Gravity - a consequence or active force?

[tonyb1969]

Hello all. I am sure this topic has been answered ad nauseum; however, I can't seem to find those answers. From my understanding of the four forces, EM, strong, and weak forces are all quite well understood and observed. However, aside from String Theory stating that gravity is possibly as strong as the other forces, but jumps to other branes, I can't find conclusive information on gravity as a force. This topic is NOT about String Theory; rather, it is an attempt for me to come up to speed on latest observations and theories regarding gravity.

Has anyone postulated that gravity may not be an "active" force? Perhaps this is why it has been so elusive.

From this line of thinking, could the "falling into the contours" of depressed space be a consequence, or at most an indirect force?

Conceptually, one can view active EM, strong, weak force particles/strings/waves acting on other matter; however, it is more than not evident how gravitons could arise from the concept of gravity being a function of distorted space.

It would seem that viewing gravity as a consequence rather than an active force does not violate any gravity-based formulae we have used for over two centuries. Also, General and Special Relativity are not violated by such a view. This approach would simply mean that we may accept the mathematical formulae that describe the effect of distorting space with mass without looking for gravitons.

Again, if this has been covered and addressed, please point me in the appropriate direction. Input greatly appreciated.


Tony

 

[A.T.]

Has anyone postulated that gravity may not be an "active" force? Perhaps this is why it has been so elusive.

What is an "acitve force" as opposed to a "consequence"?

Again, if this has been covered and addressed, please point me in the appropriate direction. Input greatly appreciated.

Try a search on "gravity real force"

 

[Crazy Tosser]

Gravity is not a force, like centrifugal force or any other illusionary force is not a force. Gravity is a curvature in space-time. For more info, google General Relativity

 

[Naty1]

Has anyone postulated that gravity may not be an "active" force?

Einstein. It's called general relativity. He showed it's curvature of spacetime as the cause.

It's believed that in the early,early development of our new universe all forces were combined...unified. This was a very high energy but unstable state and via phase transition the nascent universe downshifted to a lower energy but more stable configuration...whereupon a single "unified" force split into the four we observe today. Maybe five if the Higgs ocean is discovered.

 

[tonyb1969]

Einstein. It's called general relativity. He showed it's curvature of spacetime as the cause.

It's believed that in the early,early development of our new universe all forces were combined...unified. This was a very high energy but unstable state and via phase transition the nascent universe downshifted to a lower energy but more stable configuration...whereupon a single "unified" force split into the four we observe today. Maybe five if the Higgs ocean is discovered.

Thanks, Naty... I think I was not clear. Of course, I'm very aware of general relativity. My question could fit into your last phrase "into the four we observe today." Do we actually observe a graviton or a gravity wave? I don't think we do. We do observe the other forces: gluons, photons, and wgbosons. Perhaps the reason we don't observe gravitons is because there aren't any? I know we experience the effect of distorted/displaced space, which we call gravity, but does that mean their has to be actual particles at play?

Also, thanks AT...I found the post you referred to on the forum, and will read it.

 

[Naty1]

Do we actually observe a graviton or a gravity wave? I don't think we do. We do observe the other forces: gluons, photons, and wgbosons. Perhaps the reason we don't observe gravitons is because there aren't any?

"observe" is a complicated word, but we'll skip than and assume everyday meaning.

see http://en.wikipedia.org/wiki/LIGO for efforts to detect gravity waves...haven't confirmed them yet as far as I understand.

Lack of gravitons would not directly effect general relativity, I don't think, but might cause quantum and string theory some hiccups...

 

[Naty1]

In the preface to Principia Isaac Newton wrote

the whole task of philosophy is to find out the forces of nature by studying the phenomena of motion, and then, from those forces, to infer the remaining phenomena.

(from Relativity and Geometry, Roberto Torretti)

So he would not have likely agreed we can "observe" forces!

 

[Laidback]

Hello all. I am sure this topic has been answered ad nauseum; however, I can't seem to find those answers. From my understanding of the four forces, EM, strong, and weak forces are all quite well understood and observed. However, aside from String Theory stating that gravity is possibly as strong as the other forces, but jumps to other branes, I can't find conclusive information on gravity as a force. This topic is NOT about String Theory; rather, it is an attempt for me to come up to speed on latest observations and theories regarding gravity.

Has anyone postulated that gravity may not be an "active" force? Perhaps this is why it has been so elusive.

From this line of thinking, could the "falling into the contours" of depressed space be a consequence, or at most an indirect force?

Conceptually, one can view active EM, strong, weak force particles/strings/waves acting on other matter; however, it is more than not evident how gravitons could arise from the concept of gravity being a function of distorted space.

It would seem that viewing gravity as a consequence rather than an active force does not violate any gravity-based formulae we have used for over two centuries. Also, General and Special Relativity are not violated by such a view. This approach would simply mean that we may accept the mathematical formulae that describe the effect of distorting space with mass without looking for gravitons.

Again, if this has been covered and addressed, please point me in the appropriate direction. Input greatly appreciated.


Tony

This question I feel will never be answered in this thread or for that matter in this forum, as this forums Rules and Conditions restrict and allow only well established theory to be referred to, and that includes the referral to any maths that may well indicate the facts..

So here is a word of warning to anyone who has established a theory to the facts, in the near past..

If your theory is not known by a mentor and or administrators from this forum, be prepared to receive infractions..

Having said that, and to avoid infractions, I would suggest you consider the following..

If we have two bodies of mass in close unchanging proximity to each other in a near vacuum or what is commonly referred to as space , how would it be possible for the two to change respective proximity? As in either, "away" or "towards" the other?

I would recommend, one considers how perceived repulsion and then perceived attraction would in fact be initiated via referring to "Newtons Laws" with respects to Force and Motion..

Cheers and good Luck!

Pete..

 

[JesseM]

Do we actually observe a graviton or a gravity wave? I don't think we do. We do observe the other forces: gluons, photons, and wgbosons. Perhaps the reason we don't observe gravitons is because there aren't any? I know we experience the effect of distorted/displaced space, which we call gravity, but does that mean their has to be actual particles at play?

Gravity waves are predicted by pure general relativity, which doesn't involve any particles; for them to not exist, GR would have to be fundamentally wrong about the way that mass causes spacetime curvature. And if you want to get into quantum gravity, the whole concept of "particles" is rather ambiguous in quantum field theories, as I understand it particles are just a sort of quantized wave in the quantum fields which fill space...see this FAQ on virtual particles for more info on quantum field theories, which in the end section talks a bit about gravitons:

I hear physicists saying that the "quantum of the gravitational force" is something called a graviton. Doesn't general relativity say that gravity isn't a force at all?

You don't have to accept that gravity is a "force" in order to believe that gravitons might exist. According to QM, anything that behaves like a harmonic oscillator has discrete energy levels, as I said in part 1. General relativity allows gravitational waves, ripples in the geometry of spacetime which travel at the speed of light. Under a certain definition of gravitational energy (a tricky subject), the wave can be said to carry energy. If QM is ever successfully applied to GR, it seems sensible to expect that these oscillations will also possesses discrete "gravitational energies," corresponding to different numbers of gravitons.

Quantum gravity is not yet a complete, established theory, so gravitons are still speculative. It is also unlikely that individual gravitons will be detected any time in the near future.

Furthermore, it is not at all clear that it will be useful to think of gravitational "forces," such as the one that sticks you to the Earth's surface, as mediated by virtual gravitons. The notion of virtual particles mediating static forces comes from perturbation theory, and if there is one thing we know about quantum gravity, it's that the usual way of doing perturbation theory doesn't work.

Quantum field theory is plagued with infinities, which show up in diagrams in which virtual particles go in closed loops. Normally these infinities can be gotten rid of by "renormalization," in which infinite "counterterms" cancel the infinite parts of the diagrams, leaving finite results for experimentally observable quantities. Renormalization works for QED and the other field theories used to describe particle interactions, but it fails when applied to gravity. Graviton loops generate an infinite family of counterterms. The theory ends up with an infinite number of free parameters, and it's no theory at all. Other approaches to quantum gravity are needed, and they might not describe static fields with virtual gravitons.

 

[yuiop]

In old fashioned Newtonian physics it used to be said that a particle remained at rest or continued in a straight line unless a force acted upon it. In General Relativity we now say that a particle continues along a geodesic unless a force acts upon it. A free falling particle follows a geodesic so it follows that a falling particle does not have any forces acting upon it as far as General Relativity is concerned.

 

[Laidback]

Hi Kev,
First let me make it clear, my following comments following yours are geared so that I may better understand physics, as I find this subject matter fascinating..

In old fashioned Newtonian physics it used to be said that a particle remained at rest

I am assuming you meant, the referred particle remained in relative proximity to other particles, or am I wrong?

or continued in a straight line unless a force acted upon it.

And this is where I am really confused?..

My question is and has been for some time now, building a three preferably four dimensional model, how does one define the area to a particle or particle reactions implied by the standard model to area's thus far not defined, for example - the area that may well turn out to be deemed as a graviton?

hmm that didn't come out right?

OK maybe this may make more sense - If we reason, Force may only be Repulsive, my question has and still is to this day, why then, do we still refer to the observation of two particles that have been repulsed towards each other, Gravity or as if some magical attractive force exists? Put simply I don't understand what you mean by "Falling" in this case?

In General Relativity we now say that a particle continues along a geodesic unless a force acts upon it. A free falling

Are you referring to some undefined force, for this "free falling" casualty? And am I correct, perhaps your statement quotes some current textbook, so you really meant "some particle that is with a velocity to it?"

In General Relativity we now say that a particle continues along a geodesic unless a force acts upon it. A free falling particle follows a geodesic so it follows that a falling particle does not have any forces acting upon it as far as General Relativity is concerned.

Again I am confused?

Unless I am to ignore reference to free falling.. Argh as much as I love physics, there are many things that just don't make sense to me..

And now I have a big question and let me point out its a hard one, which if I may I point out, No-one has yet been able to answer it, so if you are unable to answer it, let me make it clear, you still stand in high regards to me..

Q/. What defines form and or defines your above particle from its environment and or its proximity to other implied particles and their defined areas and or interactions and what separates them?

I am more concerned with the reference to the force/s perhaps Energy that defines the mentioned particle with a velocity to it, and how its defined and or implied form is maintained whilst said particle is in motion relative to other particles..

Perhaps the above exercise may be best treated as a set 3 Dimensional "4 if you wish" area of Interest that contains only two particles at the onset of change, resulting with one of the particles in motion towards the other, "observed Attraction and or Gravity" the result if considered in its entirety being from some other force/particle reaction entering our area of Interest..

My point of interest is how are these two particles possible in the first place? as in what velocities and or forces do we need to consider for them to exist? and while we are at it what defines these forces? as in what opposing velocities do we need to consider created implied force and or potential of energy? and as to where do the velocities originate from in the first place? And then there's that third particle about to invoke change, to consider..


Cheers,

Pete..

 

[yogi]

If one adopts Einstein's premise that inert matter warps static space - then the issue is resolved - no force, only curvature - but what causes mass to bend space and time - perhaps it is worth looking at the issue in reverse - force causes curvature i.e., curvature is consequent rather than primary

 

[Laidback]

If one adopts Einstein's premise that inert matter warps static space - then the issue is resolved - no force, only curvature - but what causes mass to bend space and time - perhaps it is worth looking at the issue in reverse - force causes curvature i.e., curvature is consequent rather than primary

Forgive my ignorance, but when you refer to static space are you implying that an area of the Universe is completely void and importantly without change to it?

If so, I would like some sort explanation that let's say some layman such as I could understand..

BTW - What is exactly curved and or warped, as in - is it a body of energy/mass? and to what reference is this curvature or warping?

Cheers and thanks in advance,

Pete..

 

[yuiop]

Hi Pete,

A lot of questions to what I thought was a relatively un-contentious posting for me! I must admit I am not one hundred percent sure of what you are getting at but I will have a go at answering some of your questions and maybe the real experts here can fill in the gaps.

In old fashioned Newtonian physics it used to be said that a particle remained at rest...

I am assuming you meant, the referred particle remained in relative proximity to other particles, or am I wrong?And this is where I am really confused?..

Living in the modern world, by "at rest" I mean a with respect to the observer and by the same token motion is with respect to the observer. For example if I am in free space then I might consider particle A to be at rest and particle B to be moving from my point of view. Another observer co-moving with particle B will say particle B is at rest and particle A has motion and both our points of view are equally valid. Note that I have for now ignored any gravitational interaction between the observer and the observed particle.

If we go far enough back in history, they had an absolutist view of motion and something was either moving or it wasn't. Back then, it was natural to consider the Earth as stationary and everything revolved about the Earth. The Earth was to them, an absolute frame of reference. I think it was Galileo that first realized that motion was relative and he gave the example of how being inside the cabin of a moving ship was indistinguishable from being inside a stationary ship. Way back in history it was natural to consider that an object required a constant force acting upon it to continue moving. This was natural to them, because it was their everyday experience that a cart moving on a flat surface would eventually stop unless a force (eg a horse) kept it moving. Later it realized that if there was no friction from the wheels or the air that the cart would continue moving indefinitely without a horse almost as if by magic. Nowadays it is completely natural to consider that a particle continues moving in a straight line without invoking any forces (magical or otherwise) to keep the particle moving. You will see later that this idea of motion without applied forces extends very nicely to how gravity works.

The above diagram is the famous rubber sheet analogy of an embedding diagram and as an analogy it should be used with caution, but it might help make some points here. The concentric circles can be considered as the geodesics of orbiting particles with the required orbital velocity. In Newtonian physics, a particle in orbit is considered to have centrifugal force acting outwards on the particle balanced by an equal force of gravity acting inwards on the particle. A more modern interpretation is that centrifugal force is a fictitious force and only the force of gravity is acting on the particle. After all if two equal and opposite forces were acting on the particle it would follow a straight line and not the circular path we observe. General Relativity takes this process a step further and states that centrifugal force and gravitational force are both fictitious and no forces at all are acting on the orbiting particle. The orbiting particle is simply continuing to move in the equivalent of a straight line (a geodesic) in curved space. The mass of the massive body at the centre of the diagram shapes the spacetime "landscape" which redefines the notion of a straight line. The orbiting particle having mass also shapes the landscape to a much lesser degree and the landscape continually changes as the particles move within it. In this instance the rubber sheet demonstration is useful because you can see how the landscape continually changes as the rubber is flexed by the objects moving upon it. For each particle there a unique geodesic dependant on the location and velocity of the particle. For example a particle with no orbital velocity follows a geodesic that is straight downwards illustrated by the radial lines in the above diagram. The blue particle in the lower half of the diagram is following its own geodesic represented by the red dashed line.

Now take a look at this next diagram.

http://www.zamandayolculuk.com/Cetinbal/PU/spacetimeres.jpg

In this diagram the straight lines making up the grid on the rubber sheet are obviously deformed by the depression in the sheet. However, when viewed from directly above the the grid would still look like it was made up of straight lines. Now imagine running some sticky tape along one the grid lines that pass though the depression. By keeping the tape as flat as possible to the curved surface it will be seen that it deflects from the straight grid line that it is trying to follow and the tape path will not be straight when viewed from directly above. This curved path followed by keeping a tape as flat as possible on a curved surface, is the new notion a "straight line" in curved space and is basically a geodesic path. A straight line is now defined (perhaps somewhat circularly) as the path followed by a particle with a given velocity, that has no real forces acting upon it. Despite this somewhat circular definition, geodesics are exactly defined by the equations of General Relativity.

OK maybe this may make more sense - If we reason, Force may only be Repulsive, my question has and still is to this day, why then, do we still refer to the observation of two particles that have been repulsed towards each other, Gravity or as if some magical attractive force exists? Put simply I don't understand what you mean by "Falling" in this case?

Hmmm.. what do I mean by falling? I guess one definition is that an object in curved space is falling if it has no forces acting upon it. For example if I throw a ball in the air it is falling both on the way up and on the way down again. Of course I am ignoring air resistance here, which would be imparting a force on the ball. Now let's say I am standing on a tall building with a heavy lead ball in my right hand. While I am standing on top of the building, I can feel the ball pressing down on my hand, so I know there is a force acting on the ball. I have to apply this force to stop the ball following its natural geodesic which is straight down. In the same way if a heavy ball was passing me free space I would have to apply a force to bring it to rest and stop it following the geodesic it was originally on. Now if I jump from the building with the lead ball still in my hand I would notice that the ball is no longer pressing down on my hand. From my point of view (free falling with the ball) the ball is motionless and has no forces acting upon it. If I had an accelerometer in my other hand I would notice that there is no reading on the accelerometer now I am falling, while there was a reading before I jumped. So again, free falling does not involve any forces, repulsive, attractive, magical or otherwise.

Are you referring to some undefined force, for this "free falling" casualty? And am I correct, perhaps your statement quotes some current textbook, so you really meant "some particle that is with a velocity to it?" Again I am confused?

The difficulty with defining a particle as "free falling" as "some particle that is with a velocity to it" is that velocity is an observer dependent quantity. In the previous paragraph I gave the example of myself free falling along with a heavy ball. From my co-moving point of view the falling ball has no velocity.

I am assuming you meant, the referred particle remained in relative proximity to other particles, or am I wrong?And this is where I am really confused?..

...

Q/. What defines form and or defines your above particle from its environment and or its proximity to other implied particles and their defined areas and or interactions and what separates them?

You seem interested in defining location and motion of a particle relative to other particles, whereas it is normally defined relative to an observer. However we can consider the case of a cloud of dust particles shaped in the outline of a sphere falling towards a massive body. For this example the mutual gravitational interaction of the dust particles will be considered as negligible. Particles at the bottom of the dust sphere are closer to the gravitational source than the ones at the top of the dust sphere and at any given instant of time the lower particles will be moving faster and thus moving away from the particles at the top and thus elongating the sphere. At the same time particles at the side of the dust sphere will be converging towards the common gravitational centre of the massive body and making the dust sphere narrower. Interesting the volume of this distorted sphere remains constant. This distortion of the dust sphere is a measure of tidal effects and again does not involve any forces as long as the particles are free to follow their natural geodesics. For a large orbiting object such as a moon, all the component particles of the moon are not able to follow their natural geodesics because of their physical attachment to each other and in this case the tidal forces are real and can tear a moon apart.

Now you might argue that if a weight is placed on a table, the table bends and exerts an upward force on the weight and by Newton's principle of "every action has an equal and opposite reaction", there must be a downward force exerted by gravity on the weight resting the table, right? Well... maybe not. Consider for example that we have (for some weird reason) a turntable far out in flat space. A mass placed inside the spinning turntable will have a centripetal force acting inwards on it, forcing the mass to move in a circle, when what it really wants to do is follow a natural geodesic tangential to its motion and fly off in a straight line. The equal and opposite force in this case is centrifugal force acting outwards on the mass. However the centrifugal force is a fictitious force and if it was a real force that balanced the centripetal force, the mass would be traveling in a straight line because there is no net force acting on it. The centripetal force has to be continually applied because the mass is being continually deflected from its natural geodesic. It is the same with mass on the table. The gravitational force supposedly acting downwards on the mass is a fictitious force and the upward force exerted by the table on the mass is the force required to continuously deflect the mass resting on the table from following its natural geodesic.

Hopefully I have made the point that gravity does not require any forces to explain it in General Relativity and the graviton is not required. If Quantum theory comes up with a credible theory involving gravitons, the purpose of the graviton will be to shape the spacetime landscape around a massive object, rather than mediate forces directly between two objects.

 

[A.T.]

The above diagram is the famous rubber sheet analogy of an embedding diagram and as an analogy

Analogy to what? Definitely not to the mass attraction model in GR. See this thread:
https://www.physicsforums.com/showthread.php?p=2046692

The concentric circles can be considered as the geodesics of orbiting particles with the required orbital velocity.

The concentric circles are obviously not geodesics in the curved space displayed here. They are projections of geodesics in curved spacetime which is not shown.

In Newtonian physics, a particle in orbit is considered to have centrifugal force acting outwards on the particle balanced by an equal force of gravity acting inwards on the particle.

Only in a rotating frame there is a centrifugal force.

A more modern interpretation is that centrifugal force is a fictitious force

That is not a "more modern interpretation". There never was a different one.

The orbiting particle is simply continuing to move in the equivalent of a straight line (a geodesic) in curved space.

Not in curved space but In curved spacetime. The paths of free falling object are not geodesics in space in general.

For example a particle with no orbital velocity follows a geodesic that is straight downwards illustrated by the radial lines in the above diagram.

How does it know it has to go downwards along this geodesic? Why this initial direction, when it is initially at rest in space?

Now imagine running some sticky tape along one the grid lines that pass though the depression. By keeping the tape as flat as possible to the curved surface it will be seen that it deflects from the straight grid line that it is trying to follow and the tape path will not be straight when viewed from directly above. This curved path followed by keeping a tape as flat as possible on a curved surface, is the new notion a "straight line" in curved space and is basically a geodesic path.

That is correct but explains only the minor effects of curved space, Not the main mass attraction effect of curved space time.

Effects of curved space time:

http://www.physics.ucla.edu/demoweb/demomanual/modern_physics/principal_of_equivalence_and_general_relativity/curved_time.gif

Effects of curved space:

http://www.physics.ucla.edu/demoweb/demomanual/modern_physics/principal_of_equivalence_and_general_relativity/curved_space1.gif
http://www.physics.ucla.edu/demoweb/demomanual/modern_physics/principal_of_equivalence_and_general_relativity/curved_space2.gif

Taken from:
http://www.physics.ucla.edu/demoweb..._and_general_relativity/curved_spacetime.html

 

[Laidback]

Hi Pete,

A lot of questions to what I thought was a relatively non contentious posting for me! I must admit I am not one hundred percent sure of what you are getting at but I will have a go at answering some of your questions and maybe the real experts here can fill in the gaps.



Living in the modern world, by "at rest" I mean a with respect to the observer and by the same token motion is with respect to the observer. For example if I am in free space then I might consider particle A to be at rest and particle B to be moving from my point of view. Another observer co-moving with particle B will say particle B is at rest and particle A has motion and both our points of view are equally valid. Note that I have for now ignored any gravitational interaction between the observer and the observed particle.

If we go far enough back in history, they had an absolutist view of motion and something was either moving or it wasn't. Back then, it was natural to consider the Earth as stationary and everything revolved about the Earth. The Earth was to them, an absolute frame of reference. I think it was Galileo that first realized that motion was relative and he gave the example of how being inside the cabin of a moving ship was indistinguishable from being inside a stationary ship. Way back in history it was natural to consider that an object required a constant force acting upon it to continue moving. This was natural to them, because it was their everyday experience that a cart moving on a flat surface would eventually stop unless a force (eg a horse) kept it moving. Later it realized that if there was no friction from the wheels or the air that the cart would continue moving indefinitely without a horse almost as if by magic. Nowadays it is completely natural to consider that a particle continues moving in a straight line without invoking any forces (magical or otherwise) to keep the particle moving. You will see later that this idea of motion without applied forces extends very nicely to how gravity works.

The above diagram is the famous rubber sheet analogy of an embedding diagram and as an analogy it should be used with caution, but it might help make some points here. The concentric circles can be considered as the geodesics of orbiting particles with the required orbital velocity. In Newtonian physics, a particle in orbit is considered to have centrifugal force acting outwards on the particle balanced by an equal force of gravity acting inwards on the particle. A more modern interpretation is that centrifugal force is a fictitious force and only the force of gravity is acting on the particle. After all if two equal and opposite forces were acting on the particle it would follow a straight line and not the circular path we observe. General Relativity takes this process a step further and states that centrifugal force and gravitational force are both fictitious and no forces at all are acting on the orbiting particle. The orbiting particle is simply continuing to move in the equivalent of a straight line (a geodesic) in curved space. The mass of the massive body at the centre of the diagram shapes the space-time "landscape" which redefines the notion of a straight line. The orbiting particle having mass also shapes the landscape to a much lesser degree and the landscape continually changes as the particles move within it. In this instance the rubber sheet demonstration is useful because you can see how the landscape continually changes as the rubber is flexed by the objects moving upon it. For each particle there a unique geodesic dependant on the location and velocity of the particle. For example a particle with no orbital velocity follows a geodesic that is straight downwards illustrated by the radial lines in the above diagram. The blue particle in the lower half of the diagram is following its own geodesic represented by the red dashed line.

Now take a look at this next diagram.

http://www.zamandayolculuk.com/Cetinbal/PU/spacetimeres.jpg

In this diagram the straight lines making up the grid on the rubber sheet are obviously deformed by the depression in the sheet. However, when viewed from directly above the the grid would still look like it was made up of straight lines. Now imagine running some sticky tape along one the grid lines that pass though the depression. By keeping the tape as flat as possible to the curved surface it will be seen that it deflects from the straight grid line that it is trying to follow and the tape path will not be straight when viewed from directly above. This curved path followed by keeping a tape as flat as possible on a curved surface, is the new notion a "straight line" in curved space and is basically a geodesic path. A straight line is now defined (perhaps somewhat circularly) as the path followed by a particle with a given velocity, that has no real forces acting upon it. Despite this somewhat circular definition, geodesics are exactly defined by the equations of General Relativity.



Hmmm.. what do I mean by falling? I guess one definition is that an object in curved space is falling if it has no forces acting upon it. For example if I throw a ball in the air it is falling both on the way up and on the way down again. Of course I am ignoring air resistance here, which would be imparting a force on the ball. Now let's say I am standing on a tall building with a heavy lead ball in my right hand. While I am standing on top of the building, I can feel the ball pressing down on my hand, so I know there is a force acting on the ball. I have to apply this force to stop the ball following its natural geodesic which is straight down. In the same way if a heavy ball was passing me free space I would have to apply a force to bring it to rest and stop it following the geodesic it was originally on. Now if I jump from the building with the lead ball still in my hand I would notice that the ball is no longer pressing down on my hand. From my point of view (free falling with the ball) the ball is motionless and has no forces acting upon it. If I had an accelerometer in my other hand I would notice that there is no reading on the accelerometer now I am falling, while there was a reading before I jumped. So again, free falling does not involve any forces, repulsive, attractive, magical or otherwise.



The difficulty with defining a particle as "free falling" as "some particle that is with a velocity to it" is that velocity is an observer dependent quantity. In the previous paragraph I gave the example of myself free falling along with a heavy ball. From my co-moving point of view the falling ball has no velocity.



You seem interested in defining location and motion of a particle relative to other particles, whereas it is normally defined relative to an observer. However we can consider the case of a cloud of dust particles shaped in the outline of a sphere falling towards a massive body. For this example the mutual gravitational interaction of the dust particles will be considered as negligible. Particles at the bottom of the dust sphere are closer to the gravitational source than the ones at the top of the dust sphere and at any given instant of time the lower particles will be moving faster and thus moving away from the particles at the top and thus elongating the sphere. At the same time particles at the side of the dust sphere will be converging towards the common gravitational centre of the massive body and making the dust sphere narrower. Interesting the volume of this distorted sphere remains constant. This distortion of the dust sphere is a measure of tidal effects and again does not involve any forces as long as the particles are free to follow their natural geodesics. For a large orbiting object such as a moon, all the component particles of the moon are not able to follow their natural geodesics because of their physical attachment to each other and in this case the tidal forces are real and can tear a moon apart.

Now you might argue that if a weight is placed on a table, the table bends and exerts an upward force on the weight and by Newton's principle of "every action has an equal and opposite reaction", there must be a downward force exerted by gravity on the weight resting the table, right? Well... maybe not. Consider for example that we have (for some weird reason) a turntable far out in flat space. A mass placed inside the spinning turntable will have a centripetal force acting inwards on it, forcing the mass to move in a circle, when what it really wants to do is follow a natural geodesic tangential to its motion and fly off in a straight line. The equal and opposite force in this case is centrifugal force acting outwards on the mass. However the centrifugal force is a fictitious force and if it was a real force that balanced the centripetal force, the mass would be traveling in a straight line because there is no net force acting on it. The centripetal force has to be continually applied because the mass is being continually deflected from its natural geodesic. It is the same with mass on the table. The gravitational force supposedly acting downwards on the mass is a fictitious force and the upward force exerted by the table on the mass is the force required to continuously deflect the mass resting on the table from following its natural geodesic.

Hopefully I have made the point that gravity does not require any forces to explain it in General Relativity and the graviton is not required. If Quantum theory comes up with a credible theory involving gravitons, the purpose of the graviton will be to shape the space-time landscape around a massive object, rather than mediate forces directly between two objects.

<sigh> Thanks for a fantastic effort Kev,

But alas, I feel I have not asked my question in a correct manner..
This post of mine along with your answer is a little long, so I will post again, which I hope will get a response more to the point, how relativity is involved at all scales, including as some refer to the macro level..

BTW - If my next Post has not been posted, please stand by as I may be having difficulties in honing in, to what I feel physics is missing..
BTW the below models actually point to a gross error when it comes to relativity..

http://theory.uwinnipeg.ca/users/gabor/black_holes/images/slide5.gif
http://www.zamandayolculuk.com/Cetinbal/PU/spacetimeres.jpg

Please stand by, and I will post my case as to why and why it has much to do with my question..

Cheers,

Pete..

 

[Laidback]

Let us refer to a cubic area that is with a density of mass or energy that implies as if a near Vacuum..

Now let's have this area first consisting of a single particle, now my question is what form would the entire area of this particle imply?

http://www.zamandayolculuk.com/Cetinbal/PU/spacetimeres.jpg

If we remove the above grid-ding, and then applied our own grid-ding, but apply it from all directions with straight lines all crossing at the most central point, the above model would better reflect to the actual fact's and or maths..

It would also point out physical Particles are in fact compression points, or that Energy at at the very core of where our grid-ding suggests triangles rather than cubic areas, also suggests blue-shifting and red-shifting, of course this may only be first apparent to those who deal with mass on daily basis..anyway,

For example if we were to take a core sample of said particle the sampled areas density increases the closer to the core sample we point our interest towards..

Much like our Earths atmosphere where at sea level it is much denser than the atmosphere a few kilometres from the core of our planet, in fact if we could take a 3D sample at sea level and then release it way above, it would take mere seconds for it to spread out on its release.. also if one is to take an accurate cubic area that is to match a little closer to our upper atmosphere, it would need to resemble a lopped of pyramid rather than a cube, simply because the lower area is more compressed..

Anyway getting back to a single particles area much the same should be evident, so the way we should see it, is where ever opposing velocities need to traverse each other they end up as a compression point..

To clarify this - Let me refer to a core sample of a compression point, created by two opposing velocities or two photons meeting..

"- -" moment one, please note that a void by me simply is not possible, so the blanks in between the dashes by me are treated as a near vacuum that is not propagating a photon, while the dashes may be treated as a near vacuum with a single photon being propagated through the near vacuum, also note this means each area in interest is one second in length by a single potential or Photon in height, also my model is a closed system that is for the moment four photons wide by one photon high..

" -- " moment two

" = " moment three whereby, the two velocities at the speed of light combined are now only one second in duration, the result would be the two velocities cancel out or in fact are now traversing an opposing velocity and or photon, and with this we have what I refer to a compression point, because we will also note we now have an area that is two photons in value or a potential of two photons in value, also we should note our closed model has exchanged its width dimension to its height dimension, and if this model were open and joined with other systems these systems would present Gravity and or an observed attraction..

"---"->" = "<-"---" as in from all directions the whole Universe would experience inward momentum, by this new Black-hole..

Now let's imagine if photons and or velocities were to cross from all directions at a single point, and it is this crossing point that is my point of interest, as it defines structural density to particles.

So have I made myself clear as to what is a velocity and or force and mass is as I understand it?
if not please let me know if I am in error in any way or if you feel, I am one mother of a whack job, err~I hope its OK by this forum for one to insult themselves?

NOW - If we refer to the above image, and treat each grid in a 2D manner that is to be with an inward momentum, one could imply each grid equates to Mc^2 and each grid equals a single mass and or density, so that if a grids energy is to move through and or combine with another grid of energy the result at one point would be double the density to a single grids area, or if more grids are to cross at the same time, density increases by whatever areas are to enmesh in that one single area, the result is beyond this area it also also is curved resulting as per space-time, because as kinetic energy "electromagnetic waves" and or "Light" is propagated from grid to grid, each grid I reason experiences increases and decrease of energy states, but when two precise opposing velocities happen to meet, the kinetic energy is exchanged to potential energy, and this can be visualised I hope by MY ABOVE SIMPLE MODEL, that is - if we define height as potential energy and width as Kinetic energy to the model, so that when we merge two photons to a single photons area, the result is a compression point, now imagine photons and or velocities enmeshing from all directions? And consider how long it would take if another velocity were to enmesh in a area that is compressed, being mindful the more dense the more a given velocity must contend with as in reality the compressed area is in fact a greater area, and so it will seem to take much longer for a photon to be propagated through it, as the area is presented to an observer to be less kinetic in energy, when in fact photons always remain at c and or the speed of light in reference to all other involved velocities at "c"..

Hmm very hard to explain..

So here's another example, If we have a 1 kmh breeze but a bird is flying in the opposite direction at 1 kmh, is the bird moving in any direction other than flapping it wings?

The bird is with a potential to move at 1 kmh, but only once it has traversed the breeze, now imagine the whole universe is a body of Potential and kinetic energy, and if kinetic energy is stored implies an increase in density. resulting in basic Standard model particles..

Ok before I waffle on any further, have I made myself clear and is anyone seeing how I reason space-time should be treated thus far?

As I am itching to get back to my first question..

By referring to static space are you implying that an area of the Universe is completely void and importantly without any change to it?

Cheers,

Pete..