is there absolute speed of an object, relative to the expansion of the universe?

[Maartenn100]

Hello,

 

I learned that a stationary observer is stationary relative to the expansion of the universe. This observer doesn't travel through space, but it travels at light speed through time. Why do physicists not use this reference frame to talk about absolute speed through space.  If physicists talk about a stationary object (no motion through space, only moving with the expansion of the universe), they imply that there is absolute speed through space possible. (instead of relative motion). 

 

(ps: to moderation: I didn't ask this question before in another thread).

Edited April 30, 2019 by Maartenn100

[Strange]

3 minutes ago, Maartenn100 said:

I learned that a stationary observer is stationary relative to the expansion of the universe. 

I'm not sure what "relative to the expansion of the universe" means.

"Stationary" can be defined relative to any frame of reference. There is no absolute or special definition of "stationary". There is no reason to refer any one frame of reference other than convenience for a particular purpose.

4 minutes ago, Maartenn100 said:

This observer doesn't travel through space, but it travels at light speed through time.

What does that mean? Speed is a change of spatial position with time. So how can an observer who does not move through space have speed?

 

[Maartenn100]

The more you travel through space, the less you travel through time and vice versa, not? Together it must be light speed, not?

Someone told me, that there is a frame of reference that is "the Hubble flow". Where objects are stationary, relative to space so to speak, but only comoving together with the expansion of the universe. But they are going at lightspeed through time. They are called 'stationary observers'. 

Maybe that's the wrong information then. 

 

Edited April 30, 2019 by Maartenn100

[Strange]

12 minutes ago, Maartenn100 said:

Someone told me, that there is a frame of reference that is "the Hubble flow". Where objects are stationary, relative to space so to speak, but only comoving together with the expansion of the universe. 

Co-moving coordinates is just one arbitrary frame of reference. There is nothing special about it. It is not "absolute", it is just convenient for some purposes.

13 minutes ago, Maartenn100 said:

 But they are going at lightspeed through time. They are called 'stationary observers'.

That is always true for someone who is considered stationary, in any frame of reference. 

 

[Maartenn100]

36 minutes ago, Strange said:

Co-moving coordinates is just one arbitrary frame of reference. There is nothing special about it. It is not "absolute", it is just convenient for some purposes.

 

Thank you for this information. For which purposes, if I may ask? What makes the comoving frame more useful for some purposes then other frames of reference?

Edited April 30, 2019 by Maartenn100

[Strange]

9 minutes ago, Maartenn100 said:

Thank you for this information. For which purposes, if I may ask? What makes the comoving frame more useful for some purposes then other frames of reference?

The coming frame is convenient for cosmology. But an Earth-centred frame of reference is more useful for navigating your car, for example. A Sun-centred frame of reference is more useful for sending a space probe to other planets. And so on.

[Conjurer]

8 minutes ago, Maartenn100 said:

Thank you for this information. For which purposes, if I may ask? What makes the comoving frame more useful for some purposes then other frames of reference?

The reason why people talk about the speed of an object relative to the expansion of space is due to a problem physicist have with describing the universe to fit the data from cosmic background radiation.  Einstein discovered that mass increases when in object is seen to be in relative motion to another object, but the mass increase of other galaxies was never detected to fit that theory.  It is as though they are in relative motion to us while still being considered to be at rest, since they are not affected by relative motion in this way.  This is explained as being due to them still being at rest relative to space itself.  Then it was found that a universal theory would have to allow the Big Bang to be faster than the speed of light in order to fit the cosmic background data.  Then they concluded that an object cannot travel faster than the speed of light relative to the expansion of space in their theories, but space itself can expand faster than the speed of light.  

[koti]

1 hour ago, Maartenn100 said:

The more you travel through space, the less you travel through time and vice versa, not? Together it must be light speed, not?

Someone told me, that there is a frame of reference that is "the Hubble flow". Where objects are stationary, relative to space so to speak, but only comoving together with the expansion of the universe. But they are going at lightspeed through time. They are called 'stationary observers'. 

Maybe that's the wrong information then. 

 

The "Hubble Flow" is the motion of galaxies due to the expansion of the universe. It's not a frame of reference, its just a phenomena that occurs due to the fact that the space around us is stretching so the distance between any two pieces of matter is getting larger.

[swansont]

If it’s relative, it’s not absolute. It’s right there in the name.