# Naked Science Forum

## Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: MikeS on 06/02/2012 14:49:02

Title: What is the difference between moving in space and stationary in moving space?
Post by: MikeS on 06/02/2012 14:49:02
A moving clock is seen to run slower than the clock in your reference frame.
What is the difference between the above which would be seen as a red-shift and the red shift due to the creation of space?
The first is a clock moving in space.  The second, a stationary clock in moving space.
Title: Re: What is the difference between moving in space and stationary in moving space?
Post by: Bill S on 06/02/2012 15:11:44
As I understand it, relativity tells us that ther is no difference; but I'm relatively ingorant where these complications are concerned, so I could be wrong. :)
Title: Re: What is the difference between moving in space and stationary in moving space?
Post by: simplified on 06/02/2012 17:21:54

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The first is a clock moving in space.  The second, a stationary clock in moving space.
If space is reduced then a clock is stationary and space is moving.If space is normal then a moving clock is moving in space. :P
Title: Re: What is the difference between moving in space and stationary in moving space?
Post by: wolfekeeper on 08/02/2012 03:53:52
If it's expanding space then it's always red shift, but if it's moving and you get in front of it, it's actually blue shifted, but directly to the side it's red shifted.
Title: Re: What is the difference between moving in space and stationary in moving space?
Post by: Soul Surfer on 08/02/2012 08:42:22
Remember that there must be two clocks that are being compared one local and the other distant and the situation is totally symmetrical.   Let us call the creatures looking a the clocks A and B. neither of them consider themselves to be moving and there is no such thing as "moving through space"  (for two objects only se below) however A sees B moving away and notes that B's clock runs slow B also sees A moving away and notes that A's clock runs slow.  There is no difference between the results if they are moving apart really or space is expanding between them however if it is space that is expanding the velocity of light is not a limitation the only difference is that if the space was expanding faster than the velocity of light they would never see each other.

An interesting thought is what might happen if the expansion of space was accelerating  They would initially see each other and then slowly fade out as the red shift increased taking signals right down to radio long waves and vanish when it became DC.  However I do not think that such a thing is observable because the local low frequency noise and the cosmic microwave background would drown it out.

Alternatively if the expansion was slowing down, new things would be slowly appearing out of radio waves at great distances. Again they would not be observable until they appeared reasonably well up the spectrum.  However the changes would be extremely slow and not compatible with human lifetimes.

Moving through space.  To form an opinion about moving through space on needs to be able to observe the relative locations and or velocities of many other objects and take a consensus on what is happening.  This depends however on what we are looking at.   If we are driving along a road it is perfectly obvious to us that we are "moving through space" along a road and not that the road is moving past us as we stand still. however if we had in the back of the truck a well equipped astronomer he could tell us how we are moving in our orbit round the sun hoe wthe sun is moving in its orbit round the galaxy how our galaxy is moving with respect to our local group of galaxies.  How our local group of galaxies is moving with respect to the virgo supercluster etc right up to how we are moving with respect to the cosmic microwave background radiation.  Of course none of this is relevant when we come to a bend in the road.   :)
Title: Re: What is the difference between moving in space and stationary in moving space?
Post by: yor_on on 08/02/2012 11:35:52
Space as a classical concept is 'nothing', and nothing can't 'move'. You need references to define that space from, and those references may seem to 'move', relatively so naturally. From a QM perspective we expect different kind of 'bosons' to exist and 'propagate'. But what is then that 'energy' we expect to 'transform' from photons for example, into space and time. It's also a question about how you define it, if we have relativistic red shifted photons (waves), due to an expansion, you might say that we are 'losing energy' as the universe 'grows'. But if you define it as 'photon/particles' existing at some position, then there will be the same amount at that 'place' even after that expansion, as some sees it. And therefore no 'energy loss'.
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It all goes back to what 'space' is to me.