This is something called an error-correcting code.
So if somehow during transmission some of the 0s get changed to a 1
or vice-versa, this code is able to pick up
that a mistake has been made.
Now I'm going to need a volunteer who's going to be a bit of interference
to scramble my message, so yeah would you like to come up.
Okay so you're gonna be a little bit of noise on the line
so what's your name?
– Lauren
– Lauren, okay Lauren, what I want you to do
is you're going to change one of these numbers over,
so instead of a 1 it becomes a 0, so if you look down here Lauren,
it's on the other side there's a zero okay, like that.
So I haven't memorized this but I'm going to get evil Andy,
could you blindfold me, and yeah boo. We want your chocolates.
Anyway he's gonna blindfold me, once I'm blindfolded I'll turn my back,
just change one number over and hopefully I'll be able to detect
which number you've changed, okay.
So blindfold me up.
Woarh, gosh,
that's a bit vicious Andy, gosh.
Okay so when you're ready you tell me
when you've changed a number over please.
Just one number.
Okay, right I'm going to remove my blindfold
and hopefully I can spot which one you've done.
So as I said I haven't memorised this.
Okay, let's see, right.
Beginning to get a feel for it.
Okay I think that you changed this number here
Okay, pretty good. Was that magic?
[APPLAUSE]
Thank you, thank you
So how did I do that?
It wasn't magic at all, it was a bit of mathematics, okay.
So actually the message sent by the computer
isn't the whole thing but just the top 4 by 4 block.
So this is actually the message they want to send,
so I'm going to separate this off.
So the message sent by the computer is actually this top block here
and the other digits are used to keep check
of what's happening inside the message.
and actually at the bottom here if you look at the bottom column
this number here will be a 1 if there are an odd number of 1s in this column.
Okay, and if there are an even number of 1s,
so in this column, I put a 0, okay.
So when you turned one of the things over,
it didn't check out, so for example if I turn that over
then I've got, well they're meant to be an even number of 1s there,
so I know there's a mistake in that column.
And the same thing for the rows over here, okay.
Why I'm telling this to you because you're gonna have a go yourself now
to see if you can correct a mistake.
Okay, so you can work out which column is wrong
by checking something wrong down here,
and which of the rows is wrong.
OK? Want to take on the challenge?
–OK –All right.
Okay we're gonna blindfold her, and you can close your eyes as well
if you want to do a challenge. so let's get you over here, all right.
I won't be so vicious as Andy, sort of almost took my head off.
Okay and we're also not going to show the viewers at home
so they can have a challenge at this as well.
I'm gonna change one of the numbers over now
yeah cover your eyes, and we'll see whether you can correct the error.
Okay, I'm done so let's see whether you can do it.
[LAUREN TALKS OFF MIC]
– Zero is even well done,
something in this column then is wrong, yeah.
What about the rows?
[LAUREN TALKS OFF MIC]
– That's right, even number of 1s there.
[LAUREN TALKS OFF MIC] – And it's odd...
– So it's first row...
[LAUREN TALKS OFF MIC] – Did you change this one?
– No you had the second column, that's right that's right,
so it was this one exactly right,
so give her a big round of applause for correcting the error, well done.
[APPLAUSE]
Now you might like to have a think about what happens if one of these numbers
gets changed on the rows and the columns which are doing the checking,
you can even correct those as well.
Now error correcting codes like this are used all over the place
in CDs and satellite communication, for example when NASA
sends pictures back from outer space there's a lot of interference,
they use even more sophisticated mathematics
this can correct one number, but they need to correct lots of numbers
for example here's a picture that was sent back
before it was corrected, this is Saturn, it's pretty fuzzy,
but using the mathematics and error correction,
they managed to change it into this – much more crystal clear.