Where does energy come from? Where does energy go?
Energy is by its physical definition the ability of a body that has mass to perform mechanical work. By this definition the energy comes from the quantity of movement (speed) a mass has or from the position of a mass relative to a zero energy level inside a force field that is conservative. The energy that comes from the movement of a mass is called kinetic whereas the position energy is a force field is called potential energy. In this understanding the total energy of a mass (the sum of kinetic and potential energies) conserves. The kinetic energy is transformed into potential energy and viceversa. In a newer understanding energy is a property of any body that is related to its mass by the well known relation Energy = mass*c^2 where c is the speed of light.In this understanding energy comes from the equivalence relation between mass and energy and hence from the transformation of the mass itself into energy and viceversa. Examples when this energy is created or destroye (energy transformed into mass or viceversa) are the nuclear fission and fusion reactions. In this understanding the total energy plus the total mass a body has is the same. One is transforming into other.
I a larger sense of speaking and from the newest point of views in physics energy is a property of any quantity of space (does not matter it is filled with mass or not) and it comes from the initial formation of the universe. In this understanding a part the energy liberated from the initial explosion of the universe (Bigbang) still fills up the space nowadays. The other part that is not found into today energy that fills the space has been transformed into mass (stars, planets and galaxies). In this understanding the total energy liberated from the initial BigBang is not conserved. A large quantity of the initial energy was converted to mass into matter and antimatter. It has beed demonstarted in laboratory that an energy field can create from nothin 9but energy) a pair of particle antiparticle (like electro-positron) that can be separated further.
In the first two meanings described above the energy is subject to the law of conservation of energy which states that a form of energy can be transformed into another form of energy but the total energy (the sum of all types of energy a mass has) is allways the same.