Computer simulation, as already mentioned, matches the short-period comets to the Kuiper Belt. Similar studies of long-period comets, even from the 1950s, pointed to their origin in the Oort Cloud. All in all, a great deal of computer work has been done that supports and refines the above models. The astronomical community treats them, at the very least, as excellent working hypotheses. That there is some kind of large comet reservoir beyond the range of our telescopes follows directly from a simple observation.
Astronomers detect new long-period comets at the rate of about one per month.
Orbital analysis show that these approaching comets generally take several million years to orbit the sun, and, as they are more or less randomly distributed in their orbits, we may deduce that the bulk of them are presently beyond the range of our telescopes. Only the exceptional comet, at any given moment, would be in that small portion of its orbit which crosses the inner solar system. For the sake of argument, suppose that it takes each of these comets four million years to orbit the sun. Thus, we would have about 48 million comets altogether. However, even that figure is extremely low since only the exceptional comet would have an elongated orbit which takes it anywhere near the sun.