gsmith@brahms.BERKELEY.EDU (Gene Ward Smith) (03/27/86)
Let's go back to the Russell quote:
his predecessors is merely one of convenience; all motion
is relative, and there is no difference between the two
statements: `the earth rotates once a day' and `the heavens
revolve about the earth once a day.' The two mean exactly the
same thing, just as it means the same thing if I say a certain
length is six feet or two yards. Astronomy is easier if we
take the sun as fixed than if we take the earth, just as
accounts are easier in decimal coinage. {Signet, pp. 13-14}
>Whatever Bertrand Russell's qualifications in mathematics are, no one
>would ever accuse him of being a great physicist. One of the paramount
>features of General Relativity is that the laws of physics should
>appear the same in ALL reference frames. In a reference frame which
>is fixed with respect to the average motion of the nearby stars, those
>stars all appear to be traveling with low (relatively) velocities. In a
>'reference frame' which is fixed to the spinning Earth, the nearby stars
>appear to be traveling MUCH FASTER than the speed of light. (Consider A-
>Centauri: radius of 'orbit' around Earth is 4.2 light years, it 'orbits'
>once per day, total distance traveled per day is 2*4.2*PI light years or
>about 26 light years per day.) The consequences of stars being tachyons in
>one 'frame' and not being tachyons in the other would cause the observers
>in the two frames to come to different conclusions about the laws of
>physics in Earth local space (that is, the only way to reconcile the two
>observations is to assume that there is a space-time singularity between
>the two observers, but when they go to look they won't find one).
>
>The bottom line is that rotation is LOCALLY discernable and is therefore
>NOT a property of Einstein's reference frames (whether they are lorentz
>frames or not). One way of locally measuring rotation is with a foucault
>pendulum (which you even mentioned). Meanwhile ALL Einstein frames are
>LOCALLY indistinguishable from lorentz frames.
>
In article <1005@lanl.ARPA> jlg@a.UUCP (Jim Giles) writes:
>In article <438@batcomputer.TN.CORNELL.EDU> cpf@batcomputer (Courtenay Footman) writes:
After several very bad articles on this subject, there have recently
been some very good ones, especially the one that noted that the Earth
does rotate, and that this is unambiguous because the geometry near the
Earth is a Kerr geometry. However, I feel that the lack of significance of
coordinate frames should be stated forcefully. [Footman]
>
>Bravo!! I have been trying to get this point across for some time now. I
>have confined my discussion to coordinate systems because it is easier to
>explain that way. But the bottom line is still - 'The Earth DOES rotate,
>and this is UNAMBIGUOUS'. There are some on the net who will take an
>overzealous remark by Bertrand Russell at face value over the whole of GR -
>and then accuse anyone who disagrees with them of ignorance! [Giles]
You confused the hell out of a lot of people with the way you talked
about coordinate systems. Your non-standard terminology and confused
statements were hardly Matthew Wiener's fault. But we finally seem to
be agreeing on the physics, anyway -- no more wild tachyon talk. Read
Russell again, and I think you will see that his remarks, while perhaps
unfortunately phrased, show that he DID understand the physics. He was
just trying to say that the formulation was covariant with change of
coordinate system. Matthew was the one who posted comments about Kerr
geometry in the first place. You should try to READ what other people
write before jumping on them.
No one (or at least not Matthew or I) was EVER trying to deny that
a rotating earth was different than a non-rotating one! Nor, as far as
I can see, was Russell denying it.
ucbvax!brahms!gsmith Gene Ward Smith/UCB Math Dept/Berkeley CA 94720
"The *evident* character of this defective cognition of which mathematics
is proud, and on which it plumes itself before philosophy, rests solely on
the poverty of its purpose and the defectiveness of its stuff, and is therefore
of a kind that philosophy must spurn." -- G. W. F. Hegel