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The weak anthropic principle states that in a universe that is large or infinite in space and/or time, the conditions necessary for the development of intelligent life will be met only in certain regions that are limited in space and time.
According to this theory, there are either many different universes or many different regions of a single universe, each with its own initial configuration and, perhaps, with its own set of laws of science. In most of these universes the conditions would not be right for the development of complicated organisms; only in the few universes that are like ours would intelligent beings develop and ask the question, “Why is the universe the way we see it?” The answer is then simple: if it had been different, we would not be here!
In the case of a universe that is approximately uniform in space, one can show that this negative gravitational energy exactly cancels the positive energy represented by the matter. So the total energy of the universe is zero.
After Hubble discovered the expansion of the universe, there was no need for a cosmological constant and it is now generally believed to be zero.
even if space-time is warped so that it would be possible to travel into the past, what happens in space-time must be a consistent solution of the laws of physics.
you wouldn’t have free will to do what you wanted.
One would avoid these problems if what I call the chronology protection conjecture holds. This says that the laws of physics conspire to prevent macroscopic bodies from carrying information into the past.
Laplace’s determinism was incomplete in two ways. It did not say how the laws should be chosen and it did not specify the initial configuration of the universe. These were left to God. God would choose how the universe began and what laws it obeyed, but he would not intervene in the universe once it had started.
These quantum theories are deterministic in the sense that they give laws for the evolution of the wave with time. Thus if one knows the wave at one time, one can calculate it at any other time.
When we combine quantum mechanics with general relativity, there seems to be a new possibility that did not arise before: that space and time together might form a finite, four-dimensional space without singularities or boundaries,
if we do discover a complete theory, it should in time be understandable in broad principle by everyone, not just a few scientists. Then we shall all, philosophers, scientists, and just ordinary people, be able to take part in the discussion of the question of why it is that we and the universe exist. If we find the answer to that, it would be the ultimate triumph of human reason—for then we would know the mind of God.
“Equations are more important to me, because politics is for the present, but an equation is something for eternity.”
If the no boundary proposal (this page) is correct, an infinity of universes exist in parallel. Each of these universes might well have a different strength for antigravity, especially if string theory is on the right track to a complete understanding of physics. We would then, naturally, live in one of the universes with a comfortably small dark energy; the anthropic principle (this page) reminds us that, if galaxies had never formed, we would not be here to discuss the matter.
Asking what came before the big bang is meaningless according to the no boundary proposal, because there is no notion of time available to refer to. It would be like asking what lies north of the North Pole.
Eternal inflation and the no boundary proposal together predict that our universe is not unique. Instead, from the quantum fuzz at the big bang many different universes emerge, possibly with different local laws of physics and chemistry.
