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Andrew Strominger: Black Holes, Quantum Gravity, and Theoretical Physics | Lex Fridman Podcast #359

Andrew Strominger is a theoretical physicist at Harvard. Please support this podcast by checking out our sponsors:
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EPISODE LINKS:
Andrew’s website: https://www.physics.harvard.edu/people/facpages/strominger.
Andrew’s papers:
Soft Hair on Black Holes: https://arxiv.org/abs/1601.00921
Photon Rings Around Warped Black Holes: https://arxiv.org/abs/2211.

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Clips playlist: https://www.youtube.com/playlist?list=PLrAXtmErZgOeciFP3CBCIEElOJeitOr41

OUTLINE:
0:00 — Introduction.
1:12 — Black holes.
6:16 — Albert Einstein.
25:44 — Quantum gravity.
29:56 — String theory.
40:44 — Holographic principle.
48:41 — De Sitter space.
53:53 — Speed of light.
1:00:40 — Black hole information paradox.
1:08:20 — Soft particles.
1:17:27 — Physics vs mathematics.
1:26:37 — Theory of everything.
1:41:58 — Time.
1:44:24 — Photon rings.
2:00:05 — Thought experiments.
2:08:26 — Aliens.
2:14:04 — Nuclear weapons.

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Brain implant startup backed by Bezos and Gates is testing mind-controlled computing on humans

Synchron’s BCI is inserted through the blood vessels, which Oxley calls the “natural highways” into the brain. Synchron’s stent, called the Stentrode, is fitted with tiny sensors and is delivered to the large vein that sits next to the motor cortex. The Stentrode is connected to an antenna that sits under the skin in the chest and collects raw brain data that it sends out of the body to external devices.

Peter Yoo, senior director of neuroscience at Synchron, said since the device is not inserted directly into the brain tissue, the quality of the brain signal isn’t perfect. But the brain doesn’t like being touched by foreign objects, Yoo said, and the less invasive nature of the procedure makes it more accessible.

“There’s roughly about 2,000 interventionalists who can perform these procedures,” Yoo told CNBC. “It’s a little bit more scalable, compared to, say, open-brain surgery or burr holes, which only neurosurgeons can perform.”

Space travel influences the way the brain works

Scientists of the University of Antwerp and University of Liège (Belgium) have found how the human brain changes and adapts to weightlessness after being in space for six months. Some of the changes turned out to be lasting—even after eight months back on Earth. Raphaël Liégeois, soon to be the third Belgian in space, acknowledges the importance of the research “to prepare the new generation of astronauts for longer missions.”

A child who learns not to drop a glass on the floor, or a predicting the course of an incoming ball to hit it accurately are examples of how the incorporates the physical laws of gravity to optimally function on Earth. Astronauts who go to space reside in a weightless environment, where the brain’s rules about gravity are no longer applicable.

A new study on in cosmonauts has revealed how the brain’s organization is changed after a six-month mission to the International Space Station (ISS), demonstrating the adaptation that is required to live in weightlessness. The findings are published in the journal Communications Biology.

How gut hormones shape reward: A systematic review of the role of ghrelin and GLP-1 in human fMRI

The gastrointestinal hormones ghrelin and glucagon-like peptide-1 (GLP-1) have opposite secretion patterns, as well as opposite effects on metabolism and food intake. Beyond their role in energy homeostasis, gastrointestinal hormones have also been suggested to modulate the reward system. However, the potential of ghrelin and GLP-1 to modulate reward responses in humans has not been systematically reviewed before. To evaluate the convergence of published results, we first conduct a multi-level kernel density meta-analysis of studies reporting a positive association of ghrelin (Ncomb = 353, 18 contrasts) and a negative association of GLP-1 (Ncomb = 258, 12 contrasts) and reward responses measured using task functional magnetic resonance imaging (fMRI). Second, we complement the meta-analysis using a systematic literature review, focusing on distinct reward phases and applications in clinical populations that may account for variability across studies. In line with preclinical research, we find that ghrelin increases reward responses across studies in key nodes of the motivational circuit, such as the nucleus accumbens, pallidum, putamen, substantia nigra, ventral tegmental area, and the dorsal mid insula. In contrast, for GLP-1, we did not find sufficient convergence in support of reduced reward responses. Instead, our systematic review identifies potential differences of GLP-1 on anticipatory versus consummatory reward responses. Based on a systematic synthesis of available findings, we conclude that there is considerable support for the neuromodulatory potential of gut-based circulating peptides on reward responses. To unlock their potential for clinical applications, it may be useful for future studies to move beyond anticipated rewards to cover other reward facets.

A Physical Theory For When the Brain Performs Best

Early critiques pointed out that proving a network was near the critical point required improved statistical tests. The field responded constructively, and this type of objection is rarely heard these days. More recently, some work has shown that what was previously considered a signature of criticality might also be the result of random processes. Researchers are still investigating that possibility, but many of them have already proposed new criteria for distinguishing between the apparent criticality of random noise and the true criticality of collective interactions among neurons.

Meanwhile, over the past 20 years, research in this area has steadily become more visible. The breadth of methods being used to assess it has also grown. The biggest questions now focus on how operating near the critical point affects cognition, and how external inputs can drive a network to move around the critical point. Ideas about criticality have also begun to spread beyond neuroscience. Citing some of the original papers on criticality in living neural networks, engineers have shown that self-organized networks of atomic switches can be made to operate near the critical point so that they compute many functions optimally. The deep learning community has also begun to study whether operating near the critical point improves artificial neural networks.

The critical brain hypothesis may yet prove to be wrong, or incomplete, although current evidence does support it. Either way, the understanding it provides is generating an avalanche of questions and answers that tell us much more about the brain — and computing generally — than we knew before.

Sean Carroll on Quantum Spacetime

Interview with Prof. Sean Carroll, Research Professor of Physics at Caltech and an External Professor at the Santa Fe Institute. We mainly talk about quantum spacetime: the idea that our familiar spacetime might be actually emergent from some complex quantum mechanical system. We cover entanglement, decoherence, entropic gravity, the AdS/CFT correspondence, string theory, black holes, along with several philosophical questions concerning these topics, including reduction and emergence, substantivalism vs. relationalism, monism, and much more.

Sean’s website: https://www.preposterousuniverse.com/
His recent book concerning these topics: https://www.preposterousuniverse.com/somethingdeeplyhidden/
His papers on these topics can be found here: https://www.preposterousuniverse.com/research/annotated-publications/
His podcast: https://www.preposterousuniverse.com/podcast/
And his Twitter: https://twitter.com/seanmcarroll/

Hong Kong Plans to Allow Retail Crypto Trading

Hong Kong plans to let retail investors trade digital tokens. It’s being seen as a major step toward its goal of becoming a crypto hub. Joanna Ossinger reports on Bloomberg Television.
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Researchers propose new mechanism for early chemical evolution

Scientists from The Ohio State University have a new theory about how the building blocks of life—the many proteins, carbohydrates, lipids and nucleic acids that compose every organism on Earth—may have evolved to favor a certain kind of molecular structure.

It has to do with a concept called chirality. A geometric property inherent to certain , chirality can dictate a molecule’s shape, chemical reactivity, and how it interacts with other matter. Chirality is also sometimes referred to as handedness, as it can be best described as the dichotomy between our hands: Though they are not identical, the right and the left hand are mirror images of each other, and can’t be superimposed, or exactly overlaid on one another.

In the journal ACS Earth and Space Chemistry, researchers now propose a new model of how the molecules of life may have developed their “handedness.”

The enigmatic black behemoths that govern our galaxy

Scientists try to unravel the birth, growth and power of black holes, some of the most forceful yet difficult-to-detect objects in our universe.

It was only last year that astronomers were finally able to unveil the first pictures of the supermassive black hole at the center of our Milky Way galaxy. But you couldn’t actually see the black hole itself, not directly. That’s because it is so dense that its gravitational pull prevents even light from escaping.

But the image of Sagittarius A, as our galaxy’s black hole is known, revealed a glowing halo of gas around the object—an object that we now know has a million times more mass than our sun.