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ufonaut99

ufonaut99

January 12 2015, 11:18 PM 

Jose : Ufonaut99, we have had this discussion a year or two ago. You didn't retain much from then.
First of all, let's just use unit dimensions. ... Secondly, The pulse must have a duration....

Ohhh, I've retained. I just don't agree with all that any more now than I did then happy.gif

Unit dimensions – OK. Personally, I don’t see how you find nano-seconds easier to deal with than actual seconds (I think it’s easier to see that there’s a difference between 2:59:50 and 2:59:55 than between 2:59:59.99999999 and 2:59:59.999999999, for example). Still, if you want to use lengths and times scaled on nano-seconds, that’s what we’ll run with. You'll have noticed that I gave a "realistic" length platform rather than Light-seconds long one, for example.

Duration, and things like “the actual distance between the Earth and the Sun is continually changing” I still find needlessly pedantic and pointless. Mathematics, by its very nature, is an idealisation of points and lines. Pointing out (repeatedly) the obvious fact that nature does not match this idealisation, not only adds nothing to the discussion - in fact, it detracts from it. Since mathematics is an idealisation, it succinctly captures and exposes the behaviour being studied. Bringing in all the real-life messiness around it does nothing but obscure and distract from that behaviour with irrelevant detail - not to mention increasing the workload of equations, etc.

I’m curious, though – would you make these same complaints about all physics equations (eg, Newton’s), or reserve them only for Relativity?

Ok, onto the main topic. Firstly, to clarify :
Jose : If the bolt strikes a single spot on each end of the platform, these spots will become scorched lines on the side of the train. ....

Great ! If you hadn't mentioned scorch-marks, I would have - you beat me to it happy.gif.

Jose : if you meant that I was directly across from you when you saw the flashes simultaneously, I would have been 75 feet to the rear of the midpoint between scorch marks on the train. (In which case I would see the pulses more or less simultaneously just as you


Yes, that is exactly what I meant, and I tried to phrase it to make that as clear and unambiguous as possible when I said “just at that moment, the wavefronts from lightening strikes at the front and rear of the platform reach our eyes” (so no, I have not made any fallacy about you being in two places at once).

I'm also glad that you've correctly identified your position (the bit I've underlined); I'll mention that bit again in a moment.

Jose : Likewise the duration of time I would be aligned* with you would be in the femtosecond range. Not much time to be setting clocks..

Again, it's not relevant how long we were aligned; any information transfer can happen while we are.

One small, but IMHO important, point though. I said "yes, we both happened to notice that our watches both happened to read exactly the same time as we were passing". Notice that - I never said "I set my watch" - I said it was already reading that, just as yours was already that as well.

Why is that important? Because I'm implying/asserting that every watch on the train was ALREADY synchronised before the experiment started - in other words, that the time IN THE TRAIN FRAME was 3pm. Ditto, of course, for every clock on the platform - just as you implicitly and correctly picked-up on / implied / asserted when you said "100 nanoseconds before 3 o'clock,".

Of course, I could have said "set my watch to 3pm and every clock on the train automatically synchronised as well" (which gets the same end result), but that's an unnecessary extra layer of detail/confusion - not to mention that it also means that none of the clocks would have been synchronised at the time the lightening struck. It's much simpler and more consistent to simply make it part of the given initial conditions happy.gif

Jose : If you had synchronized clocks located at the points of the strikes, they would show the strikes started 100 nanoseconds before 3 o'clock,(When at 3 o'clock you saw the pulses arrive at your midway station,)


Now, I have 8 questions for you. Since we're still in SR mode, remember that I measure light travelling at one foot per nanosecond relative to me, and you sitting on the train also measure light travelling at one foot per nanosecond relative to you.

Ok, but as we're about to compare clock readings, let's adopt the standard, clear, unambiguous and specific way of showing clock readings in hours:minutes:seconds format (eg "2:59:59.98765")

Q1) What time do I reckon that the lightening strike at the front of the platform started.
Q2) What time do I reckon that the lightening strike at the front of the platform ended.
Q3) What time do I reckon that the lightening strike at the rear of the platform started.
Q4) What time do I reckon that the lightening strike at the rear of the platform ended.

Q5) What time do you reckon that the lightening strike at the front of the train started.
Q6) What time do you reckon that the lightening strike at the front of the train ended.
Q7) What time do you reckon that the lightening strike at the rear of the train started.
Q8) What time do you reckon that the lightening strike at the rear of the train ended.

To clarify, the phrase "what time do you / I reckon" could equally well have been re-phrased as "If your / my clock at the site of each strike, stops at the first (or last) instant the lightening strike touches it, then what time would it be left showing?"

Now of course, the lightening strikes on the platform WERE the strikes on the train, but your measurements would always relate to your reference frame (which is also something to think about if your initial reaction is that the answers to 5-8 would be the same as 1-4 - remember that bit of your response that I underlined above ).

Finally, for myself, I reckon just the 4 odd-numbered questions (or just the even numbered ) would be sufficient for the point - but of course, I know durations are important to you, so you'll want to complete all 8 of them, eh ? wink.gif

 
 
ufonaut99

Re: Relativity of Simultaneity (Not Quite)

January 12 2015, 11:19 PM 

Nakayama: From just above, plane waves of light are coming horizontally. At the front edge and rear edge each on the roof of a moving passenger car, a sensor and a light source is set. In response to a special change of plane waves, the two flash. Two flashes will be simultaneous also to an observer stands on the ground. “relativity of simultaneity” seems not to stand up.


Hi Nakayama,

Sorry, haven't forgotten you happy.gif

I hope you can see the similarity between your scenario above, and the train scenario I'm discussing with Jose. Suppose that when the plane wave arrives, the flashing of the light sources is so hot that it causes scorch marks on both the passenger car (ie train) and the ground (ie. Platform). Replace "light source" with "lightening strikes that are simultaneous in the ground's frame", and it's the same scenario.

Given that, have a shot at answering the questions I've just asked Jose (maybe just the odd-numbered ones!). After all, it's not enough to just pluck scenarios out of thin air and just declare SR is wrong without even working out what SR says in the first place ! Since we're interested in what SR says here, answer the questions on the (temporary) assumption that both postulates are true.

... And yes, I know I could just go ahead and give my answers, but it's by working through scenarios and discussing disagreements as they arise that everybody benefits happy.gif

 
 
Jose Rodriguez

Re: Relativity of Simultaneity (Not Quite)

January 13 2015, 3:16 AM 

UFO: "Ohhh, I've retained. I just don't agree with all that any more now than I did then happy.

"Unit dimensions – OK. Personally, I don’t see how you find nano-seconds easier to deal with than actual seconds (I think it’s easier to see that there’s a difference between 2:59:50 and 2:59:55 than between 2:59:59.99999999 and 2:59:59.999999999, for example). Still, if you want to use lengths and times scaled on nano-seconds, that’s what we’ll run with. You'll have noticed that I gave a "realistic" length platform rather than Light-seconds long one, for example."
I chose what I did because light nanoseconds automatically gives the distance or duration directly when the opposite type of measure is known.
UFO: "Duration, and things like “the actual distance between the Earth and the Sun is continually changing” I still find needlessly pedantic and pointless. Mathematics, by its very nature, is an idealization of points and lines. Pointing out (repeatedly) the obvious fact that nature does not match this idealization, not only adds nothing to the discussion - in fact, it detracts from it. Since mathematics is an idealization, it succinctly captures and exposes the behavior being studied. Bringing in all the real-life messiness around it does nothing but obscure and distract from that behavior with irrelevant detail - not to mention increasing the workload of equations, etc.
And leaves you with some imaginative, void of logic fantasy.
UFO: "I’m curious, though – would you make these same complaints about all physics equations (eg, Newton’s), or reserve them only for Relativity?
I look at everything as best I can what happens in real life. The Devil is in the details.
Jose: "If the bolt strikes a single spot on each end of the platform, these spots will become scorched lines on the side of the train."
UFO: "Great ! If you hadn't mentioned scorch-marks, I would have - you beat me to it happy."
I didn't say "scorch marks" except in the first paragraph. I missed changing it to "scorch lines." The lightning strikes are in the platform frame.
Jose: "if you meant that I was directly across from you when you saw the flashes simultaneously, I would have been 75 feet to the rear of the midpoint between scorch marks on the train. (In which case I would see the pulses more or less simultaneously just as you"
UFO: "Yes, that is exactly what I meant, and I tried to phrase it to make that as clear and unambiguous as possible when I said “just at that moment, the wavefronts from lightening strikes at the front and rear of the platform reach our eyes” (so no, I have not made any fallacy about you being in two places at once).
"I'm also glad that you've correctly identified your position (the bit I've underlined); I'll mention that bit again in a moment."
I meant to edit that out after rereading your post. But stay on your toes.
Jose: "Likewise the duration of time I would be aligned* with you would be in the femtosecond range. Not much time to be setting clocks"
UFO: "Again, it's not relevant how long we were aligned; any information transfer can happen while we are."
I forgot. we are in fantasy land. Anything goes.
UFO: "One small, but IMHO important, point though. I said "yes, we both happened to notice that our watches both happened to read exactly the same time as we were passing". Notice that - I never said "I set my watch" - I said it was already reading that, just as yours was already that as well.

"Why is that important? Because I'm implying/asserting that every watch on the train was ALREADY synchronized before the experiment started - in other words, that the time IN THE TRAIN FRAME was 3pm. Ditto, of course, for every clock on the platform - just as you implicitly and correctly picked-up on / implied / asserted when you said "100 nanoseconds before 3 o'clock,".
Of course, I could have said "set my watch to 3pm and every clock on the train automatically synchronized as well" (which gets the same end result), but that's an unnecessary extra layer of detail/confusion - not to mention that it also means that none of the clocks would have been synchronized at the time the lightening struck. It's much simpler and more consistent to simply make it part of the given initial conditions happy."
You claim you are in SR mode. In that fantasy land, clocks in one frame run at a different rate than in the other. So what kind of coincidence caused all the clocks in both frames to read "3PM"? In fact SR predicts that clocks run both faster and slower simultaneously.
Jose: "If you had synchronized clocks located at the points of the strikes, they would show the strikes started 100 nanoseconds before 3 o'clock,(When at 3 o'clock you saw the pulses arrive at your midway station,"
UFO: "Now, I have 8 questions for you. Since we're still in SR mode, remember that I measure light traveling at one foot per nanosecond relative to me, and you sitting on the train also measure light traveling at one foot per nanosecond relative to you.

"Ok, but as we're about to compare clock readings, let's adopt the standard, clear, unambiguous and specific way of showing clock readings in hours:minutes:seconds format (eg "2:59:59.98765")"
Let's not.
UFO: "Q1) What time do I reckon that the lightening strike at the front of the platform started.
Q2) What time do I reckon that the lightening strike at the front of the platform ended.
Q3) What time do I reckon that the lightening strike at the rear of the platform started.
Q4) What time do I reckon that the lightening strike at the rear of the platform ended.

"Q5) What time do you reckon that the lightening strike at the front of the train started.
Q6) What time do you reckon that the lightening strike at the front of the train ended.
Q7) What time do you reckon that the lightening strike at the rear of the train started.
Q8) What time do you reckon that the lightening strike at the rear of the train ended.

"To clarify, the phrase "what time do you / I reckon" could equally well have been re-phrased as "If your / my clock at the site of each strike, stops at the first (or last) instant the lightening strike touches it, then what time would it be left showing?"
If you notice I gave parameters for the leading edge, each instance.
UFO: "Now of course, the lightening strikes on the platform WERE the strikes on the train, but your measurements would always relate to your reference frame (which is also something to think about if your initial reaction is that the answers to 5-8 would be the same as 1-4 - remember that bit of your response that I underlined above )."
I said that there is a place on the train where the strikes are seen simultaneously. It is not midway between the scorch lines on the train. The train moves away from the strikes, even as they happen. The light pulses travels at a foot /nanosecond from the platform points regardless of the speed of any train. Regardless of it's speed or direction. In SR, the several trains find the platform shrunk, but to various lengths depending on the speed of the receding platform.
UFO: "Finally, for myself, I reckon just the 4 odd-numbered questions (or just the even numbered ) would be sufficient for the point - but of course, I know durations are important to you, so you'll want to complete all 8 of them, eh ?"
I spoze not. Let's stipulate burn marks on both the platform and the train, exactly where both of us see the lightening bolts strike simultaneously. Or do you claim that there is no spot on the train that one can see both you and the lightning strikes simultaneously?

There is only one light sphere at each lightning strike. They are continuously expanding in the platform frame. They cannot detach themselves from there and also expand in any other reference frame. The scorch marks on the platform make a scorched line on the train. The point that you love at the platform strikes are not points in the train frame.

According to SR, the platform sees the train clocks running slow and the train sees the platform clocks run slow, yet all you want to fret about is what time it is.




 
 
Jose Rodriguez

Re: Relativity of Simultaneity (Not Quite)

January 13 2015, 10:17 AM 

UFO, Einstein uses the "measure the train length from the platform" gedankin to show how the moving train ends up measuring shorter from the platform reference frame. It goes something like this: The train's length is marked at rest with the platform. "When the front of the train reaches the far end of the platform,(at the platform "at rest mark" for the train length) the engineer there on the platform signals the rear of the platform engineer to mark the rear of the train. (The signal is traveling against the motion of the train.) Since the signal has to travel at c to the back of the train, and the back of the train is still moving forward, the moving train measures shorter than it did when at rest with the platform. (His gedankin uses the wave front travel. Anything else is circular reasoning.)

Now, If the opposite engineer (the one that just received the signal from the front of the train) sends the "mark" signal to the front of the train, from the original platform mark, now the signal is traveling with the motion of the train, and since the train is still moving, the train measures longer than it was when it was at rest. Starting the measurement from the rear of the passing train is just as legitimate as the original way Einstein did the gedankin, therefor the train is both shorter and longer than when it is at rest He uses wave fronts to do the gedankin. So your remark about "this has nothing to do with the arrival of wave fronts" is a bluff. Having the lightning bolts mark both ends of the platform and the train simultaneously, gets around the signals having to travel down the train to measure it, so what makes the train shorter then when at rest with the platform? Just the imagination of Einstein and his followers.


In your scenario, all the clocks are regulated to the same rate and time of day when they are at rest with the platform. The train is then backed up a great distance and then passes the platform at 3/4 c. Somehow, magically, I, in the train, end up right across from you right when you see the initiation of both lightning strikes, and right when your clock and mine both read 3 O'clock. At that point all the clocks on the platform read 3 O'clock. Now, according to you, the train clocks are running slow because the train is in motion. However, since all the train clocks are regulated and set to the same time of day, all those clocks register 3 O'clock too, at this moment.

So, if we go back in time to when the lightning strikes actually hit the platform, (100 nanoseconds before 3 O'clock on the platform clocks), what time do you say the train's clocks indicate at the actual lightning strikes? What ever time you say it is, all the clocks on the train will report the identical time.(but not because they all see the simultaneous strikes.) That means that both the rear train's clock and the front train's clock will show identical times for their respective strikes, but not for the opposite ended strikes.

One thing for sure is that from the train reference frame, I cannot be half way between the two strikes to see them simultaneously.







 
 
nakayama

Re: Relativity of Simultaneity (Not Quite)

January 13 2015, 10:30 PM 

I am sorry for an irrelevant posting to the flow of discussion.

“Relativity of simultaneity”, “ Constancy of light speed (to observers)” both seem not to stand up (a picture below is done in vacuum).

From windows of a moving passenger car, flashes are sent to the right and the left at 90 degrees. Regard two flashes as two photons. Ahead of each photon, a wall stands on the ground and on the wall, a vertical line is drawn. This line is 90 degrees to the emitted point of the photon. The photon will hit on the point out of the line a little (to the moving direction of the passenger car ; there is no rest frame).

But, what does it mean ? Imagine light sphere that is formed in the passenger car and photons in this sphere. From viewpoint of an observer on the ground, every photon will have the same motion component v (to the moving direction of the passenger car).

 
 
Jose Rodriguez

Re: Relativity of Simultaneity (Not Quite)

January 13 2015, 11:50 PM 

Nakayama: "I am sorry for an irrelevant posting to the flow of discussion."
Don't be sorry about your posts. I just haven't responded because they are a bit obtuse. In what follows, I will suggest some pointers which you may want to incorporate in your questions and examples. Or not.

Nakayama: "Relativity of simultaneity”, “ Constancy of light speed (to observers)” both seem not to stand up (a picture below is done in vacuum)."
I agree.

Nakayama: "From windows of a moving passenger car, flashes are sent to the right and the left at 90 degrees. Regard two flashes as two photons. Ahead of each photon, a wall stands on the ground and on the wall, a vertical line is drawn. This line is 90 degrees to the emitted point of the photon. The photon will hit on the point out of the line a little (to the moving direction of the passenger car; there is no rest frame)."
A restatement of what I think you mean to communicate:

A pair of lasers are oriented perpendicular (transverse or normal) to their straight line motion, (with respect to the ground) whose pulses are emitted directly opposite (diametrically to) each other . Walls, a good distance from the line of motion, on either side , and parallel to the direction of their motion, have a line normal (perpendicular) to the ground engraved upon each of them.

Your conjecture is that if a switch, firing the lasers, is placed in the line of motion such that the placement removes the latency of the switch; This placement will fire the lasers exactly when they are aimed directly at the distant lines on the walls. Your prediction is that they will miss the lines in the direction of their motion.

I agree.

My humble opinion is that it is less confusing (in naming reference frames) ifn one refers to the source frame and the receiving frame. The source frame is the lasers, the receiving frame is the ground and the walls.
Nakayama: "But, what does it mean ? Imagine light sphere that is formed in the passenger car and photons in this sphere. From viewpoint of an observer on the ground, every photon will have the same motion component v (to the moving direction of the passenger car)."
Restatement:

You think that laser pulses will have the transverse component of the velocity of the lasers themselves, all with respect to the ground. (The ground is moving in the opposite direction from the laser point of view.) I agree with this idea, unless there is an aether with motion not common to either reference frame.


 
 
nakayama

Re: Relativity of Simultaneity (Not Quite)

January 15 2015, 9:48 PM 

Thank you Jose so much for your reply ! Yes, two photons cannot recognize the ground at all. So, photons will miss the lines.

About aether, I wrote my view in my web-site. I guess, within moon – earth scale, aether will have no effect.

 
 
nakayama

Re: Relativity of Simultaneity (Not Quite)

January 15 2015, 9:55 PM 

About optional two points in the space, if some condition (of a light wave) guarantees the simultaneity, Newton’s absolute time will revive.

 
 
nakayama

Re: Relativity of Simultaneity (Not Quite)

January 17 2015, 12:29 AM 

Allow mw to rewrite yesterday’s comment on aether.
“In everywhere of universe, emitted light will follow the emission theory for a few seconds. And then, light will follow aethe frame, I guess”.

 
 
nakayama

Re: Relativity of Simultaneity (Not Quite)

January 17 2015, 8:46 PM 

About Newton’s absolute time

Imagine optional two points (but the two are not in a relative motion, also are not in an orbital motion) in space. It’s possible to settle a light source at the position in the same distance from the two points. By the above, simultaneity of two points will be guaranteed. Newton’s absolute time will be flowing in this space.

 
 
nakayama

Re: Relativity of Simultaneity (Not Quite)

January 18 2015, 10:26 PM 

In the picture of a moving passenger car and light, light will reach the roof and the floor at the same time (if it’s the same time for an observer in the car). Something is not clean.

 
 
nakayama

Re: Relativity of Simultaneity (Not Quite)

January 19 2015, 9:08 PM 

The following is a question about a familiar illustration shown in books. In it, two light rays are emitted horizontally in a moving passenger car. And an observer stands on the ground sees that the end of one ray doesn’t reach yet the receding wall a little. Now, imagine the third ray emitted diagonally from the roof. Clearly, the product (to the wall) is longer. How is it explained ?

 
 
nakayama

Re: Relativity of Simultaneity (Not Quite)

January 20 2015, 10:20 PM 

Allow me to rewrite yesterday’s post as follows.

The following is a question about a familiar illustration shown in books. In it, two light rays are emitted horizontally in a moving passenger car. Now, two rays are slanted at 5 degrees upward. The points on the walls where two rays hit will be different to two observers (in the car and stands on the ground).

 
 
nakayama

Re: Relativity of Simultaneity (Not Quite)

January 23 2015, 3:32 AM 

Allow me to rewrite my post (Dec 31) as follows.

Between two long mirrors, two laser beams form paths like continuous letter X (sent to the left). At each crossing point, interference fringes are visible. This interference fringes will be the same to all, including the one who is moving in a relative motion (to the mirror). "Relativity of simultaneity" seems to be unacceptable.

 
 
nakayama

Re: Relativity of Simultaneity (Not Quite)

January 27 2015, 8:34 PM 

In front of an observer stands on the ground, a passenger car is moving. An illustration of books shows that two light rays are emitted from a light source (set at the center of the car). But now, replace light rays with a light sphere (or a circular wave seen from the observer). In an illustration about simultaneity, light sphere doesn’t follow passenger car’s motion. On the other hand, in an illustration about light clock, it (hemisphere) seems to follow passenger car’s motion. Am I wrong ?

 
 
nakayama

Re: Relativity of Simultaneity (Not Quite)

January 31 2015, 12:05 AM 

This is a thought experiment about simultaneity. I myself am not certain. So, regard this as a problem posing, please.

Imagine optional two points A, B (at a standstill) in an inertial frame. It’s possible to settle a light source C at a position in the same distance from the two points A, B. By the above, simultaneity of two points A, B will be guaranteed. Thus, simultaneity of whole frame will be guaranteed also.

But, how about between different inertial frame ? From the above, if simultaneity is broken between different inertial frame, simultaneity will probably be broken always between optional different inertial frames (frames each will have their own simultaneity). Now, in the above picture, suppose that two points A, B are receding (symmetrically with respect to C) at the same speed. Simultaneity will be guaranteed.

 
 
nakayama

Re: Relativity of Simultaneity (Not Quite)

January 31 2015, 7:39 PM 

Allow me to rewrite yesterday’s post, please.

Imagine optional two points A, B (at a standstill) in an inertial frame. It’s possible to settle a light source C at the position in the same distance from two points A, B. By the above, simultaneity of two points A, B will be guaranteed. So, simultaneity between every point of this frame will be guaranteed also.

But, how about between different inertial frame ? In the above, suppose that two points A, B are receding (symmetrically with respect to C) at the same speed. By the above, simultaneity of A, B will be guaranteed. So, simultaneity between two optional inertial frames and also between optional inertial frames will be guaranteed.

 
 
nakayama

Re: Relativity of Simultaneity (Not Quite)

February 3 2015, 9:05 PM 

Allow me to rewrite again the latter half of my above post. Only Newton’s absolute time will be flowing.

But, how about between different inertial frame ? In the above, suppose that an equilateral triangle (C is the apex) is enlarging at a constant speed. By the above, simultaneity of A, B will be guaranteed. So, simultaneity between optional two inertial frames will be guaranteed also.

 
 
nakayama

Re: Relativity of Simultaneity (Not Quite)

February 23 2015, 8:16 PM 

To above my post (Feb 3), allow me to add "(the three points each is in an inertial frame)". after "is enlarging at a constant speed".

 
 
nakayama

Re: Relativity of Simultaneity (Not Quite)

February 27 2015, 8:35 PM 

In a moving passenger car, planetarium is projected. Position of stars will be the same also to an observer stands on the ground. Light sphere will follow passenger car’s motion. Simultaneity will be absolute.

 
 
 
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