Will the universe keep on expanding forever or is there enough gravity to slow down the expansion?
The Universe will expand forever, as today's research says so. There's this mysterious force called Dark Energy, that is accelerating (or speeding up) the expansion of the Universe.
There is a larger amount of this mysterious dark energy than gravity and it is much stronger. There are only theories about what will happen to the Universe. One is that the density of the Universe (therefore the gravity) will increase if the number of galaxies and their sizes increase. It will slow down the Universe and could possibly cause the Universe to collapse.