this is not to argue or persuade but just to share a calculation.(adsbygoogle = window.adsbygoogle || []).push({});

no answer needed unless you particularly like something about it.

several websites, eg. NedWright's Cosmology tutorial have formulas for things like the critical density and the estimate that

real density is very close to critical and that it is comprised of some 5 percent ordinary matter, 30 percent dark matter and 65 percent dark energy. Seems to be a fair amount of agreement about the rough percentages. And also that Hubble time is 14 billion years.

So it would be fairly easy for anybody to calculate from all that what the density of dark energy is---in whatever units---if anybody wanted to know. It is just a curiosity, what is it actually. How about calculating it in Planck units? Seem weird?

Well I did and I got that critical density is 1.77 E-123 planck.

And (dark energy + dark matter + usual matter) is

(1.17 + 0.53 + 0.07)E-123 planck. Or thereabouts---allowing for some variation in the percentages people cite.

If you want to check the reckoning

Planck density is c^7/hbar G^2

A day is 1603E45 planck time.

So Hubble time 14E9 years is 8.19 E60 planck time

Critical density is 3/8pi (hubbletime)^2 and that works out

fairly easily to 1.77E-123 and the rest is straightforward.

This 1.17E-123 agrees with what I've found on the web by way of estimates of the density of dark energy but expressed in other units like electronvolts etc.

Having dark energy density in some system of units lets one compare it to other energy densities. One rather nice comparison: it is one tenthousandth of the density of sunlight energy at this distace from the sun. Like....how much sunlight energy is there in a cubic kilometer in any one instant? Well, the dark energy is one tenthousandth of that much energy.

Anybody here besides me like knowinging how much dark energy there is around?

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Density of dark energy in Planck units

**Physics Forums | Science Articles, Homework Help, Discussion**