Remember brains in a vat and the five-minute hypothesis? (You can click on the links to look at them again, if you want.) They're philosophical brain teasers to remind us we can't know with absolute certainty the true nature of reality. (Paradoxically, we are absolutely certain we can't be absolutely certain!)
Of course, just living our lives day by day we don't think much about this situation. I mean, the "reality" we appear to be experiencing seems like it's hanging together pretty well, wouldn't you say? Consider:
The sun rises every morning.
Gravity doesn't suddenly turn off, hurling us into space.
We can't eat at Chick-fil-A on Sunday.
There are probably other examples, but these are the main ones. Point is, reality works as expected. So why make a big deal about it, right?
Well I'm normally a pretty cheerful person, but I'm also a realist. (See what I did there? That's for you, beloved readers.) And I'm noticing this reality is not eternal. Think about it. Everything we perceive in this reality exists within time. We might conceive an idea or concept about something outside time, something eternal; but in our reality we're bound within time. I think even the evil scientist with a big vat of brains floating in brain goo is operating within time!
In fact, according to the second law of thermodynamics this whole place is going to heck in a handbasket. (Editor's note: Will doesn't condone the use of the filthy words, and has modified this well-known expression to make it suitable for all readers, including youngsters.) The entire universe is entropying like nobody's business. So doesn't it follow there will come a time (even if it's still a long way off) when this reality will END?
Now don't get scared, everybody. It's going to be all right, even after everything we've ever perceived passes into TOTAL OBLIVION. But to understand what will happen at the END, we must be willing to conceive a different type of reality. This act of our will, our willingness to have an idea about a different kind of reality, is what we call FAITH, of course.