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Re: Will The Universe Expand For Ever???Why???

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Posted by Larry Burford/">Larry Burford on June 11, 1998 10:51:19 UTC

The Big Bang (BB) theory postulates an explosion of space (nothingness) itself, not an explosion of matter into space. In the latter case, it would be possible to analyse the motions of galaxies and determine where, in space, the explosion occured. In other words, it would be possible to find the center of the universe.

In the former case, there is a limited amount of space, but it is expanding. Inside the universe there is matter and there is space. Outside the universe there is... ( ? !! ? ).

Since we SEEM to be at the center of currently observed motion (the "velocity of recession interpretation" of observed redshift data), and since it's very unlikely that this is acutally the case, BB assumes that any obesrver anywhere in the universe would also see their location as the center of motion. (We have no choice but to ASSUME this until we can actually go somewhere else in the universe to see if it's really true. Stand by.)

According to most cosmologists today, the most likely explanation for all observers seeming to see their location as the center of motion is the expansion of space itself.

The usual analogy offered to help visualize this is to place several marks on the surface of a balloon. These marks represent stars or galaxies. As the balloon is inflated more and more, the skin of the balloon stretches and the marks get further and further appart. Note that the marks themselves also get larger as the various parts of each mark move away from each other. This analogy is not bad, depending on how well you can translate it in your head from two dimensions to three dimensions.

This expansion is counteracted by the attractive force of gravity. This force is assumed to have infinite range (stand by as above for confirmation), and the question of how long expansion will continue depends on the total mass of the universe. If that total is below a certain critical value, the universe will expand forever. If it is below the critical value, expansion will halt some day and then the universe will begin contracting (ultimately ending in a Big Crunch?). If it is exactly at the critical value, the universe expands more and more slowly, forever, getting so close to zero that we might not be able to measure the diffenerce, but never quite stops.

Current observations indicate that the total mass of the universe its less than 10 percent of the critical value. The universe will expand forever if this is correct.

And if the Big Bang is correct. And if gravity's range is really infinite.

Unless there is a significant amount of Dark Matter in the universe. But that is another story for another day.

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