We see very distant stars and galaxies as it were unbilievebly long time ago.If we can measure the receding velocities as a Hubble flow by measuring the Doppler effect for the wavelength and increase of receding velocities by the change of the Doppler effect for the wavelength is then easy measure the Hubble parameter for a time 5 billion years ago just by measuring the same parameter for the part of space distant 5 billion light years? That is acctually an image of that part of space as it was 5 billion years ago so its measured Hubble parameter should be for that time and not acctual.


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