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Archive for the ‘cosmology’ category: Page 30

Jul 13, 2024

Gauge-invariant cosmological perturbations in general teleparallel gravity

Posted by in categories: cosmology, evolution, physics

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…

Jul 11, 2024

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Posted by in categories: cosmology, physics

But when it comes to the origin of the Universe, we don’t know what forces are at play. We actually can’t know, since to know such force (or better, such fields and their interactions) would necessitate knowledge of the initial state of the Universe. And how could we possibly glean information from such a state in some uncontroversial way? In more prosaic terms, it would mean that we could know what the Universe was like as it came into existence. This would require a god’s eye view of the initial state of the Universe, a kind of objective separation between us and the proto-Universe that is about to become the Universe we live in. It would mean we had a complete knowledge of all the physical forces in the Universe, a final theory of everything. But how could we ever know if what we call the theory of everything is a complete description of all that exists? We couldn’t, as this would assume we know all of physical reality, which is an impossibility. There could always be another force of nature, lurking in the shadows of our ignorance.

At the origin of the Universe, the very notion of cause and objectivity get entangled into a single unknowable, since we can’t possibly know the initial state of the Universe. We can, of course, construct models and test them against what we can measure of the Universe. But concordance is not a criterion for certainty. Different models may lead to the same concordance — the Universe we see — but we wouldn’t be able to distinguish between them since they come from an unknowable initial state. The first cause — the cause that must be uncaused and that unleashed all other causes — lies beyond the reach of scientific methodology as we know it. This doesn’t mean that we must invoke supernatural causes to fill the gap of our ignorance. A supernatural cause doesn’t explain in the way that scientific theories do; supernatural divine intervention is based on faith and not on data. It’s a personal choice, not a scientific one. It only helps those who believe.

Still, through a sequence of spectacular scientific discoveries, we have pieced together a cosmic history of exquisite detail and complexity. There are still many open gaps in our knowledge, and we shouldn’t expect otherwise. The next decades will see us making great progress in understanding many of the open cosmological questions of our time, such as the nature of dark matter and dark energy, and whether gravitational waves can tell us more about primordial inflation. But the problem of the first cause will remain open, as it doesn’t fit with the way we do science. This fact must, as Einstein wisely remarked, “fill a thinking person with a feeling of humility.” Not all questions need to be answered to be meaningful.

Jul 11, 2024

Astronomers find the largest water reservoir in the universe

Posted by in category: cosmology

Astronomers have identified the largest and most distant water reservoir ever detected in the universe. This immense collection of water, equivalent to 140 trillion times the water in Earth’s oceans, surrounds a quasar over 12 billion light-years away.

“The environment around this quasar is very unique in that it’s producing this huge mass of water,” stated Matt Bradford from NASA’s Jet Propulsion Laborator y. “It’s another demonstration that water is pervasive throughout the universe, even at the very earliest times.” Bradford leads one of the teams behind this groundbreaking discovery. Their research, partially funded by NASA, appears in the Astrophysical Journal Letters.

Quasars are powered by enormous black holes that consume surrounding gas and dust, emitting vast amounts of energy. The quasar in question, APM 08279+5255, harbors a black hole 20 billion times more massive than the sun and produces energy equivalent to a thousand trillion suns.

Jul 11, 2024

Webb’s Infrared Eyes Expose Black Hole Mysteries in Vivid Detail

Posted by in category: cosmology

Webb’s image of RX J1131-1231 uses gravitational lensing to explore the quasar ’s black hole and dark matter, revealing details about its growth and the universe’s mass composition.

This new James Webb Space Telescope image features the gravitational lensing of the quasar known as RX J1131-1231, located roughly six billion light-years from Earth in the constellation Crater. It is considered one of the best-lensed quasars discovered to date, as the foreground galaxy smears the image of the background quasar into a bright arc and creates four images of the object.

Continue reading “Webb’s Infrared Eyes Expose Black Hole Mysteries in Vivid Detail” »

Jul 10, 2024

Astronomers spot a mysterious black hole nestled in a cluster of stars

Posted by in category: cosmology

A report from Nature shows that astronomers may have found a medium-sized black hole, a kind they’ve long looked for.

Jul 10, 2024

Does the Universe Have a Purpose? What’s the Point of Universe’s Evolution?

Posted by in categories: computing, cosmology, neuroscience, quantum physics

The Omega Point cosmo-teleology emerges from the intersection of quantum cosmology, teleology, and complex systems theory. Originally conceptualized by French philosopher Pierre Teilhard de Chardin, the Omega Point envisions the universe evolving towards a state of maximum complexity and consciousness (Teilhard de Chardin, 1955). Such a state represents the ultimate goal and culmination of cosmic evolution, wherein the convergence of mind and matter leads to a unified superintelligence.

The Omega Point theory postulates that the universe’s evolution is directed towards increasing complexity and consciousness, a teleological process with a purposeful end goal (Teilhard de Chardin, 1955). The concept was further refined by physicists and cosmologists, including John David Garcia (Garcia, 1996), Paolo Soleri (Soleri, 2001), Terence McKenna (McKenna, 1991), Frank Tipler (Tipler, 1994), and Andrew Strominger (Strominger, 2016).

A complementary perspective to the Omega Point theory is found in the Holographic Principle, which posits that all information within our universe is encoded on its boundary. Such an idea suggests our three-dimensional reality is a projection from this two-dimensional surface (Bekenstein, 2003). In the holographic universe, everything we perceive is a reflection of data encoded at the cosmic edge, which could imply that our entire universe resides within a black hole of a larger universe (Susskind, 1995). This perspective aligns with the concept of maximum informational density at the Omega Point and highlights the profound interconnectedness of all phenomena, blurring the boundaries between mind, matter, and the cosmos into a singular, computational entity.

Jul 9, 2024

Quasars are ‘cosmic signposts’ pointing to rare supermassive black hole pairs

Posted by in categories: cosmology, physics

The findings could aid the hunt for these monstrous duos using gravitational waves, tiny ripples in space and time (united as a 4-dimensional entity called space-time), which were first predicted in Einstein’s theory of general relativity in 1915.

“These findings are useful for targeted searches for supermassive black hole binaries, in which we search specific galaxies and quasars for continuous gravitational waves from individual supermassive black hole binaries,” research lead author Andrew Casey-Clyde, a doctoral candidate at the University of Connecticut and visiting researcher at Yale University, told Space.com.

“Our results mean that these targeted searches will be up to seven times more likely to find gravitational waves from a supermassive black hole binary in a quasar than in a random massive galaxy,” Casey-Clyde said.

Jul 9, 2024

One of the greatest mysteries of science could be one step closer to being solved

Posted by in categories: cosmology, particle physics, quantum physics, science

Around 80% of the universe’s matter is dark, meaning it is invisible. Despite being imperceptible, dark matter constantly streams through us at a rate of trillions of particles per second. We know it exists due to its gravitational effects, yet direct detection has remained elusive.

Researchers from Lancaster University, the University of Oxford, and Royal Holloway, University of London, are leveraging cutting-edge quantum technologies to build the most sensitive dark matter detectors to date. Their project, titled “A Quantum View of the Invisible Universe,” is featured at the Royal Society’s Summer Science Exhibition. Related research is also published in the Journal of Low Temperature Physics

The team includes Dr. Michael Thompson, Professor Edward Laird, Dr. Dmitry Zmeev, and Dr. Samuli Autti from Lancaster, Professor Jocelyn Monroe from Oxford, and Professor Andrew Casey from RHUL.

Jul 9, 2024

Sean Carroll — Physics of Consciousness

Posted by in categories: cosmology, neuroscience, quantum physics

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How to explain our inner awareness that is at once most common and most mysterious? Traditional explanations focus at the level of neuron and neuronal circuits in the brain. But little real progress has motivated some to look much deeper, into the laws of physics — information theory, quantum mechanics, even postulating new laws of physics.

Continue reading “Sean Carroll — Physics of Consciousness” »

Jul 9, 2024

This Tiny Particle Could Upend Everything We Know About Gravity—And the Universe—Scientists Say

Posted by in categories: cosmology, particle physics, quantum physics

A scientific breakthrough on the tiniest scale could soon help us answer the universe’s greatest mysteries.

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