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First and foremost I want to say that by no means am I a physics guru, but I still ponder this question. While I can understand from my current understanding of physics that a perpetual machine is yet,by current understanding, unattainable, does that mean that there is no hope for a free source of energy? Confined to the forces of the Earth we are bound by gravity, a constant form of energy acting on all, but what is the reasoning for not attempting such a feat in the midst of space where the levels of interference with the generation of energy(again from my current understanding) is so minimal? I understand that there would technically be friction on a molecular scale with particles bouncing and colliding with each other, and other potential space debris. However, other than that what is stopping us from achieving the goal of this, or am I simply missing information?

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  • $\begingroup$ Perpetual motion can't exist. $\endgroup$
    – Kyle Kanos
    Nov 30 '16 at 19:40
  • $\begingroup$ not perpetual, read $\endgroup$ Nov 30 '16 at 19:41
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    $\begingroup$ am I simply missing information? You are missing a specific question or suggestion for harnessing gravity, as far as I can tell. Your post seems very general to me. What is free energy exactly? $\endgroup$
    – user108787
    Nov 30 '16 at 19:49
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    $\begingroup$ @Austin: You added the modifier yet to the front of unattainable. By doing so, you've changed the meaning of your statement from "not possible" to "not possible now." $\endgroup$
    – Kyle Kanos
    Nov 30 '16 at 19:50
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    $\begingroup$ I'm reminded of The Last Question $\endgroup$ Dec 1 '16 at 0:17
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Energy has to come from somewhere. In a hydroelectric dam, it's stored as the potential energy of the water elevated by the dam, in a coal power plant, it's stored the chemical energy in the fuel. Anytime you use energy to do something useful, like power a light bulb or run an engine, some of that energy actually does the useful thing you intended to do, and some is lost as unrecoverable heat. You can never get more energy out of a system than what it started with.

Moving into space doesn't change anything. No matter what your source of energy is, it isn't infinite. It will eventually be depleted by doing useful things, while losing a small amount of waste energy. If you want to charge your system up again, you'll need some other source of energy - and what do you do once that's exhausted?

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Energy is not the problem, After all, energy is conserved, so you could ask why we should be concerned with energy conservation if it is already conserved? What we want is not energy per se but energy in a low entropy form. A simple example: to heat your home in winter you need an energy source, the energy present outside at low temperature cannot be used to heat your home, you need at least another energy source to be able to extract energy from the cold outside environment, see this article on heat pumps.

However, suppose that on cold winter's day the temperature near the ground is -10 C while deeper below the surface it is +2 C. Then you can extract energy from only the outside environment, the temperature differences present in the outside environment allow you to operate a heat engine that can be used to provide the work necessary to operate a heat pump.

Clearly the limitations are always due to entropy, the second law of thermodynamics is far more relevant than the first law of thermodynamics.

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