# Clock synchronization

1. Dec 21, 2007

### bernhard.rothenstein

Please tell me if it is compulsory to start teaching special relativity with describing the clock synchronization procedure?
Which is the best way to do it in your opinion?
Thanks

2. Dec 21, 2007

### Staff: Mentor

I would start with the two postulates. The Einstein synchronization procedure is a direct result of the second postulate.

3. Dec 21, 2007

### bernhard.rothenstein

Thanks for your answer and I agree with you. Do you consider that x=ct and x'=ct' are equivalent with clock sybchronization? Do you consider that it is correct to arrive at the Lorentz transformations without to mention the concept of clock and to make a link between the involved time coordinates and the readings of clocks? I know a lot of such examples.
Regards

4. Dec 22, 2007

### Staff: Mentor

The equation x=ct describes a light cone originating from the origin propagating at c. Then x'=ct' is simply a restatement of the second postulate, i.e. the light cone from the origin also propagates at c in the primed frame.

It can certainly be done correctly, but I have never taught relativity, so I don't know if it would be clear to a student. I tend to think that a derivation of the Lorentz transform and an introduction to Minkowski geometry and spacetime diagrams should be done as early as feasible, but I don't know exactly when that is.

5. Dec 22, 2007

### pervect

Staff Emeritus
For some research into how students learn relativity, and specifically how they learn about clock synchronization, look up Scherr from U of W. One paper is http://arxiv.org/abs/physics/0207109 Another paper is http://aapt-doorway.org/TGRU/articles/Vokos-Simultaneity.pdf [Broken] also at arxiv http://arxiv.org/abs/physics/0207081

(Both papers were published in journals as well as being on arxiv).

Some of the results are pretty gloomy looking. Especially with traditional instruction, students never really learned relativity properly, i.e. they couldn't get the test answers right, even after taking a course in relativity :-(.

It does (in at least one of the above papers) appear to be helpful to review some basic non-relativistic concepts first, at least part of the problem was an incorrect student understanding of synchronization even without relativity. The classic example is confusing seeing two events at the same time with having them occur at the same time.

Some of the statistics are really pretty depressing :-(.

Last edited by a moderator: May 3, 2017
6. Dec 22, 2007

### robphy

My personal opinion is that part of the problem that such misconceptions and misunderstandings continue in special relativity is that the introductory textbooks still focus on the spatial-viewpoint of "moving frames of reference" (following Einstein's presentation) rather than a spacetime-geometric-viewpoint (developed by the mathematician Minkowski, and subsequently being developed by modern-day relativists).

7. Dec 22, 2007

### country boy

For the novice student, it may be best to begin with the basic concepts of coincidence (two things happening at the same time and place) and simultaneity (two things happening at the same time at different places). These are central to understanding relativity and do not require math in the initial discussion. Coincidence is a good place to start, because it is not an inherently relativistic concept, and the student usually has a good idea of it's meaning already. Simultaneity is harder, because it seems to be the same thing as coincidence until the student is shown how the finite speed of light makes the timing of separated events relative. Clock synchronization can then be introduced to explain how the observer defines simultaneity.

8. Dec 23, 2007

### bernhard.rothenstein

Thanks to all participants. Do you consider that testing what students respond to different tests without analysing the ways in which they were tought lead to relevant results?
A student who states "The Lorentz transformation relates the space-time coordinates of two events (x,x') which take place at the same point in space when the clocks of the involved inertial reference frame located at that point and synchronized a la Einstein read t and t' respectively" would pass the examination?

9. Dec 23, 2007

### Staff: Mentor

Thank you very much for these references. I did not appreciate how fundamentally difficult the relativity of simultaneity is to grasp for a typical student. Although, now that I have read these it makes sense that most of the "paradoxes" I have seen invented by crackpots simply reduce to a failure to correctly apply the relativity of simultaneity. I struggled for years, but I attributed it to a poor textbook presentation rather than an inherent difficulty in the concept. Maybe my textbook wasn't so bad.

Last edited by a moderator: May 3, 2017
10. Dec 23, 2007

### Staff: Mentor

You and I have discussed this point before, and I am inclined to agree with you. My own personal experience is that relativity made no sense until I discovered spacetime diagrams, Minkowski geometry, and spacetime intervals. Then it suddenly "clicked".

I note that the presentations and questions in the articles referenced above were all from a traditional "spatial-viewpoint". With this approach it required the pretty drastic "tutorial workgroup" approach to get even a 50% success with some concepts. That success only came after the students were required to directly confront and discard their assumptions themselves.

I wonder if the geometric-viewpoint that you and I like would result in students that could work problems but would still hold to the underlying incorrect assumptions. In other words, would they avoid challenging their preconceptions altogether, or would the geometric approach give students the tools they need to challenge their fundamental assumptions more successfully? I really don't have a good idea.

Last edited: Dec 23, 2007
11. Dec 23, 2007

### robphy

Until so-called "relativistic effects" become a part of daily life, I think that many preconceptions will persist. However, as you suggest, the more tangible geometric approach would provide tools to help students analyze problems and try to overcome misconceptions.

In similar sense, a free-body diagram can be used to analyze problems and overcome misconceptions in mechanics.