Three Air Tight Reasons Why No Object Can Ever Reach An Event Horizon

[OceanBreeze]

I may not quite understand what you're saying here Popeye, but infinity is not involved here, is it? The object could be approaching from a distance much less than infinite. Nor is an object necessarily approaching a black hole in "free fall."

 

 

 

 

No, no need to have the falling mass start at infinity. It is just a convention, although a confusing one, to use infinity as a reference when working problems involving gravitational potential energy. The reason being is, physicists want a standard reference they can use for all problems. If they used the center of the earth as a reference, what will they do when working a problem about Jupiter or Mars? So, they use infinity, but that also causes confusion because the potential must decrease as an object falls. So, they resort to a double reversal in defining infinity as the height where gravitational potential energy is Zero and make the potential energy negative. In that way, as it falls toward the gravitational attractor the PE does decrease, because Zero is the highest value a negative number can have! Now you are probably sorry you asked that question!

 

Anyway, thankfully I am not a physicist so I just used a positive result in my calculation which results in the object reaching c at the event horizon. That is the highest velocity an object can theoretically ever reach under gravitational attraction. In reality, objects can fall in at lesser velocities.

 

What I like about my calculation is that the highest velocity the distant observer sees is 0.385c and that agrees well with what was observed in the experiment that you cited.

 

According to the source:

 

They found that spectra was red-shifted and the matter they were observing was falling into the black hole at about 100,000 km/s, or about 30% of the speed of light. In astronomical terms the matter was very close to the hole. Its distance from the hole is only 20 times the size of the hole itself, and the matter had barely any rotational energy.

 

So the matter wasn’t rotating but falling straight inwards, at least that is how I interpret the information.

 

At 20 times the radius, this matter was more distant than the 3 times the size of the hole that I calculated. Maybe it reaches 0.385c at 3 times radius? I don’t know, but I am satisfied with the fairly good agreement between the math and the experimental evidence.

 

I've seen physicists claim that an object can enter a black hole at any speed between 0 and c.  The idea seems to be that accretion disks surrounding the black hole will show down the approaching object and put in a series of orbits which spiral toward the black hole.

 

 

 

No doubt matter does often spiral into black holes but, not being a physicist, I tried to make the problem as simple as possible.

I don't pretend to have all the answers.

[Moronium]

No, no need to have the falling mass start at infinity. It is just a convention, although a confusing one, to use infinity as a reference when working problems involving gravitational potential energy. 

 

 

That's also my understanding, but perhaps for different reasons.

 

Suppose that an object leaves earth's "event horizon" at a velocity equaling  earth's escape velocity.  Further suppose that there is no other matter in the universe.  Now what?

 

For the sake of argument, let's say the escape velocity is 17,000 mph.  Having escaped at that speed, does the object just continue to go 17,000 mph forever?

 

No. Even though it will never be pulled all the way back to earth, it is still being affected by the Earth's gravitational pull.  So it gradually slows down.  At infinity it slows to zero velocity.  Now if you reversed the math, starting from there, THEN it would eventually reach earth's "event horizon" at the same velocity it originally left at, i.e., 17,000 mph.

 

But let's say an object is currently 5 feet from the earth's event horizon and is approaching earth at the rate of 10,000 mph at that point.  It will not speed up to 17,000 over the next five feet, eh?  It will enter at a speed that is lower than the escape velocity.

Edited April 7, 2019 by Moronium

[OceanBreeze]

I find it somewhat disconcerting that I can't help Popeye, normally a reasonable guy, see this.  He just equates "time" with clock ticking rates.

 

No, I equate time with change. As long as something is changing, time is passing. If the rate of ALL change is slowing down, (and not just somebody’s clock) then time itself must be slowing down.

 

What is your definition of time?

[OceanBreeze]

That's also my understanding, but perhaps for different reasons.

 

Suppose that an object leaves earth's "event horizon" at a velocity equaling  earth's escape velocity.  Further suppose that there is no other matter in the universe.  Now what?

 

For the sake of argument, let's say the escape velocity is 17,000 mph.  Having escaped at that speed, does the object just continue to go 17,000 mph forever?

 

No. Even though it will never be pulled all the way back to earth, it is still being affected by the Earth's gravitational pull.  So it gradually slows down.  At infinity it slows to zero velocity.  Now if you reversed the math, starting from there, THEN it would eventually reach earth's "event horizon" at the same velocity it originally left at, i.e., 17,000 mph.

 

But let's say an object is currently 5 feet from the earth's event horizon and is approaching earth at the rate of 10,000 mph at that point.  It will not speed up to 17,000 over the next five feet, eh?  It will enter at a speed that is lower than the escape velocity.

 

 

Of course. But a black hole is not the same as the earth. There is no escape velocity from a BH.

[Moronium]

No, I equate time with change. As long as something is changing, time is passing. If the rate of ALL change is slowing down, (and not just somebody’s clock) then time itself must be slowing down.

 

What is your definition of time?

 

Well, it's a hard thing to define.  But I don't equate it with change.  It's true that in order to "measure" time, you would have to observe some regularly occurring changes.  But, again, that would not stop time itself, just our subjective ability to perceive it.  Some say that time started with the Big Bang.  I don't see why that follows. An eternity could have preceded the BB.

[Moronium]

Of course. But a black hole is not the same as the earth. There is no escape velocity from a BH.

 

 

I agree.  The escape velocity of a black hole exceeds c.   But we were talking about the speed at which an object enters a black hole, not the speed at which it escapes  it.

[OceanBreeze]

Well, it's a hard thing to define.  But I don't equate it with change.  It's true that in order to "measure" time, you would have to observe some regularly occurring changes.  But, again, that would not stop time itself, just our subjective ability to perceive it.  Some say that time started with the Big Bang.  I don't see why that follows. An eternity could have preceded the BB.

 

So, you don't have a definition. Time = Change may not be right in a God's-eye viewpoint but as far as we humans go it does fairly well.

[OceanBreeze]

I agree.  The escape velocity of a black hole exceeds c.   But we were talking about the speed at which an object enters a black hole, not the speed at which it escapes  it.

 

Yes, and my calculation was c, based on integrating from infinity. As I said, in reality objects probably fall through the EH going slower. I don't think anyone knows the answer to exactly how much slower.

[Moronium]

So, you don't have a definition. Time = Change may not be right in a God's-eye viewpoint but as far as we humans go it does fairly well.

 

That's true.  But there is still a very important conceptual distinction between what we can "see" (measure) and what is.  Mixing the two concepts results in conceptual confusion.

[Moronium]

Yes, and my calculation was c, based on integrating from infinity. As I said, in reality objects probably fall through the EH going slower. I don't think anyone knows the answer to exactly how much slower.

 

Someone might know, but that someone wouldn't be me.  As I mentioned, I've heard it argued by physicists that an object can enter a black hole at any speed between 0 and c.

[OceanBreeze]

That's true.  But there is still a very important conceptual distinction between what we can "see" (measure) and what is.  Mixing the two concepts results in conceptual confusion.

 

 

But you have no definition of what time "is"

[Moronium]

But you have no definition of what time "is"

 

Well, my definition would probably be similar to Newton's (which I can probably find, if you're interested), and he said it better than I can.  Time is merely an idealized concept.  It is not a thing.

[OceanBreeze]

Someone might know, but that someone wouldn't be me.  As I mentioned, I've heard it argued by physicists that an object can enter a black hole at any speed between 0 and c.

 

You "heard" that? I cannot imagine anything falling into such a massive gravitational field at 0.

 

But this is getting to be more philosophical than mathematical science and I try to avoid wasting my time on that.

[Moronium]

Here's part of Newton's explanation, lifted from wiki:

 

According to Newton, absolute time and space respectively are independent aspects of objective reality:

 

Absolute, true and mathematical time, of itself, and from its own nature flows equably without regard to anything external, and by another name is called duration: relative, apparent and common time, is some sensible and external (whether accurate or unequable) measure of duration by the means of motion, which is commonly used instead of true time. (Newton)

 

 

According to Newton, absolute time exists independently of any perceiver and progresses at a consistent pace throughout the universe. Unlike relative time, Newton believed absolute time was imperceptible and could only be understood mathematically. According to Newton, humans are only capable of perceiving relative time, which is a measurement of perceivable objects in motion (like the Moon or Sun). From these movements, we infer the passage of time.

 

 

 

 

https://en.wikipedia.org/wiki/Absolute_space_and_time#cite_note-Newton-4

Edited April 7, 2019 by Moronium

[Moronium]

You "heard" that? I cannot imagine anything falling into such a massive gravitational field at 0.

 

But this is getting to be more philosophical than mathematical science and I try to avoid wasting my time on that.

 

It would have to be greater than 0 obviously.  I said BETWEEN 0 and c.

[OceanBreeze]

Here's part of Newton's explanation, lifted from wiki:

 

 

 

 

https://en.wikipedia.org/wiki/Absolute_space_and_time#cite_note-Newton-4

 

 

Not wishing to argue with Newton, but if this True time is imperceptible then it is a useless concept.

[OceanBreeze]

It would have to be greater than 0 obviously.  I said BETWEEN 0 and c.

 

OK. Calm down.