Teaching vs Doing: The Role of Concepts in Research - Insights from Physics

[pmb_phy]

Speaking of Steve Carlip - He claimed once that nobody uses (relativistic) mass in GR. Yet he published a paper in the American Journal of Physics on this point, i.e.

Kinetic Energy and the Equivalence Principle, Steve Carlip, Am.J.Phys. 65
(1998) 409-413

Online at - http://xxx.lanl.gov/PS_cache/gr-qc/pdf/9909/9909014.pdf
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Abstract - According to the general theory of relativity, kinetic energy
contributes to gravitational mass. Surprisingly, the observational evidence
for this prediction does not seem to be discussed in the literature. I
reanalyze existing experimental data to test the equivalence principle for
the kinetic energy of atomic electrons, and show that fairly strong limits
on possible violations can be obtained. I discuss the relationship of this
result to the occasional claim that ``light falls with twice the
acceleration of ordinary matter.''
--------------------------------------

The contribution of gravitational mass is exactly what relativistic mass is all about!

Pete

 

[mahesh_2961]

hai,
my point is that the theories of Einstein theory that matter will shrink to zero size and will have infinite mass when traveling at the speed of light is something like saying "there are green faced men on moon who can sense our coming to moon and there by hide and we can never find them" .. My point is that such findings of Eienstien can never be experimentally proved ... The statement itself makes it impossible to prove ... This is my opinion and i apologize if i hurt any of u

regards
Mahesh

 

[ZapperZ]

hai,
my point is that the theories of Einstein theory that matter will shrink to zero size and will have infinite mass when traveling at the speed of light is something like saying "there are green faced men on moon who can sense our coming to moon and there by hide and we can never find them" .. My point is that such findings of Eienstien can never be experimentally proved ... The statement itself makes it impossible to prove ... This is my opinion and i apologize if i hurt any of u

regards
Mahesh

Then you obviously have no clue what the REST of his theory is saying. The fact that you DO get a relativistic mass is a clear experimental evidence. If you don't believe me, just visit any accelerator facility and see if they don't laugh right in your face when you tell them relativistic mass hasn't been observed experimentally. I work with 18 MeV electrons, and all of our beam diagnostics will give us nonsensical results if we neglect to consider the electron's relativistic mass.

The problem here is that you seem to only be focusing ONE result of this idea, being the situation where v=c. This is highly dubious since it isn't something that makes any sense. When a solution blows up like that, it means that physics cannot be used there! This applies not just in Special Relativity, but ALL of physics, and it does occur in all of physics! So if you are arguing that SR isn't "proven" because we can never detect the v=c situation because it goes to infinity, then you should also say ALL of physics isn't proven because in none of those cases can we "prove" the condition when the description goes infinite. This is absurd!

Empirical verification isn't just verifying a description at just ONE point. It is the verification of the description at several situations so that one not only obtains quantitative values, but also verify the TREND and qualitative description. You don't verify that Hooke's law is obeyed by a spring by measuring only one set of values for force and the corresponding extension. YOu measure a series of force vs. extension relationship and observe the corresponding trend. This has been done for practically ALL of the consequences of SR! We do not need to go to v=c cases to know that they work!

BTW, if SR doesn't work, your electronics will go bonkers. This is because many of the materials that are used in semiconductors that make up your processors have band structure calculations that had to include relativistic corrections. I also suggest you do not fly in a commercial airplane, since they ALL used GPS systems that incorporate SR/GR.

Zz.

P.S. Your "opinion" doesn't hurt me, it hurts you.

 

[pmb_phy]

The fact that you DO get a relativistic mass is a clear experimental evidence.

I must say, Zz, that I find that to be a very refreshing observation. Too bad more students don't learn this all too basic point.

Thank you!

Pete

 

[mahesh_2961]

Thank u for pointing out the flaws in my thinking ... in this case all were flaws
i understood my mistake

mahesh

 

[Stingray]

Would you do this and if so then why?

Yes, I think I would talk about subjects I wouldn't want to use myself. If I didn't have much time to cover a subject (but was forced to do it anyways), then I might go over certain concepts I didn't like just to get the students' interest, or to introduce something more quickly. It is very time consuming to describe everything with all the disclaimers one might want. It also tends to confuse people when you tell them things are "almost true."

In my limited teaching experience so far (as a TA only), I actually have made more of an effort to comment on the limitations of a particular concept than most do. This is the way I would've liked to have been taught, but I think it is very difficult to do it correctly. I usually just get a lot of blank stares. I suppose it's hard enough to understand one piece of material without being told a bunch of things about when it's really valid to use it.

 

[pmb_phy]

Yes, I think I would talk about subjects I wouldn't want to use myself. If I didn't have much time to cover a subject (but was forced to do it anyways), then I might go over certain concepts I didn't like just to get the students' interest, or to introduce something more quickly.

I think you missed the gist of the question. I'm not talking about a minor thing mentioned by an author. I'm talking about one of the more major themes in the entire text.

Thanks

Pete

 

[Stingray]

I think you missed the gist of the question. I'm not talking about a minor thing mentioned by an author. I'm talking about one of the more major themes in the entire text.

Then no, I wouldn't do that.

 

[pmb_phy]

Then no, I wouldn't do that.

A quick example comes to mind. In Schutz's new text Gravity from the Ground Up he has a section called Special Relativity: general consequences. He states that in that section he lists the most important consequences of the principle of relativity. If Schutz actually believes that all those items are the most important consequences of SR then one shouldn't expect him to ignore anyone of them in his own research.

At least in my opinion.

Thanks Stingray

Pete

 

[Stingray]

If Schutz actually believes that all those items are the most important consequences of SR then one shouldn't expect him to ignore anyone of them in his own research.

Yes, you're right. Unless he's talking from a purely historical perspective, which would probably be obvious from the context. Is that part of the book online?

 

[pmb_phy]

Yes, you're right. Unless he's talking from a purely historical perspective, which would probably be obvious from the context. Is that part of the book online?

No. I have the the book.

Pete

 

[pmb_phy]

Then you obviously have no clue what the REST of his theory is saying. The fact that you DO get a relativistic mass is a clear experimental evidence. If you don't believe me, just visit any accelerator facility and see if they don't laugh right in your face when you tell them relativistic mass hasn't been observed experimentally.

Speaking of which

Apparatus to measure relativistic mass increase, John W. Luetzelschwab, Am. J. Phys. 71 (9), September 2003
http://physics.dickinson.edu/~dept_web/activities/papers/relativity.pdf

An apparatus that uses readily available material to measure the relativistic mass increase of beta particles from a radioactive ²⁰⁴Tl source is described. Although the most accurate analysis uses curve fitting or a Kurie plot, students may just use the raw data and a simple calculation to verify the relativistic mass increase.

Pete