Does the universe end?
The universe had a beginning some 15 billion years ago, but it has an end?
Can you tell?
If the universe is infinite or not depends on how much matter is actually out there. Astronomers have observed that the universe is expanding. All galaxies in the universe move away from each other. If we think in reverse, so they must indeed have been closer to each other before. Physicists have calculated that if we, so to speak would rewind the film must surely everything in the universe have been in one place for about 15 billion years ago!
It's so scientists think the universe's beginning, in a ursmäll or the Big Bang. But when will the expansion end? and then what? This question has no simple answer.
It is very difficult to imagine a universe expands. To the extent that we even think like we think probably very Newtonian: There is a room, much like a graph paper, and if
there is something that expands as we think of course that it expands in that room. But in fact it is not happening. Even when the universe was less so there was nothing outside it as it extended itself in. In fact created the space between the galaxies. The universe is everything, no matter how big it is! It is the very room that gets bigger. (Are you with me?)
What weighs universe?
But continues to expand in all eternity?
It has to do with how much matter there is in the universe.
If there is enough matter, the expansion to a halt. Maybe the universe and even shrink back together. We need astoundingly little matter of that expansion will stagnate. Suffice average of three puny hydrogen atoms per cubic meter in the universe. (The best vacuum we can achieve on Earth has a trillion times greater density than that.) Universe critical density is called the density required for the expansion of the universe will cease.
How much are there out there? To find out, the researchers assume that all stars weighs about as much as our sun. Because they know how fast the earth moves around the sun, and at what distance it is from us, so they can figure out how heavy it is. (Good luck with the nut, Leon.) Then it's time to count how many stars there are on average of a galaxy, and how many galaxies there are in the universe. If you do that, you can find out how much all matter in the universe weighs. Roughly.
When one discovers that there is only one hundredth of what it takes to expansion will stagnate. So if there are only such matter we can see, the expansion will continue at all eternity and then has not the universe no end. Then it just becomes colder and colder and we go against what physicists call "the big chill".
The large crusher
(The Big Crunch)
Now, however, so that there is more matter in the universe than we can see.
The invisible matter, we consequently "weigh" the other way.
One way is to see how various objects moving relative to each other in the universe.
Looking for examples of how the stars move in galaxies and, more floaters, how galaxies are moving in so-called galaxy clusters. With the help of gravity, one can then calculate how much mass that should be there.
Then you discover that there are about 10 times more matter than we
see and what we call dark matter (Mats G).
What we saw was therefore only a hundredth of what is required for the universe to stop. But if we now expect even the dark matter we have about a tenth of what is needed. We also have theoretical reasons to believe that there is more dark matter than has been measured. Actually just so much that we would reach the critical density. The universe would then, after an almost infinitely long halt in its expansion. But it would be even more exciting is if there was more matter in the universe than the critical density. Then the expansion not only terminated, but turned into a collapse again. That would mean that there is less and less denser and denser. It would be really like to run the film backwards towards what is called "the great crusher". So the opposite of the Big Bang. When pressed all matter together and it gets so hot and so tightly that galaxies and stars no longer exist as objects. We will return to a state of a lot of exciting and exotic elements particles. And probably it ends in a point! All matter in the universe is sucked into one big black hole.
It's been quite a pain to work with this, because I have not had much time, due to other work, homework and tests.
But finally it was finished ...
The work is a little picture-resolved because I write all about the universe, and the universe itself, there's no picture on! It's probably too large to fit on the image ...