by Adriana V. Araujo, Diego F. López and José G. Pereira
The Quest for Consistency in Spacetime Kinematics
Newton’s inception of the theory for the gravitational interaction in 1642 was a landmark for modern physics. In addition to explaing all known gravitational phenomena of that time, Newton’s gravitational theory was consistent with the kinematic rules of the Galilei group, known as Galilei relativity. Such consistency provided an atmosphere of intellectual comfort, which lasted for more than two centuries.
From left to right, José, Adriana and Diego. Click here to see the authors taking advantage of all dimensions of a space section of the universe.
By the mid nineteenth century, most secrets of the electric and magnetic fields were already unveiled. Those advancements culminated with the publication by Maxwell of a comprehensive treatise on the unification of electricity and magnetism, which became known as Maxwell’s theory. This theory brought to the scene the first inconsistency of our tale. In fact, it became immediately clear that the electromagnetic theory was inconsistent with the Galilei relativity: electromagnetism was claiming for a new relativity. In response to this claim, and with contributions from Lorentz and Poincaré, Einstein published in 1905 the basics of what is know today as Einstein special relativity. According to this theory, for velocities near the velocity of light, spacetime kinematics would no longer be ruled by Galilei, but by the Poincaré group. Most importantly, electromagnetism was consistent with Einstein special relativity! Mission accomplished? Not quite! Continue reading
by Serena Vinciguerra
A neuroscience perspective on the gravitational wave community.
INSIDE OUT is not only a Pixar cartoon, but also a very intelligent slogan. I am not talking about emotions, but more generally about our brain. A more common view of our brain might be OUTSIDE IN: we use the brain to interpret the inputs we receive from outside. However, the brain is also the most powerful computer ever known, so why not try the INSIDE OUT modality, and be inspired by our brains as computational models?
The brain is a biological network composed of nerve cells (neurons) connected to each other. We can imagine neurons as calculation units which compute a weighted sum of the received electric inputs. If this sum reaches a particular threshold, a new electric signal is generated, propagated and finally transmitted to other neurons.
Serena hiking on the Forra del Lupo (Folgaria) trail – Italy
Artificial neural networks (ANNs) and their success clearly represent the strength of applying the mechanisms which drive our mind to other subjects. ANNs find many applications in research, including in the science of gravitational waves (GW). In searches for un-modelled GW transients, ANNs have been used to classify noisy events, to search for GWs associated with short gamma ray bursts as well as for signal classification. What are the eyes, the ears, the nose and the mouth which make up an identifiable face in GW transients or glitches? These are the kind of questions ANNs have to answer to perform classification/identification tasks. To find out how good they are, take a look to these papers [1, 2]
by Astrid Eichhorn, Sebastian Mizera and Sumati Surya
Silence is a rare commodity in our everyday, technology-driven lives; from the outright blare of car horns in India, to the quieter, but persistent sounds of mobile phones in Germany, constantly alerting us to the incoming messages, to the 24 hour news cycle on Canadian TV. Finding a few quiet moments, unhindered by the constant onslaught of information requires a considerable effort. Indeed, it often feels that noise, not silence is the generic state of our world.
Sebastian Mizera is a graduate student at Perimeter Institute working on various aspects of quantum field theories. He enjoys quiet evenings reading a book.
Sumati Surya is on the faculty of the Raman Research Institute, in Bangalore, India and is currently an Emmy-Noether visiting fellow at the Perimeter Institute, Canada. Although she loves the quiet she also loves the sounds created by her two very active and engaging daughters.
Astrid Eichhorn is currently an Emmy-Noether junior research group leader at the University of Heidelberg, where she and her group explore the fundamental quantum structure of spacetime and matter. When she isn’t exploring asymptotic silence in quantum gravity, she likes to look for silence in the colder more remote regions of our planet.
by Ivan Agullo, Abhay Ashtekar and Brajesh Gupt
Can observations determine the quantum state of the very early Universe?
Can we hope to know even in principle what the universe was like in the beginning? This ancient metaphysical question has acquired new dimensions through recent advances in cosmology on both observational and theoretical fronts. To the past of the surface of last scattering, the universe is optically opaque. Yet, theoretical advances inform us that dynamics of the universe during earlier epochs leaves specific imprints on the cosmic microwave background (CMB). Therefore, we can hope to deduce what the state of the universe was during those epochs. In particular, success of the inflationary scenario suggests that the universe is well described by a spatially flat Friedmann, Lemaître, Robertson, Walker (FLRW) space-time, all the way back to the onset of the slow roll phase. This is an astonishingly early time when space-time curvature was some times that on the horizon of a solar mass black hole and matter density was only 11 orders of magnitude smaller than the Planck scale.
Clockwise from top left: Brajesh Gupt (Pennsylvania State University), Abhay Ashtekar (Pennsylvania State University) and Ivan Agullo (Louisiana State University)
It’s been a busy few weeks for CQG – we’ve been to the Era of Gravitational Wave Astronomy conference in Paris, hosted the annual Editorial Board meeting in London, attended the Loops17 conference in Warsaw and now it’s time to fly off to California for Amaldi12.
Amaldi12, named after Edoardo Amaldi, will be held at the Hilton Hotel in Pasadena, CA from 9th – 14th July. The conference will explore the science around gravitational waves and their detection, particularly in light of the confirmed detections by LIGO-Virgo and new advances with the LISA mission.
I will be at the conference Monday through Friday with a table top booth at the event, located near the international ballroom in the hotel. I’m really interested in hearing your thoughts about the journal, so please do stop by say hello and have a chat.
At the beginning of next week Jennifer Sanders and I will be representing the CQG editorial team at the Loops’ 17 conference at the University of Warsaw in Poland.
At the beginning of next week I will be attending the Era of Gravitational Wave Astronomy conference (or TEGRAW 2017, for short) at the Institut D’Astrophysique in Paris, France.
The conference aims to highlight the most recent developments in both theoretical works (such as the two-body problem, effective theories, numerical relativity, and tests of gravity theories) and experimental works (such as future detectors, both on ground and in space).
IOP Publishing/ CQG will have a small table top booth at the event so feel free to stop by if you fancy having a chat. I’ll only be there Monday through Wednesday (unfortunately missing the social event) but am looking forward to meeting you.
I hope to see you in Paris!
by J. Fernando Barbero G., Benito A. Juárez-Aubry, Juan Margalef-Bentabol and
Eduardo J. S. Villaseñor.
Boundaries are ubiquitous in physics, if anything because most material objects tend to have one… In the context of gravity they play a number of interesting roles: from the definition of conserved quantities in asymptotically flat spacetimes to holography (no lasers here, sorry) or the modeling of black holes. A natural question in the context of the canonical quantization of gravitational theories is how to obtain their Hamiltonian description – in particular the constraints – in the presence of boundaries.
Eduardo and Fernando trying to get inspiration for the new group logo
“Juan, can you hear us?”
“Yes, the connection seems to be working better these days.”
“Hi Benito. Good to see you! Can you also see us?”
“Sorry for the delay, it is early in the morning here. Yeah, I can see you perfectly. Hi, Eduardo and Fernando! Hi, Juan!”
“So, as I told you in my last email, we have to write this CQG+ Insight piece about our traces paper. You know, it should be informative, informal and infused with deep physical insights, so, any suggestions? — Yes, Fernando.”
Stanley Deser is emeritus Ancell Professor of Physics at Brandeis University and a Senior Research Associate at Caltech
Prior to Supergravity’s (SUGRA’s) inception, the ideas in the air came from two new, quite different realms. One realm was supersymmetry (SUSY); the other arose from the emerging difficulties in achieving consistent interactions between gravity and higher (s > 1) spin gauge fields.
Indeed, the Western discoverers of SUSY, Julius Wess and Bruno Zumino , would frequently visit Boston from NYU to spread the SUSY gospel, which did get even our blasé attention after a while, especially since the simplest SUSY multiplet pattern (s; s + 1/2) linking adjoining Fermi-Bose fields had no obvious reason to stop at the s = 0 and s = 1/2 models that had been studied thus far.