SR Simultaneous Lines Drawn in the Sand

[geistkiesel]

The Einstein Train Gedunken


The observer O’ in the moving frame at M’ arrives at M, the midpoint of A and B in the stationary frame, at t0’ when A and B emit photons.

Later a photon from B is detected when M’ is at t1’; the photon from A is detected when M’ is at t2’ in the moving frame. For convenience the velocity of the moving frame is v = 1 and dt = t2' – t1'.
t0'
--------------------------------------t0'|--------t1'-|----------|-t2'
||||||||||||---------------------------M’------------------------------------||||||||||||||| -> motion

-----A-----------------------------------M------------------------------------------B

There are added sections of photo-sensitive strips ||||| such that A and B afre guaranteed to be within a section length when the photons are emitted at A and B. The midpoint of the photo-sensitive strips was determined using the same techniques used to determine M the midpoint of A and B. The strips are numbered starting from the inside positions and then consecutively to the ends of the sections. Each equally numbered pair of photo-sensitive strips have a common midpoint at M’. The resolution of the strips is in the sub-micron range.

As photons are emitted at A and B the photo-sensitive strips located within one photon wave length of A and B, or less, are exposed.

The postulates of special relativity theory state that the laws of physics and the measure of the constancy of the speed of light are invariant in all inertial frames. From special relativity theory observers in the moving frame conclude the events of the emitted photons were not simultaneous in the moving frame.

Are the emitted photon events that are simultaneous in the stationary frame simultaneous in the moving frame?

1.Comments on experimental arrangements or conditions are gratefully accepted.

2.Comments on explicit or implicit stipulations and/or assumptions are gratefully accepted.

3. Other comments..

 

[Doc Al]

Einstein's argument

The Einstein Train Gedunken


The observer O’ in the moving frame at M’ arrives at M, the midpoint of A and B in the stationary frame, at t0’ when A and B emit photons.

I'll rephrase this a bit. In the stationary frame (O), M is the midpoint of two light sources A and B. Lights A and B are switched on at the exact moment that a moving observer O' passes M as observed in the stationary frame. All observations in the stationary frame confirm that the lights were turned on at the same time. For simplicity, let's call that time t = 0.

Since the entire issue is whether or not observers in the moving frame will agree with the stationary frame's assessment that the lights were turned on simultaneously, we must take care to make no assumptions about simultaneity in the moving frame.

Einstein's argument is simple. Rather than add things (like length measurements) which may only serve to confuse the issue, let's deal with Einstein's argument itself (as I recall it).

Einstein reasons thusly:

(1) If an observer is exactly between two lights when they emit pulses simultaneously (according to the observer), then
(2) the pulses from both sources will be detected (received) by the observer simultaneously.

Do you not agree then, that if statement (1) is true, that statement (2) must follow?

Let us also stipulate, per Einstein, that since the speed of light is an invariant in any frame, this argument applies regardless of the speed of the observer. It equally applies to the stationary observer or to the moving observer.

There is no question that for the stationary observer both statements are satisfied. But what can we conclude about the moving observer?

Einstein argues that, from the viewpoint of the stationary observers, O' is moving towards B and away from A. Thus light from B must reach O' before light from A. Do you agree with this? Do you agree that every observer (in any frame) must agree that the light from A and B reached O' at different times?

If you agree with this conclusion, which follows from the invariance of the speed of light, then you agree that statement (2) of Einstein's argument is denied.

Since Einstein's argument is of the form:

If A, then B.
not B,
thus not A.​

We are forced to conclude that statement (1) is not true! Thus O' must conclude that the lights were switched on at different times (according to his observations).

That's Einstein's gedanken experiment. Can you point out an error in that argument?

Later a photon from B is detected when M’ is at t1’; the photon from A is detected when M’ is at t2’ in the moving frame. For convenience the velocity of the moving frame is v = 1 and dt = t2' – t1'.
t0'
--------------------------------------t0'|--------t1'-|----------|-t2'
||||||||||||---------------------------M’------------------------------------||||||||||||||| -> motion

-----A-----------------------------------M------------------------------------------B

There are added sections of photo-sensitive strips ||||| such that A and B afre guaranteed to be within a section length when the photons are emitted at A and B. The midpoint of the photo-sensitive strips was determined using the same techniques used to determine M the midpoint of A and B. The strips are numbered starting from the inside positions and then consecutively to the ends of the sections. Each equally numbered pair of photo-sensitive strips have a common midpoint at M’. The resolution of the strips is in the sub-micron range.

As photons are emitted at A and B the photo-sensitive strips located within one photon wave length of A and B, or less, are exposed.

Not sure what you are measuring with these photo-sensitive strips.

The postulates of special relativity theory state that the laws of physics and the measure of the constancy of the speed of light are invariant in all inertial frames. From special relativity theory observers in the moving frame conclude the events of the emitted photons were not simultaneous in the moving frame.

Right!

Are the emitted photon events that are simultaneous in the stationary frame simultaneous in the moving frame?

No.

 

[ram2048]

uhh.

before a photon even hits the moving observer he's already moved to t'1 (b photon). then he's already moved to t'2 before the second one hits him (a photon)

all motion aside, put an observer at t'0 t'1 and t'2 and which observer does the photon from B hit first?

the one from t'2 of course.

it's quite rudimentary, i am not understanding the confusion behind all this

 

[ram2048]

Einstein reasons thusly:

(1) If an observer is exactly between two lights when they emit pulses simultaneously (according to the observer), then
(2) the pulses from both sources will be detected (received) by the observer simultaneously.

are you sure that's what he's reasoning? because he would have to assume light travels instantaneously in order for that to be true.

as another observation, if a person arrives AT the midpoint M at the exact time to be hit by photons from A and B, NO MATTER what direction speed acceleration, we can safely assume the photons were emitted from the sources simultaneously, even if they were not calibrated to do so.

but this is simply an observation of speeds and distance midpoints known by any elementary school student

 

[Doc Al]

are you sure that's what he's reasoning? because he would have to assume light travels instantaneously in order for that to be true.

Obviously the pulses are emitted and detected at different times.

as another observation, if a person arrives AT the midpoint M at the exact time to be hit by photons from A and B, NO MATTER what direction speed acceleration, we can safely assume the photons were emitted from the sources simultaneously, even if they were not calibrated to do so.

Not true. If you get hit by two bullets simultaneously, can you conclude that they were fired simultaneously? Of course not: it depends on where they were when they were fired.

but this is simply an observation of speeds and distance midpoints known by any elementary school student

Time to move to a better school district.

 

[ram2048]

Not true. If you get hit by two bullets simultaneously, can you conclude that they were fired simultaneously? Of course not: it depends on where they were when they were fired.

if the bullets ALWAYS traveled the same speed AND i was at the MIDPOINT distance between the shooters WHEN HIT.

yes, yes i could

 

[Doc Al]

if the bullets ALWAYS traveled the same speed AND i was at the MIDPOINT distance between the shooters WHEN HIT.

Nope. It doesn't matter where the shooters are when you are hit, it only matters where they were when they pulled the trigger.

Think about it. By the time the bullets reach you, the shooters have moved.

 

[ram2048]

the shooters don't move. they're stationary, the observer is the only thing moving in my example

sorry if you were confused by that

 

[Pergatory]

This is the same as the other two "SR questions of the century" that have been posted earlier on this forum. I'll admit I didn't read those all the way through because they were so long! But I'll take a shot at this one.

Using M as the point of origin (so that AM = MB = AB/2, and A = -B), at the point when observer O reaches t1, the photon from B will also be at t1 (by definition) but the photon from A will be at -t1. Given the same duration of local time, both photons will have traveled an equal distance regardless of the frame of reference. At the point when observer O and photon A reach t2, photon B will be at -t2 (the photons have both passed M).

(1) If an observer is exactly between two lights when they emit pulses simultaneously (according to the observer), then
(2) the pulses from both sources will be detected (received) by the observer simultaneously.

#2 is true only if the observer is exactly between the lights when the photons are DETECTED. It does not matter where the observer is when they are emitted. In fact, the observer does not even need to exist when they are emitted. Look at the stars tonight. Consider how long it has been since the light you are seeing has been emitted. Have you really been alive that long? The events you are seeing are not occurring, they have already occurred in the past.

Time is local, so simultaneity is a matter of your frame of reference.

 

[ram2048]

#2 is true only if the observer is exactly between the lights when the photons are DETECTED. It does not matter where the observer is when they are emitted

exactly, which was the point i was trying to make, but i left out that the emitters do not move <woops>

 

[baffledMatt]

Have you ever looked at the so-called 'pole-vaulter paradox'? That's an interesting one as it shows you explicitely how according to SR you must lose simultaneity or face paradox.

Matt

 

[Doc Al]

#2 is true only if the observer is exactly between the lights when the photons are DETECTED.

Incorrect. In fact, exactly the opposite is true. I don't care where the lights are when the photons are detected--they need not even exist by that time.

It does not matter where the observer is when they are emitted.

It matters if you wish to make a deduction about whether the pulses are detected simultaneously. Which is the entire point.

In fact, the observer does not even need to exist when they are emitted.

The thought experiment assumes that both observers have existed forever traveling at the same speed. The point is that statement (2) follows from statement (1). That's all.

Look at the stars tonight. Consider how long it has been since the light you are seeing has been emitted. Have you really been alive that long? The events you are seeing are not occurring, they have already occurred in the past.

True, but I don't see the relevance to Einstein's argument.

Time is local, so simultaneity is a matter of your frame of reference.

Now that I agree with!

 

[Pergatory]

Incorrect. In fact, exactly the opposite is true. I don't care where the lights are when the photons are detected--they need not even exist by that time.

It matters if you wish to make a deduction about whether the pulses are detected simultaneously. Which is the entire point.

My apologies for not being clear. What I meant by the light, is A and B. Not the physical light, you're right, it could be removed once the photons have been emitted, it does not matter.

My point is that in order for the photons to arrive at the observer at the same time, the observer must be equidistant from both originating locations at the point in time when both photons are observed. It does not matter where the observer is or is not when the photons are emitted. THAT was my point.

Please don't waste your time by further tearing apart minor details of my responses, and focus solely on the point I'm trying to prove in response to the point you've tried to make. If we lose focus, it will turn into another 4-page discussion and there will be another identical thread created in a few days discussing the same principal.

 

[Doc Al]

the shooters don't move. they're stationary, the observer is the only thing moving in my example

From the observer's point of view, the shooters are moving. Regardless, all that matters for the current argument (in analogy with Einstein's) is where the shooters were (with respect to the observer) at the moment the guns were fired. If the observer (victim?) was exactly between the shooters at the time they fired, then we can deduce that the bullets will arrive simultaneosly. (These are special photon bullets, of course, that always travel the same speed with respect to all observers. )

 

[Doc Al]

My point is that in order for the photons to arrive at the observer at the same time, the observer must be equidistant from both originating locations at the point in time when both photons are observed. It does not matter where the observer is or is not when the photons are emitted. THAT was my point.

I believe I understood your point the first time. You're still wrong. The position of the lights at the moment the photons are detected is irrelevant.

Please focus on the argument at hand: If statement (1) is true, then statement (2) is true.

Please don't waste your time by further tearing apart minor details of my responses, and focus solely on the point I'm trying to prove in response to the point you've tried to make. If we lose focus, it will turn into another 4-page discussion and there will be another identical thread created in a few days discussing the same principal.

I am completely focused. The point of yours that I am "tearing apart" is not a minor detail.

 

[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 let's 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!

 

[ram2048]

that makes NO sense.

A and B flash. observer M is in the middle WHEN they flash. He immediately accelerates to light speed in the direction of B.

Photon from A never reaches him.

Photon B is intercepted halfway to B

 

[jdavel]

ram2048,

Sounds like you have a real solid understanding of this theory!

 

[ram2048]

what part of photons traveling the speed of light is hard to understand?

if you travel AWAY from a clock AT LIGHT SPEED and look to see what time it says what do you see?

NOTHING. no new photons are hitting your eyes from that direction

 

[quantumdude]

what part of photons traveling the speed of light is hard to understand?

if you travel AWAY from a clock AT LIGHT SPEED and look to see what time it says what do you see?

NOTHING. no new photons are hitting your eyes from that direction

I think what jdavel is hinting at is that you can't accelerate to light speed.

 

[ram2048]

fine. i AM a photon

i'm looking behind me at a clock :P

 

[geistkiesel]

The line in the sand : remain where you are or step across.

I'll rephrase this a bit. In the stationary frame (O), M is the midpoint of two light sources A and B. Lights A and B are switched on at the exact moment that a moving observer O' passes M as observed in the stationary frame. All observations in the stationary frame confirm that the lights were turned on at the same time. For simplicity, let's call that time t = 0.

Sure, but also as to the moving observers their clocks are t' = 0. The two '0' are the same.

Since the entire issue is whether or not observers in the moving frame will agree with the stationary frame's assessment that the lights were turned on simultaneously, we must take care to make no assumptions about simultaneity in the moving frame.

Right. We only define simultaneity as "the photons emitted at the same time in the frame." This is the question, not the answer. OK?

Einstein's argument is simple. Rather than add things (like length measurements) which may only serve to confuse the issue, let's deal with Einstein's argument itself (as I recall it).

Einstein reasons thusly:

(1) If an observer is exactly between two lights when they emit pulses simultaneously (according to the observer), then
(2) the pulses from both sources will be detected (received) by the observer simultaneously.

Do you not agree then, that if statement (1) is true, that statement (2) must follow?

Your observer here is the stationary observer, right? No ambiguity here, right?

I agree. The sequence goes like this: 1.The stationary observer is at the midpoint of A and B 2. Photons are emitted from A and B simultaneously. 3. Later, thw photons from A and B arrive at M (the observer) at the same time, simultaneously. You logic is correct. At this point characteristics of the speed of light have no special significance as long as what we are calling photons move with the same speed to the mindpoint. The photons could be crawling ants.

Let us also stipulate, per Einstein, that since the speed of light is an invariant in any frame, this argument applies regardless of the speed of the observer. It equally applies to the stationary observer or to the moving observer.

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?

There is no question that for the stationary observer both statements are satisfied. But what can we conclude about the moving observer?

Einstein argues that, from the viewpoint of the stationary observers, O' is moving towards B and away from A. Thus light from B must reach O' before light from A. Do you agree with this? Do you agree that every observer (in any frame) must agree that the light from A and B reached O' at different times?

This is effectively the same as stated above. The answer is yes, whether we are using crawling ants emitted from A and B, or light photons. Yes.

If you agree with this conclusion, which follows from the invariance of the speed of light, then you agree that statement (2) of Einstein's argument is denied.

Since Einstein's argument is of the form:

If A, then B.
not B,
thus not A.​

We are forced to conclude that statement (1) is not true! Thus O' must conclude that the lights were switched on at different times (according to his observations).

That's Einstein's gedanken experiment. Can you point out an error in that argument?

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.

I am scrutinizing the operation of the postulates. I am not testing the factual reality of that postulated. Do you see the difference?

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.

Not sure what you are measuring with these photo-sensitive strips.

Right!

No.

The photo-sensitive strips in the moving frame are arranged such that the photons emitted at A and B immediately expose the closest ps-strips in the sections, which are located within one wave length of the photon source when the moving frame passes by. Using the same laws of physics that determined M the midpoint of A and B, the moving frame scientists have determined the midpoint M' of all co-numbered ps-strips at each end of the measuring rod.

 

[russ_watters]

fine. i AM a photon

Fine. I am Elvis.

Saying it doesn't make it true and a thought experiment is only useful if it conforms to the theory it is used to describe.

 

[geistkiesel]

line in thwe sand

uhh.

before a photon even hits the moving observer he's already moved to t'1 (b photon). then he's already moved to t'2 before the second one hits him (a photon)

all motion aside, put an observer at t'0 t'1 and t'2 and which observer does the photon from B hit first?

the one from t'2 of course.

it's quite rudimentary, i am not understanding the confusion behind all this

The sequence of events: T0 the moving frame M' = M in the stationary frame at t0' = t0.
You cannot do as you say. The photon from B strikes the moving observer at t1', later the photon from A, behind, strikes the moving observer at t2'. You are mixing spatial location with timed points.

 

[geistkiesel]

line in the sand

are you sure that's what he's reasoning? because he would have to assume light travels instantaneously in order for that to be true.

as another observation, if a person arrives AT the midpoint M at the exact time to be hit by photons from A and B, NO MATTER what direction speed acceleration, we can safely assume the photons were emitted from the sources simultaneously, even if they were not calibrated to do so.

but this is simply an observation of speeds and distance midpoints known by any elementary school student

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. He really is saying that an observer at M in the stationary frame will see the photons arrive at M simultaneously. 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.

 

[geistkiesel]

Obviously the pulses are emitted and detected at different times.

Not true. If you get hit by two bullets simultaneously, can you conclude that they were fired simultaneously? Of course not: it depends on where they were when they were fired.

Time to move to a better school district.

Not true. Bullets fired from 1 km to the midpoint at the instant bullets fired from fired from 2 kim to the midpoint reach a point 1 km to the midpoint, will arrive at the same time. The same holds for photons emitted at the same locations as those launching the bullets. The farthest emitted photon will arrive simultaneously with the nearest emitted photon.

This isn't trivial for everybody?

 

[geistkiesel]

Nope. It doesn't matter where the shooters are when you are hit, it only matters where they were when they pulled the trigger.

Think about it. By the time the bullets reach you, the shooters have moved.

This is what I mean abiout dishonesty. After the bullets are launched, or photons are launched the location of the point of emitted entities is still the same point.

ram2048 - you must see the Doc Al 'confuse and distract methodology'

read the first pot again. The issue under disussion is whether the photons that were emitted simultaNeously when M' of the moving frame was at M in the stationary frame, which is the instant the photons were emitted at A and B were also emitted simultaneously in the moving frame, THIS IS THE THE SAME TIME THEY WERE EMITTED IN THE STATIONARY FRAME. SR THEORY CALCULATES THE PHOTONS WERE NOT EMITTED SIMULTANEOUSLY IN THE MOVING FRAME.

Doc Al knows this, he is consciously throwing distractions and bull **** into the conversation. Doc Al is not being honest, do you get it everybody?

 

[geistkiesel]

line in the sand

This is the same as the other two "SR questions of the century" that have been posted earlier on this forum. I'll admit I didn't read those all the way through because they were so long! But I'll take a shot at this one.

Using M as the point of origin (so that AM = MB = AB/2, and A = -B), at the point when observer O reaches t1, the photon from B will also be at t1 (by definition) but the photon from A will be at -t1. Given the same duration of local time, both photons will have traveled an equal distance regardless of the frame of reference. At the point when observer O and photon A reach t2, photon B will be at -t2 (the photons have both passed M).



#2 is true only if the observer is exactly between the lights when the photons are DETECTED. It does not matter where the observer is when they are emitted. In fact, the observer does not even need to exist when they are emitted. Look at the stars tonight. Consider how long it has been since the light you are seeing has been emitted. Have you really been alive that long? The events you are seeing are not occurring, they have already occurred in the past.

Time is local, so simultaneity is a matter of your frame of reference.

Pergatory, you have just finished you probationary period. Step up to the big time. You have said it all perfectly. I would only add the observation that SR theory does not agree with your assesment of SR theory. SR theory says that the moving observer will detect the photons as not being emitted simultaneously in the moving frame.

Of course the photons do not arrive simultaneously, but this is not sufficient to prove they weren't emitted simultaneously.
http://frontiernet.net/~geistkiesel/index_files/

There is a simple method described in the link to determine if the phoons were emitted simultaneously in the moving frame.

 

[geistkiesel]

My apologies for not being clear. What I meant by the light, is A and B. Not the physical light, you're right, it could be removed once the photons have been emitted, it does not matter.

My point is that in order for the photons to arrive at the observer at the same time, the observer must be equidistant from both originating locations at the point in time when both photons are observed. It does not matter where the observer is or is not when the photons are emitted. THAT was my point.

Please don't waste your time by further tearing apart minor details of my responses, and focus solely on the point I'm trying to prove in response to the point you've tried to make. If we lose focus, it will turn into another 4-page discussion and there will be another identical thread created in a few days discussing the same principal.

What you say is true. The moving observer who was at the midpoint of the photons when they were emitted later observes the photons arriving at different times as he is moving towards one of the photons and away from the other.

SR theory says, that the different arrival times at the moving observer means the photons were emitted at differnt time in the moving frame. This is different than saying his mere preception is the photons were emitted at diifferent times. SR theory has the PHYSICAL EMISSION of the photons into the moving frame not being simultaneous. This is fundamental SR.

Doc Al is being dishonest.

 

[ram2048]

so. here's what I'm getting from everyone trying to confuse the issue...

if I'm in the middle of A and B, and they emit photons towards me, no matter WHAT i do, move left right up down side to side stand on my head, WHATEVER...

i will always get hit by photons A and B at the same time.

is THAT what they're saying?

 

[geistkiesel]

that makes NO sense.

A and B flash. observer M is in the middle WHEN they flash. He immediately accelerates to light speed in the direction of B.

Photon from A never reaches him.

Photon B is intercepted halfway to B

your statement is recognition of the stupidity of SR theory.

 

[geistkiesel]

Fine. I am Elvis.

Saying it doesn't make it true and a thought experiment is only useful if it conforms to the theory it is used to describe.

it is also useful if the thiought proes the theory wrong.

 

[geistkiesel]

so. here's what I'm getting from everyone trying to confuse the issue...

if I'm in the middle of A and B, and they emit photons towards me, no matter WHAT i do, move left right up down side to side stand on my head, WHATEVER...

i will always get hit by photons A and B at the same time.

is THAT what they're saying?

No. If you are the middle of he photons when they are emitted and you reamin there th ephiotons will arrive at the saem time. If you move like the experiment here, the photons will arrive at difeent times. Bullets, photons or craw;ing ants, the same is true. Keep everything in a straight line. It is the simplest of simple.

Doc Al is throwing useless bull **** around to distract.
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.

 

[geistkiesel]

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 let's 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!

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?

 

[ram2048]

No. If you are the middle of he photons when they are emitted and you reamin there th ephiotons will arrive at the saem time. If you move like the experiment here, the photons will arrive at difeent times. Bullets, photons or craw;ing ants, the same is true. Keep everything in a straight line. It is the simplest of simple

so they DON'T hit you at the same time if i move left or right.

which is what i thought, so why the arguments if everyone agrees?