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John S
Guest

Tue Aug 23, 2016 1:22 am   



On 8/22/2016 8:06 AM, Martin Brown wrote:
Quote:
On 22/08/2016 12:41, David Brown wrote:
On 22/08/16 11:38, rickman wrote:
On 8/22/2016 4:44 AM, David Brown wrote:
On 22/08/16 10:02, Martin Brown wrote:
On 18/08/2016 18:56, makolber_at_yahoo.com wrote:
On Thursday, August 18, 2016 at 11:43:38 AM UTC-4, David Brown wrote:
On 18/08/16 17:14, makolber_at_yahoo.com wrote:


It depends on the observer.

An outside observer viewing the spaceship will see time slowing
down, and the ship appears to get smeared out on the event horizon
rather than passing through it.

Not quite. The spaceship fades out becoming ever more redshifted
and the
photons ever more widely spaced in time.

But to an observer on the
spaceship, there is nothing special about the event horizon. The

Also true for a sufficiently large BH so that there is plenty of
time to
see the world from inside the BH before spagettification occurs.

passage of time is completely different to two observers. So the
spaceship can turn around and fly out again, but the outside
observer cannot see this happening as it has never seen the ship
falling past the event horizon in the first place.

This is completely wrong.

No, it is not /completely/ wrong - and not for the reasons you say
below. But after reading a bit more, I can see I'm /mostly/ wrong
here.

Completely wrong stands.

My first point - that the passage of time is completely different for
the two observers - is, I think correct.

That much is true. Since they are at radically different gravitational
potentials. The Mossbauer nuclear resonance provided an exquisite test
of the GR predictions of clocks, frequency and time.

https://en.wikipedia.org/wiki/Pound%E2%80%93Rebka_experiment

The latest atomic clocks are now so good that moving them up or down by
a couple inches is a detectable systematic error. Time ticks more slowly
in a deep gravitational well when viewed from outside.

But the spaceship cannot escape from the black hole even by thrusting
its way out. This is not because of the escape velocity, as Rick keeps
saying - my reasoning there was sound from a Newtonian viewpoint
(and by
keeping a low speed, I had hoped to remain Newtonian). But when you
look at the /energy/ involved, there is no escape - you'd have to have
infinite energy to get out. Relativity is unavoidable here.

Well, duh! There is no amount of energy that will allow you to return
from inside the black hole. How does it matter if you call it
relativistic or "escape velocity"? The point is your earth escape
velocity analogy is not appropriate to a black hole which is what I
said. Just two ways of explaining the same thing.

No, they are different things.

Not really. They are a consequence of the infinite energy required to
propel any finite mass at the speed of light.

Before relativity, the concept of "Newtonian black holes" was
considered, with a horizon which had an escape velocity equal to the
speed of light. A /powered/ spaceship could still escape.

Laplace first considered this possibility of a massive object so compact
that its surface escape velocity was greater than the speed of light.
Back then they believed that Newtonian dynamics held good. That is that
acceleration adds the same delta_V no matter how fast you are going. We
now know that assumption to be false.

What you told me - repeatedly - was that you can't escape from a black
hole because you can't accelerate to faster than the speed of light.
That is simply an incorrect justification.

It is just another way of looking at it. Inside the black hole by any
reasonable definition (made more difficult by the lack of any inertial
frames of reference) you are potentially travelling faster than the
speed of light to your doom at the central singularity.

Spacetime itself is quite literally falling into the singularity.


Spacetime has had lots of singularities to fall into and a long time to
do it. Why do we still have any Spacetime?

rickman
Guest

Tue Aug 23, 2016 4:47 am   



On 8/22/2016 7:41 AM, David Brown wrote:
Quote:
On 22/08/16 11:38, rickman wrote:
On 8/22/2016 4:44 AM, David Brown wrote:
On 22/08/16 10:02, Martin Brown wrote:
On 18/08/2016 18:56, makolber_at_yahoo.com wrote:
On Thursday, August 18, 2016 at 11:43:38 AM UTC-4, David Brown wrote:
On 18/08/16 17:14, makolber_at_yahoo.com wrote:


It depends on the observer.

An outside observer viewing the spaceship will see time slowing
down, and the ship appears to get smeared out on the event horizon
rather than passing through it.

Not quite. The spaceship fades out becoming ever more redshifted and the
photons ever more widely spaced in time.

But to an observer on the
spaceship, there is nothing special about the event horizon. The

Also true for a sufficiently large BH so that there is plenty of time to
see the world from inside the BH before spagettification occurs.

passage of time is completely different to two observers. So the
spaceship can turn around and fly out again, but the outside
observer cannot see this happening as it has never seen the ship
falling past the event horizon in the first place.

This is completely wrong.

No, it is not /completely/ wrong - and not for the reasons you say
below. But after reading a bit more, I can see I'm /mostly/ wrong here.

My first point - that the passage of time is completely different for
the two observers - is, I think correct.

But the spaceship cannot escape from the black hole even by thrusting
its way out. This is not because of the escape velocity, as Rick keeps
saying - my reasoning there was sound from a Newtonian viewpoint (and by
keeping a low speed, I had hoped to remain Newtonian). But when you
look at the /energy/ involved, there is no escape - you'd have to have
infinite energy to get out. Relativity is unavoidable here.

Well, duh! There is no amount of energy that will allow you to return
from inside the black hole. How does it matter if you call it
relativistic or "escape velocity"? The point is your earth escape
velocity analogy is not appropriate to a black hole which is what I
said. Just two ways of explaining the same thing.

No, they are different things.

Before relativity, the concept of "Newtonian black holes" was
considered, with a horizon which had an escape velocity equal to the
speed of light. A /powered/ spaceship could still escape.


You keep saying that without understanding what it means in the context
of a black hole.


Quote:
What you told me - repeatedly - was that you can't escape from a black
hole because you can't accelerate to faster than the speed of light.
That is simply an incorrect justification.


No, you need to understand what it means. The gravity of the black hole
is equivalent to acceleration. To move outward from the black hole is
like accelerating at a much higher rate than in earth's gravity, even if
you are barely moving. Given the extreme gravity moving outward at all
is like exceeding the speed of light. Do you understand that? There is
*no* amount of thrust possible that will accelerate you at *any* speed
outward from inside a black hole.


Quote:
A correct justification is that you would need an infinite amount of
energy to keep up the thrust needed to escape. Alternatively, you would
need your thrust to be pushed out with an infinite total momentum.

And of course, you can say that space-time is so warped that every
direction is "down", but that is much harder to understand.


I didn't say that. I simply mention that it is impossible to move
outward from inside a black hole because of the escape velocity. You
seem to be focused solely on the idea that escape velocity implies
moving at that speed. No one else here has said that. It is simply a
way to quantifying the effort required to escape a gravitational field.
Once that velocity reaches the speed of light, you can't even move
against it at all.


Quote:
I understand now that there is no escape for the spaceship once it has
passed through the event horizon - as I noted, I am not an expert in
this subject, and I have learned a little more during this thread. But
I don't think your "escape velocity" explanation is any better than my
one just because it happens to match the correct end result.


Yes, I see that. It's because you don't understand what escape velocity
means.


Quote:
Once the spaceship is inside the BH it will
fall to the centre in a finite clock time by its metric.

Not a problem, either from the Newtonian or relativity viewpoints - you
just have to turn round within that finite time.

Turn around? There is no amount of energy that will even keep you from
falling once inside the black hole.


As a stand-alone reason, this is not enough. From the viewpoint of the
spaceship, the inside of the black hole is not that special - it sees no
discontinuity or jump as it passes through the event horizon.


No one said it did. But there is a fundamental difference in what
happens whether there is a sign post stating "You have entered the
Twilight Zone" or not.

--

Rick C

rickman
Guest

Tue Aug 23, 2016 4:53 am   



On 8/22/2016 9:58 AM, makolber_at_yahoo.com wrote:
Quote:


It isn't that special in terms that they notice nothing special about
going into the BH provided that it is big enough not to shred them.
However, they are in for a big shock when they do try to leave - it is
like the Hotel California in that respect. You can never leave.

--
Regards,
Martin Brown

Maybe the entire universe is a gigantic black hole and everything is "falling in", and that is what causes the passage of time?

you can't reverse the passage of time
m


Yes, that would make sense if you could somehow show that "in" becomes
"out" inside a black hole. Isn't our universe expanding?

--

Rick C

rickman
Guest

Tue Aug 23, 2016 4:55 am   



On 8/22/2016 3:22 PM, John S wrote:
Quote:
On 8/22/2016 8:06 AM, Martin Brown wrote:
On 22/08/2016 12:41, David Brown wrote:
On 22/08/16 11:38, rickman wrote:
On 8/22/2016 4:44 AM, David Brown wrote:
On 22/08/16 10:02, Martin Brown wrote:
On 18/08/2016 18:56, makolber_at_yahoo.com wrote:
On Thursday, August 18, 2016 at 11:43:38 AM UTC-4, David Brown
wrote:
On 18/08/16 17:14, makolber_at_yahoo.com wrote:


It depends on the observer.

An outside observer viewing the spaceship will see time slowing
down, and the ship appears to get smeared out on the event
horizon
rather than passing through it.

Not quite. The spaceship fades out becoming ever more redshifted
and the
photons ever more widely spaced in time.

But to an observer on the
spaceship, there is nothing special about the event horizon. The

Also true for a sufficiently large BH so that there is plenty of
time to
see the world from inside the BH before spagettification occurs.

passage of time is completely different to two observers. So the
spaceship can turn around and fly out again, but the outside
observer cannot see this happening as it has never seen the ship
falling past the event horizon in the first place.

This is completely wrong.

No, it is not /completely/ wrong - and not for the reasons you say
below. But after reading a bit more, I can see I'm /mostly/ wrong
here.

Completely wrong stands.

My first point - that the passage of time is completely different for
the two observers - is, I think correct.

That much is true. Since they are at radically different gravitational
potentials. The Mossbauer nuclear resonance provided an exquisite test
of the GR predictions of clocks, frequency and time.

https://en.wikipedia.org/wiki/Pound%E2%80%93Rebka_experiment

The latest atomic clocks are now so good that moving them up or down by
a couple inches is a detectable systematic error. Time ticks more slowly
in a deep gravitational well when viewed from outside.

But the spaceship cannot escape from the black hole even by thrusting
its way out. This is not because of the escape velocity, as Rick
keeps
saying - my reasoning there was sound from a Newtonian viewpoint
(and by
keeping a low speed, I had hoped to remain Newtonian). But when you
look at the /energy/ involved, there is no escape - you'd have to have
infinite energy to get out. Relativity is unavoidable here.

Well, duh! There is no amount of energy that will allow you to return
from inside the black hole. How does it matter if you call it
relativistic or "escape velocity"? The point is your earth escape
velocity analogy is not appropriate to a black hole which is what I
said. Just two ways of explaining the same thing.

No, they are different things.

Not really. They are a consequence of the infinite energy required to
propel any finite mass at the speed of light.

Before relativity, the concept of "Newtonian black holes" was
considered, with a horizon which had an escape velocity equal to the
speed of light. A /powered/ spaceship could still escape.

Laplace first considered this possibility of a massive object so compact
that its surface escape velocity was greater than the speed of light.
Back then they believed that Newtonian dynamics held good. That is that
acceleration adds the same delta_V no matter how fast you are going. We
now know that assumption to be false.

What you told me - repeatedly - was that you can't escape from a black
hole because you can't accelerate to faster than the speed of light.
That is simply an incorrect justification.

It is just another way of looking at it. Inside the black hole by any
reasonable definition (made more difficult by the lack of any inertial
frames of reference) you are potentially travelling faster than the
speed of light to your doom at the central singularity.

Spacetime itself is quite literally falling into the singularity.

Spacetime has had lots of singularities to fall into and a long time to
do it. Why do we still have any Spacetime?


Like Jay Leno said in the Tostitos commercial... "Eat all you want,
we'll make more!". Is there only a finite amount of space-time?

I don't like the idea of space-time "falling into" a black hole. I'm
not even sure what that means.
--

Rick C

John S
Guest

Tue Aug 23, 2016 1:07 pm   



On 8/21/2016 3:42 AM, Jasen Betts wrote:
Quote:
On 2016-08-18, rickman <gnuarm_at_gmail.com> wrote:
On 8/18/2016 8:31 AM, David Brown wrote:
On 16/08/16 23:32, rickman wrote:
On 8/16/2016 5:17 PM, Dave Platt wrote:


yoager 1 was never traveling 11km/s, it has never exceeded 2km/s and yet it
escaped earth. thust makes a difference.


Not so.

"Travelling at about 17 kilometers per second (11 mi/s) it has the
fastest heliocentric recession speed of any spacecraft. As Voyager 1
headed for interstellar space, its instruments continued to study the
Solar System."

Also "The orbital velocity needed to maintain a stable low Earth orbit
is about 7.8 km/s."

This information is easy to find.

Martin Brown
Guest

Tue Aug 23, 2016 4:52 pm   



On 22/08/2016 14:02, Reinhardt Behm wrote:
Quote:
John Devereux wrote:

David Brown <david.brown_at_hesbynett.no> writes:

I understand now that there is no escape for the spaceship once it has
passed through the event horizon - as I noted, I am not an expert in
this subject, and I have learned a little more during this thread. But
I don't think your "escape velocity" explanation is any better than my
one just because it happens to match the correct end result.

One of the links I followed says that, mathematically, space itself is
falling into the BH. At the event horizon, you have to moving at the
speed of light just to stay where you are. Beyond, you can't even do
that.

All this reasoning still uses classical (even Special Relativity). But to
describe a BH GR (general relativity) applies. To talk about speed you need
a frame of reference. But GR does not allow to construct a global frame of
reference, only local ones covering a region of space where its curvature is
small. But in the vicinity of a BH the curvature is large even on small
scales. It gets infinite at the event horizon.


No. Curvature doesn't become infinite at the event horizon of a
Schwarzchild black hole (at least not for a large galactic mass one).

The apparent singularity at Rs is an illusion due to a poor choice of
coordinates and no more significant than the breakdown of latitude and
longitude at the North Pole on planet Earth. See for example:

https://en.wikipedia.org/wiki/Schwarzschild_metric#Singularities_and_black_holes

Only at r=0 is there a hard unavoidable physical singularity.

Quote:
Inside of the Schwarzschild region (event horizon) all usual calculations
just do not work. We can only describe the physics outside of the event
horizon. We do not have real theory to describe what happens inside.
So any arguments based on more or less classical physics and even GR can
only give meaningless results.


There are equations that will work across the boundary although their
interpretation is somewhat more difficult (and testing them impossible).
The usual calculations are easier for all practical purposes but
solutions have been found that span the boundary.

Think of the event horizon as a semipermeable membrane that will let
anything go through it but only in the inwards direction. Once inside it
is inevitable that you will end up crunched at r=0 in finite clock time
no matter how hard you try to avoid your fate.

--
Regards,
Martin Brown

Martin Brown
Guest

Tue Aug 23, 2016 5:43 pm   



On 22/08/2016 23:53, rickman wrote:
Quote:
On 8/22/2016 9:58 AM, makolber_at_yahoo.com wrote:


It isn't that special in terms that they notice nothing special about
going into the BH provided that it is big enough not to shred them.
However, they are in for a big shock when they do try to leave - it is
like the Hotel California in that respect. You can never leave.

Maybe the entire universe is a gigantic black hole and everything is
"falling in", and that is what causes the passage of time?

you can't reverse the passage of time
m

Yes, that would make sense if you could somehow show that "in" becomes
"out" inside a black hole. Isn't our universe expanding?


Not only expanding but instead of decelerating it is accelerating away
from itself hence the need for Dark Energy to balance the books.

There is no way our universe is enclosed inside a BH - the density of
mass energy in the observable universe is not sufficiently high.
(even including the dark matter contribution)

--
Regards,
Martin Brown

Jasen Betts
Guest

Sat Aug 27, 2016 3:20 pm   



On 2016-08-22, rickman <gnuarm_at_gmail.com> wrote:
Quote:
On 8/22/2016 3:26 AM, Jasen Betts wrote:
On 2016-08-21, rickman <gnuarm_at_gmail.com> wrote:
On 8/21/2016 4:42 AM, Jasen Betts wrote:
On 2016-08-18, rickman <gnuarm_at_gmail.com> wrote:
On 8/18/2016 8:31 AM, David Brown wrote:
On 16/08/16 23:32, rickman wrote:
On 8/16/2016 5:17 PM, Dave Platt wrote:

Therefore it is not possible to move
against a gravitational field that has an escape velocity greater than
the speed of light.

That does not follow. and furthermore, is contrary to relativity.

??? How is it "contrary" to relativity?


I was thinking something involving frames of reference... not sure
exactly what though, none of it makes sense to me now.

> I see David Brown has finally figured it out. What's holding you back?

"Lag" mainly. Gotta agree with you now.

--
This email has not been checked by half-arsed antivirus software

Albert van der Horst
Guest

Sun Jan 08, 2017 6:01 pm   



In article <np54eh$dpd$2_at_dont-email.me>, rickman <gnuarm_at_gmail.com> wrote:
Quote:
On 8/18/2016 4:55 AM, David Brown wrote:
On 16/08/16 19:56, rickman wrote:
On 8/16/2016 1:42 PM, George Herold wrote:
On Tuesday, August 16, 2016 at 12:47:18 PM UTC-4, rickman wrote:
On 8/16/2016 12:30 PM, George Herold wrote:
On Tuesday, August 16, 2016 at 12:20:24 PM UTC-4, Tim Wescott wrote:
On Tue, 16 Aug 2016 01:23:34 -0400, bitrex wrote:

On 08/16/2016 01:04 AM, rickman wrote:
I was explaining black holes to a friend who asked about the LHC and
thought about what might happen if a tiny black hole were created.

I believe matter falling into a microscopic black hole would still
enter it in a similar manner to large black holes elsewhere in the
universe by orbiting the tiny black hole while being accelerated
causing energy to be emitted before crossing the event horizon.

A microscopic black hole, if such a thing could exist, would radiate
itself away via Hawking radiation before it had much of a chance
to do
anything.


https://en.wikipedia.org/wiki/
Micro_black_hole#Stability_of_a_micro_black_hole

If such a thing as Hawking radiation exists.
IIRC Hawking radiation mostly follows from thermo-dynamics.
It's like black body radiation... Black holes have some temperature.
(Finding the temperature of a black hole is the hard part... :^)

I'm not sure that is a valid way to look at it. Everything that makes
up a black hole is on the other side of the event horizon. It may well
have a temperature, but we'll never feel any effect from it as nothing
can cross back through the event horizon. In a sense, the event horizon
of a black hole is an infinite heat sink at 0 °K. There may be
radiation from the space around the black hole, but nothing from the
black hole itself.

--

Rick C

Ahh, Rick I understand you are a smart guy. There are plenty of other
smart guys
out there. I think the best (clearest) explanation I've seen/ read
(and it's been a while) was in a set of video lectures by Leonard
Susskind.
Googling he's got a bunch... I don't recall which ones. Advanced
stat. mech.
or maybe QM.

Black holes have a temperature. That's pretty cool. (NPI)
Here's wiki...(I only looked at the first few paragraphs.)
https://en.wikipedia.org/wiki/Hawking_radiation

Trouble is all of this is speculation and none is proven. I like a nice
mechanical explanation. Saying matter leaves a black hole by it
swallowing matter is not a very good argument. That's what Hawking
Radiation says.


Unfortunately, general relativity is not amenable to nice mechanical
explanations. And quantum effects are even less amenable to such
explanations. And with black holes, you've got the most extreme
situations for the relativity effects /and/ the most extreme quantum
effects. You are never going to get a nice, clear, intuitive "bouncing
ball bearings" picture here.

Fine, but quantum theory has been verified repeatedly. Hawking
radiation has not.


You can't do that to physics theories. The Hawking radiation fits into
and completes a picture we have of a universe. It predicts very faint
radiation of largish black holes that we can predict not to be observable
by the means we have available now.

Quote:

I too like a nice mechanical explanation - but here you are going to
have to accept weird things if you want to understand. (Not that I am
claiming to understand this stuff.)

I don't have problems with weird things. It's not the weirdness that is
at issue. It's the lack of connection between the particle pair and the
black hole.


Huh? The particle pairs are everywhere. The black hole only makes them
visible, but not to the naked eye.

>Rick C
--
Albert van der Horst, UTRECHT,THE NETHERLANDS
Economic growth -- being exponential -- ultimately falters.
albert_at_spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst


Guest

Mon Jan 09, 2017 3:53 am   



On Monday, January 9, 2017 at 9:07:33 AM UTC+11, rickman wrote:
Quote:
On 1/8/2017 11:01 AM, Albert van der Horst wrote:
In article <np54eh$dpd$2_at_dont-email.me>, rickman <gnuarm_at_gmail.com> wrote:
On 8/18/2016 4:55 AM, David Brown wrote:
On 16/08/16 19:56, rickman wrote:
On 8/16/2016 1:42 PM, George Herold wrote:
On Tuesday, August 16, 2016 at 12:47:18 PM UTC-4, rickman wrote:
On 8/16/2016 12:30 PM, George Herold wrote:
On Tuesday, August 16, 2016 at 12:20:24 PM UTC-4, Tim Wescott wrote:
On Tue, 16 Aug 2016 01:23:34 -0400, bitrex wrote:

On 08/16/2016 01:04 AM, rickman wrote:
I was explaining black holes to a friend who asked about the LHC and
thought about what might happen if a tiny black hole were created.

I believe matter falling into a microscopic black hole would still
enter it in a similar manner to large black holes elsewhere in the
universe by orbiting the tiny black hole while being accelerated
causing energy to be emitted before crossing the event horizon..

A microscopic black hole, if such a thing could exist, would radiate
itself away via Hawking radiation before it had much of a chance
to do
anything.


https://en.wikipedia.org/wiki/
Micro_black_hole#Stability_of_a_micro_black_hole

If such a thing as Hawking radiation exists.
IIRC Hawking radiation mostly follows from thermo-dynamics.
It's like black body radiation... Black holes have some temperature.
(Finding the temperature of a black hole is the hard part... :^)

I'm not sure that is a valid way to look at it. Everything that makes
up a black hole is on the other side of the event horizon. It may well
have a temperature, but we'll never feel any effect from it as nothing
can cross back through the event horizon. In a sense, the event horizon
of a black hole is an infinite heat sink at 0 °K. There may be
radiation from the space around the black hole, but nothing from the
black hole itself.

--

Rick C

Ahh, Rick I understand you are a smart guy. There are plenty of other
smart guys
out there. I think the best (clearest) explanation I've seen/ read
(and it's been a while) was in a set of video lectures by Leonard
Susskind.
Googling he's got a bunch... I don't recall which ones. Advanced
stat. mech.
or maybe QM.

Black holes have a temperature. That's pretty cool. (NPI)
Here's wiki...(I only looked at the first few paragraphs.)
https://en.wikipedia.org/wiki/Hawking_radiation

Trouble is all of this is speculation and none is proven. I like a nice
mechanical explanation. Saying matter leaves a black hole by it
swallowing matter is not a very good argument. That's what Hawking
Radiation says.


Unfortunately, general relativity is not amenable to nice mechanical
explanations. And quantum effects are even less amenable to such
explanations. And with black holes, you've got the most extreme
situations for the relativity effects /and/ the most extreme quantum
effects. You are never going to get a nice, clear, intuitive "bouncing
ball bearings" picture here.

Fine, but quantum theory has been verified repeatedly. Hawking
radiation has not.

You can't do that to physics theories. The Hawking radiation fits into
and completes a picture we have of a universe. It predicts very faint
radiation of largish black holes that we can predict not to be observable
by the means we have available now.

And therefore it has *not* been verified. Simple enough, no?


Not exactly. The LIGO gravity wave detector has "seen" a couple of relatively small black holes in the process of merging to make a slightly bigger small black hole, so we do know that they exist. Their properties can be deduced from regular physics.
Quote:


I too like a nice mechanical explanation - but here you are going to
have to accept weird things if you want to understand. (Not that I am
claiming to understand this stuff.)

I don't have problems with weird things. It's not the weirdness that is
at issue. It's the lack of connection between the particle pair and the
black hole.

Huh? The particle pairs are everywhere. The black hole only makes them
visible, but not to the naked eye.


They would be visible to the naked eye, if the eye was close enough to black hole. No human eye could survive there, but the effect would be visible at a greater distance, for a sufficiently small black hole that was emitting Hawking radiation sufficiently rapidly.

--
Bill Sloman, Sydney

rickman
Guest

Mon Jan 09, 2017 5:07 am   



On 1/8/2017 11:01 AM, Albert van der Horst wrote:
Quote:
In article <np54eh$dpd$2_at_dont-email.me>, rickman <gnuarm_at_gmail.com> wrote:
On 8/18/2016 4:55 AM, David Brown wrote:
On 16/08/16 19:56, rickman wrote:
On 8/16/2016 1:42 PM, George Herold wrote:
On Tuesday, August 16, 2016 at 12:47:18 PM UTC-4, rickman wrote:
On 8/16/2016 12:30 PM, George Herold wrote:
On Tuesday, August 16, 2016 at 12:20:24 PM UTC-4, Tim Wescott wrote:
On Tue, 16 Aug 2016 01:23:34 -0400, bitrex wrote:

On 08/16/2016 01:04 AM, rickman wrote:
I was explaining black holes to a friend who asked about the LHC and
thought about what might happen if a tiny black hole were created.

I believe matter falling into a microscopic black hole would still
enter it in a similar manner to large black holes elsewhere in the
universe by orbiting the tiny black hole while being accelerated
causing energy to be emitted before crossing the event horizon.

A microscopic black hole, if such a thing could exist, would radiate
itself away via Hawking radiation before it had much of a chance
to do
anything.


https://en.wikipedia.org/wiki/
Micro_black_hole#Stability_of_a_micro_black_hole

If such a thing as Hawking radiation exists.
IIRC Hawking radiation mostly follows from thermo-dynamics.
It's like black body radiation... Black holes have some temperature.
(Finding the temperature of a black hole is the hard part... :^)

I'm not sure that is a valid way to look at it. Everything that makes
up a black hole is on the other side of the event horizon. It may well
have a temperature, but we'll never feel any effect from it as nothing
can cross back through the event horizon. In a sense, the event horizon
of a black hole is an infinite heat sink at 0 °K. There may be
radiation from the space around the black hole, but nothing from the
black hole itself.

--

Rick C

Ahh, Rick I understand you are a smart guy. There are plenty of other
smart guys
out there. I think the best (clearest) explanation I've seen/ read
(and it's been a while) was in a set of video lectures by Leonard
Susskind.
Googling he's got a bunch... I don't recall which ones. Advanced
stat. mech.
or maybe QM.

Black holes have a temperature. That's pretty cool. (NPI)
Here's wiki...(I only looked at the first few paragraphs.)
https://en.wikipedia.org/wiki/Hawking_radiation

Trouble is all of this is speculation and none is proven. I like a nice
mechanical explanation. Saying matter leaves a black hole by it
swallowing matter is not a very good argument. That's what Hawking
Radiation says.


Unfortunately, general relativity is not amenable to nice mechanical
explanations. And quantum effects are even less amenable to such
explanations. And with black holes, you've got the most extreme
situations for the relativity effects /and/ the most extreme quantum
effects. You are never going to get a nice, clear, intuitive "bouncing
ball bearings" picture here.

Fine, but quantum theory has been verified repeatedly. Hawking
radiation has not.

You can't do that to physics theories. The Hawking radiation fits into
and completes a picture we have of a universe. It predicts very faint
radiation of largish black holes that we can predict not to be observable
by the means we have available now.


And therefore it has *not* been verified. Simple enough, no?


Quote:
I too like a nice mechanical explanation - but here you are going to
have to accept weird things if you want to understand. (Not that I am
claiming to understand this stuff.)

I don't have problems with weird things. It's not the weirdness that is
at issue. It's the lack of connection between the particle pair and the
black hole.

Huh? The particle pairs are everywhere. The black hole only makes them
visible, but not to the naked eye.

Rick C


--

Rick C


Guest

Mon Jan 09, 2017 7:27 am   



On Monday, January 9, 2017 at 3:06:11 PM UTC+11, rickman wrote:
Quote:
On 1/8/2017 8:53 PM, bill.sloman_at_ieee.org wrote:
On Monday, January 9, 2017 at 9:07:33 AM UTC+11, rickman wrote:
On 1/8/2017 11:01 AM, Albert van der Horst wrote:
In article <np54eh$dpd$2_at_dont-email.me>, rickman <gnuarm_at_gmail.com> wrote:
On 8/18/2016 4:55 AM, David Brown wrote:
On 16/08/16 19:56, rickman wrote:
On 8/16/2016 1:42 PM, George Herold wrote:
On Tuesday, August 16, 2016 at 12:47:18 PM UTC-4, rickman wrote:
On 8/16/2016 12:30 PM, George Herold wrote:
On Tuesday, August 16, 2016 at 12:20:24 PM UTC-4, Tim Wescott wrote:
On Tue, 16 Aug 2016 01:23:34 -0400, bitrex wrote:

On 08/16/2016 01:04 AM, rickman wrote:
I was explaining black holes to a friend who asked about the LHC
and thought about what might happen if a tiny black hole were
created.
I believe matter falling into a microscopic black hole would
still enter it in a similar manner to large black holes
elsewhere in the universe by orbiting the tiny black hole while
being accelerated causing energy to be emitted before crossing
the event horizon.

A microscopic black hole, if such a thing could exist, would
radiate itself away via Hawking radiation before it had much of a
chance to do anything.

https://en.wikipedia.org/wiki/
Micro_black_hole#Stability_of_a_micro_black_hole

If such a thing as Hawking radiation exists.

IIRC Hawking radiation mostly follows from thermo-dynamics.
It's like black body radiation... Black holes have some temperature.
(Finding the temperature of a black hole is the hard part... :^)

I'm not sure that is a valid way to look at it. Everything that
makes up a black hole is on the other side of the event horizon. It
may well have a temperature, but we'll never feel any effect from it
as nothing can cross back through the event horizon. In a sense,
the event horizon of a black hole is an infinite heat sink at 0
°K. There may be radiation from the space around the black hole,
but nothing from the black hole itself.

Ahh, Rick I understand you are a smart guy. There are plenty of
other smart guys out there. I think the best (clearest) explanation
I've seen/ read (and it's been a while) was in a set of video
lectures by Leonard Susskind.
Googling he's got a bunch... I don't recall which ones. Advanced
stat. mech. or maybe QM.

Black holes have a temperature. That's pretty cool. (NPI)
Here's wiki...(I only looked at the first few paragraphs.)
https://en.wikipedia.org/wiki/Hawking_radiation

Trouble is all of this is speculation and none is proven. I like a
nice mechanical explanation. Saying matter leaves a black hole by it
swallowing matter is not a very good argument. That's what Hawking
Radiation says.


That is one way of understanding it.

Quote:
Unfortunately, general relativity is not amenable to nice mechanical
explanations. And quantum effects are even less amenable to such
explanations. And with black holes, you've got the most extreme
situations for the relativity effects /and/ the most extreme quantum
effects. You are never going to get a nice, clear, intuitive "bouncing
ball bearings" picture here.

Fine, but quantum theory has been verified repeatedly. Hawking
radiation has not.

You can't do that to physics theories. The Hawking radiation fits into
and completes a picture we have of a universe. It predicts very faint
radiation of largish black holes that we can predict not to be observable
by the means we have available now.

And therefore it has *not* been verified. Simple enough, no?

Not exactly. The LIGO gravity wave detector has "seen" a couple of relatively small black holes in the process of merging to make a slightly bigger small black hole, so we do know that they exist. Their properties can be deduced from regular physics.

You mean what we *assume* are black holes... Regardless. Even if they
exist, that says nothing about Hawking radiation.


We don't "assume" black holes - we postulate them to explain facts that otherwise seem impossible to explain. Electrons are equally hypothetical.

Hawking radiation is a necessary consequence of Dirac pair production and an event horizon.

The problem with modern physics is that it is a package deal - you get the counter-intuitive bits as part of the package. Reject them and you are back to flint axes.

Quote:
I too like a nice mechanical explanation - but here you are going to
have to accept weird things if you want to understand. (Not that I am
claiming to understand this stuff.)

I don't have problems with weird things. It's not the weirdness that is
at issue. It's the lack of connection between the particle pair and the
black hole.

Huh? The particle pairs are everywhere. The black hole only makes them
visible, but not to the naked eye.

They would be visible to the naked eye, if the eye was close enough to black hole. No human eye could survive there, but the effect would be visible at a greater distance, for a sufficiently small black hole that was emitting Hawking radiation sufficiently rapidly.

Someday we will create black holes in the lab and may observe Hawking
radiation. My understanding is that the strength of the radiation would
be *inversely* proportional to the size of the black hole, so if we created
a very small one it would in essence explode immediately. I think we could
detect that.


Or something considerably larger, and sufficiently long-lived that we could move it off to safe distance before it came apart.

--
Bill Sloman, Sydney

rickman
Guest

Mon Jan 09, 2017 8:30 am   



On 1/8/2017 8:53 PM, bill.sloman_at_ieee.org wrote:
Quote:
On Monday, January 9, 2017 at 9:07:33 AM UTC+11, rickman wrote:
On 1/8/2017 11:01 AM, Albert van der Horst wrote:
In article <np54eh$dpd$2_at_dont-email.me>, rickman <gnuarm_at_gmail.com> wrote:
On 8/18/2016 4:55 AM, David Brown wrote:
On 16/08/16 19:56, rickman wrote:
On 8/16/2016 1:42 PM, George Herold wrote:
On Tuesday, August 16, 2016 at 12:47:18 PM UTC-4, rickman wrote:
On 8/16/2016 12:30 PM, George Herold wrote:
On Tuesday, August 16, 2016 at 12:20:24 PM UTC-4, Tim Wescott wrote:
On Tue, 16 Aug 2016 01:23:34 -0400, bitrex wrote:

On 08/16/2016 01:04 AM, rickman wrote:
I was explaining black holes to a friend who asked about the LHC and
thought about what might happen if a tiny black hole were created.

I believe matter falling into a microscopic black hole would still
enter it in a similar manner to large black holes elsewhere in the
universe by orbiting the tiny black hole while being accelerated
causing energy to be emitted before crossing the event horizon..

A microscopic black hole, if such a thing could exist, would radiate
itself away via Hawking radiation before it had much of a chance
to do
anything.


https://en.wikipedia.org/wiki/
Micro_black_hole#Stability_of_a_micro_black_hole

If such a thing as Hawking radiation exists.
IIRC Hawking radiation mostly follows from thermo-dynamics.
It's like black body radiation... Black holes have some temperature.
(Finding the temperature of a black hole is the hard part... :^)

I'm not sure that is a valid way to look at it. Everything that makes
up a black hole is on the other side of the event horizon. It may well
have a temperature, but we'll never feel any effect from it as nothing
can cross back through the event horizon. In a sense, the event horizon
of a black hole is an infinite heat sink at 0 °K. There may be
radiation from the space around the black hole, but nothing from the
black hole itself.

--

Rick C

Ahh, Rick I understand you are a smart guy. There are plenty of other
smart guys
out there. I think the best (clearest) explanation I've seen/ read
(and it's been a while) was in a set of video lectures by Leonard
Susskind.
Googling he's got a bunch... I don't recall which ones. Advanced
stat. mech.
or maybe QM.

Black holes have a temperature. That's pretty cool. (NPI)
Here's wiki...(I only looked at the first few paragraphs.)
https://en.wikipedia.org/wiki/Hawking_radiation

Trouble is all of this is speculation and none is proven. I like a nice
mechanical explanation. Saying matter leaves a black hole by it
swallowing matter is not a very good argument. That's what Hawking
Radiation says.


Unfortunately, general relativity is not amenable to nice mechanical
explanations. And quantum effects are even less amenable to such
explanations. And with black holes, you've got the most extreme
situations for the relativity effects /and/ the most extreme quantum
effects. You are never going to get a nice, clear, intuitive "bouncing
ball bearings" picture here.

Fine, but quantum theory has been verified repeatedly. Hawking
radiation has not.

You can't do that to physics theories. The Hawking radiation fits into
and completes a picture we have of a universe. It predicts very faint
radiation of largish black holes that we can predict not to be observable
by the means we have available now.

And therefore it has *not* been verified. Simple enough, no?

Not exactly. The LIGO gravity wave detector has "seen" a couple of relatively small black holes in the process of merging to make a slightly bigger small black hole, so we do know that they exist. Their properties can be deduced from regular physics.


You mean what we *assume* are black holes... Regardless. Even if they
exist, that says nothing about Hawking radiation.


Quote:
I too like a nice mechanical explanation - but here you are going to
have to accept weird things if you want to understand. (Not that I am
claiming to understand this stuff.)

I don't have problems with weird things. It's not the weirdness that is
at issue. It's the lack of connection between the particle pair and the
black hole.

Huh? The particle pairs are everywhere. The black hole only makes them
visible, but not to the naked eye.

They would be visible to the naked eye, if the eye was close enough to black hole. No human eye could survive there, but the effect would be visible at a greater distance, for a sufficiently small black hole that was emitting Hawking radiation sufficiently rapidly.


Someday we will create black holes in the lab and may observe Hawking
radiation. My understanding is that the strength of the radiation would
be proportional to the size of the black hole, so if we created a very
small one it would in essence explode immediately. I think we could
detect that.

--

Rick C


Guest

Mon Jan 09, 2017 12:01 pm   



On Monday, January 9, 2017 at 8:20:45 PM UTC+11, rickman wrote:
Quote:
On 1/9/2017 12:27 AM, bill.sloman_at_ieee.org wrote:
On Monday, January 9, 2017 at 3:06:11 PM UTC+11, rickman wrote:
On 1/8/2017 8:53 PM, bill.sloman_at_ieee.org wrote:
On Monday, January 9, 2017 at 9:07:33 AM UTC+11, rickman wrote:
On 1/8/2017 11:01 AM, Albert van der Horst wrote:
In article <np54eh$dpd$2_at_dont-email.me>, rickman <gnuarm_at_gmail.com> wrote:
On 8/18/2016 4:55 AM, David Brown wrote:
On 16/08/16 19:56, rickman wrote:
On 8/16/2016 1:42 PM, George Herold wrote:
On Tuesday, August 16, 2016 at 12:47:18 PM UTC-4, rickman wrote:
On 8/16/2016 12:30 PM, George Herold wrote:
On Tuesday, August 16, 2016 at 12:20:24 PM UTC-4, Tim Wescott wrote:
On Tue, 16 Aug 2016 01:23:34 -0400, bitrex wrote:

On 08/16/2016 01:04 AM, rickman wrote:
I was explaining black holes to a friend who asked about the
and thought about what might happen if a tiny black hole were
LHC created.
I believe matter falling into a microscopic black hole would
still enter it in a similar manner to large black holes
elsewhere in the universe by orbiting the tiny black hole while
being accelerated causing energy to be emitted before crossing
the event horizon.

A microscopic black hole, if such a thing could exist, would
radiate itself away via Hawking radiation before it had much of
a chance to do anything.

https://en.wikipedia.org/wiki/
Micro_black_hole#Stability_of_a_micro_black_hole

If such a thing as Hawking radiation exists.

IIRC Hawking radiation mostly follows from thermo-dynamics.
It's like black body radiation... Black holes have some
temperature.(Finding the temperature of a black hole is the hard > >>>>>>>>>>> part... :^)

I'm not sure that is a valid way to look at it. Everything that
makes up a black hole is on the other side of the event horizon.
It may well have a temperature, but we'll never feel any effect
from it as nothing can cross back through the event horizon. In a
sense, the event horizon of a black hole is an infinite heat sink
at 0 °K. There may be radiation from the space around the black
hole, but nothing from the black hole itself.

Ahh, Rick I understand you are a smart guy. There are plenty of
other smart guys out there. I think the best (clearest) explanation
I've seen/ read (and it's been a while) was in a set of video
lectures by Leonard Susskind.
Googling he's got a bunch... I don't recall which ones. Advanced
stat. mech. or maybe QM.

Black holes have a temperature. That's pretty cool. (NPI)
Here's wiki...(I only looked at the first few paragraphs.)
https://en.wikipedia.org/wiki/Hawking_radiation

Trouble is all of this is speculation and none is proven. I like a
nice mechanical explanation. Saying matter leaves a black hole by it
swallowing matter is not a very good argument. That's what Hawking
Radiation says.

That is one way of understanding it.

Unfortunately, general relativity is not amenable to nice mechanical
explanations. And quantum effects are even less amenable to such
explanations. And with black holes, you've got the most extreme
situations for the relativity effects /and/ the most extreme quantum
effects. You are never going to get a nice, clear, intuitive
"bouncing ball bearings" picture here.

Fine, but quantum theory has been verified repeatedly. Hawking
radiation has not.

You can't do that to physics theories. The Hawking radiation fits into
and completes a picture we have of a universe. It predicts very faint
radiation of largish black holes that we can predict not to be
observable by the means we have available now.

And therefore it has *not* been verified. Simple enough, no?

Not exactly. The LIGO gravity wave detector has "seen" a couple of relatively small black holes in the process of merging to make a slightly bigger small black hole, so we do know that they exist. Their properties can be deduced from regular physics.

You mean what we *assume* are black holes... Regardless. Even if they
exist, that says nothing about Hawking radiation.

We don't "assume" black holes - we postulate them to explain facts that otherwise seem impossible to explain. Electrons are equally hypothetical.

There is little observational evidence about black holes that require
them to be black holes. Mostly it is the lack of other things like
radiation, but then the black holes are actually known by all the
indirect radiation. We have to postulate, as you say, because we have
yet to observe a black hole directly.


http://hubblesite.org/reference_desk/faq/answer.php.id=64&cat=exotic

We can see the stars orbiting about a black hole - telling us its mass - and we can see them close enough to the black hole to know that the total mass in the volume available implies a black hole. That's as visible as a black hole is ever going to get.

Quote:
Regardless, it is Hawking radiation we were talking about.

Hawking radiation is a necessary consequence of Dirac pair production and an event horizon.

Except that we don't fully understand black holes... so we may have this
wrong.


We understand them well enough to know that they are going to have an event horizon, which is all you need for Hawking radiation.
Quote:

The problem with modern physics is that it is a package deal - you get the counter-intuitive bits as part of the package. Reject them and you are back to flint axes.

It's not a question of what is intuitive, it is a matter of what is
proven. We fully expected the Higgs boson, but we looked for it to
prove it.


Not the same problem. We fully expected a Higgs boson, but nobody knew exactly how heavy it was going to be.

Quote:
We fully believed the theory of relativity, but we looked for
proof for a very long time and are still happy when we can find
something new that verifies it.


We test the theory of relativity whenever we can, and are happy when it comes up trumps once again. We've got to the point where anything that replaces the theory of relativity has got to make the same predictions with remarkably high precision.

Newtonian physics didn't explain the precession of the orbit of Mercury, and it was recognised as problem before Einstein came up with his explanation..

http://physics.ucr.edu/~wudka/Physics7/Notes_www/node98.html

Einstein's relativity still hasn't been reconciled with quantumn theory, but that's a different class of problem.

Quote:
I too like a nice mechanical explanation - but here you are going to
have to accept weird things if you want to understand. (Not that I am
claiming to understand this stuff.)

I don't have problems with weird things. It's not the weirdness that
is at issue. It's the lack of connection between the particle pair
and the black hole.

Huh? The particle pairs are everywhere. The black hole only makes them
visible, but not to the naked eye.

They would be visible to the naked eye, if the eye was close enough to black hole. No human eye could survive there, but the effect would be visible at a greater distance, for a sufficiently small black hole that was emitting Hawking radiation sufficiently rapidly.

Someday we will create black holes in the lab and may observe Hawking
radiation. My understanding is that the strength of the radiation would
be *inversely* proportional to the size of the black hole, so if we created
a very small one it would in essence explode immediately. I think we could
detect that.

Or something considerably larger, and sufficiently long-lived that we could move it off to safe distance before it came apart.


You are still looking for something that fits your intuitions, even if it doesn't feel that way to you.

--
Bill Sloman, Sydney

David Brown
Guest

Mon Jan 09, 2017 3:31 pm   



On 08/01/17 23:07, rickman wrote:
Quote:
On 1/8/2017 11:01 AM, Albert van der Horst wrote:
In article <np54eh$dpd$2_at_dont-email.me>, rickman <gnuarm_at_gmail.com
wrote:
On 8/18/2016 4:55 AM, David Brown wrote:
On 16/08/16 19:56, rickman wrote:
On 8/16/2016 1:42 PM, George Herold wrote:
snip
Black holes have a temperature. That's pretty cool. (NPI)
Here's wiki...(I only looked at the first few paragraphs.)
https://en.wikipedia.org/wiki/Hawking_radiation

Trouble is all of this is speculation and none is proven. I like a
nice
mechanical explanation. Saying matter leaves a black hole by it
swallowing matter is not a very good argument. That's what Hawking
Radiation says.


Unfortunately, general relativity is not amenable to nice mechanical
explanations. And quantum effects are even less amenable to such
explanations. And with black holes, you've got the most extreme
situations for the relativity effects /and/ the most extreme quantum
effects. You are never going to get a nice, clear, intuitive "bouncing
ball bearings" picture here.

Fine, but quantum theory has been verified repeatedly. Hawking
radiation has not.

You can't do that to physics theories. The Hawking radiation fits into
and completes a picture we have of a universe. It predicts very faint
radiation of largish black holes that we can predict not to be observable
by the means we have available now.

And therefore it has *not* been verified. Simple enough, no?


"Sonic black holes" have been verified to have Hawking radiation, if I
remember correctly. I agree it is not verification for the case of
"ordinary" black holes, but it is a strong indication that the theory is
correct.

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