Science News Magazine: An atomic clock measured how general relativity warps tim
e across a millimeter.
[1]https://www.sciencenews.org/article/atomic-clock-general-relativity-time-warp
-millimeter-physics

   Jim Bell's comment:

   Who really knows what time it is?

   https://youtu.be/7uy0ldI_1HA

References

   1. https://www.sciencenews.org/article/atomic-clock-general-relativity-time-warp-millimeter-physics