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Author Topic: What does a local observer near a black hole measure?  (Read 7723 times)

Offline itisus

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Near but outside a black hole horizon, space and time are transformed as given in the Schwarzschild solution.  I generally understand the basics of the distant observer viewpoint, but how is that related to the viewpoint of a local stationary observer?  It also seems to me that uncertainty in the radial direction should increase (as seen by the local observer); what do you think?  Of course the same effects apply here in miniature, but black holes are more macho.

Extra credit: If Earth were compressed almost to a black hole, could Santa Claus visit every house in one night?


 

Offline Mr. Scientist

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What does a local observer near a black hole measure?
« Reply #1 on: 30/12/2008 06:35:01 »
Outside the black hole you would see nothing but a hole. This hole is spinning at the speed of light, and it just looks like a hole, because the transformations beyond its boundary have not only twisted space and time around, but its got an escape velocity of tachyonic speeds, so since light cannot escape, it will look to any outside observer as a hole, and nothing much more. It's only when you go into a black hole, does an observer begin to see anything spectacular, providing parallel universes exist.

Secondly, i hope the second question was just a joke?
 

Offline yor_on

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What does a local observer near a black hole measure?
« Reply #2 on: 30/12/2008 11:10:31 »
Itisus?
Are you endowing Santa with a magnifying glass here?
Won't he need it just to find that planet.

I would hate to see what that proposal would do to those poor rangifer tarandus:)

Yes that is artic reindeers, if I've learnt to use the correct nomenclature for matter I from now will expect it at all times.
And Yes. I insist that Santa is from the Nordic side of the world.
His magnificent beard, so alike us vikings.
And those ruddy red cheeks smiling at us, lightening up all conversations..
Awh yes, a proud example of manhood he is.
Nordic I say:)



-------

And the event horizon (EV)is the question here right?
And the definition of it as the place where 'gravity' becomes so strong that nothing can escape.
That should mean that when you starts to come near EV everything will become 'twisted' just as when you starts to get near 'c'
(if I think right?)

And 'c' here is 'represented' by the EV.
As it keeps light 'under' it.

Also it seems to differ if we're talking about a spinning BH or a, relative us, not spinning.
Isn't that 'frame dragging' where spacetime will 'deform' around that spinning object, depending on rotational speed.

So it will take with it spacetime as it rotates, and that should make for some quite interesting phenomena?

If you look out at spacetime while traveling near the speed of light, you will see (being inside that moving/accelerating frame) some very strange visual 'deformations' around you and those effects should present them selves near that spinning EV too.


 

Offline DoctorBeaver

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What does a local observer near a black hole measure?
« Reply #3 on: 30/12/2008 12:30:13 »
This hole is spinning at the speed of light...

That isn't so. The spin of a black hole is due to the spin of the star that originally formed the black hole - taking conservation of angular momentum into account. Anything falling into the black hole will, obviously, have a greater or lesser effect on the spin but not to the extent that the spin could be anywhere near the speed of light.

Are you maybe getting confused between the speed of light and the event horizon being where the escape velocity equals the speed of light? They are very different things.
« Last Edit: 30/12/2008 12:32:38 by DoctorBeaver »
 

Offline LeeE

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What does a local observer near a black hole measure?
« Reply #4 on: 30/12/2008 20:33:04 »
Quote
If Earth were compressed almost to a black hole, could Santa Claus visit every house in one night?

If the Earth were compressed almost to a black hole it would be about 9 mm diameter, iirc, so as yor_on points out, he'd have more trouble just finding it than visiting every home in a single night, which he can do already.
 

Offline Mr. Scientist

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What does a local observer near a black hole measure?
« Reply #5 on: 31/12/2008 04:26:14 »
This hole is spinning at the speed of light...

That isn't so. The spin of a black hole is due to the spin of the star that originally formed the black hole - taking conservation of angular momentum into account. Anything falling into the black hole will, obviously, have a greater or lesser effect on the spin but not to the extent that the spin could be anywhere near the speed of light.

Are you maybe getting confused between the speed of light and the event horizon being where the escape velocity equals the speed of light? They are very different things.

I've not done a lot of work on black holes, however, i do remember learning that somewhere.
 

Offline yor_on

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What does a local observer near a black hole measure?
« Reply #6 on: 01/01/2009 19:51:58 »
DB you are quite correct in stating that "The spin of a black hole is due to the spin of the star that originally formed the black hole "

But there is also a added possibility that the " spin rate depends on how long the black hole has been devouring matter from its companion star, a process that makes the black hole spin faster. Black holes with more rapid spin, XTE J1650-500 and GX 339-4, have low-mass companion stars."
http://chandra.harvard.edu/press/03_releases/press_091703.html

As for how fast they might spin?
I found this one.
http://www.universetoday.com/2007/05/29/supermassive-black-holes-spin-at-the-limits-of-relativity/

And those supermassive black holes is what we seem to have in the middle of all galaxies:)
Some think that it is them who 'stacked up' the rest of the invariant mass creating our galaxies and universe.

But they also 'brake' further creations as their "jets pump enormous amounts of energy into their surroundings, heating up gas. Since stars can only form when there are large clouds of cold gas, these process of heating can stall star formation in the host galaxy."
http://www.universetoday.com/2008/01/10/black-holes-seen-spinning-at-the-limits-predicted-by-einstein/
« Last Edit: 01/01/2009 20:23:40 by yor_on »
 

Offline DoctorBeaver

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What does a local observer near a black hole measure?
« Reply #7 on: 01/01/2009 22:15:17 »
Well I never!  :o

I must say, I didn't realise they could spin that fast. I apologise unreservedly for my previous comment.
 

Offline Make it Lady

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What does a local observer near a black hole measure?
« Reply #8 on: 01/01/2009 22:26:12 »
Santa dropped his presents off this year with a giant pair of tweasers. So maybe he squashes us to the black hole size, delivers the presents and then unsquashes us again. I've always wondered how he does it. Does anyone know how to get reindeer poop out of shag pile?
 

Offline DoctorBeaver

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What does a local observer near a black hole measure?
« Reply #9 on: 01/01/2009 22:29:39 »
Santa dropped his presents off this year with a giant pair of tweasers. So maybe he squashes us to the black hole size, delivers the presents and then unsquashes us again. I've always wondered how he does it. Does anyone know how to get reindeer poop out of shag pile?

FOG!
 

Offline yor_on

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What does a local observer near a black hole measure?
« Reply #10 on: 01/01/2009 23:05:45 »
DB as far as I can see you don't have to apologize for nothing.
I was as surprised as you, when I read the velocity's mentioned.
And reading you I have a distinct feeling you know 'your stuff'

There is no guarantee for those kind of rotational velocities, it just fits the observations.
And as always it's, 'for now'..
That will be on my tombstone btw.
Dead 'for now' :)

Am I bicycling when I compare the event horizon with its ability to contain light to light itself?
'the irresistible force meeting the immovable barrier' sort of.
It seems to me that there are some 'thresholds' we can't pass?

Like absolute zero degrees kelvin (K) "temperature scale is an extension of the degree Celsius scale down to absolute zero.
A hypothetical temperature characterized by a complete absence of heat energy."

And lights velocity in a vacuum.
And the event horizon. 
And 'HUP'(Heisenberg's uncertainty principle)?

What more are there?
Or is it just me being confused again?



« Last Edit: 01/01/2009 23:08:51 by yor_on »
 

Offline Make it Lady

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What does a local observer near a black hole measure?
« Reply #11 on: 01/01/2009 23:08:21 »
I didn't think absolute zero was hypothetical. Explain?
 

Offline yor_on

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What does a local observer near a black hole measure?
« Reply #12 on: 01/01/2009 23:20:41 »
As far as I understand we can't come down to that temperature.
It's another example of us needing an 'unlimited' source of energy to 'steal' away the energy:)

------

Sorry missed here.
A rewrite is better...

The only thing we have coming close to that temperature is what is called a Bose–Einstein condensate.
http://en.wikipedia.org/wiki/Bose-Einstein_condensate

"A BEC is a state of matter (Bose–Einstein condensate).
It occurs when the particles get close enough together for their quantum wavepackets to start to overlap sufficiently.
In practice, BECs in dilute atomic vapours, occur at about 1 nK above absolute zero (thats 0.000 000 001 degree about absolute zero)."

You can read a very cool description of it at http://www.colorado.edu/physics/2000/bec/how_its_made.html

Looking at it I got this idea about how it worked.

They do it by using monochrome light (laserlight) that act as a coherent stream of photons slowing down atoms.by 'bouncing' on them. Then by magnetically trapping the Atoms they can stop all movement. When all movement are gone from an atom it will be at from 400 billionths of a degree above absolute zero down to 50 billionths or even lower?

" Peder Sjölund and Anders Kastberg from Umeå University used a technique called laser cooling to trap and control a cloud of Cesium atoms.
This involves cooling the atoms to just above absolute zero, which slows their microscopic random Brownian motion from hundreds of kilometers per hour to just a few meters per second. The atoms can then be "locked" in place using a lattice of laser beams. "The lasers create a regular system of atoms, somewhat like a crystal," says Kastberg. "They work as a kind of egg crate for atoms." .."
http://www.newscientist.com/article/dn9121-laser-cages-control-unruly-atoms.html

But what they were cooling was Atoms, not photons. To cool the photons you use this condensate and shoot laser beams through it " One laser is shot across the width of the cloud of condensate. This controls the speed of a second pulsed laser beam shot along the length of the cloud. The first laser sets up a "quantum interference" such that the moving light beams of the second laser interfere with each other. When everything is set up just right, the light can be slowed by a factor of 20 million. "

That slows / cools the photons so that they become a still image, or 'natures memory' if you like. Depending on how you view it they are now a frozen wave or frozen particles. There are nothing in physics that disallows light from slowing down, it does it whenever it penetrates materials like water or glass.

But we can't reach absolute zero (kelvin)
This is as I understands it (for now:) due to both HUP and The third law of thermodynamics:
http://en.wikipedia.org/wiki/Third_law_of_thermodynamics

The Heisenberg's uncertainty principle forbids you to know all parameters in any given QM system.
http://www.answers.com/topic/uncertainty-principle

In fact it (HUP), according to some scientists, seems to work on a macroscopic scale too?
http://www.seedmagazine.com/news/2008/06/the_reality_tests_1.php

Hope this makes better sense than what I wrote first.

I will probably find errors if I read it through:)
So I think I will 'chicken out'
Ahhh, for now::))
« Last Edit: 02/01/2009 00:56:19 by yor_on »
 

Offline Mr. Scientist

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What does a local observer near a black hole measure?
« Reply #13 on: 02/01/2009 06:50:10 »
Well I never!  :o

I must say, I didn't realise they could spin that fast. I apologise unreservedly for my previous comment.

Nothing to apologize for.
 

Offline DoctorBeaver

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What does a local observer near a black hole measure?
« Reply #14 on: 02/01/2009 11:45:43 »

And reading you I have a distinct feeling you know 'your stuff'




I know practically nothing! I am very much an amateur.
 

Offline yor_on

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What does a local observer near a black hole measure?
« Reply #15 on: 02/01/2009 12:21:27 »
Good, then we are two:)
 

Offline DoctorBeaver

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What does a local observer near a black hole measure?
« Reply #16 on: 02/01/2009 12:24:04 »
That's a relief. I was beginning to think there was more than 1 of me!
 

Offline yor_on

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What does a local observer near a black hole measure?
« Reply #17 on: 02/01/2009 13:38:41 »
Math huh.
Better stay away from that.

It 'poisons' so much of the excellent physics I produce::))
 

Offline Make it Lady

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What does a local observer near a black hole measure?
« Reply #18 on: 02/01/2009 22:12:15 »
Thanks Mr Yorin, sorry yor_on, that has explained a lot. I'm fascinated by absolute zero.
 

Offline yor_on

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What does a local observer near a black hole measure?
« Reply #19 on: 02/01/2009 22:49:26 »
Yeah, me too.
It is a very strange state.

Having a 'cold' will never be as simple as before:)

------

Maybe one can look at as the opposite to 'high energy physics' aka a neutron star/black hole.
Both seems to produce a 'soup' as they develop.
A 'soup' of particles(?)

and now someone will correct my misapprehension:)
And then I (hopefully) will learn something more.
I kind of love this..
« Last Edit: 02/01/2009 22:54:49 by yor_on »
 

Offline DoctorBeaver

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What does a local observer near a black hole measure?
« Reply #20 on: 02/01/2009 22:58:26 »
Soup? I'd like to see you lift a spoonful of it!  ;D
 

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What does a local observer near a black hole measure?
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