- #1

meteor

- 933

- 0

I see often that rhocrit(the critical density of matter), is expressed this way:

rhocrit=(3*(H^2))/(8*pi*G)

This is not correct because a cosmological constant is missed.

This is the Friedmann Equation:

H^2=((8*pi*G*rhocrit)/3)+(lambda/3)-(k/(a^2))

Since it is known that the curvature(k)of the universe is zero, the Friedmann equation can be reduced to this:

H^2=((8*pi*G*rhocrit)/3)+(lambda/3)

and rhocrit is:

rhocrit=(3*((H^2)-(lambda/3)))/(8*pi*G)

Now, i would like to solve this equation. I have a value for rhocrit of 10^(-26)kg/m^3, but i need the value of the cosmological constant to complete the equation. You know the value? (in SI units, please)

also given that H=((da/dt)/da), being a the scale factor and H=Hubble constant, it would be nice to know the current value of the scale factor

rhocrit=(3*(H^2))/(8*pi*G)

This is not correct because a cosmological constant is missed.

This is the Friedmann Equation:

H^2=((8*pi*G*rhocrit)/3)+(lambda/3)-(k/(a^2))

Since it is known that the curvature(k)of the universe is zero, the Friedmann equation can be reduced to this:

H^2=((8*pi*G*rhocrit)/3)+(lambda/3)

and rhocrit is:

rhocrit=(3*((H^2)-(lambda/3)))/(8*pi*G)

Now, i would like to solve this equation. I have a value for rhocrit of 10^(-26)kg/m^3, but i need the value of the cosmological constant to complete the equation. You know the value? (in SI units, please)

also given that H=((da/dt)/da), being a the scale factor and H=Hubble constant, it would be nice to know the current value of the scale factor

Last edited: