Does electrical-magnetic fields curve spacetime?

[gonegahgah]

You posted while I was composing Naty. Forums are good for that.

On to another related topic. This one should be okay but explain if it isn't.

One of your standard household magnets can lift up a steel ball bearing but can't lift a steel car. However, if the steel car (minus all non-steel bits) were somehow to fit into the space of the ball bearing (all 1+ tonne of it) then I'm guessing the standard household magnet would be able to lift the entire car; despite its heavy weight; though I couldn't then lift the magnet itself; I would need a crane.

I'm basing that on the magnetic field being non-reduceable by usage like gravitation is. ie. no matter the size of the gravitational respondent it will deviate by the same rate; and doesn't use up any of the gravity in the process.

Similar occurs for magnetism does it not?
The steel doesn't use up any of the magnetism that passes through it does it? Or some similar process?
So each part of the steel responds to the presence of the magnet and deviates towards the magnet.

The reason a non-compressed steel car can't be lifted by a standard magnet is because the magnet can't penetrate the expanded space without dropping off to too small an amount that the further metal doesn't respond enough to overcome gravity. Is that okay?

 

[Antenna Guy]

I like the hill and valley analogy, but it is probably more appropriately used to understand Newtonian gravity than GR. In Newtonian gravity the "altitude" of a given location would represent the gravitational potential at that location. In your scenario, one large mass by itself rests at the bottom of a deep valley, but when you add a second large mass then the "sum" of the two valleys results in each mass being slightly off of the deepest point in the valley. They therefore go downhill towards each other despite the fact that between them there is always a "saddle-ridge".

The difference with GR and Newtonian gravity is that with Newton the solution of the two masses is simply the sum of the solutions for each individual mass, but the same is not true for GR.

This is an interesting description that begs a question:

If three masses are placed at the corners of an equilateral triangle, and the "force" on anyone corner can be determined using the "center of gravity" of the other two corners, does the "deepest point in the valley" occur at any individual mass - or the "center of gravity" of the system?

Regards,

Bill

 

[Dale]

The steel doesn't use up any of the magnetism that passes through it does it?

Actually it does, at least temporarily. The http://hyperphysics.phy-astr.gsu.edu/hbase/HFrame.html" which is proportional to B². You can think of the reason that a north pole attracts a south pole is that such a configuration reduces the B field and therefore leads to a lower energy state. Similarly with the attraction to a piece of steel, the magnet's field causes the microscopic magnetic domains in the steel to orient themselves with the external field, North to South, so as to reduce the total field and cause a lower energy state. So you cannot, even in theory, use the magnet to do more work lifting an object than is contained in the magnet's field.

 

[Dale]

If three masses are placed at the corners of an equilateral triangle, and the "force" on anyone corner can be determined using the "center of gravity" of the other two corners, does the "deepest point in the valley" occur at any individual mass - or the "center of gravity" of the system?

I don't know, I would have to work the math. By symmetry, if it is not at the center then there must be three equally-deep wells near the masses.

 

[gonegahgah]

Sorry again Dale. You are going to have to explain about this branch to me as well if you would.

Firstly, can you insulate against magnetism?

 

[Dale]

If three masses are placed at the corners of an equilateral triangle, and the "force" on anyone corner can be determined using the "center of gravity" of the other two corners, does the "deepest point in the valley" occur at any individual mass - or the "center of gravity" of the system?

I went ahead and worked the math on this one. I hope you can read a topographical map, the contour plot was easier for me to understand than the 3D surface plot. The darker the color the "deeper" the potential at that contour in the "hill and valley" analogy. There are 3 equally-deep deepest points each located at the center of one of the darkest contours.

The white rings represent the surface of the spherical mass. Note that the center of the mass does not correspond to the deepest point in the "valley". Therefore each mass will experience a net force which will pull it towards this deepest point.

 

[Dale]

Firstly, can you insulate against magnetism?

Yes, it is done all the time in the construction of MRI suites. Usually iron is used.

 

[gonegahgah]

I find that drawing very good Dale and very easy to understand.

When you go inside a planet I have been told that the decrease in gravity occurs proportional to 1/r. Is that correct?

You have shown this as well via the almost petrie dish like shapes that are about the sizes of the masses and which centre close to the centre of those masses. That is correct isn't it?

 

[gonegahgah]

So if you had one of those floating picture frames and you put a sheet of iron between the upper arm and the top of the frame the frame would fall down too?

 

[Naty1]

Naty you talk of generic local spacetimes & of still only one space-time fabric in the same post.

I sometimes think of it this way: a coordinate grid, analogous to a graph paper in two dimensions...with different plots in different parts of the graph paper...like putting three or four different plots on a single page...in spacetime each "plot" (say mass) flows into the other, unlike plots on paper, so each local spacetime reflects a tiny piece of the universe within causal distance...in other words, forces like gravity and electromagnetic waves have a loooooong reach

 

[Dale]

I find that drawing very good Dale and very easy to understand.

When you go inside a planet I have been told that the decrease in gravity occurs proportional to 1/r. Is that correct?

You have shown this as well via the almost petrie dish like shapes that are about the sizes of the masses and which centre close to the centre of those masses. That is correct isn't it?

Yes, both of those are correct.

 

[Dale]

So if you had one of those floating picture frames and you put a sheet of iron between the upper arm and the top of the frame the frame would fall down too?

If it was thick enough and big enough. It often takes a lot of iron, e.g. for a 7 T MRI scanner it can take on the order of 700 tons of iron in order to reduce it from 7 T down to 5 Gauss.