Re: The Spin Proviso to Relativity

From: sal (pragmatist_at_nospam.org)
Date: 10/20/04 

Date: Wed, 20 Oct 2004 15:52:28 -0400

On Wed, 20 Oct 2004 21:06:20 +0200, Paul B. Andersen wrote:

>
> "Ben Bean" <kavs_delethis_@sysmatrix.net> skrev i melding
> news:B8SdncZcW_z2v-ncRVn-oA@sysmatrix.net...
>> I am eager to hear wisdoms in answer to the quandary below stated.
>>
>> SCENARIO: You stand on a planet just like Earth, but there's no
>> atmosphere. You stand on the equator and hold your hands up to the air
>> so that they are a meter apart. [Relax, this is NOT a study in relative
>> simultaneity like the Barn/Pole thing.] As you stand there a huge
>> spacecraft coasts by just overhead, just beyond your reach. The ship
>> seems motionless to you, hovering, because it is going eastward at a
>> speed to exactly match the planet's tangential rotational speed. As you
>> reach up, your outstretched fingertips are just about touching the
>> 842-meter mark and the 843-meter mark on the rule graduated on the
>> enormous ship's straight exterior.
>>
>> Here's the quandary: the spaceship occupants can EMPHATICALLY assert
>> that an all-way light beacon pulse emitted midway between their ship's
>> 842 & 843-meter marks will hit the two nearby meter marks
>> simultaneously, according to their native frame's clocks and such. Yet
>> the guy on the planet cannot make the same claim?? When does an
>> arbitrary local span become tantamount to an SR scenario. In spite of
>> Sagnac, there must surely be some carry-over; I mean you're just about
>> TOUCHING that other frame, comoving.
>>
>> -Ben
>
> Of course the guy on the planet will agree that the light will hit the two
> metre marks simultaneously. That is, if he had one clock at each side of
> himself, and he E-synched those clocks, they would show the same when hit
> by the light.
> However, if the two clocks were showing UTC, they would NOT show the same
> when hit by the light.
> Clocks on the surface of the Earth showing UTC are NOT synchronous in the
> Earth fixed frame. They are synchronous in the non rotating ECI-frame.

Paul, what do you mean by "Earth fixed frame"? Do you mean the
inertial frame which is momentarily comoving with the surface at one
particular point? 

-- 
I can be contacted through http://www.physicsinsights.org

Relevant Pages

  • Re: Limitations of Sagnac generality
    ... Whether or not those EM signals hit the goal posts "simultaneously" ... If you synchronize your clocks in the inertial frame you mentioned, ... your clocks in the ECI frame then the signal will hit the west goalpost ...
    (sci.physics.relativity)
  • Re: Limitations of Sagnac generality
    ... > If you synchronize your clocks in the inertial frame you mentioned, ... > the EM sitnal will hit the goalposts simultaneously. ...
    (sci.physics.relativity)
  • Re: relativity of simultaneity - real or perceived?
    ... Let us assume that in frame 1 we set up two ... >>assert that if both light pulses hit the detectors at the same ... > continually examine the clocks to see if they are stopped, and if so, ...
    (sci.physics.relativity)
  • Re: The Spin Proviso to Relativity
    ... >> However, if the two clocks were showing UTC, they would NOT show the same ... >> when hit by the light. ... I mean the rotating frame fixed to the Earth and rotating along ...
    (sci.physics.relativity)