# Hubble constant

1. Mar 25, 2013

### nikhilb1997

1. The problem statement, all variables and given/known data
If $$\phi$$ is a usual field is it possible that
$$H\dot{\phi}=-\partial^2\phi/{\partial x^2}$$
Where H is the hubble constant and the dot denotes time derivative

2. Relevant equations
$$H\dot{\phi}=-\partial^2\phi/{\partial x^2}$$

3. The attempt at a solution
I tried different ways but am not able to find the particular expression for hubble constant used here.

Last edited: Mar 25, 2013
2. Mar 27, 2013

### fzero

On a curved spacetime, the Klein-Gordon equation for a massless scalar field is $\nabla^\mu \nabla_\mu \phi =0$. If the spacetime is of the FRW type, then there will be a term proportional to $H\dot{\phi}$. You seem to have missed the $\ddot{\phi}$ term in your expression, so you might want to go through the exercise of working this out from first principles.

3. Mar 28, 2013

### nikhilb1997

Thanks a lot. I did miss that term because this was the part i was confused about but i guess that was important too.