Who doesn't like birthday cakes?
And what I'm going to show you today is that
there are good ways and there are bad ways
of cutting a cake.
And the classic way, the bad way,
is like this, which would be normal.
You put the knife in the center.
One bit of a slice,
Other bit of a slice... [laughter]
Brady Haran: It's like the classic. Alex Bellos: It is the classic. Isn't it?
It's almost like a pie chart.
You know, one thing about the word pie chart.
In France they call them Camembert, which is like a cheese.
It's actually like a cheese chart in France.
Interesting cultural differences in math speak.
So this is what you would do. You take this, you would put this over here,
you eat it, and then you leave this in the fridge overnight.
And the reason why this is a really bad way of cutting a cake
is that these bits here are just going to get dry.
So when you come the following day to have your cake,
you know, you do another one,
another slice like this
This side here, hmm, lovely and soft
This will be dry and horrible.
You know, maximizing the amount of gastronomic pleasure
that you can make out of this cake.
There is a better way, a way that is more than a hundred years old
and was discovered or invented
by one of Britain's most famous and brilliant mathematical scientists.
This is a copy of Nature, the famous science magazine,
from December the 20th 1906.
And in the Letters To The Editor here it says:
The headline: Cutting a round cake on scientific principles.
"The ordinary method of cutting out a wedge", he writes, "is very faulty".
What he suggests is, and he gives an illustration for it,
The proper way, the scientific way,
the mathematically perfect way of cutting a round cake
and it is as follows.
So we have another cake
The first slice will be like this.
Breaking all the rules of a cake etiquette.
Perfect. OK? So this is the first one,
and then I need to find a way of...
taking it out...
OK. We can stick that there.
And that is got to be the prime steak of that cake. Isn't it?
It's the T-bone cut.
Here's what we need to do...
We need to close the cake together, like this.
And it's going to come apart, so look what I've got here...
I have got some rubber bands to make sure it stays together.
The following day...
All the flesh, the sponge is going to be nice and soft.
So, how do we do the second slice?
The second slice... I guess it's not your birthday anymore,
so you're not going to have one quite as big...
It will be interesting to work out the actual proportions.
This is...
You get a lovely break in the elastic bands too, which is exciting.
This is slice two.
Or, it actually is slice two which has two slices, two parts.
So you put this back together. And we can keep on going.
Obviously, I'm going to want to use the elastic band to put the cake...
Yeah, That is perfect. That is going to stay so fresh for day three.
Day three. Brady Haran: Actually do day three, Gab.
Alex Bellos: Let's turn it around.
I think this is going to be the slice for day three.
Again, the satisfying snap of the elastic bands...
And... I don't know if you thought about if before,
but these triangular slices are really annoying anyway, because...
It's not very satisfying. Having a nice uniform slice like that is a lot better.
So, here we go again...
At the end of day three... This is for... And this is going to be perfect.
And gradually we are slicing it, keep on going.
I think for the mathematical loners
who don't want to share their cakes it could be useful.
Brady Haran: For a bit more of this interview
including more about the guy that came up with this cake cutting method
have a look at the extra footage over Numberphile 2.
And if you just like to hear more great stories from Alex,
he's got a new book out just recently:
"Alex through the Looking Glass -
How Life Reflects Numbers and Numbers Reflect Life".
It's really good. It's also just out in the US,
but it has a different name in the US.
It's called "The Grapes of Math".
I'll put links to it in the video description.