Today&#39;s video is about Richard Feynman--

a lot of people&#39;s favorite scientist--

But I just wanted to point out at the start that most safes,

or secure filing cabinets, actually have one dial.

And if you&#39;ve got a three number combination, for

example, you&#39;ll turn that dial in one direction, then the

other direction, and then back in the other direction.

But the mock up that we&#39;ve used in this video--

It&#39;s about as far from a safe as you could get.

That kind of makes things a bit more visual, a bit easier

But in most cases, the sort of safes we&#39;re talking about will

I don&#39;t want to get all the safe enthusiasts out there too

fired up and angry in the comments section.

But for now, here&#39;s Professor Bowley with his pretend safe

and the story of Richard Feynman and his World War II

PROFESSOR ROGER BOWLEY: I&#39;m talking about Feynman and how

he managed to crack safes when he was working on the atomic

bomb project in Los Alamos in the early &#39;40s.

And he was stuck in the middle of Los Alamos,

It was a sort of desert area around there.

He was stuck with lots of other theoretical physicists.

And as a hobby, he tried cracking open all the safes in

Now, they had new, purpose built safes with locks on them

You can imagine 100 numbers for this, 100 numbers for

And if you fiddle them around, it&#39;ll take about five

So if you tried to crack it, it will take

On the average, it&#39;d be 30 days, but 60 days if you screw

So he was given one of these in his office to keep all the

top secret files that he might come up with.

So he knew how this worked mechanically, because he

And he found by trial and error, suppose the number

Actually, it started at 25, and a lot of people didn&#39;t

And if he wanted to crack the safe, a lot of times, people

left it in the default setting, because it&#39;s the

Now, he found that if he tried to set it at 20 and it opened,

he could also set it to 21 and it would open, or 22.

So there was a bit of tolerance, plus or minus 2 on

every single number, which meant that if you set it at

and the same for this dial and the same for this dial.

So now, if you go through all the combinations, you only

Now, there are only 20 settings for this, 20 for

So automatically, that&#39;s gone down, oh, I can&#39;t do it.

He found that most people will set a birthday, an

anniversary, some well-defined date that--

I don&#39;t know, the Independence Day in the United States of

And it would not be an ordinary number, because if

it&#39;s going to be, say, my birthday, which is the 21st of

April if anybody wants to send me presents.

And I&#39;m born in 1946, which is down there.

So for the top one, which is the days of the month, there

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