Author Archives: Adam Day

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About Adam Day

Adam Day is the former publisher of Classical and Quantum Gravity. His background is mostly in publishing, where he thoroughly enjoyed working with the gravitational physics community. He now works as a Data Scientist for SAGE Publishing.

General Relativity turns 100!

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Clifford M 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.

November 4, 1915 was a Thursday. It was the day that Albert Einstein gave the first of a series of four weekly lectures to the Prussian Academy of Sciences in Berlin. His life was a mess. He was separated from his wife Mileva, who had moved to Zurich taking his sons with her. He was having an affair with his second cousin Elsa. He was working night and day, was barely eating, and was suffering from stomach pains. He had agreed to give these lectures to present his theory of gravity but he still didn’t have it. To make matters worse, David Hilbert was racing to find the field equations first, and Einstein feared he would be beaten. Yet by the third lecture, Continue reading →

Building a practically perfect gyroscope

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Mac Keiser

Mac Keiser was the chief scientist of the Gravity Probe B program. He is now a Senior Research Scientist, Emeritus, at Stanford.

Spherical, electrostatically-supported gyroscopes have been used for navigation for more than 40 years but their accuracy is far from what was needed to measure the effects predicted by general relativity. Fortunately, the accuracy could be significantly improved by reducing the forces required to support the gyroscope, improving the sphericity of the rotor, and increasing the gyroscope spin speed. Operating in a satellite reduces the support forces by a factor of 107, and using one of the gyroscopes as a drag-free sensor brings a further reduction of nearly 104. Improving the sphericity of the rotor further reduces the support-dependent torques but leads to the additional questions about how to spin-up and measure the spin-axis orientation of the rotor. Using a superconducting readout that Continue reading →

Gravity Probe B, the simplest data analysis ever

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John Conklin

John W. Conklin is assistant professor in the University of Florida’s Department of Mechanical and Aerospace Engineering. Photo: Aurora M Agüero

What could be simpler than fitting a straight line to a set of data? The slope of the line is the science result for NASA’s Gravity Probe B experiment, a landmark satellite test of two predictions of general relativity. Prior to launch, the data analysis for GP-B was thought to be straight forward. After precise calibration of the measured data (not as easy as fitting a straight line), the resulting signal should change at a constant rate over time. Our goal was to measure this rate of change, hopefully with an accuracy of 1%.

In the fall of 2005, as the year-long science mission was concluding, the GP-B science team began producing plots of the science data collected from the Earth-orbiting probe.  The figure shows one such plot. The slope of the best-fit straight line to these data is the magnitude of the elusive frame dragging effect, the main science goal of Gravity Probe B. Fear began to set it in. Where was the straight line? Continue reading →

CQG Highlights now live

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Adam Day

Adam Day is the Publisher of Classical and Quantum Gravity and CQG+.  Follow him on Twitter and Facebook.

I am delighted to announce the CQG Highlights of 2014-2015.  The collection is free to read until 31 December 2016.

How are the Highlights selected?

Each summer, the Editorial Board of Classical and Quantum Gravity convene in London for the journal’s annual Editorial Board meeting. In advance of the meeting, Board members submit proposed Highlights published in CQG in the previous 12 months. That list is discussed in the meeting: some papers are added to the list, others removed. Ultimately, the Highlights are approved by the Editor-in-Chief.

It’s a thorough process and the result is perhaps the best recognized collection in gravitational physics.

I would like to congratulate every author whose work was selected to be a Highlight this year and invite all authors to publish with CQG. A paper submitted today could be a Highlight by this time next year.

CQG LettersDon’t forget that you can now publish Letters in CQG. CQG Letters are required to be high quality, so they stand a good chance of being selected as Highlights.  CQG Letters will also feature in promotions here at CQG+. Submit your CQG Letter today.

CQG Letters – open for submission

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Clifford Will

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

I am very pleased to announce the launch of CQG’s new Letters section.

In a recent survey of CQG’s authors and readers, we identified a strong desire among gravitational physicists for CQG to launch this section.

The Letter article type is now available and I invite you to submit your next Letter to the journal.

The benefits

CQG’s peer review will ensure the best possible consideration for your Letter – certifying, not just Continue reading →

4 questions about CQG Letters

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Adam Day

Adam Day is the Publisher of Classical and Quantum Gravity and CQG+

At the 2015 CQG Editorial Board meeting in London, it was agreed that a subset of the gravitational physics community should be surveyed to find out if there was interest in launching a Letters section for CQG.

In this survey, a number of gravitational physicists were asked to answer a set of questions about Letters. Just to make things interesting, invitees were split into 2 groups: one group was asked to think as authors and the other as readers.

Here are the results. Continue reading →

New realizations of quantum geometry

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Bianca Dittrich is faculty researcher at Perimeter Institute, previously she has been at the Max Planck Institute for Gravitational Physics and at Utrecht University.

Bianca Dittrich is faculty researcher at Perimeter Institute, previously she has been at the Max Planck Institute for Gravitational Physics and at Utrecht University.

The main lesson taught by Einstein’s theory of gravity is that the gravitational field has a geometrical nature, while that of quantum theory is that fields are quantized and come with fundamental excitations. This suggest a realization of quantum gravity in terms of quantum geometry.

In loop quantum gravity, this idea is realized explicitly, and observables encoding the intrinsic and extrinsic data of a spatial geometry are represented as quantum operators on a Hilbert space. This allows to discuss rigorously the quantum properties of geometrical operators measuring the area or Continue reading →

Interview with Patricia Schmidt, winner of the 2015 GPG thesis prize

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Patricia Schmidt

Patricia Schmidt is a Postdoctoral Scholar in TAPIR at Caltech

What was the most interesting thing that happened during your PhD?

The most interesting thing was that literally every day, you would do something new. Even looking at the same set of equations again and again you would get new ideas and new insights.

Were there any big surprises?

The biggest surprise was that it actually worked out! We didn’t have a path set out to reach this result when we started, so who would have thought when Mark and I set out that we would actually have exactly Continue reading →

Book Review: On the topology and future stability of the universe, by Hans Ringström

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Mihalis Dafermos

Mihalis Dafermos is Professor of Mathematics at Princeton University

This impressive new book is first and foremost an original and thought-provoking contribution to the study of cosmology in research monograph form, in the best tradition of the kind of deep mathematical work which has played a crucial role in the development of the subject. At the same time, the book doubles as a dependable introduction and  reference for several foundational results in the analysis of the Einstein equations and relativistic kinetic theory which are hard to find elsewhere but which form the basis of so much current (and hopefully, future!) work.

Both these roles are most welcome.

Let me first discuss what this Continue reading →

Subtleties of holographic entanglement

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Fischetti Marolf Wall

Sebastian Fischetti (left) is a graduate student of Professor Don Marolf (middle) at UCSB. Aron Wall (right) is a member of the School of Natural Sciences at the Institute for Advanced Study.

One of the most useful features of gauge/gravity duality is that it converts difficult problems in certain types of gauge theories into (relatively) simple geometric problems in gravity in one higher dimension. For example, the Hubeny-Rangamani-Takayagani (HRT) conjecture says that Continue reading →