2013 June 02
originally posted on facebook

I am prepared to believe (though I have not heard an adequate explanation of the fact) that in general relativity, an infinite universe homogeneously filled with mass will tend to contract. In A Brief History of Time, however, Hawking repeatedly insists that the same is true in Newtonian physics. This seems to me obviously false, but surely Hawking would not make such an elementary mistake? What am I overlooking? Is the problem just that “Newtonian physics” is ill-defined?

p. 5 “The correct approach […] is to consider the finite situation, in which the stars all fall in on each other, and then to ask how things change if one adds more stars roughly uniformly distributed outside this region. According to Newton’s laws, the extra stars would make no difference at all to the original ones on average, so the stars would fall in just as fast. We can add as many stars as we like, but they will still always collapse in on themselves. We now know it is impossible to have an infinite static model of the universe in which gravity is always attractive.”

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