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Category: physics – Page 61

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.

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DESI Survey announces the most precise measurements of our expanding #universe using the BAO signal in 6.1 Million #galaxies and #Quasars from Year 1, tracing dark energy through cosmic time.

With 5,000 tiny robots in a mountaintop telescope, researchers can look 11 billion years into the past. The light from far-flung objects in space is just now reaching the Dark Energy Spectroscopic Instrument (DESI), enabling us to map our cosmos as it was in its youth and trace its growth to what we see today. Understanding how our universe has evolved is tied to how it ends, and to one of the biggest mysteries in physics: dark energy, the unknown ingredient causing our universe to expand faster and faster.

To study dark energy’s effects over the past 11 billion years, DESI has created the largest 3D map of our cosmos ever constructed, with the most precise measurements to date. This is the first time scientists have measured the expansion history of the young universe with a precision better than 1%, giving us our best view yet of how the universe evolved.

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“Gravity pulls matter together, so that when we throw a ball in the air, the Earth’s gravity pulls it down toward the planet,” Mustapha Ishak-Boushaki, a professor of physics in the School of Natural Sciences and Mathematics (NSM) at UT Dallas, and member of the DESI collaboration, said in a statement. “But at the largest scales, the universe acts differently. It’s acting like there is something repulsive pushing the universe apart and accelerating its expansion. This is a big mystery, and we are investigating it on several fronts. Is it an unknown dark energy in the universe, or is it a modification of Albert Einstein’s theory of gravity at cosmological scales?”

DESI’s data, however, shows that the universe may have evolved in a way that isn’t quite consistent with the Lambda CDM model, indicating that the effects of dark energy on the universe may have changed since the early days of the cosmos.

“Our results show some interesting deviations from the standard model of the universe that could indicate that dark energy is evolving over time,” Ishak-Boushaki said. “The more data we collect, the better equipped we will be to determine whether this finding holds. With more data, we might identify different explanations for the result we observe or confirm it. If it persists, such a result will shed some light on what is causing cosmic acceleration and provide a huge step in understanding the evolution of our universe.”

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The total solar eclipse isn’t the only reason to keep your eyes to the sky this year. For the first time in 80 years, a star system 3,000 light years away will be visible to the naked eye thanks to a once-in-a-lifetime nova outburst.

NASA announced that the nova, which will create a “new” star in the night sky, will light up the night sky some time between now and September and be as bright as the North Star. One of only five recurring novae in our galaxy, it will be visible for a week before it fades back down.

Jonathan Blazek, an assistant professor of physics at Northeastern University, says this is an exciting moment for amateur astronomers and astrophysicists alike. It’s not technically a new star, just a star that is now bright enough for people to see more clearly, Blazek says, but it provides an opportunity to see and understand the cosmos in a new way.

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After three years of collecting scores of data on hundreds of stars, the ULLYSES (Ultraviolet Legacy Library of Young Stars as Essential Standards) survey conducted by NASA’s Hubble Space Telescope officially ended in December 2023, culminating in 220 total stars examined during the survey on data regarding their size, distance from Earth, temperature, chemical characteristics, and rotational speed. Additionally, ULYYSES also contains another 275 stars from the Hubble archive, providing researchers with several decades of new stellar data and holds the potential to help astronomers gain new insights into stellar formation and evolution throughout the universe.

Hubble image of a star-forming region known as the Tarantula Nebula, which contains massive, young blue stars, which was observed during the ULYYSES survey (top panel). Artist’s illustration of a cooler, redder, young star smaller than our Sun that is still gathering material from its planet-forming disk (bottom panel). (Credit: NASA, ESA, STScI, Francesco Paresce (INAF-IASF Bologna), Robert O’Connell (UVA), SOC-WFC3, ESO)

“I believe the ULLYSES project will be transformative, impacting overall astrophysics – from exoplanets, to the effects of massive stars on galaxy evolution, to understanding the earliest stages of the evolving universe,” said Dr. Julia Roman-Duval, who is Implementation Team Lead for ULLYSES and an Associate Astronomer at the Space Telescope Science Institute (STScI). “Aside from the specific goals of the program, the stellar data can also be used in fields of astrophysics in ways we can’t yet imagine.”

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A new theoretical framework for plastic neural networks predicts dynamical regimes where synapses rather than neurons primarily drive the network’s behavior, leading to an alternative candidate mechanism for working memory in the brain.

The brain is an immense network of neurons, whose dynamics underlie its complex information processing capabilities. A neuronal network is often classed as a complex system, as it is composed of many constituents, neurons, that interact in a nonlinear fashion (Fig. 1). Yet, there is a striking difference between a neural network and the more traditional complex systems in physics, such as spin glasses: the strength of the interactions between neurons can change over time. This so-called synaptic plasticity is believed to play a pivotal role in learning. Now David Clark and Larry Abbott of Columbia University have derived a formalism that puts neurons and the connections that transmit their signals (synapses) on equal footing [1]. By studying the interacting dynamics of the two objects, the researchers take a step toward answering the question: Are neurons or synapses in control?

Clark and Abbott are the latest in a long line of researchers to use theoretical tools to study neuronal networks with and without plasticity [2, 3]. Past studies—without plasticity—have yielded important insights into the general principles governing the dynamics of these systems and their functions, such as classification capabilities [4], memory capacities [5, 6], and network trainability [7, 8]. These works studied how temporally fixed synaptic connectivity in a network shapes the collective activity of neurons. Adding plasticity to the system complicates the problem because then the activity of neurons can dynamically shape the synaptic connectivity [9, 10].

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