from the result of the paper published today (and the companion papers to come) this expectation was completely wrong.

6) Finally, my bets for the Nobel Prize (in random order)

Rainer Weiss, one of the founders of LIGO

Roy Kerr, who discovered the unique solution of General Relativity describing a spinning black hole

Kip Thorne, one of the cofounders of LIGO, and of the fathers of modern General Relativity
(plus one of the creator of the movie Interstellar)

Visit to CERN

I am just back from CERN, where I stayed over this week to visit Diego Blas at the CERN THeory Division and to give the talk "Compact Objects as Dark-Matter Probes".

Some sparse thoughts on the visit:

1) On the first night, I checked in at a hotel in Geneva instead of staying at the CERN hostel. That was a very bad move. Everything in Geneva is unbelievable expensive and the hotel (albeit 3 star and averaged rated) turned out to be quite bad. I got bed bugs, i am still full of pinches, and i'm still trying to disinfect my clothes at home...

2) On the other hand, the hostel at CERN (where I stayed for the rest of the week) was excellent. The room was clean and cozy and equipped with a large desk. Everything at CERN seems to be designed to simply researchers' life and work.

3) I was impressed by the low average age of people working at CERN. About 10K work at the center and most of them are young PhDs or postdocs. The comparison with the average Italian university, where most of the faculty members and staff are over 40, is impressive. I recently read an interview by CERN Director Fabiola Gianotti, who was precisely commenting on this fact. However, experiencing it directly is a different kettle of fish.

4) Although CERN is big and experiments are scattered around a 27-km underground ring, I enjoyed the fact that most offices are located in a handful of buildings which are connected among each other. This basically means that theorists can chat over a coffee with experimentalists, or that it is easy to attend the (enormous) number of talks and lectures that are organized on a daily basis. The canteen is also common for all buildings and researchers from different collaborations and experiments meet there to have lunch (and sometimes dinner) together.

5) Overall, the atmosphere is definitely suggestive, even for someone like me who's used to see so many physicists in the same place (I guess that for the numerous students who regularly visit CERN during a school trip it must be really a unique experience).

6) I had the opportunity to meet various friends with whom I went to college in Cagliari (some of them are also authors of this blog). Funny enough, the excess of physicists from Cagliari University, especially in the LHCb experiment, is beyond 5 sigma. Thus, I had the opportunity to visit the LHCb experiment and control room, as this picture testifies:

Visit to the LHCb experiment. 
From the left to the right: Andrea (aka Scrilly), Francesco (both CERN Fellows) and me.

7) BTW, I also had the opportunity to hear more rumors around the 750 GeV diphoton resonance. Every theorist I talked to was extremely excited and sometimes confident about the possibility that ATLAS and CMS experiments have detected something new. Funny enough, every experimentalist I talked to was instead extremely cautious and, most of the time, pessimistic. I should definitely write about this in a next post but, as you probably have heard, this coming week the spotlight will all be on LIGO's announcement of the first direct detection of gravitational waves (!) No doubts on the topic of my next post (after Thursday).

Vitor Cardoso's and Thomas Sotiriou's visits @Sapienza

In the last two months we had two guests at our Department:

• Vitor Cardoso, leader of the strong gravity group at IST, was a Visiting Professor at Sapienza in December and January; some weeks ago he gave a talk on "Black holes as laboratories of fundamental physics"
• Thomas Sotiriou, leader of the gravity group "Challenging General Relativity" at Nottingham University, visited our group during the last week of January and gave a talk on "Lorentz violations, causality, and black holes".

Group picture taken [1] after a goodbye social dinner in the historical center of Rome. 
From the left to the right: Leonardo, Thomas, Vitor, Paolo, Ana and Leonardo Macelloni (an old friend from the University of Mississippi who I met at the time of my first moka machine)

[1] By chance, this picture was taken by the bodyguard of President of the Senate Renato Schifani, who was passing by while we were looking for a random photographer.

Recommended by us: Science Pie - A podcast about physics, history, literature and much more

Dennis Schulz, a physics student, and Annika Brockschmidt, a history and German student, are two podcast enthusiasts based in Heidelberg (Germany).

They created the independent podcast Science Pie, focussing on the variety of subjects science can offer. Their topics range from history to physics, from literature to engineering, in particular interdisciplinary work - a range of topics hard to find in the jungle of podcasts. They often use interviews with an involved researcher or professor as a base for the episodes.
And all of this is provided in a bilingual version (English/German) and a special care for details.

Dennis and Annika’s podcast successfully meets the effort of joining science curiosities, interesting stories about people and a collection of knowledge and facts on history, literature and myths. Join them and enjoy!

AstronomiAmo

Domani saro' ospite della trasmissione web dell'Associazione AstronomiAmo  per parlare di "Stelle di neutroni e buchi neri come laboratori per la rivelazione di materia oscura".

La serata e' condotta da Stefano Capretti e sara' trasmessa in diretta sulla pagina web dell'associazione e sul canale Youtube, nel quale trovate tutte le trasmissioni precedenti e che vi invito caldamente a seguire.

Appuntamento domani, Martedi' 19 Gennaio alle 21:30.

La locandina dei prossimi eventi online organizzati dall'Associazione AstronomiAmo.

Aggiornamento: Ecco il video della serata

Meetings in Lisboa

Right before Christmas I visited Lisbon to attend a conference and a workshop held at the Instituto Superior Técnico. It was a great opportunity to come back to Portugal after almost one year and meet a lot of friends and colleagues there.

Visit to Shangai

Many things have happened in the last few weeks, including the Centenary of General Relativity. On November 25th, I wanted to write a post on this event, but I couldn't because I was visiting Cosimo Bambi's gravity group at Fudan University in Shangai and, as it is infamously known, Google products (including this webpage) are inaccessible from China. None of the standard workaround really worked for me so, as a part of my Chinese trip, I have experienced how one feels being without access to gmail, google maps, facebook, etc... (it turned out to be not that bad in fact..)

During the visit, we had a mini-workshop with astrophysicists Javier Garcia-Martinez (Harvard-Smithsonian CfA), Thomas Dauser (Erlangen-Nuremberg) and Matt Middleton (Cambridge) who are working on different aspects of the electromagnetic emission from accretion disks as a possible way to measure the black-hole spin.

Shangai's skyline as viewed from one of the skyscrapers of Fudan University. The city is simply ENORMOUS..

Recommended by us: Einstein's Special Theory of Relativity postulates explained by a teenager

""
Eighteen-year-old student Ryan Chester has just won US$400,000 for this video explaining Einstein’s Special Theory of Relativity as part of the inaugural Breakthrough Junior Challenge - an international competition that aims to inspire the next generation of scientists and science communicators. And it’s not hard to see why. If you heard the words, "Einstein’s Special Theory of--" and tuned out because it’s all too hard, we have a feeling Ryan will change your mind.

 Original Sciencealert article here

""

TAUP 2015 or On my first international conference

Mr. What and Mr. Why

Topics in Astroparticle and Underground Physics (TAUP), is an international biennal conference arrived at its XIV edition. It covers topics from cosmology and particle physics, to trans dark matter and neutrino physics and to continue with high energy astrophysics, cosmic rays and gravitational waves. Theoretical perspectives as well as experimental strategies and developments are included.

TAUP is born at the Laboratori Nazionali del Gran Sasso (LNGS) of the Istituto Nazionale di Fisica Nucleare (INFN) and we are equal in
age, besides that, because of the biennal frequency, it is a sparkling teenager. About me, well...  I am already a PhD student and I have attended the conference with a nice group of colleagues.

Visit to EGO-VIRGO

A meeting of the theoretical and experimental groups of the Italian Institute for Nuclear Physics (INFN) working on the detection of gravitational waves and on theoretical aspects related to them was held at the European Gravitational Observatory (EGO) in Cascina, near Pisa.

The site hosts Virgo, a detector of gravitational waves which -in one year from now- will be ready to join its U.S. cousin Ligo in the decade-long search of gravitational waves from compact objects.

Me standing in front of one of the 3-km long arms of Virgo. Is the motion due to the passage of a gravitational wave? Hope not since the detector is still offline...

What is a gravitational wave?

Summer Reading

Last year was "Fifty shades of Grey". This summer --no matter if you are sunbathing, hiking or enjoying desolated cities-- if you start pondering about black holes, superradiance, and related subjects, we got you covered:

The book will be soon available on the Springer webpage and on Amazon. Hurry up to buy a copy containing the typo in Vitor's name before they fix it. Those copies will be priceless hundred years from now :)

The book will be available in August but can be already pre-ordered. It costs $60 in the U.S. and about 45 Euros in Europe and the authors get about the 10% of the profit. This means that each of the authors (Richard, "Victor" and I) will get about 3 Euros for each sold copy. Taking "50 shades of Grey" as a reference, a back-of-the-envelope estimate suggests we might become rich in ~10^9 years.

CQG+ article on "Black-hole superradiance and the hunt for dark matter"

Our recent paper on black-hole superradiance has been highlighted in the journal Classical and Quantum Gravity, which contains a CQG+ Section where the authors of highlighted papers are asked to write informally about their work. You can find our contribution here:

http://cqgplus.com/2015/06/11/black-hole-superradiance-and-the-hunt-for-dark-matter/

Monte Carlo simulation of the end-state of the superradiant instability in the so-called “Regge plane”. Each point represents the final black-hole mass and spin after the superradiant evolution. As a result of the instability, old black holes do not populate the region above the green threshold curve, leaving a “hole” in the Regge plane as predicted by a linearized analysis. The experimental points with error bars refer to observed supermassive black holes. The three panels refer to different gas accretion rates.

Enjoy the reading!

Workshop + Conference @ The Fields Institute

"The year of the 100th anniversary of the formulation of Einstein's General Relativity will be remembered as the least productive one for the general-relativity community."

This is what I've heard more than once during the time spent at The Fields Institute in Toronto these weeks :-)
The Institute is organizing a long Focus Program to celebrate the centenary of one of Einstein's greatest achievements, the formulation of a relativistic theory of gravitational interactions, General Relativity for short.

The reason for the pessimist statement above is that this is only one of the numerous events that have been organized around the world to celebrate this important discovery. Now that the term ended, scientists are more free to travel to conferences and workshops and, to save time and money, it's very common to go directly from one conference to another on the week after. This does not leave too much time to sit down and do "actual" work.

Last week I've attended a very interesting workshop on Perturbation Theory which was organized here at the Field Institute as part of the Focus Program. This week instead the Institute is hosting a conference on Black Holes which ends today. Speakers at the conference included Clifford Will, Saul Teukolsky, Robert Wald, Eric Poisson, Gary Horowitz and William Unruh, to mention a few. Personally, I found the workshop much more stimulating and useful than the conference, but it's certainly suggestive to take the opportunity to discuss with some of the fathers of modern General Relativity.

This coming summer will be very busy with other events, especially in July and August, so I tend to agree that year 2015 will not be the most fruitful one in terms of actual work done.

On the other hand, do not underestimate the importance for the community to gather together and discuss open problems and (possibly) crazy ideas! Peer discussion and new collaborations are at the core of the scientific process and they are a crucial part of the duties of any scientist.  For this reason I am positive that the discussions and the collaborations that originate during these meetings will certainly contribute to solve open problems in the field and, who knows, perhaps the next breakthrough is just around the corner in 2016!

Doing a short tour of Toronto with Helvi Witek. Helvi was Ph.D. student in Lisbon when I moved there 4 years ago and she is now postdoc at Cambridge University working on numerical simulations of black-hole systems.

All roads lead to....

I didn't have much time to write lately. The reason is the map below, which shows the places i'll be visiting in the next 45 days... it's going to be a very busy period!

I'm flying tomorrow to Boston for 10 days, then I will attend 3 workshops (in Bremen, Toronto and Lisbon), a friend reunion in Barcelona, a wedding in my home town, Cagliari, and each time touching base in Rome (where all roads lead after all!). I am also co-organizing the NRHEP Meeting and will chair one parallel section at Marcel Grossman Meeting in July. Fortunately, these latter two will not involve any travel, since the venue will be Sapienza for both.

I'll try to report more or less constantly during this crazy schedule, especially from the conferences which looks very interesting and i'm pretty much looking forward to attend.

Jan Steinhoff @ Sapienza

Last week Jan Steinhoff from the Albert Einstein Institute visited our group in Rome, giving a seminar on "Effective action for compact objects and universal relations". Over the weekend, we went for some city sightseeing. Here, from left to right, Jan, Paolo and special guest Matteo are visiting the magnificient Caracalla's baths.

Recommended by us: A Cosmic Quest for Dark Matter

In the following I attached an article appeared two days ago in The Wall Street Journal about the DarkSide-50 experiment located in the Gran Sasso National Laboratory, in which I am deeply involved since I am a member of the collaboration. I was there in those days and for this reason I know also some funny behind the scenes :)

By the way, I was lucky enough to see even more snow than that you see at the beginning of the video, thanks to a big snow storm that happened just a day after the realization of the following interview.

I have attached also some pictures of my stay during the DarkSide General meeting.

Enjoy the read!

“

A Cosmic Quest for Dark Matter 

Scientists are hunting one of the biggest prizes in physics: tiny particles called wimps that could unlock some of the universe’s oldest secrets

By GAUTAM NAIK
Feb. 13, 2015 1:32 pm E.T.

A mile under Italy's Gran Sasso mountain, scientists are seeking one of the smallest objects in the universe—and one of the most biggest prizes in physics: a wimp.

A wimp—a weakly interacting massive particle—is thought to be the stuff of dark matter, an invisible substance that makes up about a quarter of the universe but has never been seen by humans.

Gravity is the force that holds things together, and the vast majority of it emanates from dark matter. Ever since the big bang, this mystery material has been the universe’s prime architect, giving it shape and structure. Without dark matter, there would be no galaxies, no stars, no planets. Solving its mystery is crucial to understanding what the universe is made of.

Two Supposedly Fun Things I'll Never Do Again

Writing a review is like pregnancy (as far as I can imagine being pregnant and with due respect to real mothers...), one starts super-excited, then begins to realize the initial expectations were too optimistic and that the entire experience is going to be much tougher than originally expected; and while the "baby" is growing, everything becomes tougher and tougher, to the point that one starts looking forward to the delivery (and THAT is probably the toughest part).

This is why finishing two reviews (here and here) in the same week is pretty much like having a twin childbirth, and now I feel like one of those exhausted mothers who stares at their babies with extreme joy.

For those who missed the reference in the title, one of the best books ever..nothing less than a must-read! 

The first work is an overview on superradiance. [If you are curious about what superradiance is... well, read the book! Meanwhile, in very few words superradiance is a broad class of phenomena related to energy amplification in dissapative systems. Because of dissipation, in special kinematic configurations the energy stored in some body/medium can be transferred to another body or to radiation, thus producing a sort of amplifier].

The Century of Strong Gravity

The following is a popular science article that Richard, Vitor and I have written for the IST Physics Magazine "Pulsar" (here is the Facebook page) and that will also appear in the Portuguese Physics Magazine "Gazeta de Fisica". A pdf version is available here (in English), and here (in Portuguese).

1. One Hundred Years of Gravity

The latest Christopher Nolan's movie, Interstellar, is about a future human civilization able to undertake cosmic travels to black holes using special shortcuts, ``wormholes''. Science-fiction as it might seem, Interstellar screenplayers --who happen to be the Nolan brothers-- have worked side by side with Kip Thorne, a professor of Theoretical Physics at the California Institute of Technology and one of the fathers of modern General Relativity, the theory that explains what wormholes and black holes are and how they form in the Universe.

Thorne's contribution is to ensure that the movie --starring Matthew McConaughey and Anne Hathaway among others-- doesn't contain scenes that would make Albert Einstein cringe.
Does this mean that travel agencies are about to sell (roundtrip!) tickets to a black hole? Not quite, but in a few years from now, theoretical physicists and astronomers will be able to study them as never before. The scientific payoff of these studies will largely overcome Interstellar's box-office, with all due respect to Mr. Nolan!