Isaac Newton’s Principia describes how the Universe works using the law of gravity and $$F=md^2r/dt^2$$. But this description lead to two paradoxes (called Bentley’s paradox and Olber’s paradox) which were irreconcilable in the Newtonian framework. Bentley’s paradox states that if the Universe is finite in size then, since gravity I always attractive, all the stars and galaxies should collapse into each other. The second part of this paradox states that if the size of the Universe is infinite, then all the stars and galaxies should be torn apart by the force of gravity. Newton proposed that there is only one possible scenario which doesn’t lead to this paradox: the Universe’s size must be infinite and the distribution of mast must be totally uniform throughout this infinite space. But there are two problems with this scenario. First and most importantly, we know from observation (and the CMBR in particular) that the mass distribution in the Universe is not perfectly uniform. Second, in this scenario the solution $$r(t)$$ to the differential equation $$F=md^2r/dt^2$$ is an unstable solution. That is to say even the slightest “nudge” exerted on a star would cause a slight deviation from uniformity in mass distribution and would create a “cascade” effect causing galaxies to collapse. Thus Newton’s law of gravity breaks down when applied to the Universe as a whole.