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## Is 'charged black hole' an oxymoron?

 Quote by Q-reeus And if PeterDonis gets around to answering my little personal challenge on that issue in #294 (nicely boldfaced just to make sure it didn't get missed somehow)
I didn't miss it, as my last post should make clear. But I can't even try to answer it until you define more precisely what you mean by "what happens to the field lines". The gravitational lensing has an unambiguous observable: the direction from which the light comes to my detector changes when the lensing object is in the path. What is the unambiguous observable that tells me whether or not something has happened to the field lines?

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 Quote by Q-reeus *All* matter/energy at rest in the potential well of a large gravitating mass M adds a reduced gravitating mass m' to M according to m' = m(1-2GM/(rc2)), where m<
This is not true in *all* cases. It is only true in cases where a quantity of energy exactly equal to (m-m')c^2 is extracted from the system. There are many ways to add an additional mass that do not involve radiating this quantity of energy away.

In those situations where the energy was radiated away it seems strange to call that process "redshift", but regardless of what you call it, it seems more like a statement about energy flux across a surface than about any gravitational effect.

 Quote by Q-reeus So the example(s) I gave much earlier of say drawing two small test charges transversely apart to form a dipole will require less energy than with M absent - by that (1-2GM/(rc2)) factor.
How do you conclude this? The change in the global mass, whether Schwarzschild M, Bondi, ADM, or Komar, tells you nothing about a local interaction like this. I actually think that you can make a case for this concept using parallel transport, but I would encourage you to think about this rigorously.

 Quote by Q-reeus Requiring I refer to which mass is 'really' locally redshifted is spurious in that all matter at that potential is.
Not true.

 Quote by Q-reeus However if one lowers mass down a rope and then annihilates it as radiation escaping back to infinity, there is properly a sense that the redshift was 'localized' since just those atoms disappeared, to be replaced with redshifted radiation.
I agree. Again, this concept is related to parallel transport.

 Quote by Q-reeus NOW FOLLOW THIS BIT THROUGH CAREFULLY. MY 'INTUITION' IS THAT THE VERY EXISTENCE OF A RN BH IMPLIES GRAVITATIONAL POTENTIAL (READ REDSHIFT FACTOR (1-2GM/(rc2))) CANNOT ALLOW ANY CHANGE IN FIELD STRENGTH - OR FIELD DIRECTION/PATTERN, FOR SUCH DIPOLE OR INDEED ANY CHARGE DISTRIBUTION. THIS MUST *LOGICALLY* EXTEND TO INTERACTION OF CHARGE WITH ANY GRAVITATING MASS. FOLLOW THAT LOGIC/'INTUITION' THROUGH. IT MEANS ANY AND EVERY CHARGE IS A MIRACULOUS BEACON OF FLAT SPACETIME - IT CANNOT BE EFFECTED IN ANY WAY BY SAY THE CLOSE PROXIMITY OF A MASSIVE BH (ASSUMING OF COURSE STATIC SEPARATION IS SOMEHOW MAINTAINED). A REDICULOUS TO ME CONCLUSION BUT ONE THAT INEVITABLY FOLLOWS IF RN BH CAN EXIST. THINK ABOUT IT.
I agree that the conclusion is ridiculous.

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 Quote by Q-reeus Well no controversy here then. In every posting of mine where a process of mass/energy/charge 'redshift' has occurred, it's always assumed - as in the typical 'winching down' examples, net loss of system energy is just that. We discard that which the winch has received - it's now exterior to the system of interest.
Which makes your redshift concept a statement about net energy flux rather than gravitation.

Originally Posted by Austin0

 If a mass is transported to a lower altitude it then requires more energy to maintain a state of rest wrt the gravitating body .
 Quote by DaleSpam It doesn't require any energy to maintain a state of rest wrt the gravitating body. E.g. consider a book on a table.
Is that actually the case?

The book creates deformation stresses on the table. The table necessarily counters this force through electrostatic and nuclear forces (Van der Walls etc). This is a continuing condition so implies a continuing flow of energy.
How to analyze this in terms of energy conservation is beyond me as the electrostatic and nuclear forces seem to be effectively inexhaustible but it seems that there has to be energy in play. Just as simply standing in gravity requires additional energy.
We consider that the table surface is accelerating upward even though there is n o coordinate displacement. Doesn't acceleration imply force/energy?
SO comparably shouldn't we view the book as having inertial momentum downward , exerting force on the table , even though in this case also there is no coordinate motion??

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 Quote by Austin0 The book creates deformation stresses on the table. The table necessarily counters this force through electrostatic and nuclear forces (Van der Walls etc). This is a continuing condition so implies a continuing flow of energy.
This is an incorrect understanding of energy. Once the small deformation is done there is no motion, so no work is being done. Energy does not need to continually flow in order to provide a static force.

 Quote by DaleSpam This is an incorrect understanding of energy. Once the small deformation is done there is no motion, so no work is being done. Energy does not need to continually flow in order to provide a static force.
Oh i certainly understand the normal view of energy you are presenting here , having thought exactly the same until encountering this situation .
So if there can be acceleration without motion perhaps it is possible to have energy expenditure without action. At this point I am just looking at the situation from all sides without any conclusions. In the end I may end up right where I started, agreeing with your view.

So are you saying that the book ceases to exert downward force on the table once the initial adjustment is made?
If so i would say my rear contact with my chair seat disagrees with you.

If the book is hovering under thrust at an equivalent height this would necessitate continuing energy of acceleration.This also implies that the book is effecting an equivalent continuing counter force ( momentum?). yes?
The EP would seem to suggest, as the book's force is the same in both cases, the upward acceleration/force would be equivalent .Isn't this the basis of the EP ? An accelerometer doesn't measure the downward force but rather the upward force acting against the inertia of some internal mass of the instrument?
Maybe it is my understanding of the EP that is lacking? ;-(

 Quote by DaleSpam This is an incorrect understanding of energy. Once the small deformation is done there is no motion, so no work is being done. Energy does not need to continually flow in order to provide a static force.
This would be correct only if the table is considered an inertial object (as it is done in most practical physics exercises, there is a lab frame considered to be at rest,it is an idealization that works great for most practical problems), but we know that is not the case in reality, the table is non-inertial and in continuous motion so there is work done. An accelerometer in the surface of the earth measures proper acceleration.

 Quote by Austin0 Oh i certainly understand the normal view of energy you are presenting here , having thought exactly the same until encountering this situation . So if there can be acceleration without motion perhaps it is possible to have energy expenditure without action. At this point I am just looking at the situation from all sides without any conclusions. In the end I may end up right where I started, agreeing with your view. So are you saying that the book ceases to exert downward force on the table once the initial adjustment is made? If so i would say my rear contact with my chair seat disagrees with you. If the book is hovering under thrust at an equivalent height this would necessitate continuing energy of acceleration.This also implies that the book is effecting an equivalent continuing counter force ( momentum?). yes? The EP would seem to suggest, as the book's force is the same in both cases, the upward acceleration/force would be equivalent .Isn't this the basis of the EP ? An accelerometer doesn't measure the downward force but rather the upward force acting against the inertia of some internal mass of the instrument? Maybe it is my understanding of the EP that is lacking? ;-(
Your rear is entitled to disagree.

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 Quote by Austin0 So are you saying that the book ceases to exert downward force on the table once the initial adjustment is made?
No, I am most definitely not saying that. I explicitly said "Energy does not need to continually flow in order to provide a static force." I.e. there is a continued force, it does not require energy.

 Quote by Austin0 If the book is hovering under thrust at an equivalent height this would necessitate continuing energy of acceleration.This also implies that the book is effecting an equivalent continuing counter force ( momentum?). yes? The EP would seem to suggest, as the book's force is the same in both cases, the upward acceleration/force would be equivalent .
In the thrust example the KE of the exhaust is being increased (a lot), therefore energy is being used. None of that energy is going into the book whose KE and PE are remaining constant.

 Quote by Austin0 Isn't this the basis of the EP ? An accelerometer doesn't measure the downward force but rather the upward force acting against the inertia of some internal mass of the instrument? Maybe it is my understanding of the EP that is lacking? ;-(
Probably it is more a misunderstanding of physics in non-inertial frames. Please see my response to Tricky Dicky below.

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 Quote by TrickyDicky This would be correct only if the table is considered an inertial object (as it is done in most practical physics exercises, there is a lab frame considered to be at rest,it is an idealization that works great for most practical problems), but we know that is not the case in reality, the table is non-inertial and in continuous motion so there is work done. An accelerometer in the surface of the earth measures proper acceleration.
No, I am not considering the table an inertial object, if the table were inertial then the force on the book would be 0.

You misunderstand how energy works in a non-inertial frame. In a non-inertial frame, like the usual frame attached to the surface of the earth, there is a fictitious force. The fictitious force, in this case, is equal to mg and directed downwards. We know that there is a fictitious force on the book precisely because an accelerometer measures a proper acceleration of g directed upwards and yet the book is not accelerating relative to our frame.

Now, work is f.d, so as an object is moved upwards against this fictitious force it requires an amount of work equal to f.d=mgh. Conversely, as an object is lowered the fictitious force does an amount of work equal to mgh. So, the ficitious force has an associated potential energy. (remember, energy is frame variant)

So, the book, sitting on the table at rest, has no change in KE. It also has no change in PE. No work is being done on it. There is no change to its internal structure or temperature nor anything else where energy could go. There is no change in any energy associated with the book. Despite the fact that there is a force on the book (two forces actually) and the book measures a proper acceleration and is therefore non-inertial.

 Quote by DaleSpam You misunderstand how energy works in a non-inertial frame. In a non-inertial frame, like the usual frame attached to the surface of the earth, there is a fictitious force. The fictitious force, in this case, is equal to mg and directed downwards. We know that there is a fictitious force on the book precisely because an accelerometer measures a proper acceleration of g directed upwards and yet the book is not accelerating relative to our frame.
 Quote by DaleSpam (remember, energy is frame variant)
Not exactly, KE is frame dependent, energy is a conserved quantity in newtonian mechanics (I understand you are restricting this to the newtonian mechanics POV since you were talking about fictitious forces).
 Quote by DaleSpam So, the book, sitting on the table at rest, has no change in KE. It also has no change in PE. No work is being done on it. There is no change to its internal structure or temperature nor anything else where energy could go. There is no change in any energy associated with the book. Despite the fact that there is a force on the book (two forces actually) and the book measures a proper acceleration and is therefore non-inertial.
You are forgetting here that work, like KE is a frame dependent quantity. I know the example of the book and the table is considered to have 0 net moment, with net moment defined as change in KE, that is not what I referred to when I said work was being done.
The conventional Newtonian treatment with fictitious forces is fine, I have nothing against it as long as one understands its range of validity.
I was pointing to a more realistic treatment, more like GR's Schwarzschild solution (so energy is not frame dependent) for instance. In which the table would be preventing the book from following its geodesic path. And in order to do that Work in the form of a quantity proportional to the EM force in the table material times distance from the theorical geodesic path of the book, must be done.
I know is not the conventional way work is referred to in Newtonian physics(wich is the way you were defending it in your post, and as I said I perfectly understand the use of fictitious forces and work in newtonian physics). But I think by introducing some GR ingredients in the situation it gets closer to reality.

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 Quote by TrickyDicky Not exactly, KE is frame dependent, energy is a conserved quantity in newtonian mechanics
All energy is frame dependent, not just KE. And yes, energy is conserved (in SR generally, in GR in static spacetimes). I think you may be mixing up conservation with frame invariance, they are two separate concepts. Energy is conserved, but frame variant.

 Quote by TrickyDicky (I understand you are restricting this to the newtonian mechanics POV since you were talking about fictitious forces).
No, all of my comments above were wrt GR, not Newtonian physics. What makes you think that GR doesn't have ficitious forces? In fact, GR provides a very easy and consistent mechanism for determining fictitious forces through the Christoffel symbols.

http://en.wikipedia.org/wiki/Curvili...ar_coordinates
http://www.mathpages.com/home/kmath641/kmath641.htm
http://theoretical-physics.net/dev/s...nertial-frames

 Quote by TrickyDicky And in order to do that Work in the form of a quantity proportional to the EM force in the table material times distance from the theorical geodesic path of the book, must be done.
This is an incorrect definition of work. If you believe otherwise then please provide a mainstream scientific reference that defines work as the force times the "distance from the theorical geodesic path".

 Quote by TrickyDicky I know is not the conventional way work is referred to in Newtonian physics(wich is the way you were defending it in your post, and as I said I perfectly understand the use of fictitious forces and work in newtonian physics). But I think by introducing some GR ingredients in the situation it gets closer to reality.
No, all of my comments above are GR comments. In GR there are fictitious forces, just like in Newtonian mechanics. See the references above.

The difference is that in Newtonian mechanics gravity is considered a real force and in GR it is considered fictitious. I refered to mg as a fictitious force, so I was definitely discussing from the GR perspective. You are clearly misunderstanding how non-inertial frames and fictitious forces are treated in GR.

 Great then, if you are considering gravity as a fictitious force then you indeed are using a GR perspective, sorry I didn't notice it. Yor conclusions made me think you were only considering the Newtonian view. But then you are reinforcing my point, thanks. From wikipedia page on Fictitious forces: "Fictitious forces can be considered to do work, provided that they move an object on a trajectory that changes its energy from potential to kinetic." If the EM forces of the table (and the earth) didn't hold the book, it would spontaneously fly towards its geodesic path.

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 Quote by TrickyDicky But then you are reinforcing my point, thanks. From wikipedia page on Fictitious forces: "Fictitious forces can be considered to do work, provided that they move an object on a trajectory that changes its energy from potential to kinetic." If the EM forces of the table (and the earth) didn't hold the book, it would spontaneously fly towards its geodesic path.
Far from reinforcing your point, this completely contradicts your point. See the last two paragraphs of 316.

 Those two paragraphs look wrong to me. You have the fictitious force of gravity on the book acting in an upward and downward direction at the same time on the same object. That is not possible.

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 Quote by TrickyDicky Those two paragraphs look wrong to me. You have the fictitious force of gravity on the book acting in an upward and downward direction at the same time on the same object. That is not possible.
Nonsense. Where did I say that?

The fictitious force of gravity always acts downwards. In fact, it is what defines the direction "down". I never said anything to the contrary.

 Quote by DaleSpam Nonsense. Where did I say that?

 Quote by DaleSpam Now, work is f.d, so as an object is moved upwards against this fictitious force it requires an amount of work equal to f.d=mgh. Conversely, as an object is lowered the fictitious force does an amount of work equal to mgh. Despite the fact that there is a force on the book (two forces actually) and the book measures a proper acceleration and is therefore non-inertial.
Here maybe it is your wording but you seem to have the book going up and down in a strange way, and you even transform the fictitious force into Ątwo forcesĄ. Make up your mind, is the fictitious force of gravity one or two forces? is the book going up or down? I'm afraid it can't go up and down at the same time.