Hi,
For understanding the red shift of galaxies on great distances one is always
comparing this with the doppler effect but we know that this shift is made
during the time the light travels in space by the expanding space ( I think
so ).
With the red shift one knows the velocity and with that the Hubble constant.
One says that the Hubble constant is the value for now and could be ( is )
different for the past and for the future.
But the light comes from several gyr and has to go in expanding space in the
past where the expanding velocity may be different.
How can be the red shift and thus the Hubble constant and thus the expanding
velocity the value for today ?
It is all confusing to me.
Thanks for any response.