# Plane of perspective

1. Jun 28, 2004

### north

Michio

when we look at our galaxy we will see it from our plane of perspective,which say for arguements sake is north, and that from here we say that gravity is pulling things into the center of the galaxy.but what if i were to rotate this plane 180 degrees so that north becomes south and south becomes north.the spirals are now moving in the opposite direction,so now gravity would be pulling in the opposite direction, would not each perspective cancel each other out and produce a neutral effect? and how do you prove which plane of gravity is right?

2. Jun 28, 2004

Staff Emeritus
The direction things orbit is not based on the direction of gravity, which is symmetrical. It is based on the "initial conditions". Presumably at some early date the cloud from which the galaxy condensed had a net angular momentum in the particular direction that leads to today's rotation. The same arguments applies to the orbits of planets in the solar systm.

3. Jun 28, 2004

### north

but how do we tell which plane, say for our galaxy,is the inital condition?,both seem equally plausable.

4. Jun 29, 2004

Staff Emeritus
Changing the plane of perspective is a coordinate change. General Relativity is invariant under (differntiable) coordinate change: the physics doesn't change. That's the point I was trying to make.

5. Jun 29, 2004

### north

i wonder then if there is a way to tell which plane is the inital condition?perhaps there is slightly more energy coming from one plane more than the other? just curious, does Austrailia see a different plane of our galaxy than we do in the north?

6. Jun 29, 2004

### sol2

Thanks for the reminder about Gr in the Quantum world.. It has to be taken a step further, would you care to elaborate?

I am looking for geometrical consistancy. Not only the quest for understanding of higher geometries, something had to be realized once topological forms could ever be entertained.

Regards

7. Jun 29, 2004

### LURCH

No plane is the initial condition. The initial condition is merely the state in which the current galaxy began, regardless of the plane along which one views it.

8. Jun 29, 2004

### north

then can we say that our galaxies gravity has settled into one or the other plane, since that is where our gravities direction seems to be taken from. then which plane do we take,since each plane is a valid perspective.

9. Jun 30, 2004

### LURCH

I would not say that gravity has settled into a particular plane, as it still works equally in all directions. The influence of gravitation is spherical, or three dimensional, and cannot be restricted to a two-dimensional plane. The debris of which our galaxy is made has spread out along a plane, and that plane is aligned to the direction in which the momentum was unbalanced when the system first began to form.

10. Jun 30, 2004

### north

___________________________________________

i find this kind of confusing because the graphics when showing gravity,and then blackholes always show a plane,in which the spiral arms are suppose to be falling into the center,or the old rubber sheet description, is there a more up to date graphic for gravity.also i think it would be fair to say that most if not all galaxies seem to the same structure the center with the spirals formed approximately at its equator,could you apply what you said above to all galaxies.

i myself tend to look at the structure of the galaxies in a more fluid-dynamic way.

11. Jul 1, 2004

Staff Emeritus
The reason the galaxies (or for that matter the planets in our solar system) lie predominantly in a plane is rotation. LURCH is right that gravity is symmetrical in three dimensions, but rotation selects a plane. The reason that the bulk of the stars (like the planets) rotate in the SAME plane is initial conditions, that is, the net angular momentum of the clouds out of which they condensed.

The rubber sheet analogy is just a device to give you some idea of spacetime curvature, since nobody can really visualize it. The analogy is inherently two dimensional, but that doesn't mean the real spacetime is restricted to a two dimensional symmetry.

12. Jul 1, 2004

### LURCH

Ah, now I see the heart of the problem, and I am once again reminded of the inherent weakness of the standard graphic used to show gravity. As Selfadjoint has already mentioned, this is only an analogy; a symbolic representation of reality. In the analogy, is shown as a two-dimensional sheet possessing only the dimensions of "left to right", and "front to back". This sheet is curved or warped in a third direction (up and down), to show how three-dimensional space is curved in a fourth direction that we three-dimensional beings are unable to see, or even imagine.

13. Jul 1, 2004

### north

thanks guys for the input but does this mean that the blackhole can from both north and south poles so to speak,if so, would they still not cancel each other?

14. Jul 1, 2004

Staff Emeritus
I think you left out a word there, between can and from. The BH can generate magnetic fields outside its event horizon, and they will configure somewhat like the magnetic field of earth, with strong manifestation at the poles. The magnetic fields (which remember are OUTSIDE the BH) will accelerate ions and produce brilliant "fountains" at its poles.

All of this more or less normal physics exists mixed in with the spacetime bending and "frame dragging" produced relativistically by the BH's immense spinning mass. This forms a very complex and intricate field of physics, which has been studied intensively for the last twenty years and on which there is still a lot of research to be done.

15. Jul 2, 2004

### north

these fountains,are these the jets we see in some galaxies?

16. Jul 2, 2004