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The reason why this is so subtle is that it's not a given that you're in a cubicle. It's more likely for you to be put in a cubicle the more people who are put

The reason why this is so subtle is that it's not a given that you're in a cubicle. It's more likely for you to be put in a cubicle the more people who are put into cubicles.

baddox 12y ago
> The reason why this is so subtle is that it's not a given that you're in a cubicle. The way the problem is presented, it is a given that you're in a cubicle. If you wanted to be more explicit about it, you could say that God, before creating humanity, flipped a coin, and then created either 10 or 100 humans and placed them into cubicles. You wake up and have to estimate the probability of that coin flip.
- bluecalm 12y ago
  It is given that you are but it's not given that that was a sure thing to happen. Imagine this: God flips a coin, creates 10 cubicles. If the coin is heads he puts you in one of them if it tails the God flips another coin and if it tails again he puts you in one of the cubicles but if it heads he doesn't. You wake up in a cubicle. It's given that you are in one! what are the chances the first coin landed heads ? The probability isn't 50% because there is underlying probability that you would be in cubicle at all (1 vs 0.5 after first flip). There is the same problem with doomsday argument just better masked.
  - lisper 12y ago
    Ah, I see. It makes more sense if you forget about cubicles and just call the final outcomes A or B. Call the outcomes of the two coin flips H1/T1 and H2/T2. We have: H1->A, T1,H1->A, T1,T2->B. P(H1|A) is therefore 67% if the coin is fair, but in any event P(H1|A)>P(H1). So the doomsday argument is actually correct. :-) But it's really nothing more than the (IMO vacuous) observation that (say) half of the people who ever live will have a birth order number greater than the median, and so the odds are 50-50 that fewer people will be born after you than before you. More generally, the odds that N times as many people will be born after you as before you is equal to 1/2N.

The reason why this is so subtle is that it's not a given that you're in a cubicle. It's more likely for you to be put in a cubicle the more people who are put into cubicles.

baddox 12y ago

> The reason why this is so subtle is that it's not a given that you're in a cubicle. The way the problem is presented, it is a given that you're in a cubicle. If you wanted to be more explicit about it, you could say that God, before creating humanity, flipped a coin, and then created either 10 or 100 humans and placed them into cubicles. You wake up and have to estimate the probability of that coin flip.

bluecalm 12y ago
It is given that you are but it's not given that that was a sure thing to happen. Imagine this: God flips a coin, creates 10 cubicles. If the coin is heads he puts you in one of them if it tails the God flips another coin and if it tails again he puts you in one of the cubicles but if it heads he doesn't. You wake up in a cubicle. It's given that you are in one! what are the chances the first coin landed heads ? The probability isn't 50% because there is underlying probability that you would be in cubicle at all (1 vs 0.5 after first flip). There is the same problem with doomsday argument just better masked.
- lisper 12y ago
  Ah, I see. It makes more sense if you forget about cubicles and just call the final outcomes A or B. Call the outcomes of the two coin flips H1/T1 and H2/T2. We have: H1->A, T1,H1->A, T1,T2->B. P(H1|A) is therefore 67% if the coin is fair, but in any event P(H1|A)>P(H1). So the doomsday argument is actually correct. :-) But it's really nothing more than the (IMO vacuous) observation that (say) half of the people who ever live will have a birth order number greater than the median, and so the odds are 50-50 that fewer people will be born after you than before you. More generally, the odds that N times as many people will be born after you as before you is equal to 1/2N.