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Author Topic: Why isn't gravity polar?  (Read 5705 times)

Offline Emetsipe

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Why isn't gravity polar?
« on: 23/04/2008 02:06:40 »
I'm currently a student in physics and we're doing our advanced gravitation unit, and I'm wondering why gravity isn't polar?
most of the other forces i know (magnetism, electricity (charged particles attracting and repelling not necessarily current)) are polar, having two ends that repel and attract. but as far as i know gravity always attracts. why?

also, it talks about how space can be warped by gravity and it shows the parallel paths and everything but does that really mean space is skewed? just because two things at a certain velocity aimed past earth would eventually touch in the middle doesn't mean actual space is warped does it? i mean, just because there's a force there doesn't mean space is skewed. it means there's a force there. if we were all made of iron would we say that a magnetic field skews space?

see I'm in AP physics which is at the same period as the regular physics class, and the teacher pretty much teaches regular physics and lets us "AP folks" pretty much learn on our own so I'm looking for some answers...


 

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Why isn't gravity polar?
« Reply #1 on: 23/04/2008 03:03:58 »
Magnetism is merely a manifestation of charge, so cannot really be considered as separate forces.

On the other hand, neither the strong nor the weak force are polar, so one might say that the coulomb force is in fact the exception rather than the rule (although a very prevalent exception, it being the dominant force in everyday life).
 

Offline JP

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Why isn't gravity polar?
« Reply #2 on: 23/04/2008 04:22:30 »
General relativity does really mean that space-time is curved.  The idea of a gravitational "force" is described by the way things move around in a curved space-time.

The basic physics is that objects acting under the effect of gravity are going to try to move along the shortest possible path through space-time.  The earth's gravity, however, curves this space-time around it so that the shortest paths are curves towards the earth.

If you don't have gravity, then space-time is flat and the shortest paths are just straight lines, which is what you'd expect for something not experiencing the force of gravity.

As for why electromagnetism doesn't seem to curve space-time, I think it has to do with it both attracting and repelling things.  Einstein tried to include electromagnetism in general relativity and couldn't.  There have been other attempts: http://en.wikipedia.org/wiki/Kaluza-Klein_theory, and physicists are still working on it. 
 

Offline Soul Surfer

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Why isn't gravity polar?
« Reply #3 on: 23/04/2008 09:29:47 »
You could say that's just the way it is but if you need a logical approach.

Think of it this way the forces and particles we see and experience are all built out of the fabric of space time.  The fact that they can be changed into each other in high energy experiments shows this.

The most familiar force electric charge and its dynamic counterpart magnetism is a bipolar force.  the weak force is very closely related but with heavy "and charged "photons" and a short range  the strong nuclear force is tripolar with three sorts of "colour" charge  so there is a bipolar and a tripolar force so that leaves room for a unipolar force that is gravity  because of its weakness and unipolar nature it is the force that dominates the structure of the universe on the largest scales.

Everything we experience in the properties of materials (other than gravity of course) is electromagnetic  and the strong force is only important on the tiny scale of the nuclei of atoms
 

Offline LeeE

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Why isn't gravity polar?
« Reply #4 on: 23/04/2008 16:02:40 »
Gravity appears to act as a force so it would seem natural that it is bi-polar.  However, as jpetruccelli says, GR means that spacetime is curved.  Elaborating on that a little bit, the presence of matter distorts the spacetime within which that matter exists.  Gravity then, instead of being a force that acts on matter and creates the distortion, is actually just another way of describing the the distortion itself.

If I'm allowed to misquote you :) just because space is skewed, there is a force.

I'm a bit rusty on this bit and may be remembering incorrectly but because there are no universal reference points in spacetime any distortion of that spacetime is neither positive or negative and so can't be bi-polar.  It also might help if you think about how the mass which creates the gravity/curve in spacetime in the first place is uni-polar in nature too - we don't observe negative mass anywhere - even if we can hypothesize about it's behaviour.

In fact, because we have local reference points, we can view the force gravity as bi-polar. but only in relative terms.  From the bottom of a gravity well the direction is up but from the top of the well it is down.
 

Offline Titanscape

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Why isn't gravity polar?
« Reply #5 on: 25/04/2008 13:50:50 »
I thought gravity was caused by the collection on mass of Van Der Waals forces, even mountains and asteroids have gravity.
 

Offline graham.d

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Why isn't gravity polar?
« Reply #6 on: 25/04/2008 15:11:44 »
Electromagnetic forces are 100% consistent with Special Relativity. It was one of the features of Maxwells equations that they were not consistent with Newtonian mechanics. As someone said above, electrostatic and magnetic fields are manifestations of the same thing. The two are interchangable but just viewed from different frames of reference. Really polar behaviour is really the exception although for years (some time ago) there were people searching for a magnetic monopole (i.e. a North pole without a corresponding South Pole). This could have changed Physics a bit had they found one.

Gravity is nothing to do with Van der Waal forces, unless someone has a new theory I have not seen before.

You never know; perhaps it will turn out that dark energy is made of exotic matter that has negative gravity such that it repels all other matter. It may explain why it is hard to get hold of this stuff.
 

Offline Skelm

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Why isn't gravity polar?
« Reply #7 on: 26/04/2008 03:29:29 »
I'm currently a student in physics and we're doing our advanced gravitation unit, and I'm wondering why gravity isn't polar?
most of the other forces i know (magnetism, electricity (charged particles attracting and repelling not necessarily current)) are polar, having two ends that repel and attract. but as far as i know gravity always attracts. why?


also, it talks about how space can be warped by gravity and it shows the parallel paths and everything but does that really mean space is skewed? just because two things at a certain velocity aimed past earth would eventually touch in the middle doesn't mean actual space is warped does it? i mean, just because there's a force there doesn't mean space is skewed. it means there's a force there. if we were all made of iron would we say that a magnetic field skews space?

see I'm in AP physics which is at the same period as the regular physics class, and the teacher pretty much teaches regular physics and lets us "AP folks" pretty much learn on our own so I'm looking for some answers...


No one knows the best candidate is the hypothetical graviton if i am correct?
 

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Why isn't gravity polar?
« Reply #7 on: 26/04/2008 03:29:29 »

 

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