Greetings all, I am a newbie here. I'm also a layman, as you probably guessed by my question. And I obviously am missing something about the 1st law and how it deals with Gravity. It hit me when I was thinking about Jupiter's moon, Io, and how it is volcanically active simply because of tidal forces. This seems to me an apparent free energy of sorts, a perpetual engine. Can someone please offer an explaination why this doesn't violate the 1st law of thermodynamics (as I understood, energy cannot be created. So where's the energy coming from?) Right now I'm juggling three options, the last two which redefine our concept of gravity. 1. If there are gravitons, then graviton energy is to blame, but they will eventually decay as photons supposedly might do (I don't like this explaination BTW) 2. Gravity is a form of the observed Casimir effect, a possible realization of vacuum energy. 3. the 1st law of thermodynamics applies only to the first three or possibly four dimensions, whereas gravity reaches into higher dimensions giving it additional energy as needed. Please, somebody give me a fourth answer!!