Why not? The inverse square law predicts that two galaxies separated by 1 million parsecs and each as massive as the Milky Way will exert a mutual force of about:
F = 6.6 x 10^-8 x (3 x 10^42 grams) x ( 3 x 10^42 grams)
----------------------------------------------------
2
( 3 x 10^18 x 1 million)
= 6.6 x 10^28 dynes.
That's a heck of a big force in my books! I see no problem with this
at all!!