comoving

Maybe it is just a solution which permits us to compute some things about the universe, such as comoving of frames.

Does Space Expand? Sean 2008

So the asteroid or meteroid was not coming in at a near comoving tangent with Earth's orbit, for that would be nearly 86km/sec in heliocentric coordinates, and it could not be a part of the solar system.

Video, Images of Ireland Fireball? | Universe Today 2010

In a comoving coordinate system it does, but in conformal coordinates it continues to remain opening.

Do "Skeleton" Filaments Give Structure to the Universe? | Universe Today 2009

Rules that apply to relative velocities in special relativity, such as the rule that relative velocities cannot increase past the speed of light, do not apply to relative velocities in comoving coordinates, which are often described in terms of the “expansion of space” between galaxies.

Does Space Expand? Sean 2008

In FRW (comoving) galaxies are stationary, in others they are not.

Does Space Expand? Sean 2008

However, in general relativity, velocity is a local notion, so velocity calculated using comoving coordinates does not have any simple relation to velocity calculated locally.

Does Space Expand? Sean 2008

Despite their disagreement about the net distance traveled, the observer and emitter agree on the same elapsed time between emission and reception, because clocks tick at a uniform rate for all comoving galaxies in the FLRW metric.

Does Space Expand? Sean 2008

Some says: “… clocks tick at a uniform rate for all comoving galaxies in the FLRW metric.”

Does Space Expand? Sean 2008

It is because of this with cosmology that as one observes further out the general relativistic physics of particles comoving in a frame becomes significant.

Does Space Expand? Sean 2008

The expansion of the universe causes distant galaxies to recede from us faster than the speed of light, if comoving distance and cosmological time are used to calculate the speeds of these galaxies.

Does Space Expand? Sean 2008