by Michael Zevin.
Michael Zevin is a third-year doctoral student in astrophysics at Northwestern University. He is a member of the LIGO Scientific Collaboration, and in addition to citizen science and LIGO detector characterization his research focuses on utilizing gravitational-wave detections to learn about binary stellar evolution and the environments in which compact binaries form.
With the first observations of gravitational waves and the discovery of binary black hole systems, LIGO has unveiled a new domain of the universe to explore. Though the recent signals persisted in LIGO’s sensitive band for a second or less, these last words of the binary that were spewed into the cosmos provided an unprecedented test of general relativity and insight into the progenitor stars that subsequently formed into the colliding black holes. However, the hunt is far from over. With LIGO’s second observing run underway, we can look forward to many more gravitational-wave signals, and as is true with any new mechanism for studying the cosmos, we can also expect to find the unexpected.
The extreme sensitivity required to make such detections was acquired through decades of developing methods and machinery to isolate the sensitive components of LIGO from non-gravitational-wave disturbances. Nonetheless, as a noise-dominated experiment, LIGO is still susceptible to Continue reading
by Nicholas Loutrel.
A new method of computation aims to fill in the gaps in our knowledge of gravitational waves from eccentric binaries.
The modeling of gravitational waves (GWs) suitable for detection with ground-based detectors has been mostly focused on binary systems composed of compact objects, such as neutron stars (NSs) and black holes (BHs). Binaries that form with wide orbital separations are expected to have very small orbital eccentricity, typically less than 0.1, by the time their GW emission enters the detection band of these instruments. However, in dense stellar environments, unbound encounters between multiple compact objects can result in the formation of binaries with high orbital eccentricity (close to, but still less than unity) and whose GW emission is in band for ground-based detectors. Such systems are expected to be Continue reading
by Abhay Ashtekar and Brajesh Gupt.
Abhay Ashtekar holds the Eberly Chair in Physics and the Director of the Institute for Gravitation and the Cosmos at the Pennsylvania State University. Currently, he is a Visiting Professor at the CNRS Centre de Physique Théorique at Aix-Marseille Université.
Although our universe has an interesting and intricate large-scale structure now, observations show that it was extraordinarily simple at the surface of last scattering. From a theoretical perspective, this simplicity is surprising. Is there a principle to weed out the plethora of initial conditions which would have led to a much more complicated behavior also at early times?
In the late 1970s Penrose proposed such a principle through his Weyl curvature hypothesis (WCH) [1,2]: in spite of the strong curvature singularity, Big Bang is very special in that the Weyl curvature vanishes there. This hypothesis is attractive especially because it is purely geometric and completely general; it is not tied to a specific early universe scenario such as inflation.
However, the WCH is tied to general relativity and its Big Bang where classical physics comes to an abrupt halt. It is generally believed that quantum gravity effects would intervene and resolve the big bang singularity. The question then is Continue reading
by Massimo Giovannini.
Since 1991 Massimo Giovannini has extensively researched, taught and written on high-energy physics, gravitation and cosmology. He wrote over 180 papers and various review articles. He is the author of a book entitled “A primer on the physics of Cosmic Microwave Background” published in 2008.
Which is the origin of the temperature and polarization anisotropies of the Cosmic Microwave Background? Classical or quantum? The temperature and the polarization anisotropies of the Cosmic Microwave Background (CMB) are customarily explained in terms of large-scale curvature inhomogeneities. Are curvature perturbations originally classical or are they inherently quantum mechanical, as speculated many years ago by Sakharov?
In the conventional view these questions are quickly dismissed since the quantum origin of large-scale curvature fluctuations is, according to some, an indisputable fact of nature. This is true if and when Continue reading
by 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
by Michael Tröbs.
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
by Yasaman K. Yazdi and Niayesh Afshordi.
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