I found the following definition for the Hubble Radius:(adsbygoogle = window.adsbygoogle || []).push({});

The radius of the Hubble sphere (Hubble radius) is defined to be the distance from a fixed point O (center of coordinate system) of an object moving with the cosmological expansion at the speed of light (with respect to O).

Mathematically, R=c(a/da) , c=speed of light , a=a(t) is the scale factor ,t is time.

How's this definition valid since the Hubble radius as defined depends on the moving object?

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# About Hubble Radius (Radius of the Hubble sphere)

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