# Is spin a relative motion? **URL:** \ **Category:** Factual Questions\ **Created:** [September 19, 2017, 2:45am UTC](https://boards.straightdope.com/t/is-spin-a-relative-motion/796687 "2017-09-19T02:45:18Z")\ **Posts on this page:** 9\ **Page:** 3
**Author:** ![igor\_frankensteen](https://avatars.discourse-cdn.com/v4/letter/i/839c29/32.png) [@igor\_frankensteen](https://boards.straightdope.com/u/igor_frankensteen)\ **Post date:** [September 29, 2017, 3:00am UTC](https://boards.straightdope.com/t/is-spin-a-relative-motion/796687/41 "2017-09-29T03:00:36Z")
I think the core of this thread, is based around the challenge that awareness of relativity effects, have caused a lot of less than completely informed people (which includes most of us) to get lost here and there. Even to the point where it can seem that we are being told that NO motion is real, and that it’s ALL relative. Perhaps the better question would be to ask what EFFECTS of spin, are dependent on the spinning object being a part of a larger system, and what effects are entirely due to the object and it’s spin by itself. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 29, 2017, 3:18am UTC](https://boards.straightdope.com/t/is-spin-a-relative-motion/796687/42 "2017-09-29T03:18:32Z")
The answer is the same: So far as we can tell, the effects of spin don’t depend on any other objects. But it’s possible that they depend on the entirety of all other objects in the Universe. ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [October 17, 2017, 11:34pm UTC](https://boards.straightdope.com/t/is-spin-a-relative-motion/796687/43 "2017-10-17T23:34:25Z")
This article from the most recent issue of “American Scientist” discusses this topic and may be of general interest [https://www.americanscientist.org/article/the-forgotten-mystery-of-inertia](https://www.americanscientist.org/article/the-forgotten-mystery-of-inertia) ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [October 18, 2017, 12:58am UTC](https://boards.straightdope.com/t/is-spin-a-relative-motion/796687/44 "2017-10-18T00:58:09Z")
Spin is relative to itself, unless it’s a point, or a line rotating around it’s axis. Since in your boat analogy, it is not a single boat be a fleet of boats making up the structure, and they are moving at different rates in respect with each other. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [October 18, 2017, 2:00am UTC](https://boards.straightdope.com/t/is-spin-a-relative-motion/796687/45 "2017-10-18T02:00:09Z")
> [@Trinopus](#): > > The magical disappearance of an object is a commonplace thought-experiment in relativity, especially relating to the “speed of gravity.” If the sun suddenly disappeared, how long would it take earth’s orbit to straighten out? Nearly everyone says gravity would still “travel” through space at the speed of light, but there are a tiny handful of dissidents who say it propagates instantaneously. Unfortunately, physics makes no provision for masses “suddenly” disappearing, so the thought-experiment is null and moot. I believe that it has rather conclusively been demonstrated that the propagation of gravitational waves does not exceed the speed of light. If the α-Centauri stars were to unexpectedly crash into each other and explode into a diffuse nebula, the effect of the change in the system’s gravity would be “felt” here 4 years later, at the same time as we would be observing the collision. Just this week, a neutron star collision was detected by LIGO and the whole global astronomic community was able to train their telescopes on it to observe the visible (and extra-visible) emissions. The dissidents are standing on quicksand. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 18, 2017, 2:09am UTC](https://boards.straightdope.com/t/is-spin-a-relative-motion/796687/46 "2017-10-18T02:09:41Z")
Whoa, whoa, whoa… We got an EM-grav coincidence!? When did this happen? \ And it showed up on VIRGO, too!? Woo-hoo, with an extra dose of woo-hoo! ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [October 18, 2017, 2:53am UTC](https://boards.straightdope.com/t/is-spin-a-relative-motion/796687/47 "2017-10-18T02:53:19Z")
> [@Chronos](#): > > Whoa, whoa, whoa… We got an EM-grav coincidence!? When did this happen? > > \ > > And it showed up on VIRGO, too!? > > Woo-hoo, with an extra dose of woo-hoo! They announced it yesterday. Were you sleeping?? They found GOLD! ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [October 18, 2017, 3:30am UTC](https://boards.straightdope.com/t/is-spin-a-relative-motion/796687/48 "2017-10-18T03:30:13Z")
Ok, it was not “just this week”, the observational frenzy happened in late August. The announcement was yesterday. But it brings up an interesting on-topic question. Two neutron stars are going to ridiculous spin. But as they close in on each other, they will approach tidal locking. So, does their spin, as they move into lock-step, affect their motion? Will synchronous spin have a braking effect on their mutual spirals (extending the passage) or an accelerating effect? What happens with spins that mismatch by a great deal? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 18, 2017, 11:27am UTC](https://boards.straightdope.com/t/is-spin-a-relative-motion/796687/49 "2017-10-18T11:27:45Z")
Short answer: What happens is that a few astrophysicists get their grant application for more supercomputer time approved. That’s a very messy and chaotic (and yes, I mean that in the technical sense) problem. [Previous page](https://boards.straightdope.com/t/is-spin-a-relative-motion/796687.md?page=2)