Light inside a black hole?

David, Jan,

Jan didn't say anything about the speed of a body causing
an increase in its mass. He just said that little masses
falling onto a large mass make the large mass larger.

And he didn't describe masses falling into an existing
black hole. He was trying to describe how a black hole
forms:

JP image for a moment matter falling into a body.
JP As its mass increases, the escape speed from it will
JP increase. At some point the escape speed will be
JP greater then C, so light cannot escape, we no longer
JP see any EM waves coming from it, we call it a black
JP hole (is this correct?).

George gave a more accurate description. Jan was wrong
in suggesting that matter builds up until the escape
speed at the surface is greater than c. Instead, the
body collapses long before the escape speed is anywhere
close to c. The collapse starts at the center, which
suddenly increases the density. The event horizon forms
inside the body. It grows larger as the body becomes
smaller and denser. The event horizon quickly grows
larger than the collapsing body.

DAS Just because the light announcing the body's position
DAS is trapped near the horizon, doesn't mean the body is.
DAS This light is special. Most light from the body's
DAS passage will have preceeded it into the BH.

That's an excellent description. I was almost ready to
argue about whether things actually fall into black holes,
but I agree completely with what you said here.

If we could watch something free-fall into a black hole,
we would see it quickly redshift to invisibility at our
event horizon.

-- Jeff, in Minneapolis

"Jan Panteltje" wrote in message
...
...
George, thank you for the explanation.

For a real description of the collapse process, have
a look at Andrew Hamilton's excellent pages:

http://casa.colorado.edu/~ajsh/collapse.html

Maybe one day they will figure out some way to know what happens in
the BH.

The idea is that merging QM and GR may give some answers
but also predict some subtle effects in other areas that
might be testable.

Maybe one of those big particle accelerators will make a tiny BH, and
deduce something from that.

Even for the smallest BH, the singularity would be far
inside the EH and inaccessible to observation. In theory
spinning up a BH to expose the singularity might work.

Bear in mind that, if Hawking Radiation exists, the BH
will evaporate with quite a bang unless it is large enough
for its temperature to be at a maintainable level.

http://casa.colorado.edu/~ajsh/hawk.html#evaporation

A BH with a mass of 10^11 kg has a temperature of 10^12K
so you need one much more massive if it is to be stable.
A large BH gives of 1000 tonnes energy in the last second
of evaporation while the Hiroshima bomb converted 0.6g so
you don't want that going off in the lab. The question of
how you prevent a BH of that mass falling through the lab
floor is also not simple. For much smaller holes, the
energy would only be the mass it contains but the lifetime
will be correspondingly shorter.

George

"dlzc" wrote in message
ups.com...
Dear Jeff Root:

Jeff Root wrote:
David,

You "plonked" me long ago, so I don't know if you'll see this.

Time to clear out some entries then.

My understanding of a black hole event horizon is that its
location depends on the location and motion of the observer.

Agreed. Just like a horizon moves away from you as you move towards
it.

David, that is one reason why I have doubts about the
physicality of the transposition of space and time
coordinates. The other is that I suspect any real BH
must have a non-zero angular momentum and in the Kerr
solution the coordinates revert before the singularity.

George

Dear George Dishman:

"George Dishman" wrote in message
...

"dlzc" wrote in message
ups.com...
Dear Jeff Root:

Jeff Root wrote:
....
My understanding of a black hole event horizon is
that its location depends on the location and
motion of the observer.

Agreed. Just like a horizon moves away from you
as you move towards it.

David, that is one reason why I have doubts about the
physicality of the transposition of space and time
coordinates.

George, the physicality of length contraction and time dilation
in SR can never be answered. I don't expect this to be any
simpler.

The other is that I suspect any real BH
must have a non-zero angular momentum and in the
Kerr solution the coordinates revert before the
singularity.

You are on pretty solid ground there. Seems there was a post
here just a couple of days ago that pulsars got their spin not
from conservation of angular momentum (with "pre-formation
momentum"), but from shedding their outer layers... if BHs were
formed in some sort of "shock wave" in dense matter...

David A. Smith

Dear Jan Panteltje:

"Jan Panteltje" wrote in message
...
On a sunny day (5 Jan 2007 07:45:35 -0800) it happened "dlzc"

wrote in
. com:

Dear Jan Panteltje:

Jan Panteltje wrote:
On a sunny day (Fri, 5 Jan 2007 09:31:03 -0500) it happened
"Greg Neill"
wrote in
:

"Jan Panteltje" wrote in message
...
If you move to the centre of a black hole, where
gravitational forces sort of cancel, can light and
normal matter exist in some area there?

Gravitational forces don't cancel because the
mass of a black hole (except for the infalling
matter from its "feeding") is located at a
singlularity at the center.

But why? image for a moment matter falling
into a body. As its mass increases,

The mass of infalling matter does not increase.

I was trying to say that the mass of the body
increaes.

I finally got it. There is no black hole yet. The body you are
speaking of is at some threshold. It accumulates more mass.
Then you started talking about what happens next.

I need to practice "reading for comprehension". Sorry.

David A. Smith

N:dlzc D:aol T:com (dlzc) wrote:
"George Dishman" wrote in message
...
"dlzc" wrote in message
ups.com...
Dear Jeff Root:

Jeff Root wrote:
...
My understanding of a black hole event horizon is
that its location depends on the location and
motion of the observer.

Agreed. Just like a horizon moves away from you
as you move towards it.

David, that is one reason why I have doubts about the
physicality of the transposition of space and time
coordinates.

George, the physicality of length contraction and time dilation
in SR can never be answered.

In what way David? There is obviously the question
of whether the geometry is "truly" Riemann or it is
an emergent property but I don't see any problem
with the "physicality" of it other than the usual
semantic problem that some people include
geometric effects in "physical" while other draw a
distinction.

I don't expect this to be any
simpler.

I don't think the physics of BHs is "simple" in any
way, and it is certainly a lot harder than SR, but
that doesn't mean that the answer isn't know by
people somewhat marter than I.

The other is that I suspect any real BH
must have a non-zero angular momentum and in the
Kerr solution the coordinates revert before the
singularity.

You are on pretty solid ground there. Seems there was a post
here just a couple of days ago that pulsars got their spin not
from conservation of angular momentum (with "pre-formation
momentum"), but from shedding their outer layers... if BHs were
formed in some sort of "shock wave" in dense matter...

Regardless of their formation, suppose you had that
most elusive of objects, a non-rotating BH, say 1km in
radius. Then one atom falls into it but on an approach
trajectory that would miss the exact centre by just
1mm if projected as a straight line from the path a light
year away. Once the atom merges with the hole, the
hole has a non-zero angular momentum. I think the
Schwarzschild solution must be seen as purely
hypothetical. Even the electrical charge would have a
noise component (thermal ?) as positive and negative
ions fall in at random times even though the mean
(DC) might stay close to zero.

George

Dear George Dishman:

George Dishman wrote:
N:dlzc D:aol T:com (dlzc) wrote:
"George Dishman" wrote in message
...
"dlzc" wrote in message
ups.com...
Dear Jeff Root:

Jeff Root wrote:
...
My understanding of a black hole event horizon is
that its location depends on the location and
motion of the observer.

Agreed. Just like a horizon moves away from you
as you move towards it.

David, that is one reason why I have doubts about the
physicality of the transposition of space and time
coordinates.

George, the physicality of length contraction and time
dilation in SR can never be answered.

In what way David? There is obviously the question
of whether the geometry is "truly" Riemann or it is
an emergent property but I don't see any problem
with the "physicality" of it other than the usual
semantic problem that some people include
geometric effects in "physical" while other draw a
distinction.

I was referring to the ongoing (eternal) struggle between relativists
and "Lorentz aetherists". Nature does not allow instantaneous
signalling, so the Lorentz aether cannot yield to measurement. "Does
the moving rod really contract, or is it an artifact of measurement?"
It thought that was germaine to the question of "physicality"

I don't expect this to be any
simpler.

I don't think the physics of BHs is "simple" in any
way, and it is certainly a lot harder than SR, but
that doesn't mean that the answer isn't know by
people somewhat marter than I.

I wouldn't put a lot of money on anyone having the one-and-only answer.
Just one that is consistent with their knowledge and beliefs.

The other is that I suspect any real BH
must have a non-zero angular momentum and in the
Kerr solution the coordinates revert before the
singularity.

You are on pretty solid ground there. Seems there was a post
here just a couple of days ago that pulsars got their spin not
from conservation of angular momentum (with "pre-formation
momentum"), but from shedding their outer layers... if BHs were
formed in some sort of "shock wave" in dense matter...

Regardless of their formation, suppose you had that
most elusive of objects, a non-rotating BH, say 1km in
radius. Then one atom falls into it but on an approach
trajectory that would miss the exact centre by just
1mm if projected as a straight line from the path a light
year away. Once the atom merges with the hole, the
hole has a non-zero angular momentum. I think the
Schwarzschild solution must be seen as purely
hypothetical. Even the electrical charge would have a
noise component (thermal ?) as positive and negative
ions fall in at random times even though the mean
(DC) might stay close to zero.

Agreed.

David A. Smith

dlzc wrote:
George Dishman wrote:
N:dlzc D:aol T:com (dlzc) wrote:
....
George, the physicality of length contraction and time
dilation in SR can never be answered.

In what way David? ...

I was referring to the ongoing (eternal) struggle between relativists
and "Lorentz aetherists".

Ah, it was your inclusion of ".. in SR .." that threw me.

.. Nature does not allow instantaneous
signalling, so the Lorentz aether cannot yield to measurement.

Perhaps, though the discovery of aether particles in
the next generation of accelerator would change that.

"Does
the moving rod really contract, or is it an artifact of measurement?"
It thought that was germaine to the question of "physicality"

Between the philosophies yes, but within SR we know
the mechanism and it is just a question of how we
classify the effect.

I don't think the physics of BHs is "simple" in any
way, and it is certainly a lot harder than SR, but
that doesn't mean that the answer isn't known by
people somewhat smarter than I.

I wouldn't put a lot of money on anyone having the one-and-only answer.

I think GR gives just a single answer. Whether that
correctly models nature is a different question but
around the EH of a large BH, the indications are that
is is a good fit. Quantum effects become significant
at much smaller radii.

George