For example, the Mayan "long count" calendar and the "end of the world" on December 21, 2012. Sadly, according to one NASA web site described here that posts about this sort of thing "A lot of [the submitters] are people who are genuinely frightened..." People with computers, able to navigate to the NASA web site, questioning the future of humanity based on a calendar created by a civilization that collapsed a millenium ago.
"I've had two teenagers who were considering killing themselves, because they didn't want to be around when the world ends," the article reports, and "[T]wo women in the last two weeks said they were contemplating killing their children and themselves so they wouldn't have to suffer through the end of the world."
Sadly, just like the world does not end on the last day of your wall calendar, December 31, neither does the Mayan world.
It simply cycles around and starts over again.
But this is not the first time people have gone wacky over things like this.
There was the "end of the world as we know it" in 2000, for example. Around 1995 articles were published in various technical journals by programmers describing how things like power plants were riddled with code that simply ignored the left two digits of the year, e.g., representing 1996 and "96." The problem, of course, is that in 2000 the digits would change from 99 to 00, i.e., go backward, and reek havoc.
To a certain extent this was true, of course, but with the dawn of the internet and the notion of of "unlimited liability" companies with these sorts of problems began remediation work well ahead of 2000 and nothing particularly interesting happened.
What's interesting is that people seem to somehow think that the universe at large is somehow like a computer system.
When a computer system's clock "wraps around" any number of things might actually happen. For example, invoices with the wrong dates might be printed, accounts receivable aging reports might show all account centuries past due, things like that or worse.
But things like Mayan calendars are representations of things created by humans.
The calendars we use, nor the clocks, nor our concept of "time" in general, don't have a "physical" manifestation. Sure the earth rotates around the sun periodically - but its us who give that process significance. The sun, the galaxy, and everything else are all constantly rotating and moving so even when the earth rotates once around the sun the earth (and the sun, for that matter) are not where they were a year ago.
For me I will have a chance to live through another complete cycle of potential disaster.
The "Year 2038 Problem."
A long time ago, in about 1971, a computer operating system called Unix was invented by Ken Thompson and Dennis Richie (who I wrote about in "Elementary My Dear Watson"). Part of Unix involved a 32-bit integer representation of time which measured seconds and began Jaunary 1, 1970. Internally Unix used this representation for all sorts of things, time stamps on files, measuring time, and so forth.
I personally became involved with Unix in about 1975. Since the university lab where I worked had access to the source code for Unix we could examine it. The comments noted that the time representation was good until 2038 at which point it would "wrap around" to 1970 again.
From the perspective of 1975 this was sixty some years in the future - who would care - we figured we'd be dead by then anyway? And, at the time, the world of computing was dominated by IBM, who would ever use Unix for anything serious anyway...
Fast forward forty years.
Today my being alive in 2038 is not that far fetched - I would be 81 - my mother's age today.
So in my potential life-time a "millenium clock problem" will potentially cycle through it entire life.
The 2038 problem is serious because many small things - like computers in automobiles, pacemakers, medical equipment, and so forth all use 32-bit Unix and hence 32-bit time. Though by 2038 all computers might be 64-bit and nothing will happen at all - save for some old beater cars crapping out.
For some reason all this talk of the future trouble and angst reminds me of the Zager and Evans song "In the Year 2525."
However, I think their most of their dire predictions for mankind's future will come true far, far sooner than 2525.