Re: Q question about relativity
From: Andr? Michaud (srp_at_microtec.net)
Date: 09/04/04
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Date: 4 Sep 2004 05:48:12 -0700
"N:dlzc D:aol T:com \(dlzc\)" <N: dlzc1 D:cox T:net@nospam.com> wrote in message news:<I%8_c.84970$4o.28283@fed1read01>...
> Dear Andr? Michaud:
>
> "Andr? Michaud" <srp@microtec.net> wrote in message
> news:562f286c.0409031652.1ca93c28@posting.google.com...
> > "Harry" <harald.vanlintel@epfl.ch> wrote in message
> > news:<41388cd0$1@epflnews.epfl.ch>...
> >> "N:dlzc D:aol T:com (dlzc)" <N: dlzc1 D:cox T:net@nospam.com> wrote in
> >> message news:fH_Zc.84899$4o.84201@fed1read01...
> >> > Dear Harry:
> >> >
> >> > "Harry" <harald.vanlintel@epfl.ch> wrote in message
> >> > news:4138415c$1@epflnews.epfl.ch...
> >> > >
> >> > > "Uncle Al" <UncleAl0@hate.spam.net> wrote in message
> >> > > news:41374702.5559C306@hate.spam.net...
> >> > >> Ohad wrote:
> >> > ...
> >> > >> > Einstein said that a proof of his theory, about changing the
> >> > >> > space, is seeing that even light is bent according to
> >> > >> > gravitation.
> >> > >>
> >> > >> Learn something,
> >> > >>
> >> > >> http://arXiv.org/abs/gr-qc/9909014
> >> > >> Phys. Rev. Lett. 92 (2004) 121101
> >> > >> falling light
> >> > >
> >> > > Einstein was dead in 2004. He certainly did not write that. Learn
> >> > > something:
> >> > >
> >> > > "We easily recognize that the course of the light-rays must be bent
> >> > > with
> >> > > regard to the system of co-ordinates" - in "The foundation of the
> >> > > general
> >> > > theory of relativity", A. Einstein
> >> >
> >> > Harald, Einstein indeed died in 1955. I think Uncle Al's point is
> >> > that
> >> > the OP wasn't aware that Einstein is not the last word in relativity.
> >> > Even at the time of the formulation of the GTR, Einstein was not the
> >> > only person working on the math. And it is even being reformulated
> >> > and tested even today.
> >> >
> >> > Even Einstein chose some sloppy wording. Maybe he wasn't aware of
> >> > those
> >> > multitudes that would come after him, that would remember the *wrong*
> >> > syllogism, and not retain the bigger picture.
> >>
> >> Fine. Maybe I overreacted a bit to the "correction" that "light falls".
> >> What I object to is the mistreatment claiming that light "falls" in the
> >> sense that its frequency increases, as also some others have remarked
> >> (and
> >> even Einstein, although IMO inconsistently, in 1911).
> >> "the [redshift] phenomenon is alternatively discussed (even in some
> >> authoritative texts) in terms of an energy loss of a photon as it
> >> overcomes
> >> the gravitational attraction of the massive body. This second approach
> >> [...]
> >> we assert that it is misleading."
> >> http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=AJPIAS000068000002000115000001&idtype=cvips&gifs=yes&jsessionid=3051831093837402530
> >>
> >> > If you'll note the choice of Einstein's words, you'll see the words
> >> > "course" and "system of co-ordinates" being used, as if the photon
> >> > were
> >> > barely involved. The "course" or path is bent in the chosen "system
> >> > of
> >> > co-ordinates". The photon is unaffected, and simply follows this
> >> > path.
> >>
> >> The same can be said for a satellite in orbit around earth. Still we say
> >> that its path is bended - in our reference system.
> >
> > Not really. All satellites launched to orbit the Earth are affected. They
> > all are imperceptibly slowly spiralling down. No really stable orbit that
> > close to the Earth can apparently be established.
> >
> > All those that are not re-boosted back in a timely manner the desired
> > orbit eventually end up reintering the atmosphere and burning up.
>
> This is due primarily to interaction with a very tenuous amount of gas that
> is *not* orbiting.
Certainly a factor. But this does not really exclude the possible existence
of a yet to be pegged down "systematic" just as in the case of the far
spacecrafts trajectories.
> >> > The path is different than one a massive particle, even travelling at
> >> > 0.9999999999999c, would take. Null geodesics are like that.
> ...
> >> Then I misunderstood the paper of Carlip... Please clarify!
> >
> > Yes. I too am interested in your explanation.
>
> OK. "Different" does not mean "double". In this case "different" is "less
> than". Less curvature due to gravity of the path of a photon, than the
> curvature due to gravity experienced by the fastest massive particle.
You probably meant "more curvature" for the path of a photon since
photons are deflected more than if they were really massive (really
exactly twice the angle), more than any really massive particles. This
is precisely what struck so much the imagination of all scientists in
1919 when Eddington et al. reported the results of their observations,
which saddled GR for the duration.
Interesting, isn't it, that a massless particle (a photon) can force
spacetime to curve more locally than a massive particle passing on the
very same path.
Wonder what would happen if perchance a near light velocity neutron
grazed the Sun on the same path and at the very same moment as a
photon that flew right next to it at the critical moment.
Wonder how spacetime will succeed in providing both curvatures at the
same time at the very same location without spraining some sort of
cosmological ankel.
I wonder what GR interpretation Einstein would have made of such a
Gedankenexperiment. Or maybe he did, although I never came across
any.
André Michaud
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