Comment by lotw_dot_site | Hacker News Reader

Comment by lotw_dot_site | Hacker News Reader

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At a certain point of abstraction, theoretical physics almost never has any direct correlation with empirical reality. It is most often used as a way to give the paradigm lenses that color our thoughts nice little workouts. (One can also apply Wittgenstein's notion of language games here.)

If, by the term "black hole", a person is referring to some object that has the shape of a mathematical point, then it just doesn't make much sense to call it a thing that relates to the world of observation. (The postulates of Quantum Mechanics dictate that physical objects must be fundamentally spread out in the form of wave functions.)

Solutions to simplistic kinds of mathematics come in the form of idealizations called "points". But physical reality is fundamentally spatial, and the necessary maths must involve things like topological manifolds, which brings us directly to the doorstep of String Theory, which is not so much a "theory" but rather a broad category that consists of the entire spectrum of all possible Quantum Field Theories. String Theorists, in fact, are always speculating over the possibility of some given theory's existence, such as when Witten spoke of a mysterious "M-theory" in the mid-90's.

>a person is referring to some object that has the shape of a mathematical point

Black holes aren't points, they're space-time shapes with a singularity at the middle and a spherical event horizon. The black hole at the center of our galaxy extends across 16 million miles, or a little over eighteen times the size of our sun.

If the singularity at the middle is slightly modified to be something else according to a better theory of gravity (most physicists believe that this will eventually happen), the outlying spacetime will not change very much, for reasons similar to how Newton was able to work out how the planets moved around the sun without knowing what the sun was made of or what was inside it.

If you imagine a circus tent propped up in the middle by a square pole, it will look very much like one propped up by a round pole. That's because solutions to the Laplace equation smooth themselves out as quickly as possible as you move away from the boundary condition.

I thought wether or not a singularity sits at the center of a black hole is actively discussed.

Or to be more precise: our math seems to indicate that there is one ... and precisely because of that we think that our math might be wrong or incomplete (because every single time we have encountered an "infinite" or something resembling that in the past it turned to be an error).

General Relativity says there is a singularity, more than one depending on the metric and coordinate system chosen.

However GR is not a quantum theory and it is well known that it clashes with quantum mechanics in ways that would show up in a singularity so what the physical reality of space actually at and nearby the singularity is still a mystery because we don't yet have an accepted theory of quantum gravity.

[deleted because brain wedgie]

That's literally the rest of my comment.

Sorry about that.

>they're space-time shapes with a singularity at the middle

Upon googling "black hole singularity", the first "People also ask" is "Does black hole contain singularity" and the answer is, "No, black holes in our universe, that is to say the real universe, do not contain singularities." While this doesn't in itself invalidate your point, it does seem to raise questions.

>The black hole at the center of our galaxy extends across 16 million miles, or a little over eighteen times the size of our sun.

I think what you are doing here is conflating the physical effects of the thing (the gravitational field of force) with the mathematical description of the thing itself (a precisely defined geometric structure). If you are talking about extremely strong gravity fields, such as those that bind entire galaxies (or galaxy clusters or even larger organizational patterns), then that is one class of things (empirical), but the purely theoretical notion of physical singularities is an entirely different class of things altogether (a class, which, IMO is perfectly self-contradictory).

>That's because solutions to the Laplace equation smooth themselves out as quickly as possible as you move away from the boundary condition.

This seems incorrect. I find that solutions to the Laplace equation typically "smooth themselves out" in a quasi-linear way (ie, the way sines and cosines do). The most vexing question in Quantum Mechanics is in fact why quantum states (i.e. the eigenfunctions that are solutions to PDE's such as Laplace's equation) appear to us as localized packets rather than how their "wave functional" mathematical descriptions would dictate (diffuse). The way this conundrum is resolved in QM is by way of a perfectly ad-hoc procedure called "collapsing the wave function".

What? Lighten up on the philosophy of a topic before you understand it.

Sure, the physical reality of the singularity is a bit of a mystery as it comes up against the nature of gravity at an extreme which requires a quantum theory which includes general relativity, but that is a known unknown and not what any of this black hole physics is about.

Outside of the singularity, and definitely outside the event horizon, a black hole is a very real thing which has been seen and measured in "empirical reality" and theory has so far matched well with measurement.

Nobody is going to Euclid and claiming a point or line is a real physical entity, anything but a useful abstraction.

>Lighten up on the philosophy of a topic before you understand it

But philosophy is an activity that must necessarily be done in order for there to even be a topic that can at all be understood in the first place! We had to have someone like Descartes before we could get someone like Newton, and Newton before the quantum theorists, etc.

The idea that you can just jump straight to (and always stay within the framework of) "hard science" and do away with the malleable philosophical bits that allow for the kind of connective tissue that binds civlizations is perhaps the biggest reason why we collectively face the existential crises that we currently do.

And the other idea that everyone (or at least everyone who has jumped through the hoops to get the necessary credentials) can simply sit fat and happy in their own arcane specialties as long as they are able to "prove" their worth to the rest of us by patting each other on the back with their circles of academic citations is... well... not very sustainable. All academic disciplines, to the extent that they cannot remain "rooted" within some larger framework of philosophical sensibility will necessarily get weeded in due time.

No, this isn't about the philosophy of science, but you in particular misrepresenting a topic and then making philosophical arguments about it. You ought to understand the science you're criticizing before sharing your commentary on it.

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