according to relativity if a person takes a rocket and say travels near the speed of light moving towards a particular direction,then time slows down for him and the rocket.

But can't i say that the the rest of the universe say the earth and all other stuff moves at the above speed in the opposite direction with respect to the rocket and hence time should slow down for us and not for the rocket ( or basically from our new perspective time speeds up in the rocket).

is it that since mass of the universe >> the mass of the rocket that the later does not hold true.

But even then doesn't this imply a correction to the current equation for time dilation by considering a ratio of mass of the rocket to that of the remaining part of the universe.

Basically if hypothetically the rocket had half the mass of the universe , the time flow in the rocket and the earth should still be the same with respect to each other.