Albert Einstein's theory of general relativity tells us that gravity is a curve in the fourth dimension of space and time -- and there's proof to back him up. What causes the curve is mass. Seriously weighty objects can bend the fabric of space-time. It explains why the planets orbit around the sun. The sun is so incredibly massive it essentially bends the space around it, pulling into orbit lesser objects (like planets) nearby. Similarly, with enough mass an object can even cause an otherwise straight beam of light to curve. In astronomy, that's called gravitational lensing.
Time is not immune to the effects of gravity either. It passes more quickly the less gravity there is, a phenomenon known as gravitational time dilation. On most days you might not credit gravity with anything more than keeping your feet on the ground, but a gravitational field can also warp time. That's gravitational time dilation in a nutshell, and for an example of time dilation in action, we need look no further than the nearest geosynchronous satellite. Even with ultra-precise atomic clocks, these satellites would inevitably wind up a few microseconds fast without correctional programming. This is because massive objects such as suns and planets warp time. Yes, time passes a little slower on Earth than it does in orbit. It would pass even slower on the surface of a Jupiter-sized planet and get slower still near a black hole. NASA even purposely "misadjusts" the clocks before liftoff on space shuttle missions, so that time on the shuttle will sync properly with time down here on Earth at the space center. GPS satellites make similar time adjustments, because if they didn't we would all get lost pretty easily when the calculated location in our car's mapping system comes out wrong. All of this gravitational bending and warping factors into Albert Einstein's theory of general relativity, making us fortunate that the great physicist didn't decide to just mark time at the patent office until he could retire.
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