How Can Gravity Provide an Endless Supply of Energy?

[Lapidus]

From Greene's pop science book 'The hidden reality', I got this:

What’s vital to realize is that the gravitational field’s energy can be arbitrarily negative. Consider two particles falling toward each other under their mutual
gravitational attraction. Gravity coaxes the particles to approach each other
faster and faster, and as they do, their kinetic energy gets ever more positive.
The gravitational field can supply the particles with such positive energy
because gravity can draw down its own energy reserve, which becomes
arbitrarily negative in the process: the closer the particles approach each other,
the more negative the gravitational energy becomes (equivalently, the more
positive the energy you’d need to inject to overcome the force of gravity and
separate the particles once again). Gravity is thus like a bank that has a
bottomless credit line and so can lend endless amounts of money; the
gravitational field can supply endless amounts of energy because its own
energy can become ever more negative.

Could someone explain that I bit further? Why and how is in the gravitational field an arbitrarily large amount of energy stored?

What about the potential energy of the two approaching particles, does it not decrease, while the kinetic energy increases?

Why does the same logic from above does not apply to the em, weak and strong force?

Greene says this arbitrary gravitational energy supplied the early universe the necessary energy to inflationary expand. How?

Where else does that 'endless energy feature' of gravity show up, especially when we try quantizing gravity?

thank you

 

[Bill_K]

Since this is about gravity, why not ask it in the relativity forum?

 

[Lapidus]

Since this is about gravity, why not ask it in the relativity forum?

Yeah, if some demigod of this forum would be so kind and send my thread there...

EDIT: I just post it there again by myself.