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Mar 1, 2024
Inflation and Bounce from Classical and Loop Quantum Cosmology Imperfect Fluids
Posted by Dan Breeden in categories: cosmology, evolution, information science, quantum physics, singularity
The purpose of this work is to investigate how several inflationary and bouncing scenarios can be realized by imperfect fluids. We shall use two different theoretical frameworks, namely classical cosmology and Loop Quantum Cosmology (LQC) (see where the derivation of the Hamiltonian in LQC was firstly derived to yield the modified Friedman equation, and also see for a recent derivation of the effective Hamiltonian in LQC, which was derived by demanding repulsive gravity, as in Loop Quantum Gravity). In both cases we shall investigate which imperfect fluid can realize various inflationary and bouncing cosmology scenarios. The inflationary cosmology and bouncing cosmology are two alternative scenarios for our Universe evolution. In the case of inflation, the Universe starts from an initial singularity and accelerates at early times, while in the case of the bouncing cosmology, the Universe initially contracts until it reaches a minimum radius, and then it expands again. With regards to inflation, we shall be interested in four different inflationary scenarios, namely the intermediate inflation, the Starobinsky inflation, and two constant-roll inflation scenarios. With regards to bouncing cosmologies, we shall be interested in realizing several well studied bouncing cosmologies, and particularly the matter bounce scenario, the superbounce scenario and the singular bounce.
As we already mentioned we shall use two theoretical frameworks, that of classical cosmology and that of LQC. After presenting the reconstruction methods for realizing the various cosmologies with imperfect fluids, we proceed to the realization of the cosmologies by using the reconstruction methods. In the case of classical cosmology, we will calculate the power spectrum of primordial curvature perturbations, the scalar-to-tensor ratio and the running of the spectral index for all the aforementioned cosmologies, and we compare the results to the recent Planck data. The main outcome of our work is that, although the cosmological scenarios we study in this paper are viable in other modified gravity frameworks, these are not necessarily viable in all the alternative modified gravity descriptions. As we will demonstrate, in some cases the resulting imperfect fluid cosmologies are not compatible at all with the observational data, and in some other cases, there is partial compatibility.
We need to note that the perturbation aspects in LQC are not transparent enough and assume that there are no non-trivial quantum gravitational modifications arising due to presence of inhomogeneities. As it was shown in, a consistent Hamiltonian framework does not allow this assumption to be true. The perturbations issues that may arise in the context of the present work, are possibly more related to some early works in LQC, so any calculation of the primordial power spectrum should be addressed as we commented above.
Mar 1, 2024
Room Temperature Superconductor Evidence Coming in March
Posted by Dan Breeden in category: materials
The main researchers working on LK99-like room temperature and room pressure superconductors are in China and South Korea. There have been reports that the China researchers have successfully reproduced the weak magnetic effects indicating Meissner effect. The original South Korean team will present video evidence at the American Physical Society conference on Monday, March 4. There are new peer reviewed research paper, new preprint papers and patents being worked upon but it is unclear when those will be released.
Proof of a full and strong Meissner effect would be definitive evidence for superconductivity. The Meissner effect is a fundamental property of superconductors that distinguishes them from ordinary conductors. It refers to the complete expulsion of magnetic fields from the interior of a superconducting material when it transitions from its normal state to the superconducting state. The expulsion of magnetic fields is the result of a remarkable phenomenon known as perfect diamagnetism.
In a superconducting state, the material exhibits zero electrical resistance, allowing the unimpeded flow of electric current. When a magnetic field is applied to a superconductor, it generates circulating currents on the surface of the material. These currents create an opposing magnetic field that exactly cancels out the applied field, resulting in the expulsion of the magnetic field from the interior of the superconductor.
Mar 1, 2024
Exploring many paths to realize quantum computers
Posted by Dan Breeden in categories: computing, quantum physics
Japan’s ambitious moonshot to develop fault-tolerant computers by 2050 has a clear goal, but it remains uncertain which technology will win out.
Mar 1, 2024
Stanford’s Tiny Accelerator Promises Giant Leaps for Medical and Physics Breakthroughs
Posted by Dan Breeden in categories: biotech/medical, engineering
A new advance by Stanford engineers could lead to particle accelerators being widely available in science, medicine, and industry.
Stanford researchers are getting closer to building a tiny electron accelerator based on “accelerator-on-a-chip” technology with broad potential applications in studying physics as well as medical and industrial uses.
The researchers have demonstrated that a silicon dielectric laser accelerator, or DLA, can now both speed up and confine electrons, creating a focused beam of high-energy electrons. “If the electrons were microscopic cars, it’s as if, for the first time, we’re steering and we have our foot on the gas,” said Payton Broaddus, PhD ’23 in electrical engineering and the lead author on a paper published on February 23 detailing the breakthrough in Physical Review Letters.
Mar 1, 2024
Anything-in anything-out: A new modular AI model
Posted by Dan Breeden in category: robotics/AI
Researchers at EPFL have developed a new, uniquely modular machine learning model for flexible decision-making. It is able to input any mode of text, video, image, sound, and time-series and then output any number, or combination, of predictions.
We’ve all heard of large language models, or LLMs—massive scale deep learning models trained on huge amounts of text that form the basis for chatbots like OpenAI’s ChatGPT. Next-generation multimodal models (MMs) can learn from inputs beyond text, including video, images, and sound.
Creating MM models at a smaller scale poses significant challenges, including the problem of being robust to non-random missing information. This is information that a model doesn’t have, often due to some biased availability in resources. It is thus critical to ensure the model does not learn the patterns of biased missingness in making its predictions.
Mar 1, 2024
Researchers using pulsar measurements to probe dark matter find Milky Way galaxy is highly dynamic
Posted by Dan Breeden in categories: cosmology, physics
Dark matter comprises more than 80% of all matter in the cosmos but is invisible to conventional observation, because it seemingly does not interact with light or electromagnetic fields. Now Dr. Sukanya Chakrabarti, the Pei-Ling Chan Endowed Chair in the College of Science at The University of Alabama in Huntsville (UAH), along with lead author Dr. Tom Donlon, a UAH postdoctoral associate, have written a paper to help illuminate just how much dark matter there is in our galaxy and where it resides by studying the gravitational acceleration of binary pulsars.
Chakrabarti gave a plenary talk on this work and other methods to measure galactic accelerations at the 243rd meeting of the American Astronomical Society in New Orleans in January. The findings are also posted on the arXiv preprint server.
Pulsars are rapidly rotating neutron stars that blast out pulses of radiation at regular intervals ranging from seconds to milliseconds. A binary pulsar is a pulsar with a companion that allows physicists to test general relativity because of the strong gravitational fields accompanying these objects. “Pulsars are fantastic galactic clocks that have a timing stability that rivals atomic clocks,” Chakrabarti explains.
Mar 1, 2024
Alzheimer’s Might Not Actually Be a Brain Disease, Expert Reveals
Posted by Dan Breeden in categories: biotech/medical, neuroscience
The pursuit of a cure for Alzheimer’s disease is becoming an increasingly competitive and contentious quest with recent years witnessing several important controversies.
In July 2022, Science magazine reported that a key 2006 research paper, published in the prestigious journal Nature, which identified a subtype of brain protein called beta-amyloid as the cause of Alzheimer’s, may have been based on fabricated data.
One year earlier, in June 2021, the US Food and Drug Administration had approved aducanumab, an antibody-targeting beta-amyloid, as a treatment for Alzheimer’s, even though the data supporting its use were incomplete and contradictory.
Mar 1, 2024
Einstein Couldn’t Solve Quantum Gravity’s Code. Scientists Just Got One Step Closer
Posted by Dan Breeden in category: quantum physics
Mar 1, 2024
Quantum Resurrection: High-Performance Niobium Superconducting Qubits
Posted by Dan Breeden in categories: materials, quantum physics
For years, niobium was considered an underperformer when it came to superconducting qubits. Now scientists supported by Q-NEXT have found a way to engineer a high-performing niobium-based qubit and so take advantage of niobium’s superior qualities.
When it comes to quantum technology, niobium is making a comeback.
For the past 15 years, niobium has been sitting on the bench after experiencing a few mediocre at-bats as a core qubit material.