# Riemann curvature scalar value different in Landau and MTW ?

1. Jun 22, 2013

### zn5252

hello
For the same Friedmann metric, Landau (Classical theory of fields) finds a value for the Riemann curvature scalar which is given in section 107 :
R = 6/a3( a + d2(a)/dt2)
whereas in MTW , in box 14.5 , equation 6 , its value is :

R = 6(a-1 d2(a)/dt2 + a-2 (1 + (d(a)/dt)2 ) )

The metric is the same ! how come ? this could not be related to the fact that Landau does the replacement :
cd$\tau$ = ad$\eta$

2. Jun 22, 2013

### Bill_K

Yes, that's it exactly. the difference is that in Landau & Lifgarbagez, the dot means d/dη, not d/dt.

3. Jun 22, 2013

### zn5252

I see Bill Thanks. Not so obvious though .