I would say no, because we aren’t falling inward towards our central BH. We’re orbiting it.
actually, I take back that last bit. We orbit the center of the galaxy, and there’s a BH there.
And you have to slice definitions pretty thin to make a distinction between orbiting and falling. But your second point is correct: While the black hole is pretty big, all of the non-black-hole stuff in the core is even bigger.
But that’s Laplace’s classical (or Newtonian) description of a “Dark Star”. Which is neither a hole nor like a “Black Hole” as described by relativity.
I’d agree with those who argue the term “Black Hole” is merely generally descriptive in the conversational sense, quite poetic and evocative, but not meant to be taken in any precisely literal or scientific sense.
Kind of like saying that a system “prefers” to be in a lower energy state, or that a system “wants” to become more disordered, or attempting to describe how an electron travels from point A to point B in classical terms.
My DH is a scientist who has studied this phenomenon and I think the consensus of opinion is that no really knows what it is. The word “hole” is just a word used to describe something we don’t understand
I don’t think it is fair to say no-one knows what it is: its a theoretical object (using the term here to mean something that was predicted by theory originally) for which there is pretty good empirical evidence for its existence.
On the theoretical side there are text books that give precise mathematical definitions of what a black hole is, within the context of an asymptotically flat solution in general relativity. Also the basic black hole solutions are among the few known exact solutions of relativity and it is further known that the exterior solutions are stable under local peturbations, meaning they provide realistic models of a good deal of the behaviour of black holes.
That of course isn’t to say there aren’t plenty of open problems, but I think if we had a good enough definition of how the term “hole” should be applied, it wouldn’t be too difficult to provide a contextual answer as to whether a black hole is indeed a hole (though that said if it boils down to a topological question it could potentially be very difficult to answer). The problem then in answering the question posed by the OP is not so much what we don’t know about black holes, more the lack of definition of what a hole is.
All I know fer sure about holes in general is, when yer in one, stop diggin’.
I think it’s safe to say that anything that can describe the entire universe can measure up to the word “big”. The other problem word may actually be “the”, since the theory doesn’t really describe a singular event but an on-going process that continues today. It’s like how the theory of evolution talks about how life changes, but not how life began.
Like many things in astronomy (planetary nebula, dark matter), the Big Bang Theory has a misleading name that causes lots of misconceptions. The term “black hole” is pretty accurate in comparison.
Yes, that was what I was getting at.
There is one sense in which I thought a black hole is very hole-like : you can take a spatial slice of Schwarzschild spacetime to get an Einstein-Rosen bridge, which does look rather like a hole in anybody’s money.
There are lots of caveats here though:
-The Einstein-Rosen bridge is a 3D hypersurface rather than a 2D surface. That means that 1 dimension on the diagram above has been suppressed. To imagine how it should look without suppressing that dimension each 1D ring on the diagram should actually be a 2D sphere, in such a way that a 3D hypersurface is formed. Unfortunately I don’t think even hallucinogenic drugs would allow you to imagine that.
-The Einstein-Rosen bridge is from the maximally extended Schwarzschild solution, and part of it the diagram is in a region which an astrophysical black hole (i.e. a real black hole) doesn’t have. I believe what you would/could get with an astrophysical black hole is the same but with everything below the pinkish-purple region in the middle missing.
-The diagram just a peculiarity of a particular way of slicing spacetime. The time evolution of the diagram is that the throat elongates and then pinches off before anything can travel from one side to the other. Everything in the pinkish-purple region will hit a singularity. NB the diagram above is ‘sliced’ in such a way that the singularity (or singularities to e more accurate) is not on the diagram, but it is still unavoidable.
Which is also applicable to black holes. If your rocket ship is inside of one, you’re going to eventually reach the center and certain death, but anything you do with firing the rockets is only going to hasten that end. To maximize your remaining lifespan, you want to “stop digging”, and just coast.
I believe (I haven’t looked at this problem for a couple of years), that the maximum time experienced by an in-falling observer is the observer free-falling from rest at infinity. This means that if you are not already in this frame, the best strategy to maximize the amount of time you experience before hitting the black hole would be to fire your rockets (either away from or towards the black hole or any other direction, depending on your particular state of motion).
This is the way it was explained to me. A “singularity” is just a fancy way of saying our current understanding of physics takes us up all the way to “this” point. After that, the math falls apart and we don’t know what the heck “that” is.
Not quite. A hole is where you expect to find something that is more or less consistent with the surrounding contents of the space. Like jelly in a doughnut hole. Hole is a relative term applying to an absence of the surrounding medium. The earth occupies a hole in the ether of space. A hole in styrofoam can be filled with water, a heavier and denser medium than the styrofoam, but it still a hole.
whoops. will ask mod to kill hed.
General relativity can be produce solutions that are badly-behaved from some fundamental point of view in many different, subtle and not so subtle ways. The term “singularity” in general relativity is a lump-all term for these bad behaviors.
In the context of black holes: taking the textbook definition, plus a fairly uncontroversial classical assumption that energy density is never negative, it can be shown black holes exhibit a certain type of bad behavior. That bad behavior is something called geodesic incompleteness and specifically means for black holes that the timelines of some observers come to an abrupt halt at some point in their finite future. This can be seen though as more general to general relativity: i.e. it produces bad behavior in physically realistic situations.
The problem is how to interpret these bad behaviors. One school of thought that was fashionable among those who contributed to the golden age of relativity that started in the 1960s, is that such singularities should be taken literally: i.e. something can literally and suddenly cease to exist in a fundamental way after only experiencing a finite amount of time. I think the preferred view among more recent physicists though, who have an eye to getting general relativity to emerge out of quantum gravity or a theory of everything, is that such singularities are more likely general relativity being pushed past its limits of applicability.
I think black holes are mysterious in that they have this veil that hides not only singularities, but also possibly other bad behaviors that aren’t seen as quite fundamental enough to be classed as singularities (e.g. closed time loops, parallel Universes), but are still just as worrying from a physical point of view nonetheless. However we still know a pretty decent amount about BHs, and as we don’t have a theory that can explain all physical phenomena all physical theories fail at some point, so even if we view these bad behaviors as failures in the theory, I’d still say we have a pretty rich theoretical knowledge of black holes.