[asa] m&ms (Was Re: The Cosmological constant)

From: George Murphy <GMURPHY10@neo.rr.com>
Date: Wed Jul 16 2008 - 20:58:00 EDT

Responses to a handful of posts:

Ted is right that Einstein's primary concern had to do with symmetry - moving a magnet past a coil gives the same effect as moving the coil past the magnet. That's the 1st thing he refers to in his 1905 paper, but he immediately adds the reference to "the unsuccessful attempts to discover any motion of the earth relatively to the light medium." While there were other experiments that could be described in that way besides MM, the fact that the latter experiment had been discussed in some detail by the premier theorist of the time, Lorentz, makes it plausible that that's what he meant. (Lorentz did not just "cite" MM. His article "Michelson's Interference Experiment" is the 1st one in The Principle of Relativity.)

Whether or not MM influenced Einstein greatly is another matter. As Karl notes, it is cvertainly not an "experimentum crucis" that in itself implies special relativity. The ad hoc hypothesis of the Fitzgerald contraction will explain it & leave the rest of classical physics intact. The more natural suggestion of "aether drag" is usually disposed of today with reference to stellar aberration but apparently come physicists 100+ years ago weren't convinced by that. On the wall of my study I have a blown up picture from Sir Oliver Lodge's The Ether of Space, published in 1908. It shows some solemn Edwardian gentlemen sitting around "the ether machine" in a lab at Liverpool U. Lodge was a staunch defender of the ether well after 1905. The ether machine was essentially an interferometer with the light beams running between two rotating iron wheels which were supposed to drag the aether.

Though the MM experiment is not as important as is sometimes suggested, it is an easy way to point out to students a basic problem with classical physics. OK as long as historical & pedagogic importance aren't confused. I think - but am not sure - that Polanyi's statement that "indeed the MM experiments are inconsistent with Relativity Theory," as Murray cited, referred to the results of later experimenters, & especially Miller (about whom Vernon asked), rather than to the results that were known in 1905. Miller concluded that there was an aether drift, though not of the full amount expected from classical theory. Shankland et al reanalyzed Miller's data & concluded that the positive result was an artifact of small thermal gradients across the interferometer.

Shalom
George
http://web.raex.com/~gmurphy/
----- Original Message -----
From: "Ted Davis" <TDavis@messiah.edu>
To: "ASA" <asa@calvin.edu>; "George Murphy" <GMURPHY10@neo.rr.com>; "Murray Hogg" <muzhogg@netspace.net.au>; "Moorad Alexanian" <alexanian@uncw.edu>
Sent: Wednesday, July 16, 2008 3:07 PM
Subject: RE: The Cosmological constant (was Re: [asa] PredestinedFame:)

> Moorad asked:
>
> I believe Einstein did know of the negative result of the Michelson-Morley
> experiment before he wrote his seminal work on special relativity. Is there
> any doubt about this?
>
> ***
>
> Ted replies:
> Yes, Moorad, there is considerable doubt about this. Let me say right away
> that my knowledge of this is not really up to date, in terms of the
> historical scholarship on the development of Einstein's theory, but when my
> knowledge was up to date a quarter century ago, a good argument could be
> made that he had not actually heard of the MM Expt at the time he wrote his
> early papers on special relativity (pub 1905). There were several other
> expts by others, trying to detect the earth's motion through the ether in
> other ways, and he did know about some of those, but maybe not MM.
>
> For a clear presentation of this argument, see Gerald Holton's essay,
> "Einstein, Michelson, and the 'Crucial' Experiment," Isis 60 (1969): 133-97,
> or as reprinted in Holton's book, "Thematic Origins of Scientific Thought."
> Holton concludes, after surveying all of the evidence available to him, that
> the primary sources (that is, what was actually said at the time) "tell a
> story for which the secondary sources had not prepared us. It is a scenario
> of which we cannot, in the nature of the case, be absolutely certain, but
> one which is highly probable. Indeed, the role of the Michelson experiment
> in the genesis of Einstein's theory appears to have been so small and
> indirect that one may speculate that it would have made no difference to
> Einstein's work if the experiment had never been made at all."
>
> My own view is (and I caution people that I am no expert on Einstein) that
> the crucial insights for Einstein were theoretical and conceptual, not
> experimental. Consider for a moment the difference in how one explains what
> happens in these two cases:
>
> (1) hold a solenoid stationary (relative to you), and move a bar magnet
> through it. A current is induced, but why? The magnetic field is
> moving/changing, but the electric charges in the solenoid are not. The emf
> comes from the changing magnetic field, not from the moving charges.
>
> (2) hold a bar magnet stationary, and move the solenoid through it. A
> current is induced, but why? The magnetic field is not changing, but the
> charges are moving. The emf comes from the moving charges, not from a
> changing magnetic field.
>
> Einstein was committed to the view that the relative motion of the magnet
> and the coil was the only factor that should matter, and he sought an
> explanation that was symmetric to the two cases. You know a lot more
> physics than I do, Moorad, so you can see more clearly than me where this is
> going...
>
> Ted
>
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Received on Wed Jul 16 20:58:26 2008

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