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This said that each body in the universe was attracted toward every other body by a force which was stronger the more massive the bodies and the closer they were to each other.
We now know it is impossible to have an infinite static model of the universe in which gravity is always attractive.
But in 1929, Edwin Hubble made the landmark observation that wherever you look, distant stars are moving rapidly away from us. In other words, the universe is expanding. This means that at earlier times objects would have been closer together.
An expanding universe does not preclude a creator, but it does place limits on when He might have carried out his job.
We now know that our galaxy is only one of some hundred thousand million that can be seen using modern telescopes, each galaxy itself containing some hundred thousand million stars. We live in a galaxy that is about one hundred thousand light-years across and is slowly rotating; the stars in its spiral arms orbit around its center about once every hundred million years. Our sun is just an ordinary, average-sized, yellow star, near the outer edge of one of the spiral arms.
The only reasonable explanation of this was that the galaxies were moving away from us, and the frequency of the light waves from them was being reduced, or red-shifted, by the Doppler effect.
The discovery that the universe was expanding was one of the great intellectual revolutions of the twentieth century.
one has a singularity contained within a region of space-time known as a black hole.
Chandrasekhar calculated that a cold star of more than about one and a half times the mass of the sun would not be able to support itself against its own gravity. This mass is now known as the Chandrasekhar limit.
If the rate of expansion one second after the big bang had been smaller by even one part in a hundred thousand million million, the universe would have recollapsed before it ever reached its present size. On the other hand, if the expansion rate at one second had been larger by the same amount, the universe would have expanded so much that it would be effectively empty now.
