I just wanted to make sure whether I've understood something correctly(adsbygoogle = window.adsbygoogle || []).push({});

In the FRW equation:

[itex](\frac{ \dot a}{a})^2 = \frac{8 \pi G}{3} \rho - \frac{k}{a^2}[/itex]

...there is this curvature term. I'm confused about the meaning of this k. Sometimes they say it can ONLY be -1 , 0 or +1. Sometimes they say it's smaller, bigger or equal zero. So can it or can it not be fractional? If it can - what does it mean?

My understanding so far is, that this whole term is the Gaussian curvature:

[itex] \pm \frac{1}{a^2} [/itex]

Where a is the radius of curvature - and it changes with time as the universe expands;

And so k is there just to provide an appropriate sign for the three cases: flat, spherical or hyperbolic geometry.

Am I right, or can it be fractional?

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

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!

# The meaning of the curvature term

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