Black Holes

[Gardamorg]

I didn't know where to put this.

Nothing reaches the center of a black hole.


As an object enters a black hole it becomes smaller in volume and more condensed and heavier. So it might stay the same in mass but it still becomes smaller, and the closer it gets to the center of the black hole, the smaller it gets, this process goes on forever, the object never hits the center.

[Farsight]

Not quite, Garda. Gravitational time dilation goes infinite at the event horizon. So it takes the object forever to get past the event horizon. It never ever does. Nothing does. There are no central singularities. Every last single star or object that has collapsed into a black hole hasn't finished collapsing yet, and never ever will.

Look up "frozen stars".

[InfiniteNow]

Originally Posted by Popular

Not quite, Garda. Gravitational time dilation goes infinite at the event horizon. So it takes the object forever to get past the event horizon. It never ever does. Nothing does. There are no central singularities. Every last single star or object that has collapsed into a black hole hasn't finished collapsing yet, and never ever will.

Look up "frozen stars".

Perhaps from the perspective of an observer outside the event horizon, but not necessarily for the object within. It will become one with the infinitely dense/infinitely compact point... it becomes part of the singularity itself.

According to the math anyway.

[Farsight]

According to the maths, I can bring home a carpet measuring -4m by -4m to cover the floor of my 16 square metre study.

I'm serious about this. The maths gives you a singularity in "never-never land" beyond the end of time. The "proper time" of the infalling object is a similar abstraction with no actual reality.

[Jay-qu]

Popular you are making certain perspectives 'privelegded', which is forbidden by special relativity standards. The infalling particles have just as much claim to their own 'time' as we do. To them it is us careening into the infinite future that has the 'meaningless time'.

[Gardamorg]

Originally Posted by Popular

Not quite, Garda. Gravitational time dilation goes infinite at the event horizon. So it takes the object forever to get past the event horizon. It never ever does. Nothing does. There are no central singularities. Every last single star or object that has collapsed into a black hole hasn't finished collapsing yet, and never ever will.

Look up "frozen stars".

Thats practicully what I said, and its deffenantly what I meant.

[orbsycli]

Originally Posted by Popular

According to the maths, I can bring home a carpet measuring -4m by -4m to cover the floor of my 16 square metre study.

I'm serious about this. The maths gives you a singularity in "never-never land" beyond the end of time. The "proper time" of the infalling object is a similar abstraction with no actual reality.

Never thought about that...thanks.

[Boerseun]

Actually, as a star contracts, it spins faster. That's how we can calculate the minimum sizes of pulsars - information can only travel around the surface of the body (in this case a super-dense collapsing star) at the speed of light. In other words, if a pulsar pulses at around a hundred times a second, that says something about its rotational speed, which says something about its minimum size. Rotating faster as it contracts is analogous to sitting on a spinning chair and pulling your arms in.

As the star contracts, and its surface speed approaches that of light, it would still need to contract some in order to reach it. As it contracts further, the contraction (and surface accelleration) would seem to slow down from an external observer's point of view. From the star's surface, the speed would continuously increase and the contraction would keep on going. It would take a few minutes, hours or days from the point of view of the surface of the star, but externally, it would take more than the age of the universe before the eventual singularity is reached. It's analogous to accellerating at a constant 1g and reaching to edge of the observable universe in only 52 years, but taking more than 15 billion years from an external frame.

But that being the case, from outside a black hole, a singularity cannot exist. The universe isn't old enough for any black holes to have collapsed so far, yet. From inside a black hole, however, every black hole is a singularity shortly after the star collapsed. But the point is moot, of course - the effect a black hole has on the universe would be exactly the same from an external point of view with or without the black hole actually being a singularity. The effect would be the same, because the black hole's mass would be the same.

Of course, from the point of view of the black holes' collapsing surface (and I'm talking of the mass surface, not the event horison) the black hole should loose mass faster and faster through Hawking radiation. From outside, the black hole would take billions of years to evaporate via Hawking radiation, but from inside, it might take mere hours. Now the question is if a singularity ever actually forms before Hawking radiation would make it loose enough mass for the event horison to disappear - in which case the black hole would simply become another cold, dark, failed star.

[Farsight]

Originally Posted by Jay-qu

Popular you are making certain perspectives 'priveleged', which is forbidden by special relativity standards. The infalling particles have just as much claim to their own 'time' as we do. To them it is us careening into the infinite future that has the 'meaningless time'.

I'm writing the book on this, Jay-qu, called RELATIVITY+. Check the thread. Neither we nor those particles have any "time", just motion. Time is just the relative measure of it. I've basically gotten this from Einstein who said time is suspect and spacetime is a space. It's all about looking at the postulates of special relativity (basically: we always measure the speed of light to be the same because our time changes) and working out why they apply and what it all means.

All points noted Boerseun. I find it interesting that this presentation of a black hole as a frozen star doesn't appear much in literature, especially since the lack of an actual singularity seems to fix a GR blow-up problem. Re "cold dark failed star" I like the term "solid space" myself, but I'm not quite confident about it at the moment. In similar vein I have some doubts about Hawking Radiation, but I can't justify why right now.

[CraigD]

Originally Posted by Popular

According to the maths, I can bring home a carpet measuring -4m by -4m to cover the floor of my 16 square metre study.

This claim, or more precisely, its apparent strangeness, follows from the confusion of vector and scalar quantities.

What you’re actually saying with the phrase “a carpet measuring -4 m by -4 m”, is a carpet with edges given by the vectors -4 m,0 and 0,-4 m. The scalar length of -4 m,0 and 0,-4 m are both 4 m, the same as the vectors 4 m,0 and 0,4 m. So the area of the rectangle defined by -4 m,0,0,-4 m or 4 m,0,0,4 m is the same, 16 m.

This can also be looked at as saying: “Rolling a counting-wheel forward on a carpet from its upper-left corner to its lower-left to its lower-right corner give 2 readings, 4 m and 4 m, from which I calculate its area to be 16 m. Rolling the counting-wheel backwards from the lower-right to the lower-left to the upper-right corner gives readings -4 m and -4 m, from which I calculate its area to be 16 m.”

Now, if you brought home a carpet measuring 4i () by 4i to cover the floor of your -16 square meter study, I’d agree you were dealing in the mathematical physics of a never-never land. Negative numbers in vector quantities, however, are entirely sensible and real.