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Astrophysicists find no 'hair' on black holes
- pavel_lishin 1y ago> According to Albert Einstein’s general theory of relativity, the behavior of a black hole depends on two numbers: how heavy it is, and how fast it is rotating. And that’s it. Black holes are said to have “no hair” — no features that distinguish them from their fellows with the same mass and spin. As far as I know, there's a third property that black holes have - electric charge. Would a sufficiently strong electric charge between two black holes be detectable, whether they both have the same charge, or opposing charges? I suppose based on the article, the effects would only take places once the black holes got within 40km of each other...
- momoschili 1y agoIt has been proposed and is often studied in different contexts, but it seems unlikely that we will be able to measure it any time soon.
- raverbashing 1y agoI think you might just need a comb and some pieces of paper
- renewiltord 1y agoJudging by what the article says they can't be different > In theory, there’s a third defining property: electric charge. But real, astrophysical black holes have negligible net charge.
- fsmv 1y agoBlack holes can have charge but a charged black hole would attract ions of the opposite charge strongly and would quickly neutralize. So it would be quite difficult to get a non-negligible charge on a black hole.
- BurningFrog 1y agoSo some very advanced and bored civilization could take black holes and shoot gigantic numbers of protons into it, and get a very positively charged black hole. If you pump in enough charge that the electrical repulsion is stronger than the gravity attraction, you can then store them safely next to each other, for when you might need one.
- marcosdumay 1y agoIt also allows you to move the black hole around, somewhat freely. It may be a very useful thing if it turns out that we can make small ones.
- Terr_ 1y ago> move the black hole around, somewhat freely [...] small ones At the risk of spoiling the mystery of a 50-year-old short story, this happens in the The Borderland of Sol by Larry Niven.
- JdeBP 1y agoIf you enjoy that sort of thing, also read Killing Vector by Charles Sheffield.
- deleted 1y ago[deleted]
- pavel_lishin 1y agoI immediately thought of that story as I was reading the comment you replied to :P
- BurningFrog 1y agoFlinging one at an enemy civilization could be a clean way to resolve conflicts!
- floxy 1y agoDon't forget color charge: https://arxiv.org/abs/2310.16877 https://arxiv.org/abs/2310.16877
- behnamoh 1y agoYet another clickbait title by the quantamagazine. I'm afraid these "science popularization" techniques only make it more confusing for the general public. Just say the exact, scientific word and cut this bs.
- renewiltord 1y agoNo-hair theorem is just the name https://en.m.wikipedia.org/wiki/No-hair_theorem https://en.m.wikipedia.org/wiki/No-hair_theorem
- IAmBroom 1y agoDoes the Hairy Ball theorem apply to hairless black holes? Asking for a friend...
- jleyank 1y agoIf they finds "casual" names for scientific principles annoying, they're going to just LOVE the names for genes. hERG activity is a bad thing that gets drugs taken off the market (cardiac arrhythmia). hERG means "human ether-a-go-go-related gene". Scientists are human, and obviously playful at times. It's not a recent thing. Check out quark names and their associated properties.
- kgwgk 1y agoA few examples: https://www.wikipedia.org/wiki/List_of_unusual_biological_names https://www.wikipedia.org/wiki/List_of_unusual_biological_na... https://en.wikipedia.org/wiki/List_of_chemical_compounds_with_unusual_names https://en.wikipedia.org/wiki/List_of_chemical_compounds_wit...
- ordu 1y agoYeah. The photo of a hairy astrophysicist claiming that if black holes have hair, it is shorter than 40 km seems like a petty way to spark a public interest.
- mr_mitm 1y ago
- xeonmc 1y agoThe question of hairy black holes is intimately connected to the greatest puzzle in modern physics: How can general relativity be merged with quantum theory? Consider the situation where an object crosses a black hole’s point of no return, called the event horizon. According to general relativity, all outsiders will see is how the swallowed object contributes to the two numbers that describe the black hole: how much mass the object adds, and how much faster or slower it makes the black hole rotate. The idea that anything within the event horizon should be treated as an opaque black box -- could it be reinterpreted as saying that any property which has dependence on spatial or temporal distribution within becomes an unknowable quantity? If so, can it be tied somehow to Quantum Mechanic’s idea of the removal of degrees of freedom by observation, since now certain quantities are not unobserved but rather unobservable in principle? I am asking this from a naive laymen’s point of view, so I may be conflating entirely unrelated ideas.
- trjordan 1y agoNot exactly. Black holes are not lopsided, for instance. There isn't anything on "one side" of them, once the matter has crossed the event horizon. Rotating black holes are pretty well modeled as a spinning ring: https://en.wikipedia.org/wiki/Ring_singularity https://en.wikipedia.org/wiki/Ring_singularity
- layer8 1y agoFor one, observers inside the event horizon can still observe each other. From the point of view of an observer falling into a black hole, nothing unusual happens when they cross the event horizon. They still observe stuff falling in with them in the same way as before (assuming a large enough black hole so that the local curvature is negligible). If Hawking radiation is real, it might also expose information from inside the black hole, possibly solving the information paradox. In that sense, the inside of a black hole would still be “observable” from the outside in the QM sense. But since we don’t know how quantum gravity works, that is an open question.
- agent327 1y agoHow can that be true? Inside the event horizon, there is only one direction: down. If light cannot escape, how can it happily bounce around, reflect on something, then reach your eyes? How could signals from your feet (say) even reach your brain, assuming a feet-first entry into the black hole?
- datadrivenangel 1y agoAnother blow against string theory.
- importantstuff 1y agoYou might want to consider the article more carefully, especially the section "Short Hair, Long Hair". The predictions of string theory are in no way falsified by the analysis conducted by these researchers.
- IAmBroom 1y agoIn fact, it's hard to find predictions of string theory that are falsifiable at all.
- moralestapia 1y agoAn interesting consequence of having "no hair" on them is that information on everything that falls in them is lost forever, which leads us to an information loss paradox. Not nice.
- fpoling 1y agoYou do not need a black hole for the information loss. Just shout a flashlight into empty space. Any information encoded in photons will be lost from the point of view of the sender. And then the classical notions like information or entropy are not really compatible with General Relativity. Richard Tolman almost 100 years ago proposed interesting extension to the classical thermodynamics that is compatible and can potentially explain apparent paradox of information loss, but it is not known if that extension matches reality.
- griffzhowl 1y ago> Any information encoded in photons will be lost from the point of view of the sender. The crucial difference is "from the point of view of the sender". The black hole information paradox is that the information is lost from any possible receiver (even any possible ensemble of receivers surrounding the black hole). It's not the same thing
- fpoling 1y agoThe information is not lost from the point of view of receivers inside the black hole horizon. Which again points out that the classical notion of information just does not work in a universe with multiple causally disconnected regions.
- griffzhowl 1y agoWhat happens when the black hole evaporates then, and there is no more horizon? That's the black hole information paradox
- 1y ago
- alex1138 1y agoBlack hole goes into a barbershop Barber goes "You're kidding me, right?"
- slipperydippery 1y agoBlack hole goes into a barbershop. Barber goes, "You're kiddiinnngggg mmmmmmeeeeeeeeee, riiiiiiiiiiiiiiiiiiiiiiiiiiiiiii...."
- IAmBroom 1y agoThe bartender says "We don't serve Tachyons here." A Tachyon walks into a bar.
- FergusArgyll 1y agoThis reminds me of something I mull over; Greek style philosophy seems so smart, rational and correct until you actually observe the world. Imo the perfect example is elementary particles - the Greeks (mostly) were convinced that it's impossible for something physical to be elementary (cannot be further split) and logically it is hard to understand why can't we continue to split the particle?! but hey, we can't. Physical beings which cannot be distinguished from one another would have made their heads spin...
- JdeBP 1y agoIndeed. That's rotational frame dragging for you. (-:
- wahern 1y agoAren't quarks and, probably, electrons point-like particles? In that sense the fundamental subatomic particles aren't "physical" in the sense the Greeks would have thought of them, e.g. having a non-0 diameter, and in that way modern physics sort of vindicates their deductive reasoning. Their logic wasn't wrong, per se, it was their starting assumptions that were flawed (or at least incomplete), which is acceptable as far as deductive reasoning goes.
- JdeBP 1y agoNo. Because the GR/QM conflict comes up in the other direction that way. GR predicts infinities for zero-radius particles. Indeed, so too does classical electromagnetism. In any case, "quanta" does not really mean the same as the classical notion of point particles. * https://youtube.com/watch?v=zPZrDbPAuKs https://youtube.com/watch?v=zPZrDbPAuKs
- griffzhowl 1y agoTo be fair to the Greeks, thay also came up with the idea of elementary particles. I think it's Democritus who's credited with the idea of "atoms". It's been ages since I've read about him in any depth but I remember something about him having an idea that because of the indefinite divisibility of length then the elementary particles would have to have a diameter smaller than any given length, i.e. be infinitesimal, so they had quite sophisticated speculations