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Old 03-06-2015, 08:26 AM
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yusufcam (Colin)
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gravity 101

(just trying to get a mental image of how gravity works, thanks in advance )

if gravity is the weak force in nature and is believed to occur through the curvature of space/time. How does the sun which is comparable in scale to a soccer ball hold the earth (the size of a marble) in gravitational orbit at 200 mtrs?

either the scales are wrong, or the indentation type graphic images they use to communicate space/time curvature is misleading.
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Old 03-06-2015, 10:13 AM
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Hi Colin
I am not a scientist but I am interested in gravity.
I don't understand your concern about gravity being a weak force and the Earth and Sun.
I have not yet found the answer as to how gravity works.
Also I think that GR does not say gravity is seen as a force.
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Old 03-06-2015, 10:30 AM
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hi,

put slightly differently, the way gravity is portrayed as far as i can tell is an effect like displacement like an object in water, but curvature in space/time.

whereas there is no such similar displacement ratios, between the relative size of the sun and earth (let alone the far outer planets), which comes close to the effect that gravity has, to cause planets to orbit which is displacement orientated.

does that make sense?

Is space/time an object, if not how can an object effect it?

just trying to understand how it works, or what might be wrong with that line of understanding above, which would make it clear how it is proposed to work.

not a problem, just curious.

thanks
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Old 03-06-2015, 11:30 AM
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Colin
I spent 5 years formulating a gravity hypothesis that speculated gravity was a sort of pressure system, which could be called push gravity, in an effort to describe how gravity worked.
Having worked it out I found that the idea was not new but was first put forward in 1745 by a man named Let Sage.
That approach fell out of favour at the turn of the century but I must say I like it still.
The idea needs an eather which SR and GR does not need.
I seek an answer that required some sort of particle interaction and I don't think that is available.
GR works very well but I can not imagine the reality it describes.
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Old 03-06-2015, 11:33 AM
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Quote:
Originally Posted by yusufcam View Post
How does the sun which is comparable in scale to a soccer ball hold the earth (the size of a marble) in gravitational orbit at 200 mtrs?
If you could arrange for a soccer ball and a marble to be 200 metres apart in space, and contrive to have them with appropriate initial velocities with respect to each other, the marble would indeed orbit the soccer ball.

Let's assume the soccer ball has a mass of 1 kg, and the marble has a mass of 10 grams. For a circular orbit with a radius of 200 metres, the attractive force is 1.7 x 10^(-17) newtons, and the marble needs a tangential velocity of about 0.6 microns per second, and would have an orbital period of 69 years! (At a radius of just 1 metre, the orbital period would be "only" 9 days.)

Last edited by julianh72; 03-06-2015 at 11:54 AM.
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Old 03-06-2015, 12:00 PM
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hi julian,

hmm, interesting.

so what is gravity?
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Old 03-06-2015, 12:07 PM
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okay, so an image just came to mind. Gravity isn't a displacement force but the image in space/time of a contractual force. Thus a neutron star which is significantly more weighter (contracted) but smaller than the sun has significantly more gravity.

(hmm, just noticed a potential problem with that idea, and that is that the image would be retained where the contraction took place rather than follow the object around. Unless space/time is of a different quality to physical objects. Like the point of time of the contraction follows the object. who knows).

yes/no?
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Old 03-06-2015, 12:19 PM
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so what is gravity?
"Gravity is most accurately described by the general theory of relativity (proposed by Albert Einstein in 1915) which describes gravity, not as a force, but as a consequence of the curvature of spacetime caused by the uneven distribution of mass/energy."
http://en.wikipedia.org/wiki/Gravity

If you're asking "Why is there gravity?" or "How does gravity work?" - well, if I could answer that, I'd probably have a Nobel Prize!
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Old 03-06-2015, 12:31 PM
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I think part of the problem in visualising this is that the soccer ball vs marble scale is wrong in every way.

With reference to sun fact sheet and solar system scale a 1m diameter sun would require a 9mm (small marble) earth with orbital radius 107.5m . The scaled masses are 734kg sun 2.2g earth.

Most graphical representations just don't show this relative scale, particularly with the mass which is very relevant when talking about gravity.

Michael.
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Old 03-06-2015, 12:51 PM
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Originally Posted by michaellxv View Post
I think part of the problem in visualising this

Most graphical representations just don't show this relative scale, particularly with the mass which is very relevant when talking about gravity.

Michael.
hi michael,

yes, the exact scales i could not recall, but your right its about mass, as the issue is about, i am guessing a contracting force rather displacing force in space/time.

but its interesting.
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Old 03-06-2015, 01:01 PM
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i suppose i am just wondering if there is a simple laymens way to understand these topics.

the idea that gravity is a contraction of space/time would appear to work with the idea that time slows down under increased gravitational effects.

its just brainstorming, and interesting for me.
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Old 03-06-2015, 01:17 PM
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hi michael,

yes, the exact scales i could not recall, but your right its about mass, as the issue is about, i am guessing a contracting force rather displacing force in space/time.

but its interesting.
I don't see it as a contraction of space. If you place 2 equal mass objects in space with no motion (and no other external forces) then when released they will move through the space between them until they collide.

On the other hand gravity seems to be able to resist the expansion of space. The universe is expanding, distant galaxies are receding due to the expansion of space. But locally, in our solar system/galaxy/local group, we don't see this effect, gravity is holding it all together. Now that makes my brain hurt.
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Old 03-06-2015, 02:11 PM
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It is a curvature or distortion of space-time, caused by th epresence of mass.
More reading about the issue is here:
https://en.wikipedia.org/wiki/Gravity

Last edited by bojan; 03-06-2015 at 02:24 PM.
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Old 03-06-2015, 02:49 PM
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It is a curvature or distortion of space-time, caused by th epresence of mass.
More reading about the issue is here:
https://en.wikipedia.org/wiki/Gravity
And energy...as well as mass I believe

The question is for me is what cause the curvature...
How does mass (or energy) tell space time how to curve.
How can GR and quantum be united.
Surely space time must have a physical expression via some sort of particle to communicate
At some level there must be a physical system to communicate between mass space time and energy.
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Old 03-06-2015, 03:11 PM
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Correct.. mass = energy.

Particle (still hypothetical, of course) is Graviton :-)
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Old 03-06-2015, 04:06 PM
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The graviton seems difficult to observe.
The only hope is detecting waves of them which is still difficult..still looking for them
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Old 03-06-2015, 05:45 PM
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It's the field that is key in many of the theories that Physicists describe. The particle is a manifestation or perturbation in the field. So for example the Higgs Boson is a tiny vibration in the Higgs field (analogous to the Photon being a tiny vibration in the Electromagnetic field). Detecting a particle like the Higgs Boson (or its decay products) is evidence for the existence of a Higgs Field. The Higgs boson is difficult to detect because its difficult to produce in the laboratory. The Higgs boson is a heavy particle which doesn't interact too much with other field. You need to generate an enormous amount of energy in a tiny space to produce Higgs Bosons - hence the construction of the massive 10 billion dollar Large Hadron Collider.

The detection of the Graviton is an interesting one because it's a hypothetical particle which, like the photon, has no mass. (like the Higgs particle, the Graviton is also a boson).

If the Higgs field (particle) is responsible for the property of "mass" in the Universe, can we assume that the Higgs particle is some how intertwined with the Graviton?? (both are supposedly classified as bosons. Although the Higgs field doesnt interact with other fields? Not like the TOP quark, which is a heavier particle than the Higgs Boson but can interact and therefore a little easier to produce and detect)

Last edited by Eratosthenes; 03-06-2015 at 06:15 PM.
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Old 03-06-2015, 06:13 PM
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Thank you Peter
Let's try and describe the situation using a ball and a marble.
Is there a field between them which is a flow of gravitons travelling at or near C.
Do you know how information is transferee in a field.
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Old 03-06-2015, 06:31 PM
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Quote:
Originally Posted by xelasnave View Post
Thank you Peter
Let's try and describe the situation using a ball and a marble.
Is there a field between them which is a flow of gravitons travelling at or near C.
Do you know how information is transferee in a field.
what do you mean by information?

"information" can have a different meaning in different contexts or situation (such as in statistics, or quantum physics)

I remember the debate involving "spooky action at a distance" or entanglement where two coupled particles are separated at the extremes of the universe and an observation is made on one of the particles. For example its spin is detected - then the spin of the other particle will be determined instantaneously. Was the speed of light limit broken for this instantaneous transfer of "information" to occur?
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Old 03-06-2015, 06:48 PM
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I was more interested in how you would describe the relationship between a marble and a ball, similar to the op, using hypothetical gravitons . How do they act with the ball and the marble. I ask as much for speculation but upon the model gravitons would allow.
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