Re: Q question about relativity

From: N:dlzc D:aol T:com \(dlzc\) (net_at_nospam.com)
Date: 09/04/04 

Date: Fri, 3 Sep 2004 18:37:46 -0700

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.

>> > 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.

David A. Smith

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