The principle is assumed to apply throughout the Universe – but at the quantum level, particles do not have definite position or momentum, that is until a measurement is performed.
Don’t blame me if this doesn’t make sense – blame Niels Bohr, the Danish Physicist who developed the theory in the 1930’s. Even Einstein disliked the theory, but most theoretical physicists now accept this (note, they accept it rather than understand it).
You are correct that virtual particles don’t conserve energy in a strict sense. However, the Heisenberg Uncertainty Principle gives you a loop hole. Since you cannot precisely specify a particle’s energy at a given instant in time, you can create particles for a span of time such that the energy represented by those particles times the duration they exist is less than placks constant over two pi. The particles wink in and out of existance such that energy is conserved in a quantum mechanical sense.
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Don’t blame me if this doesn’t make sense – blame Niels Bohr, the Danish Physicist who developed the theory in the 1930’s. Even Einstein disliked the theory, but most theoretical physicists now accept this (note, they accept it rather than understand it).