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# Gravity a force or natural motion?

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Lately i have seen people theorize that gravity is not a force and it is a natural motion because gravity pulls something instantly. Like if you were to drop something it does not have any delay before it starts to fall. And they have attributed this to proving it as a natural motion. But i would like to disagree and show my arguement. First, The object begins to fall instantly because the gravity is already acting on the object. So it does not delay because gravity is already pulling on it. But your hand is stopping it in the example of holding something in your hand. So when you let go the object instantly falls to the ground. Second, The effects of LOSS of gravity as opposed to being effected by it do not take effect instantly. If the sun were to suddenly disappear then planets would fly off roughly at the rate it took for the light from the sun to reach you. So not only would the earth continue to receive light from the sun for 8 minutes but the earth would also continue to orbit around where the sun once was for 8 minutes. This is because the earth is still receiving the gravitational attraction it had to the sun . Any disagreements and arguements please post them for debate because i would love to get involved.

Oh yes and remember that this is my opinion and view and may not be fact. I am just expressing it and would like corrections and arguements.

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In GR it isn't a force, but you don't seem to be necessarily making that kind of distinction, and are still speaking in a Newtonian sense.

If I hold a ball against a compressed spring, and then let go, the spring acts instantly — there is no delay. If I hold a charged particle in an electric field and then let go, the field acts instantly — there is no delay. If I remove the source of that electric field, the charged particle will not notice instantly — the change propagates at c. Yet these are still forces.

I think that "natural motion" is an artificial distinction. There is no such thing as unnatural motion. A force is anything that tends to cause an acceleration. Redefining that and you break Newton's laws.

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In GR it isn't a force, but you don't seem to be necessarily making that kind of distinction, and are still speaking in a Newtonian sense.

If I hold a ball against a compressed spring, and then let go, the spring acts instantly — there is no delay. If I hold a charged particle in an electric field and then let go, the field acts instantly — there is no delay. If I remove the source of that electric field, the charged particle will not notice instantly — the change propagates at c. Yet these are still forces.

I think that "natural motion" is an artificial distinction. There is no such thing as unnatural motion. A force is anything that tends to cause an acceleration. Redefining that and you break Newton's laws.

Agreed, As i said it isn't simply a naturally occuring thing just because it has no delay. As i first said.

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I don't totally share your opinion. Newtonian theory can be completed by other ones. One of these other theories tells that interractions are exerted via elementary particles called bosons.

http://en.wikipedia.org/wiki/Boson

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Lately i have seen people theorize that gravity is not a force and it is a natural motion because gravity pulls something instantly. Like if you were to drop something it does not have any delay before it starts to fall. And they have attributed this to proving it as a natural motion. But i would like to disagree and show my arguement. First, The object begins to fall instantly because the gravity is already acting on the object. So it does not delay because gravity is already pulling on it. But your hand is stopping it in the example of holding something in your hand. So when you let go the object instantly falls to the ground. Second, The effects of LOSS of gravity as opposed to being effected by it do not take effect instantly. If the sun were to suddenly disappear then planets would fly off roughly at the rate it took for the light from the sun to reach you. So not only would the earth continue to receive light from the sun for 8 minutes but the earth would also continue to orbit around where the sun once was for 8 minutes. This is because the earth is still receiving the gravitational attraction it had to the sun . Any disagreements and arguements please post them for debate because i would love to get involved.

Oh yes and remember that this is my opinion and view and may not be fact. I am just expressing it and would like corrections and arguements.

It depends: in Newtonian gravity it is a force as the electromagnetic force. In general relativity it cannot be a force, because this is a geometric theory.

What we know is that the fundamental nature of gravity has to be quantum and in a quantum formulation the concept of interaction is not reduced to the classical concept of force.

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There are a lot of assertions in your post. I'll approach this by addressing them one by one.

Lately i have seen people theorize that gravity is not a force and it is a natural motion because gravity pulls something instantly.

Who are these "people" you are refering to? What do they mean by "gravity is not a force"? What do you mean when you use the phrase "natural motion"?

Like if you were to drop something it does not have any delay before it starts to fall.

I don't see a problem with that? This is where the idea of a field came into use in physics. Regarding your example, a similar thing happens when dropping a charged body in an electromagnetid field. The way these phenomena are described in modern physics is that as follows:

Source generates field at R = R(x,y,z) -> field acts on body which is located at R = R(x,y,z). Body at R = R(x,y,z) accelerates according to field strength at R = R(x,y,z).

In the case of gravity the source is anything that has matter, i.e. something with non-zero active gravitational mass.

In the case of electrdynamics the source of the electromagnetic field is anything which has charge and/or current.

Sorry but I have to cut this off here. I keep falling asleep at my desk.

Pete

It depends: in Newtonian gravity it is a force as the electromagnetic force. In general relativity it cannot be a force, because this is a geometric theory.

What we know is that the fundamental nature of gravity has to be quantum and in a quantum formulation the concept of interaction is not reduced to the classical concept of force.

It cannot be correctly argued that "gravity is not a force" just because it is a geometric theory.

From Albert Einstein, in a letter to Lincoln Barnett (1948), wrote

The concepts of Physics have always been geometrical concepts and I cannot see why the g
ik
field would be called more geometrical than f.i. the electro-magnetic field or the distance between bodies in Newtonian Mechanics. The notion probably comes from the fact that the mathematical origin of the is the Gaussian-Riemann theory of the metrical continuum which we are wont to look at as part of a geometry.

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It cannot be correctly argued that "gravity is not a force" just because it is a geometric theory.

I believe the argument is that it's not a force because free-fall in a uniform field is an inertial frame.

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It cannot be correctly argued that "gravity is not a force" just because it is a geometric theory.

From Albert Einstein, in a letter to Lincoln Barnett (1948), wrote

The concepts of Physics have always been geometrical concepts and I cannot see why the g
ik
field would be called more geometrical than f.i. the electro-magnetic field or the distance between bodies in Newtonian Mechanics. The notion probably comes from the fact that the mathematical origin of the is the Gaussian-Riemann theory of the metrical continuum which we are wont to look at as part of a geometry.

Sorry, but Einstein did many mistakes [1] and your appeal to authority (your quote does not give any technical argument) is not enough. I have read Einstein's original works on relativity, including his textbook and this could not be used today even for an introductory course in relativity!

It is not true that the concepts of physics have always been geometrical. This is plain false and this why we have geometrical optics vs physical optics, for instance (with the first being an approximation to the latter).

The reason for which gik is a metric and describes the geometry of spacetime, whereas the electromagnetic field Fik do not, has nothing to see with history, but with their respective physical and mathematical properties.

General relativity relies on the principle of equivalence or geometrisation, reason for which general relativity is often named geometrodynamics (see MTW textbook).

[1] A beautiful article by S. Weinberg, revising some Einstein's mistakes, was published in Physics Today

http://physicstoday....tml?bypassSSO=1

Edited by juanrga
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I believe the argument is that it's not a force because free-fall in a uniform field is an inertial frame.

Actualy that arguement holds for all spacetimes, not just those associated with uniform spacetimes/uniform gravitational fields. When people say that "in GR, gravity is not a force" they mean that the gravitational force is an inertial force. That means that, for a body in free-fall in a gravitational field, the 4-force on that particle is zero even though the gravitational force, a 3-force, on it is zero. They don't say this for non-inertial forces because those have a non-zero 4-force associated with them.

Sorry, but Einstein did many mistakes [1] …

Look back over my posts in this thread and you'll notice that I never said that Einstein was flawless. Nobody who was ever a physicist was ever flawless so I don't know what that comment had to do with anything. In fact I have a book on the subject which a friend on of mine wrote. The book is called Einstein's Mistakes by Hans C. Ohanian.

and your appeal to authority (your quote does not give any technical argument) is not enough.

I disagree. It is obviously is a "technical" argument since the very language in which it is written is soaked with mathematical physics. The purpose of the post was not to appeal to authority but to concern ourselves with the architect of general relativity, i.e. the theory we're talking about.

I have read Einstein's original works on relativity, including his textbook and this could not be used today even for an introductory course in relativity!

What does Einstein's books and scientific articles have to do with this thread? Those works either define the subject matter, teach the subject matter or both. I posted what I did, not because Einstein was teaching us something, but because Einstein was the one who created GR.

…this could not be used today even for an introductory course in relativity!

For a couple of his works I couldn't disagree more. For other works a text with more up-to-date notation is better. As far as it actually being used I also disagree. In the lat 90's I happened to be talking to the professor at Harvard who was teaching General Relativity and the text he used was The Meaning of Relativity - Fifth Edition by Albert Einstein, Princeton University Press

As far as some other parpers he wrote, they are listed under the Readings in General Relativity section of Exploring Black Holes by Talor and wheeler. This text is used in MITs general relativity course. The name of their GR course is Exploring General Relativity

I'll stop here since I would have similar objections to the rest of your responses and similar arguments would hold – and I'm too lazy to continue. Lol!

Edited by pmb
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Look back over my posts in this thread and you'll notice that I never said that Einstein was flawless. In fact I have a book on the subject which a friend on of mine wrote. The book is called Einstein's Mistakes by Hans C. Ohanian.

I disagree. It is obviously is a "technical" argument since the very language in which it is written is soaked with mathematical physics. The purpose of the post was not to appeal to authority but to concern ourselves with the architect of general relativity, i.e. the theory we're talking about.

What does Einstein's books and scientific articles have to do with this thread? Those works either define the subject matter, teach the subject matter or both. I posted what I did, not because Einstein was teaching us something, but because Einstein was the one who created GR.

For a couple of his works I couldn't disagree more. For other works a text with more up-to-date notation is better. As far as it actually being used I also disagree. In the lat 90's I happened to be talking to the professor at Harvard who was teaching General Relativity and the text he used was The Meaning of Relativity - Fifth Edition by Albert Einstein, Princeton University Press

I'll stop here since I would have similar objections to the rest of your responses and similar arguments would hold – and I'm too lazy to continue. Lol!

It is evident for me that you quoted Einstein as authority in your first post, instead of giving technical arguments on why you disagree. You continue now without giving any technical argument to me and merely appeal to authority again with your "to concern ourselves with the architect of general relativity", "Einstein was the one who created GR"...

Moreover, your appeal to authority is not even well-supported by the history of physics. General relativity was developed by at least three main authors. The attempt to present Einstein as the sole creator of general relativity is a typical physicists' oversimplification, with many historians disagreeing. Since this is not a thread about the history of relativity, I will not give more details.

Edited by juanrga
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It is evident for me that you quoted Einstein as authority in your first post, ..

It is obvious that I'm more qualified to interpet the reasons I post something than you are. So let's just leave it at that.

Edited by pmb
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• 4 weeks later...

Superfusion, in answer to your question and statements I must state that I am not a scientist; I am involved because of a lifelong love of physics.

With regards to the fundamental dynamic conception of gravitation, there are now only the mathematical versions (theories) using the measured parameters such as the effects of the separation in space of an unknown concept of a phenomenon we call the mass of matter. In that regard, the use of words such as gravitational pull or the pull of gravity should not be substituted for the more noncommittal word attraction.

With regards to delay, that concept is relative to our ability to respond. For a phenomenon such as a change of position of a physical entity that is activated by gravitation, the delay may be close to an infinitesimal period of that we call time. To accelerate matter, a phenomenon we refer to as force must begin to act and that involves time.

With regards gravitation being a force or a natural motion, then if an object moves then the motion is natural. However, I take it that you mean that motion due to gravitation like being compelled to following Professor Einstein’s description of geodesies is therefore a natural motion. In that regard and to enforce acceleration of the mass of matter by gravitation, a displacing phenomenon we call force must be acting and that involves an increase or loss of energy. There are no freebies in physics and all changes must be payed for by energy exchange. Therefore, gravitation is the results of interference to a phenomenon, the fundamental nature of which is now unknown by mainstream science. Given the resistance to change from the present concepts ensures that all but mathematical attempts will be regarded as pseudoscience and therefore ignored.

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In GR it isn't a force, ...

I disagree. Gravity is an inertial force and since Einstein built GR around the idea that the gravitational force was an inertial force and that inertial forces are real and GR was Einstein's theory then in GR gravity is a force.

Well known experts in GR hold this same thing even today. For example. See Was Einstein Right? Putting General Relativity to the Test. Clifford M. Will - Updated and Newly Revised. See page 94

... has its counterpart here in a velocity dependant modification of the gravitational force.

Here, Will is speaking about the velocity dependance of all forces in SR and how it has its counterpart in GR.

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I disagree. Gravity is an inertial force

Which is, by definition, non-Newtonian, and is what I meant. And you appear to agree with this.

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Which is, by definition, non-Newtonian, and is what I meant.....

I'm not sure what you mean when you said Which is, by definition, non-Newtonian, and is what I meant. Can you explain it for me? What is it that is non-Newtonian?

Edited by pmb
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I'm not sure what you mean when you said Which is, by definition, non-Newtonian, and is what I meant. Can you explain it for me? What is it that is non-Newtonian?

An inertial force does not follow Newton's laws of motion, as you posted in the other thread.

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Another way to address this problem is to look at it from another point of view. It's one I don't like but you might enjoy but you might.

First - It seems to me that asking Is gravity really a force or is it something else? starts off similarly to asking Is electricity a force or is it something else? How did we come get to ask these questions? Electricity is a science so how can it come to be that a broad field of study has a field of force to it?

Edited by pmb
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Hi

I'm working on Origin of Gravity and all I could say is that Gravity has entropic base. Motions of celestial bodies are cause or efect of entropy.

I know I'm too late for debate. Newton admited that he could not find origin of Gravity. Einstein admit that he somehow forget to add cosmological constant (lambda) but he was never able to connect quantum gravity to general relativity. That's pruf that he did many mistakes and that he has no clue about origin of gravity.

What I like from Einstein is his idea of strechy whorphy wibrating space. That would be all.

Sorry my spelling.

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Hi

I'm working on Origin of Gravity and all I could say is that Gravity has entropic base. Motions of celestial bodies are cause or efect of entropy.

I know I'm too late for debate. Newton admited that he could not find origin of Gravity. Einstein admit that he somehow forget to add cosmological constant (lambda) but he was never able to connect quantum gravity to general relativity. That's pruf that he did many mistakes and that he has no clue about origin of gravity.

What I like from Einstein is his idea of strechy whorphy wibrating space. That would be all.

Sorry my spelling.

!

Moderator Note

Hey again Gravity Guy, I'm just going to point you here:

http://www.scienceforums.net/topic/66540-traveling-at-the-speed-of-light/page__view__findpost__p__679200

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• 2 weeks later...

gravity always exists between any two bodies.....i think gravity is force which causes natural motion

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No.i think you are wrong in that sense.You should read relativity book. IT is quite different from other forces.Gravity is experienced because space-time is cured.This curvature of space-time creates gravity.And what creates this curve???

Mass of objects!! This is what it is explained in theory of relativity. It is actually a part of general theory of relativity. that is how bigger mass have even more bigger gravity.. Now just imagine,if sun is going out of the the gravity.there are two possibilies: if sun moves, earth and other planets will move in unorthodox way around the sun. Second all planets will move in straight line not in the direction of sun.This is just like an example of a stone tied to a string.if you spin the stone while spinning,if string breaks,it will move in a direction tangent to the orbital motion. since you have assumed that second case will happen,think that sun moves,as soon as the sun moves,earth and other planets will move out of the gravity of the sun. you answer is wrong for earth and right for farthest planet. if sun moves,then gravity will shift first from fartest planet.then for sun's gravity to move away from the earth it will take 8 minutes because it is close to it. i think you have got my point. Actually this will not happen.I just said that this will happen because you told me to explain it in that case.Only first case will happen if sun moves even faster..

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Einstein said that gravity is not a force but instead motion and acceleration caused by the warpage of space surrounding matter. This is the standard model of gravity. Newton proposed that gravity is a force at a distance between matter. Quantum Theory has proposed a particle, the graviton, that carries the force of gravity.

Another entry is Loop Quantum Gravity. It proposes that space can be viewed as a fine fabric or network "woven" of finite quantised loops of excited gravitational fields called spin networks. Over time these spin networks are referred to as spin-foam. Many think this model of gravity is a real theoretical contender.

Although GR has had many successes in prediction, it fails at the galactic scale without the inclusion of hypothetical dark matter which many still consider to be unproven hypothesis.

There are also a great number of lesser known models of gravity and alternative mainstream models. Any successful model of gravity that can replace General Relativity as the mainstream model, will have to be able to make predictions equal to GR but also explain other things that GR presently could have problems with, since dark matter has never been observed and GR's predictions with it are thought to be lacking compared to other predictive models at the galaxy scale.

So, is gravity a force or natural motion? In the mainstream model GR, gravity is a natural motion which is the mainstream answer to your question. It might be understood that these models mentioned are just a few of the many choices offered theoretically. Also a Force can have more than one meaning. Force can mean an a-priori force like magnetism and the other so called forces of nature. Or the gravitational force could be an applied force based upon an unknown a still unknown or unrecognized phenomena and cause. Lots of choices for gravity if you wish to consider all the so-called possibilities of future theory and formulations.

Edited by pantheory

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