# SR Simultaneous Lines Drawn in the Sand

by geistkiesel
Tags: drawn, lines, sand, simultaneous
P: 565
 Quote by Doc Al Not sure what you are measuring with these photo-sensitive strips. quote geistkiesel: "Were the photons emitted simultaneously in the stationary frame also emitted simultaneously in the moving frame?" No.
In the first post of this thread the moving observer at M' was at M the midpoint of sources of photons in the stationary frame when the photons were emitted simultaneously. These photons were instantaneously detected in the moving frame as they were emitted in the stationary frame. The moving frame detected the simultaeous emission of the photons in the moving frame.

This is an experimental observation.

And you say no they were not emmitted in the moving frame simultaneously.
P: 565
 Quote by jdavel Pergatory, Doc Al is right. If two lights flash simultaneously (in my frame) and the distance from me to each one is the same at the time of the flashes, then light from the two flashes reaches me at the same time. That's what it means for light speed to be a constant with respect to all observers. Your bullet analogy lets you down because the bullets are traveling at constant speed with respect to the shooters, but if you are moving wrt the shooters, the bullets are moving at different speeds wrt you. If you want to get to the point where constant light speed and all its consequences seem more intuitive, stop thinking about bullets!
In the first post of this thread the moving observer at M' was at M the midpoint of sources of photons in the stationary frame when the photons were emitted simultaneously. These photons were instantaneously detected in the moving frame as they were emitted in the stationary frame. The moving frame detected the simultaeous emission of the photons in the moving frame.

What are you talking about " ...seeming more intuitve . . ?.Aren't observations intuitive enough for you?
 P: 220 why must you use a moving frame and a stationary frame? i think that's what is throwing me off do one experiment where he's stationary and THEN do the exact same thing when it's moving combining the two creates unnecessary confusion :P 1) A -> ________________M________________ <- B 1) A ____ ->____________M____________<- ____ B 1) A __________ ->______M______<- __________ B 1) A _________________ xMx _________________ B 2) A -> ________________M________________ <- B 2) A ____ ->______________M__________<- ____ B 2) A __________ ->__________M__<- __________ B 2) A ________________ ->______Mx ___________ B 2) A ______________________ ->__Mx _________ B 2) A ____________________________xMx _______ B so i'm still not seeing the contradiction. everyone AGREES that the photons don't hit him at the same time in the moving frame. How hard would it be to do the calculations in reverse for the moving frame setup and acquire that the beams WERE emitted simultaneously BECAUSE of the frame shift, extrapolate it using M's velocity towards B.
P: 565
 Quote by ram2048 why must you use a moving frame and a stationary frame? i think that's what is throwing me off do one experiment where he's stationary and THEN do the exact same thing when it's moving combining the two creates unnecessary confusion :P 1) A -> ________________M________________ <- B 1) A ____ ->____________M____________<- ____ B 1) A __________ ->______M______<- __________ B 1) A _________________ xMx _________________ B 2) A -> ________________M________________ <- B 2) A ____ ->______________M__________<- ____ B 2) A __________ ->__________M__<- __________ B 2) A ________________ ->______Mx ___________ B 2) A ______________________ ->__Mx _________ B 2) A ____________________________xMx _______ B so i'm still not seeing the contradiction. everyone AGREES that the photons don't hit him at the same time in the moving frame. How hard would it be to do the calculations in reverse for the moving frame setup and acquire that the beams WERE emitted simultaneously BECAUSE of the frame shift, extrapolate it using M's velocity towards B.
Why do we need two frames?
Because SR theory says that events that are simultaneous in the stationary frame are not simultaneous in the moving frame. We are talking about the same physical event. We must do the experiment with two frames, one stationary and one moving to test the theory. Hence we have the photo-sensitive strips to measuee the emission of the photons.
Here is the contradiciton that everyone is having such a difficult time with.

[b]"Were the photons that were emitted simultaneously in the stationary frame also emitted simultaneously in the moving frame?"[/b ]

There was the record of the phosensitive strips attached to the moving frame that were exposed just when the photons were emitted in the stationary frame. These photo-sensitve strips were within a photon wave length of the emitted photons at A and B in the stationary frame when they wee exposed.

SR theory says, the photons were not emitted simultaneously in the moving frame. SR Theory gets to work backwards in time and redo the physical events that occured there.
Emeritus
PF Gold
P: 16,101
 why must you use a moving frame and a stationary frame?
Because we're disagreeing about what SR says when we analyze the exact same events from different frames.

Specifically, Geistkiesel is asserting that both of these diagrams are representing the exact same sequence of events:

A        M        B
A\       M       /B
A \      M      / B
A  \    M      /  B
A   \   M     /   B
A    \  M    /    B
A     \M    /     B
A      M   /      B
A      M  /       B
A     M  /        B
A     M /         B
A     M/          B

A       M       B
A\      M      /B
A \     M     / B
A \    M    /   B
A  \   M   /    B
A   \  M  /     B
A   \ M /       B
A    \M/        B
We have two relatively stationary light sources (A and B), and an observer who starts in the middle and moves towards A.

The first diagram depicts how things look in the rest frame of the lights, if the lights are activated simultaneously.

The second diagram depicts how things look in the rest frame of the observer, if the lights are activated simultaneously.

However, there is a very important difference between the two diagrams; in the first diagram the photons do not meet M at the same event, however in the second diagram the photons do meet M at the same event.

The conclusion is that these diagrams cannot possibly represent the same events. Among the possible assumptions we can abandon, abanding that of absolute simultaneity is by far the most reasonable; the emission of photons is simply simultaneous in one frame but not the other.
Mentor
P: 40,905
 Quote by geistkiesel Sure, but also as to the moving observers their clocks are t' = 0. The two '0' are the same.
You cannot arbitrarily set all clocks in O' to read t'=0. Doing so requires assuming that simultaneity is independent of the reference frames. Since that's what we're trying to discover, we can't just assume it.
 No stipulation. I already stipulated that a moving observer using SR theory will conclude the photons were not emitted from A and B simultaneously in the moving frame. This is my stipulation. Can you agree to this?
Absolutely not! I don't want anyone making assumptions or stipulations about simultaneity. The entire point of Einstein's simple argument is to deduce the nature of simultaneity, not make assumptions about it.
 I didn't stipulate to Einstein's postulate regarding the speed of light. I stipulated that SR theory would predct the photons were not emitted at A and B in the movinng frame. Do you have a problem with this? I am not going to debate the truth or falsity of the 'speed of light' postulate. If you say that the SOL postulate is fundamental to the SR derivation of simultaneity, so be it.
Once again, the point of Einstein's argument is to deduce the relativity of simultaneity, not assume it. The invariant speed of light is fundamental to any gedanken experiment concerning light. Without that, there is nothing to discuss.
 The difference goes like this: simultaneity(SR) is placed in an enclosed logical box that cannot be entered and the contents modified, by cleverness, wit, dishonesty or mistake, or stipulation.
Don't be cute. Re-read my post and tell me exactly where you think Einstein's argument fails. If you can't accept the starting point--the invariant speed of light--then there is no point in continuing.
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P: 40,905
 Quote by geistkiesel Doc Al is ambiguous. he is constantly observed to holding little factual tidbits so he can confuse the issue and distrct the flow of the thread. He isn't being honsest is what I am saying.
Please tell me exactly where I am being ambiguous. Refer to my post #2 in this thread. And dishonest? Come now, geistkiesel, have you run out of intellectual ammunition this early in the game?
 He really is saying that an observer at M in the stationary frame will see the photons arrive at M simultaneously.
Anyone curious as to what I actually said, can read my own words in post #2.
 I agree with your second paragraph. But some using SR theory calculate the photons that arrived at M simultaneously were NOT emitted simultaneously in the moving frame. In fact, before my exile, Doc Al and I discussed this issue in another thread.
We have "discussed" this many times. I am giving geistkiesel a golden opportunity to clearly and unambiguously point out the flaws in Einstein's argument. Is he up to the challenge?
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P: 40,905
 Quote by geistkiesel Doc Al is throwing useless bull **** around to distract. Read the first post in this thread.
Re-read my response in post #2.
 As the moving frame passes the stationary frame when M' in the moving frame was at M in the stationary frame, the photons were emitted in the stationary frame simultaneously,
Right!
 and the photons were detected at this very instant simultaneously in the moving frame.
Now what possibly can you mean by this garbled statement? Are you talking about photons being detected by O'? Or O' deducing that they were emitted simultaneously? Speak clearly and stop wasting people's time.
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P: 40,905
 Quote by geistkiesel Read the first post in this thread. As the moving frame passes the stationary frame when M' in the moving frame was at M in the stationary frame, the photons were emitted in the stationary frame simultaneously, and the photons were detected at this very instant simultaneously in the moving frame. Do you understand?
I defy anyone to understand your point. See my last post. Talk sense, man!
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P: 40,905
 Quote by geistkiesel In the first post of this thread the moving observer at M' was at M the midpoint of sources of photons when the photons were emitted simultaneously. These photons were instantaneously detected in the moving frame as the were emitted in the stationary frame. The moving frame detected the simultaeous emission of the photons in the moving frame.
Assuming observers in the moving frame were posted at the right positions, then they WILL detect the photon emissions. But what makes you think that they will detect them SIMULTANEOUSLY? Since that is the point we are arguing, please give us your argument. (Note how Einstein's simple argument does not involve multiple moving observers. Why not deal with that argument directly?)
 Using the detected arrival times of the photons in the moving frame, SR theory calculates that the photons were not emitted simultaneouslly in the moving frame.
We all agree that the moving observer detects the photons as arriving at different times. Using that fact, plus simple assumptions of the invariance of light speed, Einstein deduces that the moving observer must conclude that the photons were emitted at different times. Every observation made in the moving frame--including the direct observation of the photon emissions by the moving observers--must agree with this conclusion!
 THE PHOTONS WERE DETECTED SIMULTANEOUSLY IN THE MOVING FRAME AT THE INSTANT THE PHOTONS WERE EMITTED IN THE STATIONARY FRAME.
Again, you merely ***ume, where Einstein argues.
 All you theorists can argue all you want about SR theory, speed of light, Einstein, laws of physics, constancy of the speed of light foreever. The fact of the observation the photons were emitted simultaneously in the moving frame remains invariant under any theoretical perturbation.
I truly believe that you believe this. But you are still wrong. Rather than add questionable assumptions to Einstein's gedanken experiment, please deal directly with Einstein's simple argument.
 Your problem is one of embarrassment when you ponder: "How could I ever have accepted special relativity in the first place?" Like I said, it is your problem, you solve it.
Geistkeisel, I am making a special effort in this thread to be nice. Why don't you do the same?
P: 565
 Quote by Doc Al I defy anyone to understand your point. See my last post. Talk sense, man!
The instant photons were simultaneously emitted from A and B in the stationary frame the photo-sensitve strips in the moving frame were exposed (|||) at both ends of the moving frame, at locations equally spaced from M'. This is the point, the only point. For your convenience we give another picture.

|||----M'----||| -->moving frame-->
-A-----M-----B-| XX stationary frame XX

This is the picture the instant photons were emitted from A and B in the stationary frame.

Said another way, the instant the photo-sensitive strips were exposed in the moving frame by photons emitted in the stationary frame..

Is this enough "sense talk, man"?

I title this: A Simultaneous Line in the Sand for Doc Al.

If you were from Texas, or had spent any time in Texas, maybe, just maybe you would be able to understand. And this even though it is common knowledge that Texans have half their brains tied behind their back, leaving one loose piece of gray matter to rattle around inside their skull cavities.

You defied anyone to understand the point. OK, someone from Texas, splain it to Doc Al.
P: 565
 Quote by Doc Al Again, you merely ***ume, where Einstein argues. I truly believe that you believe this. But you are still wrong. Rather than add questionable assumptions to Einstein's gedanken experiment, please deal directly with Einstein's simple argument. Geistkeisel, I am making a special effort in this thread to be nice. Why don't you do the same?
You don't know how to be nice. There were no added assumptions that corupted Einstein's gedunken. You just haven't realized that you've lost this game.

As from me to you, this is as nice as it gets.
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P: 22,008
 Quote by geistkiesel it is also useful if the thiought proes the theory wrong.
If the thought process of the theory is wrong, then it can easily be shown to be wrong through experimentation. You you can't prove that a theory is wrong if you don't address what the theory says. You are stating (assuming, as Doc says) the theory is wrong and building a thought experiment around how you think the universe should work, then offering it up as a proof that the theory is wrong. Sorry, science doesn't work that way.

Depending on the theory you apply to the thought experiment, the outcome is different. Which is right and which is wrong? Well, that's a question answered by experimentation.

What's funny about this is you think you're making an argument against Relativity, but what you are actually doing is demonstrating you don't even understand the scientific method, much less Relativity. The other guys here aren't so much defending Relativity as trying to explain to you what it says.
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P: 40,905
 Quote by geistkiesel The instant photons were simultaneously emitted from A and B in the stationary frame the photo-sensitve strips in the moving frame were exposed (|||) at both ends of the moving frame, at locations equally spaced from M'. This is the point, the only point. For your convenience we give another picture.
Can observers in the moving frame detect the emission of the photons? Yes.
Are the marks on the photo-sensitive strips (caused by the photon emissions) in the moving frame equally spaced from the point M' (which passed M at the exact moment that the clock at M read t=0): YES!
Do the moving observers detect the photon emissions as happening simultaneously: NO!

By building incorrect assumptions into your "thought" experiment, you have left the realm of real physics. (As we know it today.)

Note that Einstein makes no such assumptions--and is able to simply deduce the relativity of simultaneity. Why not address Einstein's actual argument?
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P: 40,905
 Quote by geistkiesel There were no added assumptions that corupted Einstein's gedunken. You just haven't realized that you've lost this game.
You ***umed that:

(1) The marks on the photo-sensitive strips (caused by the photon emissions) in the moving frame are equally spaced from the point M' (which passed M at the exact moment that the clock at M read t=0): True!
(2) That the moving observers detect the photon emissions as happening simultaneously: Not true!

As long as you insist on adding these assumptions, there is no point in continuing the discussion.

However, if you would like to discuss Einstein's actual argument--which you refer to constantly but obviously fail to grasp--have at it. If you truly understand Einstein's point, this should be no problem--since he makes fewer assumptions than you do.
P: 175
 Quote by geistkiesel The instant photons were simultaneously emitted from A and B in the stationary frame the photo-sensitve strips in the moving frame were exposed (|||) at both ends of the moving frame, at locations equally spaced from M'. This is the point, the only point. For your convenience we give another picture. |||----M'----||| -->moving frame--> -A-----M-----B-| XX stationary frame XX This is the picture the instant photons were emitted from A and B in the stationary frame. Said another way, the instant the photo-sensitive strips were exposed in the moving frame by photons emitted in the stationary frame..
But how did you determine the distance between the photosensitive strips? If you made it the same length as A->B whilst in the moving frame then you have a problem because in the stationary frame this distance will be observed to be shorter than A->B due to Lorentz contraction. Thus in the stationary frame it is impossible for them to fall over A and B at the same time.

Ok, so you determined the length when the moving frame was actually stationary. But this doesn't help you either because when they start moving the moving observer will observe the distance between A and B to contract. Hence, again the strips cannot both be over the lights at the same instant in this frame.

The only way out of this mess is to accept the loss of simultaneity. This is why I suggested looking up the 'pole vaulter paradox' earlier because it points this out quite beautifully.

Matt
 P: 220 makes no sense for SR to resolve that the photons were NOT emitted simultaneously. it's a "Given" part of the experiment that they WERE emitted simultaneously as outlined in Einstein's original set up there's a billion ways we can PROVE that they were emitted simultaneously hooking them up to synchronized clocks, photosensitive strips, whatever. that's not part of the argument, though. It's not even a possibility. i think you SR supporters are somehow taking what einstein said the wrong way.
P: 202
[QUOTE=ram2048]makes no sense for SR to resolve that the photons were NOT emitted simultaneously.

it's a "Given" part of the experiment that they WERE emitted simultaneously as outlined in Einstein's original set up

 Quote by ram2048 it's a "Given" part of the experiment that they WERE emitted simultaneously as outlined in Einstein's original set up
No it's not given or automatically assumed. It is deduced, because the stationary midpoint observer received the lights at the same time. The midpoint observer just happens to receive the lights at the same time, that's the setup. Only because of this you can deduce that they were emitted simultaneously *in the stationary frame*, you can' assume anything else. You can't analyse this like you have a bird's eye view and like you can see everything at the same time. But if you want a graphical view according to SR, check this link: