What does free energy mean?
Free energy is also called Zero-point energy.
Zero point energy is present in all quantum mechanical systems (i.e. everything that uses energy and converts it to entropy). Zero point energy is the lowest amount of energy that such a quantum mechanical system can have. It is also commonly referred to as vacuum energy and remains when all matter is removed from a region of space. Since by definition zero point energy can never be depleted (a region of space can never have less than that amount), it is theoretically an unlimited and free energy source.
The energy is said to arise from various particles that spontaneously emerge, exist for fractions of a second, and are then annihilated by anti-particles. At very small distances (~10
-35 meters) this particle/anti-particle turbulence is known as quantum foam, and it is theorized to be a remnant of the birth of the universe carried over to this day. (Also partially explained in the hypothesis is that not all matter in the universe is evenly distributed).
Despite the two particles annihilating each other, a small amount of energy is detectable (demonstrated by the Casimir effect). Because of the immensely small scales of time and size, as well as the Heisenberg Uncertainty Principle, the existence and subsequent annihilation of these particles does not violate the conservation of energy.