Light shone in a train bouncing off mirrors

[altonhare]

"Simultaneous"

My point here is that observers should never disagree on qualitative, binary descriptions of what happened. To illustrate what I'm talking about here are a few such:

"A hit B"

"A moved faster than B"

"A is longer than B"

"A hit C as B hit D"

as opposed to quantitative, continuous descriptions:

"A is moving at X relative to B"

"A is Y times longer than B"

etc.

I argue that statements of the former kind are general logic statements of the form "X is Y" or "X is not Y" and that an event/entity/etc. cannot be observed to possesses some quality while also possessing the diametric opposite of that quality. If they do this is a basic logical contradiction and indicates a faulty premise on the part of the observer(s).

In general this is upheld, but in the "relativity of simultaneity" it is not. One observer says events AC and BD were not simultaneous, another says they were. This is logically unacceptable. This tells me that there is something special about either the "local frame" E that I described earlier or that there is some other "special" frame.

Then the following should be true:

My eraser is motionless if there is only one set of distances from every other entity in the universe.

As near as I can tell that is what your definition implies. If that isn't what you imply then give us a clearer definition and an example like mine with the eraser.

You do not misunderstand. If you have a single set of distances from your eraser to every other entity in the universe the eraser is motionless by definition.

No, because your redefinition gives prevalence to the “local” version, regardless the purpose.

I argue that it is illogical for two observers to ascribe diametrically opposed qualities to any observation. They may disagree on quantity/degree, but not on quality. If they disagree on quality they must check the presuppositions of their measurements/observations, at least one is ill-conceived. In all other areas we do not allow diametrically opposed qualitative descriptions. If I conclude that the metal brick is bigger than the cement brick and you conclude the opposite, we do not ascribe it to the relativity of lengths of bricks. We find out what was faulty about our method/assumptions. In this case I measured in the summer and you in the winter, perhaps. In another case I say the train is motionless and you say it isn't. As I've pointed out, the conclusion that X is motionless is impossible. I can only say it's motionless relative to me, and you will agree with this no matter what frame you're in because it is a qualitative, binary statement of logic.

This tells me that, for spatially separated events, there is either something special about the local frame or some other "special" frame. I do not know what it is and there is not an immediate practical result of this argument. As of now it is purely an argument of logic.

But only if althonhare consents to it. You are leading the thread and I would not like to contaminate your debate with a parallel discussion, especially if I only discuss with myself! Althonhare, would you consent? Otherwise I would initiate another thread, some day.

Lay it on us. Maybe someone will learn something by pointing out the author's fallacy or others will learn something by seeing it pointed out. The story may be fun also.

Let me define absolute simultaneity thus. Absolute simultaneity means that two spatially separated events regarded as simultaneous by an observer at rest in an inertial frame will also be regarded as simultaneous by ALL observers at rest in ANY other inertial frames moving relative to the first. In this sense absolute simultaneity does not exist. It does exist in some subsets of these frames e.g. observers at rest in a frame. In the definition of absolute simultaneity the words ANY and ALL are the ones that differentaiate absolute from relative.

I argue that, although the definition(s) you present seem reasonable, because they lead to a logical contradiction we conclude they are unacceptable.

 

[matheinste]

Quote:-
---I argue that, although the definition(s) you present seem reasonable, because they lead to a logical contradiction we conclude they are unacceptable. -----

Yes, the definition of absolute simultaneity does lead to logical contradictions in SR. That is exactly the point i was making.

Quote:-
----One observer says events AC and BD were not simultaneous, another says they were. This is logically unacceptable. ----

It is completely logical within SR. In fact it is fundamental. No one has to accept SR but if you do accept the light axiom of SR then you MUST accept the relativity of simultaneity. This is not just an opinion. The relativity of simultaneity follows as a logical consequence of the speed of light being the same in all inertial frames.

Quote:-
----You do not misunderstand. If you have a single set of distances from your eraser to every other entity in the universe the eraser is motionless by definition.----

Every "entity" at any point in time has a single set of distances from any and all other "entities". So by the above definition everything is always at rest. However my concern is with simultaneity. you can philosophise as much as you like but given an a set of axioms such as in SR you cannot argue against a consequence which follows logcally from these axioms. If you do not like the axioms then, fair enough, just say so. That is perfectly acceptable.

Matheinste

 

[JesseM]

"Simultaneous"

My point here is that observers should never disagree on qualitative, binary descriptions of what happened. To illustrate what I'm talking about here are a few such:

"A hit B"

"A moved faster than B"

"A is longer than B"

"A hit C as B hit D"

But the last three don't make sense except in the context of a particular reference frame, since different frames can disagree on which of two objects move faster, which of two objects is longer, and whether two spatially separated collisions happened at the same moment.

I argue that statements of the former kind are general logic statements of the form "X is Y" or "X is not Y" and that an event/entity/etc. cannot be observed to possesses some quality while also possessing the diametric opposite of that quality. If they do this is a basic logical contradiction and indicates a faulty premise on the part of the observer(s).

It's only a logical contradiction if you neglect to include the context of what reference frame you're talking about, which is always necessary for any physical claims which don't concern purely local events in SR. For example, there is nothing contradictory about the claims "X is simultaneous with Y in frame A" and "X is not simultaneous with Y in frame B".

In general this is upheld, but in the "relativity of simultaneity" it is not. One observer says events AC and BD were not simultaneous, another says they were. This is logically unacceptable.

No, neither observer claims they were or weren't simultaneous in any absolute sense, they both agree the events were simultaneous in one frame and non-simultaneous in another. This is no more logically contradictory than the notion that object A can have a larger x-coordinate than object B in a coordinate system with the origin at one position and the axes oriented at a particular angle but object B can have a larger x-coordinate than object A in a different coordinate system with the origin at a different position and the axes oriented differently (a situation which can be true in Newtonian physics, and even in ordinary algebraic geometry).

This tells me that there is something special about either the "local frame" E that I described earlier or that there is some other "special" frame.

So now you are back to saying there is such a thing as absolute simultaneity? Why? And if so, do you at least admit that there's no reason to think that the preferred frame needs to be the one where the lightning strikes were simultaneous, since as I said before in post #82:

Even if one believes in some sort of Lorentz ether theory where one frame's measurements are objectively correct and all other frames are distorted by the fact that their rulers are objectively shrunk and their clocks objectively slowed down and objectively out-of-sync, it is still perfectly possible that the observers on the ground were the ones at rest in this preferred frame while the train was moving relative to it, and thus the strikes really did happen at different times in an objective sense.

You do not misunderstand. If you have a single set of distances from your eraser to every other entity in the universe the eraser is motionless by definition.

So if even a single object in the universe has a changing distance from the eraser, the eraser is not motionless? Does this mean the only way for any object to be motionless is if every single object in the universe is at rest relative to every other object?

I argue that it is illogical for two observers to ascribe diametrically opposed qualities to any observation.

Why? If the qualities are coordinate-dependent ones, why is it problematic that there could be disagreements on which object has a greater value of the quality depending on which coordinate system is used? Again, even in simple plane geometry different coordinate systems can disagree on which of two points on the plane has a larger x-coordinate. Likewise, in one coordinate system two objects may share the same x-coordinate, while in another coordinate system they may have two different x-coordinates...how is this fundamentally different than the idea that in one frame two events may share the same t-coordinate (i.e. they are simultaneous in that frame) while in another frame the same events may have different t-coordinates (i.e. they are non-simultaneous in that frame)?

 

[jefswat]

So if even a single object in the universe has a changing distance from the eraser, the eraser is not motionless? Does this mean the only way for any object to be motionless is if every single object in the universe is at rest relative to every other object?

You have beaten me to the punch. While there may be nothing logically wrong with altonhare's definition of motion, it has no predictive power, explain's less than SR, and is utterly useless. Based on Quantum Mechanics and the Heisenburg (sp?) uncertianty principle we don't even know where any single particle may be, let alone everyone in the universe. Further more unless altonhare has a very good refidgerator that no one has ever seen before I don't think the word motionless has any interesting meaning within his framework (a pity, I am rather fond of the word). Further more, I challenge altonhare to explain, with his theory, how my eraser appears motionless to me without using relativity or even the word or concept of relativity. It can not be done which leads us back to Einstein and our friend relativity.

 

[Saw]

Lay it on us. Maybe someone will learn something by pointing out the author's fallacy or others will learn something by seeing it pointed out. The story may be fun also.

Hope so. The story is substantially equivalent to Althonhare's, but it has two advantages: (i) the author's interpretation, which is wrong, is based on the "multiple reality” approach that we contest and it clashes with a sound, less “fantastic” understanding of SR and (ii) its display gives occasion to discuss some issues that are not purely conceptual, but might have relevant practical consequences.

It is the well known story introduced by Brian Greene in the Fabric of the Cosmos. I loved the book and very much respect the author, but he seems to be wrong in this point.

Let me explain it with some adaptations:

There is a duel on a train, between duellers that we will call Back and Front, situated at the tail and the tip of the car, respectively. For their duel, they employ laser guns, of identical construction.

There are two referees: Althonhare, on the train, and myself, Saw, on the ground. The signal for the commencement of the duel is given at the precise instant when Althon and myself are lined up. Of course, it is impossible that the two referees occupy the same position in space and so the perception of this alignment would require light traveling some distance from one to the other. But we stipulate that the distance is so small that its consequences are negligible. We all agree that the alignment (which is a single event) is simultaneous in both frames.

In order to give the duellers the signal for shooting, a pile of gunpowder, set midway between them (i.e., where Althon, on the car, and myself, on the ground, are standing at that instant), explodes and thus sends flashes of light in both directions.

Was the duel fair?

Each referee has a different opinion:

* Althon is certain that light from the flare reaches the duelers simultaneously, so he raises the green flag and declares it a fair draw.

[More technically: In the train frame, the light pulses travel equal paths in their respective directions and do it at the same speed. So the two distant events (= arrival of the signals to shoot) are SIMULTANEOUS.)

* According to the author, I wildly squeal foul play, claiming that Back got the light signal from the explosion before Front did. I explain that, because the train was moving forward, Back was heading toward the light while Front was moving away from it. This means that the light did not have to travel quite as far to reach Back, since he moved closer to it; moreover, the light had to travel farther to reach Front, since he moved away from it. Since the speed of light, moving left or right from anyone’s perspective, is constant, I am supposed to claim that it took the light longer to reach Front, since it had to travel farther, rendering the duel unfair.

[Idem: In the ground frame, light towards Back travels a shorter path, since its target is heading towards it, while light towards Front travels a longer path, since its target is escaping away. As both pulses travel at the same speed, the one that hits Back arrives earlier than the one that hits Front. The two distant events are NOT SIMULTANEOUS.]

Who is right? The matter is not trivial, because the judge who has made a mistake will be sanctioned by the competent supervision body and he may not be able to exercise his profession any more.

Fortunately (?), Einstein comes to the rescue of both with a salomonic opinion:

“Einstein’s unexpected answer is that they both are (…) they simply have different perspectives on the same sequence of events. The shocking thing that Einstein revealed is that their different perspectives yield different but equally valid claims of what events happen at the same time. Of course, at everyday speeds like that of the train, the disparity is small – Saw claims that Front got the light less than a trillionth of a second after Back- but were the train moving faster, near light speed, the time difference would be substantial” (literal quotation, I just changed the names).

But I am a prudent referee. I try to do my job properly. I know that the words of the law (you shall raise a green flag if the duel is “fair”) have a practical purpose and I must interpret them in the light of this practical purpose. The duel is “fair” if the two duelers are given equal opportunities of hitting each other, in practical terms. So my opinion that “Back got the signal earlier” is only relevant for the matter to be judged if it gives Back a real advantage (or disadvantage!).

To this effect, I consider the following scenarios:

(a) Back sees the signal earlier and fires earlier as well. Can his laser pulse hit Front before the latter receives the signal?

(b) If not, they have both received the signals and shot their laser pulses. The latter will also take some time to reach their targets. During this time interval, theoretically, any dueler could try the usual trick: fire and stand aside, before being wounded. There is very little time for this deed, especially if we talk about laser guns, but we can imagine the distance arbitrary long for this purpose. Is this time interval longer for Back then for Front or vice versa?

(c) If not, we imagine Back badly wounded, kneeling on the floor of the car, but brave enough to fire a second shot. Can it reach Front before the latter has the opportunity to fire his own second shot…?

You can think of other scenarios if you wish. The more, the better. That is the point of the exercise.

Then I call a group of experts on SR and ask their answers to the practical questions. If the answers, as I expect, are negative (there is no breach of the principle of equal opportunities), then I do not “wildly squeal foul play” as Brian Greene suggests. Instead, I gently and gallantly raise a green flag, in agreement with Althonhare’s opinion. Consequently, I keep my job, anyhow, but at the same time with a clear conscience, because I’ve done a good job. Brian, in turn, keeps being a wonderful scientist but does not promote any more bold philosophical interpretations of SR.

 

[matheinste]

Can't we stick to the physics. All this stuff is quite unecessary and takes up time. The physics is very simple. I personally don't have the time to play out theatrical scenarios and so will take no more part in discussing them. My time would be better spent enhancing the limited knowledge i already have. Altonhare is incorrect as far as SR is concerned. Almost everyone agrees on that. If we cannot argue the physics sensibly without stories and getting sidetracked then count me out.

Matheinste.

 

[Saw]

Can't we stick to the physics. All this stuff is quite unecessary and takes up time. The physics is very simple.

Mathe, there are two levels at which all this (and if you take the time to study it, you will agree) may be highly relevant to physics in general and to the physics of the case in particular:

(i) To physics: There's a widespread opinion that physics has nothing to do with common sense and logic. "The universe is as it is and full stop", is the motto. In the realm of SR this view is unfortunately even more habitual. I think we do a great favour to SR, which is a beautifully true theory, if we reconcile it with common sense. Not with old common prejudices that were unjustified, as logic has proved, but with common sense truths that have succesfully resisted a most rigorous logical test.

(ii) To the phsyics: It is my humble opinion that, for example, if the duellers had used conventional guns, instead of laser guns, the solution is more complicated. In principle, SR gives the same solution for both cases: laser and conventional guns. But I have some doubts I would like to share. Maybe JesseM and others fully and convincingly dismiss my concerns, but in the meantime we will have had an enlightening discussion.

So, no need to move us to the metaphysical realm, for the time being…

 

[matheinste]

Hello w
saw.

Quote:-
----(i) To physics: There's a widespread opinion that physics has nothing to do with common sense and logic. In the realm of SR this view is unfortunately even more habitual. I think we do a great favour to SR, which is a beautifully true theory, if we reconcile it with logic.----

Physics in SR often goes against common sense in the sense that it is often counter intuitive. This is at the heart of the problem for beginners like myself. We must not hold on to our preconceived ideas when we swithc to SR. Physics has everything to do with logic. If you do not accept logical reasoning then anything can be accepted as true. Of course, on the other hand you must, having accepted a set of axioms, which of course in themselves may or not be true, you must accept the logical consequences of those axioms.

As to the scenarios used to illustrate the question of simultaneity, the normal train and embankment observer eaxample is simple and adequate for its purpose. Why introduce more complex examples to illustrate a consequence of the axioms of SR. It is a teaching aid. More complicated examples which are of the nature of a puzzle may be a useful excercise for the more competent student, as finding a resolution to the posed scenario can at that stage be a test of a thorough understanding of the principles involved. But in this case we are arguing the basics and if someone cannot understand and accept the basic principles how can they work out a resolution to the more puzzling examples.

Matheinste.

 

[JesseM]

Hope so. The story is substantially equivalent to Althonhare's, but it has two advantages: (i) the author's interpretation, which is wrong, is based on the "multiple reality” approach that we contest and it clashes with a sound, less “fantastic” understanding of SR and (ii) its display gives occasion to discuss some issues that are not purely conceptual, but might have relevant practical consequences.

It is the well known story introduced by Brian Greene in the Fabric of the Cosmos. I loved the book and very much respect the author, but he seems to be wrong in this point.

Let me explain it with some adaptations:

There is a duel on a train, between duellers that we will call Back and Front, situated at the tail and the tip of the car, respectively. For their duel, they employ laser guns, of identical construction.

There are two referees: Althonhare, on the train, and myself, Saw, on the ground. The signal for the commencement of the duel is given at the precise instant when Althon and myself are lined up. Of course, it is impossible that the two referees occupy the same position in space and so the perception of this alignment would require light traveling some distance from one to the other. But we stipulate that the distance is so small that its consequences are negligible. We all agree that the alignment (which is a single event) is simultaneous in both frames.

In order to give the duellers the signal for shooting, a pile of gunpowder, set midway between them (i.e., where Althon, on the car, and myself, on the ground, are standing at that instant), explodes and thus sends flashes of light in both directions.

Was the duel fair?

Each referee has a different opinion:

* Althon is certain that light from the flare reaches the duelers simultaneously, so he raises the green flag and declares it a fair draw.

[More technically: In the train frame, the light pulses travel equal paths in their respective directions and do it at the same speed. So the two distant events (= arrival of the signals to shoot) are SIMULTANEOUS.)

* According to the author, I wildly squeal foul play, claiming that Back got the light signal from the explosion before Front did. I explain that, because the train was moving forward, Back was heading toward the light while Front was moving away from it. This means that the light did not have to travel quite as far to reach Back, since he moved closer to it; moreover, the light had to travel farther to reach Front, since he moved away from it. Since the speed of light, moving left or right from anyone’s perspective, is constant, I am supposed to claim that it took the light longer to reach Front, since it had to travel farther, rendering the duel unfair.

[Idem: In the ground frame, light towards Back travels a shorter path, since its target is heading towards it, while light towards Front travels a longer path, since its target is escaping away. As both pulses travel at the same speed, the one that hits Back arrives earlier than the one that hits Front. The two distant events are NOT SIMULTANEOUS.]

Who is right? The matter is not trivial, because the judge who has made a mistake will be sanctioned by the competent supervision body and he may not be able to exercise his profession any more.

Fortunately (?), Einstein comes to the rescue of both with a salomonic opinion:

“Einstein’s unexpected answer is that they both are (…) they simply have different perspectives on the same sequence of events. The shocking thing that Einstein revealed is that their different perspectives yield different but equally valid claims of what events happen at the same time. Of course, at everyday speeds like that of the train, the disparity is small – Saw claims that Front got the light less than a trillionth of a second after Back- but were the train moving faster, near light speed, the time difference would be substantial” (literal quotation, I just changed the names).

But I am a prudent referee. I try to do my job properly. I know that the words of the law (you shall raise a green flag if the duel is “fair”) have a practical purpose and I must interpret them in the light of this practical purpose. The duel is “fair” if the two duelers are given equal opportunities of hitting each other, in practical terms. So my opinion that “Back got the signal earlier” is only relevant for the matter to be judged if it gives Back a real advantage (or disadvantage!).

To this effect, I consider the following scenarios:

(a) Back sees the signal earlier and fires earlier as well. Can his laser pulse hit Front before the latter receives the signal?

No. If two events are simultaneous in any frame, that must mean there is a spacelike separation between the two events, meaning neither event lies in the other event's future light cone.

(b) If not, they have both received the signals and shot their laser pulses. The latter will also take some time to reach their targets. During this time interval, theoretically, any dueler could try the usual trick: fire and stand aside, before being wounded. There is very little time for this deed, especially if we talk about laser guns, but we can imagine the distance arbitrary long for this purpose. Is this time interval longer for Back then for Front or vice versa?

Same time for both, since they're both at rest in the train frame, and they both fire at the same moment in this frame.

You can think of other scenarios if you wish. The more, the better. That is the point of the exercise.

Well, you could imagine a modified scenario where Front was at rest on the ground along with the referee, at just the right position so he happened to be right next to the front of the train when the light from the gunpowder explosion reached it. In this case, although Back and Front fire simultaneously in the train rest frame, in this frame Front is moving towards Back (and his clock is slowed down by time dilation), so Front has less time to step out of the way of Back's laser beam.

Then I call a group of experts on SR and ask their answers to the practical questions. If the answers, as I expect, are negative (there is no breach of the principle of equal opportunities), then I do not “wildly squeal foul play” as Brian Greene suggests. Instead, I gently and gallantly raise a green flag, in agreement with Althonhare’s opinion. Consequently, I keep my job, anyhow, but at the same time with a clear conscience, because I’ve done a good job. Brian, in turn, keeps being a wonderful scientist but does not promote any more bold philosophical interpretations of SR.

I think in Greene's scenario the point of the referees was just to judge whether both fired their lasers at the same time, not to judge whether the scenario was fair overall--it was really just a thought-experiment to illustrate the relativity of simultaneity, after all.

 

[Saw]

Well, you could imagine a modified scenario where Front was at rest on the ground along with the referee, at just the right position so he happened to be right next to the front of the train when the light from the gunpowder explosion reached it. In this case, although Back and Front fire simultaneously in the train rest frame, in this frame Front is moving towards Back (and his clock is slowed down by time dilation), so Front has less time to step out of the way of Back's laser beam.

That's another thought-experiment. I was asking about practical reasons why the duel might be fair for one frame and unfair for the other frame, in the original thought-experiment. The new configuration you mention is interesting but it is not "analogous". It raises a totally different discussion, which we could discuss somewhere else.

I think in Greene's scenario the point of the referees was just to judge whether both fired their lasers at the same time, not to judge whether the scenario was fair overall--it was really just a thought-experiment to illustrate the relativity of simultaneity, after all.

To go step by step, do you agree that the game was fair and that I should have raised the green flag?

 

[JesseM]

That's another thought-experiment. I was asking about practical reasons why the duel might be fair for one frame and unfair for the other frame, in the original thought-experiment. The new configuration you mention is interesting but it is not "analogous". It raises a totally different discussion, which we could discuss somewhere else.

OK, I misunderstood what you meant by "you can think of other scenarios if you wish". I wouldn't say that considering the same physical situation in a different frame is a new "scenario", it's just a different perspective on the same scenario.

To go step by step, do you agree that the game was fair and that I should have raised the green flag?

I agree the game was fair, but if your job was just to judge if the two guns were fired simultaneously in your frame, then you should not have raised the green flag because they weren't. You seem to be overthinking this, Greene really was just trying to explain about simultaneity, he wasn't making any more subtle point about the game being "fair" in one frame and "unfair" in another.

 

[Saw]

OK, I misunderstood what you meant by "you can think of other scenarios if you wish". I wouldn't say that considering the same physical situation in a different frame is a new "scenario", it's just a different perspective on the same scenario.

As Dalespam usually observes, conventional language (English or Spanish) is tricky. I say "scenario" having one meaning in mind and you read having a different meaning in mind. I have consulted my dictionary and both meanings could be acceptable. In every day language, my view (just a different plot in the same stage) might be the rule. But in specialised scientific language you admit that a different scenario may include a change of physical situation. And, by the way, in my own language, “escenario” means “stage”!

I say this because it “illustrates” very well the problems we face in our discussion. We have to be patient with one another because language will constantly play tricks on us.

But it is team work and it may be rewarding, because it may help us to better understand what our formulas and diagrams mean. Mathematics is a wonderful tool. You put concepts among its wheels, you switch on the machinery and the automat produces by itself amazing new concepts you had never thought of. However, mathematical language is not immune to the same problem: you have to understand very well the concepts with which you feed the automat. Otherwise, it may produce wrong predictions.

I agree the game was fair, but if your job was just to judge if the two guns were fired simultaneously in your frame, then you should not have raised the green flag because they weren't.

My job, as a judge, can never be just to judge if the two guns were fired simultaneously “in my frame”. My job is to make justice and I only do that if I declare the duel fair. Let us imagine that the legislator has read a little about SR, but has misunderstood it. So he has written “you shall raise the green flag if the two guns are fired simultaneously in your frame, but only in your frame, my friend”. Wouldn’t you agree that this law is defective, because it doesn’t understand how the universe works, as taught by physics? Wouldn’t you be forced, as a physic, to stand up and demand that it is amended?

You seem to be overthinking this, Greene really was just trying to explain about simultaneity, he wasn't making any more subtle point about the game being "fair" in one frame and "unfair" in another.

Yes, I overthink everything… But I don’t want to personalize on anybody and less on Brian Greene, whose writings are delicious.

If he was just describing how relativity of simultaneity is measured, without making any more subtle point, that is perfect. So we agree that the duel was fair in both frames, without forgetting what this means: this illustrates that the “discrepancy” on measurements, the relativity of simultaneity, does not entail any discrepancy at all on what may happen or may not. The film of life (reality) will be the same anyhow. I know you agree with that. But let me rhetorically ask “right?”, so that you can say “so what?”.

 

[Saw]

Physics has everything to do with logic. If you do not accept logical reasoning then anything can be accepted as true.

Hello, mathe. I fully agree.

Of course, on the other hand you must, having accepted a set of axioms, which of course in themselves may or not be true, you must accept the logical consequences of those axioms.

That is the question. You can do a better thing. You may try to grasp a better understanding of the axioms, so as to refine their meaning. This will ensure that, when you put them into the blind automat (math, geometry or logical reasoning with English), the outcome is a beautiful baby instead of a monster. That is what we are trying to do here. Although I admit it is sometimes a painful job, because words are devils!

 

[JesseM]

My job, as a judge, can never be just to judge if the two guns were fired simultaneously “in my frame”. My job is to make justice and I only do that if I declare the duel fair. Let us imagine that the legislator has read a little about SR, but has misunderstood it. So he has written “you shall raise the green flag if the two guns are fired simultaneously in your frame, but only in your frame, my friend”. Wouldn’t you agree that this law is defective, because it doesn’t understand how the universe works, as taught by physics? Wouldn’t you be forced, as a physic, to stand up and demand that it is amended?

Yeah, I agree that the law would be no good, since what's really important for the game to be "fair" is that they both have an equal amount of time on their own clocks (proper time) between firing their own gun and being hit by (or dodging) the other guy's laser.

Yes, I overthink everything… But I don’t want to personalize on anybody and less on Brian Greene, whose writings are delicious.

If he was just describing how relativity of simultaneity is measured, without making any more subtle point, that is perfect. So we agree that the duel was fair in both frames, without forgetting what this means: this illustrates that the “discrepancy” on measurements, the relativity of simultaneity, does not entail any discrepancy at all on what may happen or may not. The film of life (reality) will be the same anyhow. I know you agree with that. But let me rhetorically ask “right?”, so that you can say “so what?”.

Right, no disagreement here, and the fact that there's no disagreement about coordinate-independent facts like the proper time between two events on an observer's worldline is a key thing to understand when thinking about these kinds of thought-experiments.

 

[atyy]

Wow, relativistic jurisprudence!

 

[Saw]

the fact that there's no disagreement about coordinate-independent facts like the proper time between two events on an observer's worldline is a key thing to understand when thinking about these kinds of thought-experiments.

Hm... It seems you didn’t want to express full agreement with my statement. May you have some reservation or am I overthinking again?

On the one hand, you confirm that observers cannot disagree on coordinate-independent facts like proper time. Ok. Whenever two observers from different frames meet, they look at their respective clocks and find discrepancy in their respective proper times. What is the fact here? That the clocks show different readings and in that the observers fully agree. So far so good.

On the other hand, do you imply, sensu contrario, that they could disagree on purported coordinate-dependent "facts"? The key word here is "facts", that is to say, reality, happenings, events. After revising the story, I do not find any coordinate-dependent "facts", but only coordinate-dependent concepts, concepts (i) in whose manufacturing process facts intervene, though the observers also agree upon the occurrence of those facts, one by one, and (ii) which serve to predict future facts, in whose occurrence all observers agree. That is to say, concepts that are “innocuous” for reality.

Take for example the concept of “simultaneity”. The referees pompously disagree on whether the two events were simultaneous or not. That sounds very dramatic, like a very serious matter. In fact, if this had really entailed that the duel was fair or not, it would have been dramatic. But we have discarded this. What is hence the real meaning of the discrepancy as to the simultaneity of the two events (the arrival of the shooting signals to the duellers)?

I would say that this issue of simultaneity is just the beginning of the sentence, but if you look at the whole sentence there isn’t the slightest discrepancy. Our mistake is interrupting the speaker when he has just pronounced the first words of his speech. One referee is saying “my judgment of simultaneity” + “you have TD” + “you have LC” and so is the other. It looks as if their respective statements were contradictory. But when you are patient enough to hear the whole “opinions” you find out, as we have concluded, that both referees have the same damned opinion on what really matters (the duel is fair)!

I think that is a better way to illustrate SR: focus on the general picture, which is one of agreement, instead of on the details, in which there is only an accessory disagreement.

If you agree with this so far, I would move on to retake my failed definition of absolute simultaneity…

 

[Saw]

Wow, relativistic jurisprudence!

Yes, mixing fields is always productive. There is nothing that is really "metaphysical". But that is another war...

 

[ZapperZ]

On the one hand, you confirm that observers cannot disagree on coordinate-independent facts like proper time. Ok. Whenever two observers from different frames meet, they look at their respective clocks and find discrepancy in their respective proper times. What is the fact here? That the clocks show different readings and in that the observers fully agree. So far so good.

On the other hand, do you imply, sensu contrario, that they could disagree on purported coordinate-dependent "facts"? The key word here is "facts", that is to say, reality, happenings, events. After revising the story, I do not find any coordinate-dependent "facts", but only coordinate-dependent concepts, concepts (i) in whose manufacturing process facts intervene, though the observers also agree upon the occurrence of those facts, one by one, and (ii) which serve to predict future facts, in whose occurrence all observers agree. That is to say, concepts that are “innocuous” for reality.

Take for example the concept of “simultaneity”. The referees pompously disagree on whether the two events were simultaneous or not. That sounds very dramatic, like a very serious matter. In fact, if this had really entailed that the duel was fair or not, it would have been dramatic. But we have discarded this. What is hence the real meaning of the discrepancy as to the simultaneity of the two events (the arrival of the shooting signals to the duellers)?

It seems that you appear to not know anything with regards to the concept of "invariance". The fact that such concept (i.e. gauge invariance, etc.) is such an important aspect somehow is rather lost here.

Let's first of all get this very clear. There are plenty of physics, and certainly plenty of experiments, in which things are flying off at very high speeds of varying degree. High energy physics deals with such a thing all the time. Why do you think the values of any of the properties being measured are NEVER under any sense of confusion as far as reconciling observations made in different frames? Do you see values of the mass of various elementary particles, for example, have to be define with a particular frame, even when these particles are typically relativistic?

There is also another aspect that is lost here. Different observers in different frames can transform from one to another. There is no ambiguity. You see heads, I see tails. It doesn't mean that I cannot transform to the other side of the coin to see what you see. It is still the SAME object. It is no longer a big deal that something is simultaneous in one frame but not the other, especially when one can always choose a frame to suit one's needs. We do this in physics all the time to simplify many of our calculation. Many beam dynamics calculation are often done in the "rest frame" of the relativistic particle before transforming the end result back into the lab frame. So where is the problem here?

Zz.

 

[JesseM]

On the other hand, do you imply, sensu contrario, that they could disagree on purported coordinate-dependent "facts"? The key word here is "facts", that is to say, reality, happenings, events. After revising the story, I do not find any coordinate-dependent "facts", but only coordinate-dependent concepts, concepts (i) in whose manufacturing process facts intervene, though the observers also agree upon the occurrence of those facts, one by one, and (ii) which serve to predict future facts, in whose occurrence all observers agree. That is to say, concepts that are “innocuous” for reality.

It seems to me you are using strange personal word-definitions here--for me "coordinate-dependent fact" just means any quantitative judgement that depends on one's choice of coordinate system, I don't mean any deep philosophical implications by the use of the word "fact". If in one coordinate system an event has position coordinate x=5 meters and in another coordinate system the same event has position coordinate x=12 meters, this is a disagreement over coordinate-dependent facts, for example (and one that does not even require that the two coordinate systems are moving relative to one another, just that their origins are placed differently). Similarly, all that a disagreement over simultaneity means is that one coordinate system assigns two events identical t-coordinates while another coordinate system assigns them two different t-coordinates.

Take for example the concept of “simultaneity”. The referees pompously disagree on whether the two events were simultaneous or not. That sounds very dramatic, like a very serious matter.

Does it? To talk about the "seriousness" of a physical claim would seem to involve considerations outside of physics, so this would be more a discussion of philosophy. I suppose the fact that there is no physically preferred definition of simultaneity may have some implications for the debate over presentism vs. eternalism in philosophy (since there is no objective way to decide if two events share the same 'present', causing problems for the notion that only the present 'exists'), but if we get into this we're not talking about physics any more. Just in terms of physics, the meaning of disagreements about simultaneity is just that two events that have the same t-coordinate in one inertial frame can have different t-coordinates in another, and that the laws of physics are symmetrical between inertial frames so there is no physical basis for preferring one over another.

What is hence the real meaning of the discrepancy as to the simultaneity of the two events (the arrival of the shooting signals to the duellers)?

By the "real meaning", you mean the physical meaning defined in terms of actual physical measurements? Do you understand that every inertial coordinate system is physically defined in terms of local readings on a network of rulers and clocks at rest in that coordinate system, which have been synchronized according to the Einstein synchronization convention? With this in mind, the difference in judgments about simultaneity can be summed up by saying that if we have two clocks at either end of the train which have been synchronized in the train's frame using Einstein's convention, they will both read the same time when the lasers are fired next to them, but if we have two clocks on the ground which have been synchronized in the ground frame using Einstein's convention, and both clocks happen to be right next to the two duellers at the moment each fires his laser, then these two clocks will show different times when the lasers are fired next to them.

I would say that this issue of simultaneity is just the beginning of the sentence, but if you look at the whole sentence there isn’t the slightest discrepancy. Our mistake is interrupting the speaker when he has just pronounced the first words of his speech. One referee is saying “my judgment of simultaneity” + “you have TD” + “you have LC” and so is the other. It looks as if their respective statements were contradictory. But when you are patient enough to hear the whole “opinions” you find out, as we have concluded, that both referees have the same damned opinion on what really matters (the duel is fair)!

Why is that what "matters"? Do coordinates assigned to events not matter? Again, you seem to be referring to judgments of importance beyond the scope of physics here.

I think that is a better way to illustrate SR: focus on the general picture, which is one of agreement, instead of on the details, in which there is only an accessory disagreement.

You can't very well solve quantitative problems in SR without having a coordinate system to refer to!

If you agree with this so far, I would move on to retake my failed definition of absolute simultaneity…

Does "absolute simultaneity" mean you think one judgement of simultaneity in this problem might be "correct" while the other is "incorrect"?

 

[Saw]

It seems to me you are using strange personal word-definitions here--for me "coordinate-dependent fact" just means any quantitative judgement that depends on one's choice of coordinate system, I don't mean any deep philosophical implications by the use of the word "fact". If in one coordinate system an event has position coordinate x=5 meters and in another coordinate system the same event has position coordinate x=12 meters, this is a disagreement over coordinate-dependent facts, for example (and one that does not even require that the two coordinate systems are moving relative to one another, just that their origins are placed differently). Similarly, all that a disagreement over simultaneity means is that one coordinate system assigns two events identical t-coordinates while another coordinate system assigns them two different t-coordinates.

OK. If the disagreement is only on the values of measurements, I have no problem with that. You master the terminology, but I don’t. I wanted to be sure the agreement was full.

To talk about the "seriousness" of a physical claim would seem to involve considerations outside of physics, so this would be more a discussion of philosophy. I suppose the fact that there is no physically preferred definition of simultaneity may have some implications for the debate over presentism vs. eternalism in philosophy (since there is no objective way to decide if two events share the same 'present', causing problems for the notion that only the present 'exists'), but if we get into this we're not talking about physics any more.

I personally have no philosophical idea in mind. Just interested in discussing the physics of the case, although it is true that I am quite slow in the introduction.

By the "real meaning", you mean the physical meaning defined in terms of actual physical measurements? Do you understand that every inertial coordinate system is physically defined in terms of local readings on a network of rulers and clocks at rest in that coordinate system, which have been synchronized according to the Einstein synchronization convention? With this in mind, the difference in judgments about simultaneity can be summed up by saying that if we have two clocks at either end of the train which have been synchronized in the train's frame using Einstein's convention, they will both read the same time when the lasers are fired next to them, but if we have two clocks on the ground which have been synchronized in the ground frame using Einstein's convention, and both clocks happen to be right next to the two duellers at the moment each fires his laser, then these two clocks will show different times when the lasers are fired next to them.

Yes, I understand so and the definition is perfect for me.

Do coordinates assigned to events not matter? Again, you seem to be referring to judgments of importance beyond the scope of physics here. You can't very well solve quantitative problems in SR without having a coordinate system to refer to!

Of course. You need a coordinate system and coordinates matter. Since you answer this, it is clear that I am not expressing myself well.

Does "absolute simultaneity" mean you think one judgement of simultaneity in this problem might be "correct" while the other is "incorrect"?

Not at all. Obviously, you have no obligation to have read or to remember my previous posts… You may have a look at them, if you wish. But in any case I think that, so far, we agree on everything. I’ll come back later with a more practical question, closer to the physics of the case. Regards.

 

[Saw]

It seems to me you are using strange personal word-definitions here--for me "coordinate-dependent fact" just means any quantitative judgement that depends on one's choice of coordinate system, I don't mean any deep philosophical implications by the use of the word "fact". If in one coordinate system an event has position coordinate x=5 meters and in another coordinate system the same event has position coordinate x=12 meters, this is a disagreement over coordinate-dependent facts, for example (and one that does not even require that the two coordinate systems are moving relative to one another, just that their origins are placed differently). Similarly, all that a disagreement over simultaneity means is that one coordinate system assigns two events identical t-coordinates while another coordinate system assigns them two different t-coordinates.

Maybe we could try an understanding in this respect, because it is quite fundamental to the argument.

You say I might be handling a "strange personal word-definition" and that you do not mean yourself any "deep philosophical implication” of the word “fact"…

Well, my use of the word “fact” is quite down-to-earth. It is the most obvious meaning contained in the dictionary: “happening, occurrence, incident, event, act, deed”. Maybe I should have said, for consistency with previous comments and also with the specialised language of the theory, an “event”. But you used the word “fact” and to me, in common language, “fact” means “event”, which triggered my alarms.

For example, the hands of a clock at rest in my frame or in your frame reach a certain position. This qualifies as an event, as much as any other happening that takes place outside a measurement instrument.

Is this event “coordinate-dependent”? Not at all. The event in itself, that is to say, the occurrence of the event, is not “coordinate-dependent”. All observers agree that it has happened and could have predicted that it should happen, regardless the frame where the clock is situated. The same consensus applies to the “quantitative aspect”, since that is what the event is, after all: the hands of the clock get aligned with a certain number.

What does depend on “one’s coordinate system” is, yes, the “judgment” that you make. Because the clock is at rest in your frame (i.e., it marks time in your coordinate system), you judge that the clock reading provides you with the time coordinate of the nearby event, while another frame trusts for this purpose the reading of the clock at rest in his frame and in the vicinity of the event. There is discrepancy in this respect, but only on the judgment, not on the event.

If on top of that you find another event with the same time coordinate, you judge that the two events are “simultaneous” in your frame. Any discrepancy on events? No, only on judgments.

That is why I thought that the expression "coordinate-dependent fact" is ambiguous. I would prefer “coordinate-dependent value”, because “value” does convey the idea that the quantitative measurement, which is in itself an uncontroversial event, has a certain “value”, an utility for the measurer: it is a tool that he will combine with other values in order to solve the problem under study. Of course, the outcome of these calculations, as we all know, will not reach to any controversy on what happens, on events. Thus reality, a single reality, is preserved throughout the process.

I may be too punctilious with words, but I am not dreaming any metaphysical dream, just trying to settle solid foundations for discussion.

 

[JesseM]

Well, my use of the word “fact” is quite down-to-earth. It is the most obvious meaning contained in the dictionary: “happening, occurrence, incident, event, act, deed”.

Most people would say it's a "fact" that the word for "cat" in spanish is "gato", even though this is just a statement about a labeling convention in a certain language. Likewise, most people would say it's a "fact" that New York City is at latitude 40° 47' and longitude 73° 58' even though this is just a statement about its position in a certain human-defined coordinate system on the globe. Would you disagree? If so, I suggest that your use of the word "fact" is not, in fact, down-to-earth, but is actually quite idiosyncratic, since I'm sure pretty much everyone else would agree these things are straightforward facts. And if you would agree that these things are "facts", it's hard to understand why you wouldn't also agree that statements about coordinates of events in certain inertial coordinate systems are "facts".

That is why I thought that the expression "coordinate-dependent fact" is ambiguous. I would prefer “coordinate-dependent value”, because “value” does convey the idea that the quantitative measurement, which is in itself an uncontroversial event, has a certain “value”, an utility for the measurer: it is a tool that he will combine with other values in order to solve the problem under study. Of course, the outcome of these calculations, as we all know, will not reach to any controversy on what happens, on events. Thus reality, a single reality, is preserved throughout the process.

I may be too punctilious with words, but I am not dreaming any metaphysical dream, just trying to settle solid foundations for discussion.

Since "fact" is not a technical term with a rigorous meaning, I'm fine with defining "fact" and "value" however you prefer for the sake of this discussion. But again, if you're going to bring in your own idiosyncratic word-definitions that don't match how most people use language, you really need to explain your own definitions beforehand, rather than dispute statements by other people that use them in a more typical way without even explaining your own alternate definitions first, as this will just tend to cause confusion and miscommunications.

 

[altonhare]

Quote:-
---I argue that, although the definition(s) you present seem reasonable, because they lead to a logical contradiction we conclude they are unacceptable. -----

Yes, the definition of absolute simultaneity does lead to logical contradictions in SR. That is exactly the point i was making.

I think you misunderstand. An event, action, or entity cannot be both "X" and "not X", even from different perspectives. You hang from the ceiling and see heads on a coin, I lay on the floor and see tails. There is no contradiction here. I see tails and you see heads, neither of us disagree on these statements. If you're falling and I'm lying still we may disagree on how fast the coin is moving or how long it is. We will not disagree that it IS moving, that it is moving away from the floor (no matter how you look at it, the distance between the coin and the floor increases at successive instants), that it is moving towards the ceiling, etc.

----One observer says events AC and BD were not simultaneous, another says they were. This is logically unacceptable. ----

It is completely logical within SR. In fact it is fundamental. No one has to accept SR but if you do accept the light axiom of SR then you MUST accept the relativity of simultaneity. This is not just an opinion. The relativity of simultaneity follows as a logical consequence of the speed of light being the same in all inertial frames.

If it is the conclusion of SR that AC and BD were both simultaneous and non-simultaneous, regardless of frame, this is the definition of illogical. Both "X" and "not X".

Quote:-
----You do not misunderstand. If you have a single set of distances from your eraser to every other entity in the universe the eraser is motionless by definition.----

Every "entity" at any point in time has a single set of distances from any and all other "entities". So by the above definition everything is always at rest. However my concern is with simultaneity. you can philosophise as much as you like but given an a set of axioms such as in SR you cannot argue against a consequence which follows logcally from these axioms. If you do not like the axioms then, fair enough, just say so. That is perfectly acceptable.

Matheinste

Yes, at every instant every entity is "at rest" by definition. An object cannot move in an instant by definition. Motion necessarily requires at least two locations. Nature does not recognize motion. An object looks at itself and says,"I just have location." It is humans, with memory for where something was, that infer motion and time. In the absence of conscious observers the universe is timeless.

But the last three don't make sense except in the context of a particular reference frame, since different frames can disagree on which of two objects move faster, which of two objects is longer, and whether two spatially separated collisions happened at the same moment.

O1 and O2 are both motionless relative to each other while A and B speed away from both. They should both reach the same conclusions, of course. They say that A is longer than B and B is moving faster than A. O2 moves backwards (accelerating gently, let's stay within SR at least for now) and both A and B contract. O2 still concludes that A is longer than B and that B is moving faster than A. O2 just thinks O1, A, and B are all moving away from him/her now and calculates higher velocities for all of them, but nothing changes qualitatively.

And nothing should, logically.

It's only a logical contradiction if you neglect to include the context of what reference frame you're talking about, which is always necessary for any physical claims which don't concern purely local events in SR. For example, there is nothing contradictory about the claims "X is simultaneous with Y in frame A" and "X is not simultaneous with Y in frame B".

No matter what "frame" you're in, there are no ontological contradictions.

No, neither observer claims they were or weren't simultaneous in any absolute sense, they both agree the events were simultaneous in one frame and non-simultaneous in another. This is no more logically contradictory than the notion that object A can have a larger x-coordinate than object B in a coordinate system with the origin at one position and the axes oriented at a particular angle but object B can have a larger x-coordinate than object A in a different coordinate system with the origin at a different position and the axes oriented differently (a situation which can be true in Newtonian physics, and even in ordinary algebraic geometry).

But observers in rotated coordinate systems are not all talking about length. One is talking about length, another width, another height, and still another is talking about extent in a direction between these. There is no contradiction because they are not all talking about length.

On the other hand, with regards to simultaneity, the situation is not so. While an entity can have extent in 3 mutually perpendicular directions, there are not "different kinds" of simultaneity. There is simultaneous and there is not simultaneous.

So now you are back to saying there is such a thing as absolute simultaneity? Why? And if so, do you at least admit that there's no reason to think that the preferred frame needs to be the one where the lightning strikes were simultaneous, since as I said before in post #82:

I'll concede that there's no reason to think that the local frame "E" is special.

So if even a single object in the universe has a changing distance from the eraser, the eraser is not motionless? Does this mean the only way for any object to be motionless is if every single object in the universe is at rest relative to every other object?

Exactly. The only way for any entity to be motionless is for every entity to be motionless. And, in this case, it is impossible for one to "conclude" that something is motionless because this is necessarily an action that requires motion.

I'll come back to the "absolute simultaneity" issue you raised a little further down, where it'll make more sense.

Why? If the qualities are coordinate-dependent ones, why is it problematic that there could be disagreements on which object has a greater value of the quality depending on which coordinate system is used?

You say the "greater value of the quality". We can talk about greater or lesser values of quantities, but not qualities. Qualities are an either or situation.

As I said, in different coordinate systems observers are not all talking about length. They may disagree about the precise quantity of the length, but never on a qualitative issue such as "Does A HAVE length?" or "Is A longer than B?".

You have beaten me to the punch. While there may be nothing logically wrong with altonhare's definition of motion, it has no predictive power, explain's less than SR, and is utterly useless. Based on Quantum Mechanics and the Heisenburg (sp?) uncertianty principle we don't even know where any single particle may be, let alone everyone in the universe. Further more unless altonhare has a very good refidgerator that no one has ever seen before I don't think the word motionless has any interesting meaning within his framework (a pity, I am rather fond of the word). Further more, I challenge altonhare to explain, with his theory, how my eraser appears motionless to me without using relativity or even the word or concept of relativity. It can not be done which leads us back to Einstein and our friend relativity.

If you conclude the eraser is motionless it is due to faulty logic. If you use the definitions I have presented you will not be led astray. You can say "it looks motionless" all you want but this will not stand up to any degree of scrutiny. Indeed, to even have the thought "it's motionless" dynamic processes had to occur in your brain that debunk your conclusion. Your "eraser is motionless" conclusion is superficial.

refidgerator?

This isn't the quantum forum, but with regards to the indeterminacy principle I will say just a few words. The uncertainty in velocity (m=1 for simplicity) and position is not surprising or illogical. Qualitatively it is saying that "when an entity moves it doesn't sit still and when it sits still it doesn't move". It is impossible to assign a single location to that which is moving (by the definition of motion). It is impossible to assign a velocity to that which has a single location (by definition). The mathematical framework that correlates the world well incorporates the fundamental constant h into deriving a way to assign an "average location" to a moving entity because it is useful to know "about" where something is. The IP doesn't contradict locality, it supports it.

Most people would say it's a "fact" that the word for "cat" in spanish is "gato", even though this is just a statement about a labeling convention in a certain language. Likewise, most people would say it's a "fact" that New York City is at latitude 40° 47' and longitude 73° 58' even though this is just a statement about its position in a certain human-defined coordinate system on the globe. Would you disagree? If so, I suggest that your use of the word "fact" is not, in fact, down-to-earth, but is actually quite idiosyncratic, since I'm sure pretty much everyone else would agree these things are straightforward facts. And if you would agree that these things are "facts", it's hard to understand why you wouldn't also agree that statements about coordinates of events in certain inertial coordinate systems are "facts".

Since "fact" is not a technical term with a rigorous meaning, I'm fine with defining "fact" and "value" however you prefer for the sake of this discussion. But again, if you're going to bring in your own idiosyncratic word-definitions that don't match how most people use language, you really need to explain your own definitions beforehand, rather than dispute statements by other people that use them in a more typical way without even explaining your own alternate definitions first, as this will just tend to cause confusion and miscommunications.

I'll give "fact" a rigorous meaning. I think we need to distinguish between "facts" and "statements of facts". To understand a "fact" we need to understand the concept of the "Universal Movie". Imagine you can take a picture of the entire universe from afar. The Universal Movie is a series of such photographs of every entity at a location. In each photograph an entity only has shape and location. The semblance of motion and time is provided by the incessant flowing of frames that contain each entity. The reason sentient beings perceive motion is that we can store in our memory previous frames of the movie.

A fact, then, consists of a particular clip of the Universal Movie with nothing taken out. In other words, it contains every minute detail of what actually happened irrespective of observers. A fact consists of an uninterrupted sequence of locations of every entity in the universe.

A "statement of the facts", on the other hand, is like a regular movie. There are only selected collections of frames from the UM spliced together. We see what the presenter considers the "interesting parts". This is akin to regular movies where we don't typically see the mundane day to day activities of a regular Joe, most of this is taken out because it is irrelevant to the main point the presenter is attempting to communicate.

So, whereas a fact is an uninterrupted series of the original film, a statement of the facts includes a description of key parts of an entity(ies) that the presenter believes is necessary for the audience to keep specifically in mind in order to understand the presentation/theory.

A "testimonial" is someone's concise summary of particular parts of the Universal Movie. If the clips the person presents matches exactly the corresponding frames in the Universal Movie, we call it, by definition, "truth". Otherwise, by definition, it is called a "lie". Truth and lies have nothing to do with intentions or opinions, but whether it matches what actually happened. Humans can only opine whether testimonials are true.

In science, evidence must consist solely of parts of the genuine Universal Movie, such as a bone found in a layer of the earth. Testimonials are not allowed, the only evidence is the real thing. It is a collection of genuine, scattered fragments of the facts/UM. A bone comprises but a few frames in the immense Universal Movie. The interpretation of the bone, on the other hand, is necessarily a "statement of the facts". An opinion presented in the form of an assumption. This the presenter expects you to take at face value, it is not in contention. What IS in contention is the theory that follows, which is based on the assumption.

For example, a knife with fingerprints on it is evidence. It just so happens, as a fact, that the fingerprints match Johnny's. Whether Johnny actually touched the knife is a statement of the facts. Legally this conclusion is treated as fact, as evidence, because it is reasonable from our experience. However, in science, we must treat this as an assumption. A reasoned statement from a person is not the same as evidence/fact itself, it is not equivalent to the frames in the UM where some event actually occurred. It is not the same for a bottle to be on the table as for someone to say the bottle is on the table. The former is a fact and the latter is a statement of the facts.

So, with regards to "absolute simultaneity". We cannot be in disagreement about qualitative aspects, i.e. facts. Such as "Are the fingerprints on the knife or not?" Technically this is a statement of the facts, the knife itself is the collection of facts. We can disagree on quantitative aspects: "What is the probability that Johnny has a hidden twin brother, or cloned himself, or ...?" This depends on an individual's experience, reasoning, and perspective. If we cannot agree on qualitative aspects we cannot get to quantitative aspects because such questions have no meaning. What can it mean to ask the chances of Johnny's prints getting on the knife by X mechanism if you disagree with the facts, that his prints are on the knife? These are binary decisions.

So, how do we "know" if AC and BD were "really" simultaneous? We would have to see the entire UM for the event. I would need the successive locations of every entity in the universe. If, in the same frame, A is in contact with C and B is in contact with D, they were simultaneous.

 

[Doc Al]

I think you misunderstand. An event, action, or entity cannot be both "X" and "not X", even from different perspectives.

Of course it can, depending upon the nature of "X".

You hang from the ceiling and see heads on a coin, I lay on the floor and see tails. There is no contradiction here. I see tails and you see heads, neither of us disagree on these statements.

Looks like you just contradicted yourself by giving a counter-example to your initial claim.

If it is the conclusion of SR that AC and BD were both simultaneous and non-simultaneous, regardless of frame, this is the definition of illogical. Both "X" and "not X".

Nonsense. What would be a contradiction would be if relativity claimed that two events were both simultaneous and non-simultaneous from the same frame.

 

[jefswat]

If you conclude the eraser is motionless it is due to faulty logic. If you use the definitions I have presented you will not be led astray. You can say "it looks motionless" all you want but this will not stand up to any degree of scrutiny. Indeed, to even have the thought "it's motionless" dynamic processes had to occur in your brain that debunk your conclusion. Your "eraser is motionless" conclusion is superficial.

"You can say "it looks motionless" all you want but this will not stand up to any degree of scrutiny."

If that statement is sound, then the following will be sound. replace motionless with "traveling at 299,792,458 m/s" and it (which represents my eraser) with "a photon of light".

"You can say "a photon of light looks like its traveling at 299,792,458 m/s" all you want but this will not stand up to any degree of scrutiny."

I believe that has stood up to quite a bit of scrutiny. You are saying the speed of light being constant in a vacuum is superficial. I think it is you making conclusions based on faulty logic. The constancy of the speed of light leads us to SR which leads us to time dialations and length contractions which necessarily leads us to the conclusion that two observers will disagree on what IS simultaneous based on their frame of reference

 

[altonhare]

Of course it can, depending upon the nature of "X".

Looks like you just contradicted yourself by giving a counter-example to your initial claim.

Wrong. You agree that I see heads. I agree that you see tails. I agree that I see tails. You agree that you see heads.

Nonsense. What would be a contradiction would be if relativity claimed that two events were both simultaneous and non-simultaneous from the same frame.

In any frame two observers cannot come to diametrically opposite conclusions. This is logically inadmissable. In the coin example I don't conclude "the coin IS heads", that doesn't make any sense. I conclude,"I see heads." You conclude that I see heads too.

"You can say "it looks motionless" all you want but this will not stand up to any degree of scrutiny."

If that statement is sound, then the following will be sound. replace motionless with "traveling at 299,792,458 m/s" and it (which represents my eraser) with "a photon of light".

"You can say "a photon of light looks like its traveling at 299,792,458 m/s" all you want but this will not stand up to any degree of scrutiny."

You replaced a qualitative statement with a quantitative one, a difference I have been repeatedly harping on. The incident issue is motionless versus in motion, not quantitative velocity/speed.

Everything you said after was an irrelevant straw man.

 

[Doc Al]

In any frame two observers cannot come to diametrically opposite conclusions. This is logically inadmissable.

Right. So what point were you trying to make here?

If it is the conclusion of SR that AC and BD were both simultaneous and non-simultaneous, regardless of frame, this is the definition of illogical. Both "X" and "not X".

In relativity, simultaneity of events is frame-dependent.

 

[jefswat]

So, how do we "know" if AC and BD were "really" simultaneous? We would have to see the entire UM for the event. I would need the successive locations of every entity in the universe. If, in the same frame, A is in contact with C and B is in contact with D, they were simultaneous.

So you are saying the frame from which we see the UM is special

 

[JesseM]

But the last three don't make sense except in the context of a particular reference frame, since different frames can disagree on which of two objects move faster, which of two objects is longer, and whether two spatially separated collisions happened at the same moment.

O1 and O2 are both motionless relative to each other while A and B speed away from both. They should both reach the same conclusions, of course.

I assume O1 and O2 stand for observers? If they are both motionless relative to each other, of course they will reach the same conclusions about what is true in their own rest frames, since they share the same rest frame. But any coordinate-dependent conclusions they reach will be relative to their frame, if they understand relativity they will understand that in the context of a different reference frame one might reach different conclusions.

They say that A is longer than B and B is moving faster than A. O2 moves backwards (accelerating gently, let's stay within SR at least for now) and both A and B contract. O2 still concludes that A is longer than B and that B is moving faster than A. O2 just thinks O1, A, and B are all moving away from him/her now and calculates higher velocities for all of them, but nothing changes qualitatively.

And what if O2 accelerates until it is at rest relative to B? In this case, in the inertial frame where O2 is now at rest after the acceleration, B is at rest while A has some nonzero velocity, so "A is moving faster than B" in the context of this frame. Of course there is no logical contradiction here, because neither O1 nor O2 is claiming one is moving faster than the other in any context-free sense, the two statements are "in the context of O1's coordinate system B has a higher coordinate velocity than A" and "in the context of O2's coordinate system A has a higher coordinate velocity than B". Do you see any contradiction between these statements?

No matter what "frame" you're in, there are no ontological contradictions.

No, of course there aren't. But there's also no reason to believe there is any ontological truth about "velocity", since velocity is an inherently coordinate-dependent concept. Do you believe there's an ontological truth about which of two objects has a greater x-coordinate, or do you agree that an x-coordinate is an inherently coordinate-dependent concept?

No, neither observer claims they were or weren't simultaneous in any absolute sense, they both agree the events were simultaneous in one frame and non-simultaneous in another. This is no more logically contradictory than the notion that object A can have a larger x-coordinate than object B in a coordinate system with the origin at one position and the axes oriented at a particular angle but object B can have a larger x-coordinate than object A in a different coordinate system with the origin at a different position and the axes oriented differently (a situation which can be true in Newtonian physics, and even in ordinary algebraic geometry).

But observers in rotated coordinate systems are not all talking about length. One is talking about length, another width, another height, and still another is talking about extent in a direction between these. There is no contradiction because they are not all talking about length.

Rotated relative to what? Do you believe there is some ontological truth about which direction in space is "really" length and which is "really" width and height, or do you agree that these are arbitrary labels that each coordinate system can impose on their three coordinate axes? Of course it's true that one coordinate system's "length" direction is different from another's, but there is no objective truth about which direction is "really" length. Neither is there an objective truth about which direction is "really" the x-axis, the x-coordinate of an object is an inherently coordinate-dependent notion--do you disagree? If not, can you at least entertain the logical possibility that "velocity" is also an inherently coordinate-dependent notion, that there is no coordinate-independent ontological truth about which of two objects "really" has a greater velocity?

On the other hand, with regards to simultaneity, the situation is not so. While an entity can have extent in 3 mutually perpendicular directions, there are not "different kinds" of simultaneity. There is simultaneous and there is not simultaneous.

But different coordinate systems in SR do have time axes that are rotated in 4D spacetime relative to one another--have you ever seen a Minkowski diagram? If you just assume that there must be an objective truth about whether events are "really" simultaneous (despite the fact that different SR coordinate systems disagree about whether they share the same t-coordinate) whereas you don't think there must be an objective truth about whether events "really" share the same x-coordinate in some sense that's independent of human choices about how to define coordinate systems (i.e. you don't assume there's some ghostly 'true' x-axis in the universe and that any coordinate system whose x-axis is rotated relative to the 'true' one is incorrect in some objective sense), then you are just begging the question here, assuming what you are trying to prove.

Exactly. The only way for any entity to be motionless is for every entity to be motionless. And, in this case, it is impossible for one to "conclude" that something is motionless because this is necessarily an action that requires motion.

But if you believe there is an objective truth about whether events are simultaneous, this defines a preferred frame in SR, since only one frame's definition of simultaneity can match the "true definition". And once you have such a preferred frame, why not just go all the way and assume that anything that is motionless in this preferred frame is motionless in an absolute sense, even if other objects are moving relative to it? This would essentially just be a Lorentz ether theory (really more of an 'interpretation' of relativity than a 'theory' since it doesn't lead to any distinct experimental predictions).

Why? If the qualities are coordinate-dependent ones, why is it problematic that there could be disagreements on which object has a greater value of the quality depending on which coordinate system is used?

You say the "greater value of the quality". We can talk about greater or lesser values of quantities, but not qualities. Qualities are an either or situation.

As I said, in different coordinate systems observers are not all talking about length. They may disagree about the precise quantity of the length, but never on a qualitative issue such as "Does A HAVE length?" or "Is A longer than B?".

Again, if we forget relativity for the moment and just talk about spatial coordinate systems which are rotated relative to one another, do you think there is some objective truth about which direction in space is "length" or do you agree it's just an arbitrary label? Let's define the x-axis of a coordinate system as the "x-length" dimension, so the difference between the smallest x-coordinate which is occupied by a point on the object's surface and the largest x-coordinate which is occupied by a point on the object's surface would be its "x-length" relative to that particular coordinate system. But since different coordinate systems can have their x-axes oriented at different angles, the "x-length" relative to one coordinate system can be different than the "x-length" relative to another--this has nothing with relativity or length contraction, it's just a matter of any nonspherical object occupying more space in one direction than in other directions. Do you think there must be some objective truth about which of two objects has a greater x-length, implying there is some objective truth about which direction the universe's x-axis "really" lies, or do you agree that the very notion of an x-axis refers to human-defined coordinate systems and thus there is no coordinate-independent truth about an object's x-length, any more than there's a language-independent truth about whether a certain animal is really a "cat" or a "gato" or a "chat" or something else? (presumably you don't think there must be some language-independent truth about which of two animals has a longer name, for example).

I'll give "fact" a rigorous meaning. I think we need to distinguish between "facts" and "statements of facts". To understand a "fact" we need to understand the concept of the "Universal Movie". Imagine you can take a picture of the entire universe from afar. The Universal Movie is a series of such photographs of every entity at a location.

Here you are again just begging the question by assuming objective reality consists of a series of 3D moments--can you not at least conceive of the logical possibility of the eternalist "block universe" view where reality is inherently a 4D spacetime structure, and the choice of how to slice it up into 3D moments is a human-dependent question, just like how a 3D block could be sliced into a series of 2D planes in a variety of ways depending on the angle of the slicing blade?

 

[jefswat]

You replaced a qualitative statement with a quantitative one, a difference I have been repeatedly harping on. The incident issue is motionless versus in motion, not quantitative velocity/speed.

Everything you said after was an irrelevant straw man.

I disagree. I don't accept this:

They may disagree on quantity/degree, but not on quality. If they disagree on quality they must check the presuppositions of their measurements/observations, at least one is ill-conceived. In all other areas we do not allow diametrically opposed qualitative descriptions.

For all of your definitions you should have included one for disagree because there are two types. There is fundamental disagreement and non-fundamental disagreement.

Non-Fundamental is rooted in a disagreement about superficial things like the color of a stop light. If a color blind person and a person with normal vision will look at it they will disagree on the color. This is rooted in the color blind persons different preception of the color.

Then there is a fundamental disagreement which would be like us agreeing on all of the characteristics of the light(including its wavelength and all other sceintific measurements one could perform) but then I think its blue and you think its red(you may be inclined to think that just named if different but that is not the real case, that is a shortfall of this analogy) We think that is is fundamentally different even though agreeing on all of the characteristics.

To observers seeing different and seemingly unconnected things is an example of non fundamental disagreement. If a stationary observer and a moving observer see things that they do not agree are simultaneous, their disagreement is based in the facts not the fundamentals. In this case the observers will disagree on how fast the train is moving relative to them. They WILL NOT, IF THEY HAVE ANY SCEINTIFIC OR MATHMATICAL BACKROUND (its in all caps and bold because its important) they will not disagree on the fundamentals. More often than not the cause of Fundamental disagreement is ignorance or arrogance. If I am stationary, based on SR, I will conclude that a person moving will observe "A" while I observe "B". The person moving will likewise conclude "A" but work out that I will observe "B". There is never a contradiction that is fundamental. If you feel there is please bring it up and we will show you why it is not.

So the point here is that, if they agree on all the facts like velocity and so on(and are given enough info), any two observers will NEVER have a fundamental disagreement on either a qualitative or quantitative observation for a given frame regardless of there frame!(requiring that they know how to translate and properly predict what the frame in question will observe i.e. SR)

With that I conclude that qualitative and quantitative are linked and that they will always agree on both for a given frame after they do the math regardless of their frame. If one is just as true is the other why can I not replace it(we will ignore the fact that I think motionless means V_rel=0 while you clearly do not)

 

[altonhare]

Right. So what point were you trying to make here?

In relativity, simultaneity of events is frame-dependent.

A cannot be both X and "not X". No matter what frames we're in. Like I said, in rotated frames we're not all measuring length, there's no contradiction here.

So you are saying the frame from which we see the UM is special

It's not a frame. The UM is an abstraction that is useful for thinking and contemplating the universe. It refers to what we would see IF we could see every successive location of every entity (including photons). In this view we imagine what happens then we can go out into our limited reality to see if its consistent with what we imagined. If it's not then what we imagined is wrong.

I assume O1 and O2 stand for observers? If they are both motionless relative to each other, of course they will reach the same conclusions about what is true in their own rest frames, since they share the same rest frame. But any coordinate-dependent conclusions they reach will be relative to their frame, if they understand relativity they will understand that in the context of a different reference frame one might reach different conclusions.

And what if O2 accelerates until it is at rest relative to B? In this case, in the inertial frame where O2 is now at rest after the acceleration, B is at rest while A has some nonzero velocity, so "A is moving faster than B" in the context of this frame. Of course there is no logical contradiction here, because neither O1 nor O2 is claiming one is moving faster than the other in any context-free sense, the two statements are "in the context of O1's coordinate system B has a higher coordinate velocity than A" and "in the context of O2's coordinate system A has a higher coordinate velocity than B". Do you see any contradiction between these statements?

But of course velocity is a vector. If O2 is at rest relative to B, then the velocity of A is now negative. O2 would be contradicting himself if s/he does not maintain this kind of consistency. So no they do not contradict each other, if O2 is self-consistent (considers speed to have directionality, forward and backward). O2 will still conclude that B is moving faster than A because zero is greater than a negative number.

No, of course there aren't. But there's also no reason to believe there is any ontological truth about "velocity", since velocity is an inherently coordinate-dependent concept. Do you believe there's an ontological truth about which of two objects has a greater x-coordinate, or do you agree that an x-coordinate is an inherently coordinate-dependent concept?

There are no ontological contradictions and this scenario is no different, as I pointed out. The only one I've identified is the "relativity of simultaneity" in non colocal events. In this regard we either have to state that A) There is an absolute simultaneity or B) Simultaneity lacks meaning in the context of non-colocal events and we should stop bantering about this term.

Rotated relative to what? Do you believe there is some ontological truth about which direction in space is "really" length and which is "really" width and height, or do you agree that these are arbitrary labels that each coordinate system can impose on their three coordinate axes? Of course it's true that one coordinate system's "length" direction is different from another's, but there is no objective truth about which direction is "really" length. Neither is there an objective truth about which direction is "really" the x-axis, the x-coordinate of an object is an inherently coordinate-dependent notion--do you disagree? If not, can you at least entertain the logical possibility that "velocity" is also an inherently coordinate-dependent notion, that there is no coordinate-independent ontological truth about which of two objects "really" has a greater velocity?

Logic tells me that observers should not come to qualitatively different conclusions and that, if they do, they have made at least one mistake. If O2 concludes that A moves faster than B now s/he forgot to account for direction. If one observer says the brick is longer and another says the steel is longer, one measured in the summer and the other in the winter. If one concludes that X is longer than Y and another the opposite, at least one of their premises is wrong. Reason tells me that we cannot hang our concerns on each one's "frame" because this is an artificial construct, a matter of perspective. Perspective shouldn't change what is. Erroneous or contradictory conclusions about what is can only arise through faulty premises.

But different coordinate systems in SR do have time axes that are rotated in 4D spacetime relative to one another--have you ever seen a Minkowski diagram?

Yeah I've seen a Mink diagram.

The value of the time coordinate is a quantitative issue. Observers can disagree about these kinds of continuous, quantitative issues because they are not diametric opposites, they are not statements of logic of the form "X is A". They are essentially a bundle of descriptions. I have no problem with one observer's clock ticking slower than another observer's, I have a problem if one says X is motionless and the other says it's in motion.

If you just assume that there must be an objective truth about whether events are "really" simultaneous (despite the fact that different SR coordinate systems disagree about whether they share the same t-coordinate) whereas you don't think there must be an objective truth about whether events "really" share the same x-coordinate in some sense that's independent of human choices about how to define coordinate systems (i.e. you don't assume there's some ghostly 'true' x-axis in the universe and that any coordinate system whose x-axis is rotated relative to the 'true' one is incorrect in some objective sense), then you are just begging the question here, assuming what you are trying to prove.

Hmmm. I don't think there is a "ghostly x axis" that is "out there". I think that observers in "rotated" coordinate systems, if they report their measurements specifically and clearly, will not contradict each other. If they all report "4 meters long!" they are being ambiguous and sloppy. They have to report exactly how they made the measurement in detail. The details of the measurement process are often glossed over in presenting rel quantitatively, how the observer got the number is taken for granted. It's just assumed that "if they have a clock and a ruler they're good to go". But how do different observers measure an entity's location and extent from a distance?

For instance, O1 is observing X. S/he first gets a handle on its relative location. How does s/he do so without leaving O1's frame? O1 can do nothing without moving relative to X because there is no change to monitor. Let's say O1 is in relative motion with X, Y, and Z, which are themselves motionless with respect to each other. Now O1 can use a photon counter with the Lorentzian wavelength broadening factor to quantify distances-traveled (and infer distance). Let's say Y is "to the left" of X and Z is "above" it. Y and Z are emitting to O1 along diagonal paths. To measure distances between X, Y and Z themselves O1 just holds up a ruler and eyeballs it. Also to measure the extent of X, Y, and Z (in 2 directions, O1 can't see its width in this scenario) O1 holds up a ruler and "eyeballs" it. O1 writes down wavelengths, the corresponding distances-traveled, and the corresponding length and height.

If other observers, in other states of relative motion, perform the same procedure they will arrive at consistent conclusions without a "coordinate transform". O1 says that X was 3 "meters" in extent in the direction in which it was 10 "meters" from Y while Y is 4 meters in extent in this direction. X was 5 meters in extent in the direction in which it was 8 meters from Z and Z was 2 meters in extent. The qualitative conclusion is "X is greater in extent than Z in the direction of Z, i.e. on a line connecting X and Z and X is smaller in extent than Y in the direction of a line connecting them". O2 says that X was only 1.5 meters in extent in the direction in which it was 3 meters from Y while Y was 2 meters. X was 8 meters in extent in the direction it was 12 meters from Z, while Z was 7 meters. O3 states... etc. These statements are not contradictory, they are simply different. In these sense there is no "absolute truth" behind length, width, and height. But also observers in different "coordinate systems" do not arrive at contradictory results if they are specific about their results. If O1 simply says "X is longer than Z and shorter than Y" while O2 says "X is shorter than Y while longer than Z" then they are simply being sloppy.

But if you believe there is an objective truth about whether events are simultaneous, this defines a preferred frame in SR, since only one frame's definition of simultaneity can match the "true definition". And once you have such a preferred frame, why not just go all the way and assume that anything that is motionless in this preferred frame is motionless in an absolute sense, even if other objects are moving relative to it? This would essentially just be a Lorentz ether theory (really more of an 'interpretation' of relativity than a 'theory' since it doesn't lead to any distinct experimental predictions).

Absolutely not. The entity would be moving wrt every other non-aether entity. The aether is just another arbitrary frame, albeit it may be the most convenient one. The fact that we can find no "most convenient" frame is irrelevant to science, though engineers of communications satellites and such probably lament it. Einstein was right, the aether really was superfluous.

Here you are again just begging the question by assuming objective reality consists of a series of 3D moments--can you not at least conceive of the logical possibility of the eternalist "block universe" view where reality is inherently a 4D spacetime structure, and the choice of how to slice it up into 3D moments is a human-dependent question, just like how a 3D block could be sliced into a series of 2D planes in a variety of ways depending on the angle of the slicing blade?

I see no evidence, empirical or logical, to support the block universe ontology. As far as I can tell there is no rigor to it, but a lot of seductively right sounding analogies.

You cannot cut a 3D block into 2D planes. Whatever slice you cut off will necessarily be 3D. 2D planes are abstract objects, i.e. we can visualize them but they lack location (do not exist). It is impossible to even imagine a 2D object's location because, if there is an entity situated directly in the 2D object's plane, the distance is impossible to discern. The 2D object is invisible from this vantage point. If there isn't an entity situated in such an unfortunate location relative to the 2D object, does it suddenly blink into existence again? Does it blink out when entity's line up with it?

2D analogies are popular because 2D is visualizable, but I see no reason to ascribe it the significance which it has been placed, such as extrapolation to 4D. One person I debated a similar topic with ended up just asking if I could "consider that which I cannot imagine" or "that which is outside my realm" or "that which is simply inconceivable". Of course I cannot consider that which I cannot imagine, I cannot imagine it. I must imagine to consider. I must imagine to "conceive". These are the types of arguments I expect from theists, not scientists. The appeal to the "unknowable" is a wildcard that insists one believes without a sound reason.

 

[altonhare]

I disagree. I don't accept this:



For all of your definitions you should have included one for disagree because there are two types. There is fundamental disagreement and non-fundamental disagreement.

Non-Fundamental is rooted in a disagreement about superficial things like the color of a stop light. If a color blind person and a person with normal vision will look at it they will disagree on the color. This is rooted in the color blind persons different preception of the color.

The color blind person says "light gray" and the normal person says "red". The sounds they utter are not what is important, what is important is the physical referent of the sound, i.e. what it points to in reality. If both actually define what they mean by gray and red, they will find that they do not disagree. For instance the color-blind person defines "light gray" as the color of stop lights, stop signs, and blood. The normal person agrees, s/he just calls it something different.

More rigorously, they could define their words in terms of wavelength. In this case they will need a particular device, which should give the same results within experimental error.

Then there is a fundamental disagreement which would be like us agreeing on all of the characteristics of the light(including its wavelength and all other sceintific measurements one could perform) but then I think its blue and you think its red(you may be inclined to think that just named if different but that is not the real case, that is a shortfall of this analogy) We think that is is fundamentally different even though agreeing on all of the characteristics.

This doesn't make any sense. They did, indeed, just rename the exact same thing/phenomenon. Each observer has to define "red" or "blue" or "gray" in order to make things clear.

To observers seeing different and seemingly unconnected things is an example of non fundamental disagreement. If a stationary observer and a moving observer see things that they do not agree are simultaneous, their disagreement is based in the facts not the fundamentals. In this case the observers will disagree on how fast the train is moving relative to them. They WILL NOT, IF THEY HAVE ANY SCEINTIFIC OR MATHMATICAL BACKROUND (its in all caps and bold because its important) they will not disagree on the fundamentals. More often than not the cause of Fundamental disagreement is ignorance or arrogance. If I am stationary, based on SR, I will conclude that a person moving will observe "A" while I observe "B". The person moving will likewise conclude "A" but work out that I will observe "B". There is never a contradiction that is fundamental. If you feel there is please bring it up and we will show you why it is not.

So the point here is that, if they agree on all the facts like velocity and so on(and are given enough info), any two observers will NEVER have a fundamental disagreement on either a qualitative or quantitative observation for a given frame regardless of there frame!(requiring that they know how to translate and properly predict what the frame in question will observe i.e. SR)

With that I conclude that qualitative and quantitative are linked and that they will always agree on both for a given frame after they do the math regardless of their frame. If one is just as true is the other why can I not replace it(we will ignore the fact that I think motionless means V_rel=0 while you clearly do not)

It has nothing to do with frames, and I believe your notion of "fundamental disagreement" vs. "non-fundamental disagreement" may be misconceived. There are no qualitative contradictions ("disagreements") regardless of frame. Observers do not have to consider each other's "frame" to reconcile qualitative aspects. They simply have to report their results in full, and therew ill be no contradiction. On the other hand observers in different frames will necessarily disagree on quantitative aspects. While quantitative aspects can be equated by transforming to each other's frames, qualitative aspects don't need to be because they are never contradictory.

 

[Saw]

Most people would say it's a "fact" that the word for "cat" in spanish is "gato", even though this is just a statement about a labeling convention in a certain language. Likewise, most people would say it's a "fact" that New York City is at latitude 40° 47' and longitude 73° 58' even though this is just a statement about its position in a certain human-defined coordinate system on the globe...

Ok, if you wish to continue the analysis (after the turmoil created by Althon), I'll leave aside subtleties on words and put things in a less baroque manner.

What was the goal? To discuss about what “the difference in judgments about simultaneity” means, just in case it is in the interest of physics.

1) First, “simultaneous” in a given frame means that:

if we have two clocks at either end of the train which have been synchronized in the train's frame using Einstein's convention, they will both read the same time when the lasers are fired next to them, but if we have two clocks on the ground which have been synchronized in the ground frame using Einstein's convention, and both clocks happen to be right next to the two duellers at the moment each fires his laser, then these two clocks will show different times when the lasers are fired next to them.

You specify the origin of the clock readings, how they have been obtained (the clocks have been synched through the Einstein convention and have ticked afterwards at the corresponding rate).

(A couple of footnotes, about obvious things, which I note just in case they are useful:

- That is important to remember, because it is part of the physical content of the definition. We do not know how variations of that convention might affect the outcome (it would depend on the nature of the variations), but let us just note it.

- The observers get different values, but it’s also true that the measurements are events and so they happen in all frames and all frames agree that they happen. Furthermore, one frame can predict the quantity of the other’s measurement.)

2) Second, we must make use of the measurements of the observers for a purpose.

(Footnote: What purpose? For me, the aim of physics is “to solve problems”, like whether a duel is fair or not. Isn’t it? Can you think of a better purpose? In the context of a trial it looks as if physics were at the service of the law. But you can think of other examples. Usually, what you do is solving practical problems. Anyhow, what is important here is that there is always a purpose.)

3) Third, your measurements serve their purpose by combination with other measurements.

The judgments about simultaneity alone do not serve any purpose. For example, in our case, we have to combine them with another measurement: we must determine if “both duellers have an equal amount of time on their own clocks between firing their own gun and being hit by (or dodging) the other guy's laser”. Once we do it, the trick is done. In my frame, the proper time of Back when shot – the proper time of Back when shooting = the proper time of Front when shot – the proper time of Front when shooting. So the duel is fair.

(Footnote: Both referees agree that the other has correctly applied the formula and obtained, ultimately, the right solution. Maybe you could comment on technicalities of this operation that I might have missed.)

Conclusion: both judgments of simultaneity are right, in the sense that, after due consideration of their origin and due combination with other measurements, they serve beautifully the common practical purpose.

Did I do my homework? Does this look more reasonable?

 

[jefswat]

The color blind person says "light gray" and the normal person says "red". The sounds they utter are not what is important, what is important is the physical referent of the sound, i.e. what it points to in reality. If both actually define what they mean by gray and red, they will find that they do not disagree. For instance the color-blind person defines "light gray" as the color of stop lights, stop signs, and blood. The normal person agrees, s/he just calls it something different.

That is why I included the disclaimer. Because that notion is prone to lead people off track.

More rigorously, they could define their words in terms of wavelength. In this case they will need a particular device, which should give the same results within experimental error.

exactly, Fundamental would be, red light has wave length 600nm. the light is 600 nm. you think its blue I think its red. Non-Fundamental would be along the lines of disagreement on the wavelength and so on.

This doesn't make any sense. They did, indeed, just rename the exact same thing/phenomenon. Each observer has to define "red" or "blue" or "gray" in order to make things clear.

It doesn't make sense because one of the observers made a clear error.

It has nothing to do with frames, and I believe your notion of "fundamental disagreement" vs. "non-fundamental disagreement" may be misconceived.

I believe I cleared that up?

I have to go to class I will finish later. Do you now agree with my definitions?

 

[Doc Al]

Logic tells me that observers should not come to qualitatively different conclusions and that, if they do, they have made at least one mistake. If O2 concludes that A moves faster than B now s/he forgot to account for direction. If one observer says the brick is longer and another says the steel is longer, one measured in the summer and the other in the winter. If one concludes that X is longer than Y and another the opposite, at least one of their premises is wrong.

It's not "logic" telling you things, it's your questionable notions about the way things work. You claim that a statement such as "X is longer than Y" is some kind of "qualitative" statement and thus frame independent. Yet it involves measurements of length, which are intimately tied to our notions of simultaneity and time and which we know are frame dependent.

It's perfectly reasonable (inescapable, really), given what we mean when we say that X or Y has a length, for two different observers to disagree on which of two objects is longer. (Of course, observers who are aware of how the world actually works are not at all surprised by this.)

Reason tells me that we cannot hang our concerns on each one's "frame" because this is an artificial construct, a matter of perspective. Perspective shouldn't change what is. Erroneous or contradictory conclusions about what is can only arise through faulty premises.

Again, there is no contradiction. The fact that measurements of length and time, and thus comparisons of distances and intervals, are frame dependent presents no contradiction. You have yet to give one single instance (other than handing waving philosophy) where there is a real contradiction.

Sounds to me like you are more interested in discussing your preconceived "metaphysical" notions than in discussing physics.