
33 Questions - splike
https://github.com/MarkDunne/33-questions
======
stbullard
Fun to think about, but in the real world, no question neatly divides people,
even the gender one. To quote Reddit's u/tailcalled[1], the exo-
software/meatspace world is even less standardized than the software world:

Falsehoods programmers believe about gender:
[http://www.cscyphers.com/blog/2012/06/28/falsehoods-
programm...](http://www.cscyphers.com/blog/2012/06/28/falsehoods-programmers-
believe-about-gender/)

Falsehoods programmers believe about names:
[http://www.kalzumeus.com/2010/06/17/falsehoods-
programmers-b...](http://www.kalzumeus.com/2010/06/17/falsehoods-programmers-
believe-about-names/)

Falsehoods programmers believe about addresses:
[http://www.mjt.me.uk/posts/falsehoods-programmers-believe-
ab...](http://www.mjt.me.uk/posts/falsehoods-programmers-believe-about-
addresses/)

Falsehoods programmers believe about time:
[http://infiniteundo.com/post/25326999628/falsehoods-
programm...](http://infiniteundo.com/post/25326999628/falsehoods-programmers-
believe-about-time)

More falsehoods programmers believe about time:
[http://infiniteundo.com/post/25509354022/more-falsehoods-
pro...](http://infiniteundo.com/post/25509354022/more-falsehoods-programmers-
believe-about-time-wisdom)

Falsehoods programmers believe about geography:
[http://wiesmann.codiferes.net/wordpress/?p=15187&lang=en](http://wiesmann.codiferes.net/wordpress/?p=15187&lang=en)

[1]
[http://www.reddit.com/r/programming/comments/1fc147/falsehoo...](http://www.reddit.com/r/programming/comments/1fc147/falsehoods_programmers_believe_about_addresses/ca8sirp)

~~~
deathanatos
I dislike some of the examples of the "falsehoods programmers believe about
time" because they typically _aren 't_ falsehoods, and will always hold true
within the constraints of your system. Yes, time is a fickle thing that is
marred by history, but in building a system, I choose a representation for the
data I am storing in it. If I choose to store dates using a Gregorian calendar
(because I'm following ISO-8601), then,

> Months have either 28, 29, 30, or 31 days.

Does hold true: months do have 28 to 31 days, _by definition_. If someone
wants my Gregorian date in a different calendar system, then we must convert,
but that a display issue. Otherwise, we're comparing apples and oranges, and
of course all bets are off.

It's kind of like time: the hour "2 AM" never repeats itself on random
politically appointed days, because I have chosen to store timestamps in UTC.
If someone wants to see that timestamp in "PST" (or America/Los_Angeles), then
that's a display issue that can be accommodated, but it does not suddenly
violate the fact that "2 am" never repeats in UTC.

Of course, in real life, people don't know what timezone their date is stored
in and things love to break randomly on DST switch-overs or leap days or the
ends of leap years.

~~~
sixbrx
2am doesn't even repeat in the local timezone, it's just that the timezone
changes. So here for example, 1:59:59 am CDT increments to 1:00:00 CST, which
does not conflict with the earlier 1:00:00 CDT. I think it would be better not
to go through all this hassle though, myself.

~~~
deathanatos
Nitpicking a bit, but I'd usually argue that the TZ doesn't change: You went
from "America/Chicago" to "America/Chicago". The timezone encapsulates more
than just the offset: it also includes when and how DST works. Merely, you
went from "1:59:59 am America/Chicago DST=true" to "1:00:00 am America/Chicago
DST=false". I'd say this is just terminology, since "CDT" and "CST" work just
as well (and how I envision it in my head, mostly due to the official TZ name
being "America/Chicago").

------
powrtoch
I don't think this problem is solvable in any elegant form, but it is
solvable. You'll just end up with massively conjunctive questions that you
can't even hold in your head at once, like "27: Are you a non-practicing
Catholic with exactly three children, or an asian owner of a minivan produced
between 1998 and 2004 that isn't green, or a licensed boat mechanic with
astigmatism, or..." and so on for the next 6 pages.

In short, you can draw categories to include or exclude as precise a number as
you like, you just have to be willing to draw really, really complicated
boundaries.

~~~
measure2xcut1x
Here's my admittedly naive Sunday afternoon spitball on an elegant solution:

I like the idea of a human UUID/GUID type identifier.

I would also like to think that this is solvable using strictly biological and
physical properties, sampled at birth.

Otherwise, time and culture factors would seem make it difficult to produce a
static set of "apples to apples" questions and answers.

I wonder if the right maths applied to existing genetic and forensics big data
sets could produce the 33 questions.

~~~
ghostdiver
DNA is your UUID/GUID

~~~
pavel_lishin
Unless you're one of a set of twins/triplets/etc.

~~~
heynairb
append datetime string of birth. Boom problem solved.

~~~
rmccue
What if the twins are delivered via Caesarean, with the exact same datetime
recorded? Including datetime (even as a string) also includes the
aforementioned falsehoods about time.

------
sz4kerto
> To contribute to the project, open up a pull request and add your question
> to the list below. All questions are open to debate and discussion.

This is a completely wrong way to approach the problem. Because the questions
should all divide the population into two parts the questions should be
'matched' to each other. This approach is a bit like doing a PCA by figuring
out one component, then the other, then the rest...

One way to solve this problem is to have a lot of yes/no questions (like a big
Karnaugh-table), then everybody would have a long bitstring as his unique ID.
Now you need to compress that bitstring -- like the minimization of the
Karnaugh-table.

[http://en.wikipedia.org/wiki/Karnaugh_map](http://en.wikipedia.org/wiki/Karnaugh_map)

\-- you need to generalize this for N number of questions (which can be done),
then you'd have 33 complex questions like 'is it true that (you live in NA AND
you are male) OR (you live in Canada AND you are white AND ) .. and so on and
on.

------
Laremere
Assuming that the person doesn't necessarily need to know their answer (which
is important for babies anyways) the answer is trivial. The first question
would be "Given that we ordered all humans in order of the time of their
birth, would the 1st bit of your position in the ordering be 1?", continue the
other 32 questions with the remaining 32 bits.

~~~
fat0wl
lol too much

------
gkoberger
Very interesting thought experiment. A few random thoughts:

Reminds me of Panoptic by the EFF:
[https://panopticlick.eff.org/](https://panopticlick.eff.org/)

Everyone's ID would change as time passed (if they move, if they age, if they
get a sex change, etc).

The best questions for this are inherently "irrelevant", since "relevant"
questions tend to be statistically linked. So, questions like "Was the second
letter of your first girlfriend's middle name between A and M?" is better than
"Were you younger than 20 when you had your first girlfriend?", since we can
likely guess the latter based on the other statistics.

It's very unlikely every ID will be unique if only asking 33 yes/no questions.
I mean, look at two twins living together -- very few questions will be able
to differentiate between them.

I think it's possible to do based on a random snapshot in time, however less
possible if it's meant to last a lifetime.

I also think the questions exist, but not in a manner that we'd be able to
come up with on our own. As in, I believe that a program that knew every
detail about every human could create 33 yes/no questions that differentiated
people, however I don't believe we could do it ourselves.

I also wonder how many questions would be required to ask non-yes/no questions
and get a completely unique ID for everyone. For example, questions like
"weight? languages spoken? birth place?".

~~~
PeterisP
Only ~1/3 of population would even be able to answer a question like "Was the
second letter of your first girlfriend's middle name between A and M?".

26% of global people are pre-teens; and approx half of the remainder aren't
dating women.

Not even going into the fact that the social concept of 'girlfriend' isn't
universal, there are multimillion cultures where the relationship stages of
going from strangers to family are split differently, and none of those stages
can be equated with western 'boyfriend/girlfriend' relationship; e.g. you may
like someone but not be dating (so no girlfriend) and then move directly to
engagement or marriage; or many other possibilities.

------
tinco
33 questions is sort of the Shannon-Hartley optimal encoding of identifying
information about human beings.

That means to come up with them is identical to finding an _optimal
compression_ of identifying data.

Necessarily, as the second question already implies, for this question to
correctly divide the population in half, you would have to group large amounts
of small populations together, resulting in _very_ long questions.

For example, if you'd like to make another geographical question that's
independent of the second one, it would have to divide in half every
population of the 6 countries you mentioned. The next question would
necessarily have to divide those 12 again.

By the way, the first question you ask is already suboptimal when combined
with the second question, as those countries together probably do not have a
clean 50% male/female split. (if they do, you should really explain that as
it's not obvious)

------
psuter
Interesting exercise, which I'd call impossible in the given form. Imagine
someone magically came up with 32 statistically independent binary indicators.
Now you need to come up with the 33th question Q such that if you pick any two
persons who are similar up to the 32nd bit, that single question must allow to
distinguish them. Sounds hard.

~~~
ronaldx
Question 33 has to split any category of people formed from the first 32
questions - very awkward, as you say.

Here is a moderately-functional question 33, though:

"Are you further North than any other person who has given the same answers as
you for the first 32 questions?"

~~~
chill1
> "Are you further North than any other person who has given the same answers
> as you for the first 32 questions?"

What if one of the persons was not on the planet at the time?

------
ZirconCode
Just use:

\- Birthday (19~ bits)

\- Rough Location (remaining bits)

And base the questions around those two, for example, where you born on a
1-15th, does the city you were born in start with the letter's a-k. This part
would be an exercise in statistics, I would think.

edit: And one bit for if you were the first to be born of two identical twins
=p

~~~
scraplab
Lots of people don't know their birthday, or if they do, it was written down
as 1st Jan (or another memorable date), because their parents/carer didn't
know when they came to register them, if they ever registered them. There will
be bias towards those memorable dates.

~~~
brownbat
> Lots of people don't know...

We can go farther. People in a coma or with certain mental impairments will
fall out of the system, if knowledge of any given fact is a hard requirement.

The only way this even makes sense as a thought experiment is if you have some
magic biographical oracle that helps you answer the questions.

------
brownbat
This project assumes we can know things that are not really knowable for
everyone. It starts with gender and birthplace, both tricky questions in some
situations.

So maybe we get to assume we have some oracle that helps us simplify the hard
questions.

At that stage, it's easy. Begin with, "Assume we build a list of people sorted
by time of birth (with some arbitrary tiebreakers, like proximity of
birthplace to Barbados, or darkness of hair color...)."

Question 1: Are you on the top half or bottom half of this list?

Question 2: Are you on the top quarter or bottom quarter of the half?

Question 3: ...

~~~
deathanatos
I had come up with something similar:

Question 1: Are you north of an east-west line that perfectly divides the
population in half?

(proceed to continue to divide each section in half.)

Of course, determining the position of those lines is damn near impossible.
And as soon as someone hops on a plane, the whole thing comes crashing down.

~~~
brownbat
I like it. Maybe "were you north of an east-west line" when this list was
made.

I guess it gets tricky when people are born.

Wait a minute, just realized this whole question breaks down if we don't
recycle numbers from the dead back to the newly born... and there's no
guarantee that all of the dead will sufficiently resemble all of the newborns.
I want my money back. :)

------
abentspoon
It's not enough to find 33 independent questions that evenly split the world's
population.

An optimal, though inelegant solution to that goal might look something like
this:

"Is the {1..33}th bit of sha1(name : location : date of birth) 1?".

Clearly you'll have tons of collisions with that solution, as you would have
with any solution using 33 independent questions.

To uniquely identify people, we'd either need to use more bits, or look very
closely at the population and derive very specific questions.

~~~
upquark
> Clearly you'll have tons of collisions with that solution

Why?

If we assume the hash code assignment to one of the 2^32 people is uniformly
random from a set of 2^160 codes, the odds of finding a collision are
astronomically small (order of 2^-95 or so). Am I missing something?

~~~
jules
You are not taking the entire hash, you are only taking the first 33 bits of
the hash. Since there are only about 8.5 billion different values for the 33
bits and there are about 7 billion people, the odds are astronomically low
that each of those 7 billion people will receive a different one of those 8.5
billion possibilities.

This is the birthday paradox with instead of 365 days you have 2^33 possible
answer values and instead of 23 people you have 7 billion people. I leave it
as an exercise for the reader to fill in these values into one of the formulas
to calculate the probability of successfully giving each person a unique 33
bit answer:
[http://en.wikipedia.org/wiki/Birthday_problem](http://en.wikipedia.org/wiki/Birthday_problem)

~~~
upquark
> You are not taking the entire hash, you are only taking the first 33 bits

Right, my bad, didn't pay attention to the problem we are trying to solve :)

------
gradys
I thought it would be more plausible and probably more interesting to do this
in maybe 40 questions. To do this in 33, as several others have pointed out,
would require 33 questions that each almost perfectly bisect the population
and are almost perfectly independent of each other.

With 40 or 45, we could relax that a bit and use questions that are actually
meaningful. Two people who are within a few bits of each other would actually
be similar in ways we care about, unlike two people who are similar because
their transliterated last names both appear in the last half of the alphabet.

------
fmax30
So you want to create a data set with entropy = 1 . Think of this in terms of
a hash function , You want to create a hash which only has an address space of
33 bits. Something in terms of H(Alice) = 0x12321 {H is a function which
generates 0x12321 to store the data of alice)

Doesn't this sound like perfect hashing with limited memory. I don't really
think that this can be done with such memory constraints. Even now we cannot
produce a perfect hash function that uses 1 bit / key. The theoretical best we
can do is 1.44 bit / key. And the practical best we have done till now is 2.5
bits per key. [1]

This may just be possible without the memory constraint that is , you answer N
number of questions which uniquely identify you. (where N > 48 )

[1]
[http://en.wikipedia.org/wiki/Perfect_hash_function#Minimal_p...](http://en.wikipedia.org/wiki/Perfect_hash_function#Minimal_perfect_hash_function)

------
knowtheory
No one here seems to have mentioned Hunch
([http://en.wikipedia.org/wiki/Hunch_(website)](http://en.wikipedia.org/wiki/Hunch_\(website\))
).

Picking discrete questions like this is equivalent to building a decision tree
for humanity. This is actually something that could be approached as an
engineering problem (and there are mechanisms for optimizing decision trees).

The problem still remains in the face of both the technological capabilities
of decision trees, and practical implementations like Hunch.com, that decision
trees are reductive and discrete. Reality is neither discrete nor reductive.

It may very well be the case that there is a set of questions that could
uniquely identify humans, but the insight that could be drawn from those
questions might be essentially pointless.

For example:

* Were you born in the northern hemisphere?

* Were you born on an even numbered year in the Gregorian calendar?

* Is the country of your birth governed through a representative system?

------
tehwebguy
This reminds me of Akinator: [http://en.akinator.com](http://en.akinator.com)

It's a little spammy nowadays, but it's had enough input that it seems pretty
amazingly accurate at "guessing" what / who you are thinking of in ~ 25
questions.

~~~
kalleboo
I thought of this too, or at least a site similar to it. It has so much input
that it's good at even very obscure people/characters.

------
Zarathust
I don't think it is possible with exactly 33 questions. It will probably
require more than that. Binary numbers have the property of adding twice as
many numbers +1 for every new bit. For example if you already have 7 bits and
you add an 8th one, then you'll be able to represent 127 numbers with that bit
off and 128 numbers with that bit on.

To properly mimic this property with yes/no questions, you will have to come
up with questions that divide the whole Earth's population equally AT EVERY
NEW QUESTION. Even the most obvious one, "are you (fe)male?" is slightly
biased toward men (according to wikipedia). At every question that skew your
50/50, you'll have to add another question beyond 33 to catch up with this.

~~~
thethimble
All questions must be independent. That's too hard. I would be surprised to
find even a handful of questions that have no statistical correlation when
applied to all people in the world.

------
aria
Question 1: What is the first bit in your unique 33-bit string? Question 2:
What is the first bit in your unique 33-bit string? ...

~~~
Peaker
I'm pretty sure you didn't mean what you wrote! But maybe I'm whooshing?

------
mcphilip
I think first you have to show a question exists that effectively separates
identical twins before you spend much time working on broad questions like
gender and geography.

~~~
edsrzf
Maybe something like "Do you have more older siblings than younger siblings?"
would work. One twin has to be born before the other.

That question has some problems, but I feel like it could serve as the basis
for a more specific question that would define how an only child or middle
child would answer without introducing much bias. It would also have to define
how half-siblings are counted and probably some other things.

~~~
RogerL
So you are going to burn one entire question that is entirely worthless for
the vast majority of Chinese that have been born recently?

~~~
Intermernet
Interesting read: "One Child Policy and Arising of Man-Made Twins".
[http://paa2013.princeton.edu/papers/130113](http://paa2013.princeton.edu/papers/130113)

------
rattray
This is a fun exercise, but as others have pointed out likely impossible in
its current form.

We don't have true constraints on space though; why limit to 33 bits? How
could we still provide a meaningful UUID to each person?

A UUID based on time and location of birth might be more feasible than any
other approach, since neither will change and it's the least likely to be
ambiguous. Capturing UTC at the time of cutting or otherwise removing the
umbilical cord could be one way of choosing as precise, non-debatable a
timestamp as any. Adding lat/long and, say, the first byte of the UTF-8
character of the mother's name (or an aspect of the mother's UUID?) could get
you the rest of the way there.

Of course, this falls over in places without access to precise timing and
geolocation.

~~~
edelans
I think the limitation to 33 bits is because this is the smallest power of 2
which is higher than the world's population:

2^32 = 4.29 billions,

2^33 = 8.58 billions,

2^34 = 17 billions,

------
benstein
Do the answers have to be knowable? Time independent?

For example, "are you below the median age at this exact second?" That is not
a knowable answer, and changes by the second, but it does give you an exact
50/50 split.

Repeat N times for each split and we're getting very very close.

------
jloughry
These need to be questions that are invariant over a lifetime:

\- Were you born in the northern hemisphere or southern?

$2^{33}$ is sufficient for those alive now, but the human population is a
dynamic function. Set a bit when the person dies?

~~~
azatris
The Northern Hemisphere has roughly 90% of the population[1]. That is far from
50% what we should be looking for.

[1]:
[http://en.wikipedia.org/wiki/Northern_Hemisphere](http://en.wikipedia.org/wiki/Northern_Hemisphere)

~~~
sgustard
Are you born above or below the tropic of cancer then: replace with whatever
latitude separates humans into equal groups.

~~~
splike
This make other questions based on geography useless (as in the second
question). Thats not to say the already given second question is better than
your one

------
jloughry
Added pull requests to extend the address space from 33 bits to 36 bits to
accommodate our revered ancestors, and a bit to indicate liveness.

TODO: don't implement zombies or ghosts at this time (YAGNI principle).

------
ramanujam
On a related note, this has a very interesting significance in the world of
privacy and anonymous tracking.

[http://33bits.org/about/](http://33bits.org/about/)

------
ruswick
This is a really cool concept, but one that is totally impossible. In the
actual world, few things are truly independent. Even if you could find 33
binary questions that did not correlate with each other at all, you still run
the risk of having multiple people yield the same 33 answers.

Just because two things aren't statistically linked does not mean that they
will never overlap.

------
dkokelley
Wouldn't the best way to do this be to ask questions related to genetic
markers? You require 33 yes/no questions that independently divide the
population in half, but has near-uniform distribution otherwise (each populace
half has no relationship to the other questions).

Are there 33 genetic markers that each has no correlation on the presence of
the others?

------
anilshanbhag
33 is not the constraint. If we increase the limit to 50 and these 50
questions can fingerprint an individual then that will be really interesting.

Some hard problems :- 1\. Distinguish twins 2\. Using characters in names as
some like Chinese use non-ascii names.

~~~
vinceguidry
You could distinguish twins by first identifying the twins, then by asking
which one's name starts earlier in the alphabet, or whatever analogue exists
in languages without an alphabet. Encode appropriately.

------
yiransheng
If anyone is interested in seeing such a application in a fictional setting, I
suggest the anime Death Note, if nothing else for its entertainment value. For
those who are familiar with the story, the questions L asked in order to
narrow down Kira suspects to a limited demographics in a small region in
Japan, among billions of candidates, were some good ones. A good article that
analyzes the plot from a information theory perspective:
[[http://www.gwern.net/Death%20Note%20Anonymity](http://www.gw...](http://www.gwern.net/Death%20Note%20Anonymity\]\(http://www.gwern.net/Death%20Note%20Anonymity\)).

------
fela
Even if the questions were perfect (each question splitting the population in
two exact halves, and all questions totally independent from each other) and
therefore the algorithm would give each person a perfectly random number, the
birthday paradox [1] tells us that even for just square(2^33)=~ 93k people we
would have 50% probability of having a collision. To work we would need more
bits. (Either that or create questions that are _not_ independent, so crafted
in a way to make sure each person gets a different number)

[1]
[http://en.wikipedia.org/wiki/Birthday_problem](http://en.wikipedia.org/wiki/Birthday_problem)

~~~
deathanatos
No: the linked article requires that further questions split the previous
groups each in half. The first question must split the group in half, the
second question _must_ split those two groups in half, and so on. When we hit
the last bit, the final question is splitting groups of 2 people into the last
bit, and each person has been assigned a unique number.

In this manner, 33 bits is enough, and the birthday problem is avoided. The
page mentions all this.

------
vacri
How many questions would you need to differentiate between identical twins,
particularly if they live and work together? Take identical twin sons of a
subsistence farmer - they live together, work together on the same things,
know the same people, have the same genetic makeup, and whichever was the
first twin born may not have been recorded. You could ask their names, but
that's not a yes/no question.

Or even twins who are still babies, no work required? Some cultures wouldn't
even have named them yet.

~~~
incompatible
Multiple births would be bad enough, and then you have people with dementia
who can't remember the answer to most of the questions, and people in a coma
who can't answer questions at all. The chance of succeeding with this exercise
is approximately zero.

------
tlongren
"As an example, having the questions "Are you male?" and "Are you below the
median age?" will not work "

First question is "Are you male?". Made me laugh.

~~~
splike
I should reword that sentence to make the point clearer. As psuter said, you
can have one but not both

~~~
tlongren
It was much more clear after having it pointed out to me.

------
powertower
Another problem not mentioned is that the questions should be about the
content that does not allow for the answer to change over time. Otherwise the
ID is no good.

------
loganu
Could you not have way more than 33 questions created, (maybe a couple
hundred) but change what questions are asked based on previous answers? Use
the previous answers to determine the strongest next question to ask?

If an early answer states the candidate lives in the north hemisphere, there's
no point in asking them if they live on a landlocked African country... or
whatever much more complicated questions could arrive.

------
cbr
A boring solution:

Question n. Consider the number of your birth out of all people currently
alive. When you divide by 2^n and take the remainder, is it odd?

------
DigitalSea
This seems like it would be a lot of work. The intensity and specificity of
the questions that would need to be asked would have to be quite unique. It
might be possible, but without excluding people of the world because they get
lumped into a group, it seems like maybe 33 questions might not be enough to
uniquely identify everyone in the world.

------
ealexhudson
A useful question might revolve around language or concepts a person knows,
but then this becomes a lot more difficult if the questioner doesn't know
which language/concepts a person wouldn't understand (and therefore whether
they could even answer the question) - and if they do know, there is a priori
knowledge effectively.

------
fat0wl
The 33-question issue is a tough one for sure.

I'm instead left wondering how many extra questions (35 bits? 36 bits?) it
would have to be expanded to in order to produce unique results but without
having to be particularly clever in producing the questions. I bet it wouldn't
take as many extra as one might be inclined to think.

~~~
pit
Good point, especially because at 33 bits, storing everyone's ID would only
take about 29 gigabytes.

7,126,462,675 people * 33 bits per person / 8 bits per byte = 29,396,658,534
bytes

World population source:
[http://www.census.gov/popclock/](http://www.census.gov/popclock/)

------
S4M
Do the questions have to be constant over time? If not it can trivially be
solved by asking: Are you born before or after time _t_? 33 times, where _t_
is the median date of birth of your population. You just need to recompute _t_
33 times (and know the date of birth of every single person in the world).

------
aleprok
If the goal is to have questions which can be answered only with yes or no. I
don't think asking for location of the person is good thing, because there
would be so many questions as there is locations.

"Do you live in China, India, The United States, Indonesia, Brazil or
Pakistan?" is not good question.

~~~
kalleboo
"Were you born east or west of longitude X" (where X is a longitude that would
split the population roughly in half).

~~~
aleprok
Yes that would work and north of x..

------
stevewilhelm
Is the intent of this exercise to build a unique identifier that the
individual could reproduce over the course of their life, or does it just
uniquely identify them at the time they answered the questions?

I ask because questions like number of siblings, favorite movie, etc. would
change over time.

------
unfamiliar
Are you male? This will not split the population 50/50\. One group will be
slightly larger, and you then only have 32 questions to subdivide this larger
group into further categories which is impossible.

This is not possible unless the categories _precisely_ bisect the group each
time.

------
deletes
Seems impossible to me, for example what question would separate two identical
twins( identical in dna and when born ).

And let's say you find such a question, there is no way that question would
divide half of the population.

~~~
aroman
Well if you had conditional questions, you could ask who was born first.

~~~
deletes
That question doesn't even apply since you can only ask it to two twins, not a
single person.

~~~
30thElement
Going along with what someone said earlier, your last question can be "Were
you born after someone who answered the previous 32 questions the same as
you", which works to identify twins as well as people in general. Although I
don't know how this would work for triplets (or any larger number of "twins"
than 2); you'd have to make the previous 32 questions split them into groups
of at most 2.

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k__
Isn't this solvable to a degree by just asking a big amount of yes/no
questions to a big amout of people and then removing all those questions that
didn't identify people any further?

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jayd16
I bet you could make a lot of progress by dividing GPS coordinates evenly by
population. Simple binary search by primary residence and then leave some
space for division within a household.

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dinkumthinkum
It's an interesting idea ... But no I don't think it is possible in any way
that is not turning the list into a set of questions about their genetics or
DNA.

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Strilanc
An easy way to construct the questions is to ask for increasingly precise time
and location of birth.

There will be corner cases, but then so does asking if someone is male.

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tehwalrus
The set of questions that would do this is probably a list of genetic
questions.

"do you have the _mumble_ allele?" etc.

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jv22222
Less than half the population will be able to "read" the questions due to not
speaking English...

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jpalioto
Fun version of that ...

[http://en.akinator.com/](http://en.akinator.com/)

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IsNotMyIp
Do you speak english as your main language? Could be a good question too? What
do u think?

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obilgic
Possible, You need 33 answers but more than 33 questions.

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josscrowcroft
People have so much time on their hands.

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ye
First 33 bits of SHA512(your DNA)

First 33 bits of SHA512(your 3D GPS location)

~~~
deathanatos
As someone else mentions, this doesn't work, as the birthday problem[1]
applies here.

You need to ensure collisions won't happen; SHA512 does not to that. (The
probability of a collision in 512 bits is near impossible; in 33 bits, much
less so.)

[1]:
[http://en.wikipedia.org/wiki/Birthday_problem](http://en.wikipedia.org/wiki/Birthday_problem)

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Houshalter
This is really interesting actually. Your entire "uniqueness" can be summed up
in 33 yes or no questions, in theory.

~~~
jeffdavis
I don't think that's quite the right interpretation. Let's say that the human
population increased by a factor of 1000. Does that mean you have 10 more bits
of uniqueness? You didn't change at all.

In actuality, you already had those 10 more bits of uniqueness, and people
just need to ask more questions to find out which one of the many unique
people you are.

This is about _identification_ , not uniqueness.

