We can't tell the energy of the Universe apart from zero. According to The Uncertainty Principle, this means that the Universe may have an indefinite lifespan since
The Uncertainty Principle may also be expressed as
or in English, the product of the uncertainty in position times uncertainty in momentum is less than
We can apply this to the Universe as a whole , then the uncertainty in the momentum of the Universe multiplied by the size of the Universe is less than
By considering any direction, we can see that the momentum in any direction must be the same as the momentum in any other direction, since the size of the Universe can increase only with this condition. This then implies that on a large scale, the Universe looks the same in all directions – so is isotropic.
