# Basic Special Relativity Question

Discussion in 'Physics & Math' started by Fednis48, Apr 22, 2013.

1. ### TachBannedBanned

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Good, we're done.
If you didn't understand by now that the bit with the so-called "bending" is not happening , that it is an artifact of a non-measurable set of time stamps, you never will.

3. ### PeteIt's not rocket surgeryRegistered Senior Member

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Still can't figure out how to measure times in $S''$?
Well, keep working on it.

5. ### TachBannedBanned

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Yes, you should keep working on it, Pete. Since you never ran an experiment, you will never figure it out. The times that you want, $t^"_k=-\frac{kV\gamma'}{c^2}$ are as measurable as the amount of RoS, so you will never manage to find a way of doing the measurements. In fact, the timpoints $t^"_k$ , are the RoS values for each point on the rod, so you are guaranteed to never be able to measure them.

7. ### PeteIt's not rocket surgeryRegistered Senior Member

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Seriously? I don't know what you're thinking. Are you saying the relativity of simultaneity is not real?

You seem to think that $S'$ is priveleged in some way; that times in $S'$ are somehow more real than times in $S''$. What do you think clocks at rest in $S''$ measure? Do you think that the $S''$ observer should not use $S''$ clocks?

You've been making less and less sense as the thread progressed, taking less and less tenable positions as you abandoned your previous arguments... but now you've gone right off the edge.

8. ### TachBannedBanned

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Not the timestamps $t^"_k$. Because, if that is what you think, you are in line for the Nobel Prize, you devised a system for measuring RoS. To date, there is no such experiment . So, the only thing between you and the Nobel Prize is working out the "details" of the experimental setup. Which you have been unable to.

Not at all, what gives you this bright idea. I ma simply trying to get through your skull that you have been trying to measure RoS. Try working out the details of the experimental setup, there is a Nobel Prize awaiting you.

9. ### PeteIt's not rocket surgeryRegistered Senior Member

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Of course they do.
$S''$ clocks measure $t''$.
What else would they measure?

Working out the details is the easy part. Implementing it in practice is the problem.

First, we need a long relativistic train, or at least clocks of some kind some distance apart, moving at the same relativistic speed relative to the lab, and synchronized in their rest frame.

Or are you saying that relativity of simultaneity is not measurable in principle?

10. ### OnlyMeValued Senior Member

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I agree that in most cases parallelism would be relative. I am still having difficulty with the basic postulate of equality.., if a=b and b=c, then a=c. The rod and floor are parallel in their common frame and the floor and the platform are parallel... So the rod and the platform should be parallel. They just would not always be measured to be parallel from all frames. The fact that measurements from different frames do not agree cannot change the physical relationship. I always thought that was what the transforms were ment to do, recover the conditions or measurements of the proper frame.., or project how the physical relationship in the proper frame would "appear" or be measured from another frame.

Yes I have been following the other thread off and on. I think it is a far simpler situation with one relativistic velocity. It would have been easier yet had the diagonals not been ridged rods, but just the diagonal line between the corners. Since length contraction is only in the direction of motion the greater the velocity the less length contraction to the rod (end to end) and yet the distance from corner to corner decreases rapidly. That said and setting aside the ridged rod, the point you were trying to make remains clear and accurate for the major case of possible configurations.

The minor case where the rod is parallel to either the top/bottom or sides would be an exception, they would remain parallel.

Part of the issue with the box is that the deformation of the box seems to occur at a different rate than any corresponding length contraction of the ridged rod. But that is a minor detail to your purpose and would be eliminated by just comparring the diagonal line between the corners, which would not be subject to any independent length contraction.

11. ### PeteIt's not rocket surgeryRegistered Senior Member

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No, the rod and floor don't have a common frame.
In the rod's rest frame, the floor is moving toward the rod.
In the floor's rest frame, the rod is moving toward the floor.

When they are parallel and at rest in the same reference frame, then they are parallel in all reference frames.

12. ### OnlyMeValued Senior Member

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Two observers separated by some distance during a thunder storm. Each with synchronized clocks. They don't even have to be ideally synchronized for this, government work standard is close enough. They each record when they see a flash of lightning and how llong between the flash and the clap of thunder that follows. When the compare their measurements they find that they disagree on the time of both when and how long between.

Seems doable to me!

13. ### PeteIt's not rocket surgeryRegistered Senior Member

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That's not relative simultaneity.

14. ### OnlyMeValued Senior Member

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I should not have said common frame, (lucky you caught it instead of Tach). But really the issue remains the same when you look at it from either the rod's frame or the train's frame. In both of those frames the rod and the floor are parallel through out the rods fall to the floor. This is the physical reality of the relationship between the rod and the floor. Measurements made from other frames including the platform's may and in most case will disagree with the measurements made from the rod's and train's frame. That should not be a problem, but it should also not be assumed to represent the physical reality of the relationship between the rod and the floor.

The transforms should be being used to recover measurement as would be made from the proper frame of the event being observed. When they are transformed away from the proper frame of the event, they cannot be thought of as representing the physical relationship of the event or objects being measured.

This would not have been this kind of issue for me even a few years ago. But I have been spending a lot of time trying to unstand induced inertia, and how it can be reconciled with SR and even GR, which makes it more difficult to think these puzzles through entirely within the hypothetical frame work of SR. There seems to always be a touch of "how if fits classically and practically".

15. ### OnlyMeValued Senior Member

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Pete is is not an ideal case as described in Einstein's hypothetical, but it still demonstrates that an event can be observered and measured by two, observers separated by distance or relative velocity, and that even though they report on a single event, their measurement of the order of events, in this case when they saw the flash and heard the thuder will not agree.

16. ### Neddy BateValued Senior Member

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That makes sense in this case, because it is the rod's own reference frame which determines whether one corner of the rod will be dented or not. But your above suggestion makes little sense in other cases, such as the barn/pole paradox. The barn frame finds the pole to be length-contracted, so the pole fits inside the barn. The barn has no need to consider that, in the pole's own frame, it does not fit. Likewise, the pole frame finds the barn doors to close at different times. The pole has no need to consider that, in the barn's own frame, the doors close at the same time. This demonstrates that there are cases where it is perfectly okay for each frame to take their measurements at face value, without need for "recovering measurements" that would be made in other frames.

17. ### TachBannedBanned

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So, do it. A Nobel Prize awaits you. You will be the ONE who figured out how to measure RoS.

Bingo! It took you a looong time to get it.

18. ### PeteIt's not rocket surgeryRegistered Senior Member

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Well, I wasn't expecting that.
Do you think relativity of simultaneity is real, or not real?

19. ### TachBannedBanned

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Of course RoS is real, it is just not measurable through direct experiment. Note the absence of any "RoS test" here?

20. ### PeteIt's not rocket surgeryRegistered Senior Member

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Do you think it is physically meaningful?

21. ### TachBannedBanned

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Where is this going? aren't you supposed to be working on the experimental setup capable of detecting it?
While you are at it, have you lost interest in the proofs that length contraction, contrary to your claims, is physical?
Look, Pete, I proved you wrong, you need to live with this fact.

22. ### PeteIt's not rocket surgeryRegistered Senior Member

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I want to be sure I understand you. Do you think RoS is physically meaningful?

23. ### TachBannedBanned

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Figure a way to measure it and you will find out. The Nobel Prize awaits the one who does the experiment.