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A lot of balls

A lot of balls

Posers and Puzzles

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Originally posted by AThousandYoung
You may be able to boil an egg, but it is impossible to put balls in and take them out that quickly (i.e. infinitely fast). You can only see what the limit is as you approach infinity (t=0 in this case). That limit is

B = 2S - S = S

The number of balls equals the number of steps. As time approaches zero, the number of balls put in approaches ...[text shortened]... , not 1. That's because the numerator approaches infinity twice as quickly as the denominator.
That is the wrong operation because we're talking about elements in a set (balls in the bag). With a set with countably infinite cardinality, if you insert a new element for each element that exists the number of elements remains the same because you can still do a one-to-one correspondence (bijection) between them.
http://en.wikipedia.org/wiki/Galileo%27s_paradox

Since none of the balls is skipped and there is a one-to-one correspondence between the two sets then all balls are eventually removed.

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Lets take EXACTLY the same problem except that the ball removed is the highest number in the bag, not the lowest.

We are still putting balls in and taking balls out at the same rate.

how many balls left at time t=0

explain.

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Originally posted by wolfgang59
Lets take EXACTLY the same problem except that the ball removed is the highest number in the bag, not the lowest.

We are still putting balls in and taking balls out at the same rate.

how many balls left at time t=0

explain.
Again you completely ignore my posts and decide to rephrase the same arguments.

In that case:
Set of balls inserted : {1,2,3,4,...}
Set of balls removed: {2,4,6,...}
Set of balls remaining {1,3,5,...}

The rate is irrelevant, it's about the operations creating a one-to-one correspondence or not. In your new case, although one can create a one-to-one correspondence between the two sets, the operation skips certain balls so it does not correspond to such a bijection. If you put ten balls in but only remove the lowest even one then you'd get exactly the same balls remaining. So putting 2 or 10 balls when you insert is irrelevant.

Imagine you insert 10 balls at a time and remove the lowest even one:
Set of balls inserted at t=0 : {1,2,3,4,...}
Set of balls removed at t=0 : {2,4,6,...}
Set of balls remaining at t=0: {1,3,5,...}

Do you disagree that in this case inserting 2 or 10 balls at a time will lead to the same balls remaining at t=0?

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Originally posted by Palynka
Again you completely ignore my posts and decide to rephrase the same arguments.

In that case:
Set of balls inserted : {1,2,3,4,...}
Set of balls removed: {2,4,6,...}
Set of balls remaining {1,3,5,...}

The rate is irrelevant, it's about the operations creating a one-to-one correspondence or not. In your new case, although one can create a one-to-on ...[text shortened]... t in this case inserting 2 or 10 balls at a time will lead to the same balls remaining at t=0?
So what you are saying that the number of balls left at t=0 depends on how we number the balls?

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There is no such thing as t = 0 in your problem because you've tied the existence of t = 0 to the existence of infinities. You cannot do math with infinities. You can only do math with limits as variables approach infinity.

The technically correct way to approach this is to say "what is the limit of the number of balls in the bag as time approaches 0".

I believe your argument, Palynka, boils down to "infinity minus infinity = 0" which is fallacious.

There is no one to one correspondence between the two sets until t=0 and t cannot = 0, t can only approach 0 - because of how you've set up the problem.

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Originally posted by AThousandYoung
There is no such thing as t = 0 in your problem because you've tied the existence of t = 0 to the existence of infinities. You cannot do math with infinities. You can only do math with limits as variables approach infinity.

The technically correct way to approach this is to say "what is the limit of the number of balls in the bag as time approach ...[text shortened]... il t=0 and t cannot = 0, t can only approach 0 - because of how you've set up the problem.
Thats kind of the way my thinking is going too. As i have a strong (I think) argument for the answer to be infinite and Palynka (using set approach) has an argument for zero.

But what is the proof?

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Originally posted by AThousandYoung
There is no such thing as t = 0 in your problem because you've tied the existence of t = 0 to the existence of infinities. You cannot do math with infinities. You can only do math with limits as variables approach infinity.

The technically correct way to approach this is to say "what is the limit of the number of balls in the bag as time approach il t=0 and t cannot = 0, t can only approach 0 - because of how you've set up the problem.
Of course there is t=0, Achilles reaches the tortoise doesn't he? But you are right in the sense that the limit cannot help you there because cardinality is not continuous with respect to set theoretic limits.

And in t=0, any ball that you can think of has been removed. If there were infinite balls, I would take one out (any one) and realized that it should have been removed at a given n before t=0. Do you not think this is an issue with your view? This, I think, is a product of cardinality not being continuous in the sense above.

I also don't see how I do infinity - infinity at any point. I just say that if I removed all elements of set {1,2,3,4,...} from {1,2,3,4,...} (the same set!) then I get {}. Not Inf-Inf=0. These are not the same.

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Originally posted by Palynka
I also don't see how I do infinity - infinity at any point. I just say that if I removed all elements of set {1,2,3,4,...} from {1,2,3,4,...} (the same set!) then I get {}. Not Inf-Inf=0. These are not the same.
There are infinite elements in the first set. There are infinite elements in the second set. If I remove (subtract) all infinity elements of set 2 from set 1's infinite supply of elements I will get a set with 0 elements.

Infinity minus infinity equals zero.

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Originally posted by AThousandYoung
There are infinite elements in the first set. There are infinite elements in the second set. If I remove (subtract) all infinity elements of set 2 from set 1's infinite supply of elements I will get a set with 0 elements.

Infinity minus infinity equals zero.
I don't do any subtraction.

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Originally posted by Palynka
I don't do any subtraction.
Well, you start with a set with infinite elements, you remove from it an infinite number of elements, and conclude you now have an empty set. Sure looks like subtraction to me.

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Originally posted by Palynka
That is the wrong operation because we're talking about elements in a set (balls in the bag). With a set with countably infinite cardinality, if you insert a new element for each element that exists the number of elements remains the same because you can still do a one-to-one correspondence (bijection) between them.
http://en.wikipedia.org/wiki/Galileo%27s_ ...[text shortened]... here is a one-to-one correspondence between the two sets then all balls are eventually removed.
I have no problem with that, if you have infinite balls!

It doesn't work while we are tending towards infinity though.

note also that an_infinite_set - an_infinite_set= an_infinite_set

The number at balls at time 0 is infinite however you cut it.

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Originally posted by Palynka
Set of ALL balls inserted : {1,2,3,...}
Set of ALL balls removed: {1,2,3,...}

Same set. You're also welcome to *sigh* disprove the argument that it's impossible that there are infinite balls in the bag and there isn't a lowest numbered ball.

Again *sigh* your mistake is extrapolating cardinality follows from infinite sequences, but anyone would agree ...[text shortened]... n show that the sets
{1,2,3,...} ; {2,4,6,...}
have exactly the same cardinality.

*sigh*
Ye gods.

Once again you are saying that the series (num of balls in bag):

(1,2,3,4,5,6,7,8,9,10...}

converges to 0!!

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Originally posted by iamatiger
Ye gods.

Once again you are saying that the series (num of balls in bag):

(1,2,3,4,5,6,7,8,9,10...}

converges to 0!!
If those are cardinalities, then cardinality is not continuous like that. If you do a similar exercise for the difference of cardinalities in the set of even and natural numbers you'll find

{1,2} vs {2} => difference in the number of elements/cardinality 1
{1,2,3,4} vs {2,4} => difference in the number of elements 2
then keep going...

set of differences in the number of elements between the two sets:
{1,2,3,4,...,n}

Take n to infinity, what happens? Cardinality is the same and the sets have the same number of elements.

I'll be gone for a week. Have fun.

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Originally posted by PBE6
"If you've done six impossible things this morning, why not round if off with breakfast at Millyways?" - Douglas Adams


Suppose you and your friend come into possession of a bag of infinite capacity, along with an infinite supply of numbered balls and a stopwatch with an infinite number of gradations. After watching the universe explode ...[text shortened]...
[b]Question:
How many balls will be left in the bag when the stopwatch reads 0 seconds?[/b]
Zero.

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Originally posted by Palynka
Of course there is t=0, Achilles reaches the tortoise doesn't he? But you are right in the sense that the limit cannot help you there because cardinality is not continuous with respect to set theoretic limits.

And in t=0, any ball that you can think of has been removed. If there were infinite balls, I would take one out (any one) and realized that it shou ,...} from {1,2,3,4,...} (the same set!) then I get {}. Not Inf-Inf=0. These are not the same.
Achilles reaches the tortoise because even as the number of "catching up events" is infinite, the length of each of those events in distance (or time because velocity is constant) becomes infinitesimally small. You end up multiplying the number of "catching up events" times the distance per event which gives you a fraction in which both the numerator and denominator contain variables that approach infinity together. This can be solved via L'Hopitals rule.

In the OP problem it's not the same. There is no variable that becomes infinitesimally small as the number of ball swapping events becomes infinitely large. As time approaches zero, the person putting in and taking out the balls speeds up (unlike Achilles, who does not change speed) until at t=0 he is working infinitely fast, putting in 2 and taking out 1 each time. Thus you get infinite balls.

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