Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Seany on 01/04/2008 15:14:20

Title: Can anything be "still" in space?
Post by: Seany on 01/04/2008 15:14:20
If we put a tennis ball in space.. And we touch it so that it is very still.. Can we make it PERFECTLY still?
Is anything in space PERFECTLY STILL?
Title: Can anything be "still" in space?
Post by: lightarrow on 01/04/2008 16:58:25
If we put a tennis ball in space.. And we touch it so that it is very still.. Can we make it PERFECTLY still?
Is anything in space PERFECTLY STILL?

Still with respect to what?
Title: Can anything be "still" in space?
Post by: Seany on 01/04/2008 17:14:26
Oh.. I see your point.. Ahh.. Now that makes matter very difficult! [:P]
Title: Can anything be "still" in space?
Post by: Kryptid on 01/04/2008 19:46:14
How about still in the sense that the tennisball observes no net redshift or blueshift of the cosmic microwave background radiation?
Title: Can anything be "still" in space?
Post by: Seany on 01/04/2008 20:39:51
Yes.. [???]
Title: Can anything be "still" in space?
Post by: lightarrow on 02/04/2008 08:13:41
How about still in the sense that the tennisball observes no net redshift or blueshift of the cosmic microwave background radiation?
So there exist a frame of reference where this happens? What is it? Earth? Solar system? Our Galaxy centre? (I'm asking because Idon't know)
Title: Can anything be "still" in space?
Post by: syhprum on 02/04/2008 09:04:37
Although we all long for a frame of reference the CMBR cannot be this as it is in fact expanding (else it would still have the temperature of the 'big bang' also it is not homogeneous.
Title: Can anything be "still" in space?
Post by: Kryptid on 02/04/2008 16:52:50
If I'm not mistaken, things down on the subatomic level can't be perfectly still due to the Uncertainty Principle and/or interactions with vacuum fluctuations, right?
Title: Can anything be "still" in space?
Post by: Seany on 02/04/2008 16:59:22
That's what I was thinking..
Title: Can anything be "still" in space?
Post by: neilep on 02/04/2008 17:21:53
As a firm believer in empirical study , last night I went and looked at Space....and today I can see that it is ' still ' there !

So yes, space is ' still '  [:D]

Glad I could help.  [;)]

Title: Can anything be "still" in space?
Post by: lyner on 03/04/2008 11:11:16
You would have seen a different picture when you were born, tho - or even the day before. It's all on the move.
Title: Re: Can anything be "still" in space?
Post by: chris on 28/12/2017 09:32:00
Thought-provoking question from the archives here!

Anyone anything to add? Has thinking at least moved on since this subject was last visited?
Title: Re: Can anything be "still" in space?
Post by: Colin2B on 28/12/2017 09:48:21
It occurs to me that there are 3 ways of looking at still:
- Stationary with respect to me
- that doesnt mean still in an absolute sense
- an object will still have some internal vibrations - temperature related
- can we ever say some thing is still due to uncertainty principle

Mmm, thatís 4
Any others out there?

It also seems to me that anything in real space will be bombarded with radiation eg sun and so will gain momentum
Title: Re: Can anything be "still" in space?
Post by: Bill S on 28/12/2017 12:00:56
If space were infinite, and contained only one object, it could be argued that that object would be still.  Beyond that, it seems that all motion must be relative to something, and motion/stillness must be RF related.  Unless there is an absolute RF, surely, there can be no absolute stillness. (?)
Title: Re: Can anything be "still" in space?
Post by: jeffreyH on 28/12/2017 13:45:31
You can define still to be within a defined range of uncertainty on the microscopic scale. With that issue resolved you can then look at still with respect to the macroscopic scale. Alan recently mentioned the 21cm hydrogen line as a means of measuring velocity. If I remember correctly. The mean of measurements in all directions of the deviation of this line should give you an idea of how 'still' you are compared with selected celestial objects.
Title: Re: Can anything be "still" in space?
Post by: Bored chemist on 28/12/2017 13:59:00
The ball will have zero point energy, so it will always be vibrating a bit.
Title: Re: Can anything be "still" in space?
Post by: Bill S on 28/12/2017 14:42:41
Quote from: Jeffrey
  The mean of measurements in all directions of the deviation of this line should give you an idea of how 'still' you are compared with selected celestial objects.

My understanding of the OP was that we were looking for the possibility, or otherwise, of absolute stillness.  Accurate as this, or any,  measurement might be, it measures only relative motion/stillness, as your "...compared with selected celestial objects" recognises.
Title: Re: Can anything be "still" in space?
Post by: Colin2B on 28/12/2017 16:24:29
If space were infinite, and contained only one object, it could be argued that that object would be still. 
Or that you canít tell.
Vibrational stillness is different, in theory you could detect the micro accelerations.
Title: Re: Can anything be "still" in space?
Post by: Bill S on 28/12/2017 17:39:12
Quote
Or that you canít tell.

That's why I said "it could be argued".

Quote
Vibrational stillness is different, in theory you could detect the micro accelerations.

Would they not be relative to something.  I'm having difficulty visualising a single object (with no parts or divisions) vibrating with respect to itself, in an infinite void.
Title: Re: Can anything be "still" in space?
Post by: jeffreyH on 28/12/2017 18:18:37
Quote from: Jeffrey
  The mean of measurements in all directions of the deviation of this line should give you an idea of how 'still' you are compared with selected celestial objects.

My understanding of the OP was that we were looking for the possibility, or otherwise, of absolute stillness.  Accurate as this, or any,  measurement might be, it measures only relative motion/stillness, as your "...compared with selected celestial objects" recognises.

Relativity and uncertainty will always thwart any attempt at precision. You cannot define absolutely still for obvious reasons. You cannot define a fixed background.
Title: Re: Can anything be "still" in space?
Post by: jeffreyH on 28/12/2017 18:30:30
I am going to say something else on this matter. Say you had a lattice of photons that you decided were going to be your fixed background. How can you determine that the whole lattice is not moving in a particular direction? That the paths of the photons are in fact not those of an absolutely stationary frame. If the local frame is inertial then it is not possible to tell since the laws of physics are the same for all inertial frames of reference.
Title: Re: Can anything be "still" in space?
Post by: Bill S on 28/12/2017 20:41:07
Quote
I am going to say something else on this matter. Say you had a lattice of photons that you decided were going to be your fixed background. How can you determine that the whole lattice is not moving in a particular direction? That the paths of the photons are in fact not those of an absolutely stationary frame. If the local frame is inertial then it is not possible to tell since the laws of physics are the same for all inertial frames of reference.

Agreed, but if your lattice of photons is in an infinite void, or any infinite "space-like entity", each photon must be perceived as occupying a central position, so differentiating between them, in terms of position, is possible only within your artificially constructed IRF. Beyond that, how is it possible to determine motion if you cannot determine position?
Title: Re: Can anything be "still" in space?
Post by: evan_au on 28/12/2017 21:51:28
Quote from: Kryptid
How about still in the sense that the tennisball observes no net redshift or blueshift of the cosmic microwave background radiation?
There is a slight asymmetry in the CMBR, equivalent to a Doppler-shift of Earth traveling about 600 km/second through space. This could be due to motion of our galaxy within the local galaxy cluster.

So I guess that you could use today's very precise measurements of the CMBR as a "common" frame of reference. Not that it would make any difference to the results of any experiments that you (or anyone else) does in their laboratory - as Einstein showed, all inertial frames are equivalent.
 
See: https://en.wikipedia.org/wiki/Cosmic_microwave_background#CMBR_dipole_anisotropy
Title: Re: Can anything be "still" in space?
Post by: guest4091 on 29/12/2017 16:08:57
If motion is relative, then stillness must also be relative.
I maintain the idea of abs. rest is a result of the definitions by Newton using an  over-simplified system of two valued logic, or complementary attributes, eg. hot-cold, light-dark, etc.
In relativity, two objects can be at relative rest, if both have the same velocity.
It seems contradictory, they are moving and at rest in simultaneous observations,  (depending on who is looking).
That would be my revised definition of rest, i.e. everything is in motion in a dynamic universe.
As in fuzzy logic, when measuring one attribute, you are indirectly measuring the complementary one.
Motion can be measured over a range of values, stillness is its complement.
Abs. rest is a special case of zero motion. You can have one or the other, but not both, a case of mutual exclusion. With a container, there is fullness and emptiness, by degree, i.e. complementarity. Full and empty are mutually exclusive.
Title: Re: Can anything be "still" in space?
Post by: Bogie_smiles on 29/12/2017 21:43:01
I would like to weigh in on this one. No, as I understand the universe, nothing can be still in space.

If we could strip space clean, and have emptiness, I think I would call that stillness, but that is not the same as something being still in space, is it.
Title: Re: Can anything be "still" in space?
Post by: jeffreyH on 30/12/2017 08:59:59
Quote
I am going to say something else on this matter. Say you had a lattice of photons that you decided were going to be your fixed background. How can you determine that the whole lattice is not moving in a particular direction? That the paths of the photons are in fact not those of an absolutely stationary frame. If the local frame is inertial then it is not possible to tell since the laws of physics are the same for all inertial frames of reference.

Agreed, but if your lattice of photons is in an infinite void, or any infinite "space-like entity", each photon must be perceived as occupying a central position, so differentiating between them, in terms of position, is possible only within your artificially constructed IRF. Beyond that, how is it possible to determine motion if you cannot determine position?

Exactly! Position, or more correctly displacement, has to be relative. Therefore, you can never define an absolute position. Your position relative to what? Otherwise the constancy of the speed of light in vacuum would be violated.
Title: Re: Can anything be "still" in space?
Post by: jeffreyH on 30/12/2017 09:32:10
Let's say we have a position P in spacetime that we know with absolute certainty is stationary with respect to the rest of the universe. We travel past P for one light second and mark another absolute position to show how far light travels for us in 1 second. Other travellers do the same. Their marks are all at different distances to ours since their velocities differed as they passed point P. Since quantum mechanics shows position to be a continuum, these points form an infinite series. Thus we see an infinite amount of variation in the perceived speed of light. The traveller who is stationary at point P would see an instantaneous speed for light. Since he has not moved. However, in relativity it is not possible to tell you are moving or not in an inertial frame of reference. So it can easily be seen that relativity breaks down if we can define a fixed background.
Title: Re: Can anything be "still" in space?
Post by: Bill S on 30/12/2017 17:03:21
Great response; even I can follow that! :)

Would it be reasonable to say that it might be possible for an object, or person, to be absolutely still; but the conditions that would make it possible would be atypical and there would be no way to perceive it, or the resulting "stillness"; so one might as well say that it cannot happen?

 WYSIWYG - WYDSIWYDG. - or something!
Title: Re: Can anything be "still" in space?
Post by: jeffreyH on 31/12/2017 01:30:41
No because everything is relative. I have wrestled with the notion of an absolute frame for quite a while now. I have convinced myself through study that it cannot exist. There may still be a frame for which the stationary observer above would hold and his speed of light would be the 'true' speed of light. However it will be impossible to detect it. It would also have more than one but not all points in spacetime.

P.S. You are then talking about the interface between dark energy and gravity.
Title: Re: Can anything be "still" in space?
Post by: Bill S on 31/12/2017 13:20:29
Quote
P.S. You are then talking about the interface between dark energy and gravity.

I need a bit more, there, please.  I don't see the connection. 
Title: Re: Can anything be "still" in space?
Post by: jeffreyH on 31/12/2017 16:54:16
If you think about it gravity is trying to pull everything together while dark energy is trying to push it all apart. At some points in spacetime these forces should exactly cancel. It is a bit like the lagrange points in the gravitational field. The problem is these points of cancellation are themselves likely to be moving position. If so then that complicates things.
Title: Re: Can anything be "still" in space?
Post by: jeffreyH on 31/12/2017 16:56:38
Maybe those interfaces are what protect the galaxies themselves from being expanded.