# Basic Special Relativity Question

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

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

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How old are you, Tach? Seriously. You are artificially hiding events from the $S''$ observer, and pretending it means something.

True. The Lorentz transforms from $S'$ tell us what the $S''$ observer would directly measure.
They tell us that the $S''$ observer would directly measure this:

Good questions, for which a relativistic theory of elasticity would be needed to thoroughly answer, but Janus's post in the original thread gives big clues.

I think that the Lorentz transforms prove that the rod bends in $S''$.

Because that would be a physical contradiction. Breaking is an absolute physical effect. The rod doesn't break in $S'$, therefore it doesn't break in $S''$.
Prove it.

3. ### TachBannedBanned

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You make the same rookie mistake as Neddy Bate, Lorentz transforms do not provide you with a measuring device. When did you last do a lab experiment?
Besides, you do not have access to the times $t'(k)$, so, once again, how do you measure the times $t"(k)$?

Do you think that you can measure anything off your animations? When did you last run a lab experiment?

Nice evasion, his explanation did not address the issue. Neither does yours.

So, how come there is no "memory" of that "bending". How come that the rod doesn't break, if it "bends" too much? According to your picture "proofs" the angle is proportional with the speeds $u$ and $V$, remember? I worked out the formula for you. The higher the $u$, the higher the bending, so, at some point, if your "bending" is true, the rod should snap.

Last edited: May 7, 2013

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

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You just agreed that the Lorentz transform tells us what $S''$ observer measures.

7. ### TachBannedBanned

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How? The train car is whizzing by.

So, once again, how do you measure the times of impact? Please, stop playing games and try thinking about how you would do this in the lab.

Come on, you aren't listening. How do you measure the times of impact in the lab. The train car is open and is whizzing by at 0.8 c.

You are playing silly games now, how comethere is no "memory" of the "bending"?
If there is a lot of bending, the rod will eventually break, how come there is no breaking?
Stop playing games, Pete.

Nope, Janus didn't answer anything and no, you don't need a relativistic materials theory to answer some basic questions. Stop weaseling and start answering.

Yes, tan is proportional to BOTH $u$ and $V$. at high values, the impact angle becomes quite large, so the rod "bends" more. You never answered the question.

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

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I'm sure you can figure it out. Not that it's relevant, since this is a thought experiment, and we're not going to actually set up a relativistic train.
Good question. I don't know the answer.
I suspect it has something to do with the collision events having spacelike separation, so they don't have time to cause a lasting physical deformation.

Prove it.

To answer those questions, you do.

It is proportional to $u$ and $V\gamma'$

Correct.
Just like at high values, the train's length contracts more.
But the train is never crushed, and the rod never breaks, because both length contraction and the bending of the rod are frame-dependent.
The proper length of the train doesn't change. The proper shape of the rod doesn't change.

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

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Here you go. Same animation as before, with V changed from 0.6c to 0.8c, and a textbox added to show $t''$ at all times, and $k$ for the collision events (marked by red dots):

10. ### TachBannedBanned

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You don't get off the hook that easily, it is very relevant since you are unable to figure out how it can be done. You must have realized by now that it can't be done.

You keep trying to draw a parallel between length contraction and this "rod bending". I told you that length contraction is physical, there is experimental confirmation, the ion beams in particle accelerators are much tighter packed in the frame of the lab than in the proper frame of the ions (because the ions travel at very high speeds). There is a limit of how much the ion beams can be "packed", refuting your naive train example. By contrast, rod "bending" isn't physical, there will never be any experimental confirmation. What cannot be measured, does not exist, your rod "bending" is not physics, it is metaphysics.

11. ### TachBannedBanned

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Very cute. Animations aren't measurements. You never set foot in a lab, let alone performed an experiment.

12. ### UndefinedBannedBanned

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Pete, this is confusing me:
I have read where particle accelerator and particle packs are accelerated frames not inertial SR frames? Also that energy forces are complicated and plasma forces pinch and compress the energy packet as it increases energy intake from electromagnets and currents and all sorts of variables apart from speed? Why does Tach claim in particle accelerators it is interpretation as SR length contraction theory and not just plasma theory in accelerated frames? How true is that interpretation as SR length contraction "proof" claimed by Tach?

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

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It can't be done in practice because we don't have any 0.8c trains. Space gibbons are also in short supply.

But you really can't figure it out in theory? This is basic thought-experiment reference frame stuff.
Let the thin, open-sided train and rod be sliding along a wall of $S''$ clocks, each with their own (x'', y'') coordinates. Whenever a rod or train element passes a clock, the clock sends the event coordinates (t'', x'', y''), (and the k-value of the rod element, if applicable) to the recording computer.

Afterward, the computer displays all the recorded events as an animation, like this:

Depends on what you mean by physical. Length contraction is not what Gron and Johanessen call a 'physical effect'.
Prove it.
You're arguing with the result of the Lorentz transform.

14. ### TachBannedBanned

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You can't do it at 1000km/h. You can't do it even at 100km/h. Because you don't have a clue how to do it, you are trying to BS your way out of this.

How do you get the $t"(k)$ time stamps? You are observing (allegedly) the rod touching like a wet noodle the car floor. Measure the impact times remotely by observing the contact points $x"(k)$.

Where in the article do they claim this? Particle accelerator designers will definitely disagree with such a statement, I really doubt that Gron claimed it.

15. ### UndefinedBannedBanned

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The designers use current switching involving timing using clocking "labels" there too. So if the clock "labels" are real there, they are real for S" in this exercise aren't they? Your "mere labels" claim is one way in one scenario and the opposite way in the other. Make up your mind please.

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

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I just explained how.
The rod and train slide past a wall of $S''$ clocks. The clocks record the event coordinates whenever anything (rod or train) slides past.

Spelled out in [post=3067905]post 689[/post]:
Length contraction depends on the frame of reference, therefore it is not a 'physical effect', in the sense they mean.

And again:
Length is not Lorentz invariant, so length contraction is not a 'physical effect' in the sense they mean.

17. ### TachBannedBanned

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Are you making this stuff up all by yourself? It reads like a comedy script, so do you have a writer or you do it all by yourself?

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

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That's interesting, and I'd like to learn more. Do you have a citation?

19. ### TachBannedBanned

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No you didn't, you have no experimental means to associate an event in the train frame with a time stamp in the lab (platform) frame.

Ok, they are incorrect on this since length contraction is definitely physical in particle accelerators. It is also definitely physical in the magnetic force manifestations.

Here you are reaching, what they tell you that the rod "bending" isn't physical. I fully agree with this:

Try to keep it honest.

20. ### TachBannedBanned

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Yes, I do, I have several references of several different effects, as soon you stop playing silly games, I'll give it to you. It totally contradicts your repeated and erroneous claim that length contraction is not physical.

21. ### UndefinedBannedBanned

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You think the particles in a particle accelerator like LHC accelerate by magic? Electromagnetic energy is pumping strong into plasma state particles. What you expect, no effects from plasma turbulence and self-compressive forces and such? And the "accelerated particle beam" gives a clue about it being an accelerated frame scenario not an SR only scenario. The switching has to be precise so energy is not wasted. That precision is ensured by using clock timing (which you call "mere labels"). You are even more naive than me, that's something!

22. ### UndefinedBannedBanned

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That is playing silly games. You can't see that? Not very self aware are you? Just stump up with your "correct solution" and stop your games.

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

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I don't know what you don't understand about it.

You're using 'physical' in a different way.
They're using 'physical effect' to mean 'frame independent.'
You do agree that length contraction is frame dependent, right?

As do I.
I also fully agree with this:
:bravo:
Seriously, Tach, how old are you?