where <math>\tau</math> is proper time at event in deep space (time of deep space), <math>t</math> is coordinate time of the event (time of observer), <math>r</math> is distance to the event in deep space from observer, and <math>R_s</math> is radius of curvature of space (called by cosmologists ''[[Einstein's radius of universe]]'' or <math>R_E</math>). The above equation implies that the ''[[Hubble constant]]'' of our universe equals
+
where <math>\tau</math> is proper time at event in deep space (time of deep space), <math>t</math> is coordinate time of the event (time of observer), <math>r</math> is distance to the event in deep space from observer, and <math>R_s</math> is radius of curvature of space (about 13 billion light years, called by cosmologists ''[[Einstein's radius of universe]]'', or <math>R_E</math>). The above equation implies that the observed cosmological redshift is caused by the difference between <math>\tau</math> and <math>t</math> and the ''[[Hubble constant]]'' of our universe equals
:<math>H_o=c/R_s</math>,
:<math>H_o=c/R_s</math>,
−
where <math>c</math> is speed of light in vacuum and <math>R_s</math> is radius of curvature of space (about 13 billion light years). When this ''[[Hubble constant]]'', being in reality an exponential function
+
where <math>c</math> is speed of light in vacuum and <math>R_s</math> is as before the radius of curvature of space. When this ''[[Hubble constant]]'', being in reality an exponential function