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Most images of black holes are illustrations. Here’s what our telescopes capture

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Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#131

Post by Santosh83 »

wallace_f wrote: post #129
Santosh83 wrote: post #126

Earlier quoted context omitted.

Signals take an infinte amount of time to reach a distant observer from just outside the event horizon. Which means we cannot see the event horizon or what is beyond, and we cannot also 'see' the event horizon being formed, or any matter crossing the event horizon. When the star collapses, light takes progressively longer to reach an outside observer, and eventually becomes too dim to detect. The same thing happens w…

>we cannot also 'see' the event horizon being formed I think what you're saying here is the confusing part. If no observer in the universe can ever witness a black hole being formed, it stands to reason they cannot exist (within the reference frame of observers outside it). Now I'm not asserting this as true or not, because I wouldn't assert such contrarian conclusions on a subject I have not properly studied; rather…

What is meant when we say we expect to see a black hole, or event horizon, forming? If we mean that we can no longer detect any signal from particular region, then to that extent, we can assert that what we call as a black hole exists there. We're defining it by its negatives, but I can't see how one can say that even those negatives don't exist.

Also its gravitational effects can be detected, so that is another reason why merely claiming a black hole doesn't exist, or never forms, seems to rather miss the mark.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#132

Post by matte_black »

Santosh83 wrote: post #117
matte_black wrote: post #110

Earlier quoted context omitted.

Hard to imagine how different the resulting universe might be, what if the speed of light and causality were say 10x higher than what it is now? Or what if the speed gradually increased over time? Would we just evaporate?

I think not, though am just speculating as a layman when I say that. But physicists have theorised this in much detail: https://en.wikipedia.org/wiki/Variable_speed_of_light I would imagine that a universe that doesn't obey basic causality will not exist for long, even if it comes into existence, nor will it support complex structures that can observe and reflect (like life). Other universes' physics and evolution mi…

I would have thought in such a strange universe there could at least exist some structures capable of knowing joy, but that thought has been thoroughly eradicated.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#133

Post by InclinedPlane »

dahart wrote: post #81
oevi wrote: post #24

Black holes are an excellent example for so called "cognitive metaphors". Because we found no better analogy, we named them "holes" despite the fact that they are basically the opposite: an object with enormous mass. This influences our thinking and our language when we discuss problems concerning black holes. We talk about "inside the black hole", "light cannot escape the black hole" or "spitting things out of the b…

> Because we found no better analogy, we named them "holes" Are you sure about that? This sounds specious. This requires knowing who named them and why. It sounds like a logical explanation, but history and human events don't follow logic and can't be derived. > We talk about [...] "light cannot escape the black hole" So, light not escaping certain "dark stars" was observed and was a concept before "black hole" was a…

Neither dark star nor black hole are apt "models" for the objects. These are phenomena of space-time, not just of gravity. Light cannot escape a black hole because escaping a black hole is impossible. And it's impossible because the space-time inside an event horizon has no trajectories that go forward in time which go farther away from the singularity. Black holes are like pocket universes with one-way roads connecting them to our Universe, this is why light doesn't leave the inside of the event horizon, the path between there and here only goes one way, unlike the rest of space-time.

"Dark star" is also a misleading term in that it implies the object is a star or something physical at all. In fact to us it doesn't matter what the object is inside the black hole, and its structure is essentially unknown to us (at present), because we can't interact with it. We can only interact with the space-time phenomenon that it created, the event horizon.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#134

Post by InclinedPlane »

Santosh83 wrote: post #49
blackrock wrote: post #38

Earlier quoted context omitted.

I would prefer if black holes were called "Dark Stars". Because that really is what they are. A weird star that is so massive, its gravitational field distorted the fabric of its local space, that not even light can escape it. It is theoretically possible that the black hole is still performing fusion, and emitting light and heat, like a regular star. But its gravitational field is so intense, that even light cannot…

Gravitational collapse overwhelms fusion pressure much before the black hole stage is reached, i.e., neutron stars. Also general relativity seems to indicate unambiguously that the in-falling matter collapses to a singularity, which obviously cannot have any kind of structure or process inside it. I guess only a quantum theory of gravity can clear up this enigma.

This is untrue, gravitational collapse does not overwhelm fusion pressure, fusion stops, that's why neutron stars are created.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#135

Post by westoncb »

dsacco wrote: post #90
akvadrako wrote: post #45

Earlier quoted context omitted.

I'm pretty sure every "mathematical abstraction" is a "cognitive metaphor".

No, not really. Symmetries of an n -gon (a 2-dimensional figure with n sides) are just permutations of the n numbers representing the sides. A cognitive metaphor is to call certain types of symmetries “rotations” or “reflections”, because we can’t really describe all symmetries through a metaphor like that. The symmetries are not literally operated by picking up your figure and flipping it over. On the other hand, ma…

> Information theoretically speaking, the inside of a black hole’s event horizon does not exist

There's your metaphor. If you didn't need to qualify it that way, you could perhaps get away with saying otherwise—but with the qualification, your telling us about a different domain in which something has the same 'structure' as a (physical) hole. That's exactly how analogies/metaphors work: two things which are analogous share the same structure but have representations of those structures in differing domains.

There's a simpler way of seeing that it's metaphor still, though. You have chosen some characteristics of holes and arbitrarily decided that they are the ones which define it—but if we want to say it's literally a hole and not metaphorically, then all the attributes which familiar physical holes have should apply. For instance, there should be an interior surface, and things inserted into it should be retractable. Your description treats the singularity and event horizon as two distinct objects, which provides a kind of solution to the second—but it seems like those two things aren't as readily separable as, for instance, if we had a hole in the ground and it was filled with a powerful acid: in that case it's clear which is hole and which is thing filling it. Perhaps I'm mistaken, but I'd bet that the way in which the singularity 'fills' a black hole cannot be anything more than metaphorically.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#136

Post by dsacco »

westoncb wrote: post #135
dsacco wrote: post #90

Earlier quoted context omitted.

No, not really. Symmetries of an n -gon (a 2-dimensional figure with n sides) are just permutations of the n numbers representing the sides. A cognitive metaphor is to call certain types of symmetries “rotations” or “reflections”, because we can’t really describe all symmetries through a metaphor like that. The symmetries are not literally operated by picking up your figure and flipping it over. On the other hand, ma…

> Information theoretically speaking, the inside of a black hole’s event horizon does not exist There's your metaphor. If you didn't need to qualify it that way, you could perhaps get away with saying otherwise—but with the qualification, your telling us about a different domain in which something has the same 'structure' as a (physical) hole. That's exactly how analogies/metaphors work: two things which are analogou…

> There's your metaphor.

No, it’s not. That’s the definition, much like information theoretic death is death. Here is a metaphor: from our perspective on a street, we cannot perceive anything within a manhole, just like from outside a black hole we cannot perceive anything inside it.

Here is not a metaphor: a black hole is a hole in space, with a singularity inside of it.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#137

Post by AnimalMuppet »

qubex wrote: post #65
Santosh83 wrote: post #49

Earlier quoted context omitted.

Gravitational collapse overwhelms fusion pressure much before the black hole stage is reached, i.e., neutron stars. Also general relativity seems to indicate unambiguously that the in-falling matter collapses to a singularity, which obviously cannot have any kind of structure or process inside it. I guess only a quantum theory of gravity can clear up this enigma.

(Not to mention that once one has crossed the Schartzchild Radius time dilation becomes infinite from the perspective of the outer universe, and time freezes, so any process becomes frozen in its tracks, at least from the perspective of external observers.)

What happens in the Swartzchild Radius, stays in the Swartzchild Radius.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#138

Post by AnimalMuppet »

ars wrote: post #17
podiki wrote: post #14

Earlier quoted context omitted.

I'll take your comment in good faith, but there are very good reasons to believe black holes exist and that, for instance, the center of our galaxy contains a very massive black hole and not a neutron star. This is basic general relativity, which only has (physical and theoretical) evidence in support of it. While quantum gravity is still very much uncertain, that would (most likely) only have to do with understandin…

You skipped a step. Yes, the general relativity prediction of a black hole is solid once it exists . But you have to construct that black hole in the first place. And it's that part that's on shaky ground.

You seem to have missed the part where podiki offered the object at the center of the galaxy as evidence that a black hole currently exists. So you're arguing against the evidence when you say (over and over and over) that black holes can't form.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#139

Post by AnimalMuppet »

clarkmoody wrote: post #130
matte_black wrote: post #57

If the speed of light of this universe was raised significantly, is there some point where black holes would be impossible to form? I assume if the speed of light were lowered black holes would become far more common?

In the Death's End by Cixin Liu, there is a speed of light weapon that lowers the local speed of light to almost nothing, effectively taking an enemy out of the game until the end of the universe.

In Redshift Rendesvous (don't recall the author), there was an environment where the speed of light was just above running speed - maybe 15 m/s. You observed relativistic effects just walking around.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#140

Post by coryfklein »

InclinedPlane wrote: post #133
dahart wrote: post #81

Earlier quoted context omitted.

> Because we found no better analogy, we named them "holes" Are you sure about that? This sounds specious. This requires knowing who named them and why. It sounds like a logical explanation, but history and human events don't follow logic and can't be derived. > We talk about [...] "light cannot escape the black hole" So, light not escaping certain "dark stars" was observed and was a concept before "black hole" was a…

Neither dark star nor black hole are apt "models" for the objects. These are phenomena of space-time, not just of gravity. Light cannot escape a black hole because escaping a black hole is impossible. And it's impossible because the space-time inside an event horizon has no trajectories that go forward in time which go farther away from the singularity. Black holes are like pocket universes with one-way roads connect…

> escaping a black hole is impossible

Except for Hawking Radiation [1]

"black holes that do not gain mass through other means are expected to shrink and ultimately vanish. Micro black holes are predicted to be larger emitters of radiation than larger black holes and should shrink and dissipate faster."

[1] https://en.wikipedia.org/wiki/Hawking_radiation

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