Re: [Phys-l] New gravitational constant

["LaMontagne, Bob" <RLAMONT@providence.edu>]

I am always puzzled by the large uncertainties in G, given that we can
measure the speed of interplanetary probes so accurately. When a probe
does a fly-by of a planet, one can calculate the expected speed of the
probe after the encounter. As recently reported, 

<http://www.universetoday.com/2008/01/20/a-possible-answer-to-flyby-anom
olies/>

the speed of the probes sometimes increases by about 1 cm/sec above the
expected value. This increase is easily detectable with current
instruments. This seems remarkably precise to me given the uncertainty
in the value of G. Is the orbital speed during a slingshot maneuver
insensitive to the exact value of G? Can't these discrepancies be used
to improve G?

The tentative explanation for the speedup appears to be related to the
Unruh effect <http://arxiv.org/abs/0712.3022>, but this does not explain
why G is not required to be more precise to make the orbital
calculations. Maybe I'm missing something simple here.

Bob at PC

 

> -----Original Message-----
> From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
> bounces@carnot.physics.buffalo.edu] On Behalf Of John Denker
> Sent: Tuesday, January 22, 2008 10:54 AM
> To: Forum for Physics Educators
> Subject: Re: [Phys-l] New gravitational constant
>
> Another useful reference:
>   Lopez & Silk   http://arxiv.org/pdf/astro-ph/0112310
>
> It includes a table of G values over time, plus discussion.
> I inadvertently left this out of my previous msg.  Sorry.
>
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