Length Contraction and what not

[geistkiesel]

You can't both assume it and conclude it.

The statement went that the asumption is that Lorentz contraction is true and from this assumption he concluded that simultaneity is absolute. The logical statements of assuimption and conclusion do not focus on the same node. The statement was a progression of logic and the conslusions that are traced to the assumptions. Nothing wrong with this in the slightest, in fact this is thew way it is supposed to be: logical, rational, intuitive and instinctive.

 

Geuistkiesel

[swansont]

What is the difference if the fact is that simultaneity is an absolute. Beside the violations of grammar and ordinary uses of speech the assumption and conclusion will produce the same result.

geistkiesel

 

 

Because it's not a fact. To introduce it into an argument is to assume a priori that relativity is false. It should then come as no surprise that, having assumed this, that the logic will then show that relativity is false. But invalid logic does not constitute proof of anything.

[J.C.MacSwell]

What is the difference if the fact is that simultaneity is an absolute. Beside the violations of grammar and ordinary uses of speech the assumption and conclusion will produce the same result.

geistkiesel

 

Simultaneity is absolute if and only if you can find and define an absolute frame of reference.

 

Noone has done this.

[geistkiesel]

That is an assumption that contradicts relativity. By assuming that, you have assumed relativity is incorrect. One of the consequences of c being constant is that different observers won't necessarily agree on the order of events (that aren't causally related, at least)

Is it the agreement of obserevrs that concerns SRT so much or is it the physical implications of the data acquired in a scientific manner?. If the latter, then the loss of simultaneity has serious problems. Briefly, in Einsteins famous train-station=moving-train gedanken AE places the onus on one observer in a train load of passengers whose conclusion it was to to discard simultaneity. This was preamture and did not contain an adequate anlayctical process.

 

Photons are emitted simultaneously from A and B sources just as the train observer is located at the midpoint of the sources of the pulses of light at A and B concludes that the forward light, B, say, was emitted before the A light catchng up from behind.

 

The measurmentr sequence goe as follows:

1. The B photon measured by O ,
   
   
2. then A and B arrive simultaneously at the stationary midpoint observed by at least one passenger colocate with the nmmidpoint on the train, who also is at the midpoint when the photons arrive.
   
   
3. Then the A photon is observed by the moving observer
   
   
4. mAll passengers on he train from friont to reaer observed and tiem the arrivakl of he A and B photrons as the problem decribes and,
   
   
5. all passenegers are able to compare the arrival times of the photons just as easily as did the "official" observer.
   
   
6. Historically, the official observer concludes B must have been emitted first which necessarily means the train observer considers himself at rest wrt the train and the train station, the embankment, which is a physical imposssibility to produce in reality. The pen and paper used in analysis and writing of equations and formulae are not themselves data, they are the mere convenient tools of human mental activity.

 

If the passengers are strung out along the train and each have a perfect watch all synchronized wrt each other on the train, then the most forward passengers see the B light before the A light and conversely for the rearward located passengers. All passengers comparing the arrival times of the light from gtheir their position on the tran allows them to easily detemine that the photons were emitted simultaneously from the A and B a sources.

 

Certainly simultaneity is not up to the decision by a single member of observers on the moving frames. There has to be an objective standard, and for simultaneity I see none.

 

Further, the observer is (theoretically) justified in considering the possibility that he is indeed moving and when he takes this approach then all passengers also easily agree. If, for instance, when the moving observer was at the midpoint when the photons were emitted he could have tested for the possibility of motion by marking proper places on the train as the embankment whizzed by thereby maintaining a point that "remains at the midpoint" at least by continuously subtacting observed embankment motion from the point in space that maintained colocation with the midpoint.

 

Is there a preference for the moving observer to assume the physically impossible condition that the nonaccelerating frame, the embankment, is actually in motion and he is at rest? Probably not. And most certainly, teh embankment is never observed to accelerate ibn such a manner that relaive motion between frame and embankment are obswerved as a reulst of that accleration. Certainly we do not exclude trained (pun intended) observers conversant with motion, acceleration and even familiar with analysis and observation of experiments conducted where the train is actually at rest wrt the embankment. Clocks and observers colocated with the emitted photons on bothe front and rear extremes of the train can verify the simltaneity of emission by the comparison of data.

 

When the moving observer concludes he is at rest wrt the embankment he does so with an obvious experimental bias - gthe negation iof possible motion of the frame of reference. The assumptions of rest invariably occur before the collection and analysis of any data; Before any photons arrive; before the passengers make any comparison of the arrival times of the photons. This kind of intrinsic theoretical assumption cannot be considered a rational and scientific mode of determining the dynamics of the relative motion of frame and photon.

Certainly ignorance of factual matters on the part of observers is not a necessary postulate or attribute for the theoretical basis of SR.

 

So you have two assumptions, and a contradiction. If you assume A and assume (not A) you cannot assign the contradiction to any other cause. Your conclusion is invalid. And we've been through this before, so it shouldn't be too surprising that the rules of logic haven't changed in the last couple of months.

I do not see an assumption of contradicting statements that Assume A and assume (not A) in this thread by any participant. If you assume that the relative moion between all reference frames and photons is eternally C, then you must accept the consequences of your assumption.

 

By assuming X is a moment in time and Y another moment in time and X before Y then X before Y in all times is a normal and notextraordinary logical process. There can be no other conclusion. To assert that the foregoing results is a corruption of logic is not justified, merely because it negates a strongly held belief. Any assumption or conclusion to the contrary, withiout more, is logically erroneous. For X before Y for all times then whatever the effect of the original assumption that X and Y are different moment in time then the logical progression of the statement is used throughout and the chips fall where they may. That relativity is contradicted is equivalent to the negagtion of the measured constant of the relative velocity of frame and photon . This is not a misuse of logic; simply, it is logic being used in a most direct and proper sense..

Geistkiesel

[J.C.MacSwell]

If you put an atom in an electric field you can induce a dipole, even though the atom istelf is neutral and feels no net force. Something like that? The problem is that you can test for this to make sure there is no field.

 

Something like that, yes. However, does it feel no force, in this example, in all inertial frames?

 

I'm sorry, but I missed the context of your last sentence. Are you saying you can rule out your example so that if it had an effect on time it could be accounted for?

[geistkiesel]

Because it's not a fact. To introduce it into an argument is to assume a priori that relativity is false. It should then come as no surprise that, having assumed this, that the logic will then show that relativity is false. But invalid logic does not constitute proof of anything.

I think that the assumption regarding the truith of Lorentz contractions being true and simultaneity concluded from this as being absolute is not logically damaged by the mere fact that there are other conclusions resulting from the assumption, other than the one stated i.e. that simultaneity is absolute. Sure SR is

concluded

false,

not assumed false

 

Perhaps we have misread the statement. If this is so then we have an easy solution. We examine the statement and ultimately determine if any ambiguity exists, which has not been claimed, The error claimed as I read your post here is a claim for the truth of Lorentz contraction results in at least the absoluteness of simtaneity and consequently the falsity of SR. We must agree that such a conclusion is true For indeed, if simultaneity is absolute, then SR is false, do you not agree to this?

 

As I see the matter at this point in the progression of the thread is the necessity to establish a factual error in the assumption made. Here the truth or falsity of the of the Lorentz contraction is our only topic left to discuss. I see no ambiguities here.

I read and re read the statement and I see no corruption of the logical form. Perhaps one or both of us have misread the thread of the developed statements, buit if so they have not been pointed out to me, or to anyone else AFAIK.

[J.C.MacSwell]

Certainly simultaneity is not up to the decision by a single member of observers on the moving frames. There has to be an objective standard' date=' and for simultaneity I see none.[/indent']

 

I think this is the idea. Simultanaeity must be thrown ou the window until an objective standard/absolute reference frame, if it exists can be found/defined.

 

Certainly ignorance of factual matters on the part of observers is not a necessary postulate or attribute for the theoretical basis of SR.

 

:

 

I think this is wrong. Ignorance is key. No observer can measure the speed of light in any direction. Only round trips of light can be measured.

[swansont]

I do not see an assumption of contradicting statements that Assume A and assume (not A) in this thread by any participant. If you assume that the relative moion between all reference frames and photons is eternally C' date=' then you must accept the consequences of your assumption.

 

By assuming X is a moment in time and Y another moment in time and X before Y then X before Y in all times is a normal and notextraordinary logical process. There can be no other conclusion. To assert that the foregoing results is a corruption of logic is not justified, merely because it negates a strongly held belief.[/quote']

 

It's not a belief. It's a direct mathematical consequence of the constancy of the speed of light. If, as a result, the Lorentz contraction holds (which is what was assumed), simultaneity cannot be absolute. They are part of an overall picture. As you say, you must accept the consequences of your assumption. You don't get to discard one because you don't like it.

[swansont]

Something like that' date=' yes. However, does it feel no force, in this example, in all inertial frames?

 

I'm sorry, but I missed the context of your last sentence. Are you saying you can rule out your example so that if it had an effect on time it could be accounted for?[/quote']

 

I'm saying that in my example I can do a test to see if this force is present.

[swansont]

I think that the assumption regarding the truith of Lorentz contractions being true and simultaneity concluded from this as being absolute is not logically damaged by the mere fact that there are other conclusions resulting from the assumption' date=' other than the one stated i.e. that simultaneity is absolute. Sure SR is [i']concluded

[/i]

false,

not assumed false

 

Perhaps we have misread the statement. If this is so then we have an easy solution. We examine the statement and ultimately determine if any ambiguity exists, which has not been claimed, The error claimed as I read your post here is a claim for the truth of Lorentz contraction results in at least the absoluteness of simtaneity and consequently the falsity of SR. We must agree that such a conclusion is true For indeed, if simultaneity is absolute, then SR is false, do you not agree to this?

 

As I see the matter at this point in the progression of the thread is the necessity to establish a factual error in the assumption made. Here the truth or falsity of the of the Lorentz contraction is our only topic left to discuss. I see no ambiguities here.

I read and re read the statement and I see no corruption of the logical form. Perhaps one or both of us have misread the thread of the developed statements, buit if so they have not been pointed out to me, or to anyone else AFAIK.

 

I agree that if simultaneity is absolute then SR is false. Any assumption about simultaneity being absolute is equivalent to assuming that SR is false. To assume that an ordering of events must stay on that order in all frames falls into that category - it is a statement that implicitly assumes SR is false. i.e. It assumes the conclusion.

[geistkiesel]

I agree that if simultaneity is absolute then SR is false. Any assumption about simultaneity being absolute is equivalent to assuming that SR is false. To assume that an ordering of events must stay on that order in all frames falls into that category - it is a statement that implicitly assumes SR is false. i.e. It assumes the conclusion.

Swansont, I learned the basic rules of simultabeity initially from gedanken. One discussed by AE in his book, "Relativity" the other from David Bohm's book The Theory of Relativity" At least to my own satisfaction my analysis of these two gedanken proved that, at the very least, simultaneity could not be proved. In other words it a straight forward process to determine alternative conclusions based on unexercised possibilities by the moving observer.

 

If it is true relativistically that the observer can consider himself at rest, or moving with egalitarian equivalence, he may opt for a state of rest or motion while being assured that either option is justified for the purposes of analysis of the motion of the inertial frames. With an equivalence postulate granting equal justification to opt for a state of rest or motion the selection effectively determines one of two grossly variant results or conslusions. The option to assume a state of rest for the "train" is equivalent to assuming the embankment is moving and the determination of physical results grossly at odds with the result had the observer on the train assumed his frame of reference was in motion and the embankment at rest .This latter option drives the analysis along the lines of a classical model.

 

It is aopparent to me that under these conditions the application of the equivalence of inertial frames does not apply in a physical sense. This is not to say that the equivalnce postulate is untrue totally, only that it cannot be applied with physcal signifcicance

to granting

the choice

of motion to an obserber on

an inertial frame. The fact of physical law cannot rational be left to the arbitrary choices of human observers.

 

Do you agree? If no then please explain, If yes then please also explain..

Gristkiesel

[swansont]

Swansont, I learned the basic rules of simultabeity initially from gedanken. One discussed by AE in his book, "Relativity" the other from David Bohm's book The Theory of Relativity" At least to my own satisfaction my analysis of these two gedanken proved that, at the very least, simultaneity could not be proved. In other words it a straight forward process to determine alternative conclusions based on unexercised possibilities by the moving observer.

 

It is unclear what you mean here by "simultaneity could not be proved." Do you mean that simultaneity in one frame did not indicate simultaneity in another frame? In your "linear Sagnac" example, you seem to indicate agreement with this - if c is constant in all inertial frames, then events that are simultaneous in one frame are not in another.

 

If it is true relativistically that the observer can consider himself at rest' date=' or moving with egalitarian equivalence, he may opt for a state of rest or motion while being assured that either option is justified for the purposes of analysis of the motion of the inertial frames. With an equivalence postulate granting equal justification to opt for a state of rest or motion the selection effectively determines one of two grossly variant results or conslusions. The option to assume a state of rest for the "train" is equivalent to assuming the embankment is moving and the determination of physical results grossly at odds with the result had the observer on the train assumed his frame of reference was in motion and the embankment at rest .This latter option drives the analysis along the lines of a classical model.

 

It is aopparent to me that under these conditions the application of the equivalence of inertial frames does not apply in a physical sense. This is not to say that the equivalnce postulate is untrue totally, only that it cannot be applied with physcal signifcicance [i']to granting the choice of motion to an obserber on [/i] an inertial frame. The fact of physical law cannot rational be left to the arbitrary choices of human observers.

 

The point is that physical law is not left to the arbitrary choice of the observers. Physical law is the same in all inertial reference frames, so that there is no preferred frame in which one must do calculations. If e.g. momentum is conserved, it is conserved in all frames, and consquently if it it not conserved in one frame, it is not conserved in all frames.

 

You seem to be fixated on one example with a train, but can't two massive bodies be in relative motion in inertial frames? Which one of those is the preferred frame? What of two low-mass objects? Physics has to be true in general. What may appear to be conceptually difficult in one contrivance may not be in many other situations.

[ndmc]

hello

 

if im going at a reltavistic speed' date=' .9c, and im travelling towards point A, does pt A become a shorter distance for me due to length contraction. i see that it cant because the distance isnt moving, but im unsure about what this person would see outside. .e.g length contraction of pt A which lets say is a sun. if the sun would contract doesnt this make the distance even longer. thanks[/quote']

 

the answer is yes. that´s the way some sub-atomic particles are able to reach our planet.

 

a point does not contract! only distances contract. when you move towards a sun then it´s the distance from (f.e.) southpole to northpole which contracts. and it would contract in the same way the rest of your way would contract too.

[geistkiesel]

It is unclear what you mean here by "simultaneity could not be proved." Do you mean that simultaneity in one frame did not indicate simultaneity in another frame? In your "linear Sagnac" example, you seem to indicate agreement with this - if c is constant in all inertial frames, then events that are simultaneous in one frame are not in another.

 

No I mean that the concept of simultaneity as negated by SRT could not be proved, mathematically or physically. In Einsteins gedanken he describes an observer on a train arriving at the midpoint of photon emitters (wrt the staionary frame) just as the photons are emitted. The observer, O, sees the photon approaching from the front of the train before the photon arrives from the rear and concludes that if the photons were emitted from the midpoint of the sources then the photons could not have been emitted simultaneously because the photons did not arrive at his position on the train simultaneously (O has assumed the train's motion in a state of rest).

 

Further, Einstein went on to say that all passengers would conclude the same as the observer.

 

There are a number flaws in the argument. The observer, O, having moved wrt the embankment frame, Ve, will naturally see the arrival of the photons sequentially. However, some passengers to the rear of the observer will see the photons arriving simultaneously at the physical midpoibnt of the photon sources. These passengers, at the instant the photons arrive simultaneously at the midpoint are privvy to the information known to O:the arrival time of the photon at the O position on the train (the inewrtial frame). Therefore the arrival time of the photon from the rear of the train may also contain the arrival time of the photons simulataneously at the midpoint of the sources. The train velocity wrt to Ve can be determined and the O must therefore come to the conclusion that the train is moving, not the embankment. If, as O has determined before any data is received that he will assume the state of rest wrt Ve, the erroneous nature of the problem is foretold.

 

When O is told that passengers on the train observed the simulataneous arrival of photons at the physical midpoint of the sources of the photons what is the responnse of O that justifies his conckusion that the photons must have been emitted sequentially? In order for O to speak the truth of the matter two physiocal events must have occured:1) the embankment must have accelerated to a velocity measured as the relative velocity of train and embankement, 2.) the acceleration of the train originally that provided the original velocity that was initially measured as the realtive velocity of train and embankment must be negated.

 

These two events are both physically impossible conditions to achieve yet we are supposed to believe the mathematical contrivances of SRT as justified substitutions for the reality of observed phenomena, and to discard the rational analytic approaches, such as that performed here, and to adopt a belief in a world described by those who accepted the irrational universe of SRT that iis totally void of any physical basis.

 

Of course the gedanken of Einstein's also places special emphasis onm the observer on the train to the exclusion of the opassengers being able to observe also.

 

Now, anyone reading this thread, watch how any response contrary to that posted here (meaning by those supporting SRT) will not specifically be directed at anything specifically stated here.

 

 

 

 

 

The point is that physical law is not left to the arbitrary choice of the observers. Physical law is the same in all inertial reference frames, so that there is no preferred frame in which one must do calculations. If e.g. momentum is conserved, it is conserved in all frames, and consquently if it it not conserved in one frame, it is not conserved in all frames.

This is just more SRT. There is no one able to prove SRT, yet there are many able to memorize SRT formulae and the echoes of SRT mantras.

If as you say momentum is conserved in all inertial frames then please answer the question: What is the trajectory of the bounced ball assuming the surface on the ground is slightly grainy and hardened granite and the red balls simple golf balls. Also, and unshown, are wind defletors that remove any wind effect on the trajectory of the ball. If the observer has assumed a state of rest wrt the embankment then the surface of the embankment will impose a chip shot effect on the ball which will direct the ball to the rear of the train (the assumed velocity direction of the embankment). On the other hand if the train is the object moving and the embankment at rest, the ball will be directed up back up the trajectory used by the ball in its downward flight. So follow the bouncing ball tell us how momentum is conserved in this SRT scenario.

You seem to be fixated on one example with a train, but can't two massive bodies be in relative motion in inertial frames? Which one of those is the preferred frame? What of two low-mass objects? Physics has to be true in general. What may appear to be conceptually difficult in one contrivance may not be in many other situations.

 

You may use your imagination with the train example here. You pick the train at rest SRT you define a preferred frame, and in this instance you would pick the wrong preferred frame. It was the train that accelerated that produced the relative motion of train and embankment. OK I am fixated on trains and embankments, so what? Are you saying that trains and embankments are exceptions to SRT, but all other relative motion between frames excluding trains and embankments, is adequately described by SRT?

 

So if physics is true in general, yet trains and embankments are not included in that generality, then does SRT have a list of exceptional inertial frames that are described by SRT?

 

It is SRTists with the fixations, such as learned wherever that was. Preferred frames do not square with SRT therefore , say SRT graduate advisors, on many occasions, "preferred frames are out, othewise SRT is out". And so on.

[swansont]

When O is told that passengers on the train observed the simulataneous arrival of photons at the physical midpoint of the sources of the photons what is the responnse of O that justifies his conckusion that the photons must have been emitted sequentially? In order for O to speak the truth of the matter two physiocal events must have occured:1) the embankment must have accelerated to a velocity measured as the relative velocity of train and embankement' date=' 2.) the acceleration of the train originally that provided the original velocity that was initially measured as the realtive velocity of train and embankment must be negated.

[/quote']

 

As soon as you say "accelerated" you are trying to apply SR to a situation it doesn't cover. It applies to the comparison of inertial frames.

[swansont]

If as you say momentum is conserved in all inertial frames then please answer the question: What is the trajectory of the bounced ball assuming the surface on the ground is slightly grainy and hardened granite and the red balls simple golf balls. Also' date=' and unshown, are wind defletors that remove any wind effect on the trajectory of the ball. If the observer has assumed a state of rest wrt the embankment then the surface of the embankment will impose a chip shot effect on the ball which will direct the ball to the rear of the train (the assumed velocity direction of the embankment). On the other hand if the train is the object moving and the embankment at rest, the ball will be directed up back up the trajectory used by the ball in its downward flight. So follow the bouncing ball tell us how momentum is conserved in this SRT scenario.

[img']http://ourworld.cs.com/Sandgeist/absvel/amomdect.GIF[/img]

 

In the earth frame, the ball is moving forward and strikes the stationary earth, exerting a force on it. The earth exerts a backward force on the ball, slowing it down.

[swansont]

You may use your imagination with the train example here. You pick the train at rest SRT you define a preferred frame' date=' and in this instance you would pick the wrong preferred frame. It was the train that accelerated that produced the relative motion of train and embankment. OK I am fixated on trains and embankments, so what? Are you saying that trains and embankments are exceptions to SRT, but all other relative motion between frames excluding trains and embankments, is adequately described by SRT?

 

So if physics is true in general, yet trains and embankments are not included in that generality, then does SRT have a list of exceptional inertial frames that are described by SRT?

 

It is SRTists with the fixations, such as learned wherever that was. Preferred frames do not square with SRT therefore , say SRT graduate advisors, on many occasions, "preferred frames are out, othewise SRT is out". And so on.

[/quote']

 

SR adequately explains what happens in inertial frames. It's become clear you are fixated with acceleration, and SR simply doesn't address that part of the problem.

 

You bring up "graduate advisors" which again raises the question about whether you are speaking from experience or making this up. How many SRT graduate advisors have you known?

[geistkiesel]

As soon as you say "accelerated" you are trying to apply SR to a situation it doesn't cover. It applies to the comparison of inertial frames.

SRT covers this condition. I am saying the object that accelerated and produced the motion that is observed as relative motion wrt the embankment is seen in the literature as assumnvg a state of rest wrt the emabnkment, Thses are two conditions of physical impossibility. SRT negates the concept of motion.

[geistkiesel]

In the earth frame, the ball is moving forward and strikes the stationary earth, exerting a force on it. The earth exerts a backward force on the ball, slowing it down.

In the earth frame the train and the ball are both moving forward. The ball will effectively bounce straight up. But if the observer is assuming herself at rest and expects the ball to act accordingly to her assumption; she will be disappointed correct?

 

The observer assuimg a state of rest wrt the embankment cannot do so without violating the conservation of momentum principal. If the moving ovserver does assume a state of rest and drops the ball from the window she quickly learns that it is her frame of refererence that moves wrt to the emabnkment which remains at rest.

 

So much for the equivalence of inertial frames postulate.

[swansont]

[indent']SRT covers this condition. I am saying the object that accelerated and produced the motion that is observed as relative motion wrt the embankment is seen in the literature as assumnvg a state of rest wrt the emabnkment, Thses are two conditions of physical impossibility. SRT negates the concept of motion.[/indent]

 

SR says no such thing. SR says each observer, in an inertial frame, may see themselves at rest. It most certainly does NOT say that the two objects are at rest with respect to each other.

[swansont]

In the earth frame the train and the ball are both moving forward. The ball will effectively bounce straight up. But if the observer is assuming herself at rest and expects the ball to act accordingly to her assumption; she will be disappointed correct?

 

The observer assuimg a state of rest wrt the embankment cannot do so without violating the conservation of momentum principal. If the moving ovserver does assume a state of rest and drops the ball from the window she quickly learns that it is her frame of refererence that moves wrt to the emabnkment which remains at rest.

 

So much for the equivalence of inertial frames postulate.

 

The observer on the train sees the earth moving. An observer on the earth sees the train moving. They consider themselves at rest, but not each other.