Closed Universe?

Question

The closed universe (critical density greater than 1) is said to be unbounded (i.e. it has no edges), but finite in size. Explain was this means.

Finite in size as in galaxies, dark engery/matter, and black holes or...? Help me to explain this! thanks

Answer 1

A closed (finite in size) and unbounded (no edges or boundry) universe can best be explained by observing a globe, like Earth, or the Moon.

A globe is finite in size, you can measure its radius, diameter, circumference, etc..., however if you were to travel along its surface, you would never encounter a physical barrier (ignore contenients, oceans and such). You can consistently travel across its surface without stopping.

A closed, unbounded universe is a globe or sphere, and we inhabit its surface. There would be a measurable size to it, yet we would never encounter a barrier. In truth in this manner, it would be what is called a hypersphere. A sphere has three dimensions; length, width, height and yet has a two-dimensional surface...Think a soap bubble. A hypersphere has four dimensions, and a three dimensional surface. We inhabit the three dimensional surface.

Answer 2

the universe is a universe. it can have no edge, no boundary no matter what. we cannot ever leave our universe and so how can something that encompasses everything have an edge? there is nothing beyond it, nothing, not empty space, absolutely nothing whatsoever is beyond it. in a closed universe if you could travel far enough you would come right back to where you started from even if you moved in a straight line. the closest analogy we can come up with is a sphere. if you were a two dimensional being on the surface of a sphere you wouldn't find a boundary or an edge but you would realize that your universe is finite in size.

a closed universe will eventually collapse, this idea has pretty much been discarded now that there is evidence that the universe is actually accelerating in its expansion rather than slowing down.

Answer 3

There seem to be three possibilities so far:

• There really is a complete unified theory, which we will someday discover if we are smart enough.

• There is no ultimate theory of the universe, just an infinite sequence of theories that describe the universe more and more accurately.

• There is no theory of the universe. Events cannot be predicted beyond a certain extent but occur in a random and arbitrary manner.

Some would argue for the third possibility on the grounds that if there were complete set of laws, that would infringe on God’s freedom to change His mind and to intervene in the world. It’s a bit like the old paradox: Can God make a stone so heavy that He can’t lift it? But the idea that God might want to change His example of the fallacy, pointed out by St. Augustine, of imagining God as a being existing in time. Time is a property only of the universe that God created. Presumably, He knew what He intended when He set it up. With the advent of quantum mechanics, we have come to realize that events cannot be predicted with complete accuracy but that there is always a degree of uncertainty. If one liked, one could ascribe this randomness to the intervention of God. But it would be a very strange kind of intervention. There is no evidence that it is directed toward any purpose. Indeed, if it were, it wouldn’t be random. In modern times, we have effectively removed the third possibility by redefining the goal of science. Our aim is to formulate a set of laws that will enable us to predict events up to the limit set by the uncertainty principle.
The second possibility, that there is an infinite sequence of more and more refined theories, is in agreement with all our experience so far. On many occasions, we have increased the sensitivity of our measurements or made a new class of observations only to discover new phenomena that were not predicted by the existing theory. To account for these, we have had to develop a more advanced theory. It would therefore not be very surprising if we find that our present grand unified theories break down when we test them on bigger and more powerful particle accelerators. Indeed, if we didn’t expect them to break down, there wouldn’t be much point in spending all that money on building more powerful machines.
However, it seems that gravity may provide a limit to this sequence of “boxes within boxes.” If one had a particle with an energy above what is called the Planck energy, 1019 GeV, its mass would be so concentrated that it would cut itself off from the rest of the universe and form a little black hole. Thus, it does seem that the sequence of more and more refined theories should have some limit as we go to higher and higher energies. There should be some ultimate theory of the universe. Of course, the Planck energy is a very long way from the energies of around a GeV, which are the most that we can produce in the laboratory at the present time. To bridge that gap would require a particle accelerator that was bigger than the solar system. Such an accelerator would be unlikely to be funded in the present economic climate.
However, the very early stages of the universe are an arena where such energies must have occurred. I think that there is a good chance that the study of the early universe and the requirements of mathematical consistency will lead us to a complete unified theory by the end of the century—always presuming we don’t blow ourselves up first. What would it mean if we actually did discover the ultimate theory of the universe? It would bring to an end a long and glorious chapter in the history of our struggle to understand the universe. But it would also revolutionize the ordinary person’s understanding of the laws that govern the universe. In Newton’s time it was possible for an educated person to have a grasp of the whole of human knowledge, at least in outline. But ever since then, the pace of development of science has made this impossible. Theories were always being changed to account for new observations. They were never properly digested or simplified so that ordinary people could understand them. You had to be a specialist, and even then you could only hope to have a proper grasp of a small proportional of the scientific theories.