In what sense is gravitational potential the same as negative mass-energy?

[Paige_Turner]

TL;DR Summary

A rising but slowing pendulum...

Does "absorbing" negative energy from gravity cancel the upward momentum of the pendulum?
Or what?
Where can I see energy being negative? Does it repel stuff?
It sounds impossible.

 

[hutchphd]

All we really know is that the pendulum slows down.. You need to know the math and the experimental result. The rest of it is made up, so we can make the words mean anything we wish

 

[PeterDonis]

Does "absorbing" negative energy from gravity cancel the upward momentum of the pendulum?

Write down the actual math. Is there any "energy" in it that is negative? (Hint: you can write down the math so that there is, but it won't mean what you seem to think it means.) You can even use the Newtonian math, which is simpler.