# Thread: Reciprocity of relativistic effect

1. Physics should not be based on any "appearance."
Einstein was wrong about a reciprocal appearence
of his Relativity. In the twin experiment only
one twin sees the other's clock blueshifted.

There is no physical division of phenomenon.
So GR and SR really are inseperable.
Accelerating is what changes the relatives in SR.

Something can move through space relative to another
without that other moving through space relative to it.
Only the one moving through space has the relativistic
effects i.e. contraction of space-time.
An example would be Einstein's: When the station comes
to the train.
But the station does not move through space to get any
closer to the train. Only the train is moving through space
relative to the station.

No reciprocity. After all why should there be if only one
clock actually goes slower?

2.

3. Nick,

This appears to be a difficult concept for many people. It requires separating yourself from earthbound preconceptions. Not everyone is up to the task, but some seem to "get it" while others struggle with it.

I suggest you examine the example of two spacecraft in deep space moving with respect to each other. You can read each others speed by radar. Who is moving?

If you find yourself complicating the problem with additional reference frames, measurements of distant stars or objects, etc, then you are not understanding the issue. It's really very simple.

4. I'll add there is a tiime when there are no relatives.
If there is no motion then there are no relatives.

5. Ok. So what?

6. An example would be Einstein's: When the station comes
to the train. But the station does not move through space to get any
closer to the train. Only the train is moving through space
relative to the station.
You only say that because the station is "bigger" than the train, or because it is attached to something bigger (the planet Earth). Your are accustomed to regarding the Earth as a solid, immovable platform.

In fact, the Earth moves around the Sun, and the Sun moves around the Milky Way, and the Milky Way moves through space relative to distance galaxies.

So, why say the train moves and the Earth doesn't? Clearly, the Earth moves. It isn't a "special" point of view. Certainly no more "special" than the point of view of the train.

It makes just as much sense to say that the station comes to the train as to say the train comes to the station. All motion is relative.

7. Originally Posted by Nick
Something can move through space relative to another
without that other moving through space relative to it.
Only the one moving through space has the relativistic
effects i.e. contraction of space-time.
An example would be Einstein's: When the station comes
to the train.
But the station does not move through space to get any
closer to the train. Only the train is moving through space
relative to the station.
Hi Nick,
The Earth is rotating once per day, so the train station is moving at a thousand miles an hour or so from West to East, right?

So when a train accelerates out of the station to the West, is it really accelerating? Or is it decelerating?

Will the clocks on the train run slower than those in the station, or the other way around?

8. by James R:

"You only say that because the station is "bigger" than the train, or because it is attached to something bigger (the planet Earth). Your are accustomed to regarding the Earth as a solid, immovable platform.

In fact, the Earth moves around the Sun, and the Sun moves around the Milky Way, and the Milky Way moves through space relative to distance galaxies."
==============================================

This is the whole point, James. STR's rest frame assigns solid, immovable
coordinate points to the frame 'at rest'. The Sun moves around the Earth,
the Milky Way moves around the Earth, and distant galaxies move away
from the Milky Way and around the Earth. This applies to either the rest
frame of the train or the station, the only difference being whether the
universe is moving relative to the train or the station. In a Global Inertial
Frame, the ICRF for instance, the train will move relative to the surface of
the Earth, the Earth will rotate on its axis, the Earth will orbit the Sun, the
Sun will move around the Milky Way, etc. One is free to choose inertial or
non-inertial frames WITHIN the Global frame to more accurately describe
motion, for instance the train will move relative to the surface of the Earth,
always. You can describe the trains velocity relative to Earth's surface, or
its orbital velocity around the Sun, whatever your needs.

9. 2inq,

What are you trying to say?

10. Originally Posted by James R
An example would be Einstein's: When the station comes
to the train. But the station does not move through space to get any
closer to the train. Only the train is moving through space
relative to the station.
You only say that because the station is "bigger" than the train, or because it is attached to something bigger (the planet Earth). Your are accustomed to regarding the Earth as a solid, immovable platform.
.

So, why say the train moves and the Earth doesn't? Clearly, the Earth moves. It isn't a "special" point of view. Certainly no more "special" than the point of view of the train.
Boloney. yes the earth is moving through space around
the sun. But the motion of the train with respect to the earth
is unrelated to it. Onlyn the train is moving relative to the
embamkment. The embankment is not moving through
space relative to the train. And the station does not
move through space to get closer to the train.

That is the simple point.

11. Originally Posted by superluminal
Ok. So what?
Relatives only exist in potential to absolutes.

12. Originally Posted by 2inquisitive
You can describe the trains velocity relative to Earth's surface, or its orbital velocity around the Sun, whatever your needs.
...which is precisely the point of relativity, no?

13. Originally Posted by Pete
Originally Posted by Nick
Something can move through space relative to another
without that other moving through space relative to it.
Only the one moving through space has the relativistic
effects i.e. contraction of space-time.
An example would be Einstein's: When the station comes
to the train.
But the station does not move through space to get any
closer to the train. Only the train is moving through space
relative to the station.
Hi Nick,
The Earth is rotating once per day, so the train station is moving at a thousand miles an hour or so from West to East, right?

So when a train accelerates out of the station to the West, is it really accelerating? Or is it decelerating?

Will the clocks on the train run slower than those in the station, or the other way around?
Pete. Take the example of a ship that takes off from mars
and accelerates toward the earth. You cannot say that the
earth deviates from its orbit to get closer to the ship.
Only the ship is moving through space relative to the earth
and not the other way around.

Everything has some motion through space that is why
we can say there is no absolute rest.
Only what has accelerated(experienced weight) is
moving through space. What you have accelerated through
space relative to does not do the accelerating.
So its motion would only be a relative to that which is
actually moving through the space.

Cheers.

14. Originally Posted by Pete
Originally Posted by 2inquisitive
You can describe the trains velocity relative to Earth's surface, or its orbital velocity around the Sun, whatever your needs.
...which is precisely the point of relativity, no?
All those motions through space are absolute!

15. as was mentioned earlier you can't allow yourself to complicate the idea by adding extra frames of reference other than the ones you wish to study.

you only take into account the frames of reference that are relative to the other objects in the specified system.

16. Folks,

Judging from this guys attitude:

Boloney. yes the earth is moving through space around
the sun. But the motion of the train with respect to the earth
is unrelated to it. Onlyn the train is moving relative to the
embamkment. The embankment is not moving through
space relative to the train. And the station does not
move through space to get closer to the train.

That is the simple point.
He's not interested in learning anything. He just wants it his way or the highway. If that's not so, and he really thinks the way he's presented himself, then I don't have the energy to spend on the MONTHS of rehab it's going to take to straighten him out (can you say geist, MacM...). Good luck.

17. There are different 'inertial' frames. STR's method of always assuming
the observer is in the inertial 'rest' frame with non-moving coordinates
leads to substantial errors in reality. The ICRF I spoke of? It is a Global
inertial frame, but it is NOT a 'rest frame'. The origin of its coordinate points can be considered stationary, or relatively moving wrt a distant
object, whichever one chooses. To state the Milky Way and many other
galaxies in the local group are converging on a point near the Virgo cluster, the ICRF (coordinates points originating at the barycenter of the
solar system) is moving toward that point, it is not at rest. If you only
want to calculate the Earth's rotation (23 hrs 56 min. Sidereal time), it
is unnecessary to consider the solar system's velocity through the Milky
Way, or the Milky Way's speed toward the Virgo Cluster as that will have
no effect on the rate of rotation. Neither will it have an effect on calculating the velocity of a train relative to the surface of the Earth, but
you CAN calculate the rotational velocity of any point on Earth's surface
if the need arises.

Let me pose a little train gedankin here. Let there be train rails around the
Earth along the equator. Let there be an observer standing beside the tracks at a station with an infrared remote control, one coded to turn on
and off two atomic clocks with the same code. One clock is beside this observer at the station and the other is on the train. The train approaches
this observer at a steady speed of 1000 miles per hour, he flicks his remote and starts both clocks. The train encircles the Earth at this steady
speed and approaches the observer again. Another flick of the remote and
both clocks stop. According to STR, will the clocks agree, and if not why not? Will it make any difference if the train travels East or West? Remember the Hafele-Keating 'experiment'.

18. 2inq,

Get off the damn earth and into a true inertial frame which is all that SRT deals with. You are in a ship in space. I am in another ship in space. We are seperating at 1000mph as we both determine by radar.

Which one of us is moving?

The ICRF is just another arbitrary reference of convienience. Drop it. We don't know about this in our ships. All we know is how to work our radars.

So which one of us is moving?

Don't add ICRF's, CMB refs, "averages of galactic motion" refs. We're sipping tea at our respective radars in our ships.

Which one of us is moving?

19. Thanks, superluminal. I agree there are no true inertial frames on or near Earth. Spaceships also don't travel in straight lines unaffected by gravity.
They travel in elipses, definitely affected by gravity, whether a 'force' or
following a curvature of space-time. Except perhaps in deep interstellar space, where the effect would be minimal, but still there nonetheless.

Superluminal, my post was about time dilation, not 'which one of us is
moving'. You can go into space alone. Are you moving? How do you keep up with where you are? Damn, you are lost in space, totally unprepared

20. 2inq,

Why can't you answer my question? It's utterly simple. We're not talking about navigation here. Just who's moving and how that affects the results of time dilation for each observer. You seem to confuse a simple reference system (ICRF) with discussion of a fundamental property of the universe, namely, relative motion.

If all you are talking about is how to determine your state of motion wrt a star reference, that's trivial.

Besides, I'm only using radar because my long range subspace sensors are down for maintenance.

21. Let me pose a little train gedankin here. Let there be train rails around the
Earth along the equator. Let there be an observer standing beside the tracks at a station with an infrared remote control, one coded to turn on
and off two atomic clocks with the same code. One clock is beside this observer at the station and the other is on the train. The train approaches
this observer at a steady speed of 1000 miles per hour, he flicks his remote and starts both clocks. The train encircles the Earth at this steady
speed and approaches the observer again. Another flick of the remote and
both clocks stop. According to STR, will the clocks agree, and if not why not? Will it make any difference if the train travels East or West? Remember the Hafele-Keating 'experiment'.

Why can't you answer the question I posed FIRST? This thread is about reciprocity of time dilation. That is what my gedanken addresses. It has
a beginning, an inertial stage assumed to be unaffected by gravity, and
an ending. Your two ships which suddenly pop into existence in the middle of nowhere moving APART have no way to compare clocks, even if they had them in addition to 'radar'. You are ASSUMING there should be time
dilation because each believes he is at absolute rest and 'the other guy'
is the one moving. I believe your ships are shaped like pink polka-dot

22. Originally Posted by 2inquisitive
STR's method of always assuming
the observer is in the inertial 'rest' frame with non-moving coordinates
leads to substantial errors in reality.
You seem to have a misunderstanding of how special relativity works, 2inq.
Special relativity is about how coordinates transform between non-accelerating reference frames... it is often convenient to speak of the rest frame of an observer, but that certainly not "always assuming the observer is in the inertial 'rest' frame."

I think that the concept you are building of how the universe works is actually closer to Special Relativity than you think, for instance:

The ICRF I spoke of? It is a Global inertial frame, but it is NOT a 'rest frame'. The origin of its coordinate points can be considered stationary, or relatively moving wrt a distant object, whichever one chooses.
That's completely in accord with SR.

To state the Milky Way and many other galaxies in the local group are converging on a point near the Virgo cluster, the ICRF (coordinates points originating at the barycenter of the solar system) is moving toward that point, it is not at rest. If you only want to calculate the Earth's rotation (23 hrs 56 min. Sidereal time), it is unnecessary to consider the solar system's velocity through the Milky Way, or the Milky Way's speed toward the Virgo Cluster as that will have no effect on the rate of rotation. Neither will it have an effect on calculating the velocity of a train relative to the surface of the Earth, but you CAN calculate the rotational velocity of any point on Earth's surface if the need arises.
As is this.

Let me pose a little train gedankin here. Let there be train rails around the Earth along the equator. Let there be an observer standing beside the tracks at a station with an infrared remote control, one coded to turn on and off two atomic clocks with the same code. One clock is beside this observer at the station and the other is on the train. The train approaches this observer at a steady speed of 1000 miles per hour, he flicks his remote and starts both clocks. The train encircles the Earth at this steady speed and approaches the observer again. Another flick of the remote and both clocks stop.

According to STR, will the clocks agree, and if not why not?
According to SR, I think they will agree to within the accuracy of the measuring equipment.
However, if the train were faster, the Earth larger, or the equipment more accurate, then SR says they will not.
Why? Because the two clocks have worldlines of different lengths.

Will it make any difference if the train travels East or West?
Yes. The rotation of the Earth counts.

23. by Pete:

"Yes. The rotation of the Earth counts."
===============================================

In which frame of reference, Pete? The trains or the stations?

Why would they travel different worldlines? In minkowski space, world
lines are straight. The train sees the station circle around to meet it. The
station sees the train circle around to meet it. Symmetry. The orbit of the
Earth around the Sun has no effect on these two frames of reference,
each frame assumes itself at rest with the other in relative motion.
Coordinates are attached only to the train in one frame and the station
in the other. Again, the motions are symmetric in each frame, according
to STR.

24. In your example, there is no symmetry, as it is merely an Earthbound version of the twin journey (or paradox).
Look, from a purely kinematic point of view, provided the distance travelled and the proper time elapsed are the same, all trajectories that bring you back to your starting point are equivalent.
Right. So choose the simple out-and-back case and draw the worldline. A dog-leg, yes?
Now, in general, say that, if A is in uniform motion in B's frame, then if there is a coordinate transformation that will bring A to rest in it's own frame, A may consider itself to be at rest.

For the dog-leg worldline, no such transformation is possible, hence both A and B agree that whoever was doing the out-and-back journey was the one moving. In your example, both train and station agree that the train was moving.

25. 2inquisitive

When the train moves in 1000 mph, though its velocity is constant now, it
has to accelerate to attain the speed. The frame of train has 2 perpendicular forces acting on it - one is due to gravity and another one is due to acceleration. A free falling particle in the train does not fall straight down on the floor of the train. rather it would take a path of free falling depending on the acceleration. But the observer A in train would always observe/caluculate that a free falling particle falls perpendicular to the floor of the earth in earth's frame . It is not difficult to observe that the relative movement of the earth and the train has no effect on the particle that falls in earth's frame.

During accelerating phase :

1. in A's frame (train) the path of a particle (p1), that is free falling, is against the direction of 'g' and 'a' combination; not perpendicular to the floor of the train.

2. A observes/calulcates that a free falling particle's (say p2) path in earth's frame is only against g, perpendicular to the floor of the earth. A
concludes that :

(i) the relative movement (whether when it was zero or when it is non-zero) has no effect on the particle's (p2) path in earth's frame;

(ii) but it is in his frame that is changing.

An observer 'B' on the earth would confirm A's observation/calculation with respect to both the free falling partilces p1 and p2.

It is clear for both A and B, which frame departs from the world line (changing proper time) due to the relative movement.

The question is :

Why should A apply reciprocity of time as if the relative velocity is 1000mph from the start?

The proper applicability, rather than the validity, of both equivalence principle and reciprocity of SRT under specific conditions, result in calulating correct time on both A & Bs clocks.

Let me pose a little train gedankin here. Let there be train rails around the
Earth along the equator. Let there be an observer standing beside the tracks at a station with an infrared remote control, one coded to turn on
and off two atomic clocks with the same code. One clock is beside this observer at the station and the other is on the train. The train approaches
this observer at a steady speed of 1000 miles per hour, he flicks his remote and starts both clocks. The train encircles the Earth at this steady
speed and approaches the observer again. Another flick of the remote and
both clocks stop. According to STR, will the clocks agree, and if not why not? Will it make any difference if the train travels East or West? Remember the Hafele-Keating 'experiment'.
Now to your question, when the relative velocity is constant at 1000mph. I am rushing off now. Let me discuss a little later, why the failure of simultaneity (when one observer is supposed to start both clocks) makes both A & B's observation about other's clock is valid when they have a relative velocity at 1000mph constant.

26. Originally Posted by everneo

When the train moves in 1000 mph, though its velocity is constant now, it
has to accelerate to attain the speed. The frame of train has 2 perpendicular forces acting on it - one is due to gravity and another one is due to acceleration.
But it's perfectly legitimate to ignore the acceleration phase. If you prefer, let the train make two circumnavigations, and start the clock on it's second go around, assuming that by this stage it has constant velocity.
A free falling particle in the train does not fall straight down on the floor of the train. rather it would take a path of free falling depending on the acceleration. But the observer A in train would always observe/caluculate that a free falling particle falls perpendicular to the floor of the earth in earth's frame .
How could he do that? He is in the train. What he sees is not a vertical drop, as you said. Why should he assume that for somebody not on the train (which is more-or-less what you said) is different from what he sees? You are assuming the conclusion you are trying to show!
Moreover, accelerating or not, the train that is, the observer on the station does not see the particle fall vertically.
During accelerating phase :

1. in A's frame (train) the path of a particle (p1), that is free falling, is against the direction of 'g' and 'a' combination; not perpendicular to the floor of the train.

2. A observes/calulcates that a free falling particle's (say p2) path in earth's frame is only against g, perpendicular to the floor of the earth. A
concludes that :
No. A assumes that, because he knows about relativity. That's not allowed!

27. 2inquisitive :

OK i am back to your experiment.

When the train observer A and the earth observer B has a constant relative velocity 1000mph they have different world lines (proper time) caused during the acceleration phase to attain 1000mph relative velocity.

You said that the earth observer flicks his remote control & both clocks would be started simultaneously. There would be a delay 'dt' in starting the farther clock. But the delay 'dt' would not be same for both observers who has different proper times. This breaking of simultaneity is a direct result of their different proper times. As for as their propertimes are not similar each observer would find his calculation on other's time duration is valid.

When we talk about failure of simultaneity, i remember a discussion at sciforums, about 2 events of duration 'dt' happening in frame A and there is an information flow between them during 'dt' and are simultaneous for an observer in frame A. But few posters funnily asserted that the events would not be simultaneous for an observer in frame B that has a relative velocity v with frame A, completely ignoring failure of causality in that case. But in your gendaken experiment triggering of 2 events happening in 2 different frames with relative velocity 1000mph is clearly a candidate for breakdown of simultaneity.

28. Ha! Am I talking to myself here? Not the first time.

29. Originally Posted by Guitarist
Originally Posted by everneo

When the train moves in 1000 mph, though its velocity is constant now, it
has to accelerate to attain the speed. The frame of train has 2 perpendicular forces acting on it - one is due to gravity and another one is due to acceleration.
But it's perfectly legitimate to ignore the acceleration phase. If you prefer, let the train make two circumnavigations, and start the clock on it's second go around, assuming that by this stage it has constant velocity.
That does not erase the fact that both had same world lines once but one of them deviated due to the acceleration during relative motion and the other one has no change due to the acceleration during relative motion.

Originally Posted by Gutarist
Originally Posted by everneo
A free falling particle in the train does not fall straight down on the floor of the train. rather it would take a path of free falling depending on the acceleration. But the observer A in train would always observe/caluculate that a free falling particle falls perpendicular to the floor of the earth in earth's frame .
How could he do that? He is in the train. What he sees is not a vertical drop, as you said. Why should he assume that for somebody not on the train (which is more-or-less what you said) is different from what he sees? You are assuming the conclusion you are trying to show!
Moreover, accelerating or not, the train that is, the observer on the station does not see the particle fall vertically.
They don't just see. They calculate the path of the particle freefalling in station observer's frame to be perpendicular to the floor of earth (ie) the shortest path from dropping point to landing point. not so for the path of a freefalling particle inside the train.

Originally Posted by Gutarist
Originally Posted by everneo
During accelerating phase :

1. in A's frame (train) the path of a particle (p1), that is free falling, is against the direction of 'g' and 'a' combination; not perpendicular to the floor of the train.

2. A observes/calulcates that a free falling particle's (say p2) path in earth's frame is only against g, perpendicular to the floor of the earth. A
concludes that :
No. A assumes that, because he knows about relativity. That's not allowed!
No assumptions. Its just calculation of distance from the dropping point to landing point. The calculated path incidently happens to be a straight line perpendicular to the floor of the earth; not so inside the train. For both observers A & B.

30. Originally Posted by Guitarist
Originally Posted by everneo
That does not erase the fact that both had same world lines once but one of them deviated due to the acceleration during relative motion and the other one has no change due to the acceleration during relative motion.
Sorry. I can make no sense of this
I didn't expect you to make any.

Originally Posted by Guitarist
Originally Posted by everneo
They don't just see. They calculate the path of the particle freefalling in station observer's frame to be perpendicular to the floor of earth (ie) the shortest path from dropping point to landing point. not so for the path of a freefalling particle inside the train.
This is where you are muddled. I already expained, in a post above, why an observer making any journey whatever that brings him back to his starting point does not have the privilige of considering himself at rest. So you are reaching for the correct conclusion, but in the wrong way.

In your model, the observer on the train is accelerating, right? So, by your example you rightly say he can see that. Good. But how on earth does the observer on the train know what the observer on the station may or may not see. As I said before, unless the guy on the train knows about relativity, how can he make the calculation you suggest.

Read my earlier post (Mon 2.45pm). It's easier like that, I promise.
The question is : Whether the train moves at 1000mph with respect to station OR the track slides under the wheels, of a train that is at 'rest', in the opposite direction at 1000mph due to earth's rotation, no matter, are not the movements symmetrical & the effects are indistinguishable? if not in what way?

In my answer, I am not assumming anything to arrive at the same. The accelerating phase of the relative motion is important, no matter if you don't know who is hoping the world lines and affected by the relative motion, theres always a simple test of freefalling body to tell the tale.

You need to try hard to make sense out of this post.

31. everneo, I did not state the two clocks started simultanously. I said the
station observer clicked the IR remote starting both clocks. This same
observer clicks the remote at the end of the trip stopping both clocks.
It makes no difference if one clock starts and stops before the other, we
are measuring total accumilated time recorded by the two clocks. By
assuming an acceleration phase, you are effectively stating one clock
is already beating slower than the other due to acceleration, your different
worldlines. So, we can always go back to an acceleration phase to determine which clock is beating slower than the other in Special Theory?
There goes the whole concept of simultaneity between inertial frames.
Assume I stated my gedanken in 1905, before General Relativity was
formulated. You do see where I am going with this? Also, remember all
the STR gedankens of trains on Earth and similiar thought exercises to
illustrate relativity of simultaneity and the symmetry of time dilation
(reciprocity). I let the example come to a measurable conclusion is all.

And thanks for your participation also, Guitarist. I am not ignoring your posts, Its just that you haven't posted anything that I really disagree with.

32. Originally Posted by 2inquisitive
In minkowski space, worldlines are straight.
Not so. According to SR, a worldine is the 4D path of an object - which is not straight for accelerating objects.

The train sees the station circle around to meet it. The
station sees the train circle around to meet it. Symmetry.
The situation is most certainly not symmetrical. The rotation of the Earth is real, and (according to SR) has real effects in all frames.

If you think that relativity says otherwise, I suggest you are harbouring a misunderstanding of the theory.

The orbit of the Earth around the Sun has no effect on these two frames of reference,
I suspect it does, although I'm not sure. I can say that that is certainly a different situation, since the Earth is in freefall around the Sun, while neither the train nor the station are in freefall around the Earth.

each frame assumes itself at rest with the other in relative motion.
An (apparently common) misconcedtion. Frames assume nothing. In SR, a frame is just a coordinate system that may be in motion.

33. Nick:

Boloney. yes the earth is moving through space around the sun. But the motion of the train with respect to the earth is unrelated to it.
Are you saying the train doesn't move around the sun?

Only the train is moving relative to the embamkment. The embankment is not moving through space relative to the train.
Prove it.

Take the example of a ship that takes off from mars and accelerates toward the earth. You cannot say that the earth deviates from its orbit to get closer to the ship.
Right, because it doesn't deviate from its orbit. Instead, from the point of view of the ship, the sun and the Earth and all the other planets ALL move so that the Earth gets closer to the ship. The Earth still stays in orbit around the sun, though.

Only the ship is moving through space relative to the earth
and not the other way around.
Why not the other way round?

All those motions through space are absolute!
Which point in the universe is absolutely at rest, then, according to you?

34. Originally Posted by James R
Nick:

Boloney. yes the earth is moving through space around the sun. But the motion of the train with respect to the earth is unrelated to it.
Are you saying the train doesn't move around the sun?

Only the train is moving relative to the embamkment. The embankment is not moving through space relative to the train.
> Prove it.

OK only the train accelerated through space(experienced weight)

And only the train sees the stations/embankments
clock blueshifted.

Take the example of a ship that takes off from mars and accelerates toward the earth. You cannot say that the earth deviates from its orbit to get closer to the ship.
> Right, because it doesn't deviate from its orbit. Instead, from the point of view of the ship, the sun and the Earth and all the other planets ALL move so that the Earth gets closer to the ship. The Earth still stays in orbit around the sun, though.

Boloney. the earth does not deviate from its orbit to
get closer to the ship only the ships movement through
space gets the two any closer. You can look at
the larger picture and you still have absolute
motion through space.

Only the ship is moving through space relative to the earth
and not the other way around.
>Why not the other way round?

Because only one accelerated(exeperienced weight)

All those motions through space are absolute!
Which point in the universe is absolutely at rest, then, according to you?

35. It bears repeating that there is a union of SR and GR.
Yo cannot really devide them.
Relatives in SR are only changed by accelerations(GR)

36. Nick:

OK only the train accelerated through space(experienced weight)
That only shows that the train's motion was not inertial, whereas the station's motion was. It doesn't establish which one is at rest and which one isn't.

And only the train sees the stations/embankments clock blueshifted.
And the station sees the train's light blueshifted. So what?

Boloney. the earth does not deviate from its orbit to get closer to the ship only the ships movement through space gets the two any closer.
We agree that the earth doesn't deviate from its orbit.

But does Mohammed come to the mountain, or does the mountain come to Mohammed? There's no way to tell.

You can look at the larger picture and you still have absolute motion through space.
I notice you ignored my previous question. If you have absolute motion, it must be absolute with respect to something which is absolutely at rest. So, I'll ask again:

Which point in the universe is absolutely at rest, according to you?

It bears repeating that there is a union of SR and GR. You cannot really devide them.
Yes. SR is a subset of GR.

Relatives in SR are only changed by accelerations(GR)
I have no idea what you mean by that.

37. Originally Posted by Pete
Originally Posted by 2inquisitive
In minkowski space, worldlines are straight.
Not so. According to SR, a worldine is the 4D path of an object - which is not straight for accelerating objects.

The train sees the station circle around to meet it. The
station sees the train circle around to meet it. Symmetry.
The situation is most certainly not symmetrical. The rotation of the Earth is real, and (according to SR) has real effects in all frames.

If you think that relativity says otherwise, I suggest you are harbouring a misunderstanding of the theory.

The orbit of the Earth around the Sun has no effect on these two frames of reference,
I suspect it does, although I'm not sure. I can say that that is certainly a different situation, since the Earth is in freefall around the Sun, while neither the train nor the station are in freefall around the Earth.

each frame assumes itself at rest with the other in relative motion.
An (apparently common) misconcedtion. Frames assume nothing. In SR, a frame is just a coordinate system that may be in motion.
So Pete, you are saying one can have curved worldlines in Minkowski space due to accelerating objects, accelerating in its own INERTIAL frame?
There are only two (2) frames of reference in my gedanken. (1)The frame
of reference of the train, which does NOT accelerate during the gedanken.
(2) The frame of reference of the station/observer which does not accelerate during the gedanken. It was stipulated that we ignore gravitational acceleration as is commonly done in STR gedankens.

You state the rotation of the Earth has 'real' effects in both these frames.
Prove it. Prove the Earth rotates in either of these frames, using STR
inertial frames. Or, are you saying STR inertial frames are not applicable
on the surface of the Earth? I agree, if that is what you mean.

You keep bring GR into the example. Invoking the Earth in freefall around
the Sun in a simple STR gedanken? What is being challenged is Special Theory's statement that clocks beat relatively slower in all inertial frames of reference in which the observer is not at rest.

Uh, yes, a frame in STR is just a coordinate system in which an inertial frame may be in motion, ALWAYS the OTHER frame, never the rest frame
from which calculations are performed.

I will have to compliment you, Pete. I didn't know you could dance so well!

38. 2inquisitive:

There's no problem with having curved worldlines in Minkowski space. Objects can still accelerate when viewed in inertial frames.

Your lounge room is approximately an inertial frame (ignoring the Earth's rotation etc.) If you throw a ball in your lounge room, it follows a curved path through spacetime, as viewed from your inertial reference frame.

You state the rotation of the Earth has 'real' effects in both these frames. Prove it. Prove the Earth rotates in either of these frames, using STR inertial frames. Or, are you saying STR inertial frames are not applicable on the surface of the Earth? I agree, if that is what you mean.
You can set up an inertial frame anywhere you like.

What is being challenged is Special Theory's statement that clocks beat relatively slower in all inertial frames of reference in which the observer is not at rest.
More accurately, a clock ticks slower when viewed from any inertial reference frame in which the clock is moving.

Do you have any evidence that this is NOT true?

39. by James R:

"There's no problem with having curved worldlines in Minkowski space. Objects can still accelerate when viewed in inertial frames.

Your lounge room is approximately an inertial frame (ignoring the Earth's rotation etc.) If you throw a ball in your lounge room, it follows a curved path through spacetime, as viewed from your inertial reference frame."
===============================================

me:
Of course you can 'view' a non-inertial frame from your inertial frame.
Come now, James.
------------------------------------------------------------------------------------

by James R:

"You can set up an inertial frame anywhere you like."
==============================================

me:
That is why I just love Global inertial frames, such as the ICRF, don't you James?

40. Originally Posted by 2inquisitive
So Pete, you are saying one can have curved worldlines in Minkowski space due to accelerating objects, accelerating in its own INERTIAL frame?
Where did you pick up the idea that all worldlines are straight?
What do you mean by "its own inertial frame"? If an object is accelerating, its rest frame is not inertial.
If an object is accelerating, its worldline is curved in any non-accelerating frame.

There are only two (2) frames of reference in my gedanken. (1)The frame of reference of the train, which does NOT accelerate during the gedanken.
Sure it does! It follows a circular path, right? To do so in SR, it must accelerate.

(2) The frame of reference of the station/observer which does not accelerate during the gedanken.
Once again - the station follows part of a circular path as the Earth turns.
That means acceleration.

It was stipulated that we ignore gravitational acceleration as is commonly done in STR gedankens.
Such stipulation is meaningless on this scale - it only makes sense on a scale that allows you to pretend the Earth's surface is flat.
On the whole-Earth scale, SR must treat acceleration due to gravity in the same way as acceleration due to any other force.

Or, are you saying STR inertial frames are not applicable on the surface of the Earth? I agree, if that is what you mean.
That's good!

You keep bring GR into the example. Invoking the Earth in freefall around the Sun in a simple STR gedanken?
You introduced Earth orbiting the Sun, not me!

41. Forgive my boldness, 2inquisitive, but perhaps if you grabbed a physics text and worked through a few examples of SRT in practice you might gaina better grasp of the theory.

MacM could use the same advice.

Note that being able to apply a theory to discover its conclusions does not imply that one must necessarily agrees with it.

42. Pete:

Sure it does! It follows a circular path, right? To do so in SR, it must accelerate.
Are elipses accelerating frames also? Where do we find an STR inertial frame in our solar system? Do we pretend they exist?

Pete: You introduced Earth orbiting the Sun, not me!
Actually James R introduced the Earth orbiting the Sun on the first page in response to Nick's post. I spoke of the Earth orbiting the Sun in reference
to a Global inertial frame. The Earth orbiting the Sun was not a part of my
gedanken, only the train circling the Earth. I did, however, make reference to East or West travel of the train, so Earth rotation is to be
considered. The question was, how do you determine the Earth is rotating
from either the train's frame of reference or the station's frame of reference? I am speaking of STR inertial rest frames, in which the observer 'sees' the rest of the universe moving relative to this observer.
Remember, the observers in each of these frames assume they are at rest and the rest of the universe is moving through their stationary coordinates. How does either observer determine STR inertial frames are
not applicable from his limited worldview? They cannot see the rotating Earth from a third point of view. Gravity? Of course, but gravity is ignored
all the time in STR gedankens taking place on the surface of the Earth,
from particle accelerator examples to muons entering the Earth's gravitational field. Who determines when acceleration is to be ignored and when it is not? Isn't it just based on an 'assumption' that acceleration,
gravitational or mechanical, can be ignored?

43. Boloney james!

44. Originally Posted by 2inquisitive
Are elipses accelerating frames also?
Obviously?
Where do we find an STR inertial frame in our solar system?
You don't "find" frames, you define them.
You seem to have the impression that a frame must be attached to an object?

The question was, how do you determine the Earth is rotating
from either the train's frame of reference or the station's frame of reference?
An interesting question! You may have me.

Would a very accurate gyroscope do the trick?
At the train station, I *think* that a precise gyroscope appropriately suspended would turn over once each day.

I am speaking of STR inertial rest frames, in which the observer 'sees' the rest of the universe moving relative to this observer.
Frames do not need observers attached to them... the use of observers is an explanation tool, not part of the theory.

Remember, the observers in each of these frames assume they are at rest and the rest of the universe is moving through their stationary coordinates.
That is not a requirement of SR, but a tool of explanation. It is useful to imagine what the universe looks like to an observer who is moving relative to you, but thinks they are at rest. This is not to say that all observers [i]must[i] think assume they are at rest - that would be nonsensical.

How does either observer determine STR inertial frames are
not applicable from his limited worldview? They cannot see the rotating Earth from a third point of view. Gravity? Of course, but gravity is ignored
all the time in STR gedankens taking place on the surface of the Earth
Only on a small scale, when you can pretend the Earth's surface is flat.

from particle accelerator examples to muons entering the Earth's gravitational field.
...or when gravity does not significantly affect the motion of the object in question, for the purpose of the gedanken (I suppose that acceleration due to gravity is considered in real life).

Who determines when acceleration is to be ignored and when it is not? Isn't it just based on an 'assumption' that acceleration, gravitational or mechanical, can be ignored?
Deep understanding of a theory is required to know when it can be simplified for explanatory purposes.

I think that's really why these forums aren't a suitable place for place to denounce accepted theory - the understanding of denouncers is usually based on simplified explanations, and the denouncers do not construct deep understanding which allows them to work with assumptions appropriately.

45. Pete:
You don't "find" frames, you define them.
You seem to have the impression that a frame must be attached to an object?
===========================================

me:
OK, how do you define an inertial frame within the solar system? One in
which gravitational has no effect. One in which an object in its inertial rest
frame 'sees' the Earth moving STRAIGHT AWAY from its coordinate points
at constant relative velocity. Now, recall when Special Theory applies to a
problem. It is applicable between TWO inertial frames, not an inertial frame and a non-inertial frame. Is the Earth considered an inertial frame of reference? In the discussion above, the Earth is rightly considered a
NON-INERTIAL frame of reference. Why is it considered an inertial frame
of reference in the Twin Paradox, for example? You have not read my post here if you think I believe a frame must be attached to an object.
What on Earth gave you that idea? I have absolutely no problems knowing
my frames of reference. Do you, Pete? It seems you do. Are you having
problems distinguishing between inertial rest frames, inertial frames, Global inertial frames and non-inertial frames? I do not. Now, when the
station observer sees the train approaching, where are the coordinate points of origin that he uses for each frame of reference to determine the
trains relative velocity wrt himself? This observer is on the equator, does
he choose coordinates at Anchorage for his rest frame? Anchorage is in
his rest frame according to STR.
Pete:
Frames do not need observers attached to them... the use of observers is an explanation tool, not part of the theory.

me:
Pete, Pete, Pete. Why do you make such statements? Is it part of a
recording you have memorized to 'combat challengers to SR'? Read just a
little of my gedanken and try to remember what I wrote. I used ONE observer, TWO clocks, and TWO frames of reference. Why do you think I
presented my gedanken as I did? Do you think it was because I don't know how to present one in a 'proper STR format'? I most certainly could,
but 'validating' STR is not my intent, is it? I constructed my gedanken, on
the spur of the moment, EXACTLY as I wanted to present it. I know the
weaknesses of STR, and at least one of GR. I didn't get any of this from
crank sites, I am my own 'crank', thank you very much!
Pete:
It is useful to imagine what the universe looks like to an observer who is moving relative to you, but thinks they are at rest. This is not to say that all observers [i]must[i] think assume they are at rest - that would be nonsensical. [quote]

me:
I agree that it is nonsensical for an observer to think they are at rest. Now, give an example of an observer moving in his own STR inertial REST
frame. You always leave out 'rest frame' and just say fame. You fail to
specify WHICH observer you are referring to, the one in the rest frame
using the Lorentz transforms, or the one in the 'other' frame which is the
one always moving in Special Theory. I DO NOT get confused about frames.

46. Originally Posted by 2inquisitive
OK, how do you define an inertial frame within the solar system?
There are any number of ways!
One of the simplest would be to choose an object at some particular time, and set that event (the object at that time) as the origin, with the frame having that object's instantaneous velocity. Oh, you'll also need to set the orientation of your axes. For example, I can define a non-accelerating frame as follows:

The origin is me, now.
The x-axis points North at the origin.
The y-axis points East at the origin.
The z-axis points Up at the origin.
The frame has my instantaneous velocity at the origin event.

Naturally, The is not my rest frame, since I am accelerating while the frame isn't. I don't stay at the same spatial coordinates for long.
But it is a close approximation to my rest frame for a time, until my path deviates significantly from a straight line as the Earth spins and orbits.

Originally Posted by 2inquisitive
One in which gravitational has no effect.
Can't be done.

Originally Posted by 2inquisitive
One in which an object in its inertial rest frame 'sees' the Earth moving STRAIGHT AWAY from its coordinate points at constant relative velocity.
That would imply that the Earth is not accelerating... but it is (although it mightn't be significant if you're only considering a short time period).

Originally Posted by 2inquisitive
Now, recall when Special Theory applies to a problem.
You can always apply it, but you might need to use some interesting tricks such as calculus for some purposes.

Also, its application might not always give you results that correspond to reality, depending on how significant a role GR specific affects apply... but we don't need to bring that into the discussion, I think.

Originally Posted by 2inquisitive
It is applicable between TWO inertial frames, not an inertial frame and a non-inertial frame.
Sure, for a beginner.
Firstly, any number of frames can be used.
Secondly, non-inertial frames can be handled in a round-about way... if necessary, you can consider the infinite instantaneously comoving non-accelerating frames (what a mouthful!) that an accelerating object occupies, and get results in SR. It's not necessarily easy (I'm not up to it myself unless there's an easy simplification), but it can certainly be done.

Originally Posted by 2inquisitive
Is the Earth considered an inertial frame of reference?
In general it can not, but like I said before, it can be if for limited situation if you set up the conditions carefully. I think a reasonably deep knowledge of the theory is required to be sure you're keeping a reasonable approximation to reality.

Originally Posted by 2inquisitive
In the discussion above, the Earth is rightly considered a NON-INERTIAL frame of reference. Why is it considered an inertial frame of reference in the Twin Paradox, for example?
Because it's a simplified explanatory story. Such details are ignored to keep the story simple, and because the Earth's acceleration doesn't significantly affect the outcome. The Earth is only mentioned in the twin paradox to make it an interesting story. The story would be less interesting if it began with "The twins are somewhere in our Solar System, and aren't accelerating...", even though it would have the same result.

Now, when the station observer sees the train approaching, where are the coordinate points of origin that he uses for each frame of reference to determine the trains relative velocity wrt himself?
That's not making much sense.
Are you asking how an observer on the train station could measure the train's velocity?
It's your story... you should provide the details, yes?
Would you like some help?
Perhaps the observer could record the times at which the train passed some markers?

This observer is on the equator, does he choose coordinates at Anchorage for his rest frame? Anchorage is in his rest frame according to STR.
Anchorage (in Alaska?) is not in the same frame. It's motion is different.

I agree that it is nonsensical for an observer to think they are at rest.
Don't put words in my mouth.
I said that would be nonsensical to say that an observer must assume they are at rest.
I do not think it would be nonsensical for an observer to assume they are at rest. We do it all the time, no? When you're moving your fingers to the keys, do you assume yourself at rest, or do you consider The Earth's motion when deterining how to move your fingers?

Now, give an example of an observer moving in his own STR inertial REST frame.
It can't be done, of course.
But naturally, if an observer is accelerating, their rest frame is also accelerating.

47. For example, I can define a non-accelerating frame as follows:

The origin is me, now.
The x-axis points North at the origin.
The y-axis points East at the origin.
The z-axis points Up at the origin.
The frame has my instantaneous velocity at the origin event.

Naturally, The is not my rest frame, since I am accelerating while the frame isn't. I don't stay at the same spatial coordinates for long.
But it is a close approximation to my rest frame for a time, until my path deviates significantly from a straight line as the Earth spins and orbits.

2inquisitive wrote:
One in which gravitational has no effect.

Can't be done.
You defined an inertial frame, correctly. It is also a global inertial frame.
Now, where is your origin? You state that you do not stay at the spatial
coordinates of the origin, so you need to define those coordinates. In the
ICRF, for instance, the origin is the barycenter of the solar system. You
can also use the center of the Sun if you like, as long as you have a defined origin. In STR, the origin of the inertial frame can be at rest as
you described, or it can be moving through spacetime unaffected by gravity. Note I said THE ORIGIN unaffected by gravity. You say it can't be
done? Back to the Twin Paradox. Where is the origin of the stay-at-home
twin? Does this twin not rotate with the Earth or move with the Earth's
orbit around the SUN? You do see what I am getting at, don't you? How do
you define the orgin of the stay-at-home twin's REST frame? As I have
indicated many times, it is STR's REST FRAME that I find nonsensical.
Your example of me sitting at my computer is a perfect example. True,
I am not moving in my 'rest frame', but are the coordinates attached TO
ME in this frame moving when I 'see' my twin moving through space one
lightyear away? Do my coordinates trace a spiral trajectory around the SUN?

Quote:
Now, when the station observer sees the train approaching, where are the coordinate points of origin that he uses for each frame of reference to determine the trains relative velocity wrt himself?

That's not making much sense.
Are you asking how an observer on the train station could measure the train's velocity?
It's your story... you should provide the details, yes?
Would you like some help?
Perhaps the observer could record the times at which the train passed some markers?

Quote:
This observer is on the equator, does he choose coordinates at Anchorage for his rest frame? Anchorage is in his rest frame according to STR.

Anchorage (in Alaska?) is not in the same frame. It's motion is different.
The station observer is not moving in his STR rest frame. Anchorage AK is
not moving in the station observer's rest frame, according to Special Theory. Both locations are stationary in the same rest frame. The motions
are different for each only if you specify coordinate origin at a location other than the face of the Earth, a global inertial frame for instance. STR
places the origin of the station observer at his location in his rest frame
and the train will consider itself at rest and the station approaching it, also
the coordinates points fixed on the train. For time dilation and relativity of
simultaneity to work, it MUST be done this way. The coordinates MUST always be attached to the observer in a Special Theory REST frame, and
they MUST be stationary for each observer in his rest frame.

Also Pete, you seem to interchange acceleration and inertial motion. Do
you realize this? They are not the same.

48. Intelligent response there, Nick. Very impressive.

49. Your the one packing boloney here james.

There are only relatives when there is motion through
space. And there must be acceleration for that to happen.
Accelerations are what make the relatives in the special
theory.

How do you like that?

50. Originally Posted by 2inquisitive
You defined an inertial frame, correctly. It is also a global inertial frame.
My understanding of "global inertial frame" is a frame that is anchored with respect to the distribution of matter in the Universe. Is that what you mean by the term? The ICRF, for instance, is defined by assigning coordinates to a number of radio sources (according to my scramble for info on Google ).
The frame I defined isn't anchored in such a way. It is defined by a single event, a set of axes, and a velocity.
Perhaps what I mean by "non-accelerating frame" is the same as what you mean by "global inertial frame"?

Also Pete, you seem to interchange acceleration and inertial motion.
Example? I thought I'd kept the two distinctly separate, avoiding discussion of inertial motion altogether.
In an SR discussion, I think it's best to keep strictly to the concepts of accelerating and non-accelerating, because "inertial motion" has GR connotations.

The way I understand it is that the rest frame of something in inertial motion could be either accelerating or not accelerating. In SR, accelerating frames are treated differently to non-accelerating frames (Read this), so saying that a frame is inertial doesn't tell us how to treat it is SR.

Now, where is your origin? You state that you do not stay at the spatial coordinates of the origin, so you need to define those coordinates.
The path of the spatial origin follows unambiguosly from the definition given.
The coordinate system is four-dimensional, therefore the origin is not a point in space but a single event. That event is well defined.
The axes of the coordinate system are well-defined.
The velocity of the coordinate system is well defined.
This is sufficient to identify any point in the coordinate system, is it not?

Note I said THE ORIGIN unaffected by gravity. You say it can't be
done?
Don't be ridiculous. Why would I say such a thing?

Did you not understand bmy explanation of why attaching the stay-at-home twin to Earth is a contrived piece of story-telling that doesn't make significant difference to the outcome?
Imagine a third person (triplets!!) who also began and finished at the same point as the other twins, but had constant velocity in between. Do you think that the difference in proper time between the Earth twin and the constant velocity twin would be significant?

Your example of me sitting at my computer is a perfect example. True, I am not moving in my 'rest frame', but are the coordinates attached TO ME in this frame moving when I 'see' my twin moving through space one lightyear away? Do my coordinates trace a spiral trajectory around the SUN?
In your rest frame (which is accelerating), your coordinates are constant (this is the definition of a rest frame).
In any non-accelerating frame, your coordinates trace a spiral around the Sun.
It's not that difficult a concept, is it?

The station observer is not moving in his STR rest frame.
What exactly do you mean by "STR rest frame" as opposed to just "rest frame"?
Of course the station observer's location in their rest frame is constant - that's what rest frame means.
But it is important to note that this is an accelerating frame - which requires special treatment in SR.

Anchorage AK is not moving in the station observer's rest frame
In the observer's rotating rest frame, Anchorage's coordinates are constant. I don't think that's specifically "according to SR", I think it's by definition. Whether you consider "constant coordinates" as "not moving" is moot, I think, although the most common interpretation is that the two terms might as well be the same thing.
I'd prefer to avoid rotating frames - I don't know much about them, but I think that they again require special treatment in SR, and that you have to consider fictitious forces (eg coriolis and centrifugal).

The motions are different for each only if you specify coordinate origin at a location other than the face of the Earth, a global inertial frame for instance.
The motions are different as soon as you specify any non-rotating reference frame - for instance the non-rotating rest frame of the station (in which the station keeps the same coordinates, but turns around once per day), or any "non-accelerating frame".
I'm really beginning to suspect that what I mean by "non-accelerating frame" is the same as what you mean by "global inertial frame"...

The coordinates MUST always be attached to the observer in a Special Theory REST frame, and they MUST be stationary for each observer in his rest frame.
Again, what is a "Special Theory rest frame"?
I think you're confusing how rest frames and non-accelerating frames are treated in SR.
They are not treated the same way.
Perhaps you have drawn misleading conclusions from basic introductory examples of SR which deal only with non-accelerating rest frames?

51. My understanding of "global inertial frame" is a frame that is anchored with respect to the distribution of matter in the Universe. Is that what you mean by the term? The ICRF, for instance, is defined by assigning coordinates to a number of radio sources (according to my scramble for info on Google ).
The frame I defined isn't anchored in such a way. It is defined by a single event, a set of axes, and a velocity.
Whew, I'll try to make this post as brief as I can. OK, a global inertial frame and the ICRF. To begin with, do you understand what the barycenter of the solar system is? As I mentioned in a previous post, it CAN simply be assumed to be the center of the Sun. Unless you need a
high precision definition. You see, the Sun is not stationary within the solar system. It 'wobbles' due mostly to Jupiter's gravitational tug. The
barycenter of the solar system is a specific point in this wobble corresponding to Epoch J2000, a date in the year 2000. The barycenter is
a specific origin for the coordinates of the ICRF (and the International
Celestial Reference SYSTEM), the axis from which the coordinates extend.
The ICRF is a 'almost' absolute reference frame from which all motion, velocities and vectors of objects in the solar system or the universe at large can be ascertained, relative to this coordinate point (the barycenter).

In an SR discussion, I think it's best to keep strictly to the concepts of accelerating and non-accelerating, because "inertial motion" has GR connotations.

The way I understand it is that the rest frame of something in inertial motion could be either accelerating or not accelerating. In SR, accelerating frames are treated differently to non-accelerating frames (Read this), so saying that a frame is inertial doesn't tell us how to treat it is SR.
No, inertial motion is the bread and butter of STR (this means non-accelerating frames). A rest frame has the axis of the coordinates usually
attached to the observer, an 'observer's rest frame'. Everything else that is in motion, is in motion relative to the 'rest' coordinates of this observer.
This observer always considers himself at rest and all motion, inertial or non-inertial, is relative to his rest position.

The path of the spatial origin follows unambiguosly from the definition given.
The coordinate system is four-dimensional, therefore the origin is not a point in space but a single event. That event is well defined.
The axes of the coordinate system are well-defined.
The velocity of the coordinate system is well defined.
This is sufficient to identify any point in the coordinate system, is it not?
You have a funny way of describing frames. Events don't normally define frames, frames are used to define the spatial coordinates and time of an
event, which can be located at any position within the frame. Yes, the spatial origin of a frame IS a point in space, moving or stationary, whichever you choose. The x, y, and z spatial coordinates define the specfic location and the time component is absolutely necessary to define movement of this point.

Don't be ridiculous. Why would I say such a thing?
Maybe you misunderstood what I meant when I said frames in inertial motion followed straight worldlines. The ORIGIN of the frame, the frame
itself, must follow straight worldlines to be truely inertial IN STR. You can
'view' non-inertial (curved worldlines) frames from this frame, but you are viewing
a different frame of reference from your own frame.

In your rest frame (which is accelerating), your coordinates are constant (this is the definition of a rest frame).
In any non-accelerating frame, your coordinates trace a spiral around the Sun.
It's not that difficult a concept, is it?
You reworded what I said to make it seem more confusing to others. I would say as seen FROM a non-accelerating (inertial) frame, the twins
frame, my coordinates trace a spiral orbit around the Sun. Now, from
my 'rest' frame, what happens when I am on the opposite side of the Earth relative to this twin due to Earth's rotation?

What exactly do you mean by "STR rest frame" as opposed to just "rest frame"?
Of course the station observer's location in their rest frame is constant - that's what rest frame means.
But it is important to note that this is an accelerating frame - which requires special treatment in SR.
Yes, STR states the rest frame coordinates are FIXED to the station observer. The station observer assumes he is stationary and everything
in motion is relative to his stationary position. His frame can only be determined to be accelerating from the view of a DIFFERENT frame, one
not located on the surface of the Earth. From the frame of reference of the train, the station observer's motion is inertial, non-accelerating. He cannot 'see' around the Earth, the motion can only be seen as the two
frames approach each other, no apparent curvature is seen.

I'm really beginning to suspect that what I mean by "non-accelerating frame" is the same as what you mean by "global inertial frame"...
Pete, a 'non-accelerating frame' is an inertial frame. A Global inertial frame
is just a special type of inertial (non-accelerating) frame.

52. 2inq:

The ICRF is a 'almost' absolute reference frame from which all motion, velocities and vectors of objects in the solar system or the universe at large can be ascertained, relative to this coordinate point (the barycenter).
So what? What has this or any of the preceeding ramblings got to do with A measuring B's relative velocity and vice versa? Why is this so complicated?

53. So what? What has this or any of the preceeding ramblings got to do with A measuring B's relative velocity and vice versa? Why is this so complicated?
Complicated?? It is childishly simple, superluminal, too simplified to be of
any real use. Two spaceships are moving relative to each other somewhere in
the solar system, but they don't know where they are, which direction they are moving, or which one may be moving faster than the other. Duh!
Tell me the information you can get about Voyager 1 and Voyager 2 by
measuring their relative velocity wrt each other. You get Jack Shit that is
of any value. By using the solar system version of the ICRF, you get their
locations, their direction of movement, their true velocities within the solar
system and predictions of where they will be in x number of months, or where they were ten years ago. You can't even get an accurate distance
measurement to a spaceship leaving Earth by using 'rest frames' of STR.
The Earth observer will rotate to the opposite side of the Earth in 12 hours
and occupy a new position in orbit. The spaceship does not travel in straight lines from Earth, it travels an elipse. None of this presents a problem for the ICRF, but try to use STR rest frames.

54. Is that what this thread is about? Locating yourself in space wrt the ICRF? How boring. I thought it was about reciprocity effects. If so, the only thing that matters is what one observer claims about the other, i.e. A vs B. Duh!

The key postulates are:

1) Speed of light is measured by all inertial observers to be c.

and

2) Physics is the same for all inertial observers. (there are no privileged frames)

Place yourself in one frame and what do you observe about the other?

If A and B have relative velocity of .5c, then from A's frame B is moving and appears dilated, and from B's frame A is moving and appears dilated. That's about as complicated as it gets. Why does this disturb you (or anyone)? What exactly is the problem?

Every experiment supports the postulates of SRT. The fact that muons actually collide with each other in experiments, over distances that they could not if mutual dilation did not occurr, is proof of mutual dilation.

"Reciprocity" as some here have presented it, is a phantom. It doesen't exist.

55. With the ICRF, one can determine which observer is moving, or which is
moving faster. Clock dilations come from moving through a field, such as
the Higgs field, not from the 'I see your clock ticking slow' reciprocity.
GPS and all empirical evidence supports this conclusion.

56. .......and in any case, what do you people all mean by "reciprocity"? To me, 1/x is the reciprocal of x. Or, if you are taller that me, then I am shorter than you, is also reciprocal. Areyou useing the word in a more restricted sense?

57. Wallaby's avatar seems to gesture reciporcity...

58. Nick sez:

In the twin experiment only
one twin sees the other's clock blueshifted.

What does the blueshifted twin see?

After all why should there be if only one
clock actually goes slower?

Simple, you are viewing one other clock relative to your own. Your clock will appear to be ticking normally, so it stands to reason that the one other clock you're viewing is ticking slower.

59. Guitarist,

"Reciprocity" is an imagined idea, by some from sciforums.

Imagine two objects A and B, with relative velocity. According to SRT, since there are no privileged frames and the speed of light is measured by all inertial observers to be constant (c), A must observe clocks on B to be dilated, while B must measure clocks on A to be dilated (A or B can be considered to be rest frames. Simple, right?). This is a simple observation of mutual dilation.

Some claim, erroneously, that this implies that both clocks simultaneously "physically" read less than each other - a completely rediculous statement and is used as "proof" that SRT is wrong. This is labeled "reciprocity". Proponents of this view do not understand what SRT is saying, namely that from their own rest frame, all other moving frames will appear dilated. Only upon matching frames will there be any measured net dilation (twin "paradox") due to the asymmetrical non-inertial phase of one of the observers.

60. Originally Posted by 2inquisitive
With the ICRF, one can determine which observer is moving, or which is
moving faster. Clock dilations come from moving through a field, such as
the Higgs field, not from the 'I see your clock ticking slow' reciprocity.
GPS and all empirical evidence supports this conclusion.
Which is moving wrt the ICRF only. From the cabin of your moving spaceship, the ICRF is moving. Get a GPS design group to show that SRT is completely wrong. Submit a paper to Phys Letters.

Other empirical evidence such as what? We agreed long ago did we not 2inq, that based upon my research no experiment has ever been done of the "I see your clock dilated while you see mine dilated" variety? (Ahh my sciforums archives... lost...LOST! ). The only evidence I see is muon scattering, and that supports mutual dilation.

61. Originally Posted by superluminal
Guitarist,

"Reciprocity" is an imagined idea, by some from sciforums.

Imagine two objects A and B, with relative velocity. According to SRT, since there are no privileged frames and the speed of light is measured by all inertial observers to be constant (c), A must observe clocks on B to be dilated, while B must measure clocks on A to be dilated (A or B can be considered to be rest frames. Simple, right?). This is a simple observation of mutual dilation.
Well OK. You'd better believe I understand both the special and general theories pretty well.
I geuss my question was a bit of a spoiler. Mutual time dilation is a necessary consequence of the Lorentz transform, but I don't really understand what others mean, in this context, by reciprocity.

Some claim, erroneously, that this implies that both clocks simultaneously "physically" read less than each other - a completely rediculous statement and is used as "proof" that SRT is wrong. This is labeled "reciprocity".
I am aware of this sad fact! I have argued this point on several forums, to no effect.
Ho um. I knew I should have stuck to by original principle not to debate relativity.

62. Guitarist:

Ho um. I knew I should have stuck to by original principle not to debate relativity.
A wise choice. One I am trying to follow also.

63. OK, I'm happy to use the term "inertial frame" instead of "non-accelerating frame" in this discussion, as long as you don't try to pull a fast one later and say that an object free-falling near a large mass has an inertial rest frame.

I'm not sure what you mean by "global inertial frame".
Can you describe for me an inertial frame which is not a global inertial frame?

Do you have a handy reference where I can read about the ICRF?
Is the ICRF special compared to other global inertial frames?
Is the ICRF special compared to other inertial frames?

Originally Posted by 2inquisitive
OK, how do you define an inertial frame within the solar system? One in which gravitational has no effect.
Originally Posted by Pete
Can't be done
Originally Posted by 2inquisitive
In STR, the origin of the inertial frame can be at rest as you described, or it can be moving through spacetime unaffected by gravity.Note I said THE ORIGIN unaffected by gravity. You say it can't be done?
Originally Posted by Pete
Don't be ridiculous. Why would I say such a thing?
Originally Posted by 2inquisitive
Maybe you misunderstood what I meant when I said frames in inertial motion followed straight worldlines. The ORIGIN of the frame, the frame itself, must follow straight worldlines to be truely inertial IN STR. You can 'view' non-inertial (curved worldlines) frames from this frame, but you are viewing a different frame of reference from your own frame.
Stop. Go back.
Your challenge was to define an inertial frame in which gravity has no effect. Naturally, that can't be done - gravity does affect objects. This effect happens in all inertial frames.
Perhaps you meant to ask me to define an inertial frame on which gravity has no effect?
That's an entirely different question. Of course gravity has no effect on the coordinates of inertial frames (at least not in SR).
I agree with the concept you are expressing. The worldine defined by (0,0,0,t) is straight in inertial frames, and unaffected by gravity.

You reworded what I said to make it seem more confusing to others.
What you said almost made sense, but with ambiguity and confused terminology.
What I said was precise and unambiguous.
If you say they mean the same thing, then it seems I was successful in extracting your meaning, and that we agree on the concept. This is a good thing!
I would say as seen FROM a non-accelerating (inertial) frame, the twins frame, my coordinates trace a spiral orbit around the Sun.
"As seen from" relies on an observer's sight, which is limiting and ambiguous. It's much more precise to simply say what happens in a frame, rather than what is seen by an observer at rest in that frame (although the observer can be useful as an explanation tool for non-scientific types).
Now, from my 'rest' frame, what happens when I am on the opposite side of the Earth relative to this twin due to Earth's rotation?
Your motion due to Earth's rotation will affect your proper time during the travelling twin's trip... but by so little (in the usual formulation of the gedanken) that it is generally ignored.

Yes, STR states the rest frame coordinates are FIXED to the station observer.
That's just the definition of a rest frame - it's not specific to STR.

The station observer assumes he is stationary and everything in motion is relative to his stationary position.
That's allowed, but not mandatory.
Your idea that "...This observer always considers himself at rest and all motion, inertial or non-inertial, is relative to his rest position." is a very limiting point of view... luckily it is not required by SR.

In the station observer's rest frame, the station observer is stationary (duh!)... but that does not mean that "the station observer assumes he is stationary". The station observer isn't required to consider his rest frame as the one true frame, is he? He is free to consider his movement in the ICRF, for example.

From the frame of reference of the train, the station observer's motion is inertial, non-accelerating. He cannot 'see' around the Earth, the motion can only be seen as the two frames approach each other, no apparent curvature is seen.
This is confusing.
Yes, the station has constant motion in the station's rotating frame. But, the station's rotating frame is not an inertial frame.
Therefore, I don't think it makes sense to say that the train's motion is inertial. It would certainly be incorrect to apply SR as if it is.
Are you saying that the station's rest frame is inertial? (if so, I disagree)
Are you saying that the train's rest frame is inertial? (if so, I disagree)
Are you saying that SR dictates that the station's rest frame is inertial? (if so, I disagree)
Are you saying that SR dictates that the train's rest frame is inertial? (if so, I disagree)

Here are simple questions, with equally simple answers:
1) Is the station's path actually curved?
2) Is the station's rest frame inertial?
1) Is the train's path actually curved?
2) Is the train's rest frame inertial?

I think we agree that the answers are yes, no, yes, no...
So really... where's the problem?

64. Originally Posted by superluminal
Folks,

Judging from this guys attitude:

Boloney. yes the earth is moving through space around
the sun. But the motion of the train with respect to the earth
is unrelated to it. Onlyn the train is moving relative to the
embamkment. The embankment is not moving through
space relative to the train. And the station does not
move through space to get closer to the train.

That is the simple point.
He's not interested in learning anything. He just wants it his way or the highway. If that's not so, and he really thinks the way he's presented himself, then I don't have the energy to spend on the MONTHS of rehab it's going to take to straighten him out (can you say geist, MacM...). Good luck.
Actually SL, it is YOU guys that can use some straightening out. None of you have satisfactorily responded to the issues but only make fiat statements about what is but without any actual physical support for your arguement.

You are given clear examples of failures of your view but continue to go on to other threads completely ignoring the fact that you have not rebutted the facts provided.

You acuse us of being intrangent but we are open to change if you simply justify your claims. You have failed to do so.

Or did I miss your post showing reciprocity has been observed or recorded?

BTW: Just what is the time dilation experienced between clocks A and B when they share a relative velocity of 0.866c?

65. MacM,

I've lost interest in arguing relativity. You are correct, as you already know, that no experiments with timing devices have been done to verify mutual dilation. I don't say "reciprocity" since I think that you believe that is something different from mutual dilation and which I think dosen't exist as a part of SR.

I believe we are in a definitional phase locked loop, never to escape.

The only thing I can point to are muon collisions that could not take place were it not for mutual dilation as predicted by SR.

I'm focusing on simpler physics and religious nuts at the moment.

66. Originally Posted by superluminal
MacM,

Thanks.

I've lost interest in arguing relativity. You are correct, as you already know, that no experiments with timing devices have been done to verify mutual dilation. I don't say "reciprocity" since I think that you believe that is something different from mutual dilation and which I think dosen't exist as a part of SR.

I believe we are in a definitional phase locked loop, never to escape.

The only thing I can point to are muon collisions that could not take place were it not for mutual dilation as predicted by SR.
A couple of mis-statements on your part here.

"Mutual Dilation" is a fact and is documented. Two co-moving objects will under go mutual dilation and show no systemic change between them and is only detectable by a third party as well as in my ACB scenario where each has equal acceleration and duration but in opposite directions relative to their common point of rest.

While they will have a "Mutual Dilation" relative to the rest clock, they do not have systemic dilation predicted by Special Relativity due to their relative motion.

"Reciprocity" is the recipocal affect on each clock. That is A running slower than B at the same time that B run slower than A. This is not my idea it is spelled out many places describing Special Relativity and has been argued from the point of view by memebers here in that you cannot sense your own motion therefore you can claim you are at rest and hence the other must be dilated.

That however, is nothing more than words proclaiming something which has never been observed or recorded.

I'm focusing on simpler physics and religious nuts at the moment.
If this is an admission of failure to support the SR view I accept your resignation, if not surrender, but I see you continuing to make the same sort of claims and statements in other threads. I suggest if you are unable to support your claims you should stop making them.

67. MacM,

By my estimation, your misunderstanding is profound. You do not realize that in different frames only, do clocks appear dilated wrt each other. And each viewpoint is valid only within the rest fram under consideration. This is all there is and is called mutually observed dilation. The clocks in your thought experiments that calim to show this imaginary "reciprocity" are not in the same spacetime frames.

I've said this before but I'll say it again. Your confusion is on a par with someone claiming that while I see you smaller at a distance and you see me smaller, then optics somehow claims that we are BOTH simultaneously smaller than each other. That there is a size "reciprocity" claim. Clearly absurd, but the only difference is that your confusion involves a more complex phenomenon involving time.

Finally, I find your final statement:

If this is an admission of failure to support the SR view I accept your resignation, if not surrender, but I see you continuing to make the same sort of claims and statements in other threads. I suggest if you are unable to support your claims you should stop making them.
to be arrogant, ironic, comical, and insulting all at the same time. You are asking me to support something which you made up. It's your delusion. You support it. And I will make whatever statements of observed FACT that I wish. It is you who should stop polluting other threads with near religious fervor.

68. SuperLub: Will you never learn? This guy is deaf, profoundly so, give it up and maybe he'll go away.

69. Guitarist,

We have a history. There is much we agree on and much we don't. However I will not debate relativity in any way with anyone, as I've said. Mac just got back from vacataion and isn't aware of my new found interest in squashing radical christians.

70. Originally Posted by superluminal
Guitarist,

We have a history. There is much we agree on and much we don't.
You and I? I don't think so. Maybe you and MacM?
However I will not debate relativity in any way with anyone, as I've said. Mac just got back from vacataion and isn't aware of my new found interest in squashing radical christians.
Is that where he's coming from? Well, well, no wonder. (I confess to not reading his posts)

71. Guitarist,

Of course I mean myself and MacM.

And you misunderstand. MacM is definitely not a christian. He just has umm... interesting ideas regarding SRT.

72. Originally Posted by superluminal
MacM,

By my estimation, your misunderstanding is profound. You do not realize that in different frames only, do clocks appear dilated wrt each other. And each viewpoint is valid only within the rest fram under consideration. This is all there is and is called mutually observed dilation. The clocks in your thought experiments that calim to show this imaginary "reciprocity" are not in the same spacetime frames.

I've said this before but I'll say it again. Your confusion is on a par with someone claiming that while I see you smaller at a distance and you see me smaller, then optics somehow claims that we are BOTH simultaneously smaller than each other. That there is a size "reciprocity" claim. Clearly absurd, but the only difference is that your confusion involves a more complex phenomenon involving time.
Sorry SL but your recent effort to equate "Mutual Dilation" with "Reciprocity" is simply false or deliberately deceptive.

I frankly have no mis-conceptions regarding frames of referance regarding reciprocity.

You have never been able to understand somethings are indeed absolute. For example the time period of test is concurrent, hence simultaneous. That is universally absolute.

Your example above is childish in that you are equating perception
with accumulated time by clocks. I have never rejected reciprocity
of perception.

I'll return with a referance regarding reciprocity simply to insure
others know what the correct definition is.

Originally Posted by SL
Finally, I find your final statement:

If this is an admission of failure to support the SR view I accept your resignation, if not surrender, but I see you continuing to make the same sort of claims and statements in other threads. I suggest if you are unable to support your claims you should stop making them.
to be arrogant, ironic, comical, and insulting all at the same time. You are asking me to support something which you made up. It's your delusion. You support it. And I will make whatever statements of observed FACT that I wish. It is you who should stop polluting other threads with near religious fervor.
Now, now, just because you lost the claim that you could find
data and prove reciprocity don't get touchy.

As can be seen in the following "my" version of reciprocity is the
correct version. Your assumption that it is implied by "Mutual
Dilation" is whoafully incorrect.

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

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

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

You and Guitarist would both do well to read Muller below, and learn somethings before expressing your false condensending statements regarding my views and the rightousnous of SRT. It is false gentlemen get over it.

http://itis.volta.alessandria.it/epi...6/ep6-mull.htm

73. Mac,

As a courtesy, I'll make one more post. I'm not debating relativity in any form with anyone for the forseeable future. Thanks for your input and good luck with your theories.

SL

74. Originally Posted by superluminal
Mac,

As a courtesy, I'll make one more post. I'm not debating relativity in any form with anyone for the forseeable future. Thanks for your input and good luck with your theories.

SL
Fair enough. However, if I see you post your views regarding relativity I will indeed rightfully challenge you to support your statements.

75. 2inquisitive,