Excellent Lorentz Transformation educational video?

[Wes Tausend]

My local PBS station broadcasts a physics series on a sub-channel. They call it The Mechanical Universe locally.

PBS recently broadcast The Lorentz Transformation . It appears that one may view these on line, as the Lorentz Transformation began to load after I allowed it to pop-up. There are 52 half hour presentations altogether and they appear to be quite suitable for either high school or college classrooms.

The link I used is http://www.learner.org/resources/series42.html .

I particularily liked the mention that a major difference between Lorentz's view and Einsteins is that Lorentz considered "contraction" an apparent phenomenon and Einstein took it as a real physical demand and postulated as such to go on to describe the laws of Special Relativity(SR). Most on here know that both Poincaré and Lorentz thought along similar lines to Einstein and SR, but he published a workable synopsis first.

Wes
...

 

[harrylin]

My local PBS station broadcasts a physics series on a sub-channel. They call it The Mechanical Universe locally.

PBS recently broadcast The Lorentz Transformation . It appears that one may view these on line, as the Lorentz Transformation began to load after I allowed it to pop-up. There are 52 half hour presentations altogether and they appear to be quite suitable for either high school or college classrooms.

The link I used is http://www.learner.org/resources/series42.html .

I particularily liked the mention that a major difference between Lorentz's view and Einsteins is that Lorentz considered "contraction" an apparent phenomenon and Einstein took it as a real physical demand and postulated as such to go on to describe the laws of Special Relativity(SR). Most on here know that both Poincaré and Lorentz thought along similar lines to Einstein and SR, but he published a workable synopsis first.

Wes
...

Hi Wes,

I have not yet looked at those videos, but your particular mention makes me doubt a bit their reliability. Lorentz considered "contraction" to be a true phenomenon. Such videos are probably OK for the physics, but usually not for the history.

 

[Wes Tausend]

Hi Wes,

I have not yet looked at those videos, but your particular mention makes me doubt a bit their reliability. Lorentz considered "contraction" to be a true phenomenon. Such videos are probably OK for the physics, but usually not for the history.

harrylin,

Thanks for responding.

We might be suffering from second hand information here (mine). I may have worded it wrong. This 30 minute video, and at least one other, Magnetism, was done under auspices of Cal Tech I believe (same class instructor). I believe they also offered some impressive consultation references from other universities.

As an example of "apparence", I was struck that we currently regard the apparence of Equivalence where gravity and inertial reaction to velocity are not entirely the same literally. So we are currently stuck with two forms of natural acceleration, with possibly different cause, and absence of simple Occam's description.

Although a delicate comparison, I imagine Lorentz thought of contraction as merely mathematically "equivalent" to actually getting shorter. If you do view the video, and think otherwise, I would enjoy your take on this. You are also welcome to PM me if you like. Thanks again.

Wes
...

 

[harrylin]

[..] We might be suffering from second hand information here (mine). I may have worded it wrong. [..] I imagine Lorentz thought of contraction as merely mathematically "equivalent" to actually getting shorter. [..]

OK here's my take on this, and you may find it amusing.

Perhaps you imprecisely recalled that Lorentz has claimed something like that about time, some years later:

"The chief cause of my failure was my clinging to the idea that the variable t only can be considered as the true time and that my local time t' must be regarded as no more than an auxiliary mathematical quantity."

Surely his memory was about as poor as ours!

He may have not understood the practical value of "local time" t for clock synchronization (that was first explained by Poincare), but the facts show that he proposed time dilation as a physical phenomenon as early as in 1899:

" provided however that in S the time of vibration be kε times as great as in S0 "

Surprisingly he did not spell this out in his 1904 paper, which includes the corresponding time transformation; it appears that he had forgotten! But any reader of his papers would easily have made the connection.

And if you look carefully, you may also be able to spot an inconsistency between his declarations as cited in https://en.wikipedia.org/wiki/Hendrik_Lorentz#Lorentz_and_special_relativity .

 

[Wes Tausend]

Wes said:My local PBS station broadcasts a physics series on a sub-channel. They call it The Mechanical Universe locally.
PBS recently broadcast The Lorentz Transformation . It appears that one may view these on line, as the Lorentz Transformation began to load after I allowed it to pop-up. There are 52 half hour presentations altogether and they appear to be quite suitable for either high school or college classrooms.
The link I used is http://www.learner.org/resources/series42.html .
I particularily liked the mention that a major difference between Lorentz's view and Einsteins is that Lorentz considered "contraction" an apparent phenomenon and Einstein took it as a real physical demand and postulated as such to go on to describe the laws of Special Relativity(SR). Most on here know that both Poincaré and Lorentz thought along similar lines to Einstein and SR, but he published a workable synopsis first.
=============================================================
My apologies for not getting back promptly.

My original statement above, "Lorentz considered "contraction" an apparent phenomenon", is incorrect.

Re-watching the video, I now interpret that the object of Lorentz/Einstein contention was not contraction, but whether the agreed-upon constant speed of light was just an apparent phenonemon or worthy of reality, plus a new constant physical law that met the needs of all observers. In the suspect passage, the narrator's exact words were, "For Lorentz, the constant speed of light for all observers was a mere appearance. For Einstein, this constant speed was a principle from which all else should be derived."

Poincaré objected to Lorentz's limited explanation and urged that a new law was needed and he was right. Einstein went on to assume that the speed of light is constant for all observers, postulated it as so and continued on to reason from there, and establish a new law of space-time.

In condensing this again, I sincerely hope I haven't made my original inexcuseable error worse. It is a severe short-coming that the video may not be available to all interested parties, to hear and see all this in proper context for themselves. IMO. the beauty, the succinctness of the video, was it's ablity to clearly deliver so much in only a half hour. I hope someone else may see it and review it's worth here.

That said, without elaborating further, some differences in Lorentz 1904 paper and Einsteins 1905 were also briefly discussed. Lorentz's papers contained many of the same equations that Einstein published. But Einsteins were derived from a different angle, and used to inspire a truly deeper meaning of the reality of time and space.

Harrylin, I did just read that section of Lorentz/SR in wikipedia in the last week. Perhaps I do blend the unblendable at times.

P.S.
I just happened to notice that this video, and others in the 52 episode series, claims to be restricted to a U.S./Canadian audience:

Quote: "Due to licensing agreements, online viewing of the videos for this resource is restricted to network connections in the United States and Canada."

Wes
...

 

[harrylin]

With a little rearranging:

[..] Re-watching the video, I now interpret that the object of Lorentz/Einstein contention was not contraction, but whether the agreed-upon constant speed of light was just an apparent phenonemon or worthy of reality, plus a new constant physical law that met the needs of all observers. In the suspect passage, the narrator's exact words were, "For Lorentz, the constant speed of light for all observers was a mere appearance. For Einstein, this constant speed was a principle from which all else should be derived."
[..]
In condensing this again, I sincerely hope I haven't made my original inexcuseable error worse.

Wes, you are telling us here how you understood the video. Even if the video did not state everything exactly how you condensed it, it is what it suggested to you; and the passage that you cite, is definitely a simplification. If with "principle" they meant the light principle, then that phrase may hinder correct understanding of special relativity. It sounds as if you were set on a wrong track, so to say. Is the video suggesting that one of the postulates was a new physical law, and that Einstein's derivation was based on the light postulate as it includes the relativity principle?

The facts are different. The light postulate was based on Maxwell's theory of electrodynamics, and the relativity principle of Poincare seemed incompatible with Maxwell's hypothesis of light propagation. The challenge for Lorentz and Einstein was to come up with a theory that would solve this apparent incompatibility. Thus, Einstein presented his derivation as follows in 1905 (emphasis mine):

We will raise [..] the “Principle of Relativity” to the status of a postulate, and also introduce another postulate, which is only apparently irreconcilable with the former, namely, that light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body.
[..]
These two postulates suffice for the attainment of a simple and consistent theory of the electrodynamics of moving bodies based on Maxwell's theory for stationary bodies.
[..]
We now have to prove that any ray of light, measured in the moving system, is propagated with the velocity c, if, as we have assumed, this is the case in the stationary system; for we have not as yet furnished the proof that the principle of the constancy of the velocity of light is compatible with the principle of relativity.
- http://www.fourmilab.ch/etexts/einstein/specrel/www/

Poincaré objected to Lorentz's limited explanation and urged that a new law was needed and he was right.

When reading Poincare, I cannot find a request for a "new law". He was just unhappy about the "bottom-up" approach with which Lorentz found the solution:
- https://en.wikisource.org/wiki/The_Principles_of_Mathematical_Physics#The_Principle_of_Relativity.
- https://en.wikisource.org/wiki/Translation:On_the_Dynamics_of_the_Electron_(June)

Einstein went on to assume that the speed of light is constant for all observers, postulated it as so and continued on to reason from there, and establish a new law of space-time.

From combining the two postulates, Einstein found in a simple and straightforward manner the same transformations as Lorentz, and in the same form as Poincare. In fact, he gave an operational definition for the speed of light, as he apparently understood better than Lorentz that:
"the assertions of any such theory have to do with the relationships between rigid bodies (systems of co-ordinates), clocks, and electromagnetic processes."
Lorentz certainly agreed at the time (it slightly changed with general relativity) that the operationally defined speed of light is constant in all inertial reference systems.

It is a severe short-coming that the video may not be available to all interested parties, to hear and see all this in proper context for themselves. IMO. the beauty, the succinctness of the video, was it's ablity to clearly deliver so much in only a half hour. I hope someone else may see it and review it's worth here.

It will be hard, if not impossible, to give a comprehensive overview in half an hour that will be satisfactory to everyone!
I suppose that the video will be useful as an introduction despite the significant shortcoming that it appears to have.

PS. The following may be helpful:

https://en.wikisource.org/wiki/Rela...mple_Derivation_of_the_Lorentz_Transformation

Equation 1 follows from the light postulate.
Equation 2 must then also be valid according to the relativity postulate.

 

[Wes Tausend]

With a little rearranging:

Wes, you are telling us here how you understood the video. Even if the video did not state everything exactly how you condensed it, it is what it suggested to you; and the passage that you cite, is definitely a simplification. If with "principle" they meant the light principle, then that phrase may hinder correct understanding of special relativity. It sounds as if you were set on a wrong track, so to say. Is the video suggesting that one of the postulates was a new physical law, and that Einstein's derivation was based on the light postulate as it includes the relativity principle?

The facts are different. The light postulate was based on Maxwell's theory of electrodynamics, and the relativity principle of Poincare seemed incompatible with Maxwell's hypothesis of light propagation. The challenge for Lorentz and Einstein was to come up with a theory that would solve this apparent incompatibility. Thus, Einstein presented his derivation as follows in 1905 (emphasis mine):

We will raise [..] the “Principle of Relativity” to the status of a postulate, and also introduce another postulate, which is only apparently irreconcilable with the former, namely, that light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body.
[..]
These two postulates suffice for the attainment of a simple and consistent theory of the electrodynamics of moving bodies based on Maxwell's theory for stationary bodies.
[..]
We now have to prove that any ray of light, measured in the moving system, is propagated with the velocity c, if, as we have assumed, this is the case in the stationary system; for we have not as yet furnished the proof that the principle of the constancy of the velocity of light is compatible with the principle of relativity.
- http://www.fourmilab.ch/etexts/einstein/specrel/www/


When reading Poincare, I cannot find a request for a "new law". He was just unhappy about the "bottom-up" approach with which Lorentz found the solution:
- https://en.wikisource.org/wiki/The_Principles_of_Mathematical_Physics#The_Principle_of_Relativity.
- https://en.wikisource.org/wiki/Translation:On_the_Dynamics_of_the_Electron_(June)


From combining the two postulates, Einstein found in a simple and straightforward manner the same transformations as Lorentz, and in the same form as Poincare. In fact, he gave an operational definition for the speed of light, as he apparently understood better than Lorentz that:
"the assertions of any such theory have to do with the relationships between rigid bodies (systems of co-ordinates), clocks, and electromagnetic processes."
Lorentz certainly agreed at the time (it slightly changed with general relativity) that the operationally defined speed of light is constant in all inertial reference systems.

It will be hard, if not impossible, to give a comprehensive overview in half an hour that will be satisfactory to everyone!
I suppose that the video will be useful as an introduction despite the significant shortcoming that it appears to have.

PS. The following may be helpful:

https://en.wikisource.org/wiki/Rela...mple_Derivation_of_the_Lorentz_Transformation

Equation 1 follows from the light postulate.
Equation 2 must then also be valid according to the relativity postulate.

Harald,

I hope you do not mind me using the first name with which you signed another post. And I apologise for the delay in reply again, my wife has dragged me into redecorating. Curse redecorating when there is philosophy to be done!

You've done an excellent job clearly describing many aspects of the history of relativity and I appreciate your effort. Without providing an entire transcript, and worded visualization of the video, I cannot really transcribe it's full value in context. It does seem to me to be consistant with (not at odds) what you have just stated and my own opinion, but I am unable to easily convey that.

I am afraid that any prospective instructor will have to review the video, and first possibly prepare for certain clarifications as you suggest, before presenting it to a class. Thank you very much for your reply.

Wes
...