# Infinity Puzzle

davegage
Posers and Puzzles 03 Jun '06 22:58
1. 03 Jun '06 22:58
Suppose Chuck Norris* has infinitely many ping pong balls (the balls are labeled ball 1, ball 2, ball 3, ... , ball n, ... ). He also has a magic bucket with a special hole in the bottom.

The clock starts at time t = 0. At time t = 1, Chuck places ball 1 and ball 2 into the bucket, and ball 1 instantaneously falls out the special hole, leaving ball 2 in the bucket. At time t = 1 + 1/2, Chuck places ball 3 and ball 4 into the bucket, and ball 2 instantaneously falls out the special hole, leaving ball 3 and ball 4 in the bucket. At time t = 1 + 1/2 + 1/4, Chuck places ball 5 and ball 6 into the bucket, and ball 3 instantaneously falls out the special hole, leaving ball 4, ball 5, and ball 6 in the bucket. I think you get the idea here: generally, at time t = 1 + 1/2 + 1/4 + ... + 1/2^m, Chuck places two more balls into the bucket, and the lowest numbered ball in the bucket falls out of the bucket through the hole. Since SUM(m=0 to m=M)[1/2^m] converges to 2 as M --> infinity, after 2 units of time, Chuck is finished placing all of his ping pong balls into the bucket.

So: after 2 units of time, how many ping pong balls remain in the bucket?

*No one but Chuck could accomplish this feat.
2. sven1000
Astrophysicist
04 Jun '06 00:01
Well, for each step, one net ball is added and one net ball is dropped. Since he has infinite balls to start with, then the number in his bucket is infinity / 2, as is the number that dropped out. Infinity being what it is, there are an infinite number of balls both in and out of the bucket!
3. 04 Jun '06 00:10
Originally posted by sven1000
Well, for each step, one net ball is added and one net ball is dropped. Since he has infinite balls to start with, then the number in his bucket is infinity / 2, as is the number that dropped out. Infinity being what it is, there are an infinite number of balls both in and out of the bucket!
'nuff said
4. 04 Jun '06 00:59
Originally posted by sven1000
Well, for each step, one net ball is added and one net ball is dropped. Since he has infinite balls to start with, then the number in his bucket is infinity / 2, as is the number that dropped out. Infinity being what it is, there are an infinite number of balls both in and out of the bucket!
This is the answer most people come up with -- but it is not correct.
5. 04 Jun '06 01:00
Originally posted by thespacemonkey
'nuff said
See above.
6. royalchicken
CHAOS GHOST!!!
04 Jun '06 01:23
Originally posted by davegage
Suppose Chuck Norris* has infinitely many ping pong balls (the balls are labeled ball 1, ball 2, ball 3, ... , ball n, ... ). He also has a magic bucket with a special hole in the bottom.

The clock starts at time t = 0. At time t = 1, Chuck places ball 1 and ball 2 into the bucket, and ball 1 instantaneously falls out the special hole, leaving ball 2 ...[text shortened]... how many ping pong balls remain in the bucket?

*No one but Chuck could accomplish this feat.
Each ball went in the bucket once and fell out once, so the bucket contains no balls after two units of time.

Alternatively, consider the set of balls in the bucket when he finishes. Since it's a subset of a countable set of balls, it has an element with least number if it's nonempty. Call this ball B (B is some positive integer) and follow the algorithm. It's pretty clear that Ball B can't exist, so the set has no minimal element and is thus empty.
7. Phlabibit
Mystic Meg
04 Jun '06 02:13
Originally posted by davegage
Suppose Chuck Norris* has infinitely many ping pong balls (the balls are labeled ball 1, ball 2, ball 3, ... , ball n, ... ). He also has a magic bucket with a special hole in the bottom.

The clock starts at time t = 0. At time t = 1, Chuck places ball 1 and ball 2 into the bucket, and ball 1 instantaneously falls out the special hole, leaving ball 2 ...[text shortened]... how many ping pong balls remain in the bucket?

*No one but Chuck could accomplish this feat.
All the balls.

He stuffs the hole shut with Jack Bauer and Macgyver in the first unit of time, and Roundhouses all the balls into the bucket in half a time unit.

He uses the last half a unit to save a mother and her child from thugs.

P-
8. 04 Jun '06 02:37
Originally posted by davegage
So: after 2 units of time, how many ping pong balls remain in the bucket?
How ever many Chuck says there are!
9. 04 Jun '06 02:401 edit
Originally posted by Phlabibit
All the balls.

He stuffs the hole shut with Jack Bauer and Macgyver in the first unit of time, and Roundhouses all the balls into the bucket in half a time unit.

He uses the last half a unit to save a mother and her child from thugs.

P-
Well, I was going to say that royalchicken is right on the money with his proof by contradiction that ball B is non-existent; I was also going to add that another way to see that royalchicken must be right is to note simply that the sets {ball 1, ball 2, ... , ball n, ... } and {(ball 1, ball 2), (ball 3, ball 4), ... , (ball 2n-1, ball 2n), ... } are equipolent (one-to-one correspondence).

But now that I have seen your answer and explanation, I think we all need to re-evaluate our core beliefs. Well done, Phlabibit!
10. royalchicken
CHAOS GHOST!!!
04 Jun '06 10:44
Originally posted by Phlabibit
All the balls.

He stuffs the hole shut with Jack Bauer and Macgyver in the first unit of time, and Roundhouses all the balls into the bucket in half a time unit.

He uses the last half a unit to save a mother and her child from thugs.

P-
This is very insightful reasoning ðŸ˜€!