Highlights of 2016 now free to read 

By Clifford Will.


Clifford Will

Clifford Will is the Editor-in-Chief of Classical and Quantum Gravity, Distinguished Professor of Physics at the University of Florida, Chercheur Associé at the Institut d’Astrophysique de Paris, and James McDonnell Professor of Space Sciences Emeritus at Washington University in St. Louis.

I am delighted to present the CQG Highlights of 2016 which are now free to read.  This prestigious annual collection is selected by the editorial board and includes notable papers on gravitational waves, black holes, general relativity, cosmology, quantum gravity and more.

As well as being free to read on the web, each paper is promoted by the journal in a number of campaigns.  Watch for the CQG Highlights brochure at your next conference.

CQG Highlights remains one of CQG’s most popular promotions.  Don’t miss your chance to be included in CQG Highlights of 2017 by publishing your next great paper in CQG.

 

 

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Want to crush a singularity? First make it strong and then …

by Parampreet Singh.


Parampreet Singh

Parampreet Singh with a young student who often asks him the most difficult and so far unanswerable questions on the resolution of singularities. Dr Parampreet Singh is Associate Professor at Department of Physics and Astronomy at Louisiana State University.

Einstein’s theory of classical general relativity breaks down when spacetime curvature
becomes extremely large near the singularities. To answer the fundamental questions
about the origin of our Universe or what happens at the central singularity of the black holes thus lies beyond the validity of Einstein’s theory. Our research deals with discovering the framework which guarantees resolution of singularities.

It has been long expected that quantum gravitational effects tame the classical singularities leading to insights on the above questions. A final theory of quantum gravity is not yet there but the underlying techniques can be used to understand whether quantum gravitational effects resolve cosmological and black hole singularities. Our goal is Continue reading

Tilting laser beams in LISA

by Michael Tröbs.


Michael Troebs in the lab

Michael Tröbs in the lab. Michael Tröbs is an experimental physicist at Max Planck Institute for Gravitational Physics (AEI). The LISA optical bench test bed was built in collaboration with Airbus DS and University of Glasgow. At AEI Michael is responsible for the project.

A testbed to experimentally investigate tilt-to-length coupling for LISA, a gravitational-wave detector in space.

The planned space-based gravitational-wave detector LISA will consist of three satellites in a triangle with million kilometer long laser arms. This constellation will orbit the Sun, following the Earth. LISA is expected to be laser shot-noise limited in its most sensitive frequency band (in the Millihertz range). The second largest contribution to the noise budget is the coupling from laser beam tilt to the interferometric length measurement, which we will call tilt-to-length (TTL) coupling in the following.

How does tilt-to-length coupling come about? Continue reading

Setting space on fire

by Yasaman K. Yazdi and Niayesh Afshordi.


Niayesh Afshordi and Yasaman Yazdi discover that firewalls have consequences

Niayesh Afshordi and Yasaman Yazdi discover that firewalls have consequences. Yasaman K. Yazdi is a PhD candidate at the University of Waterloo and the Perimeter Institute for Theoretical Physics. Niayesh Afshordi is an associate professor at the University of Waterloo and the Perimeter Institute for Theoretical Physics.

Thought experiments highlight the edge of our understanding of our theories.  Sometimes, however, we can get so caught up in heated debates about the solution to a thought experiment, that we may forget that we are talking about physical objects, and that an actual experiment or observation may give the answer.  In this Insight we discuss a proposed solution to the black hole information puzzle, and a possible observational signal that might confirm it.

 

The black hole information puzzle and a potential solution

The black hole information loss problem is a decades old problem that highlights the tensions between some of the pillars of modern theoretical physics. It has evolved from being Continue reading

Happy new year!

By Clifford Will.


Clifford Will

Clifford Will is the Editor-in-Chief of Classical and Quantum Gravity, Distinguished Professor of Physics at the University of Florida, Chercheur Associé at the Institut d’Astrophysique de Paris, and James McDonnell Professor of Space Sciences Emeritus at Washington University in St. Louis.

What a year for gravitational physics!  In February, the LIGO and Virgo Collaborations (LVC) announced the first detection of gravitational waves.  The MICROSCOPE satellite test of the equivalence principle took to the skies in April and, in June, LISA Pathfinder surpassed all expectations in demonstrating the key technologies required to detect gravitational waves in space.  As if all that wasn’t enough, the LVC announced a second detection of a binary black hole merger later that month.  By September, NASA revealed that it would rejoin ESA in funding the LISA mission with a view to launching a 3-armed space interferometer by 2030.  Could we have wished for more?

CQG launched a focus issue on the topic of gravitational waves in 2016 edited by Peter Shawhan and Deirdre Shoemaker.  You can submit your next great paper on gravitational waves to the issue which is currently open to submissions and will be promoted in a number of channels throughout 2017.  All submissions will be subject to CQG’s usual high standard of peer review.

To keep track of the latest CQG publications and news in 2017, you can follow the CQG+ blog or follow the journal on social media (Twitter, Facebook).

I want to express my appreciation to all CQG authors, referees and readers who supported the journal in 2016.  I particularly wish to thank the journal’s Editorial Board Members and Advisory Panel Members who assist in directing the strategy of the journal and who oversee CQG’s peer review.  I also welcome new Board and Panel members to CQG. I look forward to working with all of you in the coming year.

With the LIGO detectors’ second observation run underway, I am certain that we have more to look forward to in 2017. Continue reading

Propagation in the absence of classical spacetime

Written by Madhavan Varadarajan


madhavan-varadarajan

The author’s research group busy at work. Madhavan Varadarajan is a Professor at the Raman Research Institute in Bangalore, India.

At the Planck scale of 10−33cm, where the very notion of classical spacetime ceases to exist due to large quantum fluctuations of spacetime geometry, can meaning be given to the notion of “causality”? We are interested in this question in the context of Loop Quantum Gravity (LQG).

The basic quantum states of LQG are labelled by graphs. Each such state describes discrete one dimensional excitations of spatial geometry along the edges of its graph label. These ‘graphical’ states provide the Continue reading

OK, so what happens now?

Written by Michael Coughlin


The future of gravitational-wave astronomy after the first detection

Michael Coughlin is currently a post-doctoral fellow at Harvard University with Prof. Christopher Stubbs. In September 2016, he successfully defended his Harvard Physics PhD, titled "Gravitational-wave astronomy in the LSST era". He began researching gravitational waves with LIGO over eight years ago as a college freshman at Carleton College in Northfield, MN and it was very exciting for him to be part of LIGO’S historical confirmation in February 2016. At Harvard, he added the Large Synoptic Survey Telescope (LSST), Pan-STARRS, and ATLAS to his research areas, including designing and building a prototype calibration system, which he nicknamed "CaBumP". Coughlin dances on the Harvard ballroom dance team and enjoys the chaos of teaching 3rd and 4th graders in an after-school math and science program at a local elementary school.

Michael Coughlin is currently a post-doctoral fellow at Harvard University with Prof. Christopher Stubbs. In September 2016, he successfully defended his physics PhD at Harvard, titled “Gravitational-wave astronomy in the LSST era”. He began researching gravitational waves with LIGO over eight years ago as a college freshman at Carleton College in Northfield, MN and it was very exciting for him to be part of LIGO’s historical confirmation in February 2016. At Harvard, he added the Large Synoptic Survey Telescope (LSST), Pan-STARRS, and ATLAS to his research areas, including designing and building a prototype calibration system, which he nicknamed “CaBumP”.

Since LIGO announced the detection of gravitational waves from binary black hole mergers in its first observing run [1-2], the most common question I have received is “What was it like to be part of such a historic scientific discovery?” The second most common question has been: “So what happens now?” The answer is a lot of stuff! Here I’ll focus on three main goals:

  1. Using LIGO to detect other sources of gravitational-waves
  2. Improving the gravitational-wave detectors in order to probe farther into the cosmos
  3. Electromagnetic follow-up of gravitational-wave events with telescopes to get a more complete picture

What else does nature have in store for us?

The detection of gravitational waves from binary black hole mergers has been incredibly exciting, and we look forward to the detection of more such systems. Of course, there are many other sources (pulsars, supernovae, binary neutron stars, etc.) that we hope to detect as well. As a member of the group in LIGO searching for a stochastic background of gravitational waves, I am particularly interested in the processes that could create such a signal. This includes backgrounds from compact binary coalescences, pulsars, magnetars, or core-collapse supernovae. A cosmological background (such as from inflation!) could be generated by various physical processes in the early universe. In particular, with the recent discovery of binary black-hole mergers, there is a really good chance of observing a stochastic gravitational-wave background from these systems [3].

There are other sources that are likely to produce long-lived transients, including emission from rotational instabilities in proto-neutron stars and black-hole accretion disk instabilities. There is ongoing significant effort to improve Continue reading

LIGO’s gravitational wave detection is Physics World 2016 Breakthrough of the Year

by Clifford M Will.


Physics World breakthrough of the year prize

The Physics World 2016 Breakthrough of the Year goes to the LIGO Scientific Collaboration for their revolutionary, first ever direct observations of gravitational waves.

Long awaited direct detection of Einstein’s gravitational-waves tops Physics World’s list of the 10 key breakthroughs in physics in 2016

It give me great pleasure to report that the LIGO Scientific Collaboration are to receive Physics World’s Breakthrough of the year award.  At the end of every year, the Physics World editorial team reveals what it believes to be the top 10 research breakthroughs for the past year and one of these is selected to be the Physics World Breakthrough of the year.

In recognition of this achievement, the Physics World team have created a short documentary movie with the assistance of members of the LIGO collaboration from Cardiff University.

The video features Samantha Usman, who recently wrote an excellent CQG+ entry about the discovery.
Continue reading

“There’s no way it’s real”

Written by Samantha Usman, who is currently pursuing an MPhil at Cardiff University, UK under the supervision of Prof. Stephen Fairhurst. She graduated in May 2016 with a BS in Mathematics and Physics at Syracuse University. While at Syracuse, Usman worked with Prof. Duncan Brown on improving LIGO’s sensitivity to gravitational waves from binary star systems. In her spare time, Usman trains in Brazilian jiu jitsu and Muay Thai kickboxing and enjoys walks with her Australian Shepherd, Marble.


The discovery of gravitational waves from an undergraduate’s perspective

Author Samantha Usman training for competition in Brazilian jiu jitsu.

Author Samantha Usman training for competition in Brazilian jiu jitsu.

The first time I learned LIGO might have detected a gravitational wave, I was listening in on a conference call on September 16, 2015. Two days earlier, ripples in the fabric of space from massive black holes crashing into each other at half the speed of light had passed through the Earth. The LIGO detectors picked up these faint changes in the length of space, but they pick up all sorts of extra noise that you’d never expect; how could we be sure this was really a gravitational wave?

On September 16th, I was an undergraduate starting my senior year at Syracuse University. I’d been doing LIGO research with my advisor, Prof. Duncan Brown, for almost two and a half years. Since LIGO had yet to start an observing run, my research had been focused on testing improvements to the codes that we use to search for gravitational waves. I’d been told in those two and a half years that it would take a few years to get our detectors to design sensitivity and not to expect a detection until I was well into graduate school.

So when I sat in my boss’ office listening to a colleague in Germany say he thought we’d really seen something, I rolled my eyes and muttered, “There’s no way it’s real.” I was convinced people were Continue reading

The possible emptiness of a final theory

Written by Jesper Møller Grimstrup, an independent danish theoretical physicist. He has collaborated with the mathematician Johannes Aastrup for more than a decade developing what they now call quantum holonomy theory. His present research is financed by an Indiegogo crowdfunding campaign (still open). Find more information on www.jespergrimstrup.org.


Could the laws of nature originate from a principle, that borders a triviality?

Does a final theory that cannot be explained by yet another, deeper theory, exist? What could such a theory possibly look like — and what might we learn from it?

J M Grimstrup

Jesper Møller Grimstrup

These are the million dollar questions. Will the ladder of scientific explanations that take us from biology to chemistry and down through atomic, nuclear and particle physics, end somewhere? Will we one day reach a point where it is clear that it is no longer possible to dig deeper into the fabric of reality? Will we reach the bottom?

Together with the mathematician Johannes Aastrup I have developed a new approach to this question. Our theory  we call it quantum holonomy theory is based on an elementary algebra, that essentially encodes how stuff is moved around in a three-dimensional space.

img_0192This algebra, which we call the quantum holonomy-diffeomorphism (QHD) algebra [1], is interesting for two reasons Continue reading