Highlights of 2015

Featured

Clifford Will

Clifford Will is the Editor-in-Chief of Classical and Quantum Gravity

The latest CQG Highlights are now available to view.  These papers represent the most interesting and important work published in CQG in 2015.  They were selected by the CQG Editorial Board and approved at CQG’s recent annual board meeting in London.

This year marks a break from the process used in past years.  CQG Highlights used to be Continue reading

CQG+ Insight: Playing with the building blocks of space

Daniele Oriti is a senior researcher and group leader at the Max Planck Institute of Gravitational Physics (Albert Einstein Institute) in Potsdam, Germany, EU. Born and educated in Italy, got a PhD from the University of Cambridge, UK, and held research position at Cambridge, Utrecht University, The Netherlands, and the Perimeter Institute for Theoretical Physics, Canada. He lives and plays with physics, philosophy, and the rest of the universe, in Berlin, with his wife and son.

In this Insight, the fundamental building blocks of quantum spacetime are described by peculiar quantum field theories, then assembled to form continuum geometries, to explain the dynamics of the early universe and black holes from first principles.


Daniele Oriti

Daniele Oriti is a senior researcher and group leader at the Max Planck Institute of Gravitational Physics (Albert Einstein Institute) in Potsdam, Germany.

What is space made of? What are its fundamental building blocks? Can we play with them? And what can we make out of them?

If these sound like a bunch of childish questions, it is because theoretical physicists manage to remain the children they once were for some time longer; and to make a living by asking childish questions and playing with the mathematical toys that accompany them.

The serious, only-for-adults part of the story is that we have learned from General Relativity that space and time are physical entities, so it is actually reasonable to ask if they have a microstructure. Moreover, we have several hints (e.g from black hole physics and cosmological singularities) that the continuum geometric description of spacetime on which General Relativity is based should give way to one in terms of discrete, non-geometric degrees of freedom. This is the goal of quantum gravity: a quantum theory of the microstructure of space and time, to understand their discrete non-geometric building blocks and how the usual continuum description arises in some approximation.

Modern approaches to quantum gravity are achieving just that. Loop quantum gravity, for example, identifies spin networks as the structures underlying space (and their interaction processes, spin foams, as underlying spacetime): purely combinatorial objects, graphs, labeled by algebraic data, i.e. group representations. The continuum world populated by Continue reading

CQG+ Insight: Chiral Gravity

by Kirill Krasnov


Kirill Krasnov

Kirill Krasnov, Professor of Mathematical Physics, University of Nottingham. Pictured here visiting Newstead Abbey, Nottinghamshire

We seem to live in four space-time dimensions, and so should take the structures available in this number of dimensions seriously. One of these is chirality, see below for clarifications on my usage of this term. Related to chirality, there is a remarkable phenomenon occurring in General Relativity (GR) in four space-time dimensions. This phenomenon is so stunning that I would like to refer to it as the chiral miracle. It is well-known to experts. Still, even after almost 40 years after it had appeared in the literature, it has not become part of the background of all GR practitioners. I would like to use this CQG+ insight format to try to rectify this.

I start by reviewing the notion of chirality in four space-time dimensions. I then describe the “chiral miracle” that allows for chiral description(s) of gravity in Continue reading

A Study of Time Delay from Different Time Zones

Netta Engelhardt (University of California, Santa Barbara) and Sebastian Fischetti (Imperial College) gave us an insight into their communication methods whilst collaborating for their research paper recently published in CQG.


Snetta

On a dark London evening and a sunny California day — January 19, 2016, to be precise — Netta sent Sebastian a Skype message:

Image_1

So began a new project for this dynamic duo, published recently in CQG. Unlike our previous project, this one presented a new challenge (with which researchers are all too familiar): we were separated by an eight-hour time difference. Thus began a three-way collaboration: Netta, Sebastian, and Skype (with the third member being the least cooperative).

The process began Continue reading

Inspiral into Gargantua; where science meets science-fiction

Niels Warburton from the Massachusetts Institute of Technology shares an insight into his latest work with Sam Gralla and Scott Hughes published in Classical and Quantum Gravity.


Niels Warburton

Niels Warburton is a Marie Curie postdoctoral fellow currently working at the Kavli Institute for Astrophysics and Space Research at the Massachusetts Institute of Technology. He works on calculating gravitational waveforms from the capture of compact objects by black holes ranging from hundreds to millions of solar masses. Outside of research he often encounters other types of waves on the waters around Boston where he is a keen sailor. Niels co-authored the article recently published in CQG with Sam Gralla of the University of Arizona and Scott Hughes at the Massachusetts Institute of Technology.

The first merging black holes recently detected by LIGO were strange objects indeed. Torturing reality so that even light cannot escape from their interiors, as they whirled around each other at over half the speed of light, the disturbances they induced in space and time propagated outwards as gravitational waves. The measured characteristic chirp, an upsweep in frequency and amplitude of the waves, signaled that the two black holes had merged into a single, larger black hole. Amazingly, though this remnant was more than sixty times as massive as our sun it could be described by just two numbers – its mass and its spin. This is an unusual property for any macroscopic object as they usually require Continue reading

Crashing Neutron Stars on the Italian Dolomites

Bruno Giacomazzo, Andrea Endrizzi, Riccardo Ciolfi, Wolfgang Kastaun share details of their latest research published in the CQG focus issue: Rattle and shine: the signals from compact binary mergers.


Bruno Giacomazzo, Andrea Endrizzi, Riccardo Ciolfi, Wolfgang Kastaun

From left to right: Bruno Giacomazzo, Andrea Endrizzi, Riccardo Ciolfi, Wolfgang Kastaun.
About the authors: Bruno Giacomazzo is an assistant professor at the Department of Physics of the University of Trento and the Principal Investigator of the numerical relativity group there. The group is currently composed of two postdocs (Riccardo Ciolfi and Wolfgang Kastaun) and two PhD students (Andrea Endrizzi and Takumu Kawamura).

At the end of 2013, after seven years spent abroad (between Germany and the USA),  Bruno Giacomazzo came back to Italy for an assistant professor position at the University of Trento in Northern Italy. He used to come to this region when he was a kid to hike or ski on the mountains, but he never thought he would have come back here to study neutron star mergers.

Thanks to financial support from MIUR (Ministry of Education, University, and Research) he was able to attract Riccardo Ciolfi and Wolfgang Kastaun from abroad and to create with them the first numerical relativity group in this part of Italy. Thanks to Continue reading

Coating thermal noise research for LIGO-India

Maya Kinley-Hanlon — an undergraduate student in the Department of Physics at the American University in Washington, DC — tells us more about her group’s work on optical coatings for LIGO-India.


Maya Kinley-Hanlon is a PhD candidate in the Department of Physics at the American University in Washington, DC.

Maya Kinley-Hanlon is an undergraduate student in the Department of Physics at the American University in Washington, DC.

Our CQG paper describes measurements of optical coatings on silica glass substrates to determine if storing the LIGO optics for many years before installing them in India will cause any problems.  The coatings are known to be fairly robust in their optical properties, but as is always the case with LIGO optics, no one has any real idea about the thermal noise properties.  Since thermal noise from the coatings is expected to be a limiting noise source in the LIGO detectors, knowing if storing the optics could cause a problem is an important issue.  I worked on this Continue reading

Waves, stability and exotic black holes

Jake Dunn and Dr Claude Warnick from the Pure Mathematics group at Imperial College, London tell us all about their research using the Klein-Gordon equation to study black holes.


Jake Dunn

Jake Dunn is a PhD student at Imperial College, London.
Claude Warnick is a Lecturer in Pure Mathematics at Imperial College, London.

There is a long standing conjecture in the theory of general relativity that the final state of the gravitational collapse of a star should be a stationary black hole modelled by the Kerr solution. To this date there remains no mathematical proof of this statement, and it seems that we may have to wait a while before this result can be established. Even the simpler problem of black hole stability is a considerable mathematical challenge.

We may think of a stationary black hole as Continue reading

What does numerical relativity have to do with detecting gravitational waves?


Heather Fong — a PhD candidate in Physics at the University of Toronto, who also loves travelling and gastronomy photography — gives us an insight into her group’s work on using numerical relativity simulations for the detection of gravitational waves.


heatherfong

Heather Fong, a PhD candidate in Physics at the University of Toronto.

Answer: quite a lot! Numerical relativity (NR) provides the most accurate solutions to the binary black hole problem, which is exactly the type of source LIGO wants to detect — and has succeeded at! Most of the time, LIGO’s data streams are overwhelmed with noise, and so we use a technique called matched-filtering to identify gravitational-wave signals. Finding and characterizing signals requires a massive amount of accurate waveforms, and we use semi-analytic waveform models as filters which are built using the results of NR simulations.

Why don’t we use NR alone to identify signals? It certainly would be ideal if the theoretical template waveforms were generated entirely from NR; not only would we be using the most accurate waveforms available, it would also allow us to Continue reading

Fractals and black hole shadows

Jake Shipley and Dr Sam Dolan work in the Particle Astrophysics and Gravitation group at the University of Sheffield, focusing on general relativity, wave propagation and black hole physics. Here they provide us with an insight into their research. 


Jake Shipley

Jake Shipley is a Ph.D student in the School of Mathematics and Statistics at the University of Sheffield. If Jake were a black hole, you would also see a lensed version of Dr Sam Dolan, standing behind the camera.

This has been a “miracle year” for relativity.

LIGO detected gravitational waves. The LISA Pathfinder mission demonstrated near-perfect freefall in space. And the era of gravitational-wave astronomy began in some style.

A century after black holes and gravitational waves were first predicted, we have learnt something truly mind-boggling: When two black holes collide, they shake the fabric of space-time with more power than is radiated by all the stars in the known universe put together!

The “chirps” from distant black hole collisions will travel for millions of years, at the speed of light, to reach our growing network of gravitational-wave detectors on Earth … and one day, out in space.

Next year, attention will turn to the Event Horizon Telescope (EHT): a global network of radio telescopes linked together to form an Earth-sized virtual telescope, using the technique of Very Long Baseline Interferometry. The EHT will Continue reading

Ever think about writing a book?

Adam Day

Contact Adam Day, Executive Editor, Classical and Quantum Gravity with your book proposal (adam.day [at] iop.org).

One of IOP Publishing’s core aims as a society publisher is to communicate physics of the highest quality to the scientific community.

Our new book programme serves the full audience of IOP’s journals.  The focus of this award-winning books initiative is on e-publishing, meaning that authors and readers will benefit from IOP’s ever-evolving digital publishing capabilities, rapid publication times and the enhanced reader experience that users have come to expect from online journal publishing.

Some of the key features of an e-first model include:

  • Flexibility: we can make updates to the books after publication.
  • No DRM. Designed specifically for electronic delivery, IOP ebooks will have no DRM constraints.

Continue reading