Lifeboat Foundation

ICYMI, Nobel Laureate Kip Thorne (BS ’62) reached across history, physics, and astronomy to highlight characters and discoveries that changed humanity’s understanding of space and time.

His talk was the 100th in Caltech Astro’s Stargazing Lecture Series.

Low-energy nuclear fusion reactions are influenced by the migration of neutrons and protons between fusing nuclei and their isospin compositions. Research conducted using high-performance computational models has shown the importance of isospin dynamics and nuclear shapes, particularly in asymmetric, neutron-rich systems, revealing significant implications for nuclear physics and potential energy applications.

Low-Energy Nuclear Fusion

Low-energy nuclear fusion reactions can potentially provide clean energy. In stars, low-energy fusion reactions during the stages of carbon and oxygen burning are critical to stellar evolution. These reactions also offer valuable insights into the exotic processes occurring in the inner crust of neutron stars as they accumulate matter. However, scientists do not fully understand the underlying dynamics governing these reactions.

Researchers reported the discovery of a new cosmic conundrum. The new object, GPM J1839-10, operates similarly to a pulsar, emitting frequent bursts of radio radiation. However, the physics that drives pulsars dictates that they would cease generating if they slowed too much, and practically every pulsar we know of blinks at least once every minute.

GPM J1839-10 has a pulse interval of 22 minutes. We don’t know what type of physics or things can power it.

For at least half a century, it has been popular to compare brains and minds to computers and programs. Despite the continuing appeal of the computational model of the mind, however, it can be difficult to articulate precisely what the view commits one to. Indeed, critics such as John Searle and Hilary Putnam have argued that anything, even a rock, can be viewed as instantiating any computation we please, and this means that the claim that the mind is a computer is not merely false, but it is also deeply confused.

Physicists and philosophers have long claimed that life can form only in a universe like ours, with three dimensions of space and one of time. That thinking may need to be revised.

Even Albert Einstein himself didn’t believe we’d be able to detect gravitational waves from the merger of two black holes.

In late 2019 the previously unremarkable galaxy SDSS1335+0728 suddenly started shining brighter than ever before. To understand why, astronomers have used data from several space and ground-based observatories, including the European Southern Observatory’s Very Large Telescope (ESO’s VLT), to track how the galaxy’s @brightness has varied. In a study out today, they conclude that they are witnessing changes never seen before in a galaxy – likely the result of the sudden awakening of the massive black hole at its core.

“Imagine you’ve been observing a distant galaxy for years, and it always seemed calm and inactive,” says Paula Sánchez Sáez, an astronomer at ESO in Germany and lead author of the study accepted for publication in Astronomy & Astrophysics. “Suddenly, its [core] starts showing dramatic changes in brightness, unlike any typical events we’ve seen before.” This is what happened to SDSS1335+0728, which is now classified as having an ‘active galactic nucleus’ (AGN) — a bright compact region powered by a massive black hole — after it brightened dramatically in December 2019 [1].

Some phenomena, like supernova explosions or tidal disruption events — when a star gets too close to a black hole and is torn apart — can make galaxies suddenly light up. But these brightness variations typically last only a few dozen or, at most, a few hundreds of days. SDSS1335+0728 is still growing brighter today, more than four years after it was first seen to ‘switch on’. Moreover, the variations detected in the galaxy, which is located 300 million light-years away in the constellation Virgo, are unlike any seen before, pointing astronomers towards a different explanation.

Katie Mack, Perimeter Institute’s Hawking Chair in Cosmology and Science Communication, takes us on journey through time by exploring the cosmic microwave background (CMB), the faint glow from the Big Bang.

The CMB shows us the universe as it was 13.8 billion years ago, revealing secrets about its…

Continue reading “Cosmic Microwave Background (CMB) Explained | Cosmology 101 Episode 2” »

Numerous open questions in gravity theory become apparent from observations in cosmology, such as the cosmic microwave background radiation [1, 2, 3, 4, 5, 6], the large scale structure [7, 8], gravitational waves [9, 10] and supernovae [11]. In order to describe these observations, one needs to study the evolution of both the universe as a whole, modeled by a homogeneous and isotropic background geometry and matter distribution, as well as perturbations of this background. A thorough understanding of such cosmological perturbations and their dynamics imposed by the gravitational interaction is therefore an important necessity for describing and explaining the modern observations in cosmology.

Cosmological perturbations in gravity have been studied for a long time, starting with the case of (pseudo-)Riemannian spacetime geometry, which is employed by the standard formulation of general relativity and the most well-known class of its extensions, in which the gravitational interaction is attributed to the curvature of the metric-compatible, torsion-free Levi-Civita connection [,13,14,15]. This task is significantly simplified by the fact by understanding how perturbations transform under gauge transformations, i.e., infinitesimal diffeomorphisms which retain the nature of the spacetime geometry as a small perturbation of a cosmologically symmetric background. From these gauge transformations, one can derive a set of gauge-invariant perturbation variables, which describe the physical information contained in the metric perturbations as well as the perturbations of the matter variables, so that they become independent of the arbitrary gauge choice. The resulting gauge-invariant perturbation theory is one of the cornerstones of modern cosmology [16,17,18,19].

Despite its overwhelming success in describing observations from laboratory scales up to galactic scales, general relativity is challenged by the aforementioned open questions, as well as the open question how it can be reconciled with quantum theory. This situation motivates the study of modified gravity theories [20]. While numerous theories depart from the standard formulation of general relativity in terms of the curvature of the Levi-Civita connection of a Riemannian spacetime, also other formulations in terms of the torsion or nonmetricity of a flat connection exist and can be used as potential starting points for the construction of modified gravity theories [21, 22]. Focusing on general relativity alone, one finds that these formulations are equivalent in the sense that they lead to field equations which possess the same solutions for the metric irrespective of the geometric properties of the connection under consideration…