[Seany (OP)]

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?

[lightarrow]

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?

[Seany (OP)]

Oh.. I see your point.. Ahh.. Now that makes matter very difficult! []

[Kryptid]

How about still in the sense that the tennisball observes no net redshift or blueshift of the cosmic microwave background radiation?

[Seany (OP)]

Yes.. []

[lightarrow]

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)

[syhprum]

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.

[Kryptid]

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?

[Seany (OP)]

That's what I was thinking..

[neilep]

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 '  []

Glad I could help.  []

[lyner]

You would have seen a different picture when you were born, tho - or even the day before. It's all on the move.

[chris]

Thought-provoking question from the archives here!

Anyone anything to add? Has thinking at least moved on since this subject was last visited?

[Colin2B]

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, that’s 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

[Bill S]

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. (?)

[jeffreyH]

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.

[Bored chemist]

The ball will have zero point energy, so it will always be vibrating a bit.

[Bill S]

  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.

[Colin2B]

If space were infinite, and contained only one object, it could be argued that that object would be still. 

Or that you can’t tell.
Vibrational stillness is different, in theory you could detect the micro accelerations.

[Bill S]

Or that you can’t tell.

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

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.

[jeffreyH]

  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.