[W]hen you apply quantum mechanics to gravity, then even space itself can pop into existence from nothing. Space and time can spontaneously pop into existence... Whole universes can pop into existence and most of them will disappear in a time scale so short you wouldn't know about it. The ones that can survive for a long time have zero total energy...

[O]ne of the great things about science is it forces us to refine our idea of what's common sense. It forces us to have our beliefs conform to the evidence of reality rather than the other way around. The universe may not be like we'd like it to be, but it doesn't really care.

[I]n science we have to be particularly cautious about 'why' questions. When we ask, 'Why?' we usually mean 'How?' If we can answer the latter, that generally suffices for our purposes. For example, we might ask: 'Why is the Earth 93 million miles from the Sun?' but what we really probably mean is, 'How is the Earth 93 million miles from the Sun?' That is, we are interested in what physical processes led to the Earth ending up in its present position. 'Why' implicitly suggests purpose, and when we try to understand the solar system in scientific terms, we do not generally ascribe purpose to it.

Now, almost one hundred years later, it is difficult to fully appreciate how much our picture of the universe has changed in the span of a single human lifetime.

As far as the scientific community in 1917 was concerned, the universe was static and eternal, and consisted of a one single galaxy, our Milky Way, surrounded by vast, infinite, dark, and empty space.

This is, after all, what you would guess by looking up at the night sky with your eyes, or with a small telescope, and at the time there was little reason to suspect otherwise.

the universe could have expanded during this inflationary period by a factor of more than 1028. While this is an incredible amount, it amazingly could have happened in a fraction of a second in the very early universe.

see also positrons; virtual particles Aristotle, 172–73 Atkins, Peter, 191 baryons, 76 Big Bang, xvii, 95, 107, 150, 173, 189 CMBR left from, see cosmic microwave background radiation dating of, 3, 15–16, 77, 87 density of protons and neutrons in,

But what we've discovered is that, in fact... the total energy of the universe could be zero, which is a first clue that maybe it could come from nothing. ...In physics, ...once you include gravity, there's positive energy and negative energy, and our universe appears as if its total energy could be precisely zero, which is the first hint that maybe it could come from nothing. That, and the great discovery... that namely empty space, you take a region of space, get rid of all the particles and all the radiation ...so there's nothing there. That empty space weighs something, and we don't understand why.