Hi, all:
A comment and two additional interesting questions.
First of all, I'm truly glad that so many of you did like my didactic quiz and posted your answers and comments. Of course, as I clearly stated in my original post, it's all a didactic, ideal, theoretical example, not concerned with being physically possible (for one thing, such a mass, if it could exist, would implode into a black hole at once), nor financially sound (inflation, bankrupts, accidents, etc).
It was simply kind of a gedankenexperiment to show my daughter just how exponential functions, however initially slowly growing, will ultimately overcome any linear (or polynomic for that matter) function, however steep its initial growing. After some calculations, she took the hint and, as I said, was amazed no end.
I wonder if any of you did try to actually imagine the situation. On the one hand, a simple, silent, boring account in a bank, sitting there doing nothing at all for 2,000 years, except silently grow, a mere figure in a paper. This is anything but exciting to watch.
On the other hand, a titanic (for lack of a better word) cylinder of solid, glowing gold, which extends from horizon to horizon in width, and farther than your sight can follow in depth, an ultra-colossal metallic wall if ever was one, which instantly surges from the ground up at such speed that before you can even realize it, it's higher than the Moon ! If done with some kind of CGI, it would be an absolutely awesome, cataclismic, mind-breaking sight ! And this goes on, at undiminished speed, for 2,000 years !! ... yet the humble account with its $1.00 at 5.00% ultimately wins. I think this pretty much makes the point, in spades. Try to impress this imagery in your children/students/colleages !
As for a final comment, I'll submit a couple of additional questions to your consideration, specially dedicated to the many Star Trek fans out there, and still firmly within the realm of the ideal, non-physically realizable model (please no inflation, cashing after one second, etc):
- Let's suppose that the cylinder has been fitted with a new technology akin to the warp drives of Intrepid-class starships (e.g.: Voyager) and can grow at warp 8 (i.e.: 1024 times the speed of light, so it would reach to Alpha Centaury in 34 hours) instead of at merely warp 1 (the speed of light). How much would you need to increase the original interest rate of 5.00% to overcome it ? 10% ? 40% ? 1024*5 = 5120% ?
- What if the cylinder was fitted with Star-Trek's interstellar radio speed, i.e: warp 9.9999 (= 199516 times the speed of light, so it would reach to Alpha Centaury in 10 min.) ? What then should the interest rate be? 10% ? 40% ? 199516*5 = aprox. 1,000,000 % ?
I hope the answer to both questions will still surprise you
(and any trekkies you might pose the question to).
[Data for ST Voyager's warp speeds taken from here]
Best regards from V.
Edited: 19 July 2004, 5:15 a.m.