Weinberg Paper: Understanding Two Loop Corrections for Gravitational Force

[romeo6]

I have been reading a Weinberg paper (the cosmological constant problem), where he writes

"...Zeldovich assumed that these were canceled leaving only the higher order effects: in particulal, the gravitational force between the particles in the vacuum fluctuations. (In Feynman diagram terms, this corresponds to throwing away te one-loop graphs, but keeping those with two loops"

Can someone help me understand this. I thought QFT said nothing about gravity. Why do the two loops correspond to the gravitational force??

 

[romeo6]

anyone??

:)

 

[Gokul43201]

You might have better luck if you cite the paper.