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The question of hairy black holes is intimately connected to the greatest puzzle in modern physics: How can general relativity be merged with quantum theory?
by xeonmc 1y ago
The 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?
- layer8 1y agoWhen you cross the event horizon, you’re falling at close to the speed of light, relative to the event horizon. But due to relativity, light bouncing off the falling objects still propagates at light speed in all directions relative to the falling objects (including the falling observer). That light can’t move outwards, due to being inside the event horizon, and accelerates towards the singularity, but the observer accelerates to the singularity faster, relative to light being reflected outwards. The falling rest frame accelerates towards the singularity, but within that accelerating rest frame, light behaves normally between objects in that frame (assuming a large enough black hole so that the differences in radial distance between the objects is negligible). Consider two cars driving on a highway at the same speed. If one of the cars decelerates, it appears to be moving backwards relative to the other car, while still continuing to move forward relative to the road. It’s similar for light and an observer falling towards the singularity. They both fall towards the singularity, but light being reflected backwards will fall a bit slower, thus appearing to move backwards relative to the observer, even though the light still moves forward toward the singularity.
- thunderbong 1y agoVery well explained. Thank you
- gus_massa 1y agoNo. The "no hair theorem" has a condition that says "after a while", but people ignore it because it's a short time. So intermediately after the object entered the black hole will have bump and will emit gravitational waves and after a while it will be a perfect sphere (if it's not rotating, or a similar round elongated shape if rotating). As far as I can understand, it totally unrelated to Quantum Mechanics.
- griffzhowl 1y agoI think the short answer is that no one knows, because a proper answer would need an understanding of how black holes and quantum theory go together, which is not currently known. The longer answer (if you want to get in to the extensive literature) is that your question seems to relate to the black hole information paradox https://en.wikipedia.org/wiki/Black_hole_information_paradox https://en.wikipedia.org/wiki/Black_hole_information_paradox
- Arwill 1y agoI think what is relevant here, is that there is a separation between the inside and the outside of the black hole. Since there is no communication between the two, on the inside it could be anything. And its not just the matter and space, even the laws of physics might be completely different. If it weren't so, then there had to be a "super-space" that communicates how ordinary space behaves on both the outside and the inside the black hole.
- anuramat 1y agowith QM, the "unobservable" stuff is just guaranteed to not be there, eg a particle detected at (x,t) is definitely not at (x',t); so you are observing it "not existing there" -- collapse just makes the measurement at (x',t) redundant meanwhile with black holes you know there is something, but you can't measure in both cases you don't get any information, but in QM it's only because you already know everything there is to know about the system could it end up being fundamentally the same thing? I don't see why not, but for it to make sense you'd have to get a nobel prize for grand unification theory first also, collapse is not real and can't hurt you anyway, see many-worlds