A YEC I have been debating for some time has recently made a video claiming that because according to general relativity, time is slowed by gravity, earth may be only ~10,000 years old while most of deep space is several billions, allowing enough time for light from very far away stars to reach us. I know that his idea of how much gravity affects time is WAYYY off, but I need to know how much, this is an excellent opportunity for me to show him that he forms conclusions far too rapidly without adequate research. So, I need to know how much time is slowed by gravity on earth(as compared to an area with essentially no gravity), and how to calculate it. I've never worked much with relativity, so the more in depth the explanation, the better.