# Thread: Theoretical problem

1. I made a series of conclusions based on my own (very little) knowledge of physics and managed to get into an imbossible situation. I just need somebody to point out where it went wrong.... Here's the problem (a ^ b <=> !a ^ b):

Sentence a:
A magneticfield has to have a speed. Otherwise it'd be able to, say, escape a black hole (so I'm assuming that black holes themselves don't have magnetic fields due to this) and therefore one could have information out of a black hole (through electromagnetic fields) which is tought to be an imbossibility.

Sentence b:
This means that if we have two magnets spinning both around fixed axises near eachother with a speed near speed of light you could get the magnets into eachothers magnetfields in a such way that you would gain potential energy without doing any work against the magnetfields. I.e. imagine two souths approaching eachother. With right distances and speed those magnets would have gone past eachother before being affected by eachothers magnetfields and then when the magnetfields meet they'd be pushing eachother so that they would gain speed which is, needless to say, impossible.

Sentence b again proves a false: If one could make energy out of thin air one could increase the mass of a black hole while inside it and therefore communicate with the outside world.

Ok obviously I made a mistake somewhere due to my lack of knowledge in physics but trust me that it's hard to find someone of my age (17) willing to debate/cabable of debating about physics so I posted this here. I'm not a native english speaker/writer so I have to apologize for my misspellings.

EDIT: In short: Sentence a="Magneticfields do have a speed" and a=true (General theory of relativity) b="if magnetic fields have a speed you can get energy out of nothing" which is supposed, obviously, to be false but somehow a => b (if a then b).

2.

3. To Zami,

By the way how do you view the speed of the magnetic field, I have heard of magneticfield strength . Magneticfield can only have the strength, stronger the field greater the strength.

4. Originally Posted by newspaper
To Zami,

By the way how do you view the speed of the magnetic field, I have heard of magneticfield strength . Magneticfield can only have the strength, stronger the field greater the strength.

My view is: If you have a electromagnet and you put it on. At which speed does it affect a piece of metal nearby? It just came to me that if magnetic fields moved faster than light one could move information in time.

This brought in to my mind that gravity escapes black hole too. Gravity fields do for a fact move at the speed of light so it means that they aren't affected by gravity=they have no mass. But somehow magnetic fields do have a mass or are somhow bound to gravityfields??

OFFTOPIC: In my own thread.. Black hole can wrap space time, right? But if at some point the gravity of a black hole was growing so fast that it wrapped the space time so fast (speed of light) gravity fields couldn't escape it. Wouldn't it mean that to an observer it'd seem like that the black hole wasn't gaining mass (while matter falls in to it) or would it teporarily be massless to an outsider..

5. Originally Posted by Zami
A magneticfield has to have a speed. Otherwise it'd be able to, say, escape a black hole (so I'm assuming that black holes themselves don't have magnetic fields due to this) and therefore one could have information out of a black hole (through electromagnetic fields) which is tought to be an imbossibility.
Black holes do have magnetic field.

The simplest black hole has no spin and no magnetic field. This is called a Schwarzschild black hole. A black hole that has a field but no spin is called a Reissner-NordstrÃ¸m black hole. One that has both a magnetic field and spin is called a Kerr black hole.

6. Originally Posted by Scifor Refugee
Originally Posted by Zami
A magneticfield has to have a speed. Otherwise it'd be able to, say, escape a black hole (so I'm assuming that black holes themselves don't have magneticfields due to this) and therefore one could have information out of a black hole (through electromagnetic fields) which is tought to be an imbossibility.
Black holes do have magnetic field.

The simplest black hole has no spin and no magnetic field. This is called a Schwarzschild black hole. A black hole that has a field but no spin is called a Reissner-NordstrÃ¸m black hole. One that has both a magnetic field and spin is called a Kerr black hole.
- Yeah I got that one wrong.. Sorry, right now I don't have the time to read the whole text so I might ask something already answered there (seemed like interesting read though). But is that magnetfield created by the matter spinning around the black hole or by the black hole itself? Why couldn't you affect the magnet field of a black hole from inside? Ultimately it comes down to what creates the magnetfield of a black hole.

Ok, mine first argument was poor but nevertheless it doesn't change the fact that magnetfields do have a speed so sentece a is still true (a="magnetfields have a speed") which is based on special relativity.

EDIT: Actually I can prove the a=>b sentence mathematically (atleast I think so ). (r=distance) Force of attraction = (F1*F2)/(r)^2 if magnet 1 accelerated suddently towards magnet 2 with 0,5c in the reference frame of magnet 1 the distance r would seem to grow (?) and therefore the repelling force would decrease (at the moment of acceleration). And theoretically if you stop in the half way you haven't done as much work (you have worked against the weaker field in your frame so when stopped you would have gained more pontential energy than you used). And from the view of the magnet 2 you wouldn't have seemed to move until you were in the half way. I.e. if magnet 1 had moved to the half way with the speed of 0,5c the magnet 2 would repel magnet 1 with the force of F2/(0,5)^2 but magnet 1 would repel the magnet 2 still with the force of F1. Ok it's true that when the magnetic field magnet 1 "sent" while moving will get to the magnet 2 only little after you stop (actually at the same time) in the half way but at that point you won't be doing work anymore! So now I'm really confused.......

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