Does Time Really Slow Down Near Massive Bodies, or Is It Just Light?

[ScienceNerd36]

If time slows down near a massive body like the Earth, is that actually the slowing down of time our is it just the slowing down of light?

 

[LJFurniss]

"Light moves at the exact same speed in all reference frames."

^ Central tenet of relativity

Our clocks run more slowly. Interestingly, this must be accounted for in GPS satellites to properly "synchronize" their clocks with our ground-based ones.

 

[ScienceNerd36]

So time actually does slow down, and it doesn't just seem like it's slowing down.

 

[A.T.]

"Light moves at the exact same speed in all reference frames."

In general relativity this is restricted to a local area. Similar question:
https://www.physicsforums.com/showthread.php?t=284018

 

[The Dagda]

This was explored quite recently in this thread:

https://www.physicsforums.com/showthread.php?t=283838

Time is relative, that's all we need or seem to know.