Today i want to talk to you

about the mathematics of love.

I think we can all agree 
that mathematicians

are famously excellent 
at finding love.

But it's not just because
of our dashing personalities

our superior conversational skills

or our excellent pencil cases,

it's also because we've done

a lot of work into the maths

of how to find the perfect partner.

in my favorite paper on the subject

which is entitled,

"Why I Don't Have a Girlfriend."

peter backus tries to rate

his chances at finding love

now, peter is not a very greedy man

of all of the available women in the UK

all that peter's looking for is

somebody who lives near him,

somebody in the right age range,

somebody with a university degree,

somebody he's likely to get on well with

somebody attractive

somebody who is likely to find him attractive

(laughter)

and comes up with an estimate of 26 women

in the whole of the UK

it's not looking very good, is it peter?

now just to put that into perspective

that's about 400 times fewer

than the best estimates

of how many intelligent
extra-terrestrial life forms there are

and it also gives peter a

1 in 285,000 of bumping
into any one of these special ladies

on a night out

I'd like to think that's why

mathematicians don't really bother

going on nights out anymore

The thing is is that i personally

don't subscribe to such a pessimistic view

i know, just as well as you do,

that love doesn't really work like that

human emotion isn't neatly ordered

rational or easily predictable

but i also know that that doesn't mean
that mathematics

doesn't have something it can offer us

because, love, as with most of life

is full of patterns

and mathematics is ultimately

all about the study of patterns

pattersn from predicting the weather

to the fluctuations of the stock market

to the movement of the planets

or the growth of cities

if we're being honest, none

of those things are neatly ordered

or easily predictable either

because i believe that mathematics

is so powerful that is has the potential

to offer us a new way of looking

at almost anything

even something as mysterious as love

and so, to try to persuade you

of how totally, excellent, 
and relevant mathematics is

I want to give you my top three

mathematically verifiable tips for love

okay, so, top tip #1

how to win at online dating

so my favorite online dating website

is OkayCupid

not least because it was

started by a group of mathematicians

now because they're mathematicians

they have been collecting

data on everyone whose been using

their site for almost a decade

and they've been trying to search

for patterns in the way that we

talk about ourselves

and the way that we interact with each other

on online dating websites

and they've come up with

seriously interesting findings

but my particular favorite

is that it turns out

that one an online dating website,

how attractive you are

does not dictate how popular you are

and actually having people

think that you're ugly can

work to your advantage

let me show you how this works

okay, in a thankfully voluntary section

you are allowed to rate how attractive people are

between 1 and 5

and if we compare this score

this average score

to how many messages a selection

of people receive

you can begin to get a sense

of how attractiveness

links to popularity on online dating

so this is a graph that the online

okay cupid guys have come up with

and the important thing

to notice is that it's not totally true

that the more attractive you are

the more messages you get

but the question arises then

of what is it about people up here

who are so much more popular

than people down here?

even though they have the

same score of attractiveness

and the reason why is that

it's not just straight forward looks

that are important

so, let me try to illustrate their findings

with an example

if you take someone like porcia di rossi

everybody agrees that porcia di rossi

is a very beautiful woman

nobody thinks that she's ugly

but she's not a supermodel

if you compare porcia di rossi

to someone like sarah jessica parker

now, a lot of people

myself included

think that sarah jessica parker

is seriously fabulous

and possibly one of

the most beautiful creatures to have evr

walked the face of the earth

but, some other people

e.i., most of the internet

seem to think that she looks a bit like a horse

(laughter)

now, i think that if you ask people

how attractive sarah jessica parker 
or porcia di rossi are

and you ask them to give them a score between one and five

i reckon that they would average out to the same score

but the way that people would vote

would be dry different

so porcia's scores would all be clustered around

the four because everybody agrees that she's

very beautiful

whereas sarah jessica parker divides opinion

there a huge spread in her scores

and actually it's this spread that counts

it's this spread that makes you more popular

on online internet dating websites

so what this means then

is that if some people think that 
you're attractive

you're actually better off
having some other people

think that you're a massive minger

that's much better than everybody
thinking that you're the cute girl next door

i think that this makes a bit more sense

when you think in terms of the people

who are sending these messages

so let's say that you think somebody's attractive

but you suspect that other people

won't necessarily be that interested

that means that there is less competition for you

and that there's an extra incentive

for you to get in touch

whereas compare that to if you think

somebody is attractive but

you suspect that everybody is going

to think they're attractive

well, why would you bother humiliating yourself

here's where the really interesting part comes

people choose the pictures
that they use on an online, dating website

they often try to minimize the things

that they think people will find unattractive

the classic example is that

people who are a little but overweight

deliberately choosing a very cropped phto

or bald men for example

deliberatly choosing pictures

where they're wearing hats

but this is the opposite of

what you should do if

want to be succesful

you should really instead

play up to whatever it is that makes you different

even if you think that

some people will find you unattractive

because the people who fancy you

are just going to fancy you anyway

and the unimportant losers who don't

well, they only play out to you r advantage

Okay, top tip #2, how to pick
the perfect partner

so let's imagine then that
you're a roaring success

on the dating scene

but the question arises of how
do you then convert

that success into longer term happiness

and in particular,

how do you decide when is the

right time to settle down

now generally, it's not advisable

to just cash in the first person

who comes along and shows you any interest

at all

but, equally, you don't want to leave it

too long if you want to maximize your 
chances of long term happiness

as my favorite author, jane austen put it,

"an unmarried woman of seven and twenty

can never hope to feel or

inspire affection again."

laughter

thanks, jane

so the question is then

how do you know when is the right

time to settle down

given all the people that you

can date in your lifetime

thankfully, there is a rather delicious bit

of mathematics that we can use to

help us out here

so lets imagine then,

that you start dating when you're 15

and ideally, you'd like to be

married by the time you're 35

the number of people that you

could potentially date across your lifetime

and they'll be at kind of varying levels

of goodness

now the rules are that when you cash in

and get married

you can't look ahead and see

what you could have had

and equally, you can't go back

and change your mind

in my experience at least

i find that people don't typically

like being recalled years after

being passed up

for somebody else, or that's just me

so the math says then

that what you should do

in the first 37 percent of your dating window

you should reject everybody 
as serious marriage potential

and then, you should pick the 
next person who comes along

who is better than everyone that you've seen before

so here's the example

now if you do