If you measure the position of a particle, you change its momentum by the very act of measurement. The variant of this principle that we use states that the uncertainty in the measurement of the energy of a system times the uncertainty in the lifetime of that system is roughly equal to Planck's constant. This does not violate the law of conservation of energy, basically because the violation is too small to be measured. In our universe, this leads to the spontaneous creation and annihilation of what are called virtual particles . One consequence of virtual particles is the evaporation of black holes.
Potential energy is negative, while rest-mass and kinetic energies are positive.
The History of the Universe 0 seconds . The Big Bang. Space begins expanding. 10 -43 seconds. The Planck time .