# Gavitity question **URL:** \ **Category:** Factual Questions\ **Created:** [March 10, 2003, 3:14pm UTC](https://boards.straightdope.com/t/gavitity-question/160310 "2003-03-10T15:14:48Z")\ **Posts on this page:** 5\ **Page:** 2
**Author:** ![dalovindj](https://avatars.discourse-cdn.com/v4/letter/d/65b543/32.png) [@dalovindj](https://boards.straightdope.com/u/dalovindj)\ **Post date:** [June 19, 2003, 6:18pm UTC](https://boards.straightdope.com/t/gavitity-question/160310/21 "2003-06-19T18:18:26Z")
I was just thinking of you **Chronos** , funny you should drop by this thread. I was about to post a link to your [Staff Report on this very subject](http://www.straightdope.com/mailbag/mgravityspeed.html). As a matter of fact I just did. Thanks for the time spent on this subject and the resulting info. It will be a very cool day when we detect gravitons. . . DaLovin’ Dj ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [June 19, 2003, 6:23pm UTC](https://boards.straightdope.com/t/gavitity-question/160310/22 "2003-06-19T18:23:00Z")
I’m skeptical about the criticism in **dalovindj** ’s link: > [@](#): > > Samuel was able to simplify the calculations of the velocity-dependent effects by shifting from a reference frame in which Jupiter is moving, as was used by Kopeikin, to a reference frame in which Jupiter is stationary and Earth is moving. When he did this, Samuel found a formula that differed from the one used by Kopeikin to analyze the data. Under this new formula, the velocity-dependent effects were considerably smaller. Even though Fomalont was able to measure a time delay of about 5 trillionths of a second this was not nearly sensitive enough to measure the actual gravitational influence of Jupiter. If Samuel is working in Jupiter’s frame of reference, why is there _any_ velocity dependent effect in the effect due to Jupiter’s gravity? Jupiter’s gravitational field isn’t time-varying. I’ll be interested in the response of the Kopeikin and Fomalont. ---
**Author:** ![dalovindj](https://avatars.discourse-cdn.com/v4/letter/d/65b543/32.png) [@dalovindj](https://boards.straightdope.com/u/dalovindj)\ **Post date:** [June 19, 2003, 7:05pm UTC](https://boards.straightdope.com/t/gavitity-question/160310/23 "2003-06-19T19:05:27Z")
Just for good measure. A [link to the related thread](http://boards.straightdope.com/sdmb/showthread.php?threadid=182869) in the “Comments on Staff Reports” forum. Seems the only thing agreed upon here is that the answer to these questions are still up in the air. I also have some doubts about the process described in that quote, **ZenBeam**. I’m kind of surprised that they performed the wrong equations initially and that this guy was just able to use the same set of numbers to get a different answer. Of course his answer was that the results are not measureable with current equipment (resolution not good enough), so it’s not like he’s found anything revealing - other than the fact that neither had those other scientists. I have a little bit of trouble visualizing how the proper experiment _should_ go once we have the tools and what the indicators of success will be. I also can’t figure out why the first guys didn’t realize they weren’t using the right numbers. . . DaLovin’ Dj ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [June 19, 2003, 9:47pm UTC](https://boards.straightdope.com/t/gavitity-question/160310/24 "2003-06-19T21:47:18Z")
I’m wondering if Samuel’s transformation from the (presumably) Earth-fixed frame of reference to the Jupiter-fixed frame of reference means that the velocity effects are reduced by a factor of 300 to 600. The 300 is the relative mass of Jupiter, and there is perhaps a factor of 2 since the quasar’s light is affected on both the approach to Jupiter, and also when leaving Jupiter (when making the calculations in the frame where Jupiter is moving), but is only affected on the approach to Earth when making calculations in the frame where the Earth is moving. Admittedly, this is some severe hand-waving, but it’s in the ballpark of the difference between the effect being barely measurable to the effect being 100 to 1000 times too small to detect. ---
**Author:** ![Ring](https://avatars.discourse-cdn.com/v4/letter/r/6a8cbe/32.png) [@Ring](https://boards.straightdope.com/u/Ring)\ **Post date:** [June 20, 2003, 2:20am UTC](https://boards.straightdope.com/t/gavitity-question/160310/25 "2003-06-20T02:20:06Z")
> [@](#): > > \*Originally posted by Achernar \* > \*\*The thing is, there’s an explicit time dependence that you left out. You have to use the values of m1 and r at the retarded time, not the current time, if gravity travels at a finite speed. \*\* I believe that in GR the retardation due to both constant velocity and constant acceleration is corrected for. I know that if the force vector didn’t point to the present (versus retarded) position of the Sun the Earth’s orbit would be unstable. I’m also sure you knew this **Achernar** so I’m just writing this for some obscure reason or other. [Previous page](https://boards.straightdope.com/t/gavitity-question/160310.md?page=1)