# A truly motionless object. Possible? **URL:** \ **Category:** Factual Questions\ **Created:** [March 28, 2003, 1:58pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771 "2003-03-28T13:58:35Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![DasUnterMensch](https://avatars.discourse-cdn.com/v4/letter/d/c6cbf5/32.png) [@DasUnterMensch](https://boards.straightdope.com/u/DasUnterMensch)\ **Post date:** [March 28, 2003, 3:40pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771/21 "2003-03-28T15:40:39Z")
So Heisenberg’;s Uncertainty applies to the macro as well? I’m totally confused now. ---
**Author:** ![MC\_Master\_of\_Ceremonies](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)\ **Post date:** [March 28, 2003, 3:47pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771/22 "2003-03-28T15:47:08Z")
Of course hesiebergs uncertainity principle applies to macroscopic objects too, it’s just that the degree of uncertainty will be microscopic (if you want to look at idealized situations). Another important thing about the hesienberg uncertainty principle is that it does not just limit the knowledge of the observer, but the ‘knowledge’ (or behaviour if you prefer) of individual particles. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [March 28, 2003, 3:50pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771/23 "2003-03-28T15:50:02Z")
If you took the background microwave radiationas a frame of reference, the Milky way galaxy would be rushing past at 600km per second, which sounds like a lot; but is a tiny fraction of the speed of light- you would hardly be able to detect any motion once the solar system had scooted away into the distance. Then you would hit another problem… you would be falling toward the centre of the galaxy…, and also toward any other object you might pass near… if you have mass you would not be able to remain stationary relative to the background radiation without accelerating against gravity. anyway, all the particles within such a 'stationary ’ object would be moving relative to each other unless it were at zero kelvin. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [March 28, 2003, 3:54pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771/24 "2003-03-28T15:54:20Z")
And as MC says, ZPE fluctuations perturb even at 0 kelvin. ---
**Author:** ![Phage](https://avatars.discourse-cdn.com/v4/letter/p/a4c791/32.png) [@Phage](https://boards.straightdope.com/u/Phage)\ **Post date:** [March 28, 2003, 4:13pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771/25 "2003-03-28T16:13:57Z")
HIJACK! ``` What is up with there not being a universal frame of reference? If nothing can move faster than the speed of light (in a vacuum), not even light, then what frame of reference is light using? If you try to shine a light forward in a craft that is moving close to the speed of light, the light would move forward at a speed which from the craft’s standpoint would be comparatively slow. So, isn’t light using a frame of reference that never changes? ``` ---
**Author:** ![MC\_Master\_of\_Ceremonies](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)\ **Post date:** [March 28, 2003, 4:19pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771/26 "2003-03-28T16:19:43Z")
No, because time is relative too, at whatever speed you are travelling at the speed of light is always the same. So it cannot be used as a reference point. ---
**Author:** ![dylan\_73](https://avatars.discourse-cdn.com/v4/letter/d/ecccb3/32.png) [@dylan\_73](https://boards.straightdope.com/u/dylan_73)\ **Post date:** [March 28, 2003, 4:44pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771/27 "2003-03-28T16:44:05Z")
> [@](#): > > \*Originally posted by Phage \* > **If you try to shine a light forward in a craft that is moving close to the speed of light, the light would move forward at a speed which from the craft’s standpoint would be comparatively slow.** No, from the craft’s viewpoint the light would move away at the speed of light. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [March 28, 2003, 4:56pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771/28 "2003-03-28T16:56:57Z")
> [@](#): > > \*Originally posted by CalMeacham \* > \*\*So the answer is “no”, you can’t have an object perfectly motionless in space, because that implies perfect knowledge of position and momentum. \*\* I think “perfectly motionless” only implies a perfect knowledge of momentum. You don’t need to know the location. Although come to think of it, you might have to set the uncertainty in position to be the size of the visible universe, or something like that. But then we get into the unknown territory where quantum mechanics and relativity collide. By the way, I think **Phage** has a point. The cosmic background radiation is uniform in only one rest frame, so that is in effect the rest frame of the universe. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [March 28, 2003, 4:58pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771/29 "2003-03-28T16:58:46Z")
> [@](#): > > \*Originally posted by other-wise \* > \*\*(I’d really like feedback on this… it caused a minor philosophical brawl among my friends just last night.) \*\* Brain bout!! Love to see 'em eggheads rolling around in a morass. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [March 28, 2003, 5:09pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771/30 "2003-03-28T17:09:23Z")
Hm, I guess I misread **Phage** ’s post. Light itself is not define a reference frame, because the speed appears constant regardless of how fast you are moving. ---
**Author:** ![Phage](https://avatars.discourse-cdn.com/v4/letter/p/a4c791/32.png) [@Phage](https://boards.straightdope.com/u/Phage)\ **Post date:** [March 28, 2003, 5:33pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771/31 "2003-03-28T17:33:17Z")
So, if the speed of light appears constant regardless of how fast you are moving, then the ship with the light would be able to flip them on and illuminate objects ahead of them with the expected speed (e.g.: something 3 light minutes away would be seen as getting brighter about 6 minutes later). How would the object illuminated perceive this approaching beam of light? If they saw the craft, it would be for only an instant as any light that hit it and returned would be only moments ahead of the ship itself. However, they would also be struck with the headlights of the ship well ahead of the ship’s passing. Wouldn’t that indicate the light from the ship’s headlights was exceeding the speed of light? ---
**Author:** ![Revtim](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/revtim/32/1042_2.png) [@Revtim](https://boards.straightdope.com/u/Revtim)\ **Post date:** [March 28, 2003, 5:43pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771/32 "2003-03-28T17:43:21Z")
Before I thought about the universe expanding, I was about to write that if _everything_ in the universe was motionless then there would only be one frame of reference, and hence “true” motionlessness achieved. But I guess expansion rules out even that theoretical possibility. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [March 28, 2003, 6:40pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771/33 "2003-03-28T18:40:31Z")
## However, they would also be struck with the headlights of the ship well ahead of the ship’s passing. Wouldn’t that indicate the light from the ship’s headlights was exceeding the speed of light? No, the light from the headlights and the image of the ship would arrive simultaneously, at the speed of light. (thats why it is called the speed of light.) ---
**Author:** ![SCSimmons](https://avatars.discourse-cdn.com/v4/letter/s/e495f1/32.png) [@SCSimmons](https://boards.straightdope.com/u/SCSimmons)\ **Post date:** [March 28, 2003, 7:14pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771/34 "2003-03-28T19:14:47Z")
> [@](#): > > ## \*Originally posted by eburacum45 \* \*\*However, they would also be struck with the headlights of the ship well ahead of the ship’s passing. Wouldn’t that indicate the light from the ship’s headlights was exceeding the speed of light? > > No, the light from the headlights and the image of the ship would arrive simultaneously, at the speed of light. > (thats why it is called the speed of light.) \*\* I think that **Phage** ’s puzzlement is that this seems inconsistent with the fact that, from the point of view of the _ship_, their headlights _do_ strike the object well ahead of the ship’s passing. How can the two events seem virtually simultaneous to the observers at the object but not to the observers on the ship? Let’s run it through from each point of view. For the ship, the object is moving toward them at, say, .99 c. Their headlights strike it as it passes three light-minutes away, then the reflected light reaches the ship three minutes later, followed ~1.8 seconds later by the object. (Evasive maneuvers, Mr. Sulu!) The light from the headlights that was first reflected from the object must therefore have been emitted while the ship was six light-minutes away (plus a few light-seconds; we can ignore that for the moment). Now, what does this look like from the point of view of the observer on the object? Well, the light from the headlights first struck the object when the ship was three light-minutes away, right? So, the ship moving at .99 c won’t arrive for more than three minutes after the glow of its headlights turn up, right? Uh, no, that can’t be right, because they collide only 1.8 seconds later, barring some impressive reaction times on Mr. Sulu’s part. So, obviously the ship only emitted that light about 1.9 seconds ago, at a distance(therefore) of only 1.9 light-seconds. But that can’t be right either! WTF?! You can find the real answer in any good textbook on special relativity. Suffice to say that the two sets of observers will report different time intervals and space separations between the three events (light emitted, light reflected, light returns to emitter), and both sets of observers will be right in spite of their disagreement … ---
**Author:** ![Phage](https://avatars.discourse-cdn.com/v4/letter/p/a4c791/32.png) [@Phage](https://boards.straightdope.com/u/Phage)\ **Post date:** [March 28, 2003, 7:16pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771/35 "2003-03-28T19:16:54Z")
eburacum45, that is my point! Your reply is in direct contrast to what dylan\_73 said: “No, from the craft’s viewpoint the light would move away at the speed of light.” Same thing with scr4’s second post. The way I see it, the light would not move away at the speed of light, it would move away at whatever speed the craft is below the speed of light. Were the light to appear to the craft to move forward at the speed of light, observers would see a craft emitting a beam moving almost twice the speed of light as far as they could tell. ---
**Author:** ![Phage](https://avatars.discourse-cdn.com/v4/letter/p/a4c791/32.png) [@Phage](https://boards.straightdope.com/u/Phage)\ **Post date:** [March 28, 2003, 7:27pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771/36 "2003-03-28T19:27:49Z")
So basically what SCSimmons is saying is that it works for each person, but in a different way… and somehow reality is ok with that. That is really f\*cked up, but it is the best explanation I have been given yet. ---
**Author:** ![Derleth](https://avatars.discourse-cdn.com/v4/letter/d/b9e5f3/32.png) [@Derleth](https://boards.straightdope.com/u/Derleth)\ **Post date:** [March 28, 2003, 7:41pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771/37 "2003-03-28T19:41:53Z")
**Phage** , you’re hitting your head on the concept of frames of reference. Each frame of reference (be it inside the craft with the headlights or on the object that craft will hit) is perfectly correct, _even if the only thing they agree on is the velocity of light._ But they are guaranteed to agree on that much (the speed of light). Common sense has no place in relativity. ---
**Author:** ![JasonFin](https://avatars.discourse-cdn.com/v4/letter/j/4af34b/32.png) [@JasonFin](https://boards.straightdope.com/u/JasonFin)\ **Post date:** [March 28, 2003, 7:51pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771/38 "2003-03-28T19:51:53Z")
**Phage** , it is an axiom of special relativity that light moves at a constant speed, c, in every inertial (non-accelerating) frame of reference. If a spaceship is moving at .99c in my frame of reference, and shines a light forward, then the light will move at c in my frame of reference (pulling ahead of the spaceship at .01c) and it will also move at c in the spaceship’s frame of reference (pulling ahead of the spaceship at c). This works out because each frame of reference will see every other frame of reference as having lengths which are contracted in the direction of motion and clocks which run slowly (both by a factor of gamma=1/Sqrt[1 - v^2/c^2]), and they will also measure different pairs of events as occuring simultaneously. In each frame, this suffices to precisely explain all disagreements. This may seem unintuitive, but the predictions of special relativity have been confirmed to an extraordinary degree of precision. It is the basis of all modern physical theories. I see on preview that **Darleth** beat me to it, but such is life. ---
**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:** [March 28, 2003, 8:25pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771/39 "2003-03-28T20:25:15Z")
If I am in any sort of reference frame whatever (a planet, a moving starship, even almost falling into a black hole) and you’re also in any frame of reference whatever, and I shine a flashlight at you, I’ll measure the exact same speed for that light that you will, and that speed will be the same as the speed anyone else would ever measure for any light. Yes, this is counterintuitive, but it’s also absolutely true. The light will, however, probably appear a different color to you. And the “quantum foam”, if it exists, almost certainly takes such a form that it can’t be used to define a reference frame, either. ---
**Author:** ![Kivick](https://avatars.discourse-cdn.com/v4/letter/k/65b543/32.png) [@Kivick](https://boards.straightdope.com/u/Kivick)\ **Post date:** [March 28, 2003, 10:14pm UTC](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771/40 "2003-03-28T22:14:55Z")
A bit of oversimplification and obvious but: It is possible to do this but from our perspective it would appear to be moving… [Previous page](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771.md?page=1) [Next page](https://boards.straightdope.com/t/a-truly-motionless-object-possible/164771.md?page=3)