First of all, we need to clarify that the word olam in Hebrew can mean either "world" in the sense of the physical planet, or "eternity." The best modern translation is probably something like "space-time continuum." (I have always wondered if this fact had any influence on Einstein's ability to imagine a point at infinity where space and time converge. He wasn't a religious Jew, but culturally he must have heard the word olam. Did the Hebrew language help facilitate the "thought experiment" that led to the Theory of Relativity? Interesting question...)
In Greek, however, there are two separate words for these two ideas: kosmos for the physical world, and aeon for a period of time or age. So already we have a major difference between Jewish thought and Greco-Roman thought when it comes to talking about "the end times." During the period when Christianity split off from Judaism, it was common in both groups to try and calculate the End of the World. But were the early Christians talking about the end of the physical kosmos, or the end of an age?
Jesus and his disciples were speaking Aramaic, a derivative of Hebrew, so most likely they were using olam. But the Gospels are written in Greek, not Hebrew, and, as far as I know, Greek does not have a single word that includes both time and space. So the Christian authors had to choose between kosmos and aeon. I'm no expert in this, but I do know that Judaism has tended to lean toward the "end of an age" rather than a literal destruction of the planet.
In fact, there is a famous quote in Avot de Rabbi Nathan (a classical Jewish commentary) that says, "If you are planting a tree and you hear the messiah has come, first finish planting your tree, then go to meet him." In other words, don't drop everything just because you hear rumors about the end of the world.
By and large, modern Judaism discourages calculating a specific date for "the end times." Why? Because setting a specific date tends to become a form of escapism. If you think the world is ending soon, and that a deity is going to appear and miraculously solve all your problems, then why bother to do anything to improve the world? Many, many times I have been told by Christians that there is no point in trying to make peace in the Middle East, because there will always be "wars and rumors of wars" until Jesus returns. Somehow, this seems defeatist and, frankly, rather callous. In contrast, Jews are commanded to actively "seek peace and pursue it " (Psalm 34:14).
|Jesus appearing in the clouds
from the Macklin Bible 1798
The problem with deus ex machina is that it doesn't work very well in real life. If we sit around waiting for a messiah to fix everything for us, then nothing ever gets fixed. This is why Jews are not "waiting for" the messiah. Rather, we are working to bring the messianic age, to beat swords into plowshares as promised by Isaiah. Each mitzvah we do brings us one step closer. Some Jews do believe there will be an actual person who is the messiah, others see "bringing messiah" as a process. But most of us would agree that it is not enough to just sit around and wait for a deus ex machina to appear and solve all our problems. We are each responsible to help make the world a better place to live in.
(If you are still worried about a literal end of the world, check out this page on the NASA website. NASA received so many inquiries about this "event," they actually posted a Q and A!)