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> If a black hole can never form, as viewed by me, then black holes don't exist. But they do -- the evidence is copious: http://www.galacticcenter.astro.ucla.

by lutusp 11y ago

> If a black hole can never form, as viewed by me, then black holes don't exist. But they do -- the evidence is copious: http://www.galacticcenter.astro.ucla.edu/animations.html http://www.galacticcenter.astro.ucla.edu/animations.html Arguing that, because the event horizon collapses the time dimension (from the perspective of a distant observer), therefore BHs aren't real, is like saying that sum(2^-n,(n,1,oo)) can't equal 1 because it's an infinite series and an infinity of additions takes too long. Think of black holes as objects of great mass, that have very bright accretion disks, surrounding an event horizon that is perpetually almost forming a singularity but never quite completes it (from the perspective of someone far from the horizon). > This means that time is stopped for the center of mass of the black hole ... From the perspective of a distant observer, the time horizon is located at the event horizon.

ars 11y ago
> But they do -- the evidence is copious: The evidence is non-existent. The only evidence is for supermassive objects, not event horizons. > Arguing that ... BHs aren't real, is like saying ... an infinite series and an infinity of additions takes too long. That's a terrible argument. One is an actual physical process, the other is a mathematical abstraction. Do you not understand infinity? Infinity means you can't actually do it. It doesn't mean you can't calculate it. > Think of black holes as objects of great mass, that have very bright accretion disks, surrounding an event horizon that is perpetually almost forming a singularity but never quite completes it (from the perspective of someone far from the horizon). Eh? If it never forms a singularity, it has no event horizon. i.e. it has none of the physic breaking properties of black holes. And accretion disks don't have to be bright BTW, as stuff falls in time dilation makes them much less bright (they "slow down", and emit photons less often). > From the perspective of a distant observer, the time horizon is located at the event horizon. When I say center of mass of the black hole I am naming the object I am talking about, not describing the location of the time horizon. Sorry if it was confusing.
- lutusp 11y ago
  >> But they do -- the evidence is copious: > The evidence is non-existent. If you're familiar with Occam's razor, you know that, for a given phenomenon, the simplest explanation is to be preferred. There certainly are massive objects at the center of most galaxies, and the most economical explanation is that they're black holes. No one is closing the book on these ideas -- that would be unscientific -- but there is strong evidence that these things are black holes. That they exist is beyond question. That they have super-high masses confined to a small space is beyond question. General Relativity then fills in the blanks in our observations. > That's a terrible argument. One is an actual physical process, the other is a mathematical abstraction. So is General Relativity. But because nature follows the same rules, General Relativity accurately predicts many aspects of reality (certainly not all). > And accretion disks don't have to be bright BTW ... Well, yes, they do -- they're giving up a huge amount of gravitational potential energy, and that energy must be conserved -- it's converted to kinetic energy, it becomes heat and light. Consider a satellite in an elliptical orbit. At the orbital apoapsis, potential energy is highest and kinetic energy is lowest. Not surprisingly, this is the point of smallest velocity. Now consider periapsis -- it's the reverse: lowest potential energy, highest kinetic energy, therefore highest velocity. In a normal planetary elliptical orbit with no friction, even though the two kinds of energy are constantly changing, they sum to a constant at each point in the orbit, so there's no net dissipation of energy. But as matter falls into a black hole, in order for it to pass through the event horizon, it must give up most of its energy (both potential and kinetic). Most of that energy is converted into heat and light. Most accretion disks preserve the rotational momentum of the infalling mass, so they're in the form of disks surrounding the event horizon. In theory, mass could fall directly into the BH without any rotation -- in that case, there would still be a huge energy conversion process and much radiated energy. Sp accretion disks are very bright. Here's a graphic of the imagined BH from "Interstellar", thought to be fairly accurate as movie graphics go: http://www.wired.com/2014/10/astrophysics-interstellar-black-hole/ http://www.wired.com/2014/10/astrophysics-interstellar-black... > Eh? If it never forms a singularity, it has no event horizon. Yes, and by the same reasoning, because a Calculus limit expression never gets to its limit, therefore Calculus is bunk. My point? Just as (1+1/n)^n approaches e as n approaches infinity (http://www.wolframalpha.com/input/?i=limit+n+-%3E+inf%2C+%281%2B1%2Fn%29%5En http://www.wolframalpha.com/input/?i=limit+n+-%3E+inf%2C+%28...), a black hole approaches its final form as mass approaches it from the perspective of a distant observer. You might as well have argued that, because this classic-physics gravitational equation: f = (G m1 m2) / r^2 assumes that all the mass is a dimensionless point at the center of the central body, therefore if m1 and m2 occupy the same point in space, the result is infinite, therefore (because infinity isn't a number) Newtonian gravitation is bunk.

by lutusp 11y ago

ars 11y ago

> But they do -- the evidence is copious: The evidence is non-existent. The only evidence is for supermassive objects, not event horizons. > Arguing that ... BHs aren't real, is like saying ... an infinite series and an infinity of additions takes too long. That's a terrible argument. One is an actual physical process, the other is a mathematical abstraction. Do you not understand infinity? Infinity means you can't actually do it. It doesn't mean you can't calculate it. > Think of black holes as objects of great mass, that have very bright accretion disks, surrounding an event horizon that is perpetually almost forming a singularity but never quite completes it (from the perspective of someone far from the horizon). Eh? If it never forms a singularity, it has no event horizon. i.e. it has none of the physic breaking properties of black holes. And accretion disks don't have to be bright BTW, as stuff falls in time dilation makes them much less bright (they "slow down", and emit photons less often). > From the perspective of a distant observer, the time horizon is located at the event horizon. When I say center of mass of the black hole I am naming the object I am talking about, not describing the location of the time horizon. Sorry if it was confusing.

lutusp 11y ago
>> But they do -- the evidence is copious: > The evidence is non-existent. If you're familiar with Occam's razor, you know that, for a given phenomenon, the simplest explanation is to be preferred. There certainly are massive objects at the center of most galaxies, and the most economical explanation is that they're black holes. No one is closing the book on these ideas -- that would be unscientific -- but there is strong evidence that these things are black holes. That they exist is beyond question. That they have super-high masses confined to a small space is beyond question. General Relativity then fills in the blanks in our observations. > That's a terrible argument. One is an actual physical process, the other is a mathematical abstraction. So is General Relativity. But because nature follows the same rules, General Relativity accurately predicts many aspects of reality (certainly not all). > And accretion disks don't have to be bright BTW ... Well, yes, they do -- they're giving up a huge amount of gravitational potential energy, and that energy must be conserved -- it's converted to kinetic energy, it becomes heat and light. Consider a satellite in an elliptical orbit. At the orbital apoapsis, potential energy is highest and kinetic energy is lowest. Not surprisingly, this is the point of smallest velocity. Now consider periapsis -- it's the reverse: lowest potential energy, highest kinetic energy, therefore highest velocity. In a normal planetary elliptical orbit with no friction, even though the two kinds of energy are constantly changing, they sum to a constant at each point in the orbit, so there's no net dissipation of energy. But as matter falls into a black hole, in order for it to pass through the event horizon, it must give up most of its energy (both potential and kinetic). Most of that energy is converted into heat and light. Most accretion disks preserve the rotational momentum of the infalling mass, so they're in the form of disks surrounding the event horizon. In theory, mass could fall directly into the BH without any rotation -- in that case, there would still be a huge energy conversion process and much radiated energy. Sp accretion disks are very bright. Here's a graphic of the imagined BH from "Interstellar", thought to be fairly accurate as movie graphics go: http://www.wired.com/2014/10/astrophysics-interstellar-black-hole/ http://www.wired.com/2014/10/astrophysics-interstellar-black... > Eh? If it never forms a singularity, it has no event horizon. Yes, and by the same reasoning, because a Calculus limit expression never gets to its limit, therefore Calculus is bunk. My point? Just as (1+1/n)^n approaches e as n approaches infinity (http://www.wolframalpha.com/input/?i=limit+n+-%3E+inf%2C+%281%2B1%2Fn%29%5En http://www.wolframalpha.com/input/?i=limit+n+-%3E+inf%2C+%28...), a black hole approaches its final form as mass approaches it from the perspective of a distant observer. You might as well have argued that, because this classic-physics gravitational equation: f = (G m1 m2) / r^2 assumes that all the mass is a dimensionless point at the center of the central body, therefore if m1 and m2 occupy the same point in space, the result is infinite, therefore (because infinity isn't a number) Newtonian gravitation is bunk.