explain about the beginning of universe
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Scientists believe that our universe began with one enormous explosion of energy and light, which we now call the Big Bang. This was the singular start to everything that exists. The beginning of the universe, the start of space, and even the initial start of time itself.
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While the concept of a cyclic universe provides a way to explore the Big Bang’s past, some scientists believe that Steinhardt and Turok have skirted the deeper issue of origins. “The real problem is not the beginning of time but the arrow of time,” says Sean Carroll, a theoretical physicist at Caltech. “Looking for a universe that repeats itself is exactly what you do not want. Cycles still give us a time that flows with a definite direction, and the direction of time is the very thing we need to explain.”
In 2004 Carroll and a graduate student of his, Jennifer Chen, came up with a much different answer (pdf) to the problem of before. In his view, time’s arrow and time’s beginning cannot be treated separately: There is no way to address what came before the Big Bang until we understand why the before precedes the after. Like Steinhardt and Turok, Carroll thinks that finding the answer requires rethinking the full extent of the universe, but Carroll is not satisfied with adding more dimensions. He also wants to add more universes—a whole lot more of them—to show that, in the big picture, time does not flow so much as advance symmetrically backward and forward.
Barbour argues that time is an illusion, with each moment—each “Now”—existing in its own right, complete and whole.
The one-way progression of time, always into the future, is one of the greatest enigmas in physics. The equations governing individual objects do not care about time’s direction. Imagine a movie of two billiard balls colliding; there is no way to say if the movie is being run forward or backward. But if you gather a zillion atoms together in something like a balloon, past and future look very different. Pop the balloon and the air molecules inside quickly fill the entire space; they never race backward to reinflate the balloon.
In any such large group of objects, the system trends toward equilibrium. Physicists use the term entropy to describe how far a system is from equilibrium. The closer it is, the higher its entropy; full equilibrium is, by definition, the maximum value. So the path from low entropy (all the molecules in one corner of the room, unstable) to maximum entropy (the molecules evenly distributed in the room, stable) defines the arrow of time. The route to equilibrium separates before from after. Once you hit equilibrium the arrow of time no longer matters, because change is no longer possible.
“Our universe has been evolving for 13 billion years,” Carroll says, “so it clearly did not start in equilibrium.” Rather, all the matter, energy, space, and even time in the universe must have started in a state of extraordinarily low entropy. That is the only way we could begin with a Big Bang and end up with the wonderfully diverse cosmos of today. Understand how that happened, Carroll argues, and you will understand the bigger process that brought our universe into being.
To demonstrate just how strange our universe is, Carroll considers all the other ways it might have been constructed. Thinking about the range of possibilities, he wonders: “Why did the initial setup of the universe allow cosmic time to have a direction? There are an infinite number of ways the initial universe could have been set up. An overwhelming majority of them have high entropy.” These high-entropy universes would be boring and inert; evolution and change would not be possible. Such a universe could not produce galaxies and stars, and it certainly could not support life.
It is almost as if our universe were fine-tuned to start out far from equilibrium so it could possess an arrow of time. But to a physicist, invoking fine-tuning is akin to saying “a miracle occurred.” For Carroll, the challenge was finding a process that would explain the universe’s low entropy naturally, without any appeal to incredible coincidence or (worse) to a miracle.