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Author Topic:   What Creates Gravity?
dkv
Member (Idle past 5732 days)
Posts: 38
Joined: 09-15-2007


Message 25 of 84 (474905)
07-12-2008 3:14 AM


Gravity is sometimes understood as geometry of space time.
General theory of relativity says that the space time wraps due to the presence of mass. There is no force just a geometry.
However I have my doubts.
General theory of relativity is based on the principle of equivalence.
Which in my opinion is fundamentally flawed.
"The principle of equivalence: There is no experiment observers can perform to distinguish whether an acceleration arises because of a gravitational force or because their reference frame is accelerating
- Douglas C. Giancoli Physics for Scientists and Engineers with Modern Physics, p. 155"
However note that GMm/r^2=ma ; a= GM/r^2 (acceleration is independent of mass but not independent of the distance from the source of gravity)
therefore as the distance between gravitational center and the center of frame decreases the acceleration increases ... this can be used to distinguish between gravitational and non-gravitational frames.
Experiment :A body falls freely towards Earth because the force is inversely propotional to distance between earth and object ,as it falls it will experience an increase in acceleration due decrease in the distance(g=9.8m/s^2 is only an approximation because change in R is small). Therefore if a sufficiently sensitive instrument is available then it should be possible to detect the increase in acceleration thus violating the equivalence principle.
Moreover spatially distributed point masses experiences different accelerations.
It is in principle possible to differentiate between a accelerating frame and gravitationally accelerating frame.

Replies to this message:
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dkv
Member (Idle past 5732 days)
Posts: 38
Joined: 09-15-2007


Message 29 of 84 (474922)
07-12-2008 8:59 AM
Reply to: Message 27 by cavediver
07-12-2008 5:53 AM


EQuivalence Principle is a principle because it is one of the basic postulates of General relativity. Experiments have supported it.(no amount of experiment can prove a theory... one single experiment can disprove a theory...observations can only "support" a theory)
There is Weak Equivalence principle and there is strong equivalence priciple using which a theory was proposed and the predictions were made.
Therefore IMO it is wrong to say that EP is a prediction of the theory.
Why do we suspend our skeptisim when discussing Einstein's theory?
Was einstein right ? Had he had the last say on nature of universe ?
No. Einstein's GR totally fails are microscopic levels...
No - you cannot detect any acceleration if you are freely falling! What you could detect with your sensitive instrument, is the difference between what is happening at the top of your frame and what is happening at the bottom of the frame. This is where the differential gravitational field will be noticed. A partcile at the top of your frame will be moving away from a particle at the bottom of your frame. Two partciles on either side of your frame will actually be moving towards each other. But again, these ar not LOCAL experiments as you are comparing partciles at different points. All you are doing is discovering that your lcoal space-time curvature is changing as you move through space-time - nothing unusual there...
That all said - it is quite possible that the equivalence principle is not infallible, but it will not be because of a failure of GR, but because of corrections to GR resulting from quantum gravity.
Local Frame from my point of view is made up of finite volume.. Which when subjected to a gravitational force experiences a non-uniform stress.
i.e the acceleration at the top and bottom of the frame is not the same.
Gravitation is Forcibly assumed UNIFORM in this local metric.
Which is not the case in reality.
"The principle of equivalence: There is no LOCAL experiment observers can perform to distinguish whether an acceleration arises because of a gravitational force or because their reference frame is accelerating"
Observers can not perform ANY experiment in the LOCAL frame as defined by GR.
Let us ask is it really a Local reference frame?
All experiments return a ratio between observed and the standard.
In a local frame we must be able to keep a standard measurement.
In the LOCAL defined by GR can we keep a standard to measure?
for example in order to measure time we need a atomic clock.. is it possible to keep a atomic clock in such a infinitely small metric.
It is obvious that we can not keep local standard measurements to define the local reference frame.
(rocket or train compartment is valid a reference frame because the local standards can be kept there.. note that everything is relative therefore it should always be possible to define the local measurements.)
Local frame as defined by GR can not be defined at all because in such case the local measurements can not be made.
Therefore IMO the EP is conceptually incorrect and therefore the GR is also incorrect.

This message is a reply to:
 Message 27 by cavediver, posted 07-12-2008 5:53 AM cavediver has replied

Replies to this message:
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dkv
Member (Idle past 5732 days)
Posts: 38
Joined: 09-15-2007


Message 31 of 84 (474932)
07-12-2008 12:26 PM


Thanks for the suggestion but there is a quote popularly attributed to Einstein.
"If facts dont fit the theory change the facts."
It is anyones guess what will happen if I challenge the fundamentals of the theory.
However isnt it obvious that any Local frame must be capable of defining its measurables... I.e it must be able to define length , volume , time and several distributed properties like pressure , temperature.An infinitely small local frame can not define those concepts.
Local frame is different from a point mass or point velocity ...
Local frame is allows the local observer to define and make observations!!

  
dkv
Member (Idle past 5732 days)
Posts: 38
Joined: 09-15-2007


Message 33 of 84 (474941)
07-12-2008 2:00 PM


If the local volume is not zero and the gravitational force is not uniform then it is possible to distinguish between accelerating frame and gravitationally accelerating frame.
That was the whole point of this discussion.
In other words a gravitational free fall can be distinguished from a induced free fall in zero gravity because both these forces act differently on a finite volume which is the metric of GR.
Another example involves a spherical shell of mass...
In a spherical shell with uniformly distributed mass there is no net force on anything inside the sperical shell.
However in this case zero acceleration is not physically equivalent to a spherical shell.In other words observations made in the local frame of reference does not translate into gravitational frame of reference.
Had it been so a mass at rest would never know whether there is speherical shell encapsulating its space?
When we study the free fall we make the local frames equivalent to gravitational frames.. in other words geometry of the free fall translates into gravity..
quote from wikipedia
Einstein’s general theory modifies the distinction between nominally "inertial" and "noninertial" effects by replacing special relativity's "flat" Euclidean geometry with a curved non-Euclidean metric. In general relativity, the principle of inertia is replaced with the principle of geodesic motion, whereby objects move in a way dictated by the curvature of spacetime. As a consequence of this curvature, it is not a given in general relativity that inertial objects moving at a particular rate with respect to each other will continue to do so. This phenomenon of geodesic deviation means that inertial frames of reference do not exist globally as they do in Newtonian mechanics and special relativity.
Which means that the inertial frame of reference exists locally and is definable such that it is indistinguishable from any normal accelerating frame of reference.
It is important that by the definition of local frame of reference the physical laws should be definable and observable...
However in differential manifold such observations can not be made at all because the defintions of length,volume , velocity ,time can not be described by living inside the metric.
A local frame is definable if and only if laws of physics can be described and studied in the differential volume independent of the external observer.

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dkv
Member (Idle past 5732 days)
Posts: 38
Joined: 09-15-2007


Message 35 of 84 (474944)
07-12-2008 2:43 PM


To make the point more clear.
1.Let us assume that differential local frame of reference is definable.
i.e dV=dX.dY.dZ is definable as a frame of reference. (mathematically dV tends to zero)
and that the equivalence principle holds.
2.Since we have defined it as our frame of reference therefore it should be possible to measure dV , dX,dY and dZ .... since these are arbitarily small quantities therefore we must propose the existence of arbitarily sensitive instruments because dV is the local frame of reference and quantities in local frame of reference can be measured independent of external observers.
3.Given the arbitarily sensitive and arbitarily miniaturizable intruments it should be possible to define and measure dX/2,dY/2 and dZ/2.
4.Given a gravitational force in dZ direction ,the dV must experience an arbitarily small spatial difference in acceleration too(for example at dZ and dZ/2) which should be measurable by the instruments.
By defintion our instruments are capable of measuring differential change.
5.Therefore it should be possible to differentiate between gravtitationally accelerating frame and non-gravitationally accelerating frame.
6.This is in contradiction with the Equivalence Principle.
7.If local frame of reference can detect gravity then it is not possible to equate the local geometry with gravitational presence because they are differentiated by the differential measuring instruments.

Replies to this message:
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dkv
Member (Idle past 5732 days)
Posts: 38
Joined: 09-15-2007


Message 36 of 84 (474946)
07-12-2008 2:51 PM


Yes I am still claiming that the GR is invalid because the local equivalence principle can not hold.
In the previous example the differential acceleration is dA=|GM/R^3|dZ
Which our instruments can easily detect because local frame of reference is definable.

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dkv
Member (Idle past 5732 days)
Posts: 38
Joined: 09-15-2007


Message 39 of 84 (474966)
07-12-2008 4:10 PM
Reply to: Message 37 by cavediver
07-12-2008 3:03 PM


Algebra can not be created because the basic principle of equivalence is wrong.
I fail to understand when you ask so what ?
Are you asking ,So what if the equivalence principle is wrong ?
In that case the theory of GR is wrong.
I thought that the thread is dedicated to gravity and physics that is why I posted here.
Anyways here is my last attempt.
Equivalence principle states that locally accelerating frame can not be distinguished from gravitationally accelerating frame.
Locally accelerating frames can be defined if and only if the physics can be defined inside those frames.
A metric which is used to represent local frame of reference is arbitarily small.
What properties must be definable inside any inertial frame?
Inside a local inertial frame the observer should be able to measure length , height , width , change in length , change in time , change in velocity...etc
What happens when we discuss a free falling BOX?
Suppose we replace that metric with a freely falling BOX then the BOX will experience an internal stress due to the dimension dependent gravitational force... the force of gravity at the top of the box will be different from the force of grvaity at the bottom.
Here we are not talking about the geodesic of the BOX in space but the force distribution on the BOX due to external gravity which is the basis of equivalence principle.
Therefore IN THE CASE OF A BOX we can easily find out whether an external force of gravity is acting on it or not by following different points on the BOX thus violating the equivalence principle.
That is why we say that GR is local theory because it must use a metric. It can not use any arbitary frame of reference.
What happens when we discuss from the point of view of a Metric?
A metric is infinitely small inertial frame of reference.
Metric holds the equivalence principle.
Everything is fine so far. BUT what is an inertial reference frame?
An inertial reference frames share common set of physical laws and it is not possible to define Absolute Value of velocity. The velocities of inertial frames are relative and equally true.
BUT a more important property which is assumed while defining these frames is that measurements in these frames can be made independently of an external observer.
The metric which is local and infinitely small must be also capable of measuring its infinitely small physical values independently of the external observer because it is an inertial frame.
Therefore in the local frame of GR an infinitely sensitive instrument must also exist so that it can independently define and verify its physical laws.
There is nothing in principle which stops this from happening. It is just matter of scaling.
ANd if infinitely small measurements are possible in infinitely small metric then the metric can be replaced with the BOX!!
Because BOX is made up of several points in a space therefore metric must also be definable in a similar fashion otherwise it can not define lines , volumes ,velocity and acceleration independent of external observer.
As I said the complete laws of motion must remain definable inside the infinitely small metric.
Which means the differential force of gravity in the local reference frame(which is now equivalent to our poor Box) can be measured violating the equivalence principle.
Hope that makes things little bit clear but I am convinced that GR doesnt hold its promise of a conceptually consitent theory.

This message is a reply to:
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dkv
Member (Idle past 5732 days)
Posts: 38
Joined: 09-15-2007


Message 41 of 84 (475053)
07-13-2008 7:32 AM


The Equivalence Principle holds only for very special Gravitational fields(homogenous).
However in actual scenario the "true" gravitational field can be found as a non vanishing metrical curvature which are held responsible for the tidal gravitational forces.
Therefore it is not a principle in a sense defined by the original statement...
It is at best an instance of Minkowski space under homogenous gravitational force... which was extended to include non-homogenous forces of gravity.

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dkv
Member (Idle past 5732 days)
Posts: 38
Joined: 09-15-2007


Message 43 of 84 (475060)
07-13-2008 8:20 AM


I was not repeating myself. The non-vanishing metric curvature is the proof of gravitational field. In a constantly acceleration frame the metric curvature of vanishes.
Anyways the point is it is most ill understood concepts of GR.

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dkv
Member (Idle past 5732 days)
Posts: 38
Joined: 09-15-2007


Message 45 of 84 (475107)
07-13-2008 12:05 PM


g ,the Metric of general relativity, represents the grvaitational field however some scientists have said that R represents the gravitational field.
Some have argued that the curvature tensor should be seen as representing the gravitational field (most prominently Synge [1]), others claim that the connection is the gravitational field's mathematical representative (e.g.Ehlers [2] and Giulini [3]).
R=0(reimann tensor) for Minkowski space with a homogeneous gravitational field.
However R is not equal to 0 if there is a real gravitational field.

  
dkv
Member (Idle past 5732 days)
Posts: 38
Joined: 09-15-2007


Message 47 of 84 (475133)
07-13-2008 2:37 PM


I still think that it is not possible to define a infinitely small frame of reference.
If infinitesimal reference frames exist then such frame should be able to make infinitesimal measurements.
Which makes the infinitesimal small frame of reference comparable with any large frame of reference.
How the infinitesimal frame of reference proposes to measure speed of ligth or laws of gravity ??
A frame of reference not only carries physical vectors and other physical attributes but also allows the inside observer to discover its own laws of space time and physics..
Such a frame runs into an infinite loop of problems.

  
dkv
Member (Idle past 5732 days)
Posts: 38
Joined: 09-15-2007


Message 49 of 84 (475254)
07-14-2008 11:41 AM


Homogeneous gravity when applied to a group of test particles the mutual attraction between them is supposed to vanish. Which means that the mutual and self interactions of points have no effect of the geodesic.
At the same time all points are considered moving reference frames...
Now as I said the a point "reference frame" is no different from large reference frame. Therefore we end up with circular logic which cant be simplified for logical deductions...in other words the point to point gravitational interactions can not be neglected in point reference frames analysis.
Therefore the GR is wrong and inconsistent.

  
dkv
Member (Idle past 5732 days)
Posts: 38
Joined: 09-15-2007


Message 56 of 84 (475463)
07-16-2008 4:02 AM


Theory of GR fails on several accounts..
1.It fails to incorporate the local variation in Gravity.
2.It fails to explain why the space time should curve.
3.It fails to explain the effects of measurement on point particles.
No measurement can be made without changing the state of the system.
4.It fails to explain why should we ignore the temperature or randomness in initial conditions...
5.It fails to explain why only curved space time should be the only solution. There are several other possibilities... Including the Whitehead solutions and the SVT solutions.
6.It fails to explain why curvature should be understood as mass(gravity).
7.It fails to explain why should mass manifest in the nature.
8.It fails to account for the zero acceleration inside a massive shell and a real zero acceleration in space.
Overall the GR theory is a waste of time.

Replies to this message:
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dkv
Member (Idle past 5732 days)
Posts: 38
Joined: 09-15-2007


Message 59 of 84 (475626)
07-17-2008 4:27 AM


1.Particles which experiences "any" force in GR moves on a curved space time along the straight lines...
However it is equally possible that particles move on flat space time along the curved lines...
Did you notice the difference ?
Moving along straight lines helps satisfy our desire for inertial movement... Except this difference the point of views are computationally same.
Moving along straight lines on curved space time is related to the flat space time but curved motion by coefficients of space metric.
There is no difference except in the choice of background geometry.
This is sign of a false theory which atleast conceptually creates an impression of absolute theory.
2.Apart from the mathematical difficulty there are physical problems too. The main problem is with the local group of particles which are used in the derivation... the point particles are assumed to be the reference frame which is either wrong or leads us into a circular logic becuase due to any small mass, the flat minkowski space time can not exist in the frame of reference of any particle.
Therefore derivation cant proceed in the beyond the ideal SR theory(non-gravitational).
It is a useless theory which creates a mathematical monster but provides no new insights into the problem expect reformulating "all" mechanical problems in hypothetical curved space time to satisfy the desire to achieve inertial motion.
Here "all" stands for all kinds of tensors... gravitational,non-gravitational.

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dkv
Member (Idle past 5732 days)
Posts: 38
Joined: 09-15-2007


Message 61 of 84 (475634)
07-17-2008 6:10 AM


I do not believe in SR or GR.. I am only exposing the logical inconsistency in the creation of SR and GR.
1.The derivation involves too many formulaes which can not be posted here for obvious reasons... space constraint.
2.However it is possible to understand it in simple English.
3.The homogeneous field of gravity is negelected in the derivation of geodesics(assuming flat space time).Instead the field of gravity is used to justify the transformation of space time from flat to curved.
4.The GR theory is a relativistic theory.It actually uses the concept of frame of reference for point particles... And that is ridiculous becuase it neglects the variation in geodesics caused due to negligibly small presence of non-homogeneous gravity.
5.It assumes that a gorup of arbitary point like particles can be considered to be in a state of rest.... Which is simply impossible becuase the no measurement can be made on such particles without disturbing the state of rest.... if such a measurement were possible then the Quatum theory would not have come into existence.
If all frame cant be assumed to exist to an arbitary small levels then the question of general covariance doesnt arise and therefore GR falls even before its first step.
6.In real world space and time make sense only if we consider the space time to be flat. Otherwise space time has no meaning at all.
A light moving in a stright line is actually moving in a straight line becuase nothing can be attributed to what can not be reached...

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