Dr Roberto Trotta

There is no question that there is an unseen world. 
The problem is, how far is it from midtown and how late is it open? 
 -- Woody Allen

I'm a theoretical cosmologist in the Astrophysics Group of Imperial College London, where I am a lecturer in astrophysics. I am a science communicator and I take part in numerous public engagement with science activities, from science festivals to radio broadcasts. I also offer statistical consultancy and custom-made data analysis solutions, as well as training, for a broad variety of clients. I work as a scientific consultant with museums, writers, film makers and artists, providing the help and support they need to make their artistic creations scientifically sound. 

Please see my LinkedIn profile for further information on my professional activities. 

My research in cosmology is about analysing, interpreting and making sense of cosmological observations, in order to learn more about the properties and nature of dark matter and dark energy. I'm also interested in the early Universe and in developing connections between cosmology and particle physics. The goal is to learn more about the history and nature of the Universe, by using cosmology as a Universe-sized laboratory for particle and high energy physics.

And here is a perhaps less technical description of my job, which uses only the most used ten hundred words in English:

I study tiny bits of matter that are all around us but that we can not see, which we call dark matter. We know dark matter is out there because it changes the way other big far away things move, such as stars, and star groups. We want to understand what dark matter is made of because it could tell us about where everything around us came from and what will happen next. 

 

To study dark matter, people like me use big things that have taken lots of money, thought and people to build. Some of those things fly way above us. Some are deep inside the ground. Some are large rings that make tiny pieces of normal matter kiss each other as they fly around very, very fast - almost as fast as light. We hope that we can hear the whisper of dark matter if we listen very carefully. 

We take all the whispers from all the listening things and we put them together in our computers. We use big computers to do this, as there are lots and lots of tiny whispers we need to look at. 

I go to places all over the world to talk to other people like me, as together we can think better and work faster. Together, perhaps we can even find new, better ways to listen to dark matter. Most of them are good people, and after we talked we go out and have a drink and talk some more.        

Between 2005 and 2008 I have been the Lockyer Research Fellow of the Royal Astronomical Society at the Astrophysics Department of Oxford University. I've also been a Junior Fellow of St Anne's College. You can find more info about my academic background here. Or if you are into communication of science, then check out my outreach page.

What's new in the Universe? 

(Last updated Apr 2013)

100 seconds physics 

 

Physics World is asking scientists to take a complex idea and explain it in 100 seconds or less using only a white board. Here is my take! 

 

What is the anthropic principle? 

 

How do we know that the Universe is flat? 

SCIENCE AND FILM/THE THEORY OF EVERYTHING

 

I had the pleasure to act as scientific advisor for a short, sponsored movie on... cosmology and love. It's a new Theory of Everything. It does sound an unlikely mix, but if you think about it, love is all-pervasive, just as dark matter and dark energy are. But judge for yourselves: 

 

 

And here is a review by Matin Durrani of Physics World: "If you think that sounds cheesy, well it could have been – in the wrong hands – but I was impressed with the film. It packs in a surprising amount of “real” science, which was accurate too, thanks to Imperial cosmologist Roberto Trotta, who acted as informal script adviser".

 

TEACHING / PHD Projects for 2013 entry 

For details about funding and how to apply, please visit this page.

 

1) Supernova type Ia cosmology

 

Supernovae type Ia (SNIa) are powerful stellar explosions of stars at the end of their lives. Their peculiar characteristic is that they are very bright and almost standard candles - thus suitable to determine distances on cosmological scales. Study of supernovae type Ia has led to the discovery of dark energy (thought to be responsible for the accelerated expansion of the Universe) and has been recognised with the Nobel Prize for Physics 2011. 

 

This project aims at developing, testing and applying novel statistical methods to extract cosmological information from present and upcoming supernova type Ia data. The main goal is to improve on present-day methods to constraint cosmological parameters from light curve observations of SNIa. The project will build on existing multi-level Bayesian hierarchical methods and expand those in various directions, in order to study and understand population-level properties of SNIa and how those impact on (and can be exploited for) determination of cosmological quantities. 

 

This project has a theoretical component, a statistical component and a numerical aspect. Good programming skills are an advantage but not required a priori. It is expected that parts of this project will be carried out in collaboration with members of the Statistics section. Interest in data analysis and coding is mandatory. 

 

2) Direct detection of dark matter and global fits 

 

Identifying the nature of the dark matter (DM) that inhabits the Universe is arguably the most compelling undertaking in astrophysics and particle physics today. Current searches for DM include:

 

- The Large Hadron Collider (LHC) at CERN collides high-energy protons with the aim of discovering new massive particles (such as the recently discovered Higgs boson). A possible explanation for DM is that it is part of a family of yet-undiscovered particles.

 

- Direct detection experiments use underground detectors to measure the recoil energy of DM particles scattering off a target material. Some experiments (DAMA/LIBRA, Cogent, CRESST) have claimed a DM signal, but are contradicted by other data (Xenon100, CDMS).

 

- Indirect detection experiments target the annihilation products of distant DM-DM collisions, such as high-energy photons (gamma rays) and neutrinos, using the space-based Fermi/LAT gamma-ray observatory and neutrino telescopes such as IceCube. 

 

Direct detection experiments are poised to make major discoveries in the next 5 years, when the first generation of ton-scale detectors comes online. This is expected to probe the totality of the favoured region of the DM parameter space for some simple supersymmetric scenarios. 

 

This project aims at developing new methods to extract DM properties from direct detection experiments data, in particular Xenon and, in the future, DARWIN, as well as to understand how astrophysical uncertainties entering in the interpretation can be brought under control. A second strand of the work will involve combining such data into the "global fits" approach, an overarching statistical framework to constrain beyond the Standard Model theories for dark matter using all of the available experimental probes (colliders, direct and indirect detection, as well as cosmology). 

 

This project has a theoretical component, a statistical component and a numerical aspect. Good programming skills are an advantage but not required a priori. Interest in data analysis and coding is mandatory. 

 

3) Cosmology and fundamental physics with the Euclid satellite 

 

Euclid is a European Space Agency mission due to be launched around 2019. Euclid is a satellite equipped with a 1.2 m telescope and three imaging and spectroscopic instruments working in the visible and near-infrared wavelength domains. The main goal of Euclid is to understand the origin of the accelerated expansion of the Universe. Euclid will explore the expansion history of the Universe and the evolution of cosmic structures by measuring shapes and redshifts of galaxies as well as the distribution of clusters of galaxies over a large fraction of the sky. It will produce an unprecedented data set - the plan is to image a billion of galaxies and measure nearly 100 millions of galaxy redshifts. This will allow cosmologists to crack the mysteries of dark energy. 

 

This project will study the capabilities of Euclid to constrain dark energy properties using multiple probes (lensing, clusters and supernovae). It will produce detailed forecasts for the measurements of fundamental physics quantities achievable with Euclid, and will develop a data analysis pipeline in view of the science extraction from Euclid. Methods and tools developed in this context will also be tested and applied on current and upcoming data sets, such as SDSS and DES. 

 

This project has a theoretical component, a statistical component and a numerical aspect. Good programming skills are an advantage but not required a priori. Interest in data analysis and coding is mandatory. 

 

 

COSMOSTATS13 / Statistical challenges from large data sets in cosmology and particle physics, Banff, Canada, March 17th-22nd 2013

 

In 2013 both the cosmic microwave background satellite Planck and the Large Hadron Collider at CERN are expected to report first science results, which makes the proposed workshop highly timely. This conference therefore aims to leverage and combine the existing knowledge and to catalyze the building up of a new, integrated framework to help us along the path of understanding our world, what it is made of and where it came from.

 

The purpose of the this conference is to bring together cosmologists, statisticians, experts in data mining and scientists from other fields, especially from particle physics (both phenomenologists and experimentalists), in order to provide a framework for a fruitful cross-fertilization of ideas across disciplines. The main objective is to foster the exchange of ideas and concepts both within the respective research directions as well as in between them. This will involve critical assessment of algorithms and software packages developed in the 'other camp' which may not be known to workers outside the respective specialities. Ample time will be devoted to informal discussions, in order to leave room for the development of collaborations and the exchange of ideas.

 

Participation to this Banff workshop is on invitation only.

HUNTING FOR DARK MATTER / KITP Programme, Santa Barbara, Spring 2013

 

Thanks to fast-paced experimental developments, the field of dark matter research is flourishing and may well lead, in the next few years, to the identification of the underlying fundamental particle(s). There is an emerging consensus that a robust and accurate identification of dark matter will probably require the combination of multiple probes. Even if signatures of new physics beyond the SM are identified at the LHC in the next couple of years, delineating the ensuing implications for the nature of dark matter and for physics beyond the Standard Model might prove to be a much harder task using LHC data alone. This is where astrophysical and cosmological observations may prove to be invaluable: for example, direct detection experiments would be able to provide a much tighter measurement of the dark matter particle mass, while tight constraints on its relic abundance coming from the Planck satellite will help determine its properties. Furthermore, the comparison of constraints from different measurements will be fundamental to assess the consistency of a given theory.

 

This program hinges on the realization that the characterization of the particle making up the cosmological dark matter will require an approach based on the combination of multiple probes: colliders (LHC), cosmology (WMAP, Planck, and other CMB and large scale structure determinations of the relic dark matter abundance), direct detection experiments (CDMS, XENON, Zeplin, WARP, ArDM and others) and indirect detection experiments - such as gamma ray detectors (Fermi from space and Cherenkov Telescopes from the ground), neutrino telescopes (IceCube, Antares), antimatter detectors (Pamela, AMS-02), as well as X-ray and radio facilities. All these probes are sensitive to different  particle properties, providing a holistic and multi-pronged approach to dark matter science.

 

Further information and how to apply for this residential programme. 

ASTROSTATISTICS / ICIC Inaugural workshop, London, Aug 20-21st 2012 

 

The Imperial Centre for Inference and Cosmology (ICIC) is a newly formed centre that aims to address the statistical challenges posed by massive and complex data streams in astrophysics, astroparticle physics, and cosmology.  It is a collaborative effort between the Astrophysics Group and the Statistics Section at Imperial College London. The ICIC will host its Inaugural Workshop on 20 and 21 August 2012.

 

COMMUNICATION OF SCIENCE / Cosmic sound

 

The sounds of space: hearing the end of the universe.

 

I am part of a podcast by Adam Smith exploring how we can use hearing to experience the cosmos in a completely new dimension. 

 

 

DarkAttack2012 / Ascona, Switzerland, 15-20 July 2012

 

For the past 80 years, astronomers have been wondering what exactly is responsible for the distribution of galaxies in the sky, and what drives the way they move about each other. Gravity as we know it, cannot explain this; not if visible matter is all there is to the Universe. Today, particle physics might be on the verge of finally unraveling this mystery.

 

Many physicists believe that the explanation for the behavior and structure of galaxies lies in the infinitely small scales of subatomic particle physics. A new type of particle, unlike any of the particles we know about, which does not emit nor absorb light, could be effectively invisible to the astronomers' instruments, yet make up most of the mass of the Universe. The detection of this new particle would shake up our understanding of the basics building blocks of the cosmos. The hunt for "Dark Matter" is on.

 

The Large Hadron Collider at CERN has begun testing some of the theories about Dark Matter. By colliding beams of particles at very high energy, this machine will re-create conditions that existed a fraction of a second after the Big Bang. Scientists believe that in this process Dark Matter particles will be produced. At the same time, other experiments (such as underground Dark Matter detector and satellites observing debris produced by Dark Matter collisions in the Universe) are being used to characterize the nature of Dark Matter, and to test whether its properties can explain the astronomers' puzzling observations.

 

This conference will bring together scientists looking for Dark Matter in particle physics, astrophysics and cosmology, in order to facilitate their collaboration and promote the exchange of new ideas across the different communities. This stimulating meeting will promote the development of a new, truly global approach to the discovery and characterization of Dark Matter, and help scientists to join forces in tackling one of the biggest unsolved mysteries of fundamental physics.

 

Talks are now online here. 

ADVANCED STATISTICS LECTURES / Copenhagen, Nov 14th-18th 2011

This elite PhD course in Copenhagen will provide the students with a wide overview of the most advanced statistical methods used for data analysis.

 

Data from experiments in high energy physics and observations in astrophysics demand nowadays a highly sophisticated statistical treatment. By inviting experts from both areas, we provide the students with the widest overview of the most advanced statistical methods. The course will cover the fundamental concepts of modern statistical data analysis, including examples derived from the two areas of science mentioned. The course is well suited and relevant for PhD students from a wide range of fields in Science, beyond the ones mentioned. The course will consist of lectures and practical problem- solving sessions (both calculations and computer exercises) and will last 5 full days.

Bayesian Methods in Cosmology: The Book 

In recent years cosmologists have advanced from largely qualitative models of the Universe to precision modelling using Bayesian methods, in order to determine the properties of the Universe to high accuracy. This timely book is the only comprehensive introduction to the use of Bayesian methods in cosmological studies, and is an essential reference for graduate students and researchers in cosmology, astrophysics and applied statistics. The first part of the book focuses on methodology, setting the basic foundations and giving a detailed description of techniques. It covers topics including the estimation of parameters, Bayesian model comparison, and separation of signals. The second part explores a diverse range of applications, from the detection of astronomical sources (including through gravitational waves), to cosmic microwave background analysis and the quantification and classification of galaxy properties. Contributions from 24 highly regarded cosmologists and statisticians make this an authoritative guide to the subject.

Buy it here.

BIG QUESTIONS DEBATE SERIES / Imperial College London 

Imperial College London Astrophysics presents a new series of debates entitled The Big Questions on topical themes in modern astrophysics and cosmology. In each debate, a member of the Astrophysics Group will discuss one of the big questions raised by cutting-edge research with a guest. The debates are aimed at the general public, who will have the opportunity to ask questions in what will be a lively and interactive discussion.

• 21 January 2010, 7-9pm: The Arabic roots of modern astronomy. Dr Rim Turkmani and Professor Jim Al-Khalili OBE
• 12 November 2009, 6.30-8.30pm: Human spaceflight: Science or spectacle? Dr David Clements vs Dr Ian Crawford
• 15 September, 6-8pm: Universe or Multiverse? Dr Roberto Trotta vs Prof. Bernard Carr
• 21 July 2009, 6-8pm: The fate of the Universe: does dark energy really exist? Prof. Andrew Jaffe vs Prof. Subir Sarkar
• 18 June 2009, 6-8pm: The origin of the Universe. Prof. Michael Rowan-Robinson vs Rev. Dr John Polkinghorne, KBE, FRS

COSMOSTATS09 / Ascona, Switzerland, July 26th-31st 2009 

In the last ten years, a wealth of observational data has revolutionized cosmology. The purpose of this workshop is to bring together world-class leading figures in cosmology, particle physics and from the statistical community in order to exchange knowledge and experience in dealing with large and complex data sets, and to meet the challenge of upcoming large cosmological surveys.

Furthermore, CosmoStats09 will host the GRavitational lEnsing Accuracy Testing 2008 (GREAT08) Challenge Final Workshop. 

Conference webpage

BBC RADIO 3 / Future Generation Thinkers 

You can listen here to a BBC Radio 3's "Future Generation Thinkers" programme (which aired on Nov 7th 2008) where I discuss dark energy and the place of humankind in the cosmos.

MICHELSON LECTURES / CWRU Michelson Prize Lectures 

In May 2008 I gave the 2008 Michelson Prize Lectures series at case Western Reserve University (Cleveland). You can find the pdf's of the talks below. 
May 5th: Bayes in the sky - Advanced statistical tools for cosmology 
May 6th: Probing dark energy with cosmology 
May 7th: Precision cosmology for the 21st century 
May 9th: Astrophysical probes of dark matter 

REVIEW ARTICLE / Bayes in the sky: Bayesian inference and model selection in cosmology 

An invited review for Contemporary Physics

Abstract: The application of Bayesian methods in cosmology and astrophysics has flourished over the past decade, spurred by data sets of increasing size and complexity. In many respects, Bayesian methods have proven to be vastly superior to more traditional statistical tools, offering the advantage of higher efficiency and of a consistent conceptual basis for dealing with the problem of induction in the presence of uncertainty. This trend is likely to continue in the future, when the way we collect, manipulate and analyse observations and compare them with theoretical models will assume an even more central role in cosmology. 

This review is an introduction to Bayesian methods in cosmology and astrophysics and recent results in the field. I first present Bayesian probability theory and its conceptual underpinnings, Bayes' Theorem and the role of priors. I discuss the problem of parameter inference and its general solution, along with numerical techniques such as Monte Carlo Markov Chain methods. I then review the theory and application of Bayesian model comparison, discussing the notions of Bayesian evidence and effective model complexity, and how to compute and interpret those quantities. Recent developments in cosmological parameter extraction and Bayesian cosmological model building are summarized, highlighting the challenges that lie ahead.

Go to the paper

SUPERSYMMETRY / SuperBayeS package

SuperBayeS is a software for fast and efficient Markov Chain Monte Carlo sampling of supersymmetric theories. It allows to explore multidimensional SUSY parameter spaces and to compare SUSY prediction with observable quantities, including sparticle masses, dark matter abundance, direct and indirect detection quantities and much more. The current release implements an even more efficient scanning technique, called MultiNest.

SuperBayeS me!

Nature feature covering some of the results

PHYSICS AND PHILOSOPHY / Probing the arche-fossil

A conversation with the philosophical magazine COLLAPSE, centering around dark matter and the ontological perspective coming from the empirical study of `ancestral phenomena' in the history of the Universe.