Since this question is causing all kinds of problems in a number of threads discussing relativity, I thought I would post an explanation of the concept, here.

You can think of a reference frame as follows:

Take an infinite number of rods of equal length, and an infinite number of identical clocks. Connect these up in a cubical lattice, so that each cube is constructed from 12 of the rods. At each corner of each cube, place one of the clocks.

The resulting (imaginary) structure stretches over the whole universe.

Now, suppose that each rod is L metres long. Follow the procedure below to synchronise the clocks.

1. Designate 1 particular clock as the coordinate (x,y,z) = (0,0,0)

The "nearest neighbour clocks" of this clock exist at the following coordinates:

(L,0,0) , (0,L,0), (0,0,L), (-L,0,0), (0,-L,0), (0,0,-L).

2. At time T on the (0,0,0) clock, send a light signal from that clock outwards in all directions.

3. When the light signal is received by a clock at distance nL from the (0,0,0) clock, set the clock receiving the signal to read T + nL/c, where c is the speed of light.

For example, when the light signal reaches the clock at (L,0,0), the time on that clock should be set to T + L/c. This is the same time as is displayed on the (0,0,0) clock at the time the (L,0,0) clock receives the signal, since the time taken for the light to travel distance L is L/c.

4. Once the synchronisation procedure has been carried out, we have an infinite set of clocks spread throughout space, all of which display the same time.

This system of synchronised clocks and rods is a reference frame.

Suppose an explosion occurs somewhere and at some time in space. To specify the location of the explosion, we count the number of rods from the (0,0,0) clock to the position where the explosion occurred, in each of the three coordinate directions. That gives the spatial coordinates of the explosion (x,y,z). To get the time coordinate, t, of the explosion, we simply read off the time displayed on the clock sitting at the point where the explosion occurred.

Thus, every event in spacetime has a unique set of spacetime coordinates (x,y,z,t).

Some points to note:

A reference frame covers the whole of space and time.
All objects in spacetime exist in all reference frames.
The spacetime coordinates of a single event are unique for a particular reference frame.

There are an infinite number of possible reference frames. For example, set up another lattice of clocks and rods, and have it move in the x direction at some speed v. This new set of clocks and rods needs a new (0,0,0) clock, which can be any chosen clock in the set. It also needs its own synchronisation. Coordinates in this new frame must be given new labels, such as (x',y',z',t').

It is obvious that events which occur in one reference frame will, in general, have different coordinates (x,y,z,t) than the coordinates in some other reference frame (x',y',z',t').

Often, we are concerned with how to translate coordinates from one reference frame to another.

3 examples are given. Coordinates in frame 1 are given without the prime (') symbol. Coordinates in frame 2 have the prime (') symbol.

Example 1 - rotated coordinate system at rest

Reference frame 1 is set up.
Reference frame 2 is chosen such that the (0,0,0)' clock is at exactly the same location as the (0,0,0) clock. The z' direction is chosen to be the same as the z direction. The x' direction is chosen to be rotated by an angle of q from the x axis.

The coordinate tranformation is:

x' = x cos(q) + y sin(q)
y' = -x sin(q) + y cos(q)
z' = z
t' = t

Example 2 - Galilean tranformation

Reference frame 1 is set up.
Reference frame 2 is chosen so that, in frame 1, the (0,0,0)' clock is located at position (vt,0,0) at any time t. In other words, frame 2 moves in the positive x direction at speed v relative to frame 1, and is not rotated in any way relative to frame 1. Universal time is assumed.

This results in Galilean transformation:

x' = x - vt
y' = y
z' = z
t ' = t

Example 3 - Lorentz transformation

Reference frame 1 is set up.
Reference frame 2 is chosen so that, in frame 1, the (0,0,0)' clock is located at position (vt,0,0) at any time t. In other words, frame 2 moves in the positive x direction at speed v relative to frame 1, and is not rotated in any way relative to frame 1. The postulates of Special Relativity are assumed.

This results in Lorentz transformation:

x' = g(x - vt)
y' = y
z' = z
t ' = g(t - xv/c²)

where g is the Lorentz factor 1/sqrt(1-(v/c)²) and c is the speed of light.

Thank you James, that's helped firm up a couple of things I was shaky on.

Example 4 - translated coordinate system at rest

Reference frame 1 is set up.
A clock (a, b, c) is chosen in Reference frame 1.
A time offset (d) is chosen.
Reference frame 2 is chosen such that the (0,0,0)' clock is at exactly the same location as the (a,b,c) clock.
The time of the Reference frame 2 clock is set to the time of the Reference frame 1 (a,b,c) clock plus the time offset d.

The coordinate tranformation is:

x' = x + a
y' = y + b
z' = z + c
t' = t + d

Example 5 - reflected coordinate system at rest

Reference frame 1 is set up.
Reference frame 2 is chosen such that the (0,0,0)' clock is at exactly the same location as the (0,0,0) clock, and is synchronized with it.
The y' direction is chosen to be the same as the y direction.
The z' direction is chosen to be the same as the z direction.
The x' direction is chosen to be in the opposite direction to the x direction.
Reference frame 2 is chosen such that the (0,0,0)' clock is at exactly the same location as the (a,b,c) clock.

The coordinate tranformation is:

x' = -x
y' = y
z' = z
t' = t

How about a shear transform - is that at all useful in this context?

Since this question is causing all kinds of problems in a number of threads discussing relativity, I thought I would post an explanation of the concept, here.

You can think of a reference frame as follows:

Take an infinite number of rods of equal length, and an infinite number of identical clocks. Connect these up in a cubical lattice, so that each cube is constructed from 12 of the rods. At each corner of each cube, place one of the clocks.

The resulting (imaginary) structure stretches over the whole universe.

Now, suppose that each rod is L metres long. Follow the procedure below to synchronise the clocks.

1. Designate 1 particular clock as the coordinate (x,y,z) = (0,0,0)

The "nearest neighbour clocks" of this clock exist at the following coordinates:

(L,0,0) , (0,L,0), (0,0,L), (-L,0,0), (0,-L,0), (0,0,-L).

2. At time T on the (0,0,0) clock, send a light signal from that clock outwards in all directions.


James R; I understand your scheme ,but I observe no practical structure in your model, no physiocal reality and as an application of a pure mathematical-geometrical abstraction. Why not define real inertial frames in real situations, where the clocks are real and doing real "clocking" and where concepts lik eequivalence of frames can be defined, where "inertial' has a physical meaning? such as:

Physical attributes* of an inertial frame of reference, the embankment, Ve:
Mass (grams): 5 x 10^27. Volume (km3) = 1.09 x 10^12 Surface area (km^2) = 5.11 x 10^8. circumference (km) = 40047. radius km 6378 escape velocity km/sec = 11.2. Gravity acceleration (cm/sec2) = 980 earth direction vector rate of change = 10^-8 degrees/sec.
Velocity components (km/sec):
rotation. = .496 orbital = 29.8 solar (galactic) 208 earth/sun radiusk =m 1.49 x 10^8 Sun distance moved in one year km 208x31472262 = 6,546 X 10 ^9 angle subtended by earth/sun radius and sun distance covered /year = tan^-1 1.49x10 ^8/6.546x10^9 = 1.303 degrees. There are no measured affects on Ve due to the intrinsic motion of Ve. The prediction of position for past, presdent and future surface and volume coordinates is as exact as conditions demand. The Ve inertial mass overwhelmingly exceeds that of any other frame(s) , combined, in inertial mass, this alone being sufficient to grant Ve official “preferred frame of reference status”, whether liked or not. All Ve surface borne frames of reference inherit all the attributes of Ve motion and, From the foregoing all Ve – Vn relative measurements necessarily require Vn to accelerate to acquire Vn > 0 and hence any assumption that Vn = 0 with respect to Ve thereafter is a proved physical impossibility, so why give it mathematical equivalence? all Ve based references frames Vn, for all n, all necessarily suffer acceleration in order to create a state of relative velocity > 0. Vn can only claim Vn = 0 under the conditions that Ve - Vn = 0. Ve never acquires a velocity other than the known motion discussed above, which mdeasurable a straight-line trajectory. The Ve trajectory is moving measurably in a staight line and is affectivley inclusive in Newton's law of motion that an object at rest remains so; an object moving in a straight line continues to do so, eternallly. This includes, of course, photons of light the equivalence of inertial frames is mostly a myth.

*Handbook of Astrionautical Engineering Volume 1 Chapter 2

geistkiesel:

I understand your scheme ,but I observe no practical structure in your model, no physiocal reality and as an application of a pure mathematical-geometrical abstraction.

That's right.

Why not define real inertial frames in real situations, where the clocks are real and doing real "clocking" and where concepts lik eequivalence of frames can be defined, where "inertial' has a physical meaning? such as:

The word "inertial" has a very specific meaning already.

The reason we don't tie the concept of a reference frame to particular physical systems such as the Earth is that doing so adds nothing useful to the concept, and in fact detracts from its usefulness. It distracts unnecessarily from what is important in particular problems.

William of Occam said, famously, "Entities should not be multiplied unnecessarily."

If we need to use characteristics of the Earth or the solar system, we can use them. But for most problems involving reference frames, these characteristics are irrelevant. And in fact, introducing them goes against the philosophy of relativity, in particular, which holds that no particular reference frame has preferential status.

geistkiesel:



That's right.



The word "inertial" has a very specific meaning already.

The reason we don't tie the concept of a reference frame to particular physical systems such as the Earth is that doing so adds nothing useful to the concept, and in fact detracts from its usefulness. It distracts unnecessarily from what is important in particular problems.

William of Occam said, famously, "Entities should not be multiplied unnecessarily."

If we need to use characteristics of the Earth or the solar system, we can use them. But for most problems involving reference frames, these characteristics are irrelevant. And in fact, introducing them goes against the philosophy of relativity, in particular, which holds that no particular reference frame has preferential status.

You, of course, repeating other statements then that SR is purely mathematical and imaginary and has absolutelyh , has nothing to do with iron, aluminium, water, wood, smashing pumpkins and people counting crows.

Then you are comitting an atrocious act of misleading the public with your assertion that SR tells it like it is, reality, I mean. You speak with forked tongue, white man.

What benefit does defining "real" places and times give you?

What benefit does defining "real" places and times give you?
Somethings, some real things, that aren't imaginary.

What do you get ouit of rejecting reality for the imaginary things? Too much for you to handle, the real stuff, I mean?

Are you jumping on the MacM band wagon, geistkiesel? That only your own prejudices are real, and everything else is imaginary?

I've previously explained to you the definition of velocity as being the time derivative of displacement, and acceleration as being the second derivative. A person on a train sees the train tracks move relative to the train, which in turn means the tracks have a velocity, and possible acceleration. That's not imaginary. The tracks actually do change their position relative to the train. To deny that is the real denial of reality.

Are you jumping on the MacM band wagon, geistkiesel? That only your own prejudices are real, and everything else is imaginary?

I've previously explained to you the definition of velocity as being the time derivative of displacement, and acceleration as being the second derivative. A person on a train sees the train tracks move relative to the train, which in turn means the tracks have a velocity, and possible acceleration. That's not imaginary. The tracks actually do change their position relative to the train. To deny that is the real denial of reality.

As in your twins arguement however, do not the tracks lack the history of GR due to acceleration forces? So acceleration is not part and parcel of such exchangability as you claim as a second derivative of time and distance.

Sorry, MacM. I don't understand the point you are trying to make.

Sorry, MacM. I don't understand the point you are trying to make.

You have referred to velocity being the 1st derivative and acceleration being the 2nd derivative of time and distance change. You also referred to the fact that there is reciprocity in the velocity between the tracks and the moving train observer.

My point was to clarify the fact the the train observer has gone through acceleration and the tracks didn't. Even though the tracks see a relativity velocity change it is not physically reciprocal to the train observer in that there is no force of accelertion.

It is not true then that the observed track velocity by the train observer is directly applicabable to the velocity observed by the observer along side the tracks of the moving train.

It is an identical circumstance to the arguement made in the twins paradox case. The two observers do not have a totally symmetrical history.

MacM:

It is not correct to say that only the train accelerates. In the train's frame, the track accelerates.

What I assume you are saying, to put it in technical terms, is that only the track's frame is inertial. The train frame is non-inertial.

In that case, we appear to be in agreement. I am still not sure why you raised the issue, though.

MacM:

It is not correct to say that only the train accelerates. In the train's frame, the track accelerates.

What I assume you are saying, to put it in technical terms, is that only the track's frame is inertial. The train frame is non-inertial.

In that case, we appear to be in agreement. I am still not sure why you raised the issue, though.
The train OBSERBVER that considers the earth moving is an idiot. You knOw and everybody knows, the ground doesn't accelerate. Only Vn accelerates and it only this acceleration that we observe relative motion between Ve and al other Vn.
to the train observefr the ground accelerates>

Did you ever try dropping a golf ball from a train that is considered at rest with respect to the Ve? Which way will the ball bounce, assuming sufficient fricitonal contact with a relatively smooth/even pavement below the moving train? Whic way will the ball bouince?

MacM:

It is not correct to say that only the train accelerates. In the train's frame, the track accelerates.

This long effort to expose Relativity is really starting to pay off by golly. Now we can see how you pick and choose when to say certain things.

Historically you have used the force of acceleration against me when I stated that B would see A accelerate etc. You made it clear that A never actually accelerates in that it lacks any non-inertial forces.

Now you want to blow off my using that same arguement. Make up your mind. Is your memory failing or do you just deliberately say whatever sounds professional at the moment when you need to redirect a discussion?.

What I assume you are saying, to put it in technical terms, is that only the track's frame is inertial. The train frame is non-inertial.

Always with trying to be the guy making corrections or clarifications. Well none were needed here. Thank you.

In that case, we appear to be in agreement. I am still not sure why you raised the issue, though.

Well, that was a long way around to being in agreement. It is really that tough for you to just say "You are right MacM?"

I raised the issue since you tried to blow off QQ by saying the track acccelerates. It doesn't. Don't repeat what I have already said and that is that the train observer sees a changing velocity but that the track isn't really accelerating because it is inertial and experiences no non-inertial forces.

Did you ever try dropping a golf ball from a train that is considered at rest with respect to the Ve? Which way will the ball bounce, assuming sufficient fricitonal contact with a relatively smooth/even pavement below the moving train? Whic way will the ball bouince?Oh come on now. At least try.

The ball bouncing in the direction the ground is moving has nothing to do with the ground being at absolute zero and the train having velocity.

If you throw a golf ball at the train it will bounce in the direction the train is moving. This has nothing at all to do with absolute zero.

And most of all, the ground IS moving. Even if you feel like believing the Earth is the center of the universe, it is still revolving.

MacM,

You seem to be confused.

I have no idea what this "A" and "B" are that you are talking about, since there have been no references to that in the thread, I think. I assume that by "B" you mean the train, and "A" the tracks.

You have also contradicted yourself.

First you say:

Historically you have used the force of acceleration against me when I stated that B would see A accelerate etc.

You're making unsupported assertions about what I have said in the past, here, but never mind. The crux of this is that you claim that the train sees the tracks accelerate, which is true.

But then you flip-flop and say:

I raised the issue since you tried to blow off QQ by saying the track acccelerates. It doesn't.

You really need to make up your mind about what you believe. Either you believe the track accelerates in the train's reference frame, or you don't.

If you don't, you're just wrong. If you do, we have no argument.

I don't really care either way. Why don't you go away and think about it for yourself?

MacM,

You seem to be confused.

Afraid not. It is you that seem confused and forgetful.

I have no idea what this "A" and "B" are that you are talking about, since there have been no references to that in the thread, I think. I assume that by "B" you mean the train, and "A" the tracks.

No. I said "Historically". Historically I had made reference to the fact that the moving observer in one frame when considered at rest see the other observer moving and also that each saw the other accelerate.

You correctly commented that the other didn't actually accelerte that one remained inertial whie the orther actually accelerted which was accompanied by the inherent forces of acceleration.

You have also contradicted yourself.

No I didn't. I said each sees a change in velocity as acceleration but clarifeid that only one actuallyaccelerates since one lacks the forces of accelertion.

You're making unsupported assertions about what I have said in the past, here, but never mind. The crux of this is that you claim that the train sees the tracks accelerate, which is true.

False. I said more technically correct than you have implied to QQ, that while the train sees the tracks undergo a change in velocity, that it isn't actually acceleration because it remained inertial.

You really need to make up your mind about what you believe. Either you believe the track accelerates in the train's reference frame, or you don't.

My mind hasn't changed. Your hasn't changed I'm sure but your presentation has changed claims from being acceleration to (historically, not in this thread) not being acceleration because it remained interial.

If you don't, you're just wrong. If you do, we have no argument.

It sounds like we have an arguement. I believe you have just said the tracks accelerate. Is that correct? If so where is the accelerating force on the tracks.?

I don't really care either way. Why don't you go away and think about it for yourself?

I'm sure you could use the rest. You seem to be getting wishy washy a sign of burn out, saying so many things to try and make a point that you are forgetting what you have said before.

MacM,

*sigh*

It seems everything needs to be explained to you in precise detail, and even then you usually end up not understanding. But, I'm reasonably patient, so I'll give it a go.

Your problem here is that you aren't using terms such as "acceleration" and "inertial" in their technical senses, whereas I am.

We are considering a situation where a train accelerates from rest to some constant speed along a railway track.

In a reference frame in which the tracks are stationary, the train is observed to accelerate. In a reference frame in which the train is stationary, the tracks accelerate. It is important to use the proper definition of acceleration. Acceleration is simply the second derivative of the displacement with respect to time. Therefore, in the train frame, it is not arguable that the tracks do not accelerate. The tracks are displaced over a period of time, and this occurs in such a way that the mathematically defined acceleration is non-zero in this frame.

That's one issue. You want to mix this up with notions of inertial and non-inertial reference frames, which is a separate issue completely.

Both observers agree that the track frame is an inertial frame, while the train frame is a non-inertial frame. An inertial frame is one in which all the laws of physics hold in their unaltered forms, which is not true in non-inertial frames.

An observer on the train "feels" the acceleration. He feels like he is pushed towards the back of the train. That is due to the inertial force which arises in his non-inertial reference frame. This inertial force does not exist in the track reference frame.

You asked what force makes the tracks accelerate, from the train's point of view. The answer is: partly the force of the train's engine pushing the tracks backwards, and partly the inertial force on the tracks due to the non-inertial frame of reference.

In light of this explanation, let's look at what you wrote.

No I didn't. I said each sees a change in velocity as acceleration but clarifeid that only one actually accelerates since one lacks the forces of accelertion.

I hope you now see why this is wrong. In the train frame, the track "actually" accelerates, just as in the Earth frame, the train "actually" accelerates. That is just a matter of knowing what acceleration is. Your vague statement about "forces of acceleration" would in fact refer to the inertial forces discussed above, if you understood the concept, but instead you mix up concepts.

False. I said more technically correct than you have implied to QQ, that while the train sees the tracks undergo a change in velocity, that it isn't actually acceleration because it remained inertial.

I hope it is clear to you why this is wrong. Clearly, you misinterpreted what I said. I was careful; you were sloppy. Hence your mistake.

It sounds like we have an arguement.

I hope that, after my clear and careful explanation, we no longer have an argument. On the other hand, with you nothing can be taken for granted.

I'm sure you could use the rest. You seem to be getting wishy washy a sign of burn out, saying so many things to try and make a point that you are forgetting what you have said before.

You continually make assertions that I contradict myself, but you can never actually point out any post where that happens. Funny, that.

MacM,

*sigh*

It seems everything needs to be explained to you in precise detail, and even then you usually end up not understanding. But, I'm reasonably patient, so I'll give it a go.

Your problem here is that you aren't using terms such as "acceleration" and "inertial" in their technical senses, whereas I am.

We are considering a situation where a train accelerates from rest to some constant speed along a railway track.

In a reference frame in which the tracks are stationary, the train is observed to accelerate. In a reference frame in which the train is stationary, the tracks accelerate. It is important to use the proper definition of acceleration. Acceleration is simply the second derivative of the displacement with respect to time. Therefore, in the train frame, it is not arguable that the tracks do not accelerate. The tracks are displaced over a period of time, and this occurs in such a way that the mathematically defined acceleration is non-zero in this frame.

That's one issue. You want to mix this up with notions of inertial and non-inertial reference frames, which is a separate issue completely.

Both observers agree that the track frame is an inertial frame, while the train frame is a non-inertial frame. An inertial frame is one in which all the laws of physics hold in their unaltered forms, which is not true in non-inertial frames.

An observer on the train "feels" the acceleration. He feels like he is pushed towards the back of the train. That is due to the inertial force which arises in his non-inertial reference frame. This inertial force does not exist in the track reference frame.

You asked what force makes the tracks accelerate, from the train's point of view. The answer is: partly the force of the train's engine pushing the tracks backwards, and partly the inertial force on the tracks due to the non-inertial frame of reference.

In light of this explanation, let's look at what you wrote.



I hope you now see why this is wrong. In the train frame, the track "actually" accelerates, just as in the Earth frame, the train "actually" accelerates. That is just a matter of knowing what acceleration is. Your vague statement about "forces of acceleration" would in fact refer to the inertial forces discussed above, if you understood the concept, but instead you mix up concepts.



I hope it is clear to you why this is wrong. Clearly, you misinterpreted what I said. I was careful; you were sloppy. Hence your mistake.



I hope that, after my clear and careful explanation, we no longer have an argument. On the other hand, with you nothing can be taken for granted.



You continually make assertions that I contradict myself, but you can never actually point out any post where that happens. Funny, that.

I'll not debate symantics but only state:

1 - I was trying to be very clear about the differance between the view of accelertion of the tracks by the train vs actual acceleration.

2 - You have said nothing here that I didn't know; accept that you can so casually mix acceleration into an inertial frame and not cause confusion.

3 - I responded as I did because you infact had corrected me in the past for having said A see B accelerate and B therefore sees A accelerate. You very specifically said I was wrong and was showing that I did not understand physics, that in the one frame it wasn't accelerating. That there was no force of accelertion.

4 - I can only ask that you stick with a consistant description of these terms. I am making a note of this ost for future reference since you have a habiot of forcing me to go back and spend time looking for statments that have been made. I am currently searching back over threads 1 1/2 years old to post where ou commented on it being imperative that I know calculsu to understand Relativity.

Perhaps that is part of your plan to keep me occuied but I will not dedicated full time I will continue to post. So that will not gain you much. In fact it is going to backfire since I will find it and I will post it.

********************************************
Well here is for starters. I'll be posting more as I find them.

James R., Invokes Absolute Universal Space-Time

Galaxies aren't moving in their local spacetime; the global (universal) spacetime is itself expanding, carrying the galaxies with it. For this reason, relativity expects no observed mass increase.


James R Tells MacM His Test is Void Because there is No Absolute Universal Time

You are trying to reinstate some kind of Newtonian world with universal time. Such a thing doesn't exist, and wishing doesn't make it so.

*******************************************

3 - I responded as I did because you infact had corrected me in the past for having said A see B accelerate and B therefore sees A accelerate. You very specifically said I was wrong and was showing that I did not understand physics, that in the one frame it wasn't accelerating. That there was no force of accelertion.

That is false. Link to the relevant post, if it exists.

I am making a note of this ost for future reference since you have a habiot of forcing me to go back and spend time looking for statments that have been made.

Good. Maybe you won't misrepresent what I've said next time.

You shouldn't make claims you can't support.

James R., Invokes Absolute Universal Time

Are you sure you have the right post?
James neither stated nor implied anything about the nature of time in that post.

Galaxies aren't moving in their local spacetime; the global (universal) spacetime is itself expanding, carrying the galaxies with it. For this reason, relativity expects no observed mass increase.

It seems that you *think* this implies absolute time.

Can you explain why?

That is false. Link to the relevant post, if it exists.



Good. Maybe you won't misrepresent what I've said next time.

You shouldn't make claims you can't support.

See above. You will be corrected this time. You have done this to many times to let it go.

James,
Thanks for that description.
It has cleared up a few things in my mind, visually.
I appreciate it.

The train OBSERBVER that considers the earth moving is an idiot. You knOw and everybody knows, the ground doesn't accelerate. Only Vn accelerates and it only this acceleration that we observe relative motion between Ve and al other Vn.
to the train observefr the ground accelerates>

geistkiesel,
Believe me, I have problems with Relativity, just as you do.
I am not sold on it's reflection of reality, but this particular aspect has no other objective way to look at it.

The Earth is not anchored to anything.
The reason there is no preferred refernce frame, is because we have nothing to consider "at rest" to measure relative movement to.
In the view you presented above, we would have to accept that the Earth is stationary, and the Sun and universe revolves around IT.
Einstein (nor James) was contending that the train is doing the work to move the Earth.
Relativity simply has to be true regarless of where you are standing, in order for it to be a valid theory.
If you are thinking like I was, you are now wondering if that means that Einstein skewed things to MAKE relativity valid.
Not quite.
In order for ANY theory that is designed to quantify movement universally it would have to do one of two things:
1.) Depict a preferred reference frame and assume it is at absolute rest (you already see the problems inherent in that, the universe not only does not revolve around the Earth, but it would be a helluva diffcult task to determine an orbit trajectory for a probe taking off on Mars, by taking the revolution of the entire universe around Earth into account as a preferred refernce).
2.) Assume that nothing is at rest since we do not have anything to measure as a backdrop. In other words EVERYTHING is in motion relative to one another. If space DID have some sort of static infinitely rigid fabric (such as reference frame 1 in James' above explanation) to consider at absolute rest, AND we had a way of observing that fabric this wouldn't be a problem.

Since we know the Earth orbits the Sun, let's make believe we view the Sun as the prefrred frame of reference...
When your car is driving down the road at 60 MPH, if your car is viewed from the Sun and the Earth were invisible it would look as if it is hurtling through space in loop-the-loop fashion with the center of it's orbit moving at over 12,000 MPH (no, I am not sure of the actual number, but it really doesn't matter) in a big eliptic circle.

From the Sun's perspective, a geocentric preferred reference frame seems like a pretty silly thing, doesn't it?
That is all relativity is saying.

(someone please correct me if I got any of this incorrect)

Are you sure you have the right post?
James neither stated nor implied anything about the nature of time in that post.



It seems that you *think* this implies absolute time.

Can you explain why?

I would like to see a different explanation other than a universal time for a defintion called "Global Universal Space-Time".

He is telling me my view requires a Universal Time and that it does not exist.

I responded as I did because you infact had corrected me in the past for having said A see B accelerate and B therefore sees A accelerate. You very specifically said I was wrong and was showing that I did not understand physics, that in the one frame it wasn't accelerating. That there was no force of accelertion.
Ummm... where was that post again?

Sorry, MacM, but taking quotes out of context doesn't cut it.

I guess I'll have to explain this one to you as well. I wrote:

Galaxies aren't moving in their local spacetime; the global (universal) spacetime is itself expanding, carrying the galaxies with it. For this reason, relativity expects no observed mass increase.

Note that I said "global (universal) spacetime" and not, as you assert "global (universal) time".

Note also the word "universal" in brackets, which is there to make it clear that I was talking about the spacetime of the universe as a whole, as distinct from spacetime in a particular local region.

Your claim that I have somehow agreed with your silly notion that some absolute standard of time exists throughout the universe, is spurious.

Try again.

I would like to see a different explanation other than a universal time for a defintion called "Global Universal Space-Time".

He is telling me my view requires a Universal Time and that it does not exist.

???

Space-time is not Time, Mac.

For example, it is easily demonstrated that in SR, the space-time interval between two events is absolute, but the time interval is not.


"Universal space-time" does not imply universal time. That's crazy talk.

Whom is accelerating is easily determined. Remember the solution to the Twins Paradox?

???

Space-time is not Time, Mac.

For example, it is easily demonstrated that in SR, the space-time interval between two events is absolute, but the time interval is not.


"Universal space-time" does not imply universal time. That's crazy talk.

I actually don't disagree here. But my point would be his repeated nit picking of my use of terms and admonitions to be precise and yet he also lacks clarity many times.

He should have simple referred to the expansion of space-time not causing the affect but instead he throws in the reference to "Global" universal space-time.

Now seperating time out of universal space-time and saying it doesn't exist is nothing more than a play on words. Space-Time are irrevocably linked in Relativity. We haven't been discussing it in time dilation but associsted with the relavtive velocity is the Lorentz contraction issue as well. Time dilation is linked to the same "Global Space-Time" to which he refers.

Sorry, MacM, but taking quotes out of context doesn't cut it.

I guess I'll have to explain this one to you as well. I wrote:

Note that I said "global (universal) spacetime" and not, as you assert "global (universal) time".

Note also the word "universal" in brackets, which is there to make it clear that I was talking about the spacetime of the universe as a whole, as distinct from spacetime in a particular local region.

Your claim that I have somehow agreed with your silly notion that some absolute standard of time exists throughout the universe, is spurious.

Try again.

I will. But first understand I did not assume you believed in UT but your post unnecessarily refers to "global (universal) space-time and you should have forgone the reference and simply stated the expansion of space time had no mass affect.

I'm still looking for the direct quote regarding your admonition with respect to acceleration.

Also, I do not see this as taken out of context. I did not crop any information which altered your statement. That paragraph stands alone in its full meaning. Another innuendo by you. That I have quoted you out of context when I have not.

I have corrected my link which inadvertantly dropped "Space-"

Whom is accelerating is easily determined. Remember the solution to the Twins Paradox?

I agree but James R switched horses here and now says the train and track both accelerate.

I agree but James R switched horses here and now says the train and track both accelerate.

Talk is cheap. Prove it.

He should have simple referred to the expansion of space-time not causing the affect but instead he throws in the reference to "Global" universal space-time.
I thought the sentence was perfectly understandable. The distinction between local spacetime and global spacetime is an important one. If you didn't understand, you should have said so.

Now seperating time out of universal space-time and saying it doesn't exist is nothing more than a play on words. Space-Time are irrevocably linked in Relativity. We haven't been discussing it in time dilation but associsted with the relavtive velocity is the Lorentz contraction issue as well. Time dilation is linked to the same "Global Space-Time" to which he refers.
There's no play on words here, Mac.

If Space and Time were individual entities, absolutes in their own right, there would be no need to combine them into space-time. That's the whole point of space-time. It is required by the fact that space and time are two elements of the same entity. Space-time is the underlying entity that manifests itself as space and time.

A space-time interval is absolute (not frame dependent) - all observers will agree on the space-time separation between two events. But the way that interval manifests as space and time is frame dependent - the distance and time between the events varies with perspective (reference frame).

I agree but James R switched horses here and now says the train and track both accelerate.
There's really no switching horses here Mac...

I understand that you're upset that think you've received mixed messages from James, but you're doing yourself a disservice by whining about it and blaming James's communication.

This is an opportunity to learn. When you receive a mixed message from someone, I think it's better to ask for clarification than to try and leverage it as some point-scoring exercise.

Why don't you look at the issue again, and try to reach some common ground with James. Here's some questions to think about:
What does "accelerate" mean?
What does "inertial frame" mean?
What does acceleration in an inertial frame feel like? Why?
What does acceleration in a non-inertial frame feel like? Why?
What does acceleration in an inertial frame feel like? Why?
What does being stationary in an inertial frame feel like? Why?
What does being stationary in a non-inertial frame feel like? Why?


Which of the preceding situations are interchangeable?
Why would you choose to consider yourself in one situation rather than another, if the two are interchangeable?

Whom is accelerating is easily determined. Remember the solution to the Twins Paradox?

You're thinking of the Special Relativity solution. Strictly speaking, SR deals only with inertial reference frames, which means that we can't use SR to treat the stay-at-home twin as accelerating.

But there are solutions to the Twin paradox in which the stay-at-home twin accelerates, and the other does not. This requires the use of non-inertial frames, meaning that General Relativity is needed to fully analyse it.

In practical terms, we used non-inertial frames all the time. For instance, as I'm sitting in my chair, I'm in a non-inertial reference frame. I maintain that I'm stationary in this frame, and that the pencil falling off my desk is accelerating, being pulled by gravity. In the non-inertial frame of the pencil in free fall, there is no gravitational force, and I'm the one accelerating - I'm being pushed up by the chair seat against my backside, hard enough to accelerate me at 10m/s/s.

Either point of view is fine, and can be used to produce the same results for any practical question.

Here is a great resource for Twin Paradox explanations, and show why all the explanations amount to the same thing:
Relativity FAQ - the broken vase (http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_vase.html)

Even though the tracks see a relativity velocity change it is not physically reciprocal to the train observer in that there is no force of accelertion.

This might be the heart of the disagreement - a simple terminology difference.

Mac agrees that the train sees the tracks change velocity.
The concept Mac is articulating is exactly the same concept James is articulating when he says that the train sees the tracks accelerate.

Mac also notes that the tracks do not experience a real force to effect this change.
The concept Mac is articulating is exactly the same concept James is articulating when he says that the track's reference frame is inertial.


Mac,
James is agreeing with you in concept, but correcting your terminology.
James is using the word "accelerate" to mean what you agreed is true - that for the train, the tracks change velocity.
James is also pointing out that the term "inertial frame" is generally used to articulate the other fact you mentioned - that the tracks feel no objective force.

Can someone please explain the difference between an inertial frame and a non-inertial frame?

Thanks

by Pete:
"In practical terms, we used non-inertial frames all the time. For instance, as I'm sitting in my chair, I'm in a non-inertial reference frame. I maintain that I'm stationary in this frame, and that the pencil falling off my desk is accelerating, being pulled by gravity. In the non-inertial frame of the pencil in free fall, there is no gravitational force, and I'm the one accelerating - I'm being pushed up by the chair seat against my backside, hard enough to accelerate me at 10m/s/s."
================================================== ==============

Yes, Pete, I do know what a non-inertial frame is and I have a general understanding
of General Relativities explaination of gravity. It is not a 'force' in GR, you are accelerating against the Earth, as you say. But I haven't been able to figure out how
the tides in the Earth's oceans are explained by GR. Perhaps you could give me a brief
explaination, not long enough to disrupt this thread, and don't forget tides occur on
both sides of the Earth at the same time. Thanks.

An inertial frame is one in which any object with no forces on it will move in a straight line at constant speed.

And a non-inertial frame, then, would simply be one in which the frame experiences a change in velocity?

Roughly speaking, yes, one_raven. A non-inertial frame is usually an accelerating frame. However, you have to be careful if you're talking about general relativity in this context, since GR says that all freely falling frames are inertial.

That's why it is probably better to stick to the definition I gave previously.

Here's my understanding:

If an object is in freefall, it is in an inertial reference frame.
Otherwise, it is in a non-inertial reference frame.

Or...
In an inertial reference frame, an accelerometer will have a zero reading.

I've never looked for a formal definition... perhaps I should!

WordIQ.com (http://www.wordiq.com/definition/General_relativity) (1):
We distinguish inertial reference frames, in which bodies maintain a uniform state of motion unless acted upon by another body, from non-inertial frames in which freely moving bodies have an acceleration deriving from the reference frame itself.

WordIQ.com (http://www.wordiq.com/definition/Inertial_frame_of_reference) (2):
In physics, an inertial frame of reference, or inertial frame for short (also descibed as absolute frame of reference), is a frame of reference in which the observers move without the influence of any accelerating or decelerating force.

Zona Land (http://id.mind.net/~zona/mstm/physics/mechanics/framesOfReference/nonInertialFrame.html):
A non-inertial frame of reference is a frame of reference with a changing velocity. The velocity of a frame will change if the frame speeds up, or slows down, or travels in a curved path.
A non-inertial frame of reference is an accelerating frame of reference.
A non-inertial frame of reference is a frame of reference in which the law of inertia does not hold.
A non-inertial frame of reference is a frame of reference in which Newton's laws of motion do not hold.
In a non-inertial frame of reference fictitious forces arise.

U.South Dakota, Modern Physics (http://www.usd.edu/phys/courses/phys431/notes/notes2.html)
An inertial frame of reference is one in which Newton's Laws of Motion are valid.
A non-inertial frame is one in which Newton's Laws of Motion are not valid.

I seem to be particularly slow tonight :)

WordIQ.com definition (1) is the best one of those. It is the same as my definition, above.

In a reference frame in which the tracks are stationary, the train is observed to accelerate. In a reference frame in which the train is stationary, the tracks accelerate. It is important to use the proper definition of acceleration. Acceleration is simply the second derivative of the displacement with respect to time. Therefore, in the train frame, it is not arguable that the tracks do not accelerate. The tracks are displaced over a period of time, and this occurs in such a way that the mathematically defined acceleration is non-zero in this frame.

When you say the tain is observed to accelerate, I am aassuming that accelerometers placed on the earth frame as well as the passenger train as the train pulls out of the station will indicate a positive accelerating force to the same degree seen by accelerometers placed ion the passenger train.

We aer3e talking about inertial frames, where inertial is meant aws the resistence to change, as in the resistance to vary the state of a being at rest. The law of inertial governs these cases and tells us the state of rest, or uniform straight-line motion of an object will remain constant until acted upon by a force external to the object under scrutinty or observation.

Special relativity is a postulate structured theory and the reason that a passenger train observes the earth frame as accelerating is because the acceleration is not a real physical process, where forces are delivered and felt by the objects undergoinf acceleration. AS acceleration is merely the second derivative of dispalcement, and a " second derivative" is a mathematical process and not a physical one means that accelerometer readings, personal sensations, direct observation of directed motion, like the 'jerking of the train' during acceleration is pureley a mathematical reality transferred by some mental dynamics based on reason, logic accumulated data are merly physical analogs being acted out for the sake of maintaining ones coherence in a world that is mathematically complex a, and subject to the necessary translation of motion by the experts who understand these sorts of things.

So the second derivative of the train displacement merely describes that same force acting on the tracks. I am starting to get it, special relativity forces are delivered by pen and ink. Where contradictory experimental results indicating real track acceleration in an equivalent manner as seen in the train acceleration we are to conclude that all accelerations are equivalent. If the train speeds up so does the train station and lucky for us all the responbsibility of managing the observations and recording critical data in modern experiments is granted to SR theorists.

We are told that an observer at rest with respect to his moving frame of reference may consider his motion at rest simply because he didn't know or was unable to detect that he was moving.If he looked out the window of the train and saw what we all see out the windows of trains, would this change any aspect of physical laws, or physical reality?

Would the train's and train station's mutual accelerations be a physical parameter assigned to the train and station motion for all times to come?

Silly little boys.

We are told that an observer at rest with respect to his moving frame of reference may consider his motion at restHe may consider himself at rest because there is no physical difference between him being at rest or having constant velocity.

He may consider himself at rest because there is no physical difference between him being at rest or having constant velocity.

According to SR, the one at rest always ages faster.

When you say the tain is observed to accelerate, I am aassuming that accelerometers placed on the earth frame as well as the passenger train as the train pulls out of the station will indicate a positive accelerating force to the same degree seen by accelerometers placed ion the passenger train.

We aer3e talking about inertial frames, where inertial is meant aws the resistence to change, as in the resistance to vary the state of a being at rest. The law of inertial governs these cases and tells us the state of rest, or uniform straight-line motion of an object will remain constant until acted upon by a force external to the object under scrutinty or observation.

Special relativity is a postulate structured theory and the reason that a passenger train observes the earth frame as accelerating is because the acceleration is not a real physical process, where forces are delivered and felt by the objects undergoinf acceleration. AS acceleration is merely the second derivative of dispalcement, and a " second derivative" is a mathematical process and not a physical one means that accelerometer readings, personal sensations, direct observation of directed motion, like the 'jerking of the train' during acceleration is pureley a mathematical reality transferred by some mental dynamics based on reason, logic accumulated data are merly physical analogs being acted out for the sake of maintaining ones coherence in a world that is mathematically complex a, and subject to the necessary translation of motion by the experts who understand these sorts of things.

So the second derivative of the train displacement merely describes that same force acting on the tracks. I am starting to get it, special relativity forces are delivered by pen and ink. Where contradictory experimental results indicating real track acceleration in an equivalent manner as seen in the train acceleration we are to conclude that all accelerations are equivalent. If the train speeds up so does the train station and lucky for us all the responbsibility of managing the observations and recording critical data in modern experiments is granted to SR theorists.

We are told that an observer at rest with respect to his moving frame of reference may consider his motion at rest simply because he didn't know or was unable to detect that he was moving.If he looked out the window of the train and saw what we all see out the windows of trains, would this change any aspect of physical laws, or physical reality?

Would the train's and train station's mutual accelerations be a physical parameter assigned to the train and station motion for all times to come?

Silly little boys.

James R naturally took exception to my claim that the station didn't accelerate but only was observed to have a changing velocity. Because the station and persons standing there felt no accelerating force.

James claimed that the station accelerates and disregards the physical principles of acceleration which is associated with an intendant force.

But more telling in the following definition posted by Pete; which James R claims is the best one and the one he goes by, it actually seems to disagree with him on this issue.

WordIQ.com (1):
We distinguish inertial reference frames, in which bodies maintain a uniform state of motion unless acted upon by another body, from non-inertial frames in which freely moving bodies have an acceleration deriving from the reference frame itself.

geistkeisel:

I have clearly explained the difference between an inertial and non-inertial reference frame. Your complaint about the train is that an accelerometer placed on the platform maintains a zero reading, while one on the train does not.

In the train's frame of reference, the accelerometer sitting on the platform is indeed accelerating, yet it shows no reading. Why? Because all parts of it accelerate at the same rate, each experiencing a force proportional to its mass. In contrast, different parts of an accelerometer on the train experience different forces (in particular, the spring, or whatever it is which measures the internal force in the accelerometer, is stretched), and so the accelerometer on the train displays a non-zero reading.

MacM: you are incorrect to claim that something I have said regarding definitions is inconsistent. If I made an error, you should be able to point it out. Please quote the contradictory statements I made, if they exist.

MacM: you are incorrect to claim that something I have said regarding definitions is inconsistent. If I made an error, you should be able to point it out. Please quote the contradictory statements I made, if they exist.

What you got and old BW Monitor? :D I highlited it in two tone color.


.....from non-inertial frames in which freely moving bodies have an acceleration deriving from the reference frame itself.


The station is not deriving acceleration from its FOR.

MacM:

Please point out where I have been inconsistent. Please quote my posts.

MacM:

Please point out where I have been inconsistent. Please quote my posts.

Here

***************Extract *****************
In a reference frame in which the tracks are stationary, the train is observed to accelerate. In a reference frame in which the train is stationary, the tracks accelerate.

It is important to use the proper definition of acceleration. Acceleration is simply the second derivative of the displacement with respect to time. Therefore, in the train frame, it is not arguable that the tracks do not accelerate. The tracks are displaced over a period of time, and this occurs in such a way that the mathematically defined acceleration is non-zero in this frame.

****************************
Definition:

.....from non-inertial frames in which freely moving bodies have an acceleration deriving from the reference frame itself.

************************


Regarding the train you say "Observed" but regarding the tracks you claim "Actual" acceleration. That appears exactly opposite what I would accept.

The train accelerates.

The tracks are observed to accelerate.

The tracks are not receiving any acceleration from its own referance frame.

That's one issue. You want to mix this up with notions of inertial and non-inertial reference frames, which is a separate issue completely.

Perhaps the definiton isn't intended specifically in the way I interprete it but when you speak of non-inertial frames you are talking about accelerating frames and to be non-inertial it must have its acceleration generated from within the frame.

The tracks do not and to say they accelerate is to claim they are non-inertial and I believe if this isn't defacto wrong, it most certainly is in poor usage of the word accelerate. Especially when discussing Relativity.

The train accelerates.
The tracks are observed to accelerate.

The words you choose make no difference, as long as you clearly indicate a reference frame. Thus, the following statements are equivalent:

"According to the train, the tracks accelerate"
"In the reference frame of the train, the tracks accelerate"
"The train sees the tracks accelerate"
"The tracks are observed to accelerate, in the train's frame"
"An observer on the train sees the tracks accelerate"

The tracks are not receiving any acceleration from its own referance frame.

As a matter of fact, they are, if you want to use the definition you quoted. The train's frame is non-inertial, and that "causes" the tracks to experience an inertial force which arises only in the train's reference frame. In a sense, it arises from the chosen reference frame.

The tracks do not and to say they accelerate is to claim they are non-inertial and I believe if this isn't defacto wrong, it most certainly is in poor usage of the word accelerate. Especially when discussing Relativity.

As I said previously, you're mixing up the difference between accelerating and being inertial. Both the train and the tracks agree that the train's motion is non-inertial, and the track's is inertial. But they disagree on whether it is the train or track which is accelerating.

Usually, this distinction is not important, but in this instance it is the crux of the matter, and is what is causing your confusion, and geistkeisel's too.

The words you choose make no difference, as long as you clearly indicate a reference frame. Thus, the following statements are equivalent:

"According to the train, the tracks accelerate"
"In the reference frame of the train, the tracks accelerate"
"The train sees the tracks accelerate"
"The tracks are observed to accelerate, in the train's frame"
"An observer on the train sees the tracks accelerate"



As a matter of fact, they are, if you want to use the definition you quoted. The train's frame is non-inertial, and that "causes" the tracks to experience an inertial force which arises only in the train's reference frame. In a sense, it arises from the chosen reference frame.



As I said previously, you're mixing up the difference between accelerating and being inertial. Both the train and the tracks agree that the train's motion is non-inertial, and the track's is inertial. But they disagree on whether it is the train or track which is accelerating.

Usually, this distinction is not important, but in this instance it is the crux of the matter, and is what is causing your confusion, and geistkeisel's too.

I'm not confused. I said it is a bad use of the term because to accelerate suggests a frame is non-inertial in relativity.

So Now JamesR is telling U all in this thread to consider a universal 0,0,0 as a frame of reference for a zero speed , that infact can be used against him when confronted with the RTT Relativity Experiment that he has shied away from and got inspiration of this thread.

JamesR U did not answer to my Q in this thread, That’s good news for science
http://www.sciforums.com/showthread.php?p=700038#post700038

RawThinkTank,

I don't know what you're thinking I said, but maybe you need to re-read the thread.

I said it is a bad use of the term because to accelerate suggests a frame is non-inertial in relativity.

Only to somebody who doesn't know the difference between acceleration and a reference frame.

Only to somebody who doesn't know the difference between acceleration and a reference frame.

I'm not going to waste time arguing over this but I thnk it is clear just who is being sloppy and who isn't.

Yes, it is.

James R naturally took exception to my claim that the station didn't accelerate but only was observed to have a changing velocity. Because the station and persons standing there felt no accelerating force.

James claimed that the station accelerates and disregards the physical principles of acceleration which is associated with an intendant force.

But more telling in the following definition posted by Pete; which James R claims is the best one and the one he goes by, it actually seems to disagree with him on this issue.

WordIQ.com (1):
We distinguish inertial reference frames, in which bodies maintain a uniform state of motion unless acted upon by another body, from non-inertial frames in which freely moving bodies have an acceleration deriving from the reference frame itself.

It seems that the reference frame that is accelerating has magical qualities to it. If the train were an open at the top boxcar and an apple suspended on a string were lowered into the confines of the boxcar just as it began to accelerate the the apple would be considered accelerating also, though there would be no measurable forces perturbing apple or string. I thoughNewton had the apple question asnswered a long time ago.

It seems from my going through your and James R's last exchanges is that James R changes definitions as determined by what happens to a physical object and this is confusing, designed on purpose to be so. I understood from James R that a physical object moving with constant velocity is an inertial frame, so why he dances all over theplace, only his therapist knows.

It seems that the reference frame that is accelerating has magical qualities to it. If the train were an open at the top boxcar and an apple suspended on a string were lowered into the confines of the boxcar just as it began to accelerate the the apple would be considered accelerating also, though there would be no measurable forces perturbing apple or string. I thoughNewton had the apple question asnswered a long time ago.

It seems from my going through your and James R's last exchanges is that James R changes definitions as determined by what happens to a physical object and this is confusing, designed on purpose to be so. I understood from James R that a physical object moving with constant velocity is an inertial frame, so why he dances all over theplace, only his therapist knows.

Agreed. It is also a reinforcement that given correct analysis he (they) will refuse to honorably agree but will resist any answer given by a non-Relativist.

For two years I have argued that time dialtion at best was an illusion of motion and that it was not and could not be reality. I have been called almost every thing imaginable and told I am stupid, ignorant, uneducated, lost, etc, etc,.

Yet in a currently running thread James R has just shown that differential clock times are 100% accounted for by length contraction to the exclusion of any clock tick rate change or time dilation.

When cornered on that issue he made the statement that the other clock cannot account for the differance in time and therefore concludes that time dilation MUST have occurred.

What a lot of crap. He has just stated that physical clock times show no time dilation and that time dilation is an illusion. Exactly what I have argued for two years. But I was wrong, I was stupid.

I introduce here some links to the arguement and its conclusion. I do not do so for the purpose of changing topics and will not debate this issue here. Any comments can therefore be made in the thread this comes from.

I introduce it here to bolster the proof as to the duplicity, lack of candor and lack of honesty in answers being given by Relativists.

My original Scenario
James R Reply and an extract of his own calculation of time differential displays causes. In frame A, given the above assumptions:

B needs to travel 9 light hours at speed 0.9c, which will take 10 hours.
Clock A will read 10 hours at the time of collision.

In frame B, given the assumptions:

A needs to travel 3.92 light hours at a speed 0.9c, which will take 4.35 hours.
Clock B will read 4.35 hours at the time of collision.

My Clarification of Actual Cause of Displayed Time Differentials and an extract: If yes then you should realise this.

d = vt, t = d/v

A: d = 9 lh, v = .9c and t = 9 lh/.9c = 10 hours

B: d = 3.92 lh, v = 0.9c, t = 3.92 lh/0.9c = 4.35 hours.

The differance in registered clock times can only be due to Lorentz Contraction. NOT Time Dilation.

The clock tick rates have not changed.


James R Reply and an extract: No. It's simply a matter of which frame you choose to look at the problem in.

From A's point of view, B has to travel 9 light hours, which takes 10 hours. A explains the final reading on B's clock by saying B's clock was running slow during the 10 hour trip.

From B's point of view, A has to travel 3.92 light hours, which takes 4.35 hours. B explains the final reading on A's clock by saying that, although A's clock was running slow, it was started long before B's own clock was started, giving it enough time to catch up to and overtake B's time.

James R Reply and an extract of his statement: They agree on final displayed times. They do not agree on total elapsed times since the start of the test. B says the test took 4.35 hours. A says it took 10 hours. The only way they can disagree about this is is time dilation effects occur.

Now clearly this says exactly what I have said for two years; noting the exception however, that I further say even this illusion is BS but at least that this is what Relativity shows that there is no time dilation or actual changing of tick rates in clocks and that it is an illusion of motion.

Relativists speak with forked tounge. Beware.



Welcome to the club James R.

geistkiesel:

I gave you concise definitions of both "acceleration" and "inertial reference frame".

It's not my fault if you can't understand them.

MacM,

Why must you try to import every argument into multiple threads? Please at least make some effort to stay on topic.

MacM,

Why must you try to import every argument into multiple threads? Please at least make some effort to stay on topic.

I stated it is not a change of topic but only clarification of the duplicity of answers being given in many threads. This issue is germaine to all threads including this one.

MacM:

This topic is about "What is a reference frame?"

If you wish to discuss the definition of a reference frame, or surrounding issues, do it here. If you want to talk about something else, do it elsewhere. It shouldn't be that hard to restrain yourself.

If U have 0,0,0 as reference frame, then that means Whenever some one is waiting at that point then they will have a zero universal speed ?

If U have 0,0,0 as reference frame, then that means Whenever some one is waiting at that point then they will have a zero universal speed ?
0,0,0 is a point in some undefined reference frame. It's not a reference frame in itself

If you are waiting at point 0,0,0, then you have zero speed in some reference frame, but not in other reference frames.

So we have a train and a track,

The train is deemed to have a velcoity of [x] by the track.
The track is deemed to have a velocity of [x] by the train.
If the frames are applied properly each frame will record the same dilation effects. But as each frame is stationary to itself and has zero velocity what dilation should if assume it has.

As far as the track is concerned the train has the dilation and is irrelavant to the track. As far as the train is concerned the track has the dilation and is irrelevant to the train.

So in summary neither frame will record dilation affected result.

Because to do so would be for that frame to assume some of what the other frame thinks it should have.
If you treat each frame as separate and take each frames perspective individualy with out corrupting the frame with the other frames dilation figures. You find that each frame records exactlly the same distance and time. [using SRT reasoning whih fails to adequately deal with dilation]

I think what is happening is that to give a frame dilation effects you have to assume an absolute frame of reference for either frame, but SRT forbids this.
So the SR reasoning in use is flawed.

if there is any actual dilation involved then it must be shared equally with both frames, thus both frames will still record the same result.

QQ:

You're reasoning is confused and hard to follow. It seems you don't know what length contraction and time dilation are. Length contraction and time dilation are not properties of any object. They are effects of comparing measurements from two different reference frames.

But I've explained this to you before. Are you having trouble understanding? It really isn't hard.

JamesR, What is confusing is that both objects would record the same results even though they may be seen by one frame to be contracted and dilated.

Simple scenario
Earth and object B. Their distance of separation is 10 earth light years
Their distance of separation is decreasing at a rate of 0.8c

Earth is deemed at rest and sees B coming towards it. estimated time of arrival = 12.5 years.

swap to B
B is deemed at rest and sees the Earth coming towards it ETA = 12.5 years.

When both come together they compare their records and both show 12.5 years.
Is this correct?

JamesR, What is confusing is that both objects would record the same results even though they may be seen by one frame to be contracted and dilated.

Simple scenario
Earth and object B. Their distance of separation is 10 earth light years
Their distance of separation is decreasing at a rate of 0.8c

Earth is deemed at rest and sees B coming towards it. estimated time of arrival = 12.5 years.

swap to B
B is deemed at rest and sees the Earth coming towards it ETA = 12.5 years.
No. Because for B, the original distance of separtion was only 6 light yrs and it will only take 7.5 years for the Earth to reach it.


When both come together they compare their records and both show 12.5 years.
Is this correct?

QQ:

When you say "Their distance of separation os 10 earth light years", you mean "as measured by somebody on Earth". That means their separation as measured by somebody on the spaceship will be shorter.

QQ, here's what we are talking about. Check out this image:
http://www.geocities.com/janus58.geo/length.html

The black and white striped bars are measuring rods moving attached to B and the Earth.

This image is from B's perspective. Note that since from B's view, The Earth is moving, the Earth and its respective measuring rod are length contracted. Thus when B is opposite the 10th unit mark of the Earth's measuring rod, there are only 6 unit marks separating B from the earth according to B's measuring rod. So B measures its distance as 6 units from the Earth.

<img src=http://www.geocities.com/janus58.geo/length.jpg>

Posted the image just to show it in context better.

Janus, thanks for your input.

My question really relates to what each RF will record not what it's mathematics sees.

Using Earths perspective Earth is deemed at rest and B has all the velocity in this Thought Experiment.
So earth has to wait 12.5 years for B to arrive. ( b's dilation is irrelevant to Earth)

You contend that the Ship B will see 6 and take 7.5 years.
But I would suggest that this is suggesting an absolute reference and not a relative one. Because as far as B is concerned Earth has all the velocity in this thought experiment and will wait 12.5 years for the Earth to arrive. Earths dilation being irrelevant to the Ship B.

If SR is applied identically to both RF and each perspective taken fully both RF will assume the other as dilated. But both frames will never record contracted distances

So in summary

Earth will wait 12.5 years for ship B to arrive but state that the ship will record 7.5 years from it's perspective which of course is not correct because from the ships perspective Earth records the 7.5 years which of course is also not correct.

Do you see the logic loop I am trying to expose?

for B to record contracted distances it woudl have to assume it has velocity but B would assume it was at rest. So it will not show contracted records.

Unless of course It assumes it has velocity simply because Earth says so......but isn't that more LR and not SR?

This image is from B's perspective. Note that since from B's view, The Earth is moving, the Earth and its respective measuring rod are length contracted. Thus when B is opposite the 10th unit mark of the Earth's measuring rod, there are only 6 unit marks separating B from the earth according to B's measuring rod. So B measures its distance as 6 units from the Earth.
And I ask what makes B's rod measurements any different to Earths Rod measurements when at all times both are at rest when using those rods?

surely you guys have asked this question yourselves at some stage in your learning of SRT.

And I ask what makes B's rod measurements any different to Earths Rod measurements when at all times both are at rest when using those rods?

B's rod's measurements do not change from its perspective. What changes is the Earth's rod, which contracts compared to B's rod from B's perpsective becuase the Earth's rod is moving relative to B.

B's rod's measurements do not change from its perspective. What changes is the Earth's rod, which contracts compared to B's rod from B's perpsective becuase the Earth's rod is moving relative to B.


So, just to be sure I understand your point:

What does the observer on B record as elapsed time for HIMSELF?

and

What does the observer on Earth record as elapsed time for HIMSELF?

When they come together and compare notes what would they show?

I'll try to tabulate what I am seeing:


>>>>>>>A<<<<<<<<>>>>>>>>B<<<<<<<<<<
>>12.5 ////7.5<<<<<>>>>>7.5////12.5<<<<<<

Where A records 12.5 but SHOULD record 7.5 according to B
Where B records 12.5 but SHOULD record 7.5 according to A


Not withstanding the SHOULD's both will record 12.5 anyway.

So, just to be sure I understand your point:

What does the observer on B record as elapsed time for HIMSELF?

7.5 years. Because that is how long it takes the Earth to Reach him at .8c from 6 ly away.


and

What does the observer on Earth record as elapsed time for HIMSELF?
12.5 years, Because that is how long it takes for B to reach him at .8c from 10 ly away

When they come together and compare notes what would they show?
B 7.5 years
Earth 12.5 years.
Assuming that B starts his clock when he passes the 10 ly marker on Earth's rod ( 6 ly distant according his own rod), and that The Earth observer also starts his clock when B passes 10 ly marker of Earth's rod as determined by the Earth Observer.

I'll try to tabulate what I am seeing:


>>>>>>>A<<<<<<<<>>>>>>>>B<<<<<<<<<<
>>12.5 ////7.5<<<<<>>>>>7.5////12.5<<<<<<

Where A records 12.5 but SHOULD record 7.5 according to B
Where B records 12.5 but SHOULD record 7.5 according to A


Not withstanding the SHOULD's both will record 12.5 anyway.

I can't, as it doesn't make any sense.

geistkiesel:

I gave you concise definitions of both "acceleration" and "inertial reference frame".

It's not my fault if you can't understand them.
So you gave definitions, so waht? I am here for the physics.

B's rod's measurements do not change from its perspective. What changes is the Earth's rod, which contracts compared to B's rod from B's perpsective becuase the Earth's rod is moving relative to B.
Here you seem to be saying that B's measurements do not change from its
perspective. Is B's meter the same as a meter from Earth's AT REST original
meter? No, it is not, it has already changed despite what you state. In B's
frame of reference, it's meter has already changed despite B considering
himself at rest and the meter attached to the moving Earth in this frame
is the THIRD change of the meter.

quote by Janus58:
"Assuming that B starts his clock when he passes the 10 ly marker on Earth's rod ( 6 ly distant according his own rod), and that The Earth observer also starts his clock when B passes 10 ly marker of Earth's rod as determined by the Earth Observer."
================================================== ======

You state the fact that B's meter has already changed yourself right here,
( 6 ly distant according his own rod). The additional change to the meter
wrt B's 'view' of the rod attached to the moving Earth in his frame is the
third change to the meter.

B=7.5 years. Because that is how long it takes the Earth to Reach him at .8c from 6 ly away. based on Earths RF and not B's RF.

This is obviously assuming Earth to be a preferred RF, an absolute RF and is LR and not SR.

The question is why we have chosen earths RF as being the preferred frame to calculate B's recording. Why not the other way round?

Maybe B keeps two record books , One for Earths perspective and one for his own.

His earth perspective book will declare he is at velocity determined by Earth.
His B perspective book will declare he has no velocity as he is at rest unto himself and earth has the veloicty instead.

Janus and JAmesR is there a reason for selecting Earth as the preferred RF?

as this is such an important fundamental issue I have drawn the following diagram.
<img src=http://www.paygency.com/Diagrams/8.jpg>

Now I ask what would Earth and B actually record and if you say B will record 7.5 years I would like to ask what velocity is B travelling at when he records that 7.5 years. And then I would ask how can he knows what that velocity is when according to SR he can only be at rest when he does his recording.


The logic problem is simply that for B to show a time of 7.5 years it would have to calculte it's velocity as 0.8c and of course he can't do that because he sees himself at rest.
So where am I going wrong Guys????????

by Quantum Quack:

"This is obviously assuming Earth to be a preferred RF, an absolute RF and is LR and not SR."
================================================== ==============

This is where both you and Mac make a mistake. In Lorentz Relativity, the Earth or
wherever the exercise started is the preferred reference frame. Earth is not an absolute reference frame in LR, ONLY if the Earth is the point of origin of the exercise.
For instance, if an exercise started on a distant planet, THAT planet would be the
preferred reference frame, not Earth. In SR, you can choose to work from either reference frame, say the Earth or the moving object. But the Earth is almost always
chosen as the preferred reference frame, just as in LR. If results of an exercise are to
be interpreted by an Earth observer, the Earth is the chosen reference frame in SR
just as in LR. Using the Earth as a reference frame does not 'make it LR.'

This is where both you and Mac make a mistake. In Lorentz Relativity, the Earth or
wherever the exercise started is the preferred reference frame. Earth is not an absolute reference frame in LR, ONLY if the Earth is the point of origin of the exercise.
For instance, if an exercise started on a distant planet, THAT planet would be the
preferred reference frame, not Earth. In SR, you can choose to work from either reference frame, say the Earth or the moving object. But the Earth is almost always
chosen as the preferred reference frame, just as in LR. If results of an exercise are to
be interpreted by an Earth observer, the Earth is the chosen reference frame in SR
just as in LR. Using the Earth as a reference frame does not 'make it LR.'
Correct except for the very first statement.

If we apply SR as Janus has suggested we are applying it in a way that makes the Earth the preferred RF. THus LR is being applied as a logic sub routine in a situation that requires SR in total.

For the ship to record 7.5 years means that Earth is the preferred RF. For the ship to record 12.5 years as at rest an unresolvable SRT logic conflict becomes evident.
And this is the reason for posting this question in this thread. Of course bringing LR into the topic may only confuse the issue.

Read it again, QQ. There is absolutely nothing wrong with using Earth as a reference
frame in SR. ONE reference frame HAS to be chosen, even in SR, to get the results
IN THAT FRAME. You know I believe SR to be based on a false concept, but what
Mac is stating about reference frames does not discredit SR in any way.

If you want to show a mistake in LR, simply start and stop your exercise in the moving
frame of reference. For example, use Earth as one point in the reference frame and the
moving spacecraft approaching Earth as the other point. Work from the moving
spacecraft's point of view, LR doesn't allow you to 'switch' frames. In LR, the moving
spacecraft would assume the position of rest when working from that frame of reference, just as SR would. End result would be the Earth observer ages less than
the spacecraft observer in LR. Is that the right answer? Of course not, LR is not an
accurate discription of reality either.

The problem is the crossing of purposes in the logic.

What is actually happening is the distance of separation is diminishing at a velocity of 0.8c.

It could be just as equally valid to assume that each RF has a velocity of -0.4 and both are dilated equally thus no difference in their recordings.

But this is not SRT.

SRT takes a single frame and attempts to extrapolate a single frames dilation and contraction. But SRT demands that both RF can have equal treatment.

If both frames are treated identically it is always the other frame that has dilation and contraction.

The only solution I can see that is valid is that the over-all dilation of 2.5 years is shared equally between the Frames. But this is not SRT.

The question is not about what is calculated for the other frame but what that other frame actually records from it's perspective.

And I simply don't see how a frame at rest can record dilation and contraction effects.

So when it is said that the ship will record 7.5 years the ship must assume that earth is at rest and the ship is moving.
So I guess that is what SR demands then that for some reason the ship has to take Earths perpsective on it's own velocity.
And if that's it then that's it.

How it works if you swap frames I can not fathom.

I do think however my diagram shows the problem very clearly.

A question simply put that ends this discussion:

Does a RF consider itself at rest when making a recording of distance/time relative to the other RF or not?
If the answer is yes then SR is in trouble. If the answer is no then RF treatment is an absolute preference and RF swapping is not allowed.

another approach would be to say both RF are at rest, no velocity happening, They are deciding to get together, they are 10 lys apart, They have a decision to make, which one gets to travel for the less time,.......don't sound to good to me, I would always take the less time.....so both of them fight over who gets to be dilated.....ha

Look out guys I am goin' to dilate you.....ha

If one wants to come as close to 'reality' as possible, an 'absolute' reference frame
needs to be chosen. But that reference frame would not be based on relative velocities
between two objects. That is the problem. It would have to be based on something
like the Milky Way's motion in the universe. The Milky Way galaxie rotates within the
universe, the reference frame could be chosen based on this movement which would
keep everything WITHIN the Milky Way in an absolute frame of reference. All movement
would be relative to this frame. Movement within the galaxie itself is where time dilation would occur, because such variations in time are actually due to movement
through the vacuum itself, not just relative to another object. But, my God, how
complicated it would be to actually calculate such movement based on an absolute
reference frame. Think of all the motions that would have to be taken into account,
from Earth's rotation to the movement of the solar system within the Milky Way.
Special Relativity is very simple in comparison, and it is unlikely it will be replaced
because anything better would be very complicated. (Disclaimer) This is just my
humble opinion and does not reflect mainstream science, of course. HeHe.

ok 2 you choose, do you want to be dilated or not? [chuckle]

Just to clairfy, relative velocity IS based on two points relative to each other. But that
does not give the 'true' picture of variations in time between the two frames. But another thing you mentioned QQ, is not exactly true. Special Relativity does not
demand the two frames to be treated identically, that is just Mac's statement. SR
states the laws of physics are the same in both frames. Tine does not have to pass
at the same rate in both frames with regards to each other, just that time will seem
to pass at the same rate as always to the observer WITHIN a particular frame of
reference. A clock in orbit runs faster in relation to a clock on Earth, but if you were
in orbit yourself holding that clock, you would never know the difference, the laws of
physics would remain unchanged for you. But that frame of reference would not be
identical to one on Earth when COMPARING THE TWO. Think of you and I sitting in
our cars on a road. I could drive away while you stayed stationary and relative velocity
could be figured from either frame correctly, the laws of physics would still hold true.
But the frames would not be identical because I burned gas in my movement while you
did not while sitting still. But in my understanding, that does not violate SR, the frames
do not have to be identical, only the laws of physics have to remain unchanged.

2,
A clock in orbit runs faster in relation to a clock on Earth, but if you were
in orbit yourself holding that clock, you would never know the difference, the laws of
physics would remain unchanged for you.
Wouldn't the clock on Earth be seen to be running fast. [by the orbiting clock]

Well then I ask you the question :Why do we swap reference frames then?
I woudl also suggest that how an object is propelled is irrelevant to SRT.

also It is not MAcM's statement it is my own derived from my thread about transfromations in a shared frame. We do at this stage agree though on this problem, but that doesn't mean I am simply applying MacM's statements. JAmesR knows from all my silly questions that this has developed free from MacM's machinations.

It just turned out that I have arrived at the same conclusion that MacM has been pushing in the twins paradox thread and many others over the last 2 years. I just couldn't see what he was trying to get at with all the BS that was flying, but now I do.

JamesR mention in one of them that SRT does not necessarilly imply symmetry or identicality [treatment of Frames] and it is this fundamental logic that I am endeavouring to clarify.

As I know the image doesn't take up file space I'll post it again,
The question being, what would make you decide a preferred frame and overrule the other frames reality?

<img src=http://www.paygency.com/Diagrams/8.jpg>

There are so many ways to show this as an issue:
another :

ship A records ship Bs time as 7.5 years,and simultaneously ship B records ship A as 7.5 years, now ship A heads back home and reports that ship B took 7.5 years and ship B does the same to his home reporting that ship A took 7.5 years.....ship B's home communicates with ship A's home and they both show a record of the other as doing 7.5 years, now they know someone must be wrong, but who is mistaken ship A or ship B?

based on Earths RF and not B's RF.
No, according to B's RF, because it is in B's RF that The Earth is 6 ly distant when B starts his clock.



This is obviously assuming Earth to be a preferred RF, an absolute RF and is LR and not SR.
No, there is no prefered RF. What do exist are distinct events, the time between which are measured by each clock.



The question is why we have chosen earths RF as being the preferred frame to calculate B's recording. Why not the other way round?
We haven't, What we have done is choose which events between which we want to measure time.


Maybe B keeps two record books , One for Earths perspective and one for his own.

His earth perspective book will declare he is at velocity determined by Earth.
His B perspective book will declare he has no velocity as he is at rest unto himself and earth has the veloicty instead.

Janus and JAmesR is there a reason for selecting Earth as the preferred RF?

No prefered frame is being chosen.

Here you seem to be saying that B's measurements do not change from its
perspective. Is B's meter the same as a meter from Earth's AT REST original
meter? No, it is not, it has already changed despite what you state. In B's
frame of reference, it's meter has already changed despite B considering
himself at rest and the meter attached to the moving Earth in this frame
is the THIRD change of the meter.
Again, In B's frame, The meter does not change. What happens is that the distance that Someone in the Earth frame would claim to be a meter is shorter than B's meter when measured from B's frame.


quote by Janus58:
"Assuming that B starts his clock when he passes the 10 ly marker on Earth's rod ( 6 ly distant according his own rod), and that The Earth observer also starts his clock when B passes 10 ly marker of Earth's rod as determined by the Earth Observer."
================================================== ======

You state the fact that B's meter has already changed yourself right here,
( 6 ly distant according his own rod). The additional change to the meter
wrt B's 'view' of the rod attached to the moving Earth in his frame is the
third change to the meter.

No, What I said was that the Distance measured by the Earth as 10 ly is measured as 6 ly by B. This is not due to any change in B's meter, but due to the fact that when B compares his meter stick to one in the Earth frame, the Earth Frame's is shorter and thus takes it takes more of them to span the same distance.

You seem to make a tacit assumption that the distance measured by the Earth is somehow the "true" distance, and in order for B to measure a different distance, B's meter must change, this is not the case.

Here's another attempt to clear this issue up for those who still seem to be confused.
http://www.geocities.com/janus58.geo/Length_con.html

Bravo, janus58!

Janus, Thanks for that, I have saved it to file for future refeerence.
The question that still worries me is not what A and B records for some other frame but simply what they record for themselves.

What does A record for himself? v=? d=? t=?
What does B record for himself? v=? d=? t=?
to cover the distance of 10 light years with a diminishment of separation rate of 0.8c

I do realise that I am seeming to just repeat myself and that the querstion has been answered already.

But I have asked this question maybe 4 times and always I get a projected data onto another frame rather than just that frames data.

I know the question seems very simple and maybe you feel it deserves no response, but I guess it's a "bottom line" question.

But if it could be answered as it requires then I may have a way to find understanding, thanks in advance.... :)

Again, In B's frame, The meter does not change. What happens is that the distance that Someone in the Earth frame would claim to be a meter is shorter than B's meter when measured from B's frame.


No, What I said was that the Distance measured by the Earth as 10 ly is measured as 6 ly by B. This is not due to any change in B's meter, but due to the fact that when B compares his meter stick to one in the Earth frame, the Earth Frame's is shorter and thus takes it takes more of them to span the same distance.

You seem to make a tacit assumption that the distance measured by the Earth is somehow the "true" distance, and in order for B to measure a different distance, B's meter must change, this is not the case.

I certainly made no assumption that either distance is the 'true' distance,
I believe exactly the opposite. So, you are stating that the 'standard'
interpretation of the moving frame 'B', having the shorter meter and the
slower clock in comparison to the rest frame is incorrect?
EDIT for added comment: So you are saying the term 'Lorentz contractions'
is a misnomer, it should be 'Lorentz expansions' since the slower clock has
the LONGER meter when compared to the faster clock? That would keep the
speed of light constant, wouldn't it? Each frame would have its own personal
speed of light based upon its velocity. Seems I have said that before?

Janus, Thanks for that, I have saved it to file for future refeerence.
The question that still worries me is not what A and B records for some other frame but simply what they record for themselves.

What does A record for himself? v=? d=? t=?
What does B record for himself? v=? d=? t=?
to cover the distance of 10 light years with a diminishment of separation rate of 0.8c

I do realise that I am seeming to just repeat myself and that the querstion has been answered already.

But I have asked this question maybe 4 times and always I get a projected data onto another frame rather than just that frames data.

I know the question seems very simple and maybe you feel it deserves no response, but I guess it's a "bottom line" question.


But we have been answering it, everytime you ask it.
B records 7.5 years from the time it starts its clock to the time it meets up with A according to B. The distance of separation according to B when B starts its clock is 6 ly. The speed of closure is .8c

A records 12.5 years from the time it starts its clock until it meets up with B according to A . The distance of separation according to B when B starts its clock is 10 ly. The speed of closure is .8c

It's all there in the link I gave you. The first set of images includes the time A's clock records; What A's clock records is what A records for itself. The same goes for the second set of images with regards to B's clock.

I don't know how to say it any clearer than that.

I certainly made no assumption that either distance is the 'true' distance,
I believe exactly the opposite. So, you are stating that the 'standard'
interpretation of the moving frame 'B', having the shorter meter and the
slower clock in comparison to the rest frame is incorrect?
As long as the comparison is being made from the "rest" frame that "B" is moving realtive to, what you call the 'standard' interpretation is correct, and I've never said otherwise. But from 'B', 'B' is the rest frame, so for 'B' its clocks never undergo any dilation nor does B's meters undergo any contraction.


EDIT for added comment: So you are saying the term 'Lorentz contractions'
is a misnomer, it should be 'Lorentz expansions' since the slower clock has
the LONGER meter when compared to the faster clock? That would keep the
speed of light constant, wouldn't it? Each frame would have its own personal
speed of light based upon its velocity. Seems I have said that before?

I don't know where you got this from anything that I said.

Look at the link I gave QQ, where in those images do I ever have the frame with the slower clock as having the longer meter?

by Janus58:
"This is not due to any change in B's meter, but due to the fact that when B compares his meter stick to one in the Earth frame, the Earth Frame's is shorter and thus takes it takes more of them to span the same distance."
================================================== =====

I never said 'B's' meter 'changed.' I said in comparison to 'A's' meter, it is longer in
'B's' frame of reference. The length of the meter is due to the constancy of the speed
of light IN THE FRAME OF THE OBSERVER DOING THE MEASURING. If I am moving through the universe at .9c, I measure to speed of light at 299,792,458 meters per
second. If you are in a different location near Earth, but in the vacuum with 0 relative
velocity wrt the Earth, for example, you also measure the speed of light at 299,792,458 meters per second. But my second is slower and my meter is longer in
comparison to your meter and your second. Both of us are correct in our frames of
reference and neither the speed of light nor the meter 'changed', they are just different when the meter and 'c' in one frame is compared to the meter and 'c' in a
different frame when there is a difference in velocities of the frames or if the frames
are in different gravitational fields.

sorry to sound pedantic but:
Can I say that the answer to my question is :

A] v=0.......distance= 0......t= 12.5years
*****
B] v= 0.8c..distance = 0.6...t= 7.5 years.

records for themselves?

a ludicrous out come is that the captain of B knows that he is going to travel 10 light years and record that it has taken 7.5 years to do it. [before he starts his journey]

No, QQ,
he does not knows that: look carefully on graphs shown in janus58 post...
It is you who, by some strange reason, want him to know that...

Just to clairfy, relative velocity IS based on two points relative to each other. But that
does not give the 'true' picture of variations in time between the two frames. But another thing you mentioned QQ, is not exactly true. Special Relativity does not
demand the two frames to be treated identically, that is just Mac's statement. SR
states the laws of physics are the same in both frames. Tine does not have to pass
at the same rate in both frames with regards to each other, just that time will seem
to pass at the same rate as always to the observer WITHIN a particular frame of
reference. A clock in orbit runs faster in relation to a clock on Earth, but if you were
in orbit yourself holding that clock, you would never know the difference, the laws of
physics would remain unchanged for you. But that