# The Doomsday Argument

• Page

of 2

• LeoliansBro 2 Oct 2013 11:23:33 44,956 posts
Seen 2 hours ago
Registered 8 years ago
 Lifted from XKCD and very interesting. Here's the relevant bit: Humans will go extinct someday. Suppose that, after this happens, aliens somehow revive all humans who have ever lived. They line us up in order of birth and number us from 1 to N. Then they divide us divide them into three groups—the first 5%, the middle 90%, and the last 5%: Now imagine the aliens ask each human (who doesn't know how many people lived after their time), "Which group do you think you're in?" Most of them probably wouldn't speak English, and those who did would probably have an awful lot of questions of their own. But if for some reason every human answered "I'm in the middle group", 90% of them will (obviously) be right. This is true no matter how big N is. Therefore, the argument goes, we should assume we're in the middle 90% of humans. Given that there have been a little over 100 billion humans so far, we should be able to assume with 95% probability that N is less than 2.2 trillion humans. If it's not, it means we're assuming we're in 5% of humans—and if all humans made that assumption, most of them would be wrong. To put it more simply: Out of all people who will ever live, we should probably assume we're somewhere in the middle; after all, most people are. If our population levels out around 9 billion, this suggests humans will probably go extinct in about 800 years, and not more than 16,000. I'm sure Lutz will be able to help us out here.

LB, you really are a massive geek.

• TheSaint 2 Oct 2013 11:26:32 14,827 posts
Seen 53 minutes ago
Registered 9 years ago
 The real question is why do they divide everyone into three groups?
• sport 2 Oct 2013 11:28:21 12,808 posts
Seen 12 hours ago
Registered 9 years ago
 You're drunk, aliens.
• DFawkes 2 Oct 2013 11:29:53 24,047 posts
Seen 11 minutes ago
Registered 9 years ago
 That's a real noodle baker. The important bit for me is the fact this theoretical doomsday is way we'll be dead and buried so I'm not really fussy. Shame for our descendants perhaps, but we all have being resurrected by aliens to look forward to so I'll chat with them then. If we even have the same language of course and it hasn't all descended into text speak.

Oh for goodness sake, I've caught my scrotum in my zip again - Margaret Thatcher, 1986

• Tonka 2 Oct 2013 11:35:33 21,345 posts
Seen 30 minutes ago
Registered 11 years ago

If you can read this you really need to fiddle with your forum settings.

• mrpon 2 Oct 2013 11:35:36 29,560 posts
Seen 11 minutes ago
Registered 8 years ago
 Only one man for this job:

Give yourself £5 or ½ gig, you're worth it.

• Carlo 2 Oct 2013 11:44:58 18,216 posts
Seen 2 hours ago
Registered 9 years ago
 LeoliansBro wrote: Lifted from XKCD and very interesting. Why is it interesting?

PSN ID: Djini

• neilka 2 Oct 2013 11:45:56 16,527 posts
Seen 12 minutes ago
Registered 9 years ago
 You should switch doors

BAAANG!!!!! EXPLOTION!!!!!

• LeoliansBro 2 Oct 2013 11:47:24 44,956 posts
Seen 2 hours ago
Registered 8 years ago
 Carlo wrote: LeoliansBro wrote: Lifted from XKCD and very interesting. Why is it interesting? Thanks for the input, invaluable.

LB, you really are a massive geek.

• pauleyc 2 Oct 2013 11:49:59 4,527 posts
Seen 19 minutes ago
Registered 13 years ago
 Stephen Baxter touched this topic in the first book of the Manifold series, Time. Quite mind-bending; the human mind is not really equipped to deal with such thought experiments like the Carter catastrophe or - to go to the extreme - physical inevitabilities like the heat death of the universe.
• Carlo 2 Oct 2013 11:51:58 18,216 posts
Seen 2 hours ago
Registered 9 years ago
 LeoliansBro wrote: Carlo wrote: LeoliansBro wrote: Lifted from XKCD and very interesting. Why is it interesting? Thanks for the input, invaluable. I'm asking you what you found interesting about this. You didn't say why it was interesting. I didn't say it wasn't.

PSN ID: Djini

• opalw00t 2 Oct 2013 11:52:46 11,297 posts
Seen 1 hour ago
Registered 10 years ago
 Stop being an arse.

not a force for good

• LeoliansBro 2 Oct 2013 12:01:20 44,956 posts
Seen 2 hours ago
Registered 8 years ago
 Fine. I find it interesting when mathematical analysis and reasoning combine to offer a projection into the future (which may be wrong, but isn't easily disproven) in a way I didn't previously think possible. I find pedantry less interesting.

LB, you really are a massive geek.

• sport 2 Oct 2013 12:03:06 12,808 posts
Seen 12 hours ago
Registered 9 years ago
 Still no email.
• RedSparrows 2 Oct 2013 12:05:35 24,183 posts
Seen 3 minutes ago
Registered 7 years ago
• Carlo 2 Oct 2013 12:48:50 18,216 posts
Seen 2 hours ago
Registered 9 years ago
 Edited by Carlo at 12:49:05 02-10-2013

PSN ID: Djini

• Moot_Point 2 Oct 2013 12:53:40 4,604 posts
Seen 37 minutes ago
Registered 2 years ago
 Slow day much?

================================================================================

mowgli wrote: I thought the 1 married the .2 and founded Islam?

• glaeken 2 Oct 2013 13:06:35 11,265 posts
Seen 12 hours ago
Registered 10 years ago
 Assuming assumption over load. We should be able to assume with 95% probability that N is less than 2.2 trillion humans. How are we assuming that exactly?
• Deleted user 2 October 2013 13:13:00
 An awful lot of assumptions involved makes the surprising conclusion not very convincing. So not really sure what to make of it.
• Deleted user 2 October 2013 13:15:16
 I did find it interesting however that there has apparently only been 100 billion humans so far. Honestly expected that to be significantly higher.
• glaeken 2 Oct 2013 13:30:36 11,265 posts
Seen 12 hours ago
Registered 10 years ago
 It's not really that surprising given population growth is an exponential curve. The population of the UK for instance 500 years ago was probably only around a couple of million. Don't they say 90% of people who have ever lived are alive today? Population growth has been massive over the last few hundred years. I guess population growth cannot continue exponentially as we must reach a point where we have the maximum supportable population vs. land area and food production abilities. Edited by glaeken at 13:33:17 02-10-2013
• monkman76 2 Oct 2013 13:32:02 5,400 posts
Seen 2 minutes ago
Registered 7 years ago
 glaeken wrote: Don't they say 90% of people who have ever lived are alive today? Population growth has been massive over the last few hundred years. Not if there have been 100 billion people, means there would be 90 billion alive today. It's about 6 or 7 billion isn't it?
• Tonka 2 Oct 2013 13:32:44 21,345 posts
Seen 30 minutes ago
Registered 11 years ago
 glaeken wrote: Don't they say 90% of people who have ever lived are alive today? Population growth has been massive over the last few hundred years. I just saw doomsayer Nick Bostrom say the exact opposite in a TED talk. Which still means that 10% are alive today which is a lot more than I would have guessed.

If you can read this you really need to fiddle with your forum settings.

• glaeken 2 Oct 2013 13:35:26 11,265 posts
Seen 12 hours ago
Registered 10 years ago
 Yeah some basic maths does seem to suggest the 90% figure has to be rubbish if the total amount of humans there has ever been really is 100 billion. I wonder where the 100 billion number comes from? The 90% thing certainly is said though. I guess it may be one of those shocking stat's that is meant to blow you mind but are not actually true. Edited by glaeken at 13:38:44 02-10-2013
• Steve_Perry 2 Oct 2013 13:38:46 5,200 posts
Seen 2 minutes ago
Registered 2 years ago
 Though provoking and I guess that's the point. I wish I was clever enough to understand it fully. /is spazz
• grey_matters 2 Oct 2013 14:00:33 3,863 posts
Seen 11 hours ago
Registered 9 years ago
 TheSaint wrote: The real question is why do they divide everyone into three groups? Half-life 3 confirmed.
• jellyBelly 2 Oct 2013 14:14:49 448 posts
Seen 19 minutes ago
Registered 9 years ago
 So what variable are these percentiles based on ?

PSN:lumulata, NN Dollodon

• BigOrkWaaagh 2 Oct 2013 16:28:41 2,302 posts
Seen 10 minutes ago
Registered 7 years ago
 I doubt Adam and Eve and the people running round in a crazed panic while the world comes crashing down around them in a giant ball of fire would say they were in the 90%.
• grey_matters 2 Oct 2013 17:13:24 3,863 posts
Seen 11 hours ago
Registered 9 years ago
 midnight_walker wrote: I doubt Adam and Eve and the people running round in a crazed panic while the world comes crashing down around them in a giant ball of fire would say they were in the 90%. I don't think getting the question right is the point, really. It's that given a small amount of information you can predict surprisingly dramatic things by using reasonably basic statistical processes (and a shit-ton of nested assumptions in this case).
• Page

of 2