Author Topic: Do we need escape velocity?  (Read 8547 times)

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Offline John Coloccia

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Re: Do we need escape velocity?
« Reply #25 on: September 19, 2015, 08:12:11 pm »
" Try to fire some rockets and you will quickly find that there is no rocket powerful enough to resist the pull of gravity."

Does this means that their weight is infinite?

No. Weight is a measure of force. F=ma. Their weight will be their mass multiplied by whatever acceleration the rocket can manage. Without the rocket firing, their weight is 0.

 

Offline vlad777Topic starter

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Re: Do we need escape velocity?
« Reply #26 on: September 19, 2015, 08:16:22 pm »
So you mean that they will eventually come back. ?
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Offline vlad777Topic starter

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Re: Do we need escape velocity?
« Reply #27 on: September 19, 2015, 08:20:11 pm »
All I care about is motion away from singularity. I don't care if the probe crashes eventually.

Edit:
So near the EH all directions are parallel to EH?

Edit2:
EH is infinitely far from the singularity? (because of curvature and stretching of space-time)
« Last Edit: September 19, 2015, 08:31:24 pm by vlad777 »
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Online tszaboo

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Re: Do we need escape velocity?
« Reply #28 on: September 19, 2015, 09:48:49 pm »
I am thinking about a probe reporting back (from inside of a black hole), so I do not need to go in orbit.
The only way I - the physics layman - know of, anything leaving a black hole is pair production. It happens when some energy is high enough, and suddenly it creates matter, usually a pozitron and an electron, but it can be other particles.
Now, if one particle falls into the hole, the other can escape.
On the other hand, I'm not sure if I would start building my rocket based on this theory just yet.
 

Offline kolonelkadat

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Re: Do we need escape velocity?
« Reply #29 on: September 20, 2015, 01:04:30 am »
I am thinking about a probe reporting back (from inside of a black hole), so I do not need to go in orbit.

how would you get a signal out of the black hole? I dont know anything about space or physics, but wouldnt it be akin to trying to wring out a towel, eg the "information" would just sort of puddle up around the antenna?


 

Offline Deathwish

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Re: Do we need escape velocity?
« Reply #30 on: September 20, 2015, 01:13:14 am »
I will ask Ambassador Spock and get back to you on this one
Electrons are typically male, always looking for any hole to get into.
trying to strangle someone who talks out of their rectal cavity will fail, they can still breath.
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Offline miguelvp

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Re: Do we need escape velocity?
« Reply #31 on: September 20, 2015, 02:32:19 am »
I am thinking about a probe reporting back (from inside of a black hole), so I do not need to go in orbit.

how would you get a signal out of the black hole? I dont know anything about space or physics, but wouldnt it be akin to trying to wring out a towel, eg the "information" would just sort of puddle up around the antenna?


Didn't read much of Hawkin's new theory (new as in just a month of less ago), but information can come out of black holes in what he calls "super translations", but it's so scrambled that you couldn't make sense of it.

The analogy I did read was taking a car through a crusher, then an industrial shredder, a wood chipper and finally through a coffee grinder. You'll end up with all of the particles but the information on how to put it together would be long lost.

Edit: of course, someone will come out with the math to get that data back to coherent form, in the future, but not possible right now.
« Last Edit: September 20, 2015, 02:34:10 am by miguelvp »
 

Offline vlad777Topic starter

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Re: Do we need escape velocity?
« Reply #32 on: September 20, 2015, 09:08:40 am »
I will ask Ambassador Spock and get back to you on this one

He won't tell you. (You know? That is the Vulcans policy with Earth)  :)
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Offline Nerull

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Re: Do we need escape velocity?
« Reply #33 on: September 20, 2015, 06:31:18 pm »
http://arxiv.org/pdf/0705.1029v2.pdf

Here's a paper examining the use of rockets inside a black hole. The results are pretty interesting - to a point you can slow your fall to the singularity, but after a certain point the more thrust you use to get away from the black hole, the faster you descend to the singularity.

Black Holes are weird, and you aren't going to understand them by thinking with Newtonian physics. Even relativity only works up to a point.
« Last Edit: September 20, 2015, 06:36:26 pm by Nerull »
 

Offline knks

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Re: Do we need escape velocity?
« Reply #34 on: September 29, 2015, 12:40:14 am »
The probe, once fallen behind the EH, would need to accelerate to a speed higher than the speed of light, to escape the Black Holes gravitational pull. And that's not possible, regardless of how much thurst you use. At least that's how I understand it.  :-//

EXACTLY!  That is what we are all told. But if you do not want to "escape the Black Holes gravitational pull", what if you just want to get high?

You can get high, but not higher than EH. The same applies to any photon you radiate.
 

Offline knks

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Re: Do we need escape velocity?
« Reply #35 on: September 29, 2015, 12:45:42 am »
Let's express this thought experiment a different way. Suppose you have a large enough black hole that the tidal forces at the event horizon are small enough not to destroy physical objects. Now suppose you have a probe attached to a long tether and you lower it down below the event horizon. What is to prevent you pulling on the tether and retrieving the probe?
Gravitational force. Probe weight will be = infinity.
 


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