Sorry, missed this at the time.
Correct me if I am wrong but isn't the reason that gravity acts at a more macro scale than the other fundemental forces i.e. weak, strong and electromagnetic is that gravity acts in one direction i.e. attraction and does not cancel itself out?
Yes, that is correct. Even though gravity is exceptionally weak compared to the other forces, it cannot be shielded. An electromagnetic charge, by its nature, attracts opposite charges that will effectively shield the original charge - atoms being the perfect example of this. Mass attracts more mass, which simply builds the attraction. This actually lies behind the reason for our existence - the reason why compact distributions have such low entropy, contrary to naive considerations of thermodynamics. But this is a big topic not for this thread!
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