I know that we are surrounded by dark matter, and I also know that the reason for gravity according to general relativity. But all the explanation about GR is explained in two dimension, where space is imagined as a fabric and placing an object creates a dip and hence pulling objects near-by and this is gravity. But why does photons of light get fallen into this dip, by the way photons have zero mass.

And also there are theory saying, as the space is stretched time runs slowly. What does stretching of space mean, is it the stretching of dark matter or matter or both? How are space and time related.

Please help me, i want to know more about space-time and also explanations with respect to quantum mechanics is also preferred..About gravitons, i have also studied the standard model.