Galaxies and their supermassive black holes evolve together, but which came first is an ongoing question. Now we may finally have an answer, says columnist Leah Crane
By Leah Crane
Category: cosmology – Page 10
A thermodynamic approach to gravity could explain cosmic acceleration without dark energy
Gravity, the force that attracts objects toward each other, is currently framed by Albert Einstein’s theory of general relativity. This framework describes gravity as the curvature of spacetime, the invisible four-dimensional fabric of the universe.
While general relativity is now the central theory of gravity, it fails to explain some cosmological phenomena and mysteries, such as the so-called cosmological constant problem. This is the unexplained mismatch between the observed energy of empty space and the far greater values predicted by quantum theories.
In a recent paper published in Physical Review Letters, researchers at Imperial College London tried to frame gravity using thermodynamics, the framework that describes how energy and heat transform. Their study builds on a seminal paper by theoretical physicist Ted Jacobson, published more than three decades ago.
The universe should look the same in all directions at large scales, but DESI data suggest otherwise
Earlier this year, the Dark Energy Spectroscopic Instrument (DESI) completed observations that mapped 47 million galaxies across 11 billion light-years, allowing astronomers to better evaluate the large-scale structure of the visible universe. After studying these data, astronomers Francesco Sylos Labini and Marco Galoppo say the universe may not look the same in all directions. Their results, published in Nature, contradict a fundamental assumption in modern cosmology.
At the scale of a single galaxy or local groups of galaxies, the universe clearly appears to be anisotropic, meaning the structure is different depending on which direction you look. In one direction, there may be more void space, while another direction may have a cluster of galaxies.
However, the cosmological principle says that at larger scales, the universe consists of matter that is more or less distributed evenly in all directions. This is based on the Copernican principle, which states that there should be no “special observers” in the universe, meaning that at large scales, the universe should look the same from anywhere else in the universe.
3 Reasons Pilot Wave Theory is The Best Interpretation of Quantum Mechanics (And 3 Reasons It’s Not)
The pilot wave interpretation of quantum mechanics is probably a lot better than you think.
Pilot wave theory makes a bold claim: that it reproduces all the predictions of quantum mechanics while resolving nearly all of its infamously difficult conceptual issues.
And that claim is justified!
But if pilot wave theory is so good, why doesn’t anyone talk about it?
Here are 3 reasons why people should talk about pilot wave theory, but also 3 reasons why people don’t.
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Quantum squeezing sidesteps the limits on mechanical transducers
From detecting the ripples of colliding black holes to imaging individual chemical bonds, mechanical transducers have repeatedly transformed our understanding of the universe. So far, however, the sensitivity of these devices has been intrinsically limited by the laws of quantum mechanics itself.
Through new research published in Physical Review Letters, researchers led by Lukas Novotny at ETH Zurich have found a way to push past that ceiling using a quantum trick called squeezing, opening a new chapter in precision measurement.
We May Never Understand Reality
What really happens in the quantum world?
In this conversation, physicist Sean Carroll explores some of the deepest mysteries in quantum mechanics: the famous double-slit experiment, wave function collapse, the Many Worlds interpretation, entropy and the arrow of time.
Speaking to New Scientist reporter Jacklin Kwan, Carroll discusses why electrons appear to behave like waves, how observation seems to affect reality and whether the universe constantly branches into countless parallel worlds. Carroll also explains the measurement problem, the challenges of interpreting quantum theory and why physicists still debate what quantum mechanics is actually telling us about the nature of reality.
Carroll is a theoretical physicist, cosmologist and author whose work focuses on the foundations of physics, quantum mechanics, cosmology and the nature of time.
Chapters.
0:00 Introduction.
0:39 The double slit experiment.
5:20 The Cophenhagen interpretation.
9:05 Is there a \.
Horizon edge states gain finite description in string theory calculation
Modern physics theories highlight the key role of horizons—boundaries beyond which information cannot reach an observer—in a variety of cosmological and gravitational phenomena. Two renowned examples of these boundaries are event horizons in black holes and the cosmological horizon of the de Sitter spacetime, a model of an expanding universe with a positive vacuum energy.
Many quantum theories predict the existence of quantum states or excitations in the proximity of horizons, which are known as edge modes. Edge modes are additional degrees of freedom that can emerge when space is divided into two distinct regions. Rather than being distributed throughout space, they are typically localized near or on the boundary that divides the two regions.
Researchers at the Abdus Salam International Center for Theoretical Physics and the University of Amsterdam recently set out to calculate the contribution of edge modes to the Euclidean partition function, a quantity that encodes information about all possible quantum states of a system and their statistical properties.
Can String Theory Be Explained with No Strings Attached?
Using a “bootstrap” approach, researchers show that a small set of assumptions may naturally lead to a string-theory description of certain high-energy processes.
String theory has been a remarkably influential conceptual framework for modern theoretical physics. While its description of nature in terms of tiny strings captures the imagination, the string framework has had profound impact in a broad range of subfields, going well beyond its lead role as a viable theory of quantum gravity. For instance, it has led to deeper understanding of black holes and their relation to entanglement and quantum information [1], and it has provided theoretical benchmarks for explaining quark–gluon plasma observations in quantum chromodynamics [2]. As a complement to direct calculations, theoretical physicists would like to understand string theory as emerging from a set of fundamental principles that any theory of nature must respect. Consistency with these bedrock conditions, so goes the idea, could perhaps make string theory inevitable.
Webb spots the birth of a giant galaxy and a supermassive black hole
Astronomers have used the James Webb Space Telescope to catch an extraordinary glimpse of a massive galaxy taking shape in the early universe. They identified a compact group of at least six galaxies that are likely to merge into a single enormous system. At the heart of this cosmic construction site lies a growing supermassive black hole.
The international study was led by astronomers at Leiden University and the University of Oxford. The findings have been published in The Open Journal of Astrophysics and Astronomy & Astrophysics.
The system observed, TGSSJ1530+1049, lies more than 12 billion light-years away. We are seeing it as it was when the universe was only about 1.5 billion years old. Researchers pointed the James Webb Space Telescope at this location because earlier radio observations had hinted at an active supermassive black hole. The new data revealed that the surrounding region is far more complex than expected. “We didn’t find a single galaxy, but an entire complex of at least six galaxies,” says Aayush Saxena of the University of Oxford.