Lifeboat Foundation

Circa 2021 Evidence of string theory by black holes as fuzzballs.

Abstract: We examine an interesting set of recent proposals describing a ‘wormhole paradigm’ for black holes. These proposals require that in some effective variables, semiclassical low-energy dynamics emerges at the horizon. We prove the ‘effective small corrections theorem’ to show that such an effective horizon behavior is not compatible with the requirement that the black hole radiate like a piece of coal as seen from outside. This theorem thus concretizes the fact that the proposals within the wormhole paradigm require some nonlocality linking the hole and its distant radiation. We try to illustrate various proposals for nonlocality by making simple bit models to encode the nonlocal effects. In each case, we find either nonunitarity of evolution in the black hole interior or a nonlocal Hamiltonian interaction between the hole and infinity; such an interaction is not present for burning coal. We examine recent arguments about the Page curve and observe that the quantity that is argued to follow the Page curve of a normal body is not the entanglement entropy but a different quantity. It has been suggested that this replacement of the quantity to be computed arises from the possibility of topology change in gravity which can generate replica wormholes. We examine the role of topology change in quantum gravity but do not find any source of connections between different replica copies in the path integral for the Rényi entropy. We also contrast the wormhole paradigm with the fuzzball paradigm, where the fuzzball does radiate like a piece of coal. Just as in the case of a piece of coal, the fuzzball does not have low-energy semiclassical dynamics at its surface at energies $E\sim T$ (effective dynamics at energies $E\gg T$ is possible under the conjecture of fuzzball complementarity, but these $E\gg T$ modes have no relevance to the Page curve or the information paradox).

From: Marcel Hughes [view email]

Scientists may have found the first “free-floating” black hole, as it moves around our Milky Way galaxy.

When large stars collapse, they are thought to leave behind black holes. If that is the case, there should be hundreds of millions scattered throughout the Milky Way, left behind after the death of those stars.

But scientists have struggled to find them. Isolated black holes are invisible.

They are part of the brain of almost every animal species, yet they remain usually invisible even under the electron microscope. “Electrical synapses are like the dark matter of the brain,” says Alexander Borst, director at the MPI for Biological Intelligence, in foundation (i.f). Now a team from his department has taken a closer look at this rarely explored brain component: In the brain of the fruit fly Drosophila, they were able to show that electrical synapses occur in almost all brain areas and can influence the function and stability of individual nerve cells.

Neurons communicate via synapses, small contact points at which chemical messengers transmit a stimulus from one cell to the next. We may remember this from biology class. However, that is not the whole story. In addition to the commonly known chemical synapses, there is a second, little-known type of synapse: the electrical synapse. “Electrical synapses are much rarer and are hard to detect with current methods. That’s why they have hardly been researched so far,” explains Georg Ammer, who has long been fascinated by these hidden cell connections. “In most animal brains, we therefore don’t know even basic things, such as where exactly electrical synapses occur or how they influence brain activity.”

An electrical synapse connects two neurons directly, allowing the electrical current that neurons use to communicate, to flow from one cell to the next without a detour. Except in echinoderms, this particular type of synapse occurs in the brain of every animal species studied so far. “Electrical synapses must therefore have important functions: we just do not know which ones!” says Georg Ammer.

Extremely interested to hear some of your opinions on this. Published in the journal Nature.

Scientists have discovered a new, mysterious particle. Of course, making new discoveries is exciting. But, perhaps the most exciting thing about this particle is that it could be a candidate for dark matter.

Incredibly, the never-before-seen particle was discovered using an experiment small enough to fit on a kitchen counter.

Continue reading “Scientists discovered a never-before-seen particle and it could be dark matter” »

Chance observations corroborate hybrid explanation for drop in brightness.

A weather satellite has helped explain why the red supergiant star Betelgeuse experienced an unprecedented dimming in 2019–20.

Its findings corroborate earlier studies that concluded the dimming was the consequence of a lower-temperature spot on the star, which reduced the heat going to a nearby gas cloud. This, astronomers believe, allowed the cloud to cool and condense into dust that blocked some of Betelgeuse’s light.

Continue reading “Weather satellite sheds light on ‘Great Dimming’ of Betelgeuse star” »