Chris and Lucy entered a building looking for Manuel. In a room they
found a note and a lighted candle. Chris looked at the note and read it aloud:
"Hi! It's 2:30, and I'm leaving to run some errands. I'll be back in a couple
of hours. BTW, the electricity is out, so I lit a candle for you. -Manuel".
Then Lucy said, "I know how we can find out how long it's been since he
left! Look, the candle has been burning since he lit it and has a significant
amount of wax that's melted and dripped down. If we figure out what the rate
is which the wax is melting and measure the amount of wax that has thus far
dripped, we can work backwards to find out how long it has been since he left."
Chris said, "Why waste your time? The note says he left at 2:30." Lucy
said, "Don't believe everything you read." Chris replied, "Look, I've known
Manuel for a long time, and this is his handwriting. Don't be ridiculous."
Lucy replied, "Ah yes, but what does he *mean* by '2:30'? A note like that
is subject to interpretation. Suppose he was talking about another time zone
or something." And so a short philosophical argument ensued about the note.
However, Lucy prevailed and insisted on performing the measurement and
A few minutes later, Lucy announced: "Well, I've got bad news for us.
Based on the amount of wax that has melted and the rate at which the wax is
melting, I can confidently tell you that it has been at least one whole day
since this guy left. He was probably talking about 2:30 yesterday. And since
he said that he'd be back 'in a couple of hours', we can assume that something
happened to him and he's not coming back at all. So much for your 'note'.
Just then, Manuel walked in. Lucy said, "Are you this guy 'Manuel'? What
took you so long?" Manuel replied, "What are you talking about? I left you
guys a note saying I'd be back in a couple of hours. It hasn't even been that
long." Lucy said, "Never mind the note. I measured the amount of wax that has
dripped off your candle, and the rate which the wax was melting. I know you've
been gone since yesterday."
Manuel replied, "First of all, that candle isn't burning anywhere near
as brightly as when I first lit it. Second of all, I didn't light a new
candle, but a used one. And thirdly, I used another candle to light this
candle and in the process the wax from that candle spilled all over this one."
Lucy said, "So you set up that candle to deceive us, to make it look
like you left the room over a day ago, when in fact it's been less than a
couple of hours." Manuel replied, "Look, I left you a note telling you
when I left. I never intended for you to conduct some silly experiment
measuring wax dripping off of a candle to figure out when I left. I put
the candle there so you guys would have some light."