Train Thought Experiment

http://groups.google.com/groups?q=sci.physics.relativity,+%22Train+Thought+Experiment%22&hl=en&sa=G&scoring=d

1 Rod Ryker Re: Train Thought Experiment dinsdag 6 maart 2001 7:47
2 Nicolaas Vroom Re: Train Thought Experiment woensdag 28 maart 2001 17:12
3 Wayne Throop Re: Train Thought Experiment woensdag 28 maart 2001 21:31
4 John Anderson Re: Train Thought Experiment donderdag 29 maart 2001 6:36
5 Nicolaas Vroom Re: Train Thought Experiment donderdag 29 maart 2001 21:50
6 Nicolaas Vroom Re: Train Thought Experiment donderdag 29 maart 2001 21:50
7 Wayne Throop Re: Train Thought Experiment donderdag 29 maart 2001 22:32
8 Wayne Throop Re: Train Thought Experiment donderdag 29 maart 2001 22:53
9 David Empey Re: Train Thought Experiment donderdag 29 maart 2001 23:47
10 Russell Blackadar Re: Train Thought Experiment vrijdag 30 maart 2001 0:46
11 Wayne Throop Re: Train Thought Experiment vrijdag 30 maart 2001 4:24
12 Nicolaas Vroom Re: Train Thought Experiment vrijdag 30 maart 2001 10:40
13 Wayne Throop Re: Train Thought Experiment vrijdag 30 maart 2001 23:46
14 Nicolaas Vroom Re: Train Thought Experiment zaterdag 31 maart 2001 16:05
15 Wayne Throop Re: Train Thought Experiment zaterdag 31 maart 2001 20:01
16 Nicolaas Vroom Re: Train Thought Experiment maandag 2 april 2001 11:20
17 Wayne Throop Re: Train Thought Experiment maandag 2 april 2001 23:17
18 Nicolaas Vroom Re: Train Thought Experiment dinsdag 3 april 2001 17:58
19 Wayne Throop Re: Train Thought Experiment dinsdag 3 april 2001 19:44
20 Nicolaas Vroom Re: Train Thought Experiment dinsdag 3 april 2001 22:48
21 Wayne Throop Re: Train Thought Experiment woensdag 4 april 2001 7:20
22 John Anderson Re: Train Thought Experiment zaterdag 7 april 2001 6:49
23 Nicolaas Vroom Re: Train Thought Experiment woensdag 11 april 2001 13:36
24 Wayne Throop Re: Train Thought Experiment woensdag 11 april 2001 20:10
25 Nicolaas Vroom Re: Train Thought Experiment donderdag 12 april 2001 10:38
26 Wayne Throop Re: Train Thought Experiment donderdag 12 april 2001 19:06
27 Nicolaas Vroom Re: Train Thought Experiment zaterdag 14 april 2001 17:57
28 Wayne Throop Re: Train Thought Experiment zaterdag 14 april 2001 18:49
29 John Anderson Re: Train Thought Experiment zondag 15 april 2001 7:20
30 Nicolaas Vroom Re: Train Thought Experiment zondag 15 april 2001 13:13
31 Nicolaas Vroom Re: Train Thought Experiment donderdag 19 april 2001 10:04
32 Nicolaas Vroom Re: Train Thought Experiment zaterdag 21 april 2001 11:12


1 Train Thought Experiment

Van: Rod Ryker
Onderwerp: Re: train thought experiment
Datum: dinsdag 6 maart 2001 7:47

ande452@attglobal.net wrote:

> Rod Ryker wrote:
> >

Rod: I am NOT trolling John ! Why can't you just put this to rest for me please ?

I am asking the following : Located on the ends of the train are light detectors . That is , the detectors are comoving with the train . These detectors release a pin point paint mark on the track after they are activated by detecting a flash of light . The track guy observes the lightening strikes (flashes) as being simultaneous . The train guy observes the front flash first then the rear flash . Now ,

1.DO THE TRAINS DETECTORS MARK THE GROUND AT THE (APPX.) POSITION ON THE TRACK , MINUS ANY LENGTH CONTRACION AND OR AIR RESISTANCE FOR THE PAINT , WHERE THE TRACK GUY OBSERVES THE LIGHTENING FLASHES STRUCK THE TRACK ?

2. Or are the paint marks *not* approximately adjacent with the actual spots the track guy seen the lightening flashes hit ?

Simple questions John , answer yes or no for each please , and I'll leave you alone for awile . I promise . :):):)

>

You're asking for answers to a problem that have given no context to. I'm not going to give one word answers. I'm going to supply some context and then answer the questions. I'm more interested in helping people understand this stuff than I am in giving you an opportunity to deliberately confuse them.

Assume the flashes are simultaneous according to the track observer, A. They occur at time = 0 according to A. The events where the flashes originate have coordinates (in (t,x) notation in A's rest frame):

(0,0) and (0,L) where L is the measured length of the train according to A. A is at spatial position L/2 and not moving in his rest frame, so that the light from both flashes reaches him at t = L/(2*c).

The lightning makes marks on the track and machines at both ends of the train make marks at the same time as the lightning. The marks are in exactly the SAME positions at spatial positions 0 and L (in A's coordinates). The will be in the same spatial positions according to any other observer.

An observer, B, on and at the center of the train when the lightning strikes will not observe the light from the flashes arrive at the same time. This is easily seen using A's coordinates. The flashes arrive at B at times L/(2*(1 - v/c)) for light from the back of the train and L/(2*(1 + v/c)) for light from the front of the train. This is because B moves toward the light from the front of the train and away from the light at the back of the train. The light arrivals are distinct events in A's rest frame. They can't be the same event in B's rest frame unless the coordinate transformation between the two frames is singular.

B, therefore, sees the arrivals as distinct events and therefore concludes that the flashes aren't simultaneous since she was midway between the lightning strikes and she believes that the speed of light is c no matter who observes it.

That is really the point of this gedanken experiment. Absolute simultaneity is inconsistent with all observers measuring the same speed of light. And that's where this ought to end.

However, there is the issue of how B resolves the fact that the lightning marks and the machine marks are at the same places. According to B, the lightning flash at the front of the train occured before the flash at the rear. Therefore, the front of the train moved beyond the front marks before the rear marks were made. Therefore, the measured length of the train according to B is longer than the length between the marks.

John Anderson

Rod: Hi John , I agree with you and Paul B. Andersen . It is 100% logical and removes *voodoo* from SR . However , Carr , Throop , Evans , and Volpe do not agree .

Rod Ryker


2 Train Thought Experiment

Van: Nicolaas Vroom
Onderwerp: Re: train though experiment
Datum: woensdag 28 maart 2001 17:12


schreef in berichtnieuws 3A9F1D29.5CC5@attglobal.net...
> Rod Ryker wrote:
> > *Snip*
> You're asking for answers to a problem that have given no context to. I'm not going to give one word answers. I'm going to supply some context and then answer the questions. I'm more interested in helping people understand this stuff than I am in giving you an opportunity to deliberately confuse them.

Assume the flashes are simultaneous according to the track observer, A. They occur at time = 0 according to A. The events where the flashes originate have coordinates (in (t,x) notation in A's rest frame):

(0,0) and (0,L) where L is the measured length of the train according to A. A is at spatial position L/2 and not moving in his rest frame, so that the light from both flashes reaches him at t = L/(2*c).

The lightning makes marks on the track and machines at both ends of the train make marks at the same time as the lightning. The marks are in exactly the SAME positions at spatial positions 0 and L (in A's coordinates). The will be in the same spatial positions according to any other observer.

An observer, B, on and at the center of the train when the lightning strikes will not observe the light from the flashes arrive at the same time. This is easily seen using A's coordinates. The flashes arrive at B at times L/(2*(1 - v/c)) for light from the back of the train and L/(2*(1 + v/c)) for light from the front of the train. This is because B moves toward the light from the front of the train and away from the light at the back of the train. The light arrivals are distinct events in A's rest frame. They can't be the same event in B's rest frame unless the coordinate transformation between the two frames is singular.

B, therefore, sees the arrivals as distinct events and therefore concludes that the flashes aren't simultaneous since she was midway between the lightning strikes and she believes that the speed of light is c no matter who observes it.

*Snip*

I agree with you. The way the experiment is set up A sees the flashes simultaneous and the flashes are simultaneous events B sees the flashes not simultaneous and the flashes are not simultaneous events, because B has speed v.

However I have two problems First you can set up the experiment in a different way with B still having the same speed v such that: A sees the flashes not simultaneous and the flashes are not simultaneous events B sees the flashes simultaneous and the flashes are simultaneous events.

The two experiments are identical. For the second experiment, from the point of view of frame of B: B has a speed 0 and A has a speed v

But are the experiments truelly identical Is there a difference between the two. IMO there is a difference in signal strength in the two flashes received.

In the first experiment A sees the flashes simultaneous but of equal strength. In the second experiment B sees the flashes simultaneous but not of equal strength.

This becomes clear if you consider both experiments in the same frame of A.

In the first experiment B has to move outside the center to see the flashes simultaneous but then B sees them also at equal strength.

In the second experiment A sees the two flashes not simultaneous but at equal strength In order for A to see the two flashes simultaneous A has to move outside the center but then A sees them at not equal strength. This is the same way (strength) as B sees them.

Select

http://users.pandora.be/nicvroom/vabsolute.htm to study the above with drawn figures. In the figures both A and B are on a train.

The second problem has to do with length contraction. When the measured length of the train in the first experiment is L (with speed v) (L is also the difference in lightning marks) Then the proper length of the train is L / SQR(1 - v/c) (with speed 0)

In the second experiment assuming that the difference in lightning marks is still L Then the proper length of the train is L * SQR(1 - v/c) (with speed 0)

See same URL as above.

That means that the length of the train at v=0 and the length of the train at v<>0 in both experiments is different. Does this not imply physical different ?


3 Train Thought Experiment

Van: Wayne Throop
Onderwerp: Re: train though experiment
Datum: woensdag 28 maart 2001 21:31

> "Nicolaas Vroom" wrote
I agree with you. The way the experiment is set up A sees the flashes simultaneous and the flashes are simultaneous events B sees the flashes not simultaneous and the flashes are not simultaneous events, because B has speed v.

B doesn't "have speed v". B is moving at v wrt A. Speed isn't something an object "has", in and of itself. It is just as accurate to say that A is moving at -v wrt B; or in the misleading terminology, that B "has" speed 0, and A "has" speed -v.

So again. B doesn't "have speed v" in any meaningful intrinsic sense.

> However I have two problems First you can set up the experiment in a different way with B still having the same speed v such that: A sees the flashes not simultaneous and the flashes are not simultaneous events B sees the flashes simultaneous and the flashes are simultaneous events.

The two experiments are identical.

You contradict yourself. You just said the experiment was set up in a different way, and then you said the experiments are identical.

In fact, if you arrante for the light to reach B at the same time, you are not doing the same experiment, even if B has v wrt A.

> The second problem has to do with length contraction. When the measured length of the train in the first experiment is L (with speed v) (L is also the difference in lightning marks) Then the proper length of the train is L / SQR(1 - v /c ) (with speed 0)

In the second experiment assuming that the difference in lightning marks is still L Then the proper length of the train is L * SQR(1 - v /c ) (with speed 0)

So you are forced to squish the train in the second case, in order to make your assumption true. So what? As we already know, you are doing a completely different experiment. The fact that you have to squish the train to make your assumed initial conditions come out right is your problem, not any problem with relativity.

Wayne Throop throopw@sheol.org http://sheol.org/throopw "He's not just a Galaxy Ranger... he's a Super-Trooper!"


4 Train Thought Experiment

Van: John Anderson
Onderwerp: Re: train thought experiment
Datum: donderdag 29 maart 2001 6:36

Nicolaas Vroom wrote:
>


schreef in berichtnieuws 3A9F1D29.5CC5@attglobal.net...

> > Rod Ryker wrote:
> > > *Snip*
> > You're asking for answers to a problem that have given no context to. I'm not going to give one word answers. I'm going to supply some context and then answer the questions. I'm more interested in helping people understand this stuff than I am in giving you an opportunity to deliberately confuse them.

Assume the flashes are simultaneous according to the track observer, A. They occur at time = 0 according to A. The events where the flashes originate have coordinates (in (t,x) notation in A's rest frame):

(0,0) and (0,L) where L is the measured length of the train according to A. A is at spatial position L/2 and not moving in his rest frame, so that the light from both flashes reaches him at t = L/(2*c).

The lightning makes marks on the track and machines at both ends of the train make marks at the same time as the lightning. The marks are in exactly the SAME positions at spatial positions 0 and L (in A's coordinates). The will be in the same spatial positions according to any other observer.

An observer, B, on and at the center of the train when the lightning strikes will not observe the light from the flashes arrive at the same time. This is easily seen using A's coordinates. The flashes arrive at B at times L/(2*(1 - v/c)) for light from the back of the train and L/(2*(1 + v/c)) for light from the front of the train. This is because B moves toward the light from the front of the train and away from the light at the back of the train. The light arrivals are distinct events in A's rest frame. They can't be the same event in B's rest frame unless the coordinate transformation between the two frames is singular.

B, therefore, sees the arrivals as distinct events and therefore concludes that the flashes aren't simultaneous since she was midway between the lightning strikes and she believes that the speed of light is c no matter who observes it.

*Snip*

> I agree with you. The way the experiment is set up A sees the flashes simultaneous and the flashes are simultaneous events B sees the flashes not simultaneous and the flashes are not simultaneous events, because B has speed v.

However I have two problems First you can set up the experiment in a different way with B still having the same speed v such that: A sees the flashes not simultaneous and the flashes are not simultaneous events B sees the flashes simultaneous and the flashes are simultaneous events.

The two experiments are identical.

No, they're not. In one experiment, light from the flashes reaches A at the same time and, in the other, light from the flashes reach B at the same time. Since A and B are at the same place when the light is emitted but not when it's received, the two experiments are not identical.

> For the second experiment, from the point of view of frame of B: B has a speed 0 and A has a speed v

There's a more fundamental difference. In the original experiment, what you write above is true also. You're looking at the same experiment from two different frames. But in either frame, the light arrives from the flashes at the same time at A, not B. In the second experiment, light arrives at the same time at B, not A.

You're describing two different experiments, not the same experiment as described in 2 different frames.

> But are the experiments truelly identical Is there a difference between the two. IMO there is a difference in signal strength in the two flashes received.

There's a more fundamental one as I pointed out above.

> In the first experiment A sees the flashes simultaneous but of equal strength. In the second experiment B sees the flashes simultaneous but not of equal strength.

No. That involves some assumptions about how the light sources are moving relative to the observers. Such assumptions are not made in Einstein's gedanken experiment. He just made assumptions about where the sources were and when they emitted the light.

You're adding extra assumptions that have nothing to do with the gedanken experiment.

You have been posting ignorant crap about this gedanken for years now. Why don't you admit to yourself that you're never going to figure it out or that you don't want to figure it out.

John Anderson


5 Train Thought Experiment

Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: donderdag 29 maart 2001 21:50

Wayne Throop schreef in berichtnieuws 985807890@sheol.org...
> > "Nicolaas Vroom" wrote
I agree with you. The way the experiment is set up A sees the flashes simultaneous and the flashes are simultaneous events B sees the flashes not simultaneous and the flashes are not simultaneous events, because B has speed v.
>

B doesn't "have speed v". B is moving at v wrt A. Speed isn't something an object "has", in and of itself. It is just as accurate to say that A is moving at -v wrt B; or in the misleading terminology, that B "has" speed 0, and A "has" speed -v.

So again. B doesn't "have speed v" in any meaningful intrinsic sense.

I agree with you A is rest frame B has speed of v relative to A

> > However I have two problems First you can set up the experiment in a different way with B still having the same speed v such that: A sees the flashes not simultaneous and the flashes are not simultaneous events B sees the flashes simultaneous and the flashes are simultaneous events.

The two experiments are identical.

>

You contradict yourself. You just said the experiment was set up in a different way, and then you said the experiments are identical.

They are different because the only thing you have to change is the length of the train

> In fact, if you arrante for the light to reach B at the same time, you are not doing the same experiment, even if B has v wrt A.

Please read the reply of John Anderson and read my comments

Unfortunate there are no comments on the issue of signal strength.

> > The second problem has to do with length contraction. When the measured length of the train in the first experiment is L (with speed v) (L is also the difference in lightning marks) Then the proper length of the train is L / SQR(1 - v /c ) (with speed 0)

In the second experiment assuming that the difference in lightning marks is still L Then the proper length of the train is L * SQR(1 - v /c ) (with speed 0)

>

So you are forced to squish the train in the second case, in order to make your assumption true. So what?

Are you aware that the power of two factors are missing ?

I prefer the description of the train thought experiment as in the book Introducing Einsteins Relativity by Ray d'Inverno at page 23 In that book the initial condition are two firing devices (lightning marks) a distance L apart. For that configuration to work at a certain speed v of the train the length of the train (in the first experiment) in the rest frame (v=0) has to be L/SQR(1- v^2/c^2) (I do not fully understand the meaning of the word squish) In the second experiment (i.e. the train observer B sees the flashes simultaneous) for that configuration to work at a certain speed v of the train the length of the train in the rest frame (v=0) has to be L*SQR(1- v^2/c^2)

Nothing special or tricky is involved.

> As we already know, you are doing a completely different experiment.

Both experiments are almost identical. If you compare the first experiment from the rest frame of A with the second experiment from the rest frame of B they seem to be identical The important part is to compare them physical both from the rest frame of A.

> The fact that you have to squish the train to make your assumed initial conditions come out right is your problem, not any problem with relativity.

You have a real problem IMO with special relativity if you compare the strength of the signals (flashes, lamps, sparks, lightning) involved.

See http://users.pandora.be/nicvroom/vabsolute.htm

See also my reply to John Anderson in this discussion.


6 Train Thought Experiment

Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: donderdag 29 maart 2001 21:50

John Anderson
schreef in berichtnieuws
3AC2BBB5.5703@attglobal.net...
> Nicolaas Vroom wrote:
> >


schreef in berichtnieuws 3A9F1D29.5CC5@attglobal.net...

> > > Rod Ryker wrote:
> > > > *Snip*
> > > You're asking for answers to a problem that have given no context to. I'm not going to give one word answers. I'm going to supply some context and then answer the questions. I'm more interested in helping people understand this stuff than I am in giving you an opportunity to deliberately confuse them.

Assume the flashes are simultaneous according to the track observer, A. They occur at time = 0 according to A. The events where the flashes originate have coordinates (in (t,x) notation in A's rest frame):

(0,0) and (0,L) where L is the measured length of the train according to A. A is at spatial position L/2 and not moving in his rest frame, so that the light from both flashes reaches him at t = L/(2*c).

The lightning makes marks on the track and machines at both ends of the train make marks at the same time as the lightning. The marks are in exactly the SAME positions at spatial positions 0 and L (in A's coordinates). The will be in the same spatial positions according to any other observer.

An observer, B, on and at the center of the train when the lightning strikes will not observe the light from the flashes arrive at the same time. This is easily seen using A's coordinates. The flashes arrive at B at times L/(2*(1 - v/c)) for light from the back of the train and L/(2*(1 + v/c)) for light from the front of the train. This is because B moves toward the light from the front of the train and away from the light at the back of the train. The light arrivals are distinct events in A's rest frame. They can't be the same event in B's rest frame unless the coordinate transformation between the two frames is singular.

B, therefore, sees the arrivals as distinct events and therefore concludes that the flashes aren't simultaneous since she was midway between the lightning strikes and she believes that the speed of light is c no matter who observes it.

*Snip*

> > I agree with you. The way the experiment is set up A sees the flashes simultaneous and the flashes are simultaneous events B sees the flashes not simultaneous and the flashes are not simultaneous events, because B has speed v.

However I have two problems First you can set up the experiment in a different way with B still having the same speed v such that: A sees the flashes not simultaneous and the flashes are not simultaneous events B sees the flashes simultaneous and the flashes are simultaneous events.

The two experiments are identical.

>

No, they're not. In one experiment, light from the flashes reaches A at the same time and, in the other, light from the flashes reach B at the same time. Since A and B are at the same place when the light is emitted but not when it's received, the two experiments are not identical.

The position of A is fixed (in the sense of A being a frame at rest) and the same in both experiments (The distance L is assumed to be the same) The position of B is different when the light is emitted and received in the first experiment. Also in the second experiment. In the first B receives the light at two different positions. In the second B receives the light simultaneous.

But this has all to do the way the experiment is setup.

> > For the second experiment, from the point of view of frame of B: B has a speed 0 and A has a speed v
>

There's a more fundamental difference. In the original experiment, what you write above is true also. You're looking at the same experiment from two different frames. But in either frame, the light arrives from the flashes at the same time at A, not B. In the second experiment, light arrives at the same time at B, not A.

In the first light arrives at the same time at A. In the second light arrives at the same time at B.

> You're describing two different experiments, not the same experiment as described in 2 different frames.

The two experiments seem identical if you compare the first experiment from the A as rest frame with second experiment from the B as rest frame.

> > But are the experiments truelly identical Is there a difference between the two. IMO there is a difference in signal strength in the two flashes received.
>

There's a more fundamental one as I pointed out above.

I do not understand what you mean

See above what John wrote: Assume the flashes are simultaneous accordingly to observer A: That is experiment 1. Next consider: Assume the flashes are simultaneous accordingly observer B: That is experiment 2. The difference between those experiments for a certain speed v is that the proper length of the trains is different.

> > In the first experiment A sees the flashes simultaneous but of equal strength. In the second experiment B sees the flashes simultaneous but not of equal strength.
>

No. That involves some assumptions about how the light sources are moving relative to the observers.

If you study from the rest frame of A the light sources are not moving, assuming that each light source emits a flash (origin is the position of the firing devices) which propagates spherical.

> Such assumptions are not made in Einstein's gedanken experiment. He just made assumptions about where the sources were and when they emitted the light.

You're adding extra assumptions that have nothing to do with the gedanken experiment.

But they can be very important. A gedanken experiment describes an ideal situation but in principle you should be able to do it in real. In real you are able to control that both signals (sparks, flashes, lightning) are emitted with the same energy. In real you are able to measure the strength of the received signals. They should be in agreement with your predictions.

Why is it not allowed to include those tests ?

All the laws of physic "are the same" in every reference frame so I am allowed to use (test) all parameters to use or chalange if that is true

> You have been posting ignorant crap about this gedanken for years now.
I am asking questions to this newsgroup because not everything is clear to me. If someone asks me a question I will always try to answer the question without "ranking" the question

> Why don't you admit to yourself that you're never going to figure it out or that you don't want to figure it out.
Only by asking questions I can learn something, not by saying "Yes I understand" because I want to please my "teacher".

Have a look at http://users.pandora.be/nicvroom/

Try the programs.

Have a look at: http://xxx.lanl.gov/abs/gr-qc/0103036 The confrontation between General Relativity and Experiment By Clifford M Will


7 Train Thought Experiment

Van: Wayne Throop
Onderwerp: Re: train thought experiment
Datum: donderdag 29 maart 2001 22:32

> > > The two experiments are identical.

> > No, they're not.

> "Nicolaas Vroom" wrote
The position of A is fixed (in the sense of A being a frame at rest) and the same in both experiments (The distance L is assumed to be the same) The position of B is different when the light is emitted and received in the first experiment. Also in the second experiment. In the first B receives the light at two different positions. In the second B receives the light simultaneous.

But this has all to do the way the experiment is setup.

It has to do with the way the experiment is set up, because you are actually setting up two different experiments.

To see this clearly, simply consider what you have to do to your first experimental setup to get the two light flashes to reach B at the same time. You have to change the times at which you generate the flashes. They are no longer simultaneous in A's coordinates. You can no longer simply send them when two local A clocks reache a single agreed-upon value. The one from which B is receeding must be sent earlier, and the one towards which B is moving must be sent later.

The physical mechanism you use to decide when to flash those two lightsources is different in the two experiments. They are, in fact, two different experiments.

> In the first light arrives at the same time at A. In the second light arrives at the same time at B.

Right. Two different experiments, two different physical setups. Two different results. This is neither surprising nor difficult to understand.

> The two experiments seem identical if you compare the first experiment from the A as rest frame with second experiment from the B as rest frame.

The two experiments don't seem identical no matter how you compare them.

> I do not understand what you mean

Somehow, strange as it may seem, this does not surprise me.

Wayne Throop throopw@sheol.org http://sheol.org/throopw "He's not just a Galaxy Ranger... he's a Super-Trooper!"


8 Train Thought Experiment

Van: Wayne Throop
Onderwerp: Re: train though experiment
Datum: donderdag 29 maart 2001 22:53

> > > First you can set up the experiment in a different way [...] The two experiments are identical.

> > You contradict yourself. You just said the experiment was set up in a different way, and then you said the experiments are identical.

> "Nicolaas Vroom" wrote: They are different because the only thing you have to change is the length of the train.

Which means, the two experiments are not identical.

Further, this experiment does not require a change in the length of the train. That's only required when you perform a THIRD experiment, in which you insist that the length of the train in B's frame in th is new experiment be what it was in A's frame in the original experiment. But that change by itself will not cause B to receive the light pulses at the same time; changing the length ofthe train is neither sufficient nor necessary to acheive that goal.

> > So you are forced to squish the train in the second case, in order to make your assumption true. So what?

> Are you aware that the power of two factors are missing ?

Oh. So you did the calculations incorrectly. So what?

> Nothing special or tricky is involved.

Exactly.

> Both experiments are almost identical.

And they get almost the same results.

> You have a real problem IMO with special relativity if you compare the strength of the signals (flashes, lamps, sparks, lightning) involved.

But, for some reason, you fail to point out any such problem. You just claim one exists, somehow, somewhere, someway.

Whereas, in fact, there is no such problem. (Where "problem" is either a self-contradiction in SR, or a mismatch between SR and experimental results.)

Wayne Throop throopw@sheol.org http://sheol.org/throopw "He's not just a Galaxy Ranger... he's a Super-Trooper!"


9 Train Thought Experiment

Van: David Empey
Onderwerp: Re: train thought experiment
Datum: donderdag 29 maart 2001 23:47

throopw@sheol.org (Wayne Throop) wrote in <985897963@sheol.org>
:

snippage

>

Right. Two different experiments, two different physical setups. Two different results. This is neither surprising nor difficult to understand.

> "Nicolaas Vroom" wrote:

> > The two experiments seem identical if you compare the first experiment from the A as rest frame with second experiment from the B as rest frame.
>

The two experiments don't seem identical no matter how you compare them.

But there's an isomorphism between them, isn't there?

Interchange A and B, and v and -v, and you'll change one experiment to the other, won't you? If I'm correct, maybe that's what Vroom is getting at.

-- Dave Empey


10 Train Thought Experiment

Van: Russell Blackadar
Onderwerp: Re: train thought experiment
Datum: vrijdag 30 maart 2001 0:46

Wayne Throop wrote:
>
> > > >

First you can set up the experiment in a different way [...] The two experiments are identical.

>
> > >

You contradict yourself. You just said the experiment was set up in a different way, and then you said the experiments are identical.

>
> >

"Nicolaas Vroom" wrote:
They are different because the only thing you have to change is the length of the train.

>

Which means, the two experiments are not identical.

Further, this experiment does not require a change in the length of the train.

Well, sometimes it's hard to understand Nicolaas's writing, but I think he has in mind that the flashes are triggered by the front and back of the train and the triggers are at fixed positions on the track. That being the case, the only way to affect the flashes' relative timing in a given frame (and at a given v) is to adjust the proper length of the train.

But why he thinks an experiment with a train of different proper length is "identical" is anyone's guess.


11 Train Thought Experiment

Van: Wayne Throop
Onderwerp: Re: train thought experiment
Datum: vrijdag 30 maart 2001 4:24

> Russell Blackadar wrote

Ah. Thank you, that does make sense.

> But why he thinks an experiment with a train of different proper length is "identical" is anyone's guess.

Yes, that's the central issue; whence the claim that these experiments are "identical", even though there are coordinate-independent physical differences in the respective setups.

Wayne Throop throopw@sheol.org http://sheol.org/throopw "He's not just a Galaxy Ranger... he's a Super-Trooper!"


12 Train Thought Experiment

Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: vrijdag 30 maart 2001 10:40

Wayne Throop schreef in berichtnieuws 985919067@sheol.org...
> > Russell Blackadar wrote

Correct. (The original comes from Ray d'Inverno) And true for both experiments And true for each speed v of experiment 1 And true for each speed v of experiment 2

> Ah. Thank you, that does make sense.
> >

But why he thinks an experiment with a train of different proper length is "identical" is anyone's guess.

First you can compare the outcome of experiment 1 for different values of v. The experiment does not work for any value of v>0 when the rest length of the train is equal to the length L i.e. the distance between the firing devices (See Ray d'Inverno) The experiment only works for any value v when the proper length of the train has a specific value i.e. L/SQR(1-v^2/c^2)

All of those experiments 1 are identical. (A simultaneous)

The next step to ask is: Is it possible to perform the same experiment (Moving train with B in center, A at track in center, 2 firing devices a distance L apart) such that B sees the two signals simultaneous. This experiment is now called experiment 2. IMO the answer is yes. IMO you can even perform exp 2 with a moving train which has the same speed v as in exp 1. If you compare those two experiments the length of the train is different. If you compare the two experiments from the rest from of A versus the rest frame of B the two are identical. In exp 1 A has speed 0 and B has speed v In exp 1 B has speed 0 and A has speed v (you can argue about sign)

(In exp 2 the proper length of the train has to be L*SQR(1-v^2/c^2)

The real challenge starts if you compare both experiments from the same reference frame (You can either select A or B) If you select A then A receives both signals at equal strength in exp 1 In exp 2 B receives both signals simultaneous but IMO not at equal strength.

The question is can I use equal strength (energy received) as a concept to describe the physical reality.

If the answer is Yes then immediate the following question appears: Does A in rest frame truelly receive both signals at equal strength ? IMO in general the answer is NO.

> Yes, that's the central issue; whence the claim that these experiments are "identical", even though there are coordinate-independent physical differences in the respective setups.
Why do you use the words coordinate-independent ? The only physical differences between each set up is the speed of the train and the length of train.

The only physical difference between each set up of resp exp 1 and exp 2 for a given value of v is the length of the train. (the proper length of the train in the rest frame A has to be different.)

http://users.pandora.be/nicvroom/vabsolute.htm


13 Train Thought Experiment

Van: Wayne Throop
Onderwerp: Re: train thought experiment
Datum: vrijdag 30 maart 2001 23:46

> "Nicolaas Vroom" wrote

Why do you think it's a "challenge" for the signal strengths to be different in different experiments? Note: you did NOT compare the same experiment (say, expriment 1) from two different frames. You compared two PHYSICALLY DIFFERENT experiments in two frames. Why you think two physically different experiments must yield identical measures remains a complete mystery.

Wayne Throop throopw@sheol.org http://sheol.org/throopw "He's not just a Galaxy Ranger... he's a Super-Trooper!"


14 Train Thought Experiment

Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: zaterdag 31 maart 2001 16:05

Wayne Throop schreef in berichtnieuws 985988783@sheol.org...
> > "Nicolaas Vroom" wrote
>

Why do you think it's a "challenge" for the signal strengths to be different in different experiments? Note: you did NOT compare the same experiment (say, expriment 1) from two different frames. You compared two PHYSICALLY DIFFERENT experiments in two frames. Why you think two physically different experiments must yield identical measures remains a complete mystery.

Specific the last line is not clear to me. The word physical is not required. Different experiments implies different physical experiments. I do not give a judgement (my opinion) if different experiments must yield identical measures.

Please identify with which specific line or lines "you" disagree

The best way to study the train thought experiment if you use to trains. When the wheels of the trains make contact you get a spark. This are the lightning signals in the previous (on going) discussion. In the book by Ray D'Inverno this are two lamps.

Train 1 is called T. T is at rest. The train T has a length L. (proper length) Train 2 is called T'. T' has a speed v. Train T' has a length L' In train T there is an observer O at the center. (Same as observer A previous) In train T' there is an observer O' at the center. (Same as observer B previous)

In exp 1 observer O (was A)sees the sparks simultaneous. In exp 1 observer O' (was B) sees the sparks not simultaneous. For exp 1 to work the proper length of train T' must be L/SQR(1-v^2/c^2)

In exp 2 observer O sees the sparks not simultaneous. In exp 2 observer O' sees the sparks simultaneous. In exp 2 Train T' has speed v and train T is at rest. For exp 2 to work the proper length of train T' must be L*SQR(1-v^2/c^2)

You can also consider exp 2 from the rest frame of train T' Train T' is at rest Train T has a speed v

If you compare exp 1 with exp 2 you get Train at rest is resp T and T' Train with speed v is resp T' and T Observer which sees the signals simultaneous is resp O and O' Observer which sees the signals not simultaneous is resp O' and O

In exp 2 if the proper length of train T' is L than in order for the experiment to work the proper length of train T (in the rest frame of T') has to be L/SQR(1-v^2/c^2)

That means exp 1 and exp 2 compared from resp frame of T and T' seem to be identical.

There is one issue that I have a problem with and that is signal strength

Assume that each spark releases (emits) the same energy. Observer O in exp 1 claims that he sees both sparks simultaneous and with equal strength. (True ?) Observer O' in exp 2 sees both sparks simultaneous and should also see both sparks at equal strength assuming that both experiments are identical. IMO O' does not. The sparks O' sees are not of equal strength. (True ?)

IMO this is in conflict with SR which is based on the concept that all processes which are in relative motion should be identical.

To use the text by Ray d'Inverno Restricted principle of SR: "All inertial observers are equivalent as far as dynamical experiments are concerned." (All observers performing the same experiment must discover the same law) Principle of SR: "All inertial observers are equivalent.


15 Train Thought Experiment

Van: Wayne Throop
Onderwerp: Re: train thought experiment
Datum: zaterdag 31 maart 2001 20:01

> "Nicolaas Vroom" wrote

It's one way. It doesn't seem to be the "best way" in any meaningful sense. Certainly studying it this way hasn't seemed to have lent Nicholaas Vroom much useful insight.

> When the wheels of the trains make contact you get a spark. This are the lightning signals in the previous (on going) discussion. In the book by Ray D'Inverno this are two lamps.

We must guess, given what follows, that this actually means "endpoints of the train" where it says "wheels".

> Train 1 is called T. T is at rest.

There exist inertial coordinates in which it is at rest, at most. To say it "is at rest" is essentially meaningless in this context. And appropriate substitutions for "make contact".

> The train T has a length L. (proper length) Train 2 is called T'. T' has a speed v.

The speed of T' in T's rest coordinates is v. It is essentially meaningless in this context to say it "has speed v" without specifying "wrt what coordinate system".

> In train T there is an observer O at the center. In train T' there is an observer O' at the center.

> In exp 1 observer O (was A)sees the sparks simultaneous. In exp 1 observer O' (was B) sees the sparks not simultaneous. For exp 1 to work the proper length of train T' must be L/SQR(1-v^2/c^2)

In exp 2 observer O sees the sparks not simultaneous. In exp 2 observer O' sees the sparks simultaneous. In exp 2 Train T' has speed v and train T is at rest. For exp 2 to work the proper length of train T' must be L*SQR(1-v^2/c^2)

Right.

> You can also consider exp 2 from the rest frame of train T' Train T' is at rest Train T has a speed v

Of course you can.

> If you compare exp 1 with exp 2 you get Train at rest is resp T and T' Train with speed v is resp T' and T Observer which sees the signals simultaneous is resp O and O' Observer which sees the signals not simultaneous is resp O' and O

Right.

> In exp 2 if the proper length of train T' is L than in order for the experiment to work the proper length of train T (in the rest frame of T') has to be L/SQR(1-v^2/c^2)

Wrong, of course. The phrase "proper length of T (in the rest frame of T') is meaningless . Specifically, proper length is frame-independent, so "in the rest frame of T'" is without meaning.

> That means exp 1 and exp 2 compared from resp frame of T and T' seem to be identical.

No, they don't. Because what you did in defining the experiments was to hold the proper length of T constant between the two. This means that the proper length of the train at rest is NOT constant between the two, and thus the experiments do not even SEEM to be identical. Because the train at rest has a completely different proper length in one experiment vs the other.

In both experiments, the train in motion has the longer proper length. But you've just arranged it so that the proper length of the train in motion in one experiment happens to equal the proper length of the train at rest in the other. Big woop.

> There is one issue that I have a problem with and that is signal strength

And it is, indeed, YOUR problem, and not a problem with relativity.

> Assume that each spark releases (emits) the same energy. Observer O in exp 1 claims that he sees both sparks simultaneous and with equal strength. (True ?) Observer O' in exp 2 sees both sparks simultaneous and should also see both sparks at equal strength assuming that both experiments are identical. IMO O' does not. The sparks O' sees are not of equal strength. (True ?)

Not true. The signal strength differs between experiment 1 and 2. But that's because the train at rest is longer in 1 than in 2.

Nevertheless, O sees identical "signal strength", and so does O'. It's jut that O sees a different "signal strength" than O'.

> IMO this is in conflict with SR

However, your opinion is incorrect.

Wayne Throop throopw@sheol.org http://sheol.org/throopw "He's not just a Galaxy Ranger... he's a Super-Trooper!"


16 Train Thought Experiment

Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: maandag 2 april 2001 11:20

Wayne Throop schreef in berichtnieuws 986061671@sheol.org...
> > "Nicolaas Vroom" wrote
>

It's one way. It doesn't seem to be the "best way" in any meaningful sense. Certainly studying it this way hasn't seemed to have lent Nicholaas Vroom much useful insight.

We will see.

> > When the wheels of the trains make contact you get a spark. This are the lightning signals in the previous (on going) discussion. In the book by Ray D'Inverno this are two lamps.
>

We must guess, given what follows, that this actually means "endpoints of the train" where it says "wheels".

Your quess is correct.

> > Train 1 is called T. T is at rest.
>

There exist inertial coordinates in which it is at rest, at most.

Correct.

> To say it "is at rest" is essentially meaningless in this context. And appropriate substitutions for "make contact".
> > The train T has a length L. (proper length) Train 2 is called T'. T' has a speed v.
>

The speed of T' in T's rest coordinates is v. It is essentially meaningless in this context to say it "has speed v" without specifying "wrt what coordinate system".

Correct.

> > In train T there is an observer O at the center. In train T' there is an observer O' at the center.
>
> >

In exp 1 observer O (was A)sees the sparks simultaneous. In exp 1 observer O' (was B) sees the sparks not simultaneous. For exp 1 to work the proper length of train T' must be L/SQR(1-v^2/c^2)

This I call sentence 1
> >

In exp 2 observer O sees the sparks not simultaneous. In exp 2 observer O' sees the sparks simultaneous. In exp 2 Train T' has speed v and train T is at rest. For exp 2 to work the proper length of train T' must be L*SQR(1-v^2/c^2)

This I call sentence 2

> Right.
> >

You can also consider exp 2 from the rest frame of train T' Train T' is at rest Train T has a speed v

>

Of course you can.

> >

If you compare exp 1 with exp 2 you get Train at rest is resp T and T' Train with speed v is resp T' and T Observer which sees the signals simultaneous is resp O and O' Observer which sees the signals not simultaneous is resp O' and O

>

Right.

> >

In exp 2 if the proper length of train T' is L than in order for the experiment to work the proper length of train T (in the rest frame of T') has to be L/SQR(1-v^2/c^2)

>

Wrong, of course. The phrase "proper length of T (in the rest frame of T') is meaningless . Specifically, proper length is frame-independent, so "in the rest frame of T'" is without meaning.

My intention was to write the above the same as sentence 1 but then from the perspective of frame T'

> > That means exp 1 and exp 2 compared from resp frame of T and T' seem to be identical.
>

No, they don't. Because what you did in defining the experiments was to hold the proper length of T constant between the two. This means that the proper length of the train at rest is NOT constant between the two, and thus the experiments do not even SEEM to be identical. Because the train at rest has a completely different proper length in one experiment vs the other.

I should have written the two experiment are almost identical except that the proper length of the trains at rest are different. The two experiments are identical because (each of) the observer at rest sees the sparks (lights) simultaneous. The two experiments are identical because (each of) the moving observer sees the sparks (lights) not simultaneous.

> In both experiments, the train in motion has the longer proper length. But you've just arranged it so that the proper length of the train in motion in one experiment happens to equal the proper length of the train at rest in the other. Big woop.
> >

There is one issue that I have a problem with and that is signal strength

>

And it is, indeed, YOUR problem, and not a problem with relativity.

> > Assume that each spark releases (emits) the same energy. Observer O in exp 1 claims that he sees both sparks simultaneous and with equal strength. (True ?)
This is Question 1
> > Observer O' in exp 2 sees both sparks simultaneous and should also see both sparks at equal strength assuming that both experiments are identical. IMO O' does not. The sparks O' sees are not of equal strength. (True ?)
This is question 2

> Not true. The signal strength differs between experiment 1 and 2. But that's because the train at rest is longer in 1 than in 2.
Question 1 is solely related to experiment 1 Question 2 is solely related to experiment 2 I do not compare the strength between exp 1 and exp 2

> Nevertheless, O sees identical "signal strength", and so does O'.
This is not clear.

Two more Questions: In exp 1 O sees sparks simultaneous O' not In order for O' to see the sparks simultaneous O' has to stay at a position out of center in train T' When O' sees the sparks then simultaneous does he see them at "equal strength" ? IMO yes See http://users.pandora.be/nicvroom/vabsolute.htm#fig2

In exp 2 O sees sparks not simultaneous O' simultaneous In order for O to see the sparks simultaneous O has to stay at a position out of center in train T When O sees the sparks then simultaneous does he see them at "equal strength" ? IMO not See http://users.pandora.be/nicvroom/vabsolute.htm#fig3

> It's just that O sees a different "signal strength" than O'.
IF O' sees them at "equal strength" than I agree with this difference caused by the way I have specified the experiments But IF O' sees them at "equal strength" is still not clear.


17 Train Thought Experiment

Van: Wayne Throop
Onderwerp: Re: train thought experiment
Datum: maandag 2 april 2001 23:17

> "Nicolaas Vroom" wrote:

It is exactly as clear as whether O sees them at equal strength. No more, and no less. To clarify the issue, you must specify more precisely what you are measuring, and how the signals are generated. You cannot meaningfully idealize them as negligably short pulses, and at the same time discuss the energy they deliver to an observer.

The issue of whether O or O' (either one) will see equal or unequal signal strengths is entirely dependent on the motion of whatever object is actually generating the light pulse.

Wayne Throop throopw@sheol.org http://sheol.org/throopw "He's not just a Galaxy Ranger... he's a Super-Trooper!"


18 Train Thought Experiment

Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: dinsdag 3 april 2001 17:58

Wayne Throop
schreef in berichtnieuws
986246248@sheol.org...
> > "Nicolaas Vroom" wrote:
>

It is exactly as clear as whether O sees them at equal strength. No more, and no less. To clarify the issue, you must specify more precisely what you are measuring, and how the signals are generated. You cannot meaningfully idealize them as negligably short pulses, and at the same time discuss the energy they deliver to an observer.

The issue of whether O or O' (either one) will see equal or unequal signal strengths is entirely dependent on the motion of whatever object is actually generating the light pulse.

In order to measure signal strength you have to be sure that the two light pulses (sparks) generated in eacht experiment
have the same energy or Luminosity. Birghtness (signal strength) is the amount of energy measured by the Observer. The book Universe by Kaufmann in chapter 18 "The nature of stars" discusses this concept in detail.

In exp 1 O receives the two sparks simultaneous. You replied (Q1) with the same strength (brightness) In exp 2 O' receives the two sparks simultaneous. You also replied (Q2) with the same strength (brightness) You also answered an extra question (Q3) and you mention that if you compare exp1 the brightness that O receives with exp 2 the brightness that O' receives than O' receives less I agree if the first two questions are true. I have however certain doubts. IMO both cannot be true. To find out I asked two more questions:

In exp 1 O sees sparks simultaneous O' not In order for O' to see the sparks simultaneous O' has to stay at a position out of center in train T' When O' sees the sparks then simultaneous does he see them at "equal strength" brightness (Q4) ? IMO yes See http://users.pandora.be/nicvroom/vabsolute.htm#fig2

In exp 2 O sees sparks not simultaneous O' simultaneous In order for O to see the sparks simultaneous O has to stay at a position out of center in train T When O sees the sparks then simultaneous does he see them at "equal strength" brightness (Q5) ? IMO not See http://users.pandora.be/nicvroom/vabsolute.htm#fig3

To know the answers of both questions is very important. I expect the best way to measure brightness is to use CCD's.

In Chapter 6 (Optics and telescopes) about CCD's is written: "When an image from a telescope is focused on the CCD, an electric charge builds up in each pixel in proportion to the intensity of the light falling on that pixel." That means IMO a CCD (one for each signal) can be used both to detect if the light signals are received simultaneous and what the brightness is.


19 Train Thought Experiment

Van: Wayne Throop
Onderwerp: Re: train thought experiment
Datum: dinsdag 3 april 2001 19:44

> "Nicolaas Vroom" wrote:
have the same energy or Luminosity.

Which is irrelevant, since the proper luminosity being equal is not at issue. The motion of the lightsource is. You have carefully not specified the motion of the lightsource, and treated the light emission as a negligably short event. Hence, your confusion.

Wayne Throop throopw@sheol.org http://sheol.org/throopw "He's not just a Galaxy Ranger... he's a Super-Trooper!"


20 Train Thought Experiment

Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: dinsdag 3 april 2001 22:48

Wayne Throop
schreef in berichtnieuws
986319868@sheol.org...
> > "Nicolaas Vroom" wrote:
have the same energy or Luminosity.
>

Which is irrelevant, since the proper luminosity being equal is not at issue.

Why
> The motion of the lightsource is.
Please explain
> You have carefully not specified the motion of the lightsource, and treated the light emission as a negligably short event. Hence, your confusion.

I do not understand your change of attitude. First you answer two of my questions Than you even answered a third question All those questions were related to signal strength and brightness

I raised two new questions and now apparently you have a problem with your previous answers, or am I wrong ?

If you want to compare signal strength (brightness) your source signals have to be identical. What have the speed of those signals to do with this issue. IMO the light emission must be a short event. If they take a long time how can you measure (establish) that they are truelly simultaneous ?

I truelly hope that you are going to answers my two new questions.


21 Train Thought Experiment

Van: Wayne Throop
Onderwerp: Re: train thought experiment
Datum: woensdag 4 april 2001 7:20

> "Nicolaas Vroom" wrote:
I raised two new questions and now apparently you have a problem with your previous answers, or am I wrong ?

I'd say that was definitely the "you are wrong" case. Neither my attitude, nor my opinion of my prior answers, has changed. But perhaps I was unclear; if we presume as a given that O sees equal signal strengths, and if the lightsources move in the O' rest frame in the second experiment as they did in the O rest frame in the first, then O' will also see equal signal strengths.

But then, you never state how the signal sources are moving. Your conclusion of a changed signal strength is unsupportable on the data you give, since you didn't include enough information to conclude either that O sees equal strength, or that O' does not, given equal proper luminosity of the sources.

> What have the speed of those signals to do with this issue.

Nothing. The speed of the signals is c, no matter which experiment, no matter which frame. The speed of the signal SOURCES, however, has a lot to "do with this issue". Or perhaps you never heard of doppler shift?

> IMO the light emission must be a short event.

But it is not negligably short if you are reckoning the energy delivered to a distance target.

> If they take a long time how can you measure (establish) that they are truelly simultaneous ?

They can be adequately modeled as taking a short time, compared to the light transit times. They cannot be adequately modeled as taking a short time, compared to the wavelength (ie, energy) of the light flashes themselves.

You can think of it as accounting for doppler shifts without accounting for the nonzero emission times; but the two notions are closely interrelated, whether you realize it or not.

Wayne Throop throopw@sheol.org http://sheol.org/throopw "He's not just a Galaxy Ranger... he's a Super-Trooper!"


22 Train Thought Experiment

Van: John Anderson
Onderwerp: Re: train thought experiment
Datum: zaterdag 7 april 2001 6:49

Nicolaas Vroom wrote:
>


schreef in berichtnieuws 3AC2BBB5.5703@attglobal.net...

> > Nicolaas Vroom wrote:
> > >


schreef in berichtnieuws 3A9F1D29.5CC5@attglobal.net...

> > > > Rod Ryker wrote:
> > > > > *Snip*
> > > > You're asking for answers to a problem that have given no context to. I'm not going to give one word answers. I'm going to supply some context and then answer the questions. I'm more interested in helping people understand this stuff than I am in giving you an opportunity to deliberately confuse them.

Assume the flashes are simultaneous according to the track observer, A. They occur at time = 0 according to A. The events where the flashes originate have coordinates (in (t,x) notation in A's rest frame):

(0,0) and (0,L) where L is the measured length of the train according to A. A is at spatial position L/2 and not moving in his rest frame, so that the light from both flashes reaches him at t = L/(2*c).

The lightning makes marks on the track and machines at both ends of the train make marks at the same time as the lightning. The marks are in exactly the SAME positions at spatial positions 0 and L (in A's coordinates). The will be in the same spatial positions according to any other observer.

An observer, B, on and at the center of the train when the lightning strikes will not observe the light from the flashes arrive at the same time. This is easily seen using A's coordinates. The flashes arrive at B at times L/(2*(1 - v/c)) for light from the back of the train and L/(2*(1 + v/c)) for light from the front of the train. This is because B moves toward the light from the front of the train and away from the light at the back of the train. The light arrivals are distinct events in A's rest frame. They can't be the same event in B's rest frame unless the coordinate transformation between the two frames is singular.

B, therefore, sees the arrivals as distinct events and therefore concludes that the flashes aren't simultaneous since she was midway between the lightning strikes and she believes that the speed of light is c no matter who observes it.

*Snip*

> > > I agree with you. The way the experiment is set up A sees the flashes simultaneous and the flashes are simultaneous events B sees the flashes not simultaneous and the flashes are not simultaneous events, because B has speed v.

However I have two problems First you can set up the experiment in a different way with B still having the same speed v such that: A sees the flashes not simultaneous and the flashes are not simultaneous events B sees the flashes simultaneous and the flashes are simultaneous events.

The two experiments are identical.

> >

No, they're not. In one experiment, light from the flashes reaches A at the same time and, in the other, light from the flashes reach B at the same time. Since A and B are at the same place when the light is emitted but not when it's received, the two experiments are not identical.

>

The position of A is fixed (in the sense of A being a frame at rest)

There is no distinction based on one frame being at rest. The gedanken experiment ARBITRARILY assumes that the flashes are simultaneous to one observer. The gedanken experiment then shows that the other observer can't agree that the flashes are simultaneous.

John Anderson


23 Train Thought Experiment

Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: woensdag 11 april 2001 13:36

Wayne Throop schreef in berichtnieuws 986361618@sheol.org...
> > "Nicolaas Vroom" wrote:
I raised two new questions and now apparently you have a problem with your previous answers, or am I wrong ?
>

I'd say that was definitely the "you are wrong" case. Neither my attitude, nor my opinion of my prior answers, has changed. But perhaps I was unclear; if we presume as a given that O sees equal signal strengths, and if the lightsources move in the O' rest frame in the second experiment as they did in the O rest frame in the first, then O' will also see equal signal strengths.

Accordingly to the book Universe by Kaufmann at page 348 brightness is calculated by the formula (1) : b = L/4*pi*r^2 This is the same as the signal strength discussed above. Assume that both lightsources have the same Luminosity L than O, being at equal distance from those lightsources will see both: the lightsources simulataneous and with equal brightness.

Assume there is a different observer O1, which passes O at the same moment when O sees the lightsources. Does O1 sees the lightsources simultaneous ? IMO yes. Does O1 sees the lightsources with equal brightness ? IMO yes if the above formula applies. My answer is undecided if doppler shift is involved.

In the first example the observer O' has a speed v relative to O (rest frame) O' is placed at center of train T' O' does not see the lightsources simultaneous. In Question 4 Observer O' is placed slightly of center such that he sees the two lightsources simultaneous. For O there is no change. IMO this situation is exactly the same as for observer O1. i.e. Does O' sees the lightsources with equal brightness ? IMO yes if the above formula applies. My answer is undecided if doppler shift is involved.

Experiment 2 is almost identical as Experiment 1 except that the length of train T' (with O') has changed. O' is at center of train T' O' sees the lightsources simultaneous. The Luminosity of the lightsources is identical. O sees the lightsources not simultaneous.

If O positions himself such that he sees the light- sources simultaneous he will say the following. - I see the light sources simultaneous - They are not of the same brightness. - The distance to the lightsources is different. - The same situation applies for observer O' - O' sees the lightsources simultaneous - O' sees them also with different brightness - Except if dobbler shift is involved

O' can only see them with equal brightness if the two effects (distance / dobbler shift) cancel out.

> But then, you never state how the signal sources are moving. Your conclusion of a changed signal strength is unsupportable on the data you give, since you didn't include enough information to conclude either that O sees equal strength, or that O' does not, given equal proper luminosity of the sources.

I hope I have made myself more clearly

> > What have the speed of those signals to do with this issue.

This should have been speed of signal sources.

> Nothing. The speed of the signals is c, no matter which experiment, no matter which frame. The speed of the signal SOURCES, however, has a lot to "do with this issue". Or perhaps you never heard of doppler shift?

For me the relation between brightness and source signal speed (frequency) is not clear. My first impression is nothing, because brightness is only a function of distance r.

> > IMO the light emission must be a short event.
>

But it is not negligably short if you are reckoning the energy delivered to a distance target.

> >

If they take a long time how can you measure (establish) that they are truelly simultaneous ?

>

They can be adequately modeled as taking a short time, compared to the light transit times. They cannot be adequately modeled as taking a short time, compared to the wavelength (ie, energy) of the light flashes themselves.

In both example 1 and 2 the emitted wavelength of the lightsources is the same in frame of observer O. (For O' in his frame they are also the same but with a different value)

> You can think of it as accounting for doppler shifts without accounting for the nonzero emission times; but the two notions are closely interrelated, whether you realize it or not.


24 Train Thought Experiment

Van: Wayne Throop
Onderwerp: Re: train thought experiment
Datum: woensdag 11 april 2001 20:10

> "Nicolaas Vroom" wrote:

Big woop. He, too, is neglecting source motion.

Wayne Throop throopw@sheol.org http://sheol.org/throopw "He's not just a Galaxy Ranger... he's a Super-Trooper!"


25 Train Thought Experiment

Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: donderdag 12 april 2001 10:38

Wayne Throop
schreef in berichtnieuws
987012631@sheol.org...
> > "Nicolaas Vroom" wrote:
>

Big woop. He, too, is neglecting source motion.

This reply leaves me in the dark. Specific on the subject Luminosity and Brightness

In my previous reply I raised the following issue:

> Assume that both lightsources have the same Luminosity L than O, being at equal distance from those lightsources will see both: the lightsources simulataneous and with equal brightness.

> Assume there is a different observer O1, which passes O at the same moment when O sees the lightsources. Does O1 sees the lightsources simultaneous ? IMO yes. Does O1 sees the lightsources with equal brightness ? IMO yes if the above formula applies. My answer is undecided if doppler shift is involved.

I hope there is someone who can explain the relation between brightness with signal source speed, observer speed distance and doppler shift


26 Train Thought Experiment

Van: Wayne Throop
Onderwerp: Re: train thought experiment
Datum: donderdag 12 april 2001 19:06

> > He, too, is neglecting source motion.

> "Nicolaas Vroom" wrote:

> I hope there is someone who can explain the relation between brightness with signal source speed, observer speed distance and doppler shift

Well, first simply consider doppler. Clearly, if the source is moving towards you, you will get more energy-per-unit-time delivered than if the equivalent source were moving away. Next, consider a symmetric emission of light in all directions (represent it, say, by evenly spaced concentric circles around the point of emission from the perspective of the source's rest frame) and then transform that to another frame of reference. You get both doppler, and if you track the corresponding points on those circles, you get a focussing effect in the direction of travel.

This is not just theoretical handwaving; both effects are experimentally observed.

Wayne Throop throopw@sheol.org http://sheol.org/throopw "He's not just a Galaxy Ranger... he's a Super-Trooper!"


27 Train Thought Experiment

Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: zaterdag 14 april 2001 17:57

John Anderson
schreef in berichtnieuws
3ACE9C6E.6F4A@attglobal.net...
> Nicolaas Vroom wrote:
> >


schreef in berichtnieuws 3AC2BBB5.5703@attglobal.net...

> > > Nicolaas Vroom wrote:
> > > >

I agree with you. The way the experiment is set up A sees the flashes simultaneous and the flashes are simultaneous events B sees the flashes not simultaneous and the flashes are not simultaneous events, because B has speed v.

However I have two problems First you can set up the experiment in a different way with B still having the same speed v such that: A sees the flashes not simultaneous and the flashes are not simultaneous events B sees the flashes simultaneous and the flashes are simultaneous events.

The two experiments are identical.

> > >

No, they're not. In one experiment, light from the flashes reaches A at the same time and, in the other, light from the flashes reach B at the same time. Since A and B are at the same place when the light is emitted but not when it's received, the two experiments are not identical.

> >

The position of A is fixed (in the sense of A being a frame at rest)

>

There is no distinction based on one frame being at rest. The gedanken experiment ARBITRARILY assumes that the flashes are simultaneous to one observer. The gedanken experiment then shows that the other observer can't agree that the flashes are simultaneous.

I agree however I prefer a slightly different description: The train gedanken experiment ARBITRARILY assumes that one observer O sees the flashes simultaneous. The gedanken experiment then shows that the other observer O' then sees the flashes not simultaneous.

However this is not all. You can also set up the experiment such that the moving observer O' sees the flashes simultaneous and the observer O at rest not. (the moving observer O' becomes than the observer at rest and vice versa) I call this experiment 2. The original set up is exp 1

IMO this raises an interesting argument: Does O agree with all the observations of O' (in both experiments) and does O' agree with all the observations with O

For example O in exp 1 can make the following statement: I see both flashes with equal brightness. O' in exp 2 can also make the following statement: I see both flashes with equal brightness.

IMO both statements are not true. IMO O will state that O's statement is false.

See my discussion with Wayne Throop for more details.


28 Train Thought Experiment

Van: Wayne Throop
Onderwerp: Re: train thought experiment
Datum: zaterdag 14 april 2001 18:49

> "Nicolaas Vroom" wrote:

And, since simultaneous is defined (you may say "arbitrarily defined") to refer to events for which light reaches a midpoint together, they are actually simultaneous to O, and actually not simultaneous to O', not merely "seen simultaneous".

> However this is not all. You can also set up the experiment such that the moving observer O' sees the flashes simultaneous and the observer O at rest not. (the moving observer O' becomes than the observer at rest and vice versa) I call this experiment 2. The original set up is exp 1

And of course, this fact is both obvious, and shows absolutely no flaw whatsoever in relativity.

> IMO both statements are not true. IMO O will state that O's statement is false.

Yes, but then your opinion is based on neglecting doppler and related effects.

Wayne Throop throopw@sheol.org http://sheol.org/throopw

"He's not just a Galaxy Ranger... he's a Super-Trooper!"


29 Train Thought Experiment

Van: John Anderson
Onderwerp: Re: train thought experiment
Datum: zondag 15 april 2001 7:20

Nicolaas Vroom wrote:
>


schreef in berichtnieuws 3ACE9C6E.6F4A@attglobal.net...

> > Nicolaas Vroom wrote:
> > >


schreef in berichtnieuws 3AC2BBB5.5703@attglobal.net...

> > > > Nicolaas Vroom wrote:
> > > > >

I agree with you. The way the experiment is set up A sees the flashes simultaneous and the flashes are simultaneous events B sees the flashes not simultaneous and the flashes are not simultaneous events, because B has speed v.

However I have two problems First you can set up the experiment in a different way with B still having the same speed v such that: A sees the flashes not simultaneous and the flashes are not simultaneous events B sees the flashes simultaneous and the flashes are simultaneous events.

The two experiments are identical.

> > > >

No, they're not. In one experiment, light from the flashes reaches A at the same time and, in the other, light from the flashes reach B at the same time. Since A and B are at the same place when the light is emitted but not when it's received, the two experiments are not identical.

> > >

The position of A is fixed (in the sense of A being a frame at rest)

> >

There is no distinction based on one frame being at rest. The gedanken experiment ARBITRARILY assumes that the flashes are simultaneous to one observer. The gedanken experiment then shows that the other observer can't agree that the flashes are simultaneous.

>

I agree however I prefer a slightly different description: The train gedanken experiment ARBITRARILY assumes that one observer O sees the flashes simultaneous. The gedanken experiment then shows that the other observer O' then sees the flashes not simultaneous.

However this is not all. You can also set up the experiment such that the moving observer O' sees the flashes simultaneous and the observer O at rest not. (the moving observer O' becomes than the observer at rest and vice versa) I call this experiment 2. The original set up is exp 1

IMO this raises an interesting argument: Does O agree with all the observations of O' (in both experiments) and does O' agree with all the observations with O

For example O in exp 1 can make the following statement: I see both flashes with equal brightness. O' in exp 2 can also make the following statement: I see both flashes with equal brightness.

IMO both statements are not true. IMO O will state that O's statement is false.

You're talking about two different experiments for which O and O' have different observations in both. What's the point of asking

"Does O agree with all the observations of O' in both experiments) and does O' agree with all the observations with O"

You have already stated that this isn't the case, so why ask the question?

I don't care about the relative brightness. It isn't the point of the gedanken experiment. The two observers don't and don't have to agree about anything in both experiments except that things that happen at the same spacetime event will be seen by both to happen at a single event.

Your obsession with this gedanken experiment is unbelievable. It isn't a cornerstone of SR. It is just a demonstration of how relativity of simultaneity is a consequence of assuming that all observers measure the same speed of light.

You need to challenge SR with real experiments, not by attacking an example of what the logical consequnces of the theory are. The example is not inconsistent unless you arbitrarily deny relativity of simultaneity.

John Anderson


30 Train Thought Experiment

Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: zondag 15 april 2001 13:13


schreef in berichtnieuws
3AD92F83.7F85@attglobal.net...
> Nicolaas Vroom wrote:
> >

I agree however I prefer a slightly different description: The train gedanken experiment ARBITRARILY assumes that one observer O sees the flashes simultaneous. The gedanken experiment then shows that the other observer O' then sees the flashes not simultaneous.

However this is not all. You can also set up the experiment such that the moving observer O' sees the flashes simultaneous and the observer O at rest not. (the moving observer O' becomes than the observer at rest and vice versa) I call this experiment 2. The original set up is exp 1

IMO this raises an interesting argument: Does O agree with all the observations of O' (in both experiments) and does O' agree with all the observations with O

For example O in exp 1 can make the following statement: I see both flashes with equal brightness. O' in exp 2 can also make the following statement: I see both flashes with equal brightness.

IMO both statements are not true. IMO O will state that O's statement is false.

>

You're talking about two different experiments for which O and O' have different observations in both. What's the point of asking

"Does O agree with all the observations of O' in both experiments) and does O' agree with all the observations with O"

You have already stated that this isn't the case, so why ask the question?

Suppose two observers perform the same experiments. The Restricted Principle of SR and Principle of SR "imply" that both observers observe the same.

Suppose each observer can observe what the other is performing. Should not each observer agree with the results of the other observer ?

I have done more or less the same except that the two experiments are not the same but similar.

I hope that this will increase my understanding.

> I don't care about the relative brightness. It isn't the point of the gedanken experiment. The two observers don't and don't have to agree about anything in both experiments except that things that happen at the same spacetime event will be seen by both to happen at a single event.

IMO in general your point of view is too restricted. I am not saying that you are wrong.

> Your obsession with this gedanken experiment is unbelievable. It isn't a cornerstone of SR. It is just a demonstration of how relativity of simultaneity is a consequence of assuming that all observers measure the same speed of light.

One of the cornerstones SR is length contraction. If the length between the contacts is L and the length of the train in the rest frame is L' than the gedanken experiment only works for one particular speed v of the train such that L' = L / SQR(1-v^2/c^2) One of the cornerstones of SR is a rest frame The implications of that concept I want to investigate.

> You need to challenge SR with real experiments,

I fully agree with you. That is why I introduce the concept of brightness (photon count with CCD's) to see if that supports the concepts of SR.

> not by attacking an example of what the logical consequences of the theory are.

I am not attacking anything. I have certain doubts. That is why, in order to explain my concern and to solve my misunderstanding I prefer to broaden the scope of the experiment.


31 Train Thought Experiment

Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: donderdag 19 april 2001 10:04

Wayne Throop
schreef in berichtnieuws
987095206@sheol.org...
> > > He, too, is neglecting source motion.
>
> >

"Nicolaas Vroom" wrote:

>
> >

I hope there is someone who can explain the relation between brightness with signal source speed, observer speed distance and doppler shift

>

Well, first simply consider doppler. Clearly, if the source is moving towards you, you will get more energy-per-unit-time delivered than if the equivalent source were moving away. Next, consider a symmetric emission of light in all directions (represent it, say, by evenly spaced concentric circles around the point of emission from the perspective of the source's rest frame) and then transform that to another frame of reference. You get both doppler, and if you track the corresponding points on those circles, you get a focussing effect in the direction of travel.

I think a more detailed explanation is required to solve the issue.

Four Questions.

1. Consider an Observer O at rest a distance r away from a light source. This light source emits a pulse with total Luminosity of L Question how much total brightness B does O measure using a CCD. Answer: B = L / ( 4 * pi * r^2 )

2. Consider an Observer O' which moves with a speed v towards the light source. O' is at the same distance r away when he receives the pulse. (O meets O' at distance r from lightsource) Question how much total brightness B' does O' measure using a CCD. Answer: B' is slightly more than B

3. Consider an Observer O'' which moves with a speed v away from the light source. O'' is at the same distance r away when he receives the pulse. (O meets O' and O'' at distance r from lightsource) Question how much total brightness B'' does O'' measure using a CCD. Answer: B'' is slightly more than B

4. Is the Total Brightness measured by O' and O'' the same. Answer: Yes


32 Train Thought Experiment

Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: zaterdag 21 april 2001 11:12

Nicolaas Vroom
schreef in berichtnieuws
_ZwD6.2026$ii.302512@afrodite.telenet-ops.be...
>

Wayne Throop
schreef in berichtnieuws 987095206@sheol.org...

> > > > He, too, is neglecting source motion.
> >
> > >

"Nicolaas Vroom" wrote:

> >
> > >

I hope there is someone who can explain the relation between brightness with signal source speed, observer speed distance and doppler shift

> >

Well, first simply consider doppler. Clearly, if the source is moving towards you, you will get more energy-per-unit-time delivered than if the equivalent source were moving away. Next, consider a symmetric emission of light in all directions (represent it, say, by evenly spaced concentric circles around the point of emission from the perspective of the source's rest frame) and then transform that to another frame of reference. You get both doppler, and if you track the corresponding points on those circles, you get a focussing effect in the direction of travel.

>

I think a more detailed explanation is required to solve the issue.

Four Questions.

1. Consider an Observer O at rest a distance r away from a light source. This light source emits a pulse with total Luminosity of L Question how much total brightness B does O measure using a CCD. Answer: B = L / ( 4 * pi * r^2 )

2. Consider an Observer O' which moves with a speed v towards the light source. O' is at the same distance r away when he receives the pulse. (O meets O' at distance r from lightsource) Question how much total brightness B' does O' measure using a CCD. Answer: B' is slightly more than B

3. Consider an Observer O'' which moves with a speed v away from the light source. O'' is at the same distance r away when he receives the pulse. (O meets O' and O'' at distance r from lightsource) Question how much total brightness B'' does O'' measure using a CCD. Answer: B'' is slightly more than B

4. Is the Total Brightness measured by O' and O'' the same. Answer: Yes

Maybe the following sequence of steps helps: 1. Consider two trains T and T'. At train T is observer O in center. At train T' is observer O' in center Train T is at rest. Train T' has a speed v. The length of train T is L. (Equivalent with distance between marker points near track) The length of train T' in the rest frame of T is L' L<>L' Observer O sees the sparks, flashes simultaneous. Observer O sees the sparks with the same brightness. Observer O' sees the sparks not simultaneous.

2. Change the length L' of train T' The speed of train T' stays v what will happen ? Observer O sees the sparks, flashes NOT simultaneous. Observer O sees the sparks with the same brightness. (The length of L did not change) Observer O' sees the sparks not simultaneous.

3. Change the length L' of train T' such that O' sees the sparks simultaneous. what will happen ? Observer O sees the sparks, flashes NOT simultaneous. Observer O sees the sparks with the same brightness. (The length of L did not change) Observer O' sees the sparks simultaneous. Observer O' sees the sparks also with equal brightness

4. That means also in step 1 and 2 O' sees the flashes with equal brightness.

5. But that is very difficult to understand for Observer O in step 1. O will argue: a. At the event of the sparks O' was equidistant b. O' moves to the right c. O' sees the right flash before the left flash because O' moves towards the right and away from the left i.e. the distance "travelled" by the flash is different (relativity of simultaneity) d O' should also see the flashes with different brightness.

6. The observation of O' and the understanding of O are different. What is the solution.


Created: 25 June 2001

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