Hubble’s law, according to Wikipedia, says that the recession velocity of a distant object P comoving with Earth is vrec=HD where H is Hubble’s constant and D is the proper distance from Earth to P.(adsbygoogle = window.adsbygoogle || []).push({});

The Hubble sphere is the area of space in which all objects comoving with Earth have vrec less than c. From Hubble’s law, one would expect the radius of the Hubble sphere to be c/H, a constant.

Yet Davis and Lineweaver (2003) say the Hubble sphere is expanding, by which I understand that the Hubble radius – the proper distance from Earth to the boundary of the Hubble sphere - is increasing.

How can the Hubble radius be increasing if both Hubble’s constant and the speed of light are constant?

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# Why is the Hubble sphere expanding?

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