# Gravitational force?

We know that two mass particle attract each other with a force $$F~=~\frac{G M_1 M_2}{r^2}.$$

But what is the reason behind that? Why does this happen?

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 Is there a particular part of the equation that you are asking about, like are you asking where say G comes from? Or why all mass attracts? – DJBunk Jul 24 '12 at 20:35 I am not asking about the equation.I am asking why all mass attracts. – orange Jul 24 '12 at 20:46 If you have a physics background Zee in 'QFT in a Nutshell' gives a rough explanation of this in chapter I.5. And Peskin mentions this on pg 126. Otherwise I don't know of a good heuristic explanation for this. – DJBunk Jul 24 '12 at 20:58