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Author Topic: How does curved space apply a force to make an object move?  (Read 5167 times)

Don Griffin

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Don Griffin asked the Naked Scientists:

How exactly does curved space apply force to make an object move?  I understand that a moving object would follow a curve in space, like a train follows a curved track, but how does curvature alone cause an object to move in the first place?  The train will follow a curved track, but the curved track will not make the train move; the train still needs an engine.

Thank you; enjoy your show very much,  

Don Griffin, Canada.
What do you think?


 

lyner

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How does curved space apply a force to make an object move?
« Reply #1 on: 17/12/2008 22:50:44 »
The analogy would be to have a track curved downhill, I think.
 

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How does curved space apply a force to make an object move?
« Reply #2 on: 17/12/2008 22:53:45 »
The usual analogy is that it is just like a ball at the top of the hill it Will roll down the hill because when it is at the bottom of the hill its energy is lower.

When you accelerate an object its energy content increases. However the gravitational field is in effect negative energy because the gravitational force is always attractive. Now the presence of a balance between positive and negative electrical charges is easily understood and accepted but the balance between the positive kinetic energy of motion in matter and the negative energy in the gravitational fields is much less well understood. most cosmological theory suggests that all the negative energy in the gravitation in the universe balances out all the positive kinetic energy so a universe is in effect something out of nothing.
 

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How does curved space apply a force to make an object move?
« Reply #3 on: 18/12/2008 09:29:28 »
Another analogy is the rubber sheet.



The difference being, of course, that a rubber sheet doesn't have as many dimensions as spacetime.
 

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How does curved space apply a force to make an object move?
« Reply #4 on: 21/12/2008 17:51:05 »
In relativity, curved space also means curved time and for any body having non-zero volume it means that it exists across a range of time, or in a time gradient - one side of the body is running at a different time rate to the opposite side.  This in turn means that any characteristic of the body that is time-based, such as frequency derived energy, will also be unequal across the body.  The end result is that unless external energy is added to the system the body moves down the gradient as entropy tries to regain equilibrium/equality and the effect is that of a directional force acting on the body.
 

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How does curved space apply a force to make an object move?
« Reply #5 on: 22/12/2008 14:12:11 »
Don Griffin asked the Naked Scientists:

How exactly does curved space apply force to make an object move?  I understand that a moving object would follow a curve in space, like a train follows a curved track, but how does curvature alone cause an object to move in the first place?  The train will follow a curved track, but the curved track will not make the train move; the train still needs an engine.
Just to precise things a little: in General Relativity there is NO gravitational field, that is, NO grav. force at all; curved space does not apply any force; according to the analogy of an elastic net warped by a massive sphere, any object "falls" in the "hole" generated by the sphere. Clearly *in this analogy*, we have to consider a gravitational field (to say that an object "falls" in the hole), but it's just an analogy and not how it really works. How it really works is that an object "must" follow the curvature. The previous sentence is what in GR replaces the concept of "force".
« Last Edit: 22/12/2008 14:15:06 by lightarrow »
 

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How does curved space apply a force to make an object move?
« Reply #6 on: 24/12/2008 20:28:16 »
Don Griffin asked the Naked Scientists:

How exactly does curved space apply force to make an object move?  I understand that a moving object would follow a curve in space, like a train follows a curved track, but how does curvature alone cause an object to move in the first place?  The train will follow a curved track, but the curved track will not make the train move; the train still needs an engine.

Thank you; enjoy your show very much

Don Griffin, Canada.
What do you think?

Look at it this way, would your car, if you drove it off the edge of a cliff  and crawl back up???

Well, since the matter in the vacuum, is present within its fabric, almost as if it is floating on it, seems to create a geometry of distortion it companies in the area of space it consumes. From a Special Relativistic sense of view, it can be seen as bent into the time dimension as well. In fact, the space and time dimension are so indestinguishable, that they are almost complimentary to the fasion that they disply codependance.

The distortion of spacetime, created by the presence of matter, and also by the presence of gravity, which is the product of acceleration, all contribute to the distorted frames of spacetime, bending into its structural geometry. If a photon (having  geodesic line), will indeed move upon the more convenient line created by the mass. The bent spacetime, will invariably be the cause of an altered trajectory.
 

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How does curved space apply a force to make an object move?
« Reply #7 on: 25/12/2008 16:32:53 »
Don :) "How exactly does curved space apply force to make an object move?"
It' doesn't and it does.
to have motion you need a force.

Space 'bends' around invariant mass, and there are no limits, as far as i know, to its influence.
Far away from the 'sources' the influence or 'downhill gradient' may be negligible, but the closer an object of mass or light comes to VMO (very massive objects) the steeper that 'downhill gradient' is becoming and your object will start to move or if you like , to fall.

Energy-wise though?
The more massive the VMO the more energy it have.
So your object are just correcting itself entropy-wise.
leveling out the energy, sort of?
Or if you like, following the path of least resistance.
I think, I think:)

In space you do not have 'up' and 'down' as a direction, other than relative your own (dis)position for the moment, so what you're thinking of as being 'bent' is to me :) just going down...

Or on a more positive note, 'up' :)

-------------

But you're right, it will accelerate when getting onto the 'slope'.
But on the other tentacle it's not as simple as that.
What happens when it is trying to pass the 'event horizon' at a Black Hole.
Considered from your status as an outside observer that 'object' nearing the event horizon will seem to slow down.
Not accelerate at all.

Why, well as it gets into that energy/gravity well 'gravity' will give your object an added effect to its own  acceleration.
Those 'forces' have the same 'effect' when seen in time.
Both acceleration and VMO:s will slow down time as observed from another reference frame.
And that's where you are observing your object 'falling/levelling out'

But then we have photons doing the same thing although they are 'mass less'?
Why would they care?
they are said to have a momentum though??

But that's why I like to define it as a 'path of least resistance' aka 'a straight path'.
As paths that doesn't cost your object anything will always be the 'best' 'straightest' 'fastest' etc etc.
But this thing about being 'fastest' is very much a matter of geometry?
So maybe I'm wrong there, but it will cost some energy to prove.

And if you didn't have a headache before, you're sure to get one now:)
But hey, you're not alone there :)

« Last Edit: 25/12/2008 17:41:38 by yor_on »
 

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How does curved space apply a force to make an object move?
« Reply #7 on: 25/12/2008 16:32:53 »

 

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