Assume a train is moving past a line of men who are standing extremely close to the passing train. Assume two small bombs have been placed on the outside of the train and they just graze the noses of the men standing along the track as they pass. The bombs will explode when light from a flash bulb, placed on the train’s side, equally distant between the bombs, reaches them. An observer on the train standing midway between the bombs observes simultaneous explosions shortly after setting off the flash bulb.

Two of the thousands of men, who were standing on the ground right next to each other and right next to the passing train are killed by the exploding bombs. The man near the end of the train dies before the one near the front. They do not die simultaneously because in the line of men’s reference frame, the light flash moving towards the rear of the train explodes its bomb before the bomb at the front of the train explodes. (During the transit of the light towards the bombs, the bomb at the rear of the train has been moving towards the on coming light, while the one at the front of the train was trying to race away from the on coming flash of light.)

Note that their “non-simultaneous deaths” is not due to the time for light to travel to any observer - I had the two (now dead) stationary observers stand right next to the bombs when they exploded. If a third stationary observer, is standing mid way between the two that get killed, that third observer would observer them die at different times. (The two delays for him to see them die, due to finite speed of light, are equal.)

CONCLUSION: Simultaneous event in one frame are not simultaneous in one moving wrt to it. This is real effect of SRT. It is not due to any delay of light traveling to an “observer” waiting to sees the events.

People who dispute SRT often claim that the events are “really” simultaneous in all frames, but only “seen to be non simultaneous.” Events (or clocks) synchronous in one frame are not synchronous in a different frame and “seeing delays” are not the reason for their lack of simultaneity as most opponents of SRT claim. Thus clocks that strike noonday chimes simultaneously in one frame can not strike them at the same time as synchronized clocks are striking noon day chimes in another frame. That is, synchronized clocks distributed about in one frame can not be synchronous with many in another frame which are correctly keeping time in that frame.

If the time dilation of SRT is computed and used to adjust the rate of clocks in one frame, it is possible to synchronize any pair of clocks in two different frames, but not all of them, if they are to correctly keep time in their own frame. The reason is simple. A set of clocks that are separated only by space in one frame are separated by a mixture of space and time in the other. Thus clocks at different locations can not be both synchronous with each others in the same frame (keep time correctly) and yet synchronized with all synchronous clocks in another frame. Take your pick, (but only one of the following two):

(1)You can have all clocks in two different frames all show the same time (Each has a unique SRT correction to it rate, which depends on the clock‘s location.) but they do not show the same time as clocks that are synchronous in their own frame. (I.e. they are not keeping correct time in their own frame.) OR
(2) You can have all clocks in both of two different frames synchronized with others in their same frame, (Keeping correct time in their own frame.) but the clocks in one frame will not be synchronous with the clocks in the other frame.

Any comments from people who claim that all clocks in two different frames can both keep time correctly in their own frame and yet be synchronized with clocks in another frame that are all also showing the correct time in their frame? I.e. people who think time is universal for all frames and thus SRT must be wrong.

Hello Billy T,

My only comment. I have not advocated universal time. However, I have said, and do say, that if in a common frame an event is simultaneous to two or more observers, that when viewed from other frames they appear to not be simultaneous, that that is merely a perception and in no manner has altered the fact of simultaneity of the events.

My only comment. I have not advocated universal time. However, I have said, and do say, that if in a common frame an event is simultaneous to two or more observers, that when viewed from other frames they appear to not be simultaneous, that that is merely a perception and in no manner has altered the fact of simultaneity of the events.
what makes two things simultaneous then? if two observers disagree, then who is right? you seem (I don't mean to put words in your mouth) to imply a master reference frame (or either) in which things are reality, and all others are illusions. I disagree with that view.

Any comments from people who claim that all clocks in two different frames can both keep time correctly in their own frame and yet be synchronized with clocks in another frame that are all also showing the correct time in their frame? I.e. people who think time is universal for all frames and thus SRT must be wrong.
BillyT, I volunteer to comment, but not because I have any claims of SRT being wrong. I doubt that my comment will have any bearing on whether SRT is valid, but it does seem an appropriate response to your challenge:

It appears that you have already built a universal clock system into your thought experiment. Every time a bomb touches a nose, the nose clock ticks one increment. Enery time a nose touches a bomb, the bomb clock advances one increment. In what way could the two clock systems not be both synchronious and correct in their reference frame?

I don't see that as a problem. each person will have a clock hit their nose, but different frames will disagree on the simultaneity of their nose/bomb collision.

what makes two things simultaneous then? if two observers disagree, then who is right? you seem (I don't mean to put words in your mouth) to imply a master reference frame (or either) in which things are reality, and all others are illusions. I disagree with that view.

Notice that I stated simultaneous in a common frame. In such a frame simultaneous means simultaneous. You are certainly free to not believe that but I find no cause to not believe simultaneity is achievable in a common frame.

Yes, it is possible in a common frame, <B>if</B> you mean <B>the same frame</B> when you say <B>common frame</B>. Duh...

sorry mac, didn't see that.

Yes, it is possible in a common frame, <B>if</I> you mean <B>the same frame</B> when you say <B>common frame</B>. Duh...

Not sure why you see the Duh as appropriate. My point was that understqanding that one should then realise that the views of others in other frames as not being simultaneous in no manner alters the fact of simultaneity of the events.

You go from physics to perception at that point. The only physics are in the frame in which they occur all else is illusion.

All events are simultaneous.

Well, the are, in some frame or the other. How can you decide which frame is right?

In the example, the events are simultaneous in the <B>moving</B> (w.r.t the platorm, at least) frame. So does that mean that they're not <I>really</I> simultaneous? And it's not an illusion of motion. What happens in each frame is 'really real', in that frame. You can't determine otherwise.

Off topic (somewhat): I was just curious about what you think about Quantum Mechaincs.

All events are simultaneous.

Well, the are, in some frame or the other. How can you decide which frame is right?

That seems fairly obvious. If two events occur in a common (same) frame such that an observer midway between the events measures them as simultaneous then they were simultaneous.

Other observers not in the center or with relative motion has to compute simultaneity based on relative velocity, distance, etc to ascertain the simultaneity.

In the example, the events are simultaneous in the <B>moving</B> (w.r.t the platorm, at least) frame. So does that mean that they're not <I>really</I> simultaneous?

Restate the example of events claimed simultaneous in the moving platform scenario.

And it's not an illusion of motion. What happens in each frame is 'really real', in that frame. You can't determine otherwise.

WHAT? You can't calculate relative velocity, distance and determine simultaneity? I can.

Off topic (somewhat): I was just curious about what you think about Quantum Mechaincs.

I don't. :D

....The only physics are in the frame in which they occur all else is illusion.I don't think it an "illusion" when in my car (my frame) I am passed by someone in their car (their frame). By your reasoning, I am only an illusion to them.

Can you clarify a little what makes something only "illusion" when the choice of frames is arbitary? I.e. physics can be equally well described in the frame with my car at rest or in the frame with his car at rest, can it not.?

I don't think it an "illusion" when in my car (my frame) I am passed by someone in their car (their frame). By your reasoning, I am only an illusion to them.

You are extrapolating "Illusion" to far. Of course you exist and are not an illusion. However, to claim either has any specific velocity is an illusion.

Can you clarify a little what makes something only "illusion" when the choice of frames is arbitary? I.e. physics can be equally well described in the frame with my car at rest or in the frame with his car at rest, can it not.?

This is the error in SRT. It leads to the physically impossible (and unobserved in 100 years of relativity) condition of reciprocity which causes in theory each clock to run slower than the other.

The facts are that each may have some velocity component contributing to the total relative velocity. SRT treats the total relative velocity as being in one or the other. Since gamma is not linear that leads to error when in fact GPS shows that one should compute gamma for each component to determine the effective gamma.

If two clocks are accelerated equally, from a common inertial rest, condition in a co-moving direction. You have NO relative velocity and no systemic time dilation between them, although both mutually dilate relative to their origin point of acceleration.

Likewise if you launch the same two clocks equally but in opposite directions from a common inertial rest positon, you now have relative velocity but you will not find any systemic time dilation between them. Each are still mutually dilated relative to the origin point of their acceleration.

That is it can be seen (if you actually look) that the process of time dilation is a function of absolute velocity change due to acceleration, not just relative velocity.

That is why if you now take the same two clocks at relative rest and only accelerate one, the one accelerated will record time dilation relative to the one that did not accelerate. AND you will not record any time dilation of the clock which remained at rest relative to the one that did accelerate.

That is what actual recorded data supports. Not what SRT claims that either may be considered as at rest and the other is dilated. Only one clock has ever been recorded as being dilated. And it is the clock that has the most acceleration.

If both are accelerated but by different amounts the one that accelerated the most will be the one that shows dilation relative to the slower clock and never vice versa according to SRT. That is the facts.

I said: “Can you clarify a little what makes something only "illusion" when the choice of frames is arbitary? I.e. physics can be equally well described in the frame with my car at rest or in the frame with his car at rest, can it not.?”
To which you replied:
[QUOTE=MacM]You are extrapolating "Illusion" too far. Of course you exist and are not an illusion. ...
Ok, I am glad we agree than neither me nor the man passing me in his car is an "illusion" How about if I am in a jet, flying north and he is in another, flying south? - I am not trying to be "cute" only trying to point out that it is possible to consider a continuum of velocity differences, steadly increasing the relative speed of the two frames well into the relativistic region where you claim he views me and my physics as "illusion." You are too smart to be claiming that with a one MPH speed increase over some critical speed, I will be transform into an illusion.

Thus, I am sure that I do not understand what you mean by "illusion" - that is why I am still asking for clarification of "illusion", not only your agreement that one car driver is not an "illusion" when passing another. Putting the question another way: If my car passing example is "extrapolating illusion too far" how great must the relative speeds be before your "illusion concept" does apply?

However, to claim either {car}has any specific velocity is an illusion....This is the error in SRT. It leads to the physically impossible ... condition of reciprocity which causes in theory each clock to run slower than the other.
I don't see any problem with the car‘s "specific velocity" - When speaking of cars, the road is the implied "rest frame” wrt which the cars speed is stated.

When speaking of objects (or reference frames) moving relative to each other with relative speed a high percent of c, trying to compare time accumulated on clocks in the two frames is more complex and we disagree on the facts. (I think SRT is correct and you that it is not.) I’ll soon to try to show that your “reciprocity argument” is too simple, confused, and wrong in its conclusion, but not just now. (The first draft is a long post. Perhaps with more review, I can shorten it and yet still keep the argument a clear chain of small logical steps, asking you at what point in the chain did I first error, in your view.)

Ok, I am glad we agree than neither me nor the man passing me in his car is an "illusion" How about if I am in a jet, flying north and he is in another, flying south? - I am not trying to be "cute" only trying to point out that it is possible to consider a continuum of velocity differences, steadly increasing the relative speed of the two frames well into the relativistic region where you claim he views me and my physics as "illusion." You are too smart to be claiming that with a one MPH speed increase over some critical speed, I will be transform into an illusion.

Thus, I am sure that I do not understand what you mean by "illusion" - that is why I am still asking for clarification of "illusion", not only your agreement that one car driver is not an "illusion" when passing another. Putting the question another way: If my car passing example is "extrapolating illusion too far" how great must the relative speeds be before your "illusion concept" does apply?

You are not applying "Illusion" to the correct parameters. Actual relative velocity is not a factor. If it applies at all relativity also applies at everyday velocities as well. It just has negligable affect.

So an illusion is an illusion at all velocities. From my perspective there is only one issue which qualifies as a real physical property and that is time dilation.

It can be observed and has been recorded. Length contraction on the other hand has not and appears to be nothing more than an illusion created mathematically based on the illusion to an observer with an inertial velocity that he is at rest and his clock still ticks at a standard rate.

It in known that clocks in motion dilate and tick slower than the resting clock. It is not merely a case of an illusion of a moving observer but becomes recorded and can be seen in a subsequent common frame.

Recognizing that therefore it becomes obvious that you cannot claim both time dilation of a clock in motion and that distance for the clock have contracted.

If time accumulated on the clock is due to spatial contraction then the clock cannot also be dilated (don't say in his frame, dilation is physical and crosses frames to show it was dilated in comparison).

If (and it is known to be the case) clocks in motion are dilated then given a velocity and a distance it will accumulate less time and there is no room to claim that distance was foreshortened.

If you try to claim both as physical realities then you compound the affect and get an incorrect answer. It is not physics to switch physical affects at the whim of the observer. Physical is physical. Anything else is an illusion.

I don't see any problem with the car‘s "specific velocity" - When speaking of cars, the road is the implied "rest frame” wrt which the cars speed is stated.

When speaking of objects (or reference frames) moving relative to each other with relative speed a high percent of c, trying to compare time accumulated on clocks in the two frames is more complex and we disagree on the facts. (I think SRT is correct and you that it is not.)

You certainly have the perogative to disagree. I just hope you are prepared to jusify your view.

I’ll soon to try to show that your “reciprocity argument” is too simple, confused, and wrong in its conclusion, but not just now. (The first draft is a long post. Perhaps with more review, I can shorten it and yet still keep the argument a clear chain of small logical steps, asking you at what point in the chain did I first error, in your view.)

I look forward to it. :D

One quick question:

Given a cesium atomic clock with a frequency of 9,192,631,770 hertz traveling at a relativistic velocity, how would using relativistic time dilation (T=&gamma;T₀) mathematically differ from using a relativistic frequency contraction (f=f₀/&gamma; )?

The latter doesn't take the doppler effect into account, I think. That is, if you're talking about actual perception, instead of reality.

Neither takes doppler effect into account. I was talking about mathematics. Unless there is a mathematical difference between an observed time being dilated and an observed frequency being contracted, the difference in reality is philosophical.

There is no difference except for what quantity you are after. Frequency is just the inverse of time.

SL is right. There is no difference.

f = 1/t

T=γT₀

1/T = 1/(γT₀)

f = f₀/γ

If there is no mathematical difference, why do proponents of SR get bent out of shape when a "quack" says that time dilation does not modify time but only the tick rate of the clock?

They are naturally bent out of shape - possibly from years and years of mental abuse. :D

Anyway, if you are talking about SR, then you must say "the tick rate as seen by such and such frame...". You cannot talk in terms of absolutes.

Given that philosophy may be considered mental abuse and physics without mathematics is philosophy, there may be some truth in your statement.

I have no problem talking about relative tick rates. It's not counter-intuitive.

....I look forward to it. :D It follows and I mean no offense by in it at points where I say your ideas are naive. Perhaps inocent would have been a better word. All I mean is that there are many things that you are not considering that corrupt your simple ideas about comparing "accumulated times" in two different frames. (You never even mention some of the most important factors and that certainly is "naive."

But first a few words about your reply: I have only just read it without a lot of thought. I think I tend to agree with you that "time dilation" is on much more solid basis that "length contraction." perhaps length contraction is only "illusion." (I am not well versed in SRT and don't really know what I think about "length contraction." I also admit that you are much better informed than me about of the evidence for and and against SRT, especially GPS, etc.)

Ok here my thought and arguments about measuring/comparing "accumulations of time" in two different inertial frames:

This post is long, so I’ll give the conclusion derived in it first. The conclusion is developed in a chain of small logical steps. My statements about the basis of MacM’s views are probably not exactly what he would like, but he only states that “reciprocity of SRT” leads to a “physical impossible” result, without giving any basis for this claim. (To him, it is obvious.) More importantly, he makes no attempt to describe how the period in which the two clocks accumulate time in their respective frames is to be defined. This omission is naive as the distance between the start and stop clock events, not SRT, usually determines the most of the difference in accumulated time measured.

CONCLUSION: MacM’s idea that “reciprocity” destroys SRT is naïve nonsense. I think he bases his claim on the plausible, but wrong, idea that in the two different frames, there must be the same amount of proper time between a “clock start event” and a “clock stop event”, if both frames use the same pair of events and there are no “perception delays.” That is, MacM thinks non accelerating clocks accumulating their own proper time between these same two events should accumulate the same proper time interval and certainly can not both record less elapsed time than each other, as he claims SRT predicts. It does not. SRT claims only that time is dilated (not that time is “perceived” to be dilated or that the dilation is only “illusion.“). I.e. SRT claims that all physical processes in the other frame take more of this frame’s proper time than the same process requires in this frame, but says nothing about the proper time accumulated between start and stop events common to both frames. There is nothing in SRT about clocks accumulating time intervals both smaller than the other. (MacM‘s “reciprocity“ is a “strawman” he set up to knock down.)

I started this thread with a “twist” to the standard "moving train" examples because trying to compare clocks (or time intervals between the occurrence of events) that are not adjacent easily confuses the facts with “perceptions.” This is because time is required for light (or signals) to travel between two separated points so events can be perceived after they have actually happened. In at least one of the two frames moving wrt each other, the “start clock” and “stop clocks” events must be physically separated, if the same events are used in both frames. This space like separation will be shown to be very important to the amount of time accumulated and can not be ignored as MacM does.

A brief summary of first post’s “twist“ follows in this paragraph: Two small bombs on side of a train, one at each end, are exploded simultaneously by flash of flashbulb, also mounted onside of train, midway between bombs. A long line of men, standing shoulder-to shoulder next to track, all have their noses just grazed by passing bombs. An unlucky pair get killed but not simultaneously in their frame as train advanced a little while light from flashbulb was traveling. (Bomb at front of train explodes after one at end of train.) No problems exist in this example with “perception delays” - dead men, with explosion stopped clocks, exist in both frames who were adjacent to the explosions when they occurred.

Step 0: An initial statement, which I hope (and expect) all can accept as “true fact.” (If you think the conclusion is not true, tell why and in which step the first error is made.):
102 units of proper time (time in the clock’s rest frame) are not the same as 1 or 2, or 3 or 4 units of proper time and physically-identical, well-made, non-accelerating clocks in different frames do measure proper time, if they are not broken. (Their physical processes are identical, require the same amount of proper time, etc. because all physics is identical in all inertial frames.)

Step1: Simultaneous explosions in train frame are not simultaneous in the station frame and this is “fact“, not "illusion". (See proof in first post of this thread.)

I express this fact as follows: “Event "F" occurrs after event "R" in the station frame, (“Event F" is the explosion at Front of train and “event R", the explosion at the train‘s Rear) but events F&R were simultaneous in the train’s frame. (Train time of event “x” will be indicated by "Tx" and station time of this same event will be designated by "Sx".)

Step 2:To be specific, lets say the temporal difference Sf - Sr = 100 units of time in the Station frame. Note that if the train were twice as long, it would be 200 units of time. I.e. grant me that some combination of train length and speed does result in Sf - Sr = 100 time units even though Tf -Tr = 0, regardless of train length or speed. (For real trains, one time unit would be much less than a second, but I will never specify the size of a “time unit” in this presentation.)

Step 3: Now I want to slightly modify the location of the flashbulb, moving it closer to the rear of the train, by approximately the distance light travels in one unit of proper train time, so that even in the train's frame the explosion at the front is slightly later than the one at the rear. I.e. Tf > Tr. Thus, Tf-Tr is approximately 2 units of train time.

Step 4: I said “approximately” in step 3 because after the move, Sr -Sr is exactly 102 units of station time. I will continue to use “Tf-Tr = 2” units of train time, but if because of “time dilation” or “length contraction” effects you think Tf - Tr should be only 0.1, or 1, or 3, or 4, etc. units of time, I will not argue with any choice you like, so long as you agree that (Sf - Sr) >> (Tr -Tr.)
If you can not agree that these two observed time intervals differ greatly, then let me increase the train length so that Sr -Sr = 100,000,000,002 units of station time, noting that Tf - Tr remains essentially 2 units regardless of train length. Them perhaps you will agree that (Sf - Sr) >> (Tr -Tr.).

Step 5: I don‘t give either the train’s speed or the exact value of (Tf - Tr) as, in the latter case, MacM would not agree I computed (Tf -Tr) correctly as I would use only the relative velocity and not MacM’s "two components of velocity" that make up the relative velocity. (Main reason why I don’t use MacM’s method is that I don’t have the slightest idea what these two velocity components are.)

Now lets state what have we have thus far. (I think everyone still agrees.):
Step 6: Sf-Sr =102 exactly and Tf-Tr = 2 or something close to 2.

Now lets get to MacM's two clocks accumulating time, using the two explosions as the “start stopwatch/clock” and “stop stopwatch/clock” events. MacM claims SRT's "reciprocity" will cause each clock accumulate less time than the other - a "physical impossibility." Because it is even a logically impossible for both A to be less than B and B to be less than A, I agree it is also a “physical impossibility“, but, as noted earlier, SRT does not claim this occurs. That claim is only MacM’s “strawman.”

What MacM consistently fails to do is describe in any detail how the two clocks, in different frames are started “at the same time” (I.e. by the same “start event”) and “stopped at the same time“ (I.e. by the same “stop event”). He appears to be naively unaware of the fact that the time accumulated by each clock between these common start and stop event depends very strongly on the distance separating the start and stop events, as is clearly demonstrated above by fact (not illusion) that (Sf -Sr)>>(Tf -Tr). In the case of the extra long train mentioned at the end of Step 4, the difference in the accumulated times, due mainly to spatial separation of the start and stop events, was 100,000,000,002 proper time units vs. essentially 2 proper time units! Also note that even if the start and stop events are collocated in one frame, they are physically separated in the other. That is, the “distance effect” upon the amount of time accumulated by at least the stopwatch/clock in one frame can never be ignored, but MacM always does.

Step 7: I hope everyone agrees that the “distance effect” upon the amount of time accumulated (demonstrated numerically above) is "true fact", not "illusion." The big difference in accumulated times observed in this numerical example is due mainly to the fact that the start and stop events were almost simultaneous on the train but well separated in time on the ground and has little or nothing to due with SRT. I also note that to avoid “perception delays” the time of the event must be measured at the site of the event. Because at least in one frame the start and stop event are physically separated, this means that synchronized clocks must be available through out the frame and at least one time accumulation period must be computed by subtracting the time displayed on the clock collocated with the start event from the time later displayed on the clock collocated with the stop event.

Step 8: Now lets bring in MacM's "reciprocity" more directly into the discussion (by noting that this "train" was a "space train" passing galactic station "z483" with a relativistic speed) such that SRT theory predict a 1 to 2 time dilation, both ways. (MacM‘s "reciprocity" problem or proof that SRT is wrong)

Now lets hear what information is exchanged between station and train observers, but please recall from the proof in first post of this thread that synchronized clocks correctly keeping proper time at different locations in one frame can not be synchronized with those correctly keeping proper time in another frame:

9a: The station observers say to the train observers:
"Your clocks are running slow by a factor of two and not synchronized. When our properly synchronized ones all show noon, each of yours, which is next to one of ours showing noon, is showing a different time at each different location."
and:
9b: The train observers say to the station observers:
"Your clocks are running slow by a factor of two and not synchronized. When our properly synchronized ones all show noon, each of yours, which is next to one of ours showing noon, is showing a different time at each different location."
then:
10a: The station observers say to the train observers: "The correct time accumulation between start and stop events R & F is 102 units, but in your frame it is 51 units, as time is passing more slowly there. Because events R &F did not take place at the same point and you computed it by the time difference between local clocks that were not synchronized you got only 2 units - nonsense."
and:
10b; The train observers say to the station observers: "The correct time accumulation between start and stop events R & F is 2 units, but in your frame it is 1 unit, as time is passing more slowly there. Because these events did not take place at the same point and you computed it by the time difference between local clocks that were not synchronized you got 102 units - nonsense. There is another reason for your error which we think you will admit. You let the time accumulate much too long before stopping your clock. More about this will follow later.”

Note that 9a, 9b, 10a & 10b are not part of the conclusion derivation. Hence the word “Step” has been omitted but the paragraph numbering has been continued for ease of reference if anyone wants to comment on the exchange between the two frame‘s observers.

Step 11: Summary of the facts: The time accumulated on the train between the start and stop events is observed to be essentially 2 units. The time accumulated in the station frame between the same start and stop events is observed to be 102 units, both using identical clocks that are synchronized correctly through out their own frame. (This was confirmed by flashing a strobe light located mid way between various pairs and seeing that all pairs displayed identical time under the strobe flash.)

Step 12: This large difference is not due to either correct or erroneous application of SRT‘s “time dilation“. It is due to the effects demonstrated in the first post of this thread. (Events simultaneous in one frame are not in another and clocks can not both keep proper time correctly and be synchronized with those through out another frame that are keeping its proper time correctly. (Thus far no one has challenged the first post demonstration of this.)

Step 13: Fundamentally this great difference in “accumulated time” is due to fact that even two successive events at one location in one frame (purely time separation) are at least partially space like separated in the other frame. (Space and time are mixed differently in the two different frames.) Thus it is nave to think one can make comparisons of time accumulations periods only considering clocks and ignoring the space like separation that must exist between the two events in at least one of the two frames.

Step 14: Thus it is excessive naive to make any statement about the time lapse intervals or “time accumulated” in two different frames even if (1) the same events are used to start and stop the clocks/ accumulators and even if (2) there are no “signal propagation delays” or “perception problems“ without describing how the clocks are started and stopped and where they are when these events occur.

A final note to clarify something that may be troubling some people:
How does the train observer explain that the station observer recorded 102 units as the time accumulated between the two events, when he knows time is progressing more slowly there by a factor of two, and he observed only 2 time units “accumulated“?

15: Superficially, one would think that if the station clocks have “ticked” 102 times while train clocks have only ticked twice, then the station clocks must be running faster, not slower. The answer is simple.

16: First note that the station’s measurement of “accumulated time” (102 units) was computed by subtracting the “time” shown on clocks two at different locations. These “station frame clocks” were not showing the same times at the start and stop instants that all the train observer’s clocks were showing, even though the train frame clocks were sitting immediately beside the station clocks. The train observer “knows” his clock are correctly synchronized, and doubts that the station clocks are. (When the adjoining train clocks all show noon, only one station clock is also showing noon. All the rest are showing different times at the instant of train’s noon.) Obviously subtracting the times shown on two different non synchronized clocks at different locations can produce nonsense.

17: In addition to this “lack of mutual synchronization” problem (The station observers also claim that the train clocks all show different times when their clocks are all showing 12 noon and thus it is the train frame’s clocks are not synchronized.), there is also the fact, admitted by the station observers, that the time delay between the flashbulb flash and the front explosion or “stop event’ was increased more than the period between the flashbulb flash and the rear explosion (start event) was reduced by the motion of the train. That is, in the station frame, the total distance light can travel during the interval between explosions is always greater than half the length of the moving train. (See numerical example at end of post if this is not obvious.)

18: In the train’s frame, during the interval between the two explosions, light can travel zero distance if the flash bulb was centered or only tiny fraction of the train’s length when the flashbulb was slightly shifted towards the rear of the train. If light can travel much farther during the interval between start and stop events used in the station‘s measurement of “accumulated time,” clearly the temporal separation of these events in the station’s proper time is much greater than the proper time between these same events in the train’s frame. (Speed of light is the same in both frames, so longer light travel distances imply longer travel intervals.) If the stations observers let their stopwatch /clock accumulate time for a much longer interval, it is not surprising that their measured of the “accumulated time” between these events is much larger, for example 102 time units vs. only 2 time units.

19: I hope it is now clear that because of the inherent conflict about whose clocks in different locations are “synchronized“ and fact that even the same pair of start and stop events can have greatly different amounts of proper time between them in the two frames, it is not possible or meaningful to try to compare “accumulated time” in two different frames. Certainly it is nonsense to make any claim of comparing “accumulated time” in different frames without at least describing how the “stopwatch accumulators” are to be started and stopped. The distance separating the start and stop events must be carefully considered, not ignored, as the above demonstration shows.

Numerical example showing light travels more than half the length of the train according to the station observers:

20: For this example, assume that train speed is 0.8c and the moving train is twenty light units long in the station frame. For convenience, let the flashbulb flash at t=0. During 5 time units, (I.e. between t=0 and t=5) light from the flashbulb moves 5 light units towards the rear of the train and the rear of the train moves 4 light units towards the oncoming light but light wave front and bomb’s optical fuse are still separated by 1 light unit. Half a time unit later (at t=5.5) the gap between bomb’s fuse and advancing light front is only 0.1 light unit. At t = 5.55 this gap is only 0.01light units, etc. That is the rear bomb explodes at time t= 5.5555555... and the distance this rearward light traveled in this interval is (55/10) light units.
The front bomb explodes at t =50 when the light has travel 50 light units and the 20 light unit long train has advanced 40 light units. Thus in this case, the station observers admit that even in their proper time, the interval between the two explosions is 44.4444444... time units. -Much more that the 2 time units available for “accumulating time on the train. This difference could be greater or less depending upon the length of the train, its speed, and how close to the train center the flashbulb is, but if it is a relativistic train this effect can not be ignored.

If I am ever really bored, I might consider reading the above..

<b<a

Nice effect you found Billy T.

BillyT:

CONCLUSION: MacM’s idea that “reciprocity” destroys SRT is naïve nonsense. I think he bases his claim on the plausible, but wrong, idea that in the two different frames, there must be the same amount of proper time between a “clock start event” and a “clock stop event”, if both frames use the same pair of events and there are no “perception delays.” That is, MacM thinks non accelerating clocks accumulating their own proper time between these same two events should accumulate the same proper time interval and certainly can not both record less elapsed time than each other, as he claims SRT predicts. It does not. SRT claims only that time is dilated (not that time is “perceived” to be dilated or that the dilation is only “illusion.“). I.e. SRT claims that all physical processes in the other frame take more of this frame’s proper time than the same process requires in this frame, but says nothing about the proper time accumulated between start and stop events common to both frames. There is nothing in SRT about clocks accumulating time intervals both smaller than the other. (MacM‘s “reciprocity“ is a “strawman” he set up to knock down.)

We have all many times tried to explain this to Mac using many of the same words. This is exactly his problem. I predict that your entire post will be labeled "rhetoric", "innuendo", or some other combination of Mac's favorite denouncements.

MacM probably won't bother reading Billy T's post, and if he does read it he will ignore it, especially the part quoted by superluminal.

I agree that the quoted paragraph is a correct description of MacM's views. MacM believes that SRT requires two clocks to "accumulate different times for the same trip", which is not in any way a correct description of SRT.

To MacM:
I know you are busy defending your views and fending off personnel attacks and that my step by step logic demonstration of your errors of omission is long. I hope you are not offended by my characterizing these omissions as “naïve.” There is nothing personal in this, I like you and respect you personnally. I continue to think you are the smartest crackpot I know.

You are completely correct that SRT implies “reciprocity” between two inertial frames, but error when you then state that this implies a “physical impossibility” (clocks in the both frames accumulating less time than the other.)

This is not what SRT states. You do not tell how the period of time accumulation is to be initiated nor how it is to be stopped but occasionally at least imply that both use the same event to start the accumulators running and the same subsequent event to stop them.

My long post concluded with a numerical example: Train traveling at 0.8c and 20 length units (20L) long had explosions set off at each end by flash of light originating 1L closer to the rear of train than the mid point of train. Because 1L is the distance light travels in 1 time unit (1T) the explosion at the front of the train (to observers on train) is 2T after the one at rear.

To observers on the ground, if t = 0 is the instant of the flash, then the explosion at rear of the train occurs at t = 5.55555... T units and the one at the front at t = 50 T or 44.44444... T units Later.

If these two explosions are the “start” and “stop” events used for accumulation of time, then without any consideration of SRT effects, the ground accumulator will record the passage of time for more than 22 times longer than the train observers.

Clearly your neglect to consider even the non-SRT effects of the fact that the start and stop event have different separations in the two frames is “naïve.” Certainly both start and stop events could be with zero spatial separation in one frame, but not in both, if they are the same events.

To drive home more clearly the effect of distance, let the train be twice as long - Then the ground accumulator accumulates time almost 45 times longer. When I make these statements I am assuming that both accumulators (clocks with stopwatch function) are identical and thus each “tick” is the same amount of “proper time”. (I think you do agree that physics is the same in all inertial frames. If it were not, it would be easy to discover a unique “absolute rest frame.”)

The unavoidable fact that at least in one frame the start and stop events are physically separated is very important in determining the time accumulated, but naively ignored by you as you never describe how the two accumulations of time are to be done (the operational procedure) but only state that it is “obvious” that both can’t be less than the other (I agree with this but note SRT makes no such claim - only that each frame’s observer find time passing more slowly in the other frame. )

IF YOU WANT TO COMPARE TIMES ACCUMULATED YOU MUST TELL HOW THE COMPARISON IS TO BE DONE. It is neither trivial nor "obvious" as you naively assume.

I made this shorter post to encourage you to go thru the longer one and tell which of the numbered paragraphs in it is the point of error in your view. If you continue to ignore a step by step logical demonstration that your claims that “reciprocity” disproves SRT are at best “naïve” then I will be forced to join others (see James R's & SL's posts below this one) in thinking you “duck and weave” to avoid hard questions.

The Lonely Astronaut Paradox

Case 1
Two space ships are approaching each other in deep space (at relativistic speeds). One has a male in it and the other has a female in it. The male looks at the female through his powerful telescope, and since he understands relativity theory, he is not surprised that she appears to move in slow motion.

Outer space is a lonely place, so the male decides to accelerate to join frames with the female. When he does this, he notices her clock start advancing faster and faster. She is no longer in slow motion, but she is actually in fast motion now. She ages a few years in just the amount of time that it takes for the ships to join frames. They fall in love and live happily ever after.

Case 2
The following variables are identical to Case 1: Same relativistic speed, same age people, same acceleration rate used to join frames.

Except this time the female ages twenty years in the time it takes for the ships to join frames. The reason for this difference is because the ships had been in relative motion for a longer period of time. Since the rate of the female's clock was dilated for a longer period of relative motion, this translated to greater aging during the frame-joining acceleration period.

Questions
Where is the velocity history information stored? How can equal acceleration in the two different cases result in different rates of clock "speeding up" during the acceleration without such velocity history? Or is it more accurate to say that the rate change for the clock will be the same in both cases due to the identical acceleration?

To MacM:
I know you are busy defending your views and fending off personnel attacks and that my step by step logic demonstration of your errors of omission is long. I hope you are not offended by my characterizing these omissions as “naïve.” There is nothing personal in this, I like you and respect you personnally. I continue to think you are the smartest crackpot I know.

HeHe :D You do present a mixed bag of flatery and insult. We have a number of differances of views but nothing you have ever posted has offended. I do tend to see your statement as selfserving and not informative as to this list of omissions you mention.

You are completely correct that SRT implies “reciprocity” between two inertial frames, but error when you then state that this implies a “physical impossibility” (clocks in the both frames accumulating less time than the other.)

This is not what SRT states.

Here we do disagree. It is not my interpretation but is clearly stated in most literature on relativity. It states in specific terms that given a inertial relative velocity between "A" and "B" that "A" sees himself as at rest and that "B" has ALL motion and "B" IS dilated relative to "A". Likewise at the same time (which it must be to be relative motion) "B" also sees himself as at rest and that it is "A" that has ALL motion and "A" IS dilated relative to "B".

Now I suggest we clear up this issue at this point since anyother issues are moot.

You do not tell how the period of time accumulation is to be initiated nor how it is to be stopped but occasionally at least imply that both use the same event to start the accumulators running and the same subsequent event to stop them.

That can be done but is not necessary. The issue is not linked to simultaneity but to the statements of reciprocity from above. Tick rates need not have simultaneous start/stop times but is a comparison of ongoing ticks within the same time period of relative velocity.

Accumulated time, "yes" you must then provide start/stop conditions. But even accumulated time is based on comparative tick rates. So one doesn't need to complicate the issue by evaluating time dilation and reciprocity from the vantage point of accumulated time but merely comparative tick rates.

So do you want to claim that during periods of relative velocity between "A" and "B" that each has a tick rate slower than the other?

Once (if it ever happens) we can agree on the issue of tick rates and reciprocity then I would be more than happy to debate a scenario which includes specific start/stop and simultaneity issues.

Questions
Where is the velocity history information stored? Haven't you heard of the matrix? I thought people knew these things. :m:


How can equal acceleration in the two different cases result in different rates of clock "speeding up" during the acceleration without such velocity history? Or is it more accurate to say that the rate change for the clock will be the same in both cases due to the identical acceleration? No need to worry, the relativity of simultaneity fixes everything. All is well.

MacM probably won't bother reading Billy T's post, and if he does read it he will ignore it, especially the part quoted by superluminal.
Wrong again. Further more you don't seem to have a clue as to what my view is, or you simply enjoy distorting it and making up crap that you can argue against. You certainly aren't arguing anything to do with my views.


I agree that the quoted paragraph is a correct description of MacM's views. MacM believes that SRT requires two clocks to "accumulate different times for the same trip", which is not in any way a correct description of SRT.

As I said you don't have a clue. From point "A" to point "B" is the same trip but you of course choose to believe it is a different distance; which I have shown is shaear nonsense.

We have all many times tried to explain this to Mac using many of the same words. This is exactly his problem. I predict that your entire post will be labeled "rhetoric", "innuendo", or some other combination of Mac's favorite denouncements.

Don't you get tired of being wrong? :D

It follows and I mean no offense by in it at points where I say your ideas are naive. Perhaps inocent would have been a better word. All I mean is that there are many things that you are not considering that corrupt your simple ideas about comparing "accumulated times" in two different frames. (You never even mention some of the most important factors and that certainly is "naive."

But first a few words about your reply: I have only just read it without a lot of thought. I think I tend to agree with you that "time dilation" is on much more solid basis that "length contraction." perhaps length contraction is only "illusion." (I am not well versed in SRT and don't really know what I think about "length contraction." I also admit that you are much better informed than me about of the evidence for and and against SRT, especially GPS, etc.)

Ok here my thought and arguments about measuring/comparing "accumulations of time" in two different inertial frames:

This post is long, so I’ll give the conclusion derived in it first. The conclusion is developed in a chain of small logical steps. My statements about the basis of MacM’s views are probably not exactly what he would like, but he only states that “reciprocity of SRT” leads to a “physical impossible” result, without giving any basis for this claim. (To him, it is obvious.) More importantly, he makes no attempt to describe how the period in which the two clocks accumulate time in their respective frames is to be defined. This omission is naive as the distance between the start and stop clock events, not SRT, usually determines the most of the difference in accumulated time measured.

CONCLUSION: MacM’s idea that “reciprocity” destroys SRT is naïve nonsense. I think he bases his claim on the plausible, but wrong, idea that in the two different frames, there must be the same amount of proper time between a “clock start event” and a “clock stop event”, if both frames use the same pair of events and there are no “perception delays.” That is, MacM thinks non accelerating clocks accumulating their own proper time between these same two events should accumulate the same proper time interval and certainly can not both record less elapsed time than each other, as he claims SRT predicts. It does not. SRT claims only that time is dilated (not that time is “perceived” to be dilated or that the dilation is only “illusion.“). I.e. SRT claims that all physical processes in the other frame take more of this frame’s proper time than the same process requires in this frame, but says nothing about the proper time accumulated between start and stop events common to both frames. There is nothing in SRT about clocks accumulating time intervals both smaller than the other. (MacM‘s “reciprocity“ is a “strawman” he set up to knock down.)

Entirely mis-stated. Yes my examples are often simplified because I believe they can and should be. True time dilation has nothing to do with simultaneity or start/stop events. Measureing accumulated time that becomes another matter.

But true time dilation MUST be based on a differential of clock tick rates. That is how time accumulates. If there is no tick rate differentail then there is no time dilation. Tick rates are not subject to simultaneity and require no start/stop synchronizaton. To attempt to debate time dilation interjecting simultaneity, etc is to simply cloud the issue.

Keep it simple. Given an inertial relative velocity between "A" and "B",in accordance with SRT from "A's" frame "B" has ALL motion and "B" is dilated (its tick rate is slower) relative to "A".

Likewise during the SAME absolute period (Which must be the case if the motion is relative) SRT claims that it is equally true that "B" is at rest and "A" has ALL motion and that "A" is dilated relative to "B" (it's tick rate must be lower than "A").

This space like separation will be shown to be very important to the amount of time accumulated and can not be ignored as MacM does.

MacM doesn't ignore it. MacM just understands that it is not part of the issue. Only tick rate and not simultaneity of start/stop, etc must be evaluated to determine if reciprocity of time dilation can be reality.

I appreciate the effort you have put into this long scenario, however, I see no justification to chase simultaneity issues. The issue is reciproicty of time dilation which is based on dilated clock tick rates and are not subject to simultaneity.

If you can answer my simple question first and it then merits it I will go through your scenario but I fail to see it's relavance other than to confuse the issue.

I will soon reply to MacM but that takes longer.

Neddy Bate states: “…looks at the female through his powerful telescope …” so already he opening the door to confusion between what is real now and what happen long ago.

I started this thread with a scenario that avoids the perception vs. reality problems and hope others who introduce their own scenarios will try to do the same. This subject (SRT) is confusing enough without dragging the problem of “perceptions” in.

None the less I will comment briefly on Neddy’s scenario:

His case 2 differs from case 1, I think, in that initially the two ships are farther apart. This will produce the extra 20 years. I don’t understand his description “the ships had been in relative motion for a longer period of time” - a statement in the past tense but what happened before “now” - the astronaught observing via telescope - would not seem to make any diffence to what will happen. Thus I will assume he means the ships in case 2 were initially farther apart than in case 1 and answer his other points/question.

He states: “…greater aging during the frame-joining acceleration period. …” This leads me to belive he thinks that the “acceleration” is responsible for the aging effect. If so this is an error. Except for the fact their bodies could not withstand the forces, the entire acceleration could only last a few seconds, by anyone’s clock. It is the relative velocity over an extended period that causes the differential aging effects.
This apparent belief in acceleration as the cause is restated in:
“How can equal acceleration in the two different cases result in different rates of clock "speeding up" during the acceleration without such velocity history? Or is it more accurate to say that the rate change for the clock will be the same in both cases due to the identical acceleration?”

As far as where the “velocity history is stored” - It is not stored anywhere. I was once, a long time ago, passing a year between ages 5 & 6. There is much more stored about that year (compared to zero) than any storage of “velocity history.” To show how strange this “velocity history” storage concept is, I ask Neddy: Is the velocity history stored in English text, binary numbers, stone tabulates, etc. - his concern was only as to where it is stored, so I can ask about the format.

First, MacM, let me congratulate you on a fine reply, in the two posts defending your position, but of course I think it fails to do so. (You really are smart and I greatly enjoy discussion with you.) Some might now be forced to admit that you did not “duck” my attack, but would say you did “weave” by transferring it to a concern over “tick rates”, but I do not say that, nor believe that.

First let me directly answer your question:
“So do you want to claim that during periods of relative velocity between "A" and "B" that each has a tick rate slower than the other? ”

Yes I do. To you this is “obviously impossible” and my long post (Only for you would I have spent several hours drafting it off line.) is an introduction of irrelevant information/ concern about “simultaneity problems” when the fundamental “impossibility” is two tick rates, both slower than the other.

I won’t comment more on your statements about frames A & B as I agree with what you said and never claimed it was your “interpretation“ That is I agree that what you said is the SRT view. I understand how it is troubling you, leads you to think that SRT must be wrong, etc. (I think) but these SRT facts do not trouble me. There is no logical (and hence no physical) “impossibility” that you infer and think “obvious” inherent in these facts. Let to try to show this:

You state in one of your two posts:
“Tick rates need not have simultaneous start/stop times but is a comparison of ongoing ticks within the same time period of relative velocity.”

In this, IMHO, you error, and once again by letting your intuition or simple view (dare I use the word “naïve“ again?) control your thoughts without thinking carefully about what is “tick rate“ and how is it measured and then compared in two different frames.

There are even two hints about where you need deeper thought in your own statement: (“comparison” & “the same time period.”)
(1) If two things are to be compared in a thought experiment, one must fully describe the operational procedure to be used. (More on this later.)

(2) One must also carefully indicate how one knows it is “the same time period.” I always have been assuming your answer to this was in essence:
“Use the “same event” in both frames to start the time period and a subsequent “same event” in both frames to stop it, being very careful not to confuse “delayed perception” of an event with when “it actually happened.” Thus, the scenario that started this thread postulated two explosions as the start and stop event, both being observed in each frame by observers collocated with the events. (actually clocks stopped by the explosions, not by dead men, as I first suggested.) If I am wrong in this assumption, tell me what procedure you prefer, but I think you agree that this is the most reasonable way to assure that the two frames are indeed using “the same time period” so I will now turn to discussion of (1) above:

First I think we agree on what “tick rate” is, but just to be clear I will give a definition:
Tick rate is the difference between the tick numbers divide by the time interval that elapsed between the ticks. For example, if tick number 3600 occurred one second later than tick number 2600, the tick rate is 1000 ticks per second or one millisecond potential error always exists with this clock.

No clock actually measures time. All use some discrete steps of some physical processes and the time interval they “measure” has an error equal to the time between successive discrete steps or “ticks.”
(I bet a smart guy like you already sees where I am going, but let me beat this dead horse a little longer.)

For example, one can conceive of a very high resolution clock using electroplating copper with large DC current of exactly known amperage (not possible actually as current comes in discrete packages we call “electrons“). Also postulate there is a scale of infinite precision. This clock “measures” time intervals between start current and stop current events by weighing the copper deposited. The precision of this clock is the time it takes to deposit one copper atom. (neglecting electrical inductance and the associated non step function of current switching, etc.)

Again: No clock measures time. All clocks use a start and stop event. (Call these events “tick m” and “tick n” or assign specific integers etc. but note they are discrete events.)

(I think that horse is surely dead now.) and that you will agree with the fact the difference in tick numbers is not a measure of time, but only an approximate measure of the time elapsed between a “start event” and a “stop event.” My point has nothing to do with “clock precession,” but that that all clocks involve start and stop events.

Yes that is right. “Tick rate” does inherently involve a start event (tick number 2600) and a stop event (tick number 3600 in my numerical example above). You can not escape this fact.

If you like, you can assign “tick numbers” to my two explosions, but you can not escape the fact that comparing tick rates inherently requires a start event and a stop event.

Thus it is “naïve” to think that “simultaneity questions” are not inherently involved in a comparison of “tick rates.” If the tick rate in one frame is to be compared to that in another, one must carefully describe how one selects the start and stop events associated regardless of whether the “start event” is the sound of a tick (precisely recorded) or the sound of an explosion (precisely recorded). I.e. my “explosions” are no different in principle than your “ticks.” - Both are conceptually discrete physical events, used as start and stop events but as you use “clock ticks” you are more subject to error than me because all clocks only approximately measure time intervals. In contrast, I define the time interval by the period between explosions. I admit that the two clocks I use to measure this defined interval have error but it is very small compared to the difference 102 T vs. 2 T I exhibited in my numerical example.

SUMMARY: It is only “intuitively plausible“, but not true, that one can compare tick rates in two different frames without worrying about the “simultaneity” of the start and stop events required for the comparison. Thus you are wrong in the other post when you said:

“Tick rates are not subject to simultaneity and require no start/stop synchronization. To attempt to debate time dilation interjecting simultaneity, etc is to simply cloud the issue.”

That is too naïve a view. Support your claim by telling me how tick rates are first measured in a single frame and then how they are to be compared between two frames without, for example, the use of a “simultaneous start event“ common to both frames. I think one compares tick rates by counting a large number (for better accuracy) of ticks that occur between some “start event“ and some “stop event“ and that both frames should use the same pair of events to start and stop the counting of ticks.
If you do not agree, how do you first measure tick rates in either frame and then compare the measured results between frames?
(Ball back in your court.)

PS I want to note (for the benefit of others) that MacM and I have both defended our views strongly by sticking to physical arguments, without resorting to the more common personal attacks some substitute for physics arguments. I.e. a high standard of behavior is possible, even in strong conflicts.

...Likewise during the SAME absolute period (Which must be the case if the motion is relative) SRT claims that it is equally true that "B" is at rest and "A" has ALL motion and that "A" is dilated relative to "B" (it's tick rate must be lower than "A"). Sorry MacM you lost me here. "absolute period" ??? and the following parenthical note??? But not much if any problem on what SRT is reported to claim - Note my "Yes i do." in loger post just made.
If you can answer my simple question first and it then merits it I will go through your scenario but I fail to see it's relavance other than to confuse the issue.I'll try, but did not see any question here, please restate it.

I also look forward to reading your reply in another thread as to how your uniKEF theory avoids the two problems for it I listed there.

Thank you for responding to my scenario, BillyT. I am genuinely trying to learn where I must be going wrong with my understanding of STR.
Neddy Bate states: “…looks at the female through his powerful telescope …” so already he opening the door to confusion between what is real now and what happen long ago.

I started this thread with a scenario that avoids the perception vs. reality problems and hope others who introduce their own scenarios will try to do the same. This subject (SRT) is confusing enough without dragging the problem of “perceptions” in.
I introduced the telescope for one reason: to show that the female is time dilated ("in slow motion") relative to the male. Is this strictly a 'perception' issue?

None the less I will comment briefly on Neddy’s scenario:

His case 2 differs from case 1, I think, in that initially the two ships are farther apart. This will produce the extra 20 years.
That last line is important. You do not deny that case 1 could yield 3 years and case 2 could yield 20 years.

I don’t understand his description “the ships had been in relative motion for a longer period of time” - a statement in the past tense but what happened before “now” - the astronaught observing via telescope - would not seem to make any diffence to what will happen.
I agree that what happened before would not seem to make any difference to what will happen in the future. That is why it becomes a paradox.

Thus I will assume he means the ships in case 2 were initially farther apart than in case 1 and answer his other points/question. Yes, I meant that the ships would have started farther apart. So the different tick rates of the two clocks has had more time to accumulate to a larger difference in clock readings. This is a reciprocal effect, I might add.

He states: “…greater aging during the frame-joining acceleration period. …” This leads me to belive he thinks that the “acceleration” is responsible for the aging effect. If so this is an error.
I specifically state that the acceleration in both cases is equal, so that would not be a very good explanation for the two different aging effects. I do believe that SRT requires that it is during acceleration that the clock readings re-align themselves to fit the final outcome. Perhaps I am in error there?

Except for the fact their bodies could not withstand the forces, the entire acceleration could only last a few seconds, by anyone’s clock.
But isn't 'changing frames' the period when all of the time dilation is supposed to accumulate to one clock or the other? Remember, in STR thought experiments, the two clocks are reciprocally dilated. Wouldn't it be very bad for reality if at least one of the clocks did not speed up radically during the acceleration phase?

It is the relative velocity over an extended period that causes the differential aging effects.
This is what causes the male to be younger than the female, and the female to be younger than the male. Even more so in case 2 where the ships started farther apart. Perhaps this is where I am getting lost? Please help.

This apparent belief in acceleration as the cause is restated in:
“How can equal acceleration in the two different cases result in different rates of clock "speeding up" during the acceleration without such velocity history? Or is it more accurate to say that the rate change for the clock will be the same in both cases due to the identical acceleration?”
I was pointing out the apparent paradox that equal acceleration is causing two different shifts in clock readings, one 3 the other 20. I entertained the question of whether it would be more appropriate for the equal acceleration to cause equal shifts in time readings for both cases, but that is my own idea, and not what SRT advocates (if I understand correctly).

As far as where the “velocity history is stored” - It is not stored anywhere. I was once, a long time ago, passing a year between ages 5 & 6. There is much more stored about that year (compared to zero) than any storage of “velocity history.” To show how strange this “velocity history” storage concept is, I ask Neddy: Is the velocity history stored in English text, binary numbers, stone tabulates, etc. - his concern was only as to where it is stored, so I can ask about the format.
Where is the information stored is something of a hypothetical question. I agree that it seems a silly concept which would lead to your hypothetical question as to what format it would be stored in. Aer said in previous post that it was stored in "the matrix" which was aptly humorous if you've seen the movie.

So, please explain to me how the different accelerations can create different shifts in clock readings. You seem to imply that the difference was there all along, essentially being 'stored' in the dilated clocks themselves. In that you seem to have forgotten the problem of reciprocal time dilation. Until acceleration occurs, it is not known which clock is going to end up ahead of which. If the female had accelerated instead of the male, it would be the male who ended up either 3 or 20 years older. The paradox remains... :confused:

...I introduced the telescope for one reason: to show that the female is time dilated ("in slow motion") relative to the male. Is this strictly a 'perception' issue?No it is real, but I am not speaking of what he sees via the telescope. I don't want (or have time) to think carefully about his view. If she is raisng her arm, the lower part of the movement was imaged by lght that traveled a longer distance to his scope (if he was not moving) than the top of the arm movement, so his perception would be even slower motion that the facts due to time passing more slowly. I try to avoid talking about the perceptions.

I agree that what happened before would not seem to make any difference to what will happen in the future. That is why it becomes a paradox. It is a paradox only if true and strange. (I am not saying it is not, only that I don't understand exactly what you are saying.)

Yes, I meant that the ships would have started farther apart. So the different tick rates of the two clocks has had more time to accumulate to a larger difference in clock readings. This is a reciprocal effect, I might add.
Good, I guessed correctly what you were trying to state. And yes it is a reciprocal effect - the biological processes of both are proceeding more slowly than if they were in the same frame. - this is the paradox MacM and I have been disputing here (He may say it is not a paradox as SRT is false on this.) I suggest you read our exchanges, I defend what seems "impossible" and MacM believes it is impossible that time can be passing more slowly in each frame than in the other. I bet it seems very clear to you that MacM must be correct on this. Again read our exchanges.

I specifically state that the acceleration in both cases is equal, so that would not be a very good explanation for the two different aging effects.
I do believe that SRT requires that it is during acceleration that the clock readings re-align themselves to fit the final outcome. Perhaps I am in error there?
...
But isn't 'changing frames' the period when all of the time dilation is supposed to accumulate to one clock or the other?
...
So, please explain to me how the different accelerations can create different shifts in clock readings.

A better way to remove acceleration as an explanation of the change in aging rates is to just let it last very short period by anybody's clock compared to the time "drifting in inertial frames". SRT predicts that the cummulated aging effects is linear in this drift time and can say nothing about the accelerating periods as SRT only applies to inertial frames (GR is much more complex and I don't generally comment on it as I am likely to be wrong.)

Yes you are wrong in your focus on the aceleration periods - forget about the accelerations.
I bet you have heard that the "twin paradox" is not symetric as only one twin experience "acceleration" and he is the one that comes home young. That is all true, but his period of acceleration does not cause his youthful state upon return.

No it is real, but I am not speaking of what he sees via the telescope. I don't want (or have time) to think carefully about his view. If she is raisng her arm, the lower part of the movement was imaged by lght that traveled a longer distance to his scope (if he was not moving) than the top of the arm movement, so his perception would be even slower motion that the facts due to time passing more slowly. I try to avoid talking about the perceptions.
You make a good point that we should avoid talking about perceptions. I guess I just assumed everyone knows to disregard doppler effect and delay-effects caused by c being finite. That way it does not have to be stipulated for every scenario. For example, if the female's ship is approaching at relativistic speed, she would appear in fast-motion not slow motion, but I referred to the slow motion because I already disredarded the doppler effect.

It is a paradox only if true and strange. (I am not saying it is not, only that I don't understand exactly what you are saying.)

Good, I guessed correctly what you were trying to state. And yes it is a reciprocal effect - the biological processes of both are proceeding more slowly than if they were in the same frame. - this is the paradox MacM and I have been disputing here (He may say it is not a paradox as SRT is false on this.) I suggest you read our exchanges, I defend what seems "impossible" and MacM believes it is impossible that time can be passing more slowly in each frame than in the other. I bet it seems very clear to you that MacM must be correct on this. Again read our exchanges.
I have been following your exchanges with MacM, and I am hoping that you or someone can finally explain away the reciprocal time dilation problem. I don't think it has been explain satisfactorily yet, but that does not mean that I reject SRT outright.

A better way to remove acceleration as an explanation of the change in aging rates is to just let it last very short period by anybody's clock compared to the time "drifting in inertial frames". SRT predicts that the cummulated aging effects is linear in this drift time and can say nothing about the accelerating periods as SRT only applies to inertial frames (GR is much more complex and I don't generally comment on it as I am likely to be wrong.)

Yes you are wrong in your focus on the aceleration periods - forget about the accelerations.
I bet you have heard that the "twin paradox" is not symetric as only one twin experience "acceleration" and he is the one that comes home young. That is all true, but his period of acceleration does not cause his youthful state upon return.
Very well, I will try not to focus on the acceleration. I knew it was not supposed to be the cause but I did think that it was during this time that the clocks changed radically.

In closing, let me ask one thing that might help me to finally grasp this:

Is there supposed to be such thing as 'real' motion which induces time dilation and 'real' rest which does not induce time dilation? I thought relativity theory forbids a preferred frame of reference. Because if I cannot focus on acceleration in the twin paradox, then how can I possibly detect which twin will be younger unless I choose a preferred frame?

Oh no, now I am totally confused. Check out this website.

http://www.phys.vt.edu/~jhs/faq/twins.html
(Scroll down to the short section at the bottom.)

This is a pretty good explanation of the twin paradox, but there is one short section at the bottom of the page that treats the twin paradox without acceleration. What the #$^&*? ...Oh lord, now it looks like there is a preferred reference frame. Someone please tell me this is wrong! :eek:

NeddyBate,

Don't fret. Notice it is just the typical slight of hand used by relativists. He has deliberately excluded reciprocity which is inherent in SRT. That is if O' is in inertial velocity and O is at rest. According to SRT it is equally valid to claim O has the velocity and O' is at rest.

Taking that fact into consideration the twin paradox vanishes and the reciprocity paradox arises. Now each twin is younger than the other. :D

Neddy:

I have been following your exchanges with MacM, and I am hoping that you or someone can finally explain away the reciprocal time dilation problem. I don't think it has been explain satisfactorily yet, but that does not mean that I reject SRT outright.

Neddy,

What problem?

dear Neddy:
You have (if I may include myself) three smart guys trying to help you!

Unfortunately we don't agree, but generally I think SL and I are singing the same tune, but that does not that proves MacM is wrong. SL says "What problem?" - I am a little more generious with MacM. I see his problem very clearly. MacM put it to me very well when he asked if I really believed that clocks in both frames A & B were ticking more slowly than in the other. (I think they do, but this is not the logical impossibility it seems to be with only superficial consideration. - As stated in some detail in my posts, one must describe how they are to be compared very completely, including the "simultaneity issues" )
Now my take on your closing question:

All motion is relative. There is no preferred rest frame. In the standard twin paradox, only one twin experiences acceleration and that one is the one who is younger when they stand side by side after his round trip thru space. No problem knowing which is the younger one, but it was the high speed traveling time that caused him to be younger than his now older brother (not the mid-trip, turn-arround, acceleration itself) when they joinly celebrate his safe return to Earth.

I think SL agrees with this, but MacM I am almost sure does not.

PS by edit: I forgot to correct your wrong comments about Doppler Effect: The DE has nothing to do with time dilation, the lady being or appearing younger or older etc. All the DE can do is make her look sad (bluer) or embarissed (red faced). DE changes the frequency of the photons, not the time for them to travel.

Neddy,

What problem?
I'll try to summarize the problem(s) with SR in the case of uniform translational motion:


Time dilation results in two clocks which are each ticking slower than the other clock
The slower rate (of each clock with respect to the other) causes time dilation to accumulate more and more time descrepency depending on how long the journey of translational motion
Acceleration is required to join the clocks in the same frame, and during this acceleration the clocks will have to reconsile their differences
Equal acceleration can cause unequal time shifts depending on how much accumulated time descrepency
No one knows where the information required to acheive the appropriate time shift would be stored
Some claim that acceleration is not even required to acheive this (see link in above post)

dear Neddy:
You have (if I may include myself) three smart guys trying to help you!
And I thank you for your help. I am not being stubborn here. If I could genuinely understand this, I would gladly say so and be on my merry way.


Unfortunately we don't agree, but generally I think SL and I are singing the same tune, but that does not that proves MacM is wrong. SL says "What problem?" - I am a little more generious with MacM. I see his problem very clearly. MacM put it to me very well when he asked if I really believed that clocks in both frames A & B were ticking more slowly than in the other. (I think they do, but this is not the logical impossibility it seems to be with only superficial consideration. - As stated in some detail in my posts, one must describe how they are to be compared very completely, including the "simultaneity issues" )
I think I should consider the simultaneity issues more closely. This is probably where I am going off-track.

Now my take on your closing question:

All motion is relative. There is no preferred rest frame. In the standard twin paradox, only one twin experiences acceleration and that one is the one who is younger when they stand side by side after his round trip thru space. No problem knowing which is the younger one, but it was the high speed traveling time that caused him to be younger than his now older brother (not the mid-trip, turn-arround, acceleration itself) when they joinly celebrate his safe return to Earth.

I think SL agrees with this, but MacM I am almost sure does not.
I tend to agree with you, but did you see the link I provided where acceleration was not considered?

PS by edit: I forgot to correct your wrong comments about Doppler Effect: The DE has nothing to do with time dilation, the lady being or appearing younger or older etc. All the DE can do is make her look sad (bluer) or embarissed (red faced). DE changes the frequency of the photons, not the time for them to travel.
Time dilation was the only thing I was considering when I said that she appeared in slow motion. I agree it is a totally different concept to the doppler effect (DE). However, I think you underestimate the capability of DE to make someone appear in 'fast' or 'slow' motion. Don't you agree that DE is more than just a color shift? I consider it to be the accumulation of light information that is in transit between the source and the receptor. So an approaching source would be sped up and a receding source would be slowed down.

I think SL agrees with this, but MacM I am almost sure does not.

Well you would lose your bet. It is indeed the only answer. That is the onc that accelerates is the only one that has had an energy level change and is the one that will dilate.

That is precisely my view. Reciprocity grants to the twin (clock) that had no change the same dilation affects and that is the error in SRT.

I think I should consider the simultaneity issues more closely. This is probably where I am going off-track. Yes, the relativity of simultaneity fixes almost every intuitive problem one may have with SR. Until you understand the relativity of simultaneity, you shouldn't really be trying to understand relativity problems without just doing the lorentz transformation and trusting the results that pop out - at least that is the advice I would give for anyone who justs wants to understand how relativity works.

...However, I think you underestimate the capability of DE {Dopler Effect} to make someone appear in 'fast' or 'slow' motion. Don't you agree that DE is more than just a color shift? I consider it to be the accumulation of light information that is in transit between the source and the receptor. So an approaching source would be sped up and a receding source would be slowed down.No, it is "just a color shift" or more correctly stated a "frequency shift/change effect." - "color" is not a property of light frequency alone, but the joint effect of the light frequency and the eye's photo receptors. This is expecially obvious if one of the three types of photo receptors is missing (I.e. a "color blind" person) or the observer is normal, but non human. (E.g. Most of the "white" flowers you see are highly colored to the bee. We can tell by measuring their UV reflectivity and also noting bees see (respond to) UV light.)

....the one that accelerates is the only one that has had an energy level change and is the one that will dilate.
That is precisely my view. Reciprocity grants to the twin (clock) that had no change the same dilation affects and that is the error in SRT.I am surprized by your first paragraph quoted above, but not the second. I could swear that you had several times in prioor posts denyed the SRT claim that they are different ages when reunited.
The statement that "reciprocity" makes both dialated is true (and not the logical conflict you think it is as I tried to show in post that ends with: "ball in your court now") but the SRT claim about the twin paradox is that the astronaught twin is younger when he gets home again than this twin brother. SRT does not claim both are younger or have the same age when reunited because they have relative motion when one was making the round trip thru space at high speed. As I read/understand you last paragraph above, that is what you say SRT claims and it does not. ("Reciprocity grants...the same dialations effects...")

I am surprized by your first paragraph quoted above, but not the second. I could swear that you had several times in prioor posts denyed the SRT claim that they are different ages when reunited.

Unfortunently, you do not seem to realize I have many times crossed the aisle to argue the point from a different vantage point. When I have claimed "No" differance in age it was based on strictly velocity (no GR) and included the issue of reciprocity advocated by SRT.

You should keep in mind the original "Twin Paradox" did not consider acceleration as a factor and simply argued the affect was due to time dilation due to velocity of the twin that had accelerated.

The issue of reciprocity made that claim null and void and the next solution was then to claim age differance due to acceleration of the one twin.

That explanation I do not believe is totally correct but is enough so (disallowing reciprocity) that I won't argue the issue.

As I read/understand you last paragraph above, that is what you say SRT claims and it does not. ("Reciprocity grants...the same dialations effects...")

************************************************** ****
http://www.mathpages.com/home/kmath307/kmath307.htm

Given this definition of inertial reference frames, the principle of relativity asserts that for any material particle in any state of motion there exists an inertial reference frame - called the rest frame of the particle - with respect to which the particle is instantaneously at rest (i.e., the change of the spatial coordinates with respect to the time coordinate is zero). This principle is usually extended to include reciprocity, meaning that for any two systems S1 and S2 of inertial coordinates, if the spatial origin of S1 has velocity v with respect to S2, then the spatial origin of S2 has velocity -v with respect to S1. The existence of this class of reference frames, and the viability of the principles of relativity and reciprocity, are inferred from experience. Once these principles have been established, the relationship between relatively moving inertial coordinate systems can then be considered.
************************************************** ***

My statements are consistant with all text descriptions of SR and reciprocity.

Unfortuantely, you do not seem to realize...If Ifail to get back to this remind me - going to bed now. See post I just made in the uniKEF thread. You will like two parts of it (More Oscom razor support for uniKEF.)

Unfortunently, you do not seem to realize I have many times crossed the aisle to argue the point from a different vantage point. When I have claimed "No" differance in age it was based on strictly velocity (no GR) and included the issue of reciprocity advocated by SRT.
If there is no period of acceleration, it is impossible for the astronaught twin to return to Earth. He can not stand beside his brother again on Earth, but is still traveling fast and far away. Thus, you have the fact, well demonstrated in first post of this thread, that the brothers in two different frames do not agree that the other made a "simultaneous" comparison of their ages.

For example, from astronaught's POV, at the instant he turned 30 his brother was only 25 and likewise from the POV of the Earth bound twin, when he turned 30, at that instant his astronaght brother was only 25. This is not a perception delay. It does not mean the "physical impossibility "of one calendar (or clock) being able to display both 30 and 25 at the same time in any one frame (Your "reciprocity" that "disprooves" SRT argument.) It only means, and is due to, the fact that what is a simultaneous comparison of ages for one brother is not done at the same time from the other one's POV. The other one, from his POV send msg to his brother saying: "Have you gone crazy? You are "comparing" our age at two different times, which are years apart!"

PS - I have noticed that you were a moving target, "crossing aisles" as you put it, but perhaps my interpretations of this admission is not what you really intended to state. :)

You should keep in mind the original "Twin Paradox" did not consider acceleration as a factor and simply argued the affect was due to time dilation due to velocity of the twin that had accelerated.velocity is limited by c, but there is no limit on acceleration, in principle, but human bodies do have a limit, but ths is a thought experiments so lets make the entire turn arround period be completed in one second. (If you worry that on the other guys clock it is 10 seconds, then accelerate 10 times faster so on the clock with the greatest measure of time in the turn arround, the turn arround time is only one second.) Let there be 25 years of earth time from launch til turn arround and the trip back is also 25 years so except for a second (or less) the Earth bound brother is 50 years older than he was at launch. (I believe that SRT is correct that the astronaught is younger when standing by is brother on Earth again.) You may call this the "earlier SRT view", I don't care. It is still the SRT view. The fact is that the period of acceleration can be neglected if the acceleration is very forceful/ rapid/ short duration on everyone's clocks compared to much longer travel in inertial frames times.

The issue of reciprocity made that claim null and void [/b] no, it did not. that is the claim of some crackpots, not SRT's "new view" that acceleration is what caused the traveling twin to be younger.
[QUOTE=MacM]and the next solution was then to claim age differance due to acceleration of the one twin.The original solution is still valid - this is nonsense you are making up that SRT now thinks it is the acceleration that is responsibel for the age difference when reunited.

That {new} explanation I do not believe is totally correct... Good at least you are not totally wrong in you post. You are correct in observing that an explaination based on the acceleration as the cause of one twin being younger whe reunited was not caused by the acceleration he experience. Pleas go farther and admit it was caused by the long time spent in two different inertial frames (outbound and return legs of the trip).

If there is no period of acceleration, it is impossible for the astronaught twin to return to Earth.

What do you mean can't return. He never left. :D Just kidding. The point wasn't that there wasno acceleration but that it was not specified or argued as part of the scenario. The claim was that the twin was younger due to his time spent at a relative velocity. No acceleration of one twin and not the other was made.

This is not a perception delay. It does not mean the "physical impossibility "of one calendar (or clock) being able to display both 30 and 25 at the same time in any one frame (Your "reciprocity" that "disprooves" SRT argument.) [/quote that isn't the arguement but thats ok continue.

[quote]PS - I have noticed that you were a moving target, "crossing aisles" as you put it, but perhaps my interpretations of this admission is not what you really intended to state. :)

From your tone I am sure you mis-interpreted. Crossing the isle means that in one case I have argued "No" age differential and in others I agree with age differential.

But I have not flip-flopped or change my view. The two different arguements apply to two different scenarios and in the one scenario they were claiming age differential for the wrong reasons and I argued that there would be no age differential.

velocity is limited by c, but there is no limit on acceleration, in principle, but human bodies do have a limit, but ths is a thought experiments so lets make the entire turn arround period be completed in one second. (If you worry that on the other guys clock it is 10 seconds, then accelerate 10 times faster so on the clock with the greatest measure of time in the turn arround, the turn arround time is only one second.) Let there be 25 years of earth time from launch til turn arround and the trip back is also 25 years so except for a second (or less) the Earth bound brother is 50 years older than he was at launch. (I believe that SRT is correct that the astronaught is younger when standing by is brother on Earth again.) You may call this the "earlier SRT view", I don't care. It is still the SRT view. The fact is that the period of acceleration can be neglected if the acceleration is very forceful/ rapid/ short duration on everyone's clocks compared to much longer travel in inertial frames times.

[QUOTE=MacM]The issue of reciprocity made that claim null and void [/b] no, it did not. that is the claim of some crackpots, not SRT's "new view" that acceleration is what caused the traveling twin to be younger.
The original solution is still valid - this is nonsense you are making up that SRT now thinks it is the acceleration that is responsibel for the age difference when reunited.

Good at least you are not totally wrong in you post. You are correct in observing that an explaination based on the acceleration as the cause of one twin being younger whe reunited was not caused by the acceleration he experience. Pleas go farther and admit it was caused by the long time spent in two different inertial frames (outbound and return legs of the trip).

I have already said that. But the point you miss is that we are no longer attributing the age differance to "Relative Velocity" but "Velocity" induced by acceleration. That is in the Twin Paradox it is not being argued that reciprocity exists where relative velocity can be argued for either twin but only applies to the twin that accelerated.

....But the point you miss is that we are no longer attributing the age differance to "Relative Velocity" but "Velocity" induced by acceleration. That is in the Twin Paradox it is not being argued that reciprocity exists where relative velocity can be argued for either twin but only applies to the twin that accelerated.Don't include me in this "we" (now bold above.) In recent post I considered the case of one twin not returning, but maintaining steady speed away form Earth. The Earth bound brother, correctly allowed/corrected for the time delay of messages (big telescope views etc.) and was so surprized to find that when he was 30 his distant traveling twin was only 25. He had arranged with his brother before launch the the traveling brother would do the same on his thirth birthday. The traveling brothe got the smae result - his Earth bound brother was only 25.
A few years later when each had learnd the results of their prearranged observation, each sent messages to the other saying: "Are you crazy? you must compare our ages at the same time aws I did."

SUMMARY: Turn arround acceleration has nothing to due the SRT prediction in the twin paradox. It is useful only in that (1) I breaks the symetry - let one know which of the two twins standing side by side after a round trip by one is the younger. and (2) avoids the Simultanity conflict that makes each think the other did not observe his age at the same time that he turned 30. (both believe the did the necessary corrections to compensate for "perceptual delays" AND THEY DID. - It is true that when T1 was 30 T2 was only 25 as "simultanious" is defined in T1's reference frame, and also true that when T2 was 30, T1 was only 25 as "simultanious" is defined in T2's reference frame.

The fact is, as clearly demonstrated in first post this thread (no one has said other wise yet) that events that are simultaneous in one frame are not simultaneous in the other. Thus both are correct in their own frames the other is younger. Their is not conflict in a local clock showing noon when (simultaneously in that frame) one in another frame is only showing 11AM, Even thought is also true that thaking the point of view of the other frame it is only 11AM when the local clock shows noon. You think clock "A" can not show both noon and 11 AM "at the same time" and this is true in any one frame, but if you consider both frames, clock A can show 11AM "at the same time" (frame B's "at the same time") that the local frame B clock is showing noon and yet at "the same time" (frame A's "at the same time") clock A is showing noon clock b is showing only 11 AM. - no problem if your realize "at the same time" is frame dependant, or as title of this thread states Time is not universal.

Don't include me in this "we" (now bold above.) In recent post I considered the case of one twin not returning, but maintaining steady speed away form Earth. The Earth bound brother, correctly allowed/corrected for the time delay of messages (big telescope views etc.) and was so surprized to find that when he was 30 his distant traveling twin was only 25. He had arranged with his brother before launch the the traveling brother would do the same on his thirth birthday. The traveling brothe got the smae result - his Earth bound brother was only 25.
A few years later when each had learnd the results of their prearranged observation, each sent messages to the other saying: "Are you crazy? you must compare our ages at the same time aws I did."

If you continue to increase your tone "Are you crazy", I may return the favor.

I think you should slow down and realize that your traveling twin is only traveling because he accelerated. Your scenario fails to consider reciprocity as advocated by SRT such that the traveling twin can equally claim to be at rest and it is his brother that has the motion and would in that case be the younger.

That is the flaw in SRT (reciprocity), not the fact that a twin in motion due to acceleration will age slower.

The fact is, as clearly demonstrated in first post this thread (no one has said other wise yet) that events that are simultaneous in one frame are not simultaneous in the other. Thus both are correct in their own frames the other is younger. Their is not conflict in a local clock showing noon when (simultaneously in that frame) one in another frame is only showing 11AM, Even thought is also true that thaking the point of view of the other frame it is only 11AM when the local clock shows noon. You think clock "A" can not show both noon and 11 AM "at the same time" and this is true in any one frame, but if you consider both frames, clock A can show 11AM "at the same time" (frame B's "at the same time") that the local frame B clock is showing noon and yet at "the same time" (frame A's "at the same time") clock A is showing noon clock b is showing only 11 AM. - no problem if your realize "at the same time" is frame dependant, or as title of this thread states Time is not universal.

You once again move from physics to perception when you start to include simultaneity affects. I don't care what you see at a distance or during motion. I am only concerned about actual time diation which is recorded by accumulated time on two clocks when compared in a common frame. That is the only actual time dilation that occurs. All else is illusion.

If you continue to increase your tone "Are you crazy", I may return the favor.That was message from one twin to the other, not intended for you. read again and it is clear.

I think you should slow down and realize that your traveling twin is only traveling because he accelerated. Your scenario fails to consider reciprocity as advocated by SRT such that the traveling twin can equally claim to be at rest and it is his brother that has the motion and would in that case be the younger. He was not necesarily accelerated, but it is complex to show how. (uses artificial fertizalation, cloning etc to get both twins born in different frames. Just as you are passenger on planet Earth and hence traveling at high speed wrt distant stars field but you never experience more than a few "Gs", they could be born already moving fast and never have acceleration,even their "parents" could have been, on different planets etc.)

How can you say I neglect reciprocity? In one post when you asked if I though both clocks were slower that the other, I said "Yes I do." even if it is superficially "crazy" and went on to defend that it is not. Also in same post I think you are responding to, I said each accurately measures the other to be 25 on his 30th birthday. - If I have the guts to state what is superficially impossible, you should not deny that I do by saying I neglect "reciprocity."

That is the flaw in SRT (reciprocity), not the fact that a twin in motion due to acceleration {or having never been accelerted but born on a different planet from his brother} will age slower. Not a flaw if one one understand the simultaneity problem, which you don't. See next responce also.

You once again move from physics to perception when you start to include simultaneity affects. I don't care what you see at a distance or during motion. I am only concerned about actual time diation which is recorded by accumulated time on two clocks when compared in a common frame. That is the only actual time dilation that occurs. All else is illusion.
Not true. Have you read the first post of this thread? Their is no "preception delay" in that proof that simultaneous events in one frame are not simultneous in another - the explosions at ends of train are locally timed /observed etc in Both frames! No delays!, No illusions! No Perception. Only facts, as they exist.

Please read first post and them tell me if you agree that "simultaneous events in one frame are not simultneous in another." or not. If you ignore the first post proof, and/or continue to not to show any error in it, then we can't discuss SRT becuase you fail to be responsive to a logical proof.

I.e. show me where there is error in the derivation that "simultaneous events in one frame are not simultneous in another" or accept this as fact. As it is now, you reject this fact and then argue that SRT is wrong as it uses the this fact and conculudes that: yes one twin brother is 30 and his brother is only 25 and conversely etc., which I admit is superficially nonsense and remains such for one who does not understand that "simultaneous events in one frame are not simultneous in another."

to MacM:

A further thought: I don't think you are in a position to state SRT facts as you reject SRT, as either internally inconsisten or inconsistent with observable facts or both (not sure which of these, perhaps all).

I defend SRT. I am even willing to defend its claims that seem superficially "crazy". Rather than you tell me what SRT states (because in MY view you don't fully understand it) why not you tell me where my defense of "simultaneous events in one frame are not simultneous in another" (first post this thread) is in error.

In analogy: I don't completely understand cricket, but know there are batters, a ball fielders, runs, sides get put out etc so I am not entirely ignorant of it either.
Do you think I am in a position to tell others what the rules of cricket imply about the game? Or would it not be better to let a cricket authority/ unpire etc, who sees no selfcontradictions in the cricket rules or result of the game state what is implied and me attack his statement (using ony them, not some I had made up) to try to expose inconsistencies?

It annoys me that you say I ignore "reciprocity" (especially when it is clear I don't). SRT has both reciprocity and the appearant nonsense of the twin paradox is a direct result of this "reciprocity", but it is not nonsense, because SRT also denys the existance of universal time. - I.e. simultaneous events in one frame are not simultneous in another. So each twin in his own frame's simultanity is simultaneously 30 when his brother in another frame is 25 etc.

</em>In recent post I considered the case of one twin not returning, but maintaining steady speed away form Earth. The Earth bound brother, correctly allowed/corrected for the time delay of messages (big telescope views etc.) and was so surprized to find that when he was 30 his distant traveling twin was only 25. He had arranged with his brother before launch the the traveling brother would do the same on his thirth birthday. The traveling brothe got the smae result - his Earth bound brother was only 25.
A few years later when each had learnd the results of their prearranged observation, each sent messages to the other saying: "Are you crazy? you must compare our ages at the same time aws I did."

SUMMARY: Turn arround acceleration has nothing to due the SRT prediction in the twin paradox...
I like the above version of the twin paradox. It is simpler than the version where one twin turns around and returns home. Plus, I see that you have specifically allowed/corrected for the time delay of messages.

However, I want to be 100% sure that the reciprocal nature of time dilation is not being caused by an incorrect allowance/correction for the time delay of messages.

So, could we please turn the situation around so that the twins start very far apart with synchronized clocks and then travel toward each other? The correction for time delay must be included in the synchronization process, but this can be done accurately because there is no length contraction of the distance between them while they are at rest.

Next, one or both of them accelerate toward each other. (If I understand correctly, it does not matter which twin accelerates?!?) When they meet again, simply passing very close to each other in space, would you still say that they are each younger than each other due to lack of simultanaety?

And finally, if one of the clocks accelerates to join the other in its frame, could someone describe the behavior of both clocks during the time when the clocks join frames? Here is an example of what I mean:

According to TwinA, just before acceleration to join frames:
TwinA = 30
TwinB = 25

According to TwinB, just before acceleration to join frames:
TwinA = 25
TwinB = 30

And this is where the paradox kicks in every time... Let's say that TwinB accelerates and joins the reference frame of TwinA (in a negligible amount of time):

According to both Twins, just after joining frames:
TwinA = ?
TwinB = ?

Next, one or both of them accelerate toward each other. (If I understand correctly, it does not matter which twin accelerates?!?) It does matter which one accelerates. I think there have been some on this forum that have incorrectly lead people to believe that it doesn't matter.

When they meet again, simply passing very close to each other in space, would you still say that they are each younger than each other due to lack of simultanaety? Your setup is ill-posed, we know not which one has accelerated. If neither accelerated, they would never meet as they started at rest far away from each other.


And finally, if one of the clocks accelerates to join the other in its frame, could someone describe the behavior of both clocks during the time when the clocks join frames? Nope. The relativity of simultaneity makes no sense :D ;) I tried to make a simulation of it once but I am 100% sure that the simulation was flawed.

That was message from one twin to the other, not intended for you. read again and it is clear.

Sorry my error.

He was not necesarily accelerated, but it is complex to show how. (uses artificial fertizalation, cloning etc to get both twins born in different frames. Just as you are passenger on planet Earth and hence traveling at high speed wrt distant stars field but you never experience more than a few "Gs", they could be born already moving fast and never have acceleration,even their "parents" could have been, on different planets etc.)

Moot point. Being born in a system that is already dilated is the same as being on the system when it accelerated and dilated. The tick rate has already been established by the energy change when the acceleration occured. Hell it could be veloicty as a resuslt of the Big Bang, it woudn't matter. It has accelerated some time in the past so as to have a relative velocity.

How can you say I neglect reciprocity? In one post when you asked if I though both clocks were slower that the other, I said "Yes I do." even if it is superficially "crazy" and went on to defend that it is not. Also in same post I think you are responding to, I said each accurately measures the other to be 25 on his 30th birthday. - If I have the guts to state what is superficially impossible, you should not deny that I do by saying I neglect "reciprocity."

OK. Are you saying reciprocity is impossible. Yes or No.?

Not a flaw if one one understand the simultaneity problem, which you don't. See next responce also.

I understadn simultaneity. It is just that simultaneity does not resolve thie issue. Relativists attempt to use it to mask the problem and create confusion but simultaneity shift does not account for any accumulated time dialation upon comparison in a common frame.

It is only time dilation when compared in a common frame that constitutes actual time shift. All else is perception or illusion.