31–40 of 81 posts
Cross-posting /r/bestof ( https://www.reddit.com/r/worldnews/comments/113casc/scientis... ) because it really does a nice job with history and breaking down the highlights (to me at least:) -------- Reading the paper, this is the best summary I can make. Note that I'm an engineer, not an astrophysicist. The basic thought is that in 1963, a guy named Kerr seems to have come up with the best approximation of black hole…
Earlier quoted context omitted.
The "no-hair theorem" says that black holes only have three properties: mass, angular momentum and electric charge. If a black hole is perturbed (for example, by merging with another black hole or swallowing a star), it will temporarily be more complicated, but then it quickly goes back to having only above three properties. The extra properties (such as the gravitational quadrupole moment) asymptomatically decay, ov…
The "no hair theorem" is a theorem of classical general relativity. Attempts to try to model it with some quantum mechanics thrown in show a tremendous amount of additional state that scales with the surface area of the black hole. This work suggests even more complications to that picture. That it looks very different from the classical theory. All of this should come with disclaimers and fudge factors because of ou…
However, to an extremely good approximation, they'll still look like objects with just three properties.
In my imagination, I always thought we could put a black box around a black hole, and it would be indistinguishable from any other mass - that is, any other mass that can be treated as a point mass. I.e. put a black hole with solar mass 1 in a black box. Put a star with solar mass 1 in another black box. From a gravitational point of view, you couldn't tell the difference, yes? But this result implies that the black…
It is my understanding that, from a gravity-only standpoint, you are right. But I actually thought that black holes slowly evaporate, i.e., lose mass, from emitting Hawking radiation. It isn't clear from the article whether the vacuum energy black holes still have that property. The article confuses me on something else. It mentions a link between black hole mass and the expansion of the universe, but then it seems t…
Earlier quoted context omitted.
The "no hair theorem" is a theorem of classical general relativity. Attempts to try to model it with some quantum mechanics thrown in show a tremendous amount of additional state that scales with the surface area of the black hole. This work suggests even more complications to that picture. That it looks very different from the classical theory. All of this should come with disclaimers and fudge factors because of ou…
Black holes probably have additional state in a full quantum theory, such as lepton number. However, to an extremely good approximation, they'll still look like objects with just three properties.
See the table on this page for the categories:
Cross-posting /r/bestof ( https://www.reddit.com/r/worldnews/comments/113casc/scientis... ) because it really does a nice job with history and breaking down the highlights (to me at least:) -------- Reading the paper, this is the best summary I can make. Note that I'm an engineer, not an astrophysicist. The basic thought is that in 1963, a guy named Kerr seems to have come up with the best approximation of black hole…
Does it expand faster next to heavy object or slower?
For those with an interest in this topic, but a disdain for "science news", I recommend checking out Sabine Hossenfelder's youtube channel: https://www.youtube.com/@SabineHossenfelder She's a theoretical physicist, and covers topics such as this from the point of view of a real expert, and doesn't "talk down" to the audience at all. (Though I must say, she does engage in clickbait-style video titles and thumbnails, b…
She already panned it on twitter. https://twitter.com/skdh/status/1626113544339980291
Cross-posting /r/bestof ( https://www.reddit.com/r/worldnews/comments/113casc/scientis... ) because it really does a nice job with history and breaking down the highlights (to me at least:) -------- Reading the paper, this is the best summary I can make. Note that I'm an engineer, not an astrophysicist. The basic thought is that in 1963, a guy named Kerr seems to have come up with the best approximation of black hole…
https://bigthink.com/starts-with-a-bang/black-holes-dark-ene...
I think the requirement for coupling from spin is due to frame-dragging, where there's basically a shear force to accommodate conservation of momentum on the stress-energy tensor.. or smth, a lot over my head. This coupling in theory goes out to infinity, but wouldn't be significant for small gravitational objects. Very large BHs spinning near lightspeed would couple very far.
From there, the intuition that helps me went like "imagine a rubber band, being pulled apart. Then imagine a pinched point somewhere along its length. As you continue to pull the whole thing, the interior pressure on the pinched part will increase." That's why the interior energy of the BH increases in connexion with the expanding space.
For those with an interest in this topic, but a disdain for "science news", I recommend checking out Sabine Hossenfelder's youtube channel: https://www.youtube.com/@SabineHossenfelder She's a theoretical physicist, and covers topics such as this from the point of view of a real expert, and doesn't "talk down" to the audience at all. (Though I must say, she does engage in clickbait-style video titles and thumbnails, b…
She's generally good but in addition to the clickbait she also has a habit of "it's so easy, it's just [controversial pet theory] and the rest of science disagrees because they are wrong". I find that most physicists in educational roles shy away from interjecting with opinions and even mild speculation more than they should but she tends to overcorrect in the other direction. This tends to attract a particular type…
That's probably the best description of her style of argument I've read, and it's honestly why I can't stand reading/watching her anymore. Much too much of it comes off to me as "What the physics establishment doesn't want you to know!!" type of stuff, so it then attracts the "yeah, she's speaking truth to power, I knew it was a conspiracy!" crowd.
I mean, there are plenty of folks that have expressed a ton of skepticism about string theory without the semi-conspiratorial angle.
In my imagination, I always thought we could put a black box around a black hole, and it would be indistinguishable from any other mass - that is, any other mass that can be treated as a point mass. I.e. put a black hole with solar mass 1 in a black box. Put a star with solar mass 1 in another black box. From a gravitational point of view, you couldn't tell the difference, yes? But this result implies that the black…
> I always thought we could put a black box around a black hole, and it would be indistinguishable from any other mass - that is, any other mass that can be treated as a point mass. Yes, that's what the standard theory of black holes says. > this result implies that the black box with the black hole will gain mass over time, even without adding any mass into the black box? Sort of. First, it's important to note that…
I only point this out because we haven't been inside a black hole, so we don't really know what an 'ordinary' one looks like.