- #106
Doc Al
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matheinste said:I hope nobody else thought that was a serious question.
matheinste said:I hope nobody else thought that was a serious question.
matheinste said:I hope nobody else thought that was a serious question.
Matheinste.
matheinste said:Isn't white light frequency shifted still white light.
Matheinste.
Doc Al said:
Doc Al said:"White" is not a good choice for a color, as it is a mix of frequencies. To understand how the frequency of light changes due to the relative speed of source and observer, look up the Doppler effect. I recommend you stick to one topic at a time.
jmallett said:It is, of course, the same subject, because the postulate at the moment is that light in a moving train is seen in one way in the train, but a different way by someone not in the train. It's just going back to some very basic stuff assumed by the experiment because there did not seem to be consensus in this forum on the understanding of the speed of light in a particular frame of reference, so I was trying, first, to define some basics which we might all agree on before jumping to the assumptions which we do not, apparently, agree on for the moment.
Nope. That might be your postulate, but it has little to do with relativity. Everyone sees the light traveling at the same speed with respect to them.jmallett said:It is, of course, the same subject, because the postulate at the moment is that light in a moving train is seen in one way in the train, but a different way by someone not in the train.
Doc Al said:Nope. That might be your postulate, but it has little to do with relativity. Everyone sees the light traveling at the same speed with respect to them.
Nope, just you.jmallett said:It is the postulate currently being made by a variety of people in this forum.
Doc Al said:Nope, just you.
jmallett said:It is, of course, the same subject, because the postulate at the moment is that light in a moving train is seen in one way in the train, but a different way by someone not in the train. It's just going back to some very basic stuff assumed by the experiment because there did not seem to be consensus in this forum on the understanding of the speed of light in a particular frame of reference, so I was trying, first, to define some basics which we might all agree on before jumping to the assumptions which we do not, apparently, agree on for the moment.
Nope. The 'stationary' observer does not make use of any length measurements made in some other frame. All his measurements are made in his own frame.jmallett said:He then took the velocity information of his frame of reference, but used it together with the iength measurement made in another frame of reference, thereby confusing two sets of data.
Nope. I've said as many times as possible: Viewed from any frame of reference, the light moves at the same speed. (Again, I have no idea what you mean when you talk of things being in 'the same frame of reference'.)Now, why do I believe you have made that postulation ?
Because you assumed that the light in the train traveled faster than the light in the stationary frame yet both were in the same frame of reference.
I've been saying that all along: The 'stationary' observer sees all light travel at the same speed with respect to him (not the train!). A basic premise of relativity is that the speed of light is the same in every frame. Now if you switch to the frame of the train, then the speed of light is also c with respect to the train.OK, so let's then agree, right ? The stationary observer sees the light in the train traveling at the same speed as the light in his own frame. Do we agree ?
There's no requirement for science--especially relativity--to be 'self-evident'. Further, science is based on logic and evidence, not merely 'belief'.jmallett said:I appreciate that you have your beliefs. I am still a skeptic. I am merely trying to understand how you believe your beliefs, because they are not to me self-evident
jmallett said:Oh, and by the way, any time someone says - "go back and read about..." it reminds me of the people you meet in various religions who when asked to give their view simply say - "you need to study Gospel x, chapter y"
I appreciate that you have your beliefs. I am still a skeptic. I am merely trying to understand how you believe your beliefs, because they are not to me self-evident
Doc Al said:Nope. The 'stationary' observer does not make use of any length measurements made in some other frame. All his measurements are made in his own frame.
Nope. I've said as many times as possible: Viewed from any frame of reference, the light moves at the same speed. (Again, I have no idea what you mean when you talk of things being in 'the same frame of reference'.)
I've been saying that all along: The 'stationary' observer sees all light travel at the same speed with respect to him (not the train!). A basic premise of relativity is that the speed of light is the same in every frame. Now if you switch to the frame of the train, then the speed of light is also c with respect to the train.
Where you are getting stuck is in not understanding how the stationary observer can see the light and the train close at a rate of 'c + v', even though both the stationary observer and the train both observe the light to move at the same speed c with respect to their own frames. This is tricky stuff.
Nope, not even close. For things to be 'in the same frame of reference' they must be moving together at the same speed. Note that anything--cars, trains, tracks, light--can be observed by anyone in any frame of reference. Just because someone in the track frame (that is, someone at rest with respect to the tracks) sees a train going by does not magically make the train somehow jump into the same frame of reference as the observer. The track frame sees the train moving (thus in a different frame); similarly, the train frame sees the track moving.jmallett said:When I say "same frame of reference" I mean a SINGLE frame of reference, for example the stationary observer has a single frame of reference. He can't see things (like light) behave differently at different times, because he can only exist in a single frame of reference, and everything he observes is now in the same frame of reference, that is to say his. This includes the various cars, trains, tracks, light, etc he has been observing throughout this discussion.
Are we on the same page ?
matheinste said:If you accept the beliefs or postulates of relativity you arrive at certain logically derived consequences. You do not have to accept any postulates if you wish not to. However, you must accept the logical reasoning used. If you do not accept the postulate of light speed, which most agree is counterintuitive, so be it, but at least apply some logic in your arguments against it.
Matheinste.
Doc Al said:Nope, not even close. For things to be 'in the same frame of reference' they must be moving together at the same speed. Note that anything--cars, trains, tracks, light--can be observed by anyone in any frame of reference. Just because someone in the track frame (that is, someone at rest with respect to the tracks) sees a train going by does not magically make the train somehow jump into the same frame of reference as the observer. The track frame sees the train moving (thus in a different frame); similarly, the train frame sees the track moving.
With respect to what? With respect to the train itself, the speed of the train is zero of course. The speed of anything is zero in its own frame.jmallett said:We will now ask a question. As far as the train is concerned what is his speed ?
The light is not part of any frame of reference. (There is no frame in which the light is at rest.)jmallett said:Then the light in the train is not in the same frame of reference as the rod ?
Doc Al said:The light is not part of any frame of reference. (There is no frame in which the light is at rest.)
All of a sudden a rod appears. How is it moving with respect to the train?jmallett said:Then where is the frame of reference in which the train and the rod are at rest ?
jmallett said:Then where is the frame of reference in which the train and the rod are at rest ?
OK. Rod and train are in the same frame.jmallett said:Stationary with respect to the train, that's where we started and that's the postulate of Einsteins equations, although Einstein didn't actually need a train, he just had the rod floating. The train got introduced somewhere a few pages back, I think, but never mind, let's assume the rod and train are stationary relative to each other. The observer on the train is trying to measure the length of the rod just as Einstein had him do, but measuring the length of the train will do just as well.
Doc Al said:OK. Rod and train are in the same frame.
jmallett said:Good. We are on the same page. Now back a step -
Then where is the frame of reference in which the train and the rod are at rest ?
Moving along with the train, like any good reference frame. (Seriously, this is getting silly. Why not read that book I gave you the link for? It goes through all this in painstaking detail.)jmallett said:Good. We are on the same page. Now back a step -
Then where is the frame of reference in which the train and the rod are at rest ?
jmallett said:Good. We are on the same page. Now back a step -
Then where is the frame of reference in which the train and the rod are at rest ?
Doc Al said:Moving along with the train, like any good reference frame. (Seriously, this is getting silly. Why not read that book I gave you the link for? It goes through all this in painstaking detail.)
Doc Al said:Moving along with the train, like any good reference frame. (Seriously, this is getting silly. Why not read that book I gave you the link for? It goes through all this in painstaking detail.)
jmallett said:Sorry you see it as silly.
Einstein places the rest frame of the rod as the frame of the stationary observer. It is an explicit assumption that it is not at rest when moving in that frame, so we are stuck with a conclusion that is in it's rest frame when it is both in the train and when it is not moving relative to the stationary observer. Forget all the stuff about light.
He measures the length "at rest" and the length rAB is inherently the length when the "rod is at rest"
The length is therefore, in his experiment, inherently measured by the stationary observer.
You're getting all twisted in knots over the term 'stationary' observer.jmallett said:Einstein places the rest frame of the rod as the frame of the stationary observer. It is an explicit assumption that it is not at rest when moving in that frame, so we are stuck with a conclusion that is in it's rest frame when it is both in the train and when it is not moving relative to the stationary observer. Forget all the stuff about light.
He measures the length "at rest" and the length rAB is inherently the length when the "rod is at rest"
The length is therefore, in his experiment, inherently measured by the stationary observer.
Doc Al said:You're getting all twisted in knots over the term 'stationary' observer.
Rather than use terms such as 'stationary' frame and 'moving' frame, let's call them the track frame and the train frame. No ambiguity there. If the train frame measures the length of the rod, then that's the length of the rod when the rod is at rest (with respect to the observer) since measurements are made in the frame where the rod is at rest. And if the track frame measures the length of the rod, then they measure the length of the moving rod since measurements are made in the frame in which the rod is moving.
OK. Now what?