[CPT ArkAngel]

The difference of time rate is due to different relative speeds. The different relative speeds are due to different inertial accelerations... Accelerations are hidden in the Maths, they are implied... C'mon, this is obvious!

I understand that you can have an acceleration without a change in speed but it is an artefact of the choice of the observer (coordinates). Another observer won't necessarily agree on how each part of the paths affect the time rate. In the end, with SR, speed rules but it is incomplete because acceleration is obviously the key...

A non accelerating frame is chosen as the observer. But why? This is the key to understand the problem. The problem is swept under the carpet from the beginning. This is a reduction to Lorentz equations.

[PhysBang]

The difference of time rate is due to different relative speeds. The different relative speeds are due to different inertial accelerations... Accelerations are hidden in the Maths, they are implied... C'mon, this is obvious!

I understand that you can have an acceleration without a change in speed but it is an artefact of the choice of the observer (coordinates). Another observer won't necessarily agree on how each part of the paths affect the time rate. In the end, with SR, speed rules but it is incomplete because acceleration is obviously the key...

A non accelerating frame is chosen as the observer. But why? This is the key to understand the problem. The problem is swept under the carpet from the beginning. This is a reduction to Lorentz equations.

Why do you ignore the part of the scenario where everyone agrees that one twin changes direction? Because of this, we have to use different kinds of reference frames for one than the other, without any trickery.

[CPT ArkAngel]

The difference of time rate is due to different relative speeds. The different relative speeds are due to different inertial accelerations... Accelerations are hidden in the Maths, they are implied... C'mon, this is obvious!

I understand that you can have an acceleration without a change in speed but it is an artefact of the choice of the observer (coordinates). Another observer won't necessarily agree on how each part of the paths affect the time rate. In the end, with SR, speed rules but it is incomplete because acceleration is obviously the key...

A non accelerating frame is chosen as the observer. But why? This is the key to understand the problem. The problem is swept under the carpet from the beginning. This is a reduction to Lorentz equations.

Why do you ignore the part of the scenario where everyone agrees that one twin changes direction? Because of this, we have to use different kinds of reference frames for one than the other, without any trickery.

I don't!

[PhysBang]

It is easy to make a twin "paradox" scenario without acceleration. One merely needs to imagine the scenario with clocks that have constant velocity that merely pass each other at the relevant points and happen to be synchronized when they pass each other

[geordief]

It is easy to make a twin "paradox" scenario without acceleration. One merely needs to imagine the scenario with clocks that have constant velocity that merely pass each other at the relevant points and happen to be synchronized when they pass each other

I don't understand. How can two clocks moving at constant velocity wrt each other meet at two separate points in space-time?

Or are you  perhaps referring to two clocks orbiting  the same body in opposite directions? (both clocks are accelerating wrt to the body around which they are both orbiting but their respective accelerations "cancel out" in a sense)

[guest4091]

The 'twins' explanation #14 using the axis of simultaneity is extraneous fluff. That convention only assigns times to events observed locally, since a system of clocks would be logistically impossible for astronomical distances. The distant events result from the behavior of the remote clock and aren't altered by the simultaneity convention.

twins-3 seg.gif (2.66 kB . 203x416 - viewed 9712 times)
Using the notation (x, t) and fig.2,
A records B leaving (0, 0) a .6c, and returning (0, 10).
B records A leaving (0, 0) at .6c, and returning (0,t= .
Does the accumulated time differ?
A experienced 10 flashes, all observed by B.
B experienced 8 flashes, all observed by A.
B is younger than A.
Within the closed course, there are no missing events.
The reversal data is irrelevant.
The perceived doppler shifts for the diverging vs converging segments is irrelevant.
The instantaneous reversal by B is irrelevant, since it's duration is zero time, i.e. equivalent to "it never happened", thus not having any catastrophic results. The discontinuity is equivalent to two B frames participating in the experiment.
There is no acceleration/*deceleration involved, just inertial motion.
* Yes, there is such a word, for those too lazy to use a dictionary.

[CPT ArkAngel]

All clocks must be synchronized in the same "rest" frame before the start for any SR experiment to be validate...

[PhysBang]

It is easy to make a twin "paradox" scenario without acceleration. One merely needs to imagine the scenario with clocks that have constant velocity that merely pass each other at the relevant points and happen to be synchronized when they pass each other

I don't understand. How can two clocks moving at constant velocity wrt each other meet at two separate points in space-time?

They just have to pass by each other. This happens every day when people pass each other in the street.

In the no acceleration twin scenario, one clock, A, sits in space and another clock, B, passes very closely by. When A and B are very close to each other, they read the same. Then B goes out and at some point, another clock, C, going the opposite direction passes by B. At the point where B and C are very close to each other, they read the same. Then, at some point, A and C pass very close to each other.

We can work out all the details for these clocks and get the same twin scenario without any object undergoing acceleration.

[PhysBang]

All clocks must be synchronized in the same "rest" frame before the start for any SR experiment to be validate...

This isn't an experiment, though similar experiments have been done. In this case, it is enough to imagine that all clocks are the same type of physical system that, if they were at rest next to each other, would remain synchronized. There is nothing in SR that demands that all clocks must be actually synchronized at some point for comparisons to be appropriate.

[CPT ArkAngel]

Even if you use relative time instead of proper time, acceleration (and deceleration) is still the key. Imagine A and B having a relative speed of V1 and being synchronized. At a later time V1 change to V2. How do you know which clock, A or B, had its time rate changed? The one that was subjected to acceleration.

[PhysBang]

Even if you use relative time instead of proper time, acceleration (and deceleration) is still the key. Imagine A and B having a relative speed of V1 and being synchronized. At a later time V1 change to V2. How do you know which clock, A or B, had its time rate changed? The one that was subjected to acceleration.

Trivially, any change in velocity is an acceleration. But it's the velocity that plays a role in the equations, not acceleration. And one can always reproduce any scenario with acceleration with one involving multiple clocks that pass each other, so no acceleration involved at all.

[geordief]

They just have to pass by each other. This happens every day when people pass each other in the street.

In the no acceleration twin scenario, one clock, A, sits in space and another clock, B, passes very closely by. When A and B are very close to each other, they read the same. Then B goes out and at some point, another clock, C, going the opposite direction passes by B. At the point where B and C are very close to each other, they read the same. Then, at some point, A and C pass very close to each other.

We can work out all the details for these clocks and get the same twin scenario without any object undergoing acceleration.

If the maths are not too complicated (actually even simple maths can defeat me) would you have a (link to a ) mathematical description of your scenario?

Is it not difficult to asses when  B and C  are "very close to each other," ? Would distance(from A)  and velocity wrt A make that very difficult to assess  physically?

[PhysBang]

Here is a nice, standard presentation of the twin scenario with the relevant numbers and a description of the clock passing scenario at the end: http://www.phys.vt.edu/~jhs/faq/twins.html

[CPT ArkAngel]

There is accelerations involved in any cases. The Maths doesn't need it because the choice of postulate is right in the SR circumstances, though it is just an approximation in reality. The acceleration is hidden by the choice you make. This is willful blindness.

We don't agree on semantic or so it seems.

My point is there is no explanation of how the time rate changes beyond the application to Lorentz equations of a constant communication speed and no preferred frame. There is no explanation on how the proper time may change. SR is more about E=MC². If you want to give an explanation, you must express all the constraints in which it is valid. The limits form a closed circle and the only exit points to "acceleration".

[yor_on]

Well yes, there are accelerations involved CPT, but you don't really need them to get a time dilation. It's a weird fact of relativity that different 'frames of reference' also have different 'time rates' relative ones wrist watch. Think of  NIST clocks at different elevations, you can place them, which do involve a acceleration. But after placing them you now 'synchronize' them to show the exact same time, and so define the experiment to start there. The clocks will lose that synchronization as they are in different frames of reference. But yes, it's rather hard to assimilate the idea in itself that all different motions, not only accelerations, as well as mass create those effects.

But if one think of it solely in terms of accelerations I think it becomes even weirder :)
=

Hmm, maybe not the best of arguments thinking of the equivalence principle in which gravity is 'indistinguishable' from a acceleration, ah well :) that means that they are 'constantly uniformly accelerating' in terms of GR. Then again, a 'frame of reference' does not only involve accelerations but also uniform motions, aka speeds. And different speeds are different frames of reference.

( A frame of reference is a set of coordinates that can be used to determine positions and velocities of objects in that frame; different frames of reference move relative to one another. ) or this Special relativity

[yor_on]

I'll give you another, remember that 'light clock'? Two mirrors 'bound' together using reflected light between them to measure a time, light 'bouncing'. Let it move at a uniform motion and geometrically seen those 'pulses' now will have a longer path to take, than for some other clock at a slower uniform motion. It's a explanation that I'm not totally happy about as it describes it in form of a geometry, but you can use it to give a reason why different uniform motions belongs to different frames of reference, presenting us with time dilation's without involving accelerations.

[PhysBang]

There is accelerations involved in any cases. The Maths doesn't need it because the choice of postulate is right in the SR circumstances, though it is just an approximation in reality. The acceleration is hidden by the choice you make. This is willful blindness.

If you would bother reading any of the links here or a decent introductory textbook on the subject, you would see that the accelerations play no role. If you still think otherwise, please go through the scenario and show, with some numbers, exactly where the accelerations are.

I'm sorry that you are wrong about this, but you really should let it go.

We don't agree on semantic or so it seems.

Sure, you keep saying things that are demonstrably false about SR, someone shows that your statements are false, then you say another demonstrably false thing or even the same thing again. You don't seem to want to agree on basic definitions of truth or falsity as they relate to the text of On the Electrodynamics of Moving Bodies, so there is not much hope that you can come to an agreement with anyone about SR.

My point is there is no explanation of how the time rate changes beyond the application to Lorentz equations of a constant communication speed and no preferred frame.

That's pretty much all of SR. You also go on to add that there is some paradox that is not resolved and this is false.

There is no explanation on how the proper time may change. SR is more about E=MC².

The energy equivalence equation is derived from SR. Again, you seem to disagree with the basic definitions of truth and false with regards to the actual text of the relevant works.

[CPT ArkAngel]

You are wrong! I understand very well everything you pointed out. But you don't understand my point of view. I know that the SR equations doesn't need acceleration to be right! But SR is incomplete.

An astronaut from planet A encounters an astronaut from planet B. They lost track of their planets and trajectories. When they met, they had an initial constant velocity. How can they know what is the difference in their proper time? They can't... To know this, they must meet in the same frame and synchronize their clocks, and only from then on they can know about their proper times. This is clear that acceleration has a key role, even though you can use the different speeds along each path to calculate a late disagreement in time. I disagree on what you define as a proof! I understand what you say but I think you don't fully understand the larger implications of SR. Einstein himself said that it is the acceleration which is important and the key to understand SR further. He said that acceleration explains the twin paradox!!! I will let you find this by yourself...

in your example without acceleration: http://www.phys.vt.edu/~jhs/faq/twins.html

Notes "According to Unprime, Prime is moving along (and always has been) at the speed v" and "Doubleprime has always been moving this way"

This proves my point!

[PhysBang]

You are wrong! I understand very well everything you pointed out. But you don't understand my point of view. I know that the SR equations doesn't need acceleration to be right! But SR is incomplete.

Dude, we can read what you wrote.

You wrote, "Within special relativity, it is a paradox. All explanations within the frame of SR alone are wrong because there is no key to differentiate the twins."

Now, you are wrong. That's OK. Just don't double down on it.

An astronaut from planet A encounters an astronaut from planet B. They lost track of their planets and trajectories. When they met, they had an initial constant velocity. How can they know what is the difference in their proper time? They can't... To know this, they must meet in the same frame and synchronize their clocks, and only from then on they can know about their proper times.

That's ridiculous. Each one knows their own "proper time", since that is the time of a clock co-moving with them. If each one is carrying some system that the other knows the rate of (i.e., a clock), then they can each use their view of that that to establish time dilation. The thing about SR is that is gives an objective standard that anyone in any frame can use.

 

I disagree on what you define as a proof!

Of course, if you are going to freely disregard truth and falsity, then you are going to disregard proof.

I understand what you say but I think you don't fully understand the larger implications of SR.

I agree that  I don't understand the implication of what you consider SR.

Einstein himself said that it is the acceleration which is important and the key to understand SR further. He said that acceleration explains the twin paradox!!!

"Citation missing"

in your example without acceleration: http://www.phys.vt.edu/~jhs/faq/twins.html

Notes "According to Unprime, Prime is moving along (and always has been]) at the speed v" and "Doubleprime has always been moving this way"

This proves my point!

Again, you are using "prove" in a way that doesn't match the usage that I expect. In that example, all the differing results of the twin "paradox" are there, but no acceleration has been used. Yet the same SR resolution is available.

[CPT ArkAngel]

I proved my point. I think you understand but you just don't want to admit it... If not, think again and look for "Einstein and the twin paradox". There are many good articles...