This site features a javaScript cosmology calculator that employs the Friedmann-Robertson-Lemaitre-Walker equations to calculate the parameters of the universe at any* point point during the past, present or future.

*This program is not accurate during inflation, but should be reliable far into the era of radiation-dominance and at all times after.
Input for calculations

Current physical parameters
Hubble parameter H0 :  km/s/Mpc
Vacuum fraction ΩΛ : 
Matter fraction Ωm : 
Radiation fraction Ωr : 


to standard empirical values

Independent variable
 : 





Output of calculations

Age of universe : s yrs
Particle horizon R : m lyrs
Event horizon : m lyrs
Temperature : K

Energy Density : J/m3
Vacuum density : J/m3
Density of matter : J/m3 kg/m3
Density of radiation : J/m3
Dominant component :

Observable mass M : kg (In particle sphere)
Event mass : kg (In event sphere)
GM/(Rc2) :
Notes and Instructions

The author of this code is Scott Funkhouser, Dept. of Physics, the Citadel. For a good reference for the physics employed by this code, please see:
L. Bergstrom and A. Goobar, Cosmology and Particle Astrophysics, John Wiley and Sons, 1999.
  • Even though the output of this code is presented using proper scientific notation, powers of ten in the input fields must be represented with "e" or "E". For instance, if a redshift of 1.3x105 is desired, it must be entered as "1.3E5" or "1.3e5".

  • This code attributes any vacuum component ΩΛ to a cosmological constant. The Gaussian curvature of the cosmos is determined implicitly from the input parameters.

  • The calculations for our current epoch are obtained by setting the redshift to 0 or the scale factor to 1.

  • The parameters of the universe may be determined for future epochs by using "Scale factor" as the independent variable and specifying a value greater than 1, which is defined to be the scale factor in this epoch.

  • Note that, since the scale factor a is related to the redshift z by a=1/(1+z), the scale factor is roughly equal to the inverse of the redshift for large z.

  • This code can be used to determine the redshift associated with the beginning of matter-dominance or vacuum-dominance. With standard cosmological parameters, specifying "3.28E3" as the "Redshift" independent variable will locate the point very near the beginning of matter-dominance. It is left as an exercise for the webuser to find the redshift associated with the beginning of vacuum-dominance!

  • Note that, for the standard empirical input parameters, the observable mass of the universe does not begin to vanish after vacuum-dominance but, rather, it approaches asymptotically a large value. This is because the particle horizon becomes proportional to the scale factor, and the observable volume this becomes proportional to the cube of the scale factor. The density is proportional to the inverse cube of the scale factor, so the observable mass approaches a constant. While the event horizon does approach an asymptotic value, it is not the event horizon that determines the observable mass.

  • This calculator presents a calculation of the event horizon -- even during matter and radiation-dominance. There is always an event horizon if there is a positive cosmological constant.