How does gravity distort time?

[adimantium]

I understand that Einstein had the idea of space as a 2 dimensional grid with "planets" sitting of the grid, stretching it out, but I don't get why this affects time.

 

[WannabeNewton]

Well for starters that is NOT what Einstein had in mind; that isn't even a correct picture of space-time. Secondly, I assume you mean the gravitational time dilation effect? There was a thread about that before: https://www.physicsforums.com/showthread.php?t=704565&highlight=gravitational+redshift

 

[phinds]

Why does gravity affect time?

Gravity doesn't affect "time", it affects "spacetime". This is not just semantics. There are plenty of place on the internet to read about this.

 

[A.T.]

I understand that Einstein had the idea of space as a 2 dimensional grid with "planets" sitting of the grid, stretching it out, but I don't get why this affects time.

Think about it: If gravity was just distortion of space, how would it ever affect objects that are initially at rest in space? The distortion of spatial distances can only affect objects which already move through space. But why would an apple start falling from rest. Obviously the time dimension must be distorted too, to affect the apple that initially advances only through time. See animation below:

https://www.youtube.com/watch?v=DdC0QN6f3G4

See also this pictures that visualize the different effects of gravity:

http://www.physics.ucla.edu/demoweb..._and_general_relativity/curved_spacetime.html