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Achilles and the Tortoise (Posted on 2002-11-22) Difficulty: 3 of 5
Suppose that the swift Achilles is having a race with a tortoise. Since the tortoise is much slower, she gets a head start. When the tortoise has reached a given point a, Achilles starts. But by the time Achilles reaches a, the tortoise has already moved beyond point a, to point b. And by the time Achilles reaches b the tortoise has already moved a little bit farther along, to point c. Since this process goes on indefinitely, Achilles can never catch up with the tortoise.

How can this be?

Taken from - http://members.aol.com/kiekeben/zeno.html

  Submitted by Raveen    
Rating: 3.0769 (13 votes)
Solution: (Hide)
This is known as Zeno's paradox, a series of paradoxes dealing with infinite series of infinitely small components. Here is another:

The Racetrack (or Dichotomy)

One can never reach the end of a racecourse, for in order to do so one would first have to reach the halfway mark, then the halfway mark of the remaining half, then the halfway mark of the final fourth, then of the final eighth, and so on ad infinitum. Since this series of fractions is infinite, one can never hope to get through the entire length of the track (at least not in a finite time).

Start ____________________1/2__________3/4_____7/8__15/16... Finish

Just as one cannot reach the end of the racecourse, one cannot even begin to run. For before one could reach the halfway point, one would have to reach the 1/4 mark, and before that the 1/8 mark, etc., etc. As there is no first point in this series, one can never really get started (this is known as the Reverse Dichotomy).

Comments: ( You must be logged in to post comments.)
  Subject Author Date
re: WellHal2006-04-22 23:35:13
Science to the rescue!Devin Mahnke2005-07-21 05:54:32
consider the followingJen2005-07-11 19:05:17
solution?CJ2005-06-17 02:10:18
Some Thoughtseh..Amon2005-05-11 01:23:29
not a solutionwhome?2005-01-23 19:57:49
The tortoise will get caughtGustavo2004-06-15 11:11:33
No SubjectPieater2004-03-11 09:02:44
Questionovertaking the tortoiseCaptain Paradox2004-01-04 11:56:45
SolutionThink physics and limit theory (solution)!Jeff2003-12-23 21:00:42
Solutionthis is not a paradox in wholeben2003-12-10 20:10:49
no paradoxC.B.2003-11-29 19:32:13
what if?Sam2003-11-26 14:40:26
re: It Can'tmichelle2003-11-11 18:30:42
What!? The tortoise...ratsnstuff2003-10-17 03:02:45
Math?vlad2003-10-09 10:26:37
WellLawrence2003-08-29 01:19:31
The tortoise and the hairy ParadoxEvan2003-08-20 05:51:53
re: Why is this a paradox?calla tah-n2003-05-23 10:58:06
simplecalla tah-n2003-05-23 10:54:59
re: re: Why is this a paradox?Berry2003-05-10 03:00:41
Old Stupid 'Paradox'Berry2003-05-10 02:53:10
Brane worldChaz2003-05-03 08:37:31
paradoxJon2003-04-11 06:53:27
Questionwhat?bik882003-03-15 14:24:16
re: Why is this a paradox?Chris2003-03-12 23:06:09
Why is this a paradox?Adam2003-03-03 08:50:18
incorrect assumption?craig2003-02-10 13:20:28
Solutioni don't know the mathematical solution, but...sach2002-12-10 10:49:32
It Can'tMatthew Bobbins2002-12-02 07:47:15
SolutionAchilles' heelTomM2002-11-22 21:22:04
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