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Category: physics – Page 239

Next time you eat a blueberry (or chocolate chip) muffin consider what happened to the blueberries in the batter as it was baked. The blueberries started off all squished together, but as the muffin expanded they started to move away from each other. If you could sit on one blueberry you would see all the others moving away from you, but the same would be true for any blueberry you chose. In this sense galaxies are a lot like blueberries.

Since the Big Bang, the universe has been expanding. The strange fact is that there is no single place from which the universe is expanding, but rather all galaxies are (on average) moving away from all the others. From our perspective in the Milky Way galaxy, it seems as though most galaxies are moving away from us – as if we are the centre of our muffin-like universe. But it would look exactly the same from any other galaxy – everything is moving away from everything else.

To make matters even more confusing, new observations suggest that the rate of this expansion in the universe may be different depending on how far away you look back in time. This new data, published in the Astrophysical Journal, indicates that it may time to revise our understanding of the cosmos.

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Light propagation is usually reciprocal, meaning that the trajectory of light travelling in one direction is identical to that of light travelling in the opposite direction. Breaking reciprocity can make light propagate only in one direction. Optical components that support such unidirectional flow of light, for example isolators and circulators, are indispensable building blocks in many modern laser and communication systems. They are currently almost exclusively based on the magneto-optic effect, making the devices bulky and difficult for integration. A magnetic-free route to achieve nonreciprocal light propagation in many optical applications is therefore in great demand.

Recently, scientists developed a new type of optical metasurface with which in both space and time is imposed on the , leading to different paths for the forward and backward light propagation. For the first time, nonreciprocal in was realized experimentally at optical frequencies with an ultrathin component.

“This is the first optical metasurface with controllable ultrafast time-varying properties that is capable of breaking optical reciprocity without a bulky magnet,” said Xingjie Ni, the Charles H. Fetter Assistant Professor in Department of Electrical Engineering at the Pennsylvania State University. The results were published this week in Light: Science and Applications.

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In an article published in Physical Review Letters, Bristol scientists have answered the fundamental question: “Is it possible to move without exerting force on the environment?”, by describing the tractionless self-propulsion of active matter.

Understanding how cells move autonomously is a fundamental question for both biologists and physicists.

Experiments on are commonly done by looking at the motion of a cell on a glass slide under a microscope.

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“Jackson is a smart guy and probably under-appreciates that about himself,” said his dad.

He’s onto planning his next reactor using the spherical tokamak method, which traps energy differently than the reactor that he’s already built. He’s also decided that he wants to pursue nuclear physics as a career because he thinks he’ll be the one to make a fusion reactor that is actually efficient.

“He certainly has a head start,” said his dad.

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The octonions themselves will never be “the answer” to how reality works, but they do provide a powerful, generalized mathematical structure that has its own unique properties. It includes real, complex, and quaternion mathematics, but also introduces fundamentally unique mathematical properties that can be applied to physics to make novel — but speculative and hitherto unsupported — predictions.

Octonions can give us and idea of which possibilities might be compelling to look at in terms of extensions to known physics and which ones might be less interesting, but there are no concrete observables predicted by the octonions themselves. Pierre Ramond, my former professor who taught me about octonions and Lie groups in physics, was fond of saying, “octonions are to physics what the Sirens were to Ulysses.” They definitely have an allure, but if you dive in, they may drag you to a hypnotic, inescapable doom.

Their mathematical structure holds an incredible richness, but nobody knows whether that richness means anything for our Universe or not.

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If you were to travel back in time to kill your grandparents — let’s ignore the ‘why’ here, for the sake of argument — you would never have been born. Which means there was nobody to kill your grandparents. Which means you were actually born after all, which… hold up, what’s going on here?!

These kinds of brain-breaking paradoxes have been puzzling us forever, inspiring stories ranging from “Back to the Future” to “Hot Tub Time Machine.”

Now, New Scientist reports that physicists Barak Shoshany and Jacob Hauser from the Perimeter Institute in Canada have come up with an apparent solution to these types of paradoxes that requires a very large — but not necessarily infinite — number of parallel universes.

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MIT physicists are reigniting the possibility, which they previously had snuffed out, that a bright burst of gamma rays at the center of our galaxy may be the result of dark matter after all.

For years, physicists have known of a mysterious surplus of energy at the Milky Way’s center, in the form of gamma rays—the most energetic waves in the electromagnetic spectrum. These rays are typically produced by the hottest, most extreme objects in the universe, such as supernovae and pulsars.

Gamma rays are found across the disk of the Milky Way, and for the most part physicists understand their sources. But there is a glow of gamma rays at the Milky Way’s center, known as the galactic center excess, or GCE, with properties that are difficult for physicists to explain given what they know about the distribution of stars and gas in the galaxy.

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