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We have no idea what dark matter is, other than it’s some source of gravity that is completely invisible but exerts way more pull that all of the regular matter. More than all of the stars, all of the gas, all of the black holes…unless dark matter is black holes, then black holes are most of everything. Dark matter constitutes 80% or so of the mass in the universe, which means even our Milky Way galaxy is mostly a vast ball of dark matter that happens to have attracted a relative sprinkling of baryons—atoms in the form of gas, which lit up as starry glitter spinning in the middle of this invisible gravitational well.
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Sandwich compounds are special chemical compounds used as basic building blocks in organometallic chemistry. So far, their structure has always been linear.
Recently, researchers of Karlsruhe Institute of Technology (KIT) and the University of Marburg were the first to make stacked sandwich complexes form a nano-sized ring. Physical and other properties of these cyclocene structures will now be further investigated. The researchers report their findings in Nature.
Sandwich complexes were developed about 70 years ago and have a sandwich-like structure. Two flat aromatic organic rings (the “slices of bread”) are filled with a single, central metal atom in between. Like the slices of bread, both rings are arranged in parallel. Adding further layers of “bread” and “filling” produces triple or multiple sandwiches.
The next generation of 2D semiconductor materials doesn’t like what it sees when it looks in the mirror. Current synthesizing approaches to make single-layer nanosheets of semiconducting material for atomically thin electronics develop a peculiar “mirror twin” defect when the material is deposited on single-crystal substrates like sapphire. The synthesized nanosheet contains grain boundaries that act as a mirror, with the arrangement of atoms on each side organized in reflected opposition to one another.
This is a problem, according to researchers from the Penn State’s Two-Dimensional Crystal Consortium-Materials Innovation Platform (2DCC-MIP) and their collaborators. Electrons scatter when they hit the boundary, reducing the performance of devices like transistors. This is a bottleneck, the researchers said, for the advancement of next-generation electronics for applications such as Internet of Things and artificial intelligence. But now, the research team may have come up with a solution to correct this defect. They have published their work in Nature Nanotechnology.
This study could have a significant impact on semiconductor research by enabling other researchers to reduce mirror twin defects, according to lead author Joan Redwing, director of 2DCC-MIP, especially as the field has increased attention and funding from the CHIPS and Science Act approved last year. The legislation’s authorization increased funding and other resources to boost America’s efforts to onshore the production and development of semiconductor technology.
They finally reached ignition again last week, according to a statement Sunday from the lab. The news was first reported by the Financial Times.
“In an experiment conducted on July 30, we repeated ignition,” the statement read. “Analysis of those results is underway. As is our standard practice, we plan on reporting those results at upcoming scientific conferences and in peer-reviewed publications.”
Unlike fission, the process used in current nuclear power plants, fusion involves smashing atoms together instead of splitting them apart. It theoretically can supply carbon-free energy without long-lasting radioactive waste. But generations of scientists have struggled to master it in a controlled reaction, even though it has been the power source of nuclear weapons for decades.
“I view string theory as the most promising way to quantize matter and gravity in a unified way. We need both quantum gravity and we need unification and a quantization of gravity. One of the reasons why string theory is promising is that there are no singularities associated with those singularities are the same type that they offer point particles.” — Robert Brandenberger.
In this thought-provoking conversation, my grad school mentor, Robert Brandenberger shares his unique perspective on various cosmological concepts. He challenges the notion of the fundamental nature of the Planck length, questioning its significance and delving into intriguing debates surrounding its importance in our understanding of the universe. He also addresses some eyebrow-raising claims made by Elon Musk about the limitations imposed by the Planck scale on the number of digits of pi.
Moving on to the topic of inflation and its potential detectability, Robert sheds light on the elusive B mode fluctuations and the role they play in understanding the flaws of general relativity. He explains why detecting these perturbations at the required scale may be beyond our current technological capabilities. The discussion further explores the motivations behind the search for cosmic strings in the microwave sky and the implications they hold for particle physics models beyond the standard model.
With his expertise in gravity and the quantization of mass, Robert Brandenberger emphasizes the need for a quantum mechanical approach to gravity. He discusses the emergence of time, space, and a metric from matrix models, offering new insights into the foundations of our understanding of the universe. The speaker’s work challenges conventional notions of inflation and proposes alternative models, such as string gas cosmology, as potential solutions.
Beyond the scientific aspects, Robert Brandenberger reflects on his role as a scientist and educator. He expresses his gratitude to a mentor and shares advice he received about navigating the academic world. Additionally, he discusses the evolution of being a professor over the past three decades and shares his thoughts on the profession as a whole.
This episode leaves us with many questions, tantalizing possibilities, and a deeper appreciation for the mysteries of the cosmos. We invite you to join us in this cosmic journey as we explore the frontiers of theoretical cosmology.
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Blog post with audio player, show notes, and transcript: https://www.preposterousuniverse.com/podcast/2023/07/31/245-…n-physics/
Physics is in crisis, what else is new? That’s what we hear in certain corners, anyway, usually pointed at “fundamental” physics of particles and fields. (Condensed matter and biophysics etc. are just fine.) In this solo podcast I ruminate on the unusual situation fundamental physics finds itself in, where we have a theoretical understanding that fits almost all the data, but which nobody believes to be the final answer. I talk about how we got here, and argue that it’s not really a “crisis” in any real sense. But there are ways I think the academic community could handle the problem better, especially by making more space for respectable but minority approaches to deep puzzles.
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“A place for everything and everything in its place”—making sense of order, or disorder, helps us understand nature. Animals tend to fit nicely into categories: Mammals, birds, reptiles, whatever an axolotl is, and more. Sorting also applies to materials: Insulator, semiconductor, conductor, and even superconductor. Where exactly a material lands in the hierarchy depends on a seemingly invisible interplay of electrons, atoms, and their surroundings.
Unlike animals, the boundaries are less sharp, and tweaking a material’s environment can force it to bounce between categories. For example, dialing down the temperature will turn some materials into superconductors. Snapping on a magnetic field might reverse this effect. Within a single category, different types of order, or phases, can emerge from the sea of particles.
Unfortunately, we can’t see this nanoscopic universe with our eyes, but scientists can use advanced imaging tools to visualize what’s going on. Every once in a while, they uncover unexpected and surprising behaviors.
Thermal field theory seeks to explain many-body dynamics at non-zero temperatures not considered in conventional quantum field theory.
The thermal field theory, as presented by Munshi G. Mustafa, bridges statistical mechanics and quantum field theory, simplifying the analysis of many-body systems and enhancing the understanding of high-energy collisions and early universe evolution.
Quantum field theory is a framework used by physicists to describe a wide range of phenomena in particle physics and is an effective tool to deal with complicated many-body problems or interacting systems.
There is a lot of speculation about the end of the universe. Humans love a good ending after all. We know that the universe started with the Big Bang and it has been going for almost 14 billion years. But how the curtain call of the cosmos occurs is not certain yet. There are, of course, hypothetical scenarios: the universe might continue to expand and cool down until it reaches absolute zero, or it might collapse back onto itself in the so-called Big Crunch. Among the alternatives to these two leading theories is “vacuum decay”, and it is spectacular – in an end-of-everything kind of way.
While the heat death hypothesis has the end slowly coming and the Big Crunch sees a reversal of the universe’s expansion at some point in the future, the vacuum decay requires that one spot of the universe suddenly transforms into something else. And that would be very bad news.
There is a field that spreads across the universe called the Higgs field. Interaction between this field and particles is what gives the particles mass. A quantum field is said to be in its vacuum state if it can’t lose any energy but we do not know if that’s true for the Higgs field, so it’s possible that the field is in a false vacuum at some point in the future. Picture the energy like a mountain. The lowest possible energy is a valley but as the field rolled down the slopes it might have encountered a small valley on the side of that mountain and got stuck there.