| 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 |
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
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
https://www.nicvroom.be/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 - vē/cē) (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 - vē/cē) (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 ?
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.
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.
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!"
Nicolaas Vroom wrote:
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*
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.
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.
There's a more fundamental one as I pointed out
above.
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
Wayne Throop
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
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
Please read the reply of John Anderson
and read my comments
Unfortunate there are no comments on the issue of signal strength.
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.
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.
You have a real problem IMO with special relativity if you compare
the strength of the signals (flashes, lamps, sparks, lightning) involved.
See
https://www.nicvroom.be/vabsolute.htm
See also my reply to John Anderson in this discussion.
John Anderson
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*
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.
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.
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.
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.
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.
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
Have a look at
https://www.nicvroom.be/
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
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.
Right. Two different experiments, two different physical setups.
Two different results. This is neither surprising nor difficult to understand.
The two experiments don't seem identical no matter how you compare them.
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!"
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.
Oh. So you did the calculations incorrectly. So what?
Exactly.
And they get almost the same results.
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!"
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.
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
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"
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.
Ah. Thank you, that does make sense.
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!"
Wayne Throop
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
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.
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.)
https://www.nicvroom.be/vabsolute.htm
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!"
Wayne Throop
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.
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 must guess, given what follows, that this actually
means "endpoints of the train" where it says "wheels".
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 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 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.
Of course you can.
Right.
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.
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.
And it is, indeed, YOUR problem, and not a problem with relativity.
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'.
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!"
Wayne Throop
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 must guess, given what follows, that this actually
means "endpoints of the train" where it says "wheels".
There exist inertial coordinates in which it is at rest, at most.
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 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
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.
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.
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.
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
https://www.nicvroom.be/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
https://www.nicvroom.be/vabsolute.htm#fig3
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!"
Wayne Throop
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
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
https://www.nicvroom.be/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
https://www.nicvroom.be/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.
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!"
Wayne Throop
Which is irrelevant, since the proper luminosity being equal
is not at issue.
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.
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.
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?
But it is not negligably short if you are reckoning the energy
delivered to a distance target.
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!"
Nicolaas Vroom wrote:
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*
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
Wayne Throop
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.
I hope I have made myself more clearly
This should have been speed of signal sources.
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.
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)
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!"
Wayne Throop
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:
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!"
John Anderson
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.
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".
And of course, this fact is both obvious, and shows absolutely
no flaw whatsoever in relativity.
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!"
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
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.
IMO in general your point of view is too restricted.
I am not saying that you are wrong.
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.
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.
Wayne Throop
"Nicolaas Vroom"
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.
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
Nicolaas Vroom
Wayne Throop
"Nicolaas Vroom"
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.
Back to my home page Contents of This Document
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.
3 Train Thought Experiment
Van: Wayne Throop
Onderwerp: Re: train though experiment
Datum: woensdag 28 maart 2001 21:31
>
"Nicolaas Vroom"
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 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)
4 Train Thought Experiment
Van: John Anderson
Onderwerp: Re: train thought experiment
Datum: donderdag 29 maart 2001 6:36
>
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.
>
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.
>
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.
5 Train Thought Experiment
Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: donderdag 29 maart 2001 21:50
> >
"Nicolaas Vroom"
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.
>
>
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)
>
>
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.
6 Train Thought Experiment
Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: donderdag 29 maart 2001 21:50
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.
> >
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.
>
> >
For the second experiment,
from the point of view of frame of B:
B has a speed 0 and A has a speed v
>
>
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.
>
> >
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.
>
>
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.
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
>
You have been posting ignorant crap about this gedanken
for years now.
Only by asking questions I can learn something, not by
saying "Yes I understand" because I want to please my "teacher".
>
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.
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"
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.
>
In the first light arrives at the same time at A.
In the second light arrives at the same time at B.
>
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.
>
I do not understand what you mean
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"
> >
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 ?
>
Nothing special or tricky is involved.
>
Both experiments are almost identical.
>
You have a real problem IMO with special relativity if you compare
the strength of the signals (flashes, lamps, sparks, lightning) involved.
9 Train Thought Experiment
Van: David Empey
Onderwerp: Re: train thought experiment
Datum: donderdag 29 maart 2001 23:47
:
>
>
"Nicolaas Vroom"
> >
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.
>
10 Train Thought Experiment
Van: Russell Blackadar
Onderwerp: Re: train thought experiment
Datum: vrijdag 30 maart 2001 0:46
>
> > > >
>
> > >
>
> >
They are different because the only thing you have to change is the
length of the train.
>
11 Train Thought Experiment
Van: Wayne Throop
Onderwerp: Re: train thought experiment
Datum: vrijdag 30 maart 2001 4:24
>
Russell Blackadar
>
But why he thinks an experiment with a train of different
proper length is "identical" is anyone's guess.
12 Train Thought Experiment
Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: vrijdag 30 maart 2001 10:40
> >
Russell Blackadar
>
Ah. Thank you, that does make sense.
> >
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.
>
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.
13 Train Thought Experiment
Van: Wayne Throop
Onderwerp: Re: train thought experiment
Datum: vrijdag 30 maart 2001 23:46
>
"Nicolaas Vroom"
14 Train Thought Experiment
Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: zaterdag 31 maart 2001 16:05
> >
"Nicolaas Vroom"
>
15 Train Thought Experiment
Van: Wayne Throop
Onderwerp: Re: train thought experiment
Datum: zaterdag 31 maart 2001 20:01
>
"Nicolaas Vroom"
>
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.
>
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)
>
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
16 Train Thought Experiment
Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: maandag 2 april 2001 11:20
> >
"Nicolaas Vroom"
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.
Your quess is correct.
>
> >
Train 1 is called T. T is at rest.
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.
Correct.
>
> >
In train T there is an observer O at the center.
In train T' there is an observer O' at the center.
>
This I call sentence 1
> >
This I call sentence 2
> >
>
Right.
> >
>
> >
>
> >
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.
>
>
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.
> >
>
This is Question 1
> >
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 2
> >
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 ?)
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
>
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.
This is not clear.
>
Nevertheless, O sees identical "signal strength", and so does 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.
>
It's just that O sees a different "signal strength" than O'.
17 Train Thought Experiment
Van: Wayne Throop
Onderwerp: Re: train thought experiment
Datum: maandag 2 april 2001 23:17
>
"Nicolaas Vroom"
18 Train Thought Experiment
Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: dinsdag 3 april 2001 17:58
schreef in berichtnieuws
986246248@sheol.org...
> >
"Nicolaas Vroom"
>
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.
19 Train Thought Experiment
Van: Wayne Throop
Onderwerp: Re: train thought experiment
Datum: dinsdag 3 april 2001 19:44
>
"Nicolaas Vroom"
have the same
energy or Luminosity.
20 Train Thought Experiment
Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: dinsdag 3 april 2001 22:48
schreef in berichtnieuws
986319868@sheol.org...
> >
"Nicolaas Vroom"
have the same
energy or Luminosity.
Why
>
Please explain
>
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.
21 Train Thought Experiment
Van: Wayne Throop
Onderwerp: Re: train thought experiment
Datum: woensdag 4 april 2001 7:20
>
"Nicolaas Vroom"
I raised two new questions and now apparently you have a problem with
your previous answers, or am I wrong ?
>
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 ?
22 Train Thought Experiment
Van: John Anderson
Onderwerp: Re: train thought experiment
Datum: zaterdag 7 april 2001 6:49
>
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.
> > >
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.
> >
>
23 Train Thought Experiment
Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: woensdag 11 april 2001 13:36
> >
"Nicolaas Vroom"
I raised two new questions and now apparently you have a problem with
your previous answers, or am I wrong ?
>
>
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.
>
> >
>
>
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"
25 Train Thought Experiment
Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: donderdag 12 april 2001 10:38
schreef in berichtnieuws
987012631@sheol.org...
> >
"Nicolaas Vroom"
>
>
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.
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"
>
I hope there is someone who can explain the relation between
brightness with signal source speed, observer speed distance and
doppler shift
27 Train Thought Experiment
Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: zaterdag 14 april 2001 17:57
schreef in berichtnieuws
3ACE9C6E.6F4A@attglobal.net...
>
Nicolaas Vroom wrote:
> >
schreef in berichtnieuws
3AC2BBB5.5703@attglobal.net...
> > >
Nicolaas Vroom wrote:
> > > >
> > >
> >
>
28 Train Thought Experiment
Van: Wayne Throop
Onderwerp: Re: train thought experiment
Datum: zaterdag 14 april 2001 18:49
>
"Nicolaas Vroom"
>
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 both statements are not true.
IMO O will state that O's statement is false.
29 Train Thought Experiment
Van: John Anderson
Onderwerp: Re: train thought experiment
Datum: zondag 15 april 2001 7:20
>
schreef in berichtnieuws
3ACE9C6E.6F4A@attglobal.net...
> >
Nicolaas Vroom wrote:
> > >
schreef in berichtnieuws
3AC2BBB5.5703@attglobal.net...
> > > >
Nicolaas Vroom wrote:
> > > > >
> > > >
> > >
> >
>
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 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.
>
not by attacking an example of what the
logical consequences of the theory are.
31 Train Thought Experiment
Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: donderdag 19 april 2001 10:04
schreef in berichtnieuws
987095206@sheol.org...
> > >
He, too, is neglecting source motion.
>
> >
>
> >
I think a more detailed explanation is required to solve the issue.
>
32 Train Thought Experiment
Van: Nicolaas Vroom
Onderwerp: Re: train thought experiment
Datum: zaterdag 21 april 2001 11:12
schreef in berichtnieuws
_ZwD6.2026$ii.302512@afrodite.telenet-ops.be...
>
schreef in berichtnieuws
987095206@sheol.org...
> > > >
He, too, is neglecting source motion.
> >
> > >
> >
> > >
> >
>
Created: 25 June 2001