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*From*: John Denker <jsd@av8n.com>*Date*: Mon, 04 Oct 2010 04:22:22 -0400

On 10/01/2010 09:25 PM, John Mallinckrodt mentioned this paper:

N. David Mermin,

"Relativity without light," AJP, 52, 119, 1984

That is indeed an important paper.

Basically it says that given Galileo's principle of relativity

plus some clever symmetry arguments, the entire structure of

spacetime is determined.

If photons and other fast-moving particles ceased to exist, it

would have *no* effect on special relativity.

I reckon the number of people who are aware of this greatly exceeds

the number of people who have actually read the article. In any case,

the article is worth reading, if you have even the slightest interest

in special relativity.

The number we call "c" is primarily a conversion factor, allowing

you to convert from conventional units of velocity to radians of

rapidity in the xt plane.

Everything else, including the existence of a limiting speed, and

the frame-independence of the limiting speed, can be seen as an

almost-trivial consequence of the geometry and trigonometry of

spacetime.

===================

There is also:

Mitchell J. Feigenbaum

"The Theory Of Relativity - Galileo’s Child"

May 25, 2008

http://arxiv.org/pdf/0806.1234

... which explains that Mermin's calculation is only good in D=1+1

dimensions (time plus one spatial dimension). The physics in

higher dimensions is much richer. To obtain these richer results

requires additional work, additional attention to detail, and

additional cleverness.

Some people may find this paper to be more than they want to deal

with, but still I would recommend reading at least the introduction

and the conclusions.

==================================

Pedagogical remarks:

Special relativity is the geometry and trigonometry of spacetime.

Some parts of Mermin's proofs are too intricate to be suitable in an

introductory class. However, the same can be said for other proofs,

including Einstein's derivation in terms of "postulates" involving

electromagnetism and whatnot. IMHO the sensible introductory strategy

is to just say "this is what spacetime looks like" in terms of 4-vectors

spacetime diagrams, et cetera ... and then work out the consequences,

showing that this structure is /consistent/ with everything else we know,

experimentally and theoretically. The proof that this is not just "a"

consistent structure but the /only/ consistent structure can wait.

**Follow-Ups**:**[Phys-l] Definition of upthrust or buoyancy***From:*carmelo@pacific.net.sg

**References**:**Re: [Phys-l] Absolute four-momentum of massless particles***From:*"Rauber, Joel" <Joel.Rauber@SDSTATE.EDU>

**Re: [Phys-l] Absolute four-momentum of massless particles***From:*"Spagna Jr., George" <gspagna@rmc.edu>

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**Re: [Phys-l] Absolute four-momentum of massless particles***From:*David Bowman <David_Bowman@georgetowncollege.edu>

**Re: [Phys-l] Absolute four-momentum of massless particles***From:*John Mallinckrodt <ajm@csupomona.edu>

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