Do you think that the universe will keep on expanding? Why or why not?
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There is really only one way for the universe to stop expanding: that is ifthere is enough mass in the universe for the gravity to overcomethe expansion. The density of mass (amount of mass per volume of space) that is required to halt the expansion is often called the"critical density." If the universe is more dense than critical, the gravity of all the stuff in the universe will beable to overcome the expansion, causing it to stop, and eventually re-collapse. If the density in the universe is smaller than the critical density, then the expansion will continue forever.It is very difficult to determine what the density of the universe is, because most of the matter in the universe doesn't give off light that we can see in our telescopes. But we can go out and measure how many galaxies are out there, and how fast they orbit each other (The more massive galaxies are, the faster they will orbit). This gives us a fairly good idea of the density. Wecan also try to directly measure howquickly the expansion is decelerating by measuring the expansion speeds of distant galaxies. This is also a very difficult experiment.
There is really only one way for the universe to stop expanding: that is ifthere is enough mass in the universe for the gravity to overcomethe expansion. The density of mass (amount of mass per volume of space) that is required to halt the expansion is often called the"critical density." If the universe is more dense than critical, the gravity of all the stuff in the universe will beable to overcome the expansion, causing it to stop, and eventually re-collapse. If the density in the universe is smaller than the critical density, then the expansion will continue forever.It is very difficult to determine what the density of the universe is, because most of the matter in the universe doesn't give off light that we can see in our telescopes. But we can go out and measure how many galaxies are out there, and how fast they orbit each other (The more massive galaxies are, the faster they will orbit). This gives us a fairly good idea of the density. Wecan also try to directly measure howquickly the expansion is decelerating by measuring the expansion speeds of distant galaxies. This is also a very difficult experiment.
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