So one thing I don't understand, gravity moves 2 masses closer together. But to move something/to exert force on something you need to expend energy. But gravity has been moving stuff and keeping it closer together for like 14 billion years now....where does that "energy" come from which enables gravity to continually keep stuff together? Well..I know gravity is itself a force..but what is it fueled from?

  • $\begingroup$ Actually, gravity is the weakest force compared to electromagnetic, weak force and strong force. Stellar explosions throw matters away from the stars to space, the energy comes from electro-weak and strong forces. On the earth, you're are not collapsed into the centre of Earth because electrostatic force on your cells counters the "gravitational collapse". However, in black holes, gravity wins. $\endgroup$ – Ng Chung Tak Feb 6 '17 at 13:22
  • $\begingroup$ Work is only done when a force acts over a distance $\endgroup$ – JMLCarter Feb 6 '17 at 13:47

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