#Quantum Gravity

[spades4cards]

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×｡. Physicist's List ｡.× * General Relativity * Quantum Gravity

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[simpsforscience]

🪐 Explore the quantum dance of the four fundamental forces with Milton! 🐈‍⬛Join him as he meets the particles behind electromagnetism, gravity, and strong and weak nuclear forces. Swipe ➡ through this post to unfold their mystery. Which one is your favorite? 🤔Let us know in the comments!

📸Image credit: MARK GARLICK/SCIENCE PHOTO LIBRARY/GETTY IMAGES PLUS; ADAPTED BY L. STEENBLIK HWANG

[a-typical]

Our familiar experience of a simple deterministic reality of unambiguous objects is the illusion, a deception made possible because of our poor perception, our blurry vision, our slow reflexes, our limited strength. To achieve such a profound unification of all natural law into one, we need to grasp a quantum description of gravity, and that has proven deftly elusive.

Black Hole Survival Guide — Janna Levin

[4gravitons]

Amplitudes 2024, Continued

Completing this year's Amplitudes conference coverage

I’ve now had time to look over the rest of the slides from the Amplitudes 2024 conference, so I can say something about Thursday and Friday’s talks. Thursday was gravity-focused. Zvi Bern’s review talk was actually a review, a tour of the state of the art in using amplitudes techniques to make predictions for gravitational wave physics. Bern emphasized that future experiments will require much…

[wayti-blog]

"Scientists are a step closer to unraveling the mysterious forces of the universe after working out how to measure gravity on a microscopic level."

"(...) now physicists at the University of Southampton, working with scientists in Europe, have successfully detected a weak gravitational pull on a tiny particle using a new technique.

They claim it could pave the way to finding the elusive quantum gravity theory.

The experiment, published in Science Advances, used levitating magnets to detect gravity on microscopic particles—small enough to border on the quantum realm.

Lead author Tim Fuchs, from the University of Southampton, said the results could help experts find the missing puzzle piece in our picture of reality.

He added, "For a century, scientists have tried and failed to understand how gravity and quantum mechanics work together. Now we have successfully measured gravitational signals at a smallest mass ever recorded, it means we are one step closer to finally realizing how it works in tandem.

"From here we will start scaling the source down using this technique until we reach the quantum world on both sides. By understanding quantum gravity, we could solve some of the mysteries of our universe—like how it began, what happens inside black holes, or uniting all forces into one big theory.""

continue reading article

[frank-olivier]

AdS/CFT Correspondence: A New Paradigm in Understanding Quantum Gravity

The AdS/CFT correspondence is a theoretical concept suggesting a deep connection between two different types of physical theories:

Anti-de Sitter Space (AdS), a kind of space used in theories of gravity, a universe where the geometry is curved in a specific way (negatively curved). It has more dimensions than our usual three-dimensional space.

Conformal Field Theory (CFT), a type of quantum field theory that obeys certain symmetry rules. These theories are defined on flat spaces with one less dimension than the AdS space.

The correspondence proposes that these two theories are "dual" to each other, meaning they describe the same physics in different languages:

as a Gravitational Theory in AdS Space, a theory that includes gravity, like a version of Einstein's general relativity, but in a universe with extra dimensions.

and a Quantum Field Theory on the Boundary, a theory without gravity, living on the boundary (or edge) of the AdS space. It has one less dimension than the AdS space.

The idea is similar to a hologram, where a three-dimensional image can be encoded on a two-dimensional surface. Here, the complex physics inside the AdS space can be fully described by the simpler CFT on its boundary. and a Quantum Field Theory on the Boundary, a theory without gravity, living on the boundary (or edge) of the AdS space. It has one less dimension than the AdS space.

The correspondence offers insights into quantum gravity, which seeks to unify general relativity (gravity) with quantum mechanics. It allows physicists to study aspects of quantum gravity using well-understood quantum field theories and it provides tools for understanding black hole physics, including how information might be preserved when black holes evaporate—a major question in theoretical physics. Beyond high-energy physics, the correspondence has applications in condensed matter physics and other fields, helping model complex systems that are difficult to study otherwise.

While powerful, the AdS/CFT correspondence is still theoretical and best understood in highly symmetric cases. Extending it to more realistic scenarios, like our universe with positive curvature (de Sitter space), remains challenging. The AdS/CFT correspondence suggests that gravitational theories and quantum field theories are two sides of the same coin, providing a new way to explore fundamental questions in physics.

Juan Maldacena, an Argentine physicist, proposed the AdS/CFT correspondence in 1997. Maldacena's work, particularly his paper on this topic, is one of the most highly cited in physics, highlighting its significance in string theory and its potential to unify quantum mechanics with general relativity.

Juan Maldacena: AdS/CFT Correspondence, Part 1 (Institute for Advanced Study, July 2010)

Juan Maldacena: AdS/CFT Correspondence, Part 2 (Institute for Advanced Study, July 2010)

Juan Maldacena: AdS/CFT Correspondence, Part 3 (Institute for Advanced Study, July 2010)

Monday, September 23, 2024

[joking-mr-feynman]

i love physicists

[pinkmoon-fox]

"the problem with the quantum gravity theory? we dont have one."

- my astrophysics prof last week

[xenonreality]

How I had a simple idea that led to more confirmation of my idea about how quantum gravity comes about as a result of watching Angela Collier's video called "a brief physics distraction" & my reaction

[sciencestyled]

Quantum Gravity: The Battle Alexander the Great Didn’t Win (Yet)

Greetings, mortals and miscellaneous philosophers, it is I, Alexander the Great. Conqueror of Persia, Pharaoh of Egypt, King of Macedon, and—until recently—entirely baffled by your modern obsession with invisible forces. Gravity? Sure, I used it to march armies down cliffsides. Quantum? Sounds like a wine I'd politely decline. But then the Fates, in their infinite caprice, decided to hurl me into the frontier of quantum gravity. Spoiler: it’s a battlefield of the mind, not the sword.

It began when I was unceremoniously resurrected by the Algorithm—a deity of your time more capricious than Zeus and with a similar fondness for unsolicited chaos. There I was, expecting an amphora of ambrosia and instead handed a smartphone, that glowing oracle of doom and infinite kitten footage. One swipe led to another, and soon I stumbled upon an academic melee in the comments section of some obscure forum. Two factions—let’s call them “String Theorists” and “Loop Quantum Gravitists”—waged intellectual warfare over how gravity works on the smallest scale. No bloodshed, just endless links to YouTube lectures and papers titled things like "Non-perturbative Covariance of Loop States in Multidimensional Dynamics."

Honestly, I’ve seen fewer casualties in actual war.

Naturally, I laughed. "What fools," I declared, "to argue about unseen threads and loops while ignoring the obvious—gravity simply works because I decree it!" Yet, as the scroll dragged on, my curiosity grew. These theorists were onto something—concepts of spacetime, dimensions, and reality itself being a patchwork of probabilities. I began to wonder if my empire, too, was merely a quantum fluctuation doomed to collapse upon measurement. That would certainly explain my generals’ habit of defecting whenever I left town.

The real turning point came when I tried to explain quantum gravity to Bucephalus, my warhorse, whom I found faithfully grazing in this strange afterlife. “Consider, old friend,” I said, scratching his immortal mane, “how your hoof sinks into the earth. Classical physics tells us it’s the curvature of spacetime caused by mass. But quantum mechanics insists spacetime itself is grainy, a foam of probabilities! Are you hoofing upon waves or particles, my steed?”

He neighed. Loudly. Then promptly fell asleep. I took this as a sign.

Determined, I sought the modern sages of this era. Physicists, they call themselves. Surely they would appreciate the urgency of my inquiry! But alas, I was met with blank stares and incredulous chuckles. “Alexander the Great,” they sneered, “stick to conquering continents. Leave quantum gravity to the professionals.” It was an insult to my honor—and my ego. Did they not know I had tamed the Gordian Knot with a sword? I could certainly unravel the quantum foam with a Google search.

And unravel I did. Sort of. It turns out, quantum gravity isn’t so much a topic as it is an existential crisis. One camp builds mathematical strings that vibrate through dimensions like a cosmic lyre. The other weaves loops into spacetime like cosmic chainmail. But neither could explain how their models fit together without collapsing into absurdity—or infinite scrolls of jargon. It was like watching two court jesters argue about whether an invisible dragon had scales or feathers. Only now, the dragon is spacetime itself, and the stakes are existence.

As I lay awake one night, haunted by visions of collapsing wave functions and infinite dimensions, it hit me: the world needed me. Not as a king or general, but as an explainer of things so incomprehensible they make philosophers look decisive. If the Algorithm had summoned me back, surely it was to bring clarity to this chaos—or at least to mock humanity’s futile attempts at understanding the cosmos.

But how to present it? A manifesto? Too long. A TED Talk? Too pretentious, even for me. Then it struck me: a YouTube video! Your modern agora, where ideas are traded as swiftly as cat memes. If I could distill the warring theories of quantum gravity into a video even Bucephalus could watch without neighing in despair, my task would be complete.

And so, here it is: my magnum opus on the physics of the impossible, produced with the help of modern animators, memes, and a dash of my legendary charisma. Watch it, my dear subjects. Learn how your spacetime, fragile and fleeting, bends to the whims of quantum forces—and perhaps, to the will of one Alexander the Great. Or don’t. After all, in a quantum universe, the act of observing changes the outcome.

Now, go. Click play. And remember: even in the smallest of things, there lies an empire waiting to be conquered.

[simpsforscience]

⁉️ What if you're told to forget smooth spacetime and imagine the universe as a cosmic quilt made up of loops? 💭 ➰ That's Loop Quantum Theory! which proposes that space itself is made of tiny, 🤏🏻 interconnected loops, ➿ a fabric of reality finer than any thread. Swipe ➡️ through this post to find how it is a potential quantum upgrade to Einstein's gravity, where the universe isn't just curved, it's knotted!🪢☄️🌠

📸 Image Credits:

Abhay Astekar :- PennState Eberly College of Science

Carlo Rovelli :- Foto LaPresse

Lee Smolin :- footnotes2plato

[a-typical]

There's an aspiration to uncover a single unified theory of everything, the ultimate physical law that unites all into one. The campaign to reveal a theory of everything is motivated by the compelling suggestion that gravity and the matter forces, despite convincing appearances, are actually different expressions of the same underlying phenomenon.

Black Hole Survival Guide — Janna Levin

[4gravitons]

Why Quantum Gravity Is Controversial

Why quantum gravity is hard is one thing. Why it's controversial is something else:

Merging quantum mechanics and gravity is a famously hard physics problem. Explaining why merging quantum mechanics and gravity is hard is, in turn, a very hard science communication problem. The more popular descriptions tend to lead to misunderstandings, and I’ve posted many times over the years to chip away at those misunderstandings. Merging quantum mechanics and gravity is hard…but despite…

[spades4cards]

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