black holes and singularities

Folks,

Before you all scream and kill this thread, please bear with me. I've
found questions like this on this group, but no really satisfactory
answers, so I'm going to try and phrase it right.

Conventional wisdom says that at the centre of your average black hole,
lies a singularity. Every book or article that I've read on this
subject is adamant about this fact.

So, my question would be, *why* the singularity. The presense of one
isn't necesary to form a black hole, all you need is a body of
sufficient density, e.g. if a sun shrinks beyond size x, it forms an
event horizon. So, while the presense of a singularity neccessitates
the presense of a blackhole, the converse isn't true.

If that assertion is correct, that a singularity isn't neccessary, then
why the assertion that they are always present? Doesn't Occam's Razor
tell us that it's simply a super-dense object of finite, non-zero
volume? Or does theory suggest that once a body reaches that sort of
density, then it can't help but continue collapse to a point mass under
its own gravity?

Of course, that raises a whole host of quantum/classical conflicts, but
those aside, what gives?

cheers,
a

"Abe" wrote in message
t...
Folks,

Before you all scream and kill this thread, please bear with me. I've
found questions like this on this group, but no really satisfactory
answers, so I'm going to try and phrase it right.

Conventional wisdom says that at the centre of your average black hole,
lies a singularity. Every book or article that I've read on this
subject is adamant about this fact.

So, my question would be, *why* the singularity. The presense of one
isn't necesary to form a black hole, all you need is a body of
sufficient density, e.g. if a sun shrinks beyond size x, it forms an
event horizon. So, while the presense of a singularity neccessitates
the presense of a blackhole, the converse isn't true.

If that assertion is correct, that a singularity isn't neccessary, then
why the assertion that they are always present? Doesn't Occam's Razor
tell us that it's simply a super-dense object of finite, non-zero
volume? Or does theory suggest that once a body reaches that sort of
density, then it can't help but continue collapse to a point mass under
its own gravity?

Of course, that raises a whole host of quantum/classical conflicts, but
those aside, what gives?

The singularity is inevitable for two reasons. First, the
collapse of the matter that formed the black hole exceeded
the electron degeneracy pressure, the last thing that was
preventing the density from growing without limit; there
is nothing known, no known force, that can support the
matter from total collapse past this point.

Second, the equations show that all trajectories below the
event horizon lead to the central singularity. Perhaps
you've heard of the strange way that time and space seem
to change roles inside a black hole? Well, similar to the
way that for us out in normal space the future is always,
inevitably ahead for us (there's no turning back!), the
singularity lays ahead for every trajectory inside the BH.
Space becomes like time below the event horizon, with the
direction of the singularity being the direction of the
"future".

On Sun, 14 Mar 2004 15:14:23 +0000, Abe wrote:

Conventional wisdom says that at the centre of your average black hole,
lies a singularity. Every book or article that I've read on this
subject is adamant about this fact.

So, my question would be, *why* the singularity. The presense of one
isn't necesary to form a black hole, all you need is a body of
sufficient density, e.g. if a sun shrinks beyond size x, it forms an
event horizon. So, while the presense of a singularity neccessitates
the presense of a blackhole, the converse isn't true.

If that assertion is correct, that a singularity isn't neccessary, then
why the assertion that they are always present? Doesn't Occam's Razor
tell us that it's simply a super-dense object of finite, non-zero
volume? Or does theory suggest that once a body reaches that sort of
density, then it can't help but continue collapse to a point mass under
its own gravity?

If you don't like a singularity - you can have a tangled ball of strings
underneath the event horizon. See :

http://www.sciencedaily.com/releases...0304073931.htm

--

Gautam Majumdar

Please send e-mails to

"Abe" schreef in bericht
t...
Folks,

Before you all scream and kill this thread, please bear with me. I've
found questions like this on this group, but no really satisfactory
answers, so I'm going to try and phrase it right.

Conventional wisdom says that at the centre of your average black hole,
lies a singularity. Every book or article that I've read on this
subject is adamant about this fact.

Where did you read that ?
Can you give me an url with a text which claims that.

IMO singularities do not exist.
A black hole is something that exists with has a certain radius 0
A singularity is a mathematical construct
which you get when radius r goes to zero.
In that case the force goes to infinity.

So, my question would be, *why* the singularity. The presense of one
isn't necesary to form a black hole, all you need is a body of
sufficient density, e.g. if a sun shrinks beyond size x, it forms an
event horizon. So, while the presense of a singularity neccessitates
the presense of a blackhole, the converse isn't true.

SNIP

Nicolaas Vroom
http://users.pandora.be/nicvroom/

In article ,
says...

The singularity is inevitable for two reasons. First, the
collapse of the matter that formed the black hole exceeded
the electron degeneracy pressure, the last thing that was
preventing the density from growing without limit; there
is nothing known, no known force, that can support the
matter from total collapse past this point.

Ah, OK. So, does this pressure limit occur at exactly the time at which
the event horizon forms?

Second, the equations show that all trajectories below the
event horizon lead to the central singularity. Perhaps
you've heard of the strange way that time and space seem
to change roles inside a black hole? Well, similar to the
way that for us out in normal space the future is always,
inevitably ahead for us (there's no turning back!), the
singularity lays ahead for every trajectory inside the BH.
Space becomes like time below the event horizon, with the
direction of the singularity being the direction of the
"future".

*brain melts*

Are you saying that the _effects_ of the singularity are turned into the
_causes_ of the singularity, due to this inversion?

In article pan.2004.03.14.18.35.06.596607.11371@XSPAMfreeuk. com,
says...
On Sun, 14 Mar 2004 15:14:23 +0000, Abe wrote:

Conventional wisdom says that at the centre of your average black hole,
lies a singularity. Every book or article that I've read on this
subject is adamant about this fact.

So, my question would be, *why* the singularity. The presense of one
isn't necesary to form a black hole, all you need is a body of
sufficient density, e.g. if a sun shrinks beyond size x, it forms an
event horizon. So, while the presense of a singularity neccessitates
the presense of a blackhole, the converse isn't true.

If that assertion is correct, that a singularity isn't neccessary, then
why the assertion that they are always present? Doesn't Occam's Razor
tell us that it's simply a super-dense object of finite, non-zero
volume? Or does theory suggest that once a body reaches that sort of
density, then it can't help but continue collapse to a point mass under
its own gravity?

If you don't like a singularity - you can have a tangled ball of strings
underneath the event horizon. See :

http://www.sciencedaily.com/releases...0304073931.htm

Yeah, I read about that. I must say it appealed to my personal sense of
aesthetics

In article ,
says...

Conventional wisdom says that at the centre of your average black hole,
lies a singularity. Every book or article that I've read on this
subject is adamant about this fact.

Where did you read that ?
Can you give me an url with a text which claims that.

Well, no, not offhand. However, I distinctly recall Thorne and Hawking
mentioning this explicitly. Perhaps my memory is faulty, or my
interpretation of what they said.

IMO singularities do not exist.
A black hole is something that exists with has a certain radius 0

Which is what I was getting at. The presense of a singularity does not
seem necessary (or even likely), but as other posters have pointed out,
this may be inevitable.

A singularity is a mathematical construct
which you get when radius r goes to zero.
In that case the force goes to infinity.

.... therefore requiring an event horizon to "hide" the singularity from
the rest of the universe.

It all seems a bit too convenient

In message , Nicolaas
Vroom writes

"Abe" schreef in bericht
et...
Folks,

Before you all scream and kill this thread, please bear with me. I've
found questions like this on this group, but no really satisfactory
answers, so I'm going to try and phrase it right.

Conventional wisdom says that at the centre of your average black hole,
lies a singularity. Every book or article that I've read on this
subject is adamant about this fact.

Where did you read that ?
Can you give me an url with a text which claims that.

IMO singularities do not exist.
A black hole is something that exists with has a certain radius 0
A singularity is a mathematical construct
which you get when radius r goes to zero.
In that case the force goes to infinity.

"According to general relativity, there must be a singularity of
infinite density and space-time curvature within a black hole".
A Brief History of Time p 88.
--
Save the Hubble Space Telescope!
Remove spam and invalid from address to reply.

"Abe" schreef in bericht
t...
In article ,
says...

Conventional wisdom says that at the centre of your average black
hole,
lies a singularity. Every book or article that I've read on this
subject is adamant about this fact.

Where did you read that ?
Can you give me an url with a text which claims that.

Well, no, not offhand. However, I distinctly recall Thorne and Hawking
mentioning this explicitly. Perhaps my memory is faulty, or my
interpretation of what they said.

May be this is the article we are looking for:
http://home.comcast.net/~ernie1001/papers/blackhole.pdf

The article claims at page 1 that there are 2 solutions
and one avoids the singularity at r = 0.

See also Conclusion at page 7.

I did a search with google with "blackhole singularity" but I did
not found anything of interest.
This url mentions a singularity
http://www.geocities.com/wasabidoh/BlackHole.html
but does not explain what it is.

Nicolaas Vroom
http://user.pandora.be/nicvroom/

"Abe" wrote in message
t...
In article ,
says...

The singularity is inevitable for two reasons. First, the
collapse of the matter that formed the black hole exceeded
the electron degeneracy pressure, the last thing that was
preventing the density from growing without limit; there
is nothing known, no known force, that can support the
matter from total collapse past this point.

Ah, OK. So, does this pressure limit occur at exactly the time at which
the event horizon forms?

This would depend upon the starting mass. For
things like neutron stars, its the degeneracy
pressure that keeps them from collapsing further;
the electrons have already been squeezed together
with protons to form neutrons, and the neutrons
are pushed together (no electrostatic force to
keep atom nuclei apart when they're all neutrons).

It's actually possible to form an event horizon
with enough perfectly normal matter. An observer,
caught in the process, might not even realize that
the event horizon had formed, yet any trajectory
he might try to follow would end up taking him
inevitably closer to the center of mass of the
system. Likewise for everything else around him
and below the event horizon. Eventually, the
singularity would form when enough matter gets
together in the center.


Second, the equations show that all trajectories below the
event horizon lead to the central singularity. Perhaps
you've heard of the strange way that time and space seem
to change roles inside a black hole? Well, similar to the
way that for us out in normal space the future is always,
inevitably ahead for us (there's no turning back!), the
singularity lays ahead for every trajectory inside the BH.
Space becomes like time below the event horizon, with the
direction of the singularity being the direction of the
"future".

*brain melts*

Are you saying that the _effects_ of the singularity are turned into the
_causes_ of the singularity, due to this inversion?

Not really. I'd have to think about what the implications
are vis-a-vis causality. Let's just say that below the EH
it's a one way trip to the center and in finite proper time.