[prince781]

> gravitational dynamics are time-reversible, so if gravity could capture you like this you could also start in orbit around a planet and spontaneously be ejected.

I don't have a strong background in physics, and perhaps this is splitting hairs, but is this true if we consider gravitational radiation? Over a very long time a body's orbital energy will be lost to gravitational waves.

[lmilcin]

It would be like saying all the school children exercises and train timetables are invalid because they don't take into account relativistic effects that obviously are still present at 60mph.

[a1369209993]

Technically? Yes! Incoming gravitational radiation of precisely the correct shape will in fact un-decay a orbit under exactly the same (modulo appropiate symmetries) circumstances as a orbit would decay by emitting (the reverse of) that radiation. (The same applies to thermal radiation cooling things off - see Liouville's Theorem.)

For practical purposes, that'll never happen, but for practical purposes gravitation radiation doesn't matter anyway.

[himinlomax]

Over a very long time, we are all very dead. From what I understand, the loss in gravitational energy would be so tiny, the length of time required for it to eventually matter in any way would be way beyond the lifespan of the sun. So it's only a finite duration if you have infinite time, which you don't.