Light shone in a train bouncing off mirrors

 Quote by altonhare Incorrect. Motion and change are synonyms. Time is essentially motion+observer. This is circular and fails to actually define motion. Motion: Two or more locations of an entity. Location: The set of distances from an entity to every other entity. Now we can use these terms consistently and meaningfully. If an entity was at two locations it moved by definition whether a particular observer saw it move or not.
I don't understand how your definition is any different from the previous. When you say the object was at two different locations then its position necessarily changed.

 Quote by ZikZak To be characterized as "in motion" means that a body's position changes with time. Observer S on the embankment observes that the train's position changes with time, and thus the train is "in motion." Observer T in the train observes that the train's position does not change with time, and thus the train is "non in motion." Observer S thus concludes X and observer T concludes non-X. Do you claim that this is a contradiction? Are we now required to change the definition of motion? What should the new definition be? Which of the observers conducts the "real" measurement, and which needs to "adjust" for his equipment, and how do we know?
Modified:
To be characterized as "in motion" means that a body's position changes with time relative to the observer. Observer S on the embankment observes that the train's position changes with time, and thus the train is "in motion" relative to him.Observer T in the train observes that the train's position does not change with time, and thus the train is "non in motion" relative to him

I see no way to refute this

 Quote by altonhare All observers will agree on if the signal reaches the chair from each side simultaneously because it's a local event. The point of the exercise is to illustrate that "simultaneous" is only meaningful (non contradictory) for local events and spatially separate events in a specific frame.
I agree with the first part. I still can't help but thinking you think the definitions of simultaneous and relatively simultaneous are the same and they are not.

Simulatneous- They happened at the same time(essentially)(only applies in special cases)

Relative Simultaneity-the concept that simultaneity is not absolute, but dependent on the observe(applies to all cases though in some cases it simplifies down to basic simultaniety)

Sorry I can't speel today

 Quote by ZikZak Strange statements from someone who claims that there is absolute simultaneity.
Unjustified and unwarranted assumption. Never have I stated that "there is absolute simultaneity".

 Quote by jefswat I don't understand how your definition is any different from the previous. When you say the object was at two different locations then its position necessarily changed.
The definition I gave does not invoke circularity. Motion=change. When you define motion as change you are saying nothing.

 Quote by jefswat Modified: To be characterized as "in motion" means that a body's position changes with time relative to the observer. Observer S on the embankment observes that the train's position changes with time, and thus the train is "in motion" relative to him.Observer T in the train observes that the train's position does not change with time, and thus the train is "non in motion" relative to him I see no way to refute this
Wrong. Motion means two or more locations of an entity where location is the set of distances from the entity to every other entity in the universe. This is the objective, scientific, and consistent definition.

Again the only reason for T to conclude that the train is motionless is if s/he thinks the train is the only other entity in the universe. At best T can only conclude that the train is not moving relative to him/her, but s/he cannot conclude that it is actually motionless.

 Quote by jefswat I agree with the first part. I still can't help but thinking you think the definitions of simultaneous and relatively simultaneous are the same and they are not. Simulatneous- They happened at the same time(essentially)(only applies in special cases) Relative Simultaneity-the concept that simultaneity is not absolute, but dependent on the observe(applies to all cases though in some cases it simplifies down to basic simultaniety) Sorry I can't speel today
Observers should never disagree on the qualitative features of what happened, although they may disagree on the quantitative aspects if they are measuring using different reference standards (different rulers, clocks, "frames").

What this means is that we can talk about what happened or didn't happen, this is a qualitative true/false binary kind of situation. Did it move, or not? Were they simultaneous, or not? Or we can talk about how fast, how long, etc. This is a continuous quantitative situation.

I argue that if, based on our definition of X, one can state that something or some event was both X and not X then this is a contradiction and demands a non contradictory redefinition of X. In the case of motion I have resolved this issue in the way I have defined it. In the case of simultaneity this is resolved by defining simultaneity as either A) Local or B) In a specific frame (frame E in my example).

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 Quote by JesseM if anyone at the trial understands physics they can show that because of the speed of the signals and the movement of the device at the center, then even though the strikes were non-simultaneous, they were timed just right so that the signals would reach the device simultaneously. So why did the jury conclude that you and Dr. Mad were innocent? Are you just assuming that the jury isn't capable of basic physics calculations, and none of the physicists who testified bothered to correct them? You also seem to be using this thought-experiment to support the idea that the strikes really were simultaneous in some objective sense. Why? 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.
I fully agree, but still think that althonhare has some valid points.

As I said in an earlier post, relative simultaneity is relative and absolute simultaneity is absolute and each concept has its own purpose and hence should have its own niche in language. The problems (the paradoxes) only arise if you use one for the purpose of the other or vice versa. But please don’t quote this clumsy paragraph in helpless isolation. I’ll try to explain myself.

Absolute simultaneity of two events is an idea, an intellectual construction, an invention of the mind. Nobody can forbid me to imagine and define that concept as such: an abstract notion, valid for discussion purposes. It means the following: if two events are “absolutely simultaneously”, that entails that they both have “happened” and hence it is logically impossible that one of them is prevented from happening. For example, if a witness from event 1 (located in a frame where that event has happened “earlier”) travelled towards the location of event 2 faster than the speed of light (that is impossible, but even if it were possible), she would not be able to avoid that event 2 happens, because it has already happened and it has not happened in isolation, it has immediately created a myriad of interactions with its surroundings (remember the butterfly effect) that cannot be blurred out, at least in this universe (leaving aside the funny idea of parallel universes). Thus this concept plays a useful role. For example, you don’t follow the threads where people talk about tricky ways to overcome the speed limit, time-travel and kill your dear grandmother before she gives birth to your father. This saves you a lot of time to study relativity.

However, and here I loosely follow Einstein himself, for practical reasons, we may have to leave aside the chimera of measuring absolute simultaneity and content ourselves with relative simultaneity. The practical reasons are the fact that our measurements are inherently relative, since they are made from a certain position and state of motion, with physical instruments affected by a physical environment and so on. In principle, one should not discard that, in spite of all that, those measurements yield homogeneous effects, at least in some respects, since there often arises the helpful phenomenon of “compensation of effects”. In fact, you would not be able to apply transformations between different relative values if you couldn’t rely on some common or homogeneous ground (absolute spacetime in SR?).

In particular, the specific measurement of simultaneity, as of today, with our current measurement technology, yields relative values. Thus the simultaneity measurements carried out in the thought-experiment from the train and from the embankment gave off frame-dependent values. Does it mean that they are not equally trustable? Yes, they are! For their purpose, they are! If you combine the RS with TD and LC, you get a coherent system where all observers make the right predictions. Hence, as long as you do not ask them to do a different thing, we cannot prefer one measurement of simultaneity over the other, we cannot say that one was wrong and the other was right: in fact, both types of measurements helped the respective measurers to predict adequately the single event, the simultaneous arrival of the two light signals at the centre of the chair. Each served the purpose for which it had been made, so it was right… in that sense, for that purpose! Of course, if someone comes to you and says that, just because in her frame one event happened earlier, your grandmother was killed before your father was born, you dismiss her immediately, because the purpose of a relative measurement of simultaneity is not to predict nonsense.

Thus the two concepts of simultaneity can live together peacefully, like good brothers, each serving its own purpose in life. This paradigm should protect us against two types of mistakes:

a) The mistake of some critiques of SR = thinking that one of the two relative measurements must be absolute for the wrong reason, just because it serves its purpose. I am sorry, but both measurements serve their purpose, the one from the train and the one from the embankment. As JesseM points out, if one thinks (for discussion purposes!) that there is an aether, a synch operation carried out with the Einstein convention at rest in the aether frame would yield a measurement of absolute simultaneity, in the above sense. But it might perfectly happen that the frame at rest in the aether is the embankment and then your criterion, althonhare (really simultaneous is what is simultaneous in the “local” frame), is not valid. Events do not belong to any frame in particular, they take place in all frames. In your trial, what makes you guilty is not the fact that the bolts are absolutely simultaneous in the train (most probably they are not), but the fact that the device had been designed so as to kill if it captured relative simultaneity as measured on the train or, if you prefer, a certain relative non-simultaneity as measured from the embankment.

b) The mistake of some SR defenders = But I am too tired now and probably little prepared for that…

Criticism for this part is welcome.

 Quote by altonhare Unjustified and unwarranted assumption. Never have I stated that "there is absolute simultaneity".
No, you've only been arguing in its favour for 6 pages. You've only been arguing that people on an embankment will be stunned with surprise when an electric chair is activated by nonsimultaneous bolts.

 Quote by saw althonhare (really simultaneous is what is simultaneous in the “local” frame), is not valid.
I argue that it is valid because it makes no sense to say "X is both Y and non Y" i.e. that "AC and BD are simultaneous and not simultaneous". We might disagree on quantity but never quality.

I'll say this in anticipation of future comments. I said that it is impossible for an observer to conclude an entity is motionless. I justified this by saying that O would have to assume that A is the only other entity in the universe. In fact, it is impossible for O to conclude that A is motionless period. Imagine observer O is watching A. The only way to conclude that A is motionless is to write down A's location L1 and it's "time" T1, then repeat with L2 and T2. Now one claims that O can measure L1=L2 and T2>T1 and this "proves" A is motionless. Wrong! The only way for the statement: T2>T1 to be true is for A to have moved relative to the clock! If the clock emitted a photon then A's location is now different relative to the photon. If an arm moved then now A's location is different relative to the arm. L2 != L1 unless T1=T2.

Therefore the only sets of logic statements with physical significance are:

L1=L2 ; T1=T2

L1!=L2 ; T1<T2

And the statements corresponding to motion and motionless:

L1!=L2 ; T1<T2 corresponds to motion

L1=L2 ; T1<T2 corresponding to motionless, which is demonstrably nonphysical

 Quote by ZikZak No, you've only been arguing in its favour for 6 pages. You've only been arguing that people on an embankment will be stunned with surprise when an electric chair is activated by nonsimultaneous bolts.
You're digging yourself in a hole. There is not a single incident of me making the claim you accused me of. Just admit you made a mistake and move on.
 Quote from #60 by altonhare:- -----Here's the deal. There is no "relativity of simultaneity" because the concept "simultaneity" only has meaning for events in their own inertial frame, i.e. in the rest frame of the train in this instance. The observers on the embankment are simply wrong if they actually conclude that the events "were not simultaneous". It doesn't matter if they tack on "in our reference frame" because such a conclusion is worthless and irrelevant to the question of *were the events actually simultaneous?*. Obviously they actually were, because Mathe is dead, so simultaneity is NOT relative. If Mathe continues to argue that simultaneity is relative he'll be happy to strap into the chair as long as nobody on the train is watching the event, and lots are on the embankment to watch the bolts be "non simultaneous"! ------ Matheinste

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 Quote by matheinste Quote from #60 by altonhare:- -----Here's the deal. There is no "relativity of simultaneity" because the concept "simultaneity" only has meaning for events in their own inertial frame, i.e. in the rest frame of the train in this instance. The observers on the embankment are simply wrong if they actually conclude that the events "were not simultaneous". It doesn't matter if they tack on "in our reference frame" because such a conclusion is worthless and irrelevant to the question of *were the events actually simultaneous?*. Obviously they actually were, because Mathe is dead, so simultaneity is NOT relative. If Mathe continues to argue that simultaneity is relative he'll be happy to strap into the chair as long as nobody on the train is watching the event, and lots are on the embankment to watch the bolts be "non simultaneous"! ------ Matheinste
Yeah, that was the quote I thought of too. Altonhare, can you explain how to interpret the sentence "obviously they actually were, because Mathe is dead, so simultaneity is NOT relative" in a way that doesn't imply there is an absolute truth about whether the bolts were simultaneous?

 Quote by JesseM Yeah, that was the quote I thought of too. Altonhare, can you explain how to interpret the sentence "obviously they actually were, because Mathe is dead, so simultaneity is NOT relative" in a way that doesn't imply there is an absolute truth about whether the bolts were simultaneous?
Yes, it requires one to redefine what is meant by "simultaneous", as I've described.

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 Quote by altonhare Yes, it requires one to redefine what is meant by "simultaneous", as I've described.
Described in what post exactly? Can you give (or quote from a previous post) the specific definition of "simultaneous" that would allow us to make sense of the claim that the lightning strikes were "really" simultaneous even if they weren't simultaneous according to the definition used in the ground frame?

If this reasoning is sound,

 Quote by altonhare Wrong. Motion means two or more locations of an entity where location is the set of distances from the entity to every other entity in the universe. This is the objective, scientific, and consistent definition. Again the only reason for T to conclude that the train is motionless is if s/he thinks the train is the only other entity in the universe. At best T can only conclude that the train is not moving relative to him/her, but s/he cannot conclude that it is actually motionless.
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.

 Quote by altonhare At best T can only conclude that the train is not moving relative to him/her, but s/he cannot conclude that it is actually motionless.
You finally agree with an established theory

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 Quote by altonhare Yes, it requires one to redefine what is meant by "simultaneous"
You are perfectly right, in a sense. I think your opponents are not recognizing that there is a good part of truth in your words. See my post #90 for a discussion on when one must play with the concept of absolute simultaneity and when with relative simultaneity. It depends on the purpose. So, in certain contexts, when the purpose so requires, one must switch to the concept of absolute simultaneity. In this you are right.

 Quote by altonhare as I've described.
No, because your redefinition gives prevalence to the “local” version, regardless the purpose. Again, see my post #90. Kindly, you are reacting to the critiques that contest your truths, but not to the ones that attack your fallacies…